U.S. patent application number 10/300913 was filed with the patent office on 2006-01-12 for treatment of solid containing material derived from effluent.
This patent application is currently assigned to IMERYS MINERALS LIMITED. Invention is credited to Jonathan Stuart Phipps.
Application Number | 20060005932 10/300913 |
Document ID | / |
Family ID | 22526885 |
Filed Date | 2006-01-12 |
United States Patent
Application |
20060005932 |
Kind Code |
A2 |
Phipps; Jonathan Stuart |
January 12, 2006 |
TREATMENT OF SOLID CONTAINING MATERIAL DERIVED FROM EFFLUENT
Abstract
Abstract of the Disclosure A method of treating solid containing
material derived from effluent or sludge from a plant for de-inking
paper, the material containing calcium in the form of one or more
insoluble calcium compounds, the method including the steps of
treating the material with an acid to cause dissolution of the
calcium thereby forming a calcium ion-containing solution in which
insoluble solids are suspended, separating the solution from the
insoluble solids and incinerating the separated solids. The
solution containing calcium ions may be treated by adding one or
more reagents to form a calcium compound precipitate, eg calcium
carbonate. The particulate solids produced following the
incineration step and following the precipitate formation may be
employed as pigments or fillers in paper making or paper
coating.
Inventors: |
Phipps; Jonathan Stuart;
(Cornwall, GB) |
Correspondence
Address: |
FINNEGAN, HENDERSON, FARABOW, GARRETT & DUNNER
901 NEW YORK AVENUE, NW
WASHINGTON
DC
20001-4413
US
|
Assignee: |
IMERYS MINERALS LIMITED
John Kesy House St. Austell
Cornwall
GB
PL25
|
Prior
Publication: |
|
Document Identifier |
Publication Date |
|
US 20030234088 A1 US 20050167060 A2 |
August 4, 2005 |
|
|
Family ID: |
22526885 |
Appl. No.: |
10/300913 |
Filed: |
November 21, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09/996,931 |
Nov 30, 2001 |
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10300913 |
Nov 21, 2002 |
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09/148,685 |
Jul 30, 2002 |
6,425,973 |
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09/996,931 |
Nov 30, 2001 |
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Current U.S.
Class: |
162/29 ;
162/4 |
Current CPC
Class: |
D21C 11/0007 20130101;
Y10S 210/928 20130101; Y10S 162/09 20130101; Y02W 30/648 20150501;
Y02W 30/64 20150501; C01F 11/18 20130101; D21C 5/02 20130101; D21H
17/01 20130101; D21H 17/67 20130101 |
Class at
Publication: |
162/029 ;
162/004 |
International
Class: |
D21B 1/08 20060101
D21B001/08 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 31, 1996 |
GB |
9616037.9 |
Claims
1. (Canceled).
2. (Canceled).
3. (Canceled).
4. (Canceled).
5. (Canceled).
6. (Canceled).
7. (Canceled).
8. (Canceled).
9. (Canceled).
10. (New) A method for treating material derived from industrial
paper plant effluent or sludge, said method comprising: (a)
treating said material with an acid to cause dissolution of
calcium, thereby forming a calcium ion-containing solution in which
insoluble solids are suspended; (b) separating the suspended
insoluble solids from the calcium ion-containing solution in (a);
and (c) incinerating the insoluble solids obtained in (b), and
wherein fibrous material in said material derived from industrial
paper plant effluent or sludge is not subjected to combustion or
ignition prior to (a).
11. (New) A method for treating fiber-containing material derived
from industrial paper plant effluent or sludge, said method
comprising: (a) treating said fiber-containing material with an
acid to cause dissolution of calcium, thereby forming a calcium
ion-containing solution in which insoluble solids are suspended;
(b) separating the suspended insoluble solids from the calcium
ion-containing solution in (a); and (c) incinerating the insoluble
solids obtained in (b).
12. (New) A method for treating material derived from industrial
paper plant effluent or sludge, said method comprising: (a)
treating said material with an acid to cause dissolution of
calcium, thereby forming a calcium ion-containing solution in which
insoluble solids are suspended; (b) separating the suspended
insoluble solids from the calcium ion-containing solution in (a);
and (c) incinerating the insoluble solids obtained in (b).
13. (New) A method for treating fiber-containing material derived
from industrial paper plant effluent or sludge, the method
including treating the fiber-containing material with an acid to
cause dissolution of calcium, thereby forming a calcium
ion-containing solution in which insoluble solids are suspended,
separating the solution from the insoluble solids, and incinerating
the insoluble solids.
14. (New) The method of any one of claims 10, 11, 12, or 13,
further comprising subjecting the incinerated insoluble solids to
at least one additional treatment.
15. (New) The method of claim 14 wherein said at least one
additional treatment comprises comminuting the incinerated
insoluble solids.
16. (New) The method according to claim 15, wherein said
comminuting comprises attrition grinding.
17. (New) The method according to claim 15, wherein said
comminuting comprises media grinding.
18. (New) The method according to claim 15, wherein said
comminuting is accomplished in dry form.
19. (New) The method according to claim 15, wherein said
comminuting is accomplished in an aqueous suspension.
20. (New) The method according to claim 14, wherein said at least
one additional treatment is chosen from particle size
classification, washing, an additional heat treatment, and the
addition of at least one chemical agent.
21. (New) A method for treating material derived from industrial
paper plant effluent or sludge, comprising: (a) obtaining a
composition comprising kaolin and combustible organic compounds,
wherein said composition has been attained by treating material
derived from industrial paper plant effluent or sludge to remove
calcium; and (b) subjecting said composition to at least one heat
treatment process to incinerate said combustible organic compounds
and calcine the remaining material.
22. (New) The method according to claim 21, wherein said calcium
has been removed from said material derived from industrial paper
plant effluent or sludge with a composition comprising at least one
acid.
23. (New) The method according to claim 22, wherein said at least
one acid is a dilute acid.
24. (New) The method according to claim 22, wherein said at least
one acid is a mineral acid.
25. (New) The method according to claim 24, wherein said mineral
acid is chosen from hydrochloric acid and sulfuric acid.
26. (New) The method according to claim 21, wherein said
composition is subjected to at least one washing process prior to
being subjected to said at least one heat treatment process.
27. (New) The method according to claim 21, wherein said at least
one heat treatment process is performed in an incineration
device.
28. (New) The method according to claim 27, wherein said
incineration device is a fluidized bed furnace.
29. (New) The method according to claim 21, wherein said at least
one heat treatment process is performed at a temperature ranging
from 800.degree. C to 1200.degree. C.
30. (New) The method according to claim 29, wherein said at least
one heat treatment process is performed at a temperature ranging
from 950.degree. C to 1050.degree. C.
31. (New) The method according to claim 21, wherein said calcined
material is provided to a paper mill.
32. (New) The method according to claim 31, wherein said calcined
material is provided to a paper mill in a dry form.
33. (New) The method according to claim 31, wherein said calcined
material is provided to a paper mill in an aqueous slurry form.
34. (New) A filler comprising a product obtained by the process of
claim 21.
35. (New) A paper composition comprising a filler according to
claim 34.
36. (New) The filler according to claim 34, wherein said filler is
a paper-making filler.
37. (New) The filler according to claim 34, further comprising at
least one additional filler.
38. (New) The filler according to claim 37, wherein said at least
one additional filler is calcium carbonate.
39. (New) The filler according to claim 37, wherein said at least
one additional filler is kaolin.
40. (New) The filler according to claim 37, wherein said at least
one additional filler is calcined kaolin.
41. (New) The filler according to claim 37, wherein said at least
one additional filler is chosen from silicates, talc, calcium
sulfate, and titanium dioxide.
42. (New) The filler according to claim 34, wherein said filler is
in the form of a dilute slurry.
43. (New) A polymer composition comprising a product obtained by
the method of claim 21.
44. (New) A coating composition comprising a product obtained by
the method of claim 21.
45. (New) A paint composition comprising a product obtained by the
method of claim 21.
46. (New) A method for processing material derived from industrial
paper plant effluent or sludge, comprising: (a) subjecting said
material to at least one heat treatment process to produce a
calcined material, wherein said material derived from industrial
paper plant effluent or sludge has previously undergone treatment
to remove calcium.
47. (New) The method of claim 46, wherein said previously undergone
treatment to remove calcium comprises treating said material
derived from industrial paper plant effluent or sludge with an acid
to cause dissolution of the calcium, thereby forming a calcium
ion-containing solution in which insoluble solids are suspended;
and (a) separating the suspended insoluble solids from the calcium
ion-containing solution.
48. (New) The method of claim 46, wherein said calcined material
comprises kaolin.
49. (New) A method for treating material derived from industrial
paper plant effluent or sludge, said method comprising: (a)
treating said material with an acid to cause dissolution of
calcium, thereby forming a calcium ion-containing solution in which
insoluble solids are suspended; (b) separating said suspended
insoluble solids from said calcium ion-containing solution in (a),
wherein said separated insoluble solids are capable of being
subjected to at least one heat treatment process to incinerate the
combustible organic compounds and calcine remaining material.
50. (New) A method for treating material derived from industrial
paper plant effluent or sludge, comprising: (a) obtaining
industrial paper plant effluent or sludge that has been treated
with an acid to cause dissolution of calcium, thereby forming a
calcium ion-containing solution in which insoluble solids are
suspended; (b) separating said suspended insoluble solids from said
calcium ion-containing solution; (c) subjecting said separated
insoluble solids to at least one heat treatment process to dry the
solids and incinerate combustible organic compounds; and (d)
subjecting said dried insoluble solids to at least one heat
treatment process to calcine remaining material.
51. (New) A pigment comprising a product obtained by the method of
any one of claims 21, 46, or 50.
52. (New) A paper making furnish comprising a product obtained by
the method of any one of claims 21, 46, or 50.
53. (New) The method of any one of claims 21, 46, or 50, further
comprising subjecting the calcined material to at least one
additional treatment.
54. (New) The method of claim 53, wherein said at least one
additional treatment comprises comminuting the calcined
material.
55. (New) The method according to claim 54, wherein said
comminuting comprises attrition grinding.
56. (New) The method according to claim 54, wherein said
comminuting comprises media grinding.
57. (New) The method according to claim 54, wherein said
comminuting is accomplished in dry form.
58. (New) The method according to claim 54, wherein said
comminuting is accomplished in an aqueous suspension.
59. (New) The method according to claim 53, wherein said at least
one additional treatment is chosen from particle size
classification, washing, an additional heat treatment, and the
addition of at least one chemical agent.
60. (New) The method according to claim 59, wherein said at least
one chemical agent is chosen from optical brightening agents and
coagulants.
61. (New) The method according to claim 59, wherein said additional
heat treatment dries the solids and incinerates combustible organic
compounds.
Description
Detailed Description of the Invention
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to the treatment of solid
containing material derived from effluent, especially to recover
useful materials therefrom.
[0003] In particular, this invention is concerned with a method for
recovering useful materials from what has hitherto been regarded as
the waste material produced by an industrial plant for treating
paper, especially for de-inking waste paper.
[0004] Paper and paperboard products are generally made by
preparing a dilute aqueous suspension containing cellulosic fibres
derived from wood or from some other suitable fibrous material, and
de-watering the suspension on a moving wire mesh belt to form a
sheet material. The suspension may also contain a proportion of a
mineral filler material which improves the brightness and opacity
of the finished paper or board. Natural cellulosic fibrous
materials are generally expensive, and the trees or other plants
from which they are obtained must be replaced if the balance of the
environment is not to be disturbed. It is therefore desirable to
incorporate in the aqueous suspension from which the sheet material
is made a substantial proportion of cellulosic fibrous material
which has been recovered from waste paper. Most waste paper which
is recycled has been printed on at least one of its surfaces, and
it is necessary to separate the printing ink residue from the
cellulosic fibres if the recovered material is to be suitable for
use as a starting material in a paper making process. If the ink is
not separated, the fibrous material will generally be unacceptably
dark in colour. Generally, printing ink contains elemental carbon
(carbon black) and other dark material which causes the dark
coloration.
[0005] Commercially operated processes for de-inking waste paper
generally comprise a pulping stage in which the waste paper is
subjected to mechanical agitation in water which also contains
sodium hydroxide which causes the fibres to swell, and which breaks
down most ink vehicles by saponification or hydrolysis, sodium
silicate which acts as a pH buffer and agglomerates detached ink
particles to a convenient size, and a surfactant which wets the ink
particles and helps to keep them in suspension. The suspension
formed in the pulper is passed through a primary screening system
in which heavy foreign bodies, such as staples, paper clips and
pieces of grit are removed. The suspension passing through the
screens is then fed to a treatment plant comprising one or more
froth flotation cells, or one or more washing units, or a
combination of washing units and flotation cells. The froth
flotation cells are each provided near the bottom with a rotating
impeller and means for admitting air under pressure in the form of
fine bubbles in the region of the impeller. It may also be
advantageous to add to the suspension, before it enters the
flotation cell, a reagent known as a collector which attaches
itself preferentially to the ink particles and increases their
affinity with air relative to that with water. As a result, the ink
particles are preferentially lifted by the air bubbles to the
surface of the suspension in the flotation cell, where they are
discharged in a froth product.
[0006] In the washing units the pulp is subjected to agitation in
fresh or recycled water, optionally containing a dispersing agent,
and the washed pulp is then drained on a screen of aperture size
such as to retain the relatively long cellulosic fibres, while
allowing to pass the mineral and organic particles and the fine
fibre fragments.
[0007] The suspension which is discharged from the bottom of the
flotation cell, and/or the suspension which passes the screens of
the washing steps, is de-watered and the de-watered material, which
consists of substantially de-inked cellulosic fibre material, may
be subjected to further purification steps before being finally
de-watered and dried for re-use in a sheet forming process.
[0008] The de-inking treatment plant reject consists of an aqueous
effluent or sludge which is produced in large volumes. The reject
from some plants is discarded and transferred to a waste disposal
site, eg a landfill site. The reject from other plants is
incinerated and this beneficially reduces the volume of the reject
and generates useful heat energy from the combustion of organic
components. The ash from the incineration is subsequently disposed
of. However, in both cases, there is an undesirable cost and
environmental impact associated with disposal. Also, potentially
useful materials are wasted by the disposal process. The de-inking
treatment plant reject generally contains, in addition to the ink
particles and various additives employed in paper, a substantial
proportion of the inorganic filler particles which were originally
present in the waste paper. These filler particles usually consist
predominantly of a mixture of kaolin clay and calcium carbonate in
various proportions, although other inorganic filler particles such
as silicates, talc, calcium sulphate or titanium dioxide may also
be present in minor proportions.
[0009] 2. Related prior art
[0010] In the prior art, various patent specifications have been
published which describe processes for incinerating waste solids
from de-inking sludge. In some of these processes the ash produced
following incineration is further treated to render the particulate
material contained in the ash suitable for re-use in a paper making
process. Examples of specifications describing such processes
include WO96/32354. Where the sludge solids treated include calcium
carbonate this can react with kaolin present to produce a glassy
composite phase which causes the particulate product to be
abrasive. As described in EP798268-A1, the incineration temperature
may be controlled so as to minimise formation of the glassy phase,
but this procedure can be relatively complicated and expensive to
operate and may cause the resulting particulate product to have
inferior optical properties, eg a reduced brightness.
SUMMARY OF THE INVENTION
[0011] The present invention allows treatment of calcium
compound-containing solids obtained from a waste paper de-inking
sludge to be carried out in a manner which does not suffer from the
problems of the prior published processes referred to earlier and
allows improved products suitable for re-use as pigments and
fillers, eg for addition to papermaking compositions, to be
obtained in a simpler and cheaper manner.
[0012] According to the present invention there is provided a
method of treating solid containing material derived from effluent
or sludge from a plant for de-inking paper, the material containing
calcium in the form of one or more insoluble calcium compounds, the
method including the steps of treating the material to cause
dissolution of the calcium thereby forming a calcium ion-containing
solution in which insoluble solids are suspended, separating the
solution from the insoluble solids and incinerating the insoluble
solids.
[0013] The treated solid containing material may comprise the said
effluent or sludge, optionally after diluting with water, and may
comprise the particulate materials described hereinbefore. The said
calcium compound may comprise calcium carbonate and/or calcium
sulfate and/or calcium silicate, and/or calcium phosphate.
[0014] The method of the invention may surprisingly and
beneficially be operated in a less costly manner than that
described in EP798268-A1, because it does not require use of the
close temperature control (which requires use of expensive
automation equipment), multiple calcination steps and recarbonation
(following aqueous dispersion) of the resulting ash all as required
in the process of EP798268-A1. As illustrated later, the product of
the method of the invention, even though produced by a less
complicated and less costly process, shows properties relevant to
re-use, eg in a paper making process, comparable with those
obtained for the product of the process of EP798268-A1.
DESCRIPTION OF THE INVENTION
[0015] The said treatment to cause dissolution of the calcium
comprises addition of an acid which may be a dilute acid. The
dilute acid used may comprise any one or more of the dilute acids
known to form soluble calcium salts. Mineral acids such as
hydrochloric acid are preferred. Some dilute acids, eg sulfuric
acid, which may be employed will cause the calcium ions released to
form a partially soluble salt, eg calcium sulfate. In this case,
the partially soluble salt will remain in the subsequently
separated and calcined solids.
[0016] In the method according to the present invention the calcium
dissolution step may be carried out with the assistance of heating
and other suitable agents, eg mechanical agitation or stirring.
[0017] After calcium has been dissolved over a sufficient period of
time, which will depend upon the amount of calcium to be dissolved,
the calcium ion-containing solution will generally have suspended
therein particulate solid material whose content will depend on the
composition of the original de-inking effluent or sludge and any
treatment which has been applied to it. The solid particulate
material may be separated from the calcium ion-containing solution
by one or more suitable known separation techniques, eg filtration,
evaporation or by use of a hydrocyclone or a centrifuge, applied in
one or more stages.
[0018] The solid material remaining after the acid dissolution step
may be treated, optionally after a drying step, by one or more heat
treatment steps which provide incineration of the combustible
organic compounds present and calcining of the remaining
particulate material which is likely to comprise principally
kaolin.
[0019] The heating step applied to calcine the kaolin-containing
particulate material may be carried out at a temperature higher
than that employed in the examples described in EP798268-A1. For
example, a single incineration and calcination step may be applied
in a known incineration device, eg a fluidised bed furnace, at a
temperature of between 900.degree.C and 1200.degree.C, desirably
from 950.degree.C to 1050.degree.C. Carbon present from the ink
contained in the de-inking sludge is oxidised quickly at this
temperature.
[0020] The resulting particulate material following incineration
and calcination may be further treated, either in a dry form or in
the form of an aqueous suspension, to improve the properties of the
particulate material, eg by comminution such as attrition or media
grinding in a known manner, particle size classification (if not
previously applied), washing, addition of chemical agents, eg
optical brightening agents, coagulants etc. The resulting
particulate product may be delivered in dry or aqueous slurry form
to a paper mill for use in a paper making or paper coating process
in a known manner optionally together with other known pigments, eg
kaolin, calcined kaolin, calcium carbonate, talc, titanium dioxide,
talc or calcium sulfate.
[0021] Where the recovered product is recycled for re-use in a
paper mill, the paper mill may be associated with the de-inking
plant from which the treated sludge has been obtained.
[0022] Where the recovered product is recycled for re-use in a
paper mill it may be used as a paper making filler in the mill in a
known manner. This filler, optionally mixed with other fillers as
described earlier, may be employed as a dilute slurry by mixture
with a dilute cellulose fiber slurry to produce a paper making
furnish. The solids of the furnish composition may for example
constitute from 0.2% to 2%, eg from about 0.5% to 1% by weight of
an aqueous suspension.
[0023] After the solid material has been separated the calcium
ion-containing solution may be treated to form a precipitate of
useful insoluble calcium compound. An alkali metal salt, eg a
sodium salt, may be added to the solution to provide the required
anion. For example, sodium carbonate may be added to the calcium
ion-containing solution to produce a calcium carbonate precipitate.
Where the calcium ion-containing solution comprises calcium
chloride, sodium chloride is left in solution.
[0024] Alternatively, an alkali metal hydroxide, eg sodium
hydroxide, may be added to release calcium hydroxide.
[0025] Where the calcium ion-containing solution contains calcium
hydroxide, formed for example by addition of an alkali metal
hydroxide to a calcium salt solution, carbon dioxide may
conveniently be added to the calcium hydroxide solution to form a
calcium carbonate precipitate. Formation of precipitated calcium
carbonate by addition of carbon dioxide to calcium hydroxide is, of
course, well known in the pigment producing art.
[0026] The insoluble calcium compound product thereby formed, eg
calcium carbonate, may be separated from the aqueous medium in
which it is formed by a suitable separation process, eg filtration,
evaporation or by use of a hydrocyclone or a centrifuge. The
product may be stored and thereafter supplied for use in one of the
applications described hereinafter, especially as a particulate
filler in the manufacture or coating of paper. Where the solution
contains little dissolved material after formation of the calcium
compound precipitate, eg after calcium hydroxide has been converted
to calcium carbonate using carbon dioxide, the suspension or slurry
containing the precipitate may itself be used optionally with
partial dewatering.
[0027] For example, the suspension may be delivered to a paper mill
for use of the suspension as a particulate filler supply for use in
paper manufacture or one of the other pigment or filler
applications described for the calcined kaolin-containing material
described earlier. The method of use may be as for that
material.
[0028] If the solution in which the insoluble calcium precipitate
is produced contains dissolved species these may optionally be
recovered and re-used. For example, where the dissolved species
comprises sodium chloride solution this may be electrolysed in a
known way to produce sodium hydroxide plus hydrogen and chlorine
gases. The gases may be recombined to produce hydrogen chloride
from which hydrochloric acid can be recovered which can be
re-cycled for re-use in the acid dissolution step. The sodium
hydroxide can be recycled for re-use as the alkali metal hydroxide
for addition to the calcium ion-containing solution. In addition,
carbon dioxide is produced in the dissolution step this may be
recycled for re-use in the precipitation step. In this way, the
need to purchase chemical reagents and to dispose of by-products
can be minimised or avoided.
[0029] The method according to the present invention beneficially
allows minimization of the amount of solid waste from a de-inking
plant thereby reducing or eliminating the cost and environmental
impact of disposal of such waste. Furthermore, the method allows
one or more useful products to be recovered in a manner which is
simpler and cheaper than the relevant prior art.
[0030] The useful product recovered includes a calcined
kaolin-containing particulate material which does not suffer
substantially from the abrasiveness normally caused by incinerating
kaolin and calcium carbonate together. In this case, the calcined
kaolin composition may be used in various pigment employing
applications, eg paper making as described earlier or in paper
coating, filling of polymers, paints and the like. Such a product
may show improved optical properties, eg brightness, compared with
products produced by incineration of solids from de-inking sludge
by prior published methods without discoloration from ink coloring
materials, eg carbon, and in a cheaper manner.
[0031] A further product, for example calcium carbonate, may also
be recovered without the dark coloration normally associated with
de-inking reject and is suitable for use in the various
applications in which precipitated calcium compounds, eg calcium
carbonate, are known to be useful, eg as a particulate filler or
extender material in paper, polymers, paints and the like or as a
coating pigment or colour ingredient for coating of paper, paper
board, plastic papers and the like.
[0032] Other particulate materials, eg silicate and aluminosilicate
material contained in the de-inking reject may, as described
hereinbefore, be converted after calcination into useful products,
eg pozzolans, and the reagents used in the method according to the
present invention may be recycled thereby minimizing reagent costs
and waste disposal.
BRIEF DESCRIPTION OF THE DRAWINGS
[0033] Figures 1 and 2 are schematic flow diagrams of alternative
methods embodying the invention.
DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS
[0034] Embodiments of the present invention will now be described
by way of example with reference to the accompanying drawings.
[0035] As shown in Figure 1, in a first example of a method
embodying the invention, input solid-containing material 1,
preferably in the form of an aqueous suspension, comprises, reject
sludge from a paper de-inking plant (not shown).
[0036] The material 1 is subject to an acid dissolution step in a
vessel 3 in which calcium present in the input material is
dissolved as a soluble salt, eg calcium chloride, by use of dilute
hydrochloric acid. The suspension formed by the acid dissolution
step is subject to a solid/liquid separation step in a separator 5.
Solids obtained by the separation step in the separator 5 is
delivered to an incinerator 9, eg operated at a temperature of
800.degree.C to 1200.degree.C as appropriate, which oxidises the
combustible organic material and carbon present in the solids and
produces an inorganic product 11 comprising predominantly calcined
kaolin (metakaolin). The product 11 optionally with further
treatment, eg comminution, particle size classification and
washing, may be delivered in dry or slurry form for use as a filler
in paper making in the manner described earlier.
[0037] The solution separated by the liquid/solid separation step
in the separator 5 may be delivered to a vessel 12 in which sodium
carbonate is added in a quantity calculated to give a required
amount of precipitated calcium carbonate according to the amount of
calcium present. The solution entering the vessel 12 may be
monitored on-line by a monitor 13 to determine its calcium ion
concentration and hence the required concentration of sodium
carbonate in the vessel 12. The solution separated by the
liquid/solid separation in the separator 5 may alternatively be
delivered to a vessel 15 via a line also monitored by a monitor 13
in which sodium hydroxide solution is added to the solution to form
calcium hydroxide which will dissolve in the water present up to
its limiting solubility. Carbon dioxide is added in a reactor 17
(which may be the same as the vessel 15 or a separate reactor). The
required amount of carbon dioxide to be added may, as an
indication, be calculated from the amount of calcium hydroxide
present which in turn can be determined from the concentration of
calcium ions monitored by the monitor 13. It is not essential to
calculate the required amount of carbon dioxide since after all
calcium hydroxide has been consumed the pH of the solution will
drop indicating that the reaction has terminated.
[0038] The precipitate-containing slurry formed either in the
vessel 11 or in the reactor 17 is subjected to dewatering, eg by
evaporation, in a concentrator 19. Output material 21 in slurry or
dry powder form, as appropriate, from the concentrator 19 is
delivered to a storage tank 23 for onward supply to a user plant,
eg a paper making mill or plant in which the material 21 is to be
used as a paper filler material in the manner described
earlier.
[0039] Liquid 22 separated by the concentrator 19 may be discharged
as effluent or may be treated to recover reagents therefrom. For
example, where the liquid 22 comprises predominantly sodium
chloride solution, this may be electrolysed to produce hydrogen and
chlorine and to leave sodium hydroxide. The hydrogen and chlorine
may be combined to produce HCl for re-use in the acid dissolution
step in the vessel 3 leaving, from the electrolysis, sodium
hydroxide in the vessel 15 which may be re-used.
[0040] An alternative method embodying the present invention is
illustrated in Figure 2. In this case, input material 25 comprises
de-inking plant effluent sludge preferably diluted with clean
water. This material 25 is delivered to an acid tolerant vessel 27
in which dilute hydrochloric acid is added. The suspension
remaining in the vessel 27 is subjected to liquid/solid separation
in a separator 29. The solid separated may be washed in a washer
unit 31 and thereafter dried in a dryer 26 and incinerated in a
fluid bed incinerator 28 operating at a temperature of about
1000.degree.C. Heat energy 36 is generated by the combustion of
organic material in the incinerator 28. Carbon is oxidized in the
incinerator. The solids output or ash from the incinerator 28
indicated by output 34 comprises predominantly calcined clay
(metakaolin). This product may be used as a pigment or filler as
described earlier, eg by re-use in paper making.
[0041] The solution indicated as 30 separated by the separator 29
and/or by the washer unit 31 is delivered to a concentrator 33.
Extracted water 32 may be re-used in the washing unit 31. The
solution concentrated by the concentrator 33 comprising mainly
calcium chloride is delivered to an electrolytic cell 35. Hydrogen
37 and chlorine 39 are produced by the cell 35 and are delivered to
a reactor 41 in which they are reacted to form hydrogen chloride
gas 42. The HCl gas 42 may be recycled after dilution as dilute
hydrochloric acid for addition in the vessel 27.
[0042] A calcium hydroxide-containing slurry formed by electrolysis
of calcium chloride in the cell 35 is delivered to a reactor 43, in
a metered amount, and an appropriate amount of carbon dioxide 45
which may be obtained as a by-product from the acid dissolution in
the vessel 27 is supplied to the reactor 43 to provide conversion
of the calcium hydroxide present to precipitated calcium carbonate.
The product slurry formed may be concentrated by dewatering in a
concentrator 46 and delivered to a storage tank 47 for onward
delivery as a product, eg as a particulate filler in paper
manufacture. Alternatively, the product slurry formed in the
reactor 43 may be delivered via the storage tank 47 for use without
dewatering. Water 46 obtained from the dewatering process in the
concentrator 46 may be recycled for dilution of the HCl output
42.
EXAMPLE
[0043] A deinking sludge having a calcium carbonate content of
about 5% by weight and a kaolin content of about 40% by weight,
based on the dry solids weight of the sludge, was treated in the
manner described with reference to Figure 1 by addition of dilute
hydrochloric acid to dissolve the calcium carbonate present
followed by incineration and calcination in a furnace at a
temperature of about 1000.degree.C for several hours overnight. The
product obtained was redispersed in water and milled by
sandgrinding and then subjected to the tests described later in
this Example. The Product is there referred to as `Product 2`. For
comparison purposes, a further product, Product 1, was made without
acid dissolution by the more complicated and costly method
described in EP798268 using carefully controlled incineration and
calcination at a temperature of 750.degree.C.
[0044] Products 1 and 2 were tested as follows:
[0045] The ISO brightness was measured and the particle size
distribution was measured using a SEDIGRAPH 5100 machine. The
results which were obtained are as shown in Table 1 as
follows.TABLE 1: PHYSICAL PROPERTIES TABLE-US-00001 Product 1
(comparative) Product 2 Brightness, ISO 82.2 83.4 PSD 100 100 %
<10 microns % <5 microns 100 100 % <2 mircrons 97 99 %
<1 mircron 88 92 % <0.5 micron 53 64 % <0.25 micron 12
24
[0046]
[0047] These results show that a better brightness and finer
particle size distribution are obtainable using a method embodying
the invention which is simpler and cheaper to run than that
described in EP798268-A1.
[0048] Products 1 and 2 were evaluated in 48gsm newsprint to
compare their performance as fillers.
[0049] Handsheets were made on a TAPPI sheet mold and dried on a
Noble & Wood drum dryer. The sheets were then conditioned
before testing. Experimental conditions for the handsheet study are
given in Table 2 below.
[0050] The handsheets were tested for brightness, opacity, caliper,
Gurley porosity, burst and % ash. Scattering and absorption
coefficients along with bulk were calculated. The handsheets were
then calendered, conditioned again and tested.
[0051] Handsheet properties are given in Table 3 below. Sheet
properties were interpolated at 5% filler to give a comparison of
the pigments. The results obtained are shown in Table 4 below.
TABLE 2: EXPERIMENTAL CONDITIONS OF SHEET FORMATION
[0052] The following handsheet preparation conditions were employed
to make handsheets in accordance with TAPPI standard T205.om-88
("Forming handsheets for physical tests of pulp"). TABLE-US-00002
Pulp: 90% TMP 10% Kraft Final consistency 0.3% solids in aqueous
suspension Grammage 48 gsm pH 4.8 Sheet Mold Tappi Calendering
conditions Machine calender at 38.degree. C. 1 nip @ 150 psi 1 nip
@ 250 psi 1 nip @ 250 psi
[0053]
[0054] For calendering preparation, the handsheets were placed in
the desiccator for 10 minutes with water to allow the moisture
content of the sheets to increase to ~8%. Between each nip the
sheets were placed back in the desiccator for 5 minutes and then
only one set was removed at a time. TABLE-US-00003 TABLE 3
UNCALENDERED HANDSHEET PROPERTIES ISO % Grammage Brightness Pigment
Tappi Hunter Optest Gurley Burst gsm Ash % Scatter Opacity L a b
Formation Porosity Index Product 1 Sample 1 47.0 2.8 59.3 2652 88.2
87.0 -1.3 14.0 90.4 13.6 1.73 Sample 2 46.4 6.0 61.6 3164 90.3 87.9
-1.3 13.2 84.1 15.0 1.75 Sample 3 45.7 8.3 61.6 2485 90.6 87.6 -1.3
12.9 76.1 8.4 1.81 Product 2 Sample 1 46.6 2.9 58.4 1995 87.5 87.1
-1.3 14.0 94.1 12.8 1.82 Sample 2 46.8 6.0 61.6 2414 89.0 88.0 -1.3
13.4 88.1 12.1 1.53 Sample 3 45.7 8.7 62.7 2236 89.6 88.4 -1.3 13.0
83.9 11.5 1.49
[0055] TABLE-US-00004 TABLE 4 UNCALENDERED HANDSHEET PROPERTIES ISO
DATA % Grammage Brightness Pigment Tappi Hunter Gurley filler gsm
Ash % Scatter Opacity L a b Porosity Product 1 Sample 1 47.0 2.8
58.9 2402 88.3 86.5 -1.2 13.7 37.1 Sample 2 46.4 6.0 61.1 2731 90.0
67.4 -1.1 13.0 35.4 Sample 3 45.7 8.3 61.3 2400 90.7 67.2 -1.1 12.6
29.4 Product 2 Sample 1 46.6 2.9 69.3 1822 87.6 86.8 -1.1 13.8 42.2
Sample 2 46.8 6.0 61.3 2014 88.6 87.6 -1.1 13.2 27.6 Sample 3 45.7
8.7 62.3 2202 89.9 88.0 -1.1 12.7 26.5
[0056] The results shown in Tables 3 and 4 illustrate that the
product obtained by the method embodying the invention gives
similar properties (which are superior in some cases) to those
obtained for the product of the process described in EP798268-A1
but, as described earlier, the product of the method embodying the
invention may be obtained by a less expensive de-inking sludge
treatment process.
* * * * *