U.S. patent application number 09/962972 was filed with the patent office on 2002-06-20 for adsorption vessels.
Invention is credited to Bailly, Peter, Kischkewitz, Jurgen, Rohbock, Klaus, Schlegel, Andreas.
Application Number | 20020074292 09/962972 |
Document ID | / |
Family ID | 27437886 |
Filed Date | 2002-06-20 |
United States Patent
Application |
20020074292 |
Kind Code |
A1 |
Schlegel, Andreas ; et
al. |
June 20, 2002 |
Adsorption vessels
Abstract
The present invention relates to a filtration unit containing
pellets or granules of fine-particle iron oxides and/or iron
oxyhydroxides with a large specific surface area, processes for
their production and processes for their use in the filtration
units.
Inventors: |
Schlegel, Andreas; (Krefeld,
DE) ; Bailly, Peter; (Odenthal, DE) ;
Kischkewitz, Jurgen; (Ratingen, DE) ; Rohbock,
Klaus; (Kempen, DE) |
Correspondence
Address: |
BAYER CORPORATION
PATENT DEPARTMENT
100 BAYER ROAD
PITTSBURGH
PA
15205
US
|
Family ID: |
27437886 |
Appl. No.: |
09/962972 |
Filed: |
September 25, 2001 |
Current U.S.
Class: |
210/681 ;
210/263; 210/282; 210/688 |
Current CPC
Class: |
B01D 15/00 20130101;
C01P 2004/10 20130101; B01J 20/06 20130101; C01P 2006/12 20130101;
C01G 49/0036 20130101; B01D 2253/10 20130101; C01G 49/0045
20130101; C01P 2004/50 20130101; C01P 2004/64 20130101; C01P
2004/62 20130101; C02F 2201/006 20130101; C01G 49/02 20130101; B01D
53/02 20130101; C02F 1/281 20130101; C02F 2101/20 20130101; B01J
20/08 20130101; Y10T 428/12993 20150115; C01G 49/06 20130101; B82Y
30/00 20130101; C02F 1/288 20130101 |
Class at
Publication: |
210/681 ;
210/263; 210/688; 210/282 |
International
Class: |
B01D 015/00 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 26, 2000 |
DE |
10047996.0 |
Sep 26, 2000 |
DE |
10047997.9 |
Mar 29, 2001 |
DE |
10115418.6 |
Jun 18, 2001 |
DE |
10129307.0 |
Claims
What is claimed is:
1. A unit suitable for the through-flow of a fluid medium for the
removal of a contaminant from the fluid medium comprising a
cartridge housing, which comprises a vessel having a centrally
positioned inlet pipe, flat filter layers, a cover ensuring the
inflow and outflow of the medium, together with a base part,
wherein the cartridge housing is filled with at least partially
some particles prepared from fine-particle iron oxide and/or iron
oxyhydroxide having a BET surface area of 50 to 500 m.sup.2/g.
2. The unit of claim 1, wherein the cartridge housing is separated
from the cover and/or from the base part by means of a plug-in or
screw fitting.
3. The unit of claim 1, wherein the inlet pipe can be removed from
the cartridge housing.
4. The unit of claim 1 wherein the fluid medium is a gas.
5. The unit of claim 4, wherein the flat filter units comprise a
hydrophobic membrane.
6. The unit of claim 5, wherein the membrane displays a pore
diameter in the range from 0.2 to 0.5 .mu.m.
7. The unit of claim 5, wherein the hydrophobic membrane comprises
polytetrafluoroethylene.
8. The unit of claim 1 wherein the fluid medium comprises a
liquid.
9. The unit of claim 8 wherein the medium comprises an aqueous
liquid.
10. The unit of claim 9, wherein the flat filter units comprise a
hydrophilic membrane.
11. The unit of claim 10, wherein the hydrophilic membrane is a
membrane adsorber.
12. The unit of claim 9, wherein the membrane displays a pore
diameter in the range from 0.2 to 0.5 .mu.m.
13. The unit of claim 1, wherein at least one of the flat filter
layers is supported on one or both sides.
14. The unit of claim 1, wherein the cover comprises a valve for
escaping gases.
15. The unit of claim 1, wherein the housing chamber is in the form
of a truncated cone.
16. The unit of claim 1, wherein the cartridge housing can
optionally contain iron oxide pigments with BET surface areas below
the above limits, whereby the maximum content of these is such that
the resistance of the particles to the forces exerted upon it by
the flowing medium is sufficiently great that the stress exerted on
the particles by the flowing medium does not lead to an undesirable
abrasion of the particles.
17. A process for treating a fluid medium in a unit of claim 1,
comprising the steps of flowing the medium through the feed nozzle,
into the inlet pipe, the strainer basket, any filter material in
the base chamber, the lower fritted plate, followed by the
adsorbent material in the contact chamber, the upper fritted plate,
the cover chamber with filter material and then the outlet pipe via
the discharge nozzle.
18. A process of claim 17, wherein the flow of the fluid medium is
reversed.
19. A process comprising the step of treating a fluid medium in a
unit according to claim 1, by contacting the fluid medium with
particles obtained by a process for the production of an
adsorbent/catalyst, wherein (a) aluminium, iron, magnesium and/or
titanium oxides or (oxy)hydroxides or ageing products and
dehydrated secondary products thereof are incorporated into an
aqueous suspension of iron oxide and/or iron oxyhydroxide,
including Fe(OH).sub.2 and then (b) either (b1) the suspension is
dried until it reaches a solid state and the solid material then
comminuted mechanically to the desired shape and/or size or (b2)
the suspension undergoes mechanical shaping, optionally in the
semisolid state after predrying, followed by additional drying
until a solid state is achieved.
20. The process of claim 19 wherein the fluid medium comprises
water.
21. The process of claim 19 comprising removing a heavy metal,
phosphorus, antimony, beryllium, selenium, tellurium or cyano
compound from water.
22. The process of claim 19 comprising removing an arsenic compound
from water.
23. A process comprising the step of treating a fluid medium in a
unit according to claim 1, by contacting the fluid medium with
particles obtained by a process for the production of particles
from fine-particle iron oxide and/or iron oxyhydroxide comprising
the steps of producing an aqueous suspension of fine-particle iron
oxides and/or iron oxyhydroxides having a BET surface area of 50 to
500 m.sup.2/g, removing the water and dissolved constituents by
either I) a) first removing only the water from the suspension, b)
introducing the residue thus obtained in water, c) filtering the
material obtained, d) washing the residue, and e) either e1)
completely dehydrating the filter cake obtained as residue and
comminuting the filter cake to the desired shape and/or size or e2)
partially dehydrating it to obtain a paste, shaping the paste and
subsequently additionally drying the paste until a pellet is
obtained, or II) a) filtering the suspension, b) washing the
residue, c) either c1) completely dehydrating the filter cake
obtained as residue in the form of a solid to semisolid paste and
then comminuting the material thus obtained to the desired shape
and/or size or c2) partially dehydrating it to obtain a paste,
shaping the paste, followed by subsequent additional drying until a
pellet is obtained.
24. The process of claim 23 wherein the fluid medium comprises
water.
25. The process of claim 23 comprising removing a heavy metal,
phosphorus, antimony, beryllium, selenium, tellurium or cyano
compound from water.
26. The process of claim 23 comprising removing an arsenic compound
from water.
27. A container able to be contacted with a fluid medium, at least
partially filled with particles agglomerated from fine-particle
iron oxide and/or iron oxyhydroxide wherein the particles are
prepared from an aqueous suspension of fine-particle iron oxides
and/or iron oxyhydroxides having a BET surface area of 50 to 500
m.sup.2/g, by removing the water and dissolved constituents.
Description
BACKGROUND OF THE INVENTION
[0001] The invention relates to filtration unit suitable for the
through-flow of a fluid medium for the removal of a contaminant
from the fluid medium, like an adsorption vessel through which a
liquid to be treated can flow, particularly a filter adsorption
vessel which, when filled with granulated or powdered, solid,
water-insoluble adsorption media, particularly iron (oxy)hydroxide,
is used for the removal of arsenic or heavy metals from drinking
water. The device can be connected to the sanitary and drinking
water supply in the home, for example.
[0002] The invention also concerns a process for the production of
the iron (oxy)hydroxide adsorbents for use in the filtration units
according to the invention.
[0003] In 1999, studies by the National Academy of Science verified
that arsenic in drinking water causes bladder, lung and skin
cancer.
[0004] A commonly occurring problem, particularly in regions where
spring water, tap water or drinking water in general is
contaminated with arsenic or other heavy metals, is that there is
no suitable drinking water treatment plant nearby or no suitable
device to hand that would continuously remove the contaminants.
[0005] Filter cartridges for cleaning liquids, preferably
contaminated water, which can also contain an adsorption medium,
are known in various forms.
[0006] For example, membrane filter cartridges in suitable housings
are used to separate solids from water.
[0007] Cartridges and devices for the treatment of liquids are
known from Brita Wasser-Filter-Systeme GmbH (DE-A 19 905 601; DE-A
19 915 829; DE-A 19 814 008, DE-A 19 615 102, DE-A 4 304 536, U.S.
Pat. No. 6,099,728). These devices are very suitable for the entire
or partial removal of salts from drinking water in domestic jugs
immediately before the drinking water is used.
[0008] A filtration unit in the form of a filter cartridge having a
bed of activated carbon particles between a polyester urethane foam
layer and a glass-fibre layer is known from U.S. Pat. No.
4,064,876.
[0009] DE-A 19 816 871 (Sartorius) describes a filtration unit for
the removal of contaminants from fluids.
[0010] RU-A 2 027 676 describes a cartridge filter with sorption
agent for drinking water purification with a connection to the
water tap in the home.
[0011] HU-A 00 209 500 describes a filter cartridge for the removal
of radioactive material and heavy metals from water, which is
filled with a mixture of ion-exchange material, activated carbon,
filter sand, zeolites, aluminium oxide and red mud.
[0012] These adsorber cartridges are generally filled with
activated carbon or ion-exchange resins. The disadvantage of
activated carbon, however, is that due to the low adsorption
capacity of activated carbon, arsenic and heavy metal salts
occurring in aqueous systems are not removed to an adequate extent,
and this has an effect on the service life of the cartridges.
[0013] The disadvantage of ion-exchange resins is that they are
very unselective in the way that they bind ions from aqueous
solution, and competitive reactions commonly occur in the
adsorption. A further disadvantage of ion exchangers is that the
adsorption capacity of the ion exchanger is extremely dependent on
the pH value of the water, such that large quantities of chemicals
are needed to adjust the pH of the water, which is not practicable
when the adsorber cartridge is used in the home.
[0014] Contact and adsorbent granules, including those based on
iron oxides and/or iron oxyhydroxides, have already been described.
They are predominantly used in continuous processes, whereby they
are conventionally found in tower or column-type units through
which the medium to be treated flows, and the chemical or physical
reaction or adsorption processes take place at the outer and inner
surface of the granules. Powdered materials cannot be used for this
purpose because they compact in the direction of flow of the
medium, thereby increasing the flow resistance until the unit
becomes blocked. If a unit is cleaned by back-flushing (see below),
large amounts of the powder are discharged and lost or cause an
unacceptable contamination of the waste water.
[0015] The flowing media also exert forces on the granules,
however, which can lead to abrasion and/or movement through to
violent agitation of the granules. Consequently the granules
collide, leading to undesirable abrasion. This results in loss of
contact or adsorbent material and contamination of the medium to be
treated.
[0016] In gas purification the agent is used in adsorbers for
binding undesirable components such as hydrogen sulfide, mercaptans
and hydrogen cyanide, as well as other phosphorus, arsenic,
antimony, sulfur, selenium, tellurium, cyano and heavy metal
compounds in waste gases. Gases such as HF, HCl, H.sub.2S,
SO.sub.x, NO.sub.x can also be adsorbed.
[0017] A filter cartridge for drying gases is described e.g. in
U.S. Pat. No. 5,110,330.
[0018] The removal of phosphorus, arsenic, antimony, selenium,
tellurium, cyano and heavy metal compounds from waste oils and
other contaminated organic solvents is also possible.
[0019] Contact and adsorbent granules based on iron oxides and/or
iron oxyhydroxides are also used for the catalysis of chemical
reactions in the gas phase or in the liquid phase.
[0020] Various methods of removing trace constituents and
contaminants from aqueous systems with the aid of adsorbents are
known.
[0021] DE-A 3 800 873 describes an adsorbent based on porous
materials such as e.g. hydrophobed chalk with a fine to medium
grain size to remove contaminants from water.
[0022] DE-A 3 703 169 discloses a process for the production of a
granulated filter medium to treat natural water. The adsorbent is
produced by granulating an aqueous suspension of kaolin with
addition of powdered dolomite in a fluidised bed. The granules are
then baked at 900 to 950.degree. C.
[0023] A process for the production and use of highly reactive
reagents for waste gas and waste water purification is known from
DE-A 40 34 417. Mixtures consisting of Ca(OH).sub.2 with additions
of clays, stone dust, entrained dust and fly ashes, made porous and
having a surface area of approx. 200 m.sup.2/g, are described
here.
[0024] The cited processes and the contacts used therein have the
shared disadvantage that the component responsible in each case for
the selective adsorption of constituents of the media to be
cleaned, in other words the actual adsorbent, must be supplemented
with large quantities of additives to enable it to be shaped into
granules. This significantly reduces the binding capacity for the
water contaminants to be removed. Moreover, subsequent reprocessing
or reuse of the material is problematic since the foreign
substances used as binders first have to be separated out.
[0025] DE-A 4 214 487 describes a process and a reactor for the
removal of impurities from water. The medium flows horizontally
through a funnel-shaped reactor, in which finely divided iron
hydroxide in flocculent form is used as a sorption agent for water
impurities. The disadvantage of this process lies in the use of the
iron hydroxide in flocculent form, which means that because there
is little difference in density between water and iron hydroxide, a
reactor of this type can be operated at only very low flow rates
and there is a risk of the sorption agent, which is possibly
already loaded with contaminants, being discharged from the reactor
along with the water.
[0026] JP-A 55 132 633 describes granulated red mud, a by-product
of aluminium production, as an adsorbent for arsenic. This consists
of Fe.sub.2O.sub.3, Al.sub.2O.sub.3 and SiO.sub.2. No mention is
made of the stability of the granules or of the granulation
process. A further disadvantage of this adsorbent is the lack of
consistency in the composition of the product, its unreliable
availability and the possible contamination of the drinking water
with aluminium. Since aluminium is suspected of encouraging the
development of Alzheimer's Disease, contamination with this
substance in particular is to be avoided.
[0027] DE-A 19 826 186 describes a process for the production of an
adsorbent containing iron hydroxide. An aqueous polymer dispersion
is incorporated into iron hydroxide in water-dispersible form. This
mixture is then either dried until it reaches a solid state and the
solid material then comminuted mechanically to the desired shape
and/or size or the mixture is shaped, optionally after a
preliminary drying stage, and a final drying stage then performed,
during which a solid state is achieved. In this way a material is
obtained in which the iron hydroxide is firmly embedded in the
polymer and which is said to display a high binding capacity for
the contaminants conventionally contained in waste waters or waste
gases.
[0028] The disadvantage of this process lies in the use of organic
binders, which further contaminate the water to be treated due to
leaching and/or abrasion of organic substances. Furthermore, the
stability of the adsorbent composite is not guaranteed in extended
use. Bacteria and other microorganisms can also serve as a nutrient
medium for an organic binder, presenting a risk that microorganisms
may populate the contact and thereby contaminate the medium.
[0029] The presence of foreign auxiliary substances, which are
required for the manufacture of the adsorbents, during
reprocessing, recycling or reuse of used adsorbents is
disadvantageous in principle because the reuse of pure substances
is less problematic than is the case with mixed substances. For
example, polymeric binders are disadvantageous when iron
oxide-based adsorption materials are reused as pigments for
concrete coloration because these binders inhibit dispersion of the
pigment in liquid concrete.
[0030] DE-A 4 320 003 describes a process for the removal of
dissolved arsenic from ground water with the aid of colloidal or
granulated iron hydroxide. Where fine, suspended iron(III)
hydroxide products are used, it is recommended here that the iron
hydroxide suspension be placed in fixed-bed filters filled with
granular material or other supports having a high external or
internal porosity. This process likewise has the disadvantage that,
relative to the adsorbent "substrate+iron hydroxide", only low
specific loading capacities are achievable. Furthermore, there is
only a weak bond between substrate and iron hydroxide, which means
that there is a risk of iron hydroxide or iron arsenate being
discharged during subsequent treatment with arsenic-containing
water. This publication also cites the use of granulated iron
hydroxide as an adsorption material for a fixed-bed reactor. The
granulated iron hydroxide is produced by freeze conditioning
(freeze drying) of iron hydroxide obtained by neutralisation of
acid iron(III) salt solutions at temperatures of below minus
5.degree. C. This production process is extremely energy-intensive
and leads to heavily salt-contaminated waste waters. Moreover, as a
result of this production process only very small granules with low
mechanical resistance are obtained. When used in a fixed-bed
reactor, this means that the size spectrum is significantly reduced
by mechanical abrasion of the particles during operation, which in
turn results in finely dispersed particles of contaminated or
uncontaminated adsorption agent being discharged from the reactor.
A further disadvantage of these granules lies in the fact that the
adsorption capacity in respect of arsenic compounds is reduced
considerably if the granules lose water, by being stored dry for
extended periods for example.
[0031] Adsorbent/binder systems obtained by removing a sufficiently
large amount of water from a mixture of (a) a crosslinkable binder
consisting of colloidal metal or non-metal oxides, (b) oxidic
adsorbents such as metal oxides and (c) an acid such that
components (a) and (b) crosslink to form an adsorbent/binder
system, are known from U.S. Pat. No. 5,948,726. According to the
embodiments, colloidal alumina or aluminium oxide is used as
binder.
[0032] The disadvantage of these compositions lies in the need to
use acid in their production (column 9, line 4) and in the fact
that they are not pure but heterogeneous substances, which is
undesirable both for the production, regeneration, removal and
permanent disposal of such adsorbents, e.g. on a waste disposal
site. The scope of disclosure of this publication is also intended
to include adsorbents that are suitable for the adsorption of
arsenic; specific examples are not provided, however. Aluminium
oxide is known to be significantly inferior to iron oxides in
regard to force of adsorption for arsenic.
[0033] Continuous adsorbers, which are commonly grouped together in
parallel for operation, are preferably used for water treatment. To
free drinking water from organic impurities, for example, such
adsorbers are filled with activated carbon. At peak consumption
times, the available adsorbers are then operated in parallel to
prevent the flow rate from rising above the maximum permitted by
the particular arrangement. At times of lower water consumption,
individual adsorbers are taken out of operation and can be
serviced, for example, whereby the adsorption material is subjected
to special loads, as described in greater detail below.
[0034] The use of granules, which can be produced by compacting
e.g. powdered iron oxide using high linear forces, has also already
been considered. Such granules have already been described as a
means of homogeneously colouring liquid concrete. The use of high
linear forces for compacting is extremely expensive and
energy-intensive, and the stability of the compacted materials is
inadequate for extended use in adsorbers. The use of such materials
in adsorbers, for example, particularly continuous models, for
water purification is therefore of no interest. During maintenance
or cleaning of adsorber plants by back-flushing in particular (see
below), such granules lose large amounts of substance due to the
associated agitation. The abraded material renders the waste water
from back-flushing extremely turbid. This is unacceptable for a
number of reasons: firstly, adsorption material, which is heavily
laden with impurities and therefore toxic after extended use, is
lost. Secondly, the stream of waste water is laden with abraded
material, which can sediment, damaging piping systems and
ultimately subjecting the waste treatment plant to undesirable
physical and toxicological stresses, to name but a few reasons.
Preferably the abrasion should be below 20% by weight, more
preferably below 15% by weight, 10% by weight or most preferably
below 5% by weight according to the method described in the
examples of the present invention.
[0035] An object underlying the present invention was therefore to
provide a filtration unit for the removal of arsenic and heavy
metals from drinking, process, mineral, garden pond, agricultural,
holy and medicinal water using iron oxyhydroxide or iron oxide
particles as a contact or adsorbent/catalyst, which guarantees a
high degree of removal of the dissolved contaminants due to the
adsorption capacity of the packing medium, which at the same time
withstands the mechanical and hydraulic stresses in the adsorber
housing and which for safety reasons, due to the filter performance
of built-in filters, additionally prevents the discharge of
suspended impurities or abraded material from the adsorbent,
possibly laden with contaminants.
[0036] This complex object is achieved by the contacts or
adsorbents/catalysts according to the invention, their preparation,
their use and units filled therewith.
SUMMARY OF THE INVENTION
[0037] The invention relates to a filtration unit suitable for the
through-flow of a fluid medium for the removal of a contaminant
from the fluid medium comprising a cartridge housing (4), which
comprises a vessel having a centrally positioned inlet pipe (6),
flat filter layers (3), (10), a cover ensuring the inflow (1) and
outflow (12) of the medium, together with a base part (9), wherein
the cartridge housing is filled at least partially some particles
prepared from fine-particle iron oxide and/or iron oxyhydroxide
having a BET surface area of 50 to 500 m.sup.2/g.
BRIEF DESCRIPTION OF THE DRAWINGS
[0038] The drawings show different embodiments of the
invention.
[0039] FIG. 1a. describes an adsorber tank with iron hydroxide
adsorbent.
[0040] FIG. 1b. describes a tapered adsorber tank with iron
hydroxide adsorbent.
[0041] FIG. 2a. describes an adsorber tank with iron
(oxy)hydroxide-containing adsorber cartridge and housing.
[0042] FIG. 2b. describes an adsorber tank operated in the reverse
direction (cf. FIG. 2a).
[0043] FIG. 3. describes a filter cartridge housing with iron
(oxy)hydroxide adsorbents.
[0044] FIG. 5. describes a bag filter with iron hydroxide
granules.
DETAILED DESCRIPTION OF THE INVENTION
[0045] The cartridge housing can optionally contain iron oxide
pigments with BET surface areas below the above limits, whereby the
maximum content of these is such that the resistance of the charge
to the forces exerted upon it by the flowing medium is sufficiently
great that the stress exerted on the charge by the flowing medium
does not lead to an undesirable abrasion of the charge
material.
[0046] The invention also relates to a process for the production
of particles from fine-particle iron oxide and/or iron oxyhydroxide
comprising the steps of producing an aqueous suspension of
fine-particle iron oxides and/or iron oxyhydroxides having a BET
surface area of 50 to 500 m.sup.2/g, removing the water and
dissolved constituents by either
[0047] I) a) first removing only the water from the suspension, b)
introducing the residue thus obtained in water, c) filtering the
material obtained, d) washing the residue, and e) either e1)
completely dehydrating the filter cake obtained as residue and
comminuting the filter cake to the desired shape and/or size or e2)
partially dehydrating it to obtain a paste, shaping the paste and
subsequently additionally drying the paste until a pellet is
obtained, or
[0048] II) a) filtering the suspension, b) washing the residue, c)
either c1) completely dehydrating the filter cake obtained as
residue in the form of a solid to semisolid paste and then
comminuting the material thus obtained to the desired shape and/or
size or c2) partially dehydrating it to obtain a paste, shaping the
paste, followed by subsequent additional drying until a pellet is
obtained.
[0049] In this process the pellet can be further subjected to a
further comminution by grinding or rough grinding.
[0050] In this process the BET surface area can be 80 to 200
m.sup.2/g.
[0051] In this process the water can be removed by evaporation.
[0052] In this process the residue can be washed until it is low in
salts.
[0053] In this process the residue can be washed until it is free
from salts.
[0054] In this process the iron oxides and/or iron (oxy)hydroxides
can be a commercial pigment.
[0055] In this process the iron oxides and/or iron (oxy)hydroxides
can be a transparent pigment.
[0056] In this process the iron oxide and/or iron oxyhydroxide can
comprise Fe(OH).sub.2.
[0057] The object of the invention is achieved by a filtration unit
consisting of a housing made from plastic, wood, glass, ceramics,
metal or a composite material, provided with inlet and outlet
openings. Simple exemplary embodiments are illustrated by FIGS. 1a
and 1b. These housings are described in detail in DE-A 19 816 871.
The inlet and outlet openings are separated from the actual housing
chamber, which contains a bed of the iron oxyhydroxide adsorption
medium, by flat filter units which cover them. The fluid to be
treated thus passes successively through the first flat filter
layer, the adsorbent particles, the second flat filter layer and
the outlet opening. The housing chamber can be entirely or
partially filled with the adsorbent particles. The housing chamber
is preferably conical or pyramidal, but may also be obtained in a
cylindrical, spherical, cuboid or spirally wound form. By tapering
the housing chamber (see FIG. 1b), the filtration can be performed
in any of the layers, for example, preventing the formation of a
bypass between the bed of adsorbent particles through which the
fluid to be filtered can pass unhindered without adsorption.
Filling the housing chamber with a bed of adsorbent particles
taking up between 97 and 99% of the volume of the housing ensures a
high flow rate of the fluid to be cleaned, since the flow of liquid
meets a low resistance due to the resistance of the adsorbent
granules.
[0058] In preferred embodiments of the invention, the housing
chamber takes the form of a truncated cone or truncated pyramid in
the tapered sections.
[0059] Depending on the area of application, a variety of materials
are shown for the flat filter layers, e.g. in DE-A 19 816 871.
[0060] FIG. 2a and 2b show an improved embodiment of an adsorber
tank. They both illustrate the domestic filter module in
longitudinal section.
[0061] The adsorber housing (4) with the iron oxyhydroxide
adsorbent material (5) with filter plates positioned top (3) and
bottom (10) at the front and a centrally positioned inlet pipe (6)
can be isolated as a unit by means of a screw fitting with the
cover (13) at the upper end and a screw fitting with the base cap
(9) at the lower end by unfastening the screw fittings. When the
cartridge is exhausted, a new one can be inserted and the base and
cover plate cleaned. At the upper end the inlet pipe (6) is firmly
attached to the feed nozzle (2) during use by means of a suitable
sealing ring. The inlet pipe can be removed from the cartridge
housing and inserted in a new, fresh cartridge housing. The
incoming liquid flows through it directly onto a strainer basket
(7), which prefilters suspended matter, algae and the like and
retains it at the entrance to the actual adsorber cartridge,
preventing the adsorbent material from caking or agglutinating. The
strainer (7) serves to distribute the incoming stream of liquid
uniformly in the base chamber, is therefore preferably conical,
i.e. in the form of a truncated cone, and completely encloses the
inlet pipe and is fixed both to this and to the surrounding filter
plate (10) by means of loose sealing rings. The straining cloth can
be made from standard fine-meshed filter materials, e.g. from
plastic, natural material or metal.
[0062] The screwed-on base part (9) can additionally contain a
suitable filter material or filter cloth (8), which can be selected
according to the type and quantity of the anticipated suspended
material. With large quantities of solid impurities, the strainer
(7) and the filter cloth (8) can easily be removed and cleaned by
unscrewing the base part. The filter plate (10), which can consist
of fine-pored ceramics, separates the base chamber (9) from the
contact chamber with the iron oxyhydroxide granules (5), preventing
adsorbent material from entering the base chamber and prefiltered
material from entering the contact chamber. As the water to be
cleaned rises up through the contact room with the iron
oxyhydroxide adsorbent, the contaminants to be removed are removed
by physisorption and/or chemisorption at the adsorbent material. An
additional filter plate at the upper end of the cartridge housing
prevents any adsorbent material from entering the outlet (12).
Elevated water pressure or extended operating life of the adsorber
tank can cause fines to abrade from the adsorbent material and pass
through the filter plate (3). To prevent these fines (which are
laden with contaminants) from entering the outlet, filter material
or filter cloth (11), which retains the fines, is embedded inside
the cover (13).
[0063] The filter layers (3) and (10) also serve to distribute the
fluid uniformly in the adsorber chamber (5) and to collect it
together again when it emerges.
[0064] The clean water, freed from impurities and contaminants,
leaves the adsorber tank via the discharge nozzle (12).
[0065] The cover (13) can also include a valve to release the gases
entrained during operation for the first time (e.g. air contained
in the cartridge housing).
[0066] Depending on the application, it can be advantageous to
operate the adsorber tank described above in the reverse sequence
(FIG. 2b). This means that the water to be cleaned now passes from
the feed nozzle (1) directly onto the prefilter (11), which retains
suspended matter and foreign material, then passes through the
filter plate (3), enters the contact chamber, where the dissolved
contaminants are adsorbed on the adsorbent material, passes through
the cartridge base plate (10) into the base chamber (9), which may
contain embedded filter material (8) to retain abraded adsorbent
material, whereby the strainer basket (7) provides additional
filtration functions, such that the cleaned water leaves the
adsorber tank through the opening (1) via the outlet pipe (6) and
the discharge nozzle.
[0067] FIG. 4 illustrates a simpler embodiment, which nevertheless
operates according to the principle described above. It shows the
adsorber tank, which contains the adsorbent granules according to
the invention, and in which the adsorber cartridge forms a
unit.
[0068] Naturally other embodiments and designs resembling the
structure described and operating by the methods described are
possible in principle, i.e. containing an inlet and outlet opening
for water and iron oxide and/or iron (oxy)hydroxide as adsorbent
media.
[0069] FIG. 5 illustrates a filter bag which, when filled with
adsorbent granules, can be fed to a body of water to be cleaned in
order to remove the contaminants contained within it by
adsorption.
[0070] Filter bags and extraction thimbles, for example, are known
in many forms and designs for the preparation of hot infusions,
particularly tea. DE-A 839 405 describes a folding bag of this
type, for example, such as is used to prepare tea and the like. A
special folding technique, by means of which a dual chamber system
is formed, ensures a thorough mixing of the eluent with the
substance to be extracted.
[0071] Conversely, however, iron oxides or iron (oxy)hydroxides in
powdered, finely granulated or coarsely granulated form can be
embedded in semipermeable bags or sachets having a filtering action
(such as the folding bag described above, for example), and these
packages fed to the body of water to be cleaned in order to remove
the contaminants from the water by adsorption on the adsorbent
material after a certain contact time (see FIG. 5). The iron oxides
and/or iron (oxy)hydroxides withstand the mechanical and hydraulic
stresses in the filter bag on the one hand and on the other hand
the filter performance of the filter membrane prevents any fines
from the adsorbent caused by abrasion from entering the water to be
cleaned.
[0072] Common to the various embodiments of the present invention
is the fact that iron hydroxide or iron oxyhydroxide in finely
granulated, coarsely granulated or powdered form is embedded in
housings having a filtering action, and the liquid to be cleaned is
allowed to flow through the filter housing or the filter pack is
fed to the liquid to be cleaned, thereby ensuring adsorption of the
contaminants.
[0073] To prepare the granules according to the invention, an
aqueous suspension of fine-particle iron oxyhydroxides and/or iron
oxides is first produced according to the prior art. The water and
constituents dissolved within it can be removed from this in two
different ways:
[0074] Method 1
[0075] For applications in which lower demands are made of the
mechanical strength of the granules/contacts, only the water is
removed initially, e.g. by evaporation. A residue is obtained which
in addition to the fine-particle iron oxide and/or hydroxide also
contains the entire salt content. This residue is redispersed in
water after being dried, for which purpose only relatively little
shear force needs to be applied. This suspension is then filtered
and the residue washed until it is substantially free from salts.
The filter cake obtained as residue is a solid to semisolid paste
which generally has a water content of between 10 and 90 wt. %.
[0076] This can then be completely or partially dehydrated, and the
material thus obtained can then be comminuted to the desired shape
and/or size. Alternatively the paste or filter cake, optionally
after predrying to achieve a sufficiently solid state, can undergo
shaping followed by (additional) drying until a pellet state is
achieved. The subsequent application of the granules determines the
preferred procedure to be followed for their production, which can
be determined by the person skilled in the art in the particular
field of application by means of simple preliminary orienting
experiments. Both the directly dried filter cake and the dried
shaped bodies can then be used as contact or adsorbent.
[0077] Method 2
[0078] For applications in which higher demands are made of the
mechanical strength of the granules/contacts, the suspension is
filtered and the residue washed until it is substantially free from
salts. The filter cake obtained as residue is a solid to semisolid
paste. This can then be completely or partially dehydrated, and the
material thus obtained can then be comminuted to the desired shape
and/or size. Alternatively the paste or filter cake, optionally
after predrying to achieve a sufficiently solid state, can undergo
shaping followed by (additional) drying until a pellet state is
achieved. The subsequent application of the granules determines the
preferred procedure to be followed for their production, which can
be determined by the person skilled in the art in the particular
field of application by means of simple preliminary orienting
experiments. Both the directly dried filter cake and the dried
shaped bodies can then be used as contact or adsorbent.
[0079] Although the products obtained according to method 1 are
less mechanically resistant, filtration can be performed more
easily and quickly. The fine-particle pigments isolated in this way
can moreover be incorporated very easily into paints and polymers,
for example, because considerably less shear force is required than
is needed to incorporate the fine-particle pigments obtained
according to method 2.
[0080] The fine-particle iron oxide and/or iron oxyhydroxide used
has a particle size of up to 500 nm, preferably up to 100 nm,
particularly preferably 4 to 50 nm, and a BET surface area of 50 to
500 m.sup.2/g, preferably 80 to 200 m.sup.2/g.
[0081] The primary particle size was determined by measurement from
scanning electron micrographs, e.g. at a magnification of 60000:1
(instrument: XL30 ESEM FEG, Philips). If the primary particles are
needle-shaped, as in the (.alpha.-FeOOH phase for example, the
needle width can be given as a measurement for the particle size.
Needle widths of up to 100 nm, but mainly between 4 and 50 nm, are
observed in the case of nanoparticle .alpha.-FeOOH particles.
.alpha.-FeOOH primary particles conventionally have a length:width
ratio of 5:1 to 50:1, typically of 5:1 to 20:1. The length:width
ratio of the needle shapes can be varied, however, by doping or by
special reaction processes. If the primary particles are isometric,
as in the .alpha.-Fe.sub.2O.sub.3, .gamma.-Fe.sub.2O.sub.3,
Fe.sub.3O.sub.4 phases for example, the particle diameters can
quite easily also be below 20 nm.
[0082] By mixing nanoparticle iron oxides or iron (oxy)hydroxides
with pigments and/or Fe(OH).sub.3, the presence of the cited
pigment or nucleus particles in their known particle morphology,
held or glued together by the nanoparticle nucleus particles or the
amorphous Fe(OH).sub.3 polymer, can be detected on the scanning
electron micrographs.
[0083] Products obtainable by methods 1) or 2) can then be
comminuted further, for example by rough grinding or grinding.
However, since the products reduce in size autogenously on first
coming into contact with water, for example when a freshly charged
adsorber unit is first filled with water, this will generally be
unnecessary.
[0084] Granulation of a semi-wet paste has proven effective as
another method of producing granules. Here pellets or strands are
formed from a semi-wet paste, e.g. using a simple perforated metal
sheet, a roll press or an extruder, and either dried immediately or
additionally shaped into a spherical or granular form by means of a
spheroniser. The still wet spherules or granules can subsequently
be dried to any moisture content whatsoever. A residual moisture
content of <50% is recommended to prevent the granules from
agglomerating. A spherical shape of this type can be advantageous
for use in fixed-bed adsorbers due to the improved packing in the
adsorber vessel that is obtained in comparison with rough-ground
granules or pellets in strand form.
[0085] The filtration performance of the suspensions can generally
be improved by the use of conventional filtration-improving
measures, such as are described for example in Solid-Liquid
Filtration and Separation Technology, A. Rushton, A. S. Ward, R. G.
Holdich, 2nd edition 2000, Wiley-VCH, Weinheim, and in Handbuch der
Industriellen Fest/Flussig-Filtration, H. Gasper, D. chsle, E.
Pongratz, 2nd edition 2000, Wiley-VCH Weinheim. Coagulants can thus
be added to the suspensions, for example.
[0086] Iron carbonates can also be used in addition to or in place
of the iron oxyhydroxides.
[0087] The products according to the invention can undergo drying
in air, and/or in vacuo, and/or in a drying oven and/or on belt
dryers or by spray drying, preferably at temperatures from -25 to
250.degree. C., particularly preferably at 60 to 120.degree. C.
[0088] The products according to the invention preferably have a
residual water content of less than 20 wt. %.
[0089] It was found that the pellets or granules obtained in this
way have a high binding capacity for contaminants contained in
water, liquids or gases and they additionally have an adequately
high resistance to flowing media in terms of mechanical or
hydraulic stressing.
[0090] It is particularly surprising that during drying,
fine-particle iron oxyhydroxides or iron oxides having large
specific surface areas solidify into very hard agglomerates, which
without the addition of binders have a high mechanical abrasion
resistance and high hydraulic resistance to contact with flowing
water, and which have a high binding capacity for the contaminants
and trace constituents contained in the water.
[0091] Transparent iron oxyhydroxide pigments, for example, having
specific surface areas of over 80 m.sup.2 are suitable for the use
according to the invention of fine-particle iron oxyhydroxides.
Correspondingly fine-particle iron oxide pigments, preferably
haematite, magnetite or maghemite, can also be used, however.
[0092] The production of yellow fine-particle iron oxyhydroxide
pigments (e.g. goethite) in the acid or alkaline pH range, known as
acid or alkaline nuclei, is prior art. The production of other
fine-particle iron oxide or iron oxyhydroxide pigments is also
prior art. Such pigments can contain structures based on .alpha.,
.beta., .gamma., .delta., .delta.', .epsilon. phases and/or
Fe(OH).sub.2 and mixed and intermediate phases thereof.
Fine-particle yellow iron oxyhydroxides can be calcined to
fine-particle red iron oxides.
[0093] The production of transparent iron oxides and iron
oxyhydroxides is known e.g. according to DE-A 2 603 050 from BIOS
1144, p. 29 to 33 or from FIAT 814, p. 1 to 26.
[0094] Fine-particle yellow iron oxihydroxide pigments are
generally synthesised by precipitating iron(II) hydroxides or
carbonates from corresponding iron(II) salt solutions such as e.g.
FeSO.sub.4, FeCl.sub.2 in pure form or as pickling solutions in the
acid or alkaline pH range, followed by oxidation to iron(III)
oxihydroxides (see inter alia G. Buxbaum, Industrial Inorganic
Pigments, VCH Weinheim, 2nd edition, 1998, p. 231ff). Oxidation of
the divalent to the trivalent iron is preferably performed with
air, whereby intensive aeration is advantageous. Oxidation with
H.sub.2O.sub.2 also leads to fine-particle iron oxyhydroxides. The
temperature chosen for precipitation and oxidation should be as low
as possible in order to obtain very fine-particle yellow pigments.
It is preferably between 15.degree. C. and 45.degree. C. NaOH is
preferably used as alkaline precipitant. Other precipitants, such
as KOH, Na.sub.2CO.sub.3, K.sub.2CO.sub.3, CaO, Ca(OH).sub.2,
CaCO.sub.3, NH.sub.3, NH.sub.4OH, MgO and/or MgCO.sub.3, can also
be used, however.
[0095] To steer the precipitated pigments in the direction of the
extremely fine-particle character that is required, the
precipitations, e.g. of yellow .alpha.-FeOOH as described in
patents U.S. Pat. Nos. 2,558,303 and 2,558,304, are performed in
the alkaline pH range with alkali carbonates as precipitants, and
modifiers such as SiO.sub.2, zinc, aluminium or magnesium salts,
hydroxycarbonic acids, phosphates and metaphosphates are generally
added. Products produced in this way are described in U.S. Pat. No.
2,558,302. Such nucleus modifiers do not interfere with the
subsequent reprocessing, recycling or any other use of the
adsorbents according to the invention. In the case of precipitation
processes in an aqueous medium, it is known that precipitations in
an alkaline environment lead to less solidly agglomerated powders
than those in an acid environment.
[0096] DE-A 4 235 945 reports on the production of fine-particle
iron oxides using a precipitation method in the acid pH range and
without modifiers.
[0097] DE-A 4 434 669 describes a process by which highly
transparent yellow, chemically pure iron oxide pigments can be
produced by secondary treatment thereof with sodium hydroxide
solution.
[0098] DE-A 4 434 972 reports on highly transparent, yellow iron
oxide pigments in the .alpha.-FeOOH modification having a specific
surface area of over 100 m.sup.2/g and high temperature
resistance.
[0099] DE-A 4 434 973 describes highly transparent yellow iron
oxide pigments, which are produced by means of the process steps of
nuclear precipitation in the acid pH range, nuclear oxidation,
nuclear maturation and pigment formulation.
[0100] Red, transparent iron oxide pigments obtained by calcining
from yellow, transparent iron oxide pigments are known from DE-A 4
434 668 and DE-A 4 235 946.
[0101] By preparing diverse phases of iron oxyhydroxides in pure
form or in any mixture from iron(II) salt solutions using the known
precipitation and oxidation reactions, separating the resultant
iron oxyhydroxides out of the suspension, optionally after a
secondary treatment, by filtering the salt solution and washing
them until they are largely free from salts, preferably down to a
residual conductivity of <5 mS/cm, then drying the solid or
semisolid filter cake just as it is or optionally after mechanical
shaping until it achieves a solid state, a mechanically highly
resistant material displaying a high binding capacity for the
contaminants conventionally contained in waste waters or waste
gases is obtained.
[0102] Drying is conveniently performed at temperatures of up to
250.degree. C. The material can also be vacuum or freeze dried. The
particle size of the material can be freely selected but is
preferably between 0.2 and 40 mm, particularly preferably between
0.2 and 20 mm. This can be achieved by shaping the semisolid, pasty
filter cake mechanically before drying in a granulation or
pelletising plant or in an extruder to form shaped bodies whose
size is in the range between 0.2 and 20 mm, with subsequent drying
in the air, on a belt dryer or in a drying oven, and/or by
mechanical comminution to the desired particle size after
drying.
[0103] The products described, the process for their production and
their use represent an improvement over the prior art. In contrast
to those based on coarse-particle iron oxyhydroxides and/or oxides,
the granules according to the invention based on fine-particle iron
(oxy)hydroxides and/or oxides can be subjected to much higher
stresses and therefore display a much greater abrasion resistance
to mechanical and hydraulic stressing. They can be used directly as
such. When used in adsorber plants for water purification, for
example, there is no need even for comminution or rough grinding of
the crude dry substance initially obtained from filter cakes or
extruders, since the coarse pellets break down independently on
contact with water. This results in a random particle-size
distribution, but no particles of such a size that they are
discharged from the adsorber to any significant extent by the
flowing medium.
[0104] There is absolutely no need for a separate granulation
process, such as would be necessary when using conventional iron
oxyhydroxides in the form of (flowable) powders, either with the
aid of foreign binders or using extremely high linear forces during
compacting.
[0105] According to the invention, the suspensions of fine-particle
iron oxyhydroxides or iron oxides can also be supplemented with
conventional powdered iron oxyhydroxides or iron oxides. The
quantities in each case are determined by the properties of these
powdered iron oxyhydroxides or iron oxides and by the requirements
of the product according to the invention in terms of its
mechanical stability and abrasion resistance. Although the addition
of powdered pigments will generally reduce the mechanical strength
of the products according to the invention, filtration of the
fine-particle suspensions is made easier. The person skilled in the
art and practising in the particular field of application will be
able to determine the optimum mixing ratio for the intended
application by means of a few orienting experiments.
[0106] A quantity of aqueous salts of Fe.sup.3+, Al.sup.3+,
Mg.sup.2+, Ti.sup.4+ or mixtures thereof corresponding to the NaOH
excess can be added to the suspensions of the alkaline
fine-particle nuclei until sufficiently poorly soluble deposits of
Fe(OH).sub.3, Al(OH).sub.3, Mg(OH).sub.2, TiO(OH).sub.2 or ageing
products and dehydrated secondary products thereof are precipitated
onto the suspended iron oxide and/or iron (oxy)hydroxide particles.
Conversely, the poorly soluble deposits of Fe(OH).sub.3,
Al(OH).sub.3, Mg(OH).sub.2, TiO(OH).sub.2 or ageing products and
secondary products thereof can be precipitated onto the iron oxide
or iron (oxy)hydroxide particles suspended in Fe.sup.3+, Al.sup.3+,
Mg.sup.2+, Ti.sup.4+ solutions by the addition of alkalis, such as
e.g. NaOH, Ca(OH).sub.2, KOH, CaCO.sub.3, Na.sub.2CO.sub.3,
K.sub.2CO.sub.3, NH.sub.4OH. The aluminium oxide or aluminium
(oxy)hydroxide can also be precipitated from an aluminate
suspension (e.g. NaAlO.sub.2) onto the iron oxide and/or iron
(oxy)hydroxide particles.
[0107] The initially amorphous Fe(OH).sub.3 or Al(OH).sub.3
produced mature over time, to the FeOOH or AlOOH phase, for
example. This ensures that the sodium hydroxide solution used in
excess to produce the alkaline nucleus is completely used up. The
materials thus obtained also display large specific surface areas.
Just like the nanoparticle iron oxyhydroxides described above, the
material is extremely suitable for use in adsorbers since it
possesses a high resistance to mechanical loading in addition to a
high adsorption capacity.
[0108] The granules according to the invention are particularly
preferably used in the cleaning of liquids, especially for the
removal of heavy metals. A preferred application in this industrial
field is the decontamination of water, particularly of drinking
water. Particular attention has recently been paid to the removal
of arsenic from drinking water. The granules according to the
invention are extremely suitable for this purpose, since levels
that not only meet but actually fall below even the lowest limiting
values set by the US authority the EPA can be achieved using the
granules according to the invention.
[0109] To this end the granules can be used in conventional
adsorber units, such as are already used with a charge of activated
carbon, for example, to remove other types of contaminants.
Batchwise operation, in cisterns or similar containers for example,
optionally fitted with agitators, is also possible. However, use in
continuous plants such as continuous-flow adsorbers is
preferred.
[0110] Since untreated water to be processed into drinking water
conventionally also contains organic impurities such as algae and
similar organisms, the surface of adsorbents, especially the outer
surface of granular adsorbents, becomes coated during use with
mostly slimy deposits, which impede or even prevent the inflow of
water and hence the adsorption of constituents to be removed. For
this reason adsorber units are periodically back-flushed with
water, a process which is preferably performed at times of low
water consumption (see above) on individual units that have been
taken out of service. The adsorbent is whirled up and the
associated mechanical stress to which the surface is subjected
causes the undesirable coating to be removed and discharged against
the direction of flow during active operation. The wash water is
conventionally sent to a sewage treatment plant. The adsorbents
according to the invention have proven to be particularly effective
in this process, since their high strength enables them to be
cleaned quickly without suffering any significant losses of
adsorption material and without the back-flush water sent for waste
treatment being rich in discharged adsorption material, which is
possibly already highly contaminated with heavy metals.
[0111] The impurities that could block the adsorber cartridge are
retained by a suitable prefilter and afterfilter.
[0112] Material abrasion is minimised by the resistance according
to the invention of the granules and by suitable packing of the
adsorber granules.
[0113] Spraying granules of iron oxyhydroxide adsorbent having a
particle size <250.mu. have proven to be particularly favourable
because they lead to a particularly good packing density.
[0114] Since the granules according to the invention are free from
foreign binders, the material is comparatively easy to dispose of
after use. For instance, the adsorbed arsenic can be removed by
thermal or chemical means in special units, for example, resulting
in an iron oxide pigment as a pure substance which can either be
recycled for use in the same application or supplied for
conventional pigment applications. Depending on the application and
legal regulations, the content of the adsorber can also be used
without prior removal of the heavy metals, for example as a pigment
for colouring durable construction materials such as concrete,
since the heavy metals removed from the drinking water are
permanently immobilised in this way and taken out of the
hydrological cycle.
[0115] The invention therefore also provides water treatment plants
or waterworks in which units filled with the granules according to
the invention are operated, and processes for the decontamination
of water by means of such units, as well as such units
themselves.
[0116] For many applications, particularly those in which a maximum
mechanical strength is not required of the granules, the addition
of powdered pigments during production of the granules according to
the invention is a preferred embodiment.
[0117] Thus, for example, up to 40 wt. % of commercial goethite
(e.g. Bayferrox.RTM. 920, Bayer AG, Leverkusen DE) can be added to
a nucleus suspension according to example 2 of the present
application if the granules obtained according to the invention are
to be used for the removal of arsenic from drinking water in
adsorbers with a through-flow of water.
[0118] The BET specific surface area of the products according to
the invention is determined by the carrier gas process
(He:N.sub.2=90:10) using the single-point method, according to DIN
66131 (1993). The sample is baked for 1 h at 140.degree. C. in a
stream of dry nitrogen before measurement.
[0119] In order to measure the adsorption of arsenic(III) and
arsenic(V), 3 litres of an aqueous solution of NaAsO.sub.2 or
Na.sub.2HAsO.sub.4, each with the specified concentration of
approx. 2-3 mg/l arsenic, are treated with 3 g of the sample to be
tested in a 5 litre PE flask for a specific period and the flask
moved on rotating rollers. The adsorption rate of As ions on iron
hydroxide over this specific period, e.g. one hour, is stated as
mg(As.sup.3+/5+)/g(FeOOH).multidot.h, calculated from the balance
of the As.sup.3+/5+ ions remaining in solution.
[0120] The adsorption of Sb.sup.3+, Sb.sup.5+, Pb.sup.2+,
Hg.sup.2+, Cr.sup.6+ or Cd.sup.2+ ions is measured in the same way,
whereby the desired concentrations are established by dissolving
appropriate amounts of Sb.sub.2O.sub.3, KSb(OH).sub.6, PbCl.sub.2,
NaCrO.sub.4 or CdCl.sub.2 in H.sub.2O and adjusting the pH value to
7-9.
[0121] The As, Sb, Cd, Cr, Hg or Pb contents of the contaminated
iron oxyhydroxide or of the solutions are determined using mass
spectrometry (ICP-MS) according to DIN 38406-29 (1999) or by
optical emission spectroscopy (ICP-OES) according to EN-ISO 11885
(1998), with inductively coupled plasma as excitation agent in each
case.
[0122] The mechanical and hydraulic abrasion resistance was
assessed using the following method: 150 ml of demineralised water
were added to 10 g of the granules to be tested, having particle
sizes >0.1 mm, in a 500 ml Erlenmeyer flask, which was rotated
on a LabShaker shaking machine (Kuhner model from Braun) for a
period of 30 minutes at 250 rpm. The >0.1 mm fraction was then
isolated from the suspension using a screen, dried and weighed. The
weight ratio between the amount weighed out and the amount weighed
in determines the abrasion value in %.
[0123] The invention is described in greater detail below by means
of examples. The examples are intended to illustrate the process
and do not constitute a limitation.
EXAMPLES
Example 1
[0124] 237 l of an aqueous iron sulfate solution with a
concentration of 150 g/l FeSO.sub.4 were prepared at 24.degree. C.
113 l of an aqueous NaOH solution (227 g/l) were then quickly added
and the light blue suspension then oxidised with 40 l of air per
hour and per mol of iron for 1.5 hours.
[0125] The yellow suspension thus obtained was filtered out through
a filter press and the solid washed until the residual filtrate
conductivity was 1 mS/cm. The filter cake was in the form of a
spreadable and kneadable paste, which was dried on metal sheets in
a circulating air drying oven at 75.degree. C. until the residual
moisture content was 3 wt. %. The dried material was then roughly
ground to produce particle sizes of between 0.5 and 2 mm. The hard
pellets thus obtained were then placed directly in an adsorber
tank.
[0126] The product consisted of 100% .alpha.-FeOOH with an
extremely short-needled habit, whereby the needles were congregated
to form solid macroscopic agglomerates. Using a scanning electron
micrograph e.g. at a magnification of 60000:1, the needle widths
were measured at between 15 and 35 nm, the needle lengths between
150 and 350 nm. The needles were extremely agglomerated.
[0127] The BET specific surface area was 122 m.sup.2/g. The
adsorption rate for NaAsO.sub.2 with an original concentration of
2.3 mg (As.sup.3+)/l was 2.14 mg(As.sup.3+)/g(FeOOH).multidot.h,
for Na.sub.2HAsO.sub.4 with an original concentration of 2.7 mg
(As.sup.5+)/l it was 2.29 mg(As.sup.5+)/g(FeOOH).multidot.h.
Example 2
[0128] 800 l of an aqueous iron sulfate solution with a
concentration of 150 g/l FeSO.sub.4 were prepared at 29.degree. C.
and 147 l of an aqueous NaOH solution (300 g/l) added over 20
minutes with stirring. 2.16 kg of a 57% aqueous glycolic acid
solution were then added to the grey-blue suspension formed and
oxidation performed for 7 hours with 38 l of air per hour and per
mol of iron.
[0129] The dark brown suspension was filtered out through a filter
press and the solid washed until the residual filtrate conductivity
was 1 mS/cm. The filter cake was dried at 70.degree. C. in a
circulating air drying oven to a residual moisture of 5%, and the
very hard blackish brown dry product was roughly ground in a roller
crusher to particle sizes of up to 2 mm. The fine fraction <0.2
mm was separated out using a screen.
[0130] An X-ray diffractogram showed that the product consisted of
100% .alpha.-FeOOH. Using a scanning electron micrograph e.g. at a
magnification of 60000:1, the needle widths were measured at
between 15 and 20 nm, the needle lengths between 50 and 80 nm. The
particles were extremely agglomerated. The BET specific surface
area was 202 m.sup.2/g. The granules thus obtained were placed
directly in an adsorber tank with no further treatment.
[0131] The granules displayed an excellent adsorption performance
in respect of the contaminants contained in the flowing water and
demonstrated a high abrasion resistance, particularly when the
adsorber tank is being back-flushed causing the granules to be
whirled up strongly. The abrasion value after 30 minutes was only
1%.
[0132] Adsorption performance: The adsorption rate for NaAsO.sub.2
with an original concentration of 2.4 mg (As.sup.3+)/l was 1.0
mg(As.sup.3+)/g(FeOOH).multidot.h, for Na.sub.2HAsO.sub.4 with an
original concentration of 2.8 mg (As.sup.5+)/l it was 2.07
mg(As.sup.3+)/g(FeOOH).multidot.h.
Example 3
[0133] 1.3 l of an aqueous 300 g/l NaOH solution were added to an
.alpha.-FeOOH suspension obtained according to example 2 after a
two-hour maturation at 30.degree. C. with stirring, and
post-oxidation was performed simultaneously for one hour with 190 l
of air. The product was processed as described in example 2.
Fine-particle needles of pure .alpha.-FeOOH with a BET specific
surface area of 130 m.sup.2/g were obtained. Using a scanning
electron micrograph e.g. at a magnification of 60000:1, the needle
widths were measured at between 15 and 20 nm, the needle lengths
between 50 and 90 nm. The needles were extremely agglomerated. The
granules proved to be very mechanically and hydraulically
resistant, and the abrasion value was only 3.9%.
[0134] Adsorption performance: The adsorption rate for NaAsO.sub.2
with an original concentration of 2.3 mg (As.sup.3+)/l was 1.1
mg(As.sup.3+)/g(FeOOH).multidot.h, for Na.sub.2HAsO.sub.4 with an
original concentration of 2.8 mg (As.sup.5+)/l it was 1.7
mg(As.sup.3+)/g(FeOOH).multidot.h.
Example 4
[0135] 306 l of an aqueous NaOH solution (45 g/l) were prepared at
31.degree. C. and 43 l of an aqueous solution of FeCl.sub.2 (344
g/l) quickly added with stirring, and oxidation was then performed
with 60 l of air per hour and per mol Fe. The dark yellow
suspension thus obtained was processed in the same way as in
example 1.
[0136] An X-ray diffractogram showed that the product consisted of
100% .alpha.-FeOOH. Using a scanning electron micrograph e.g. at a
magnification of 60000:1, the needle widths were measured at
between 15 and 50 nm, the needle lengths between 100 and 200 nm.
The needles were extremely agglomerated. The BET specific surface
area was 132 m.sup.2/g.
[0137] The granules thus obtained were placed in an adsorber tank
with no further treatment. The granules displayed an excellent
adsorption performance in respect of the contaminants contained in
the water and demonstrated a high abrasion resistance, particularly
when the adsorber tank is being back-flushed causing the granules
to be whirled up strongly. The abrasion value after 30 minutes was
only 12 wt. %.
[0138] Adsorption performance: The adsorption rate for NaAsO.sub.2
with an original concentration of 2.4 mg (As.sup.3+)/l was 2.11
mg(As.sup.3+)/g(FeOOH).multidot.h, for Na.sub.2HAsO.sub.4 with an
original concentration of 2.7 mg (As.sup.5+)/l it was 2.03
mg(As.sup.5+)/g(FeOOH).multidot.h.
Example 5
[0139] 124 l of an aqueous NaOH solution (114 g/l) were prepared at
24.degree. C. and 171 l of an aqueous solution of FeSO.sub.4 (100
g/l) quickly added with stirring, and oxidation was then performed
with 10 l of air per hour and per mol Fe. Immediately upon
completion of oxidation, 56 l of an aqueous solution of
Fe.sub.2(SO.sub.4).sub.3 (100 g/l) were added and stirred for 30
minutes. The yellowish brown suspension thus obtained was processed
in the same way as in example 1.
[0140] An X-ray diffractogram showed that the product consisted of
100% .alpha.-FeOOH. Using a scanning electron micrograph e.g. at a
magnification of 60000:1, the needle widths were measured at
between 15 and 35 nm, the needle lengths between 70 and 180 nm. The
needles were extremely agglomerated. The BET specific surface area
was 131 ml/g. The abrasion value after 30 minutes was only 7 wt.
%.
[0141] Adsorption performance: The adsorption rate for NaAsO.sub.2
with an original concentration of 2.3 mg (As.sup.3+)/l was 1.7
mg(As.sup.3+)/g(FeOOH).multidot.h, for Na.sub.2HAsO.sub.4 with an
original concentration of 2.7 mg (As.sup.5+)/l it was 1.2
mg(As.sup.5+)/g(FeOOH).multidot.h.
Example 6
[0142] 7905 kg FeSO.sub.4 were measured out, dissolved with water
to a volume of 53.3 m.sup.3, the solution cooled to 14.degree. C.
and 1000 kg MgSO.sub.4.multidot.7 H.sub.2O added to this solution.
The prepared solution was then diluted at 14.degree. C. with 5056
kg NaOH as a solution with approx. 300 g/l and then oxidised with
4000 m.sup.3/h air to a precipitation degree of >99.5%. The
batch was washed on a filter press until the residual filtrate
conductivity was <1000 .mu.S/cm and the paste pushed through a
perforated metal plate with hole diameters of 7 mm, causing it to
be formed into strands. The strands were dried on a belt dryer to a
residual moisture of approx. 3%. An X-ray diffractogram showed that
the product consisted of 100% .alpha.-FeOOH with very short
needles. Using a scanning electron micrograph e.g. at a
magnification of 60000:1, the needle widths were measured at
between 30 and 50 nm. The needle lengths could not be clearly
determined as the needles were too greatly agglomerated. The BET
specific surface area was 145 m.sup.2/g. The abrasion value after
30 minutes was only 6%.
[0143] Adsorption performance: The adsorption rate for NaAsO.sub.2
with an original concentration of 2.5 mg (As.sup.3+)/l was 1.8
mg(As.sup.3+)/g(FeOOH).multidot.h, for Na.sub.2HAsO.sub.4 with an
original concentration of 2.9 mg (As.sup.5+)/l it was 1.5
mg(As.sup.5+)/g(FeOOH).multidot.h.
Example 7
[0144] 4096 kg NaOH (as solution with approx. 300 g/l) were
prepared and diluted with water to 40 m.sup.3. 4950 kg FeSO.sub.4
were dissolved with water to form 48.5 m.sup.3 solution, cooled to
15.degree. C. and then pumped into the prepared NaOH over 1 h. The
suspension was then oxidised with 1500 m.sup.3/h air over approx. 2
h. Approx. 2 m.sup.3 of the nucleus suspension was washed on a
filter press to obtain a filtrate conductivity <1000 .mu.S/cm,
the filter cake was dried in a drying oven at 75.degree. C. and the
dried material roughly ground to particle sizes <1.5 mm. The
fine fraction <0.5 mm was separated out using a screen. The
material thus obtained had a BET specific surface area of 153
m.sup.2/g and consisted of 100% .alpha.-FeOOH. Using a scanning
electron micrograph e.g. at a magnification of 60000:1, the needle
widths were measured at between 15 and 35 nm, the needle lengths
between 50 and 100 nm. The needles were extremely agglomerated.
[0145] Adsorption performance: The adsorption rate for NaAsO.sub.2
with an original concentration of 2.7 mg (As.sup.3+)/l was 1.7
mg(As.sup.3+)/g(FeOOH).multidot.h, for Na.sub.2HAsO.sub.4 with an
original concentration of 2.8 mg (As.sup.5+)/l it was 1.4
mg(As.sup.5+) g(FeOOH).multidot.h.
Example 8
[0146] An aqueous solution of FeSO.sub.4 (100 g/l) was added to
1600 g of the alkaline nucleus suspension prepared according to
example 7 (2.7% FeOOH) at room temperature with stirring and
simultaneous aeration with 130 l/h of air until a pH of 8 was
obtained. The nucleus suspension obtained was filtered, washed and
the filter cake dried at 75.degree. C. and roughly ground to
particle sizes of between 0.5 and 2 mm as described in example 7.
The material thus obtained had a BET specific surface area of 163
m.sup.2/g and according to the X-ray diffractogram consisted of
100% .alpha.-FeOOH. The scanning electron micrograph, e.g. at a
magnification of 60000:1, showed that the needles were extremely
agglomerated. Adsorption performance: The adsorption rate for
NaAsO.sub.2 with an original concentration of 2.7 mg (As.sup.3+)/l
was 2.0 mg(As.sup.3+)/g(FeOOH).multidot.h, for Na.sub.2HAsO.sub.4
with an original concentration of 2.7 mg (As.sup.5+)/l it was 1.9
mg(As.sup.5+)/g(FeOOH).multidot.h, for KSb(OH).sub.6 (original
concentration 3.0 mg (Sb.sup.5+)/l) the adsorption was 2.5 mg
(Sb.sup.5+)/g (FeOOH).multidot.h, for Na.sub.2CrO.sub.4 (original
concentration 47 .mu.g (Cr.sup.6+)/l) 42 .mu.g
(Cr.sup.6+)/g(FeOOH).multi- dot.h were adsorbed, for PbCl.sub.2
(original concentration 0.94 mg (Pb.sup.2+)/l) 0.46 mg (Pb.sup.2+)/
g(FeOOH).multidot.h were adsorbed.
Example 9
[0147] 6.4 l of an aqueous solution of NaOH (100 g/l) were prepared
at 29.degree. C. with stirring and 12.2 l of an aqueous iron(II)
sulfate solution (100 g/l) were added with simultaneous
introduction of air until a pH of 9 was obtained. The suspension
thus obtained was processed in the same way as in example 1. The
material had a BET specific surface area of 251 m.sup.2/g and
according to the X-ray diffractogram consisted of 100%
.alpha.-FeOOH. The scanning electron micrograph shows short, stumpy
needles, which are extremely agglomerated. Abrasion performance:
5%.
[0148] Adsorption performance: The adsorption rate for NaAsO.sub.2
with an original concentration of 2.7 mg (As.sup.3+)/l was 1.1
mg(As.sup.3+)/g(FeOOH).multidot.h, for Na.sub.2HAsO.sub.4 with an
original concentration of 2.7 mg (As.sup.3+)/l it was 1.0
mg(As.sup.5+)/g(FeOOH).multidot.h.
Example 10
[0149] 4096 kg NaOH (as solution with approx. 300 g/l) were
measured out and diluted with water to 40 m.sup.3. 4950 kg
FeSO.sub.4 were dissolved with water to form 48.5 m.sup.3 solution,
cooled to 15.degree. C. and then pumped into the prepared NaOH over
1 h. The suspension was then oxidised with 1500 m.sup.3/h air in
approx. 2 h. 14.4 m.sup.3 FeClSO.sub.4 solution (113.4 g/l) were
added to approx. 87 m.sup.3 of this suspension with stirring, and
stirred for a further 30 min. The batch was washed on a filter
press until the residual filtrate conductivity was <1000
.mu.S/cm and the paste pushed through a perforated metal plate with
hole diameters of 7 mm and formed into strands. The strands were
dried on a belt dryer to a residual moisture of approx. 5%. The dry
pellets were roughly ground to obtain a particle size of 2 mm. The
material thus obtained had a BET specific surface area of 142
m.sup.2/g and consisted of 100% .alpha.-FeOOH. Using a scanning
electron micrograph e.g. at a magnification of 60000:1, the needle
widths were measured at between 15 and 50 nm, the needle lengths
between 10 and 150 nm. The needles were extremely agglomerated.
[0150] Adsorption performance: The adsorption rate for NaAsO.sub.2
with an original concentration of 2.7 mg (As.sup.3+)/l was 2.1
mg(As.sup.3+)/g(FeOOH).multidot.h, for Na.sub.2HAsO.sub.4 with an
original concentration of 2.8 mg (As.sup.5+)/l it was 2.0
mg(As.sup.5+)/g(FeOOH).multidot.h, for CdCl.sub.2 (original
concentration 2.7 mg (Cd.sup.2+)/l) the adsorption was 1.1 mg
(Cd.sup.2+)/g(FeOOH).mult- idot.h, for KSb(OH).sub.6 (original
concentration 2.6 mg (Sb.sup.5+)/l) it was 1.9 mg
(Sb.sup.5+)/g(FeOOH).multidot.h, for Sb.sub.2O.sub.3 (original
concentration 2.3 mg (Sb.sup.3+)/l) it was 2.0 mg
(Sb.sup.3+)/g(FeOOH).mu- ltidot.h, for Na.sub.2CrO.sub.4 (original
concentration 2.6 mg (Cr.sup.6+)/l) it was 1.1 mg (Cr.sup.6+), for
PbCl.sub.2 (original concentration 1.6 mg (Pb.sup.2+)/l) it was
1.57 mg (Pb.sup.2+)/g(FeOOH).multidot.h.
Example 11
[0151] 3100 kg NaOH (as solution with approx. 100 g/l) were
measured out and diluted with cold water to 31 m.sup.3. The
temperature of the solution was 26.degree. C. 3800 kg FeSO.sub.4
were dissolved with water to form about 38 m.sup.3 solution, cooled
to 13-14.degree. C. and then pumped with stirring into the prepared
NaOH. The suspension was then oxidised with 2500 m.sup.3/h air in
approx. 75 m. 18.2 m.sup.3 FeSO.sub.4 solution (100 g/l) were added
at a rate of 150 l/min to this suspension with stirring and
gassing. The suspension was filtered on a filter press and washed
until the residual filtrate conductivity was <1000 .mu.S/cm, the
paste was pushed through a perforated metal plate and were dried on
a belt dryer to a residual moisture of less than 20%. The dry
pellets were roughly ground to obtain a particle size of less than
2 mm. The portion of the particles with less then 0.5 mm was
removed. The material thus obtained had a BET specific surface area
of 145 m.sup.2/g and consisted of 100% .alpha.-FeOOH.
Example 12
[0152] 569 ml of an MgSO.sub.4 solution (100 g/l) were added to 1 l
of a suspension of Bayferrox.COPYRGT. 920 with a solids content of
50 g/l FeOOH, then 173 g of a 24% NaOH solution were added with
stirring, and stirring was continued for a further 15 min. The
yellow suspension is washed at a nutsch filter to obtain a residual
filtrate conductivity of 1 mS/cm, and the filter cake dried to a
residual moisture of <2% in a drying oven at 75.degree. C. The
product was granulated to particle sizes of between 0.5 and 2 mm
and the granules used for arsenic adsorption.
[0153] An X-ray diffractogram shows that the product consists of
.alpha.-FeOOH and Mg(OH).sub.2. The scanning electron micrograph,
e.g. at a magnification of 60000:1, shows that the .alpha.-FeOOH
type needles are agglomerated or glued together by amorphous
layers. The BET specific surface area was 43 m.sup.2/g and
therefore, compared with Bayferrox.COPYRGT. 920 (BET approx. 15
m.sup.2/g). The abrasion value after 30 minutes was only 11%.
[0154] The adsorption rate for an aqueous NaAsO.sub.2 solution with
an original concentration of 2.6 mg (As.sup.3+)/l was 1.2
mg(As.sup.3+)/g(FeOOH).multidot.h, for an Na.sub.2HAsO.sub.4
solution with an original concentration of 2.7 mg (As.sup.5+)/l it
was 1.5 mg(As.sup.5+)/g(FeOOH).multidot.h.
Example 13
[0155] 46 ml of an Al.sub.2(SO.sub.4).sub.3 solution (100 g/l
Al.sub.2O.sub.3) were added to 950 g of a suspension of an alkaline
nanoparticle nucleus of .alpha.-FeOOH (solids content: 5.26 g/l
FeOOH, 1.14% NaOH) with stirring, and stirring was continued for a
further 15 min. The brown suspension is washed at a nutsch filter
to obtain a residual filtrate conductivity of 1 mS/cm, and the
filter cake dried to a residual moisture of <2% in a drying oven
at 75.degree. C. The product was granulated to particle sizes of
between 0.5 and 2 mm and the granules used for arsenic
adsorption.
[0156] The X-ray diffractogram of the product indicated only
.alpha.-FeOOH, which, as can be seen from the scanning electron
microgram, is present as very short and extremely agglomerated
needles. The BET specific surface area was 102 m.sup.2/g. The
abrasion value after 30 minutes was only 5%.
[0157] The adsorption rate for an aqueous NaAsO.sub.2 solution with
an original concentration of 2.6 mg (As.sup.3+)/l was 2.0
mg(As.sup.3+)/g(FeOOH).multidot.h, for an Na.sub.2HAsO.sub.4
solution with an original concentration of 2.1 mg (As.sup.5+)/l it
was 1.5 mg(As.sup.5+)/g(FeOOH).multidot.h.
Embodiment Example 14
[0158] Adsorbent granules produced according to examples 1 to 12,
typically between 0.5 and 2 mm or in comminuted form are placed in
a contact chamber as shown in FIG. 1 or 2. The filtration unit
displays a flow rate for air as fluid of 2000 ml per minute at a
pressure difference of 0.1 bar.
* * * * *