U.S. patent application number 12/700193 was filed with the patent office on 2010-06-24 for desalination methods and systems that include carbonate compound precipitation.
Invention is credited to Brent R. Constantz, Kasra Farsad, Miguel Fernandez.
Application Number | 20100154679 12/700193 |
Document ID | / |
Family ID | 40159097 |
Filed Date | 2010-06-24 |
United States Patent
Application |
20100154679 |
Kind Code |
A1 |
Constantz; Brent R. ; et
al. |
June 24, 2010 |
DESALINATION METHODS AND SYSTEMS THAT INCLUDE CARBONATE COMPOUND
PRECIPITATION
Abstract
Desalination methods that include carbonate compound
precipitation are provided. In certain embodiments, feed water is
subjected to carbonate compound precipitation conditions prior to
desalination. In certain embodiments, desalination waste brine is
subjected to carbonate compound precipitation conditions. In yet
other embodiments, both feed water and waste brine are subjected to
carbonate compound precipitation conditions. Aspects of embodiments
of the invention include carbon dioxide sequestration. Embodiments
of the invention further employ a precipitate product of the
carbonate compound precipitation conditions as a building material,
e.g., a cement. Also provided are systems configured for use in
methods of the invention.
Inventors: |
Constantz; Brent R.;
(Portola Valley, CA) ; Farsad; Kasra; (San Jose,
CA) ; Fernandez; Miguel; (San Jose, CA) |
Correspondence
Address: |
Calera Corporation;Eric Witt
14600 Winchester Blvd.
Los Gatos
CA
95032
US
|
Family ID: |
40159097 |
Appl. No.: |
12/700193 |
Filed: |
February 4, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12163205 |
Jun 27, 2008 |
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12700193 |
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61073326 |
Jun 17, 2008 |
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60937786 |
Jun 28, 2007 |
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61017392 |
Dec 28, 2007 |
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Current U.S.
Class: |
106/638 ;
202/152; 203/10; 210/201; 210/202; 210/652; 210/702; 210/710;
422/162 |
Current CPC
Class: |
Y02A 20/128 20180101;
Y02A 20/124 20180101; C02F 2103/08 20130101; C02F 1/66 20130101;
B01D 2311/04 20130101; Y02A 20/131 20180101; B01D 2311/06 20130101;
C02F 1/5236 20130101; C02F 1/04 20130101; Y02W 10/33 20150501; C02F
1/441 20130101; Y02W 10/37 20150501; B01D 61/025 20130101; B01D
2311/04 20130101; B01D 2311/26 20130101; B01D 2311/06 20130101;
B01D 2311/103 20130101; B01D 2311/26 20130101 |
Class at
Publication: |
106/638 ;
422/162; 210/201; 202/152; 210/202; 210/702; 210/652; 203/10;
210/710 |
International
Class: |
C04B 7/00 20060101
C04B007/00; C02F 1/04 20060101 C02F001/04; C02F 1/52 20060101
C02F001/52; C02F 1/44 20060101 C02F001/44 |
Claims
1.-6. (canceled)
7. A system for desalinating water, said system comprising: an
input of water to be desalinated; a desalination station; a
carbonate compound precipitation reactor, wherein the precipitation
reactor is configured to contact the water and an industrial waste
source of carbon dioxide to produce a material comprising an
alkaline earth metal carbonate as a solid product and an
alkaline-earth-metal-depleted product water; and a
solids-separating system to separate the precipitate and a drying
system to dry the precipitate to form a dried composition.
8. The system according to claim 7, wherein said carbonate compound
precipitation reactor is positioned such that water from said input
passes through said reactor prior to entering said desalination
station.
9. The system according to claim 7, wherein said carbonate compound
precipitation reactor is positioned such that waste brine produced
by said desalination stations passes through said reactor.
10. The system according to claim 7, wherein said desalination
station comprises a distillation desalination apparatus, a reverse
osmosis desalination apparatus, a nano-filtration apparatus, or a
combination thereof.
11. The system according to claim 7, wherein said system further
comprises a cement production station that produces cement from
precipitate produce by said reactor.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] Pursuant to 35 U.S.C. .sctn.119 (e), this application claims
priority to the filing dates of: U.S. Provisional Patent
Application Ser. No. 61/073,326 filed on Jun. 17, 2008; U.S.
Provisional Patent Application Ser. No. 60/937,786 filed on Jun.
28, 2007 and U.S. Provisional Patent Application Ser. No.
61/017,392 filed on Dec. 28, 2007; the disclosures of which
applications are herein incorporated by reference.
INTRODUCTION
[0002] Desalination systems are desirable in many arid regions and
in marine applications where fresh water supplies are limited but
large amounts of seawater, inland waterways, rivers, or other
sources of salt containing water are available. Fresh water is also
needed in large scale for many commercial processes, including
agriculture, and electric power generation.
[0003] Most conventional desalination systems utilize reverse
osmosis or distillation processes. Both of these processes
typically result in recovery ratios of approximately 50%. Thus for
every gallon of water taken in as feed 1/2 of a gallon will become
purified product water and the other 1/2 gallon will be discharged
with a brine content approximately double in concentration of the
feed water's concentration. Discharge of this concentrated brine to
the environment can produce localized negative impacts.
Conventional desalination systems can produce a brine byproduct
that is high in salts and toxic to most organisms. Disposal of the
waste brine is potentially hazardous to the environment.
[0004] In addition, components of desalination feed waters can
adversely impact the efficiency and/or useful life of desalination
systems and components therefore. For example, in reverse osmosis
systems, the presence of divalent cations in the feed water can
cause membrane fouling or scaling, which limits the useful life of
the membranes.
SUMMARY
[0005] Desalination methods that include carbonate compound
precipitation are provided. In certain embodiments, feed water is
subjected to carbonate compound precipitation conditions prior to
desalination. In certain embodiments, desalination waste brine is
subjected to carbonate compound precipitation conditions. In yet
other embodiments, both feed water and waste brine are subjected to
carbonate compound precipitation conditions. Aspects of the
invention include carbon dioxide sequestration. Embodiments of the
invention further employ a precipitate product of the carbonate
compound precipitation conditions as a building material, e.g., a
cement. Also provided are systems configured for use in methods of
the invention.
BRIEF DESCRIPTION OF THE FIGURES
[0006] FIG. 1 provides a flow diagram of a precipitation process
according to an embodiment of the invention.
[0007] FIG. 2 provides a graph of strength attainment results as
determined for various Portland cement blends, including blends
comprising a carbonate compound precipitate according to an
embodiment of the invention, as described in greater detail in the
Experimental Section, below.
[0008] FIGS. 3A to 3C provide SEM micrographs of a precipitate
produced as described in the Experimental section below.
[0009] FIG. 4 provides an FTIR of a precipitate produced as
described in the Experimental section below.
DETAILED DESCRIPTION
[0010] Desalination methods that include carbonate compound
precipitation are provided. In certain embodiments, feed water is
subjected to carbonate compound precipitation conditions prior to
desalination. In certain embodiments, desalination waste brine is
subjected to carbonate compound precipitation conditions. In yet
other embodiments, both feed water and waste brine are subjected to
carbonate compound precipitation conditions. Aspects of the
invention include carbon dioxide sequestration. Embodiments of the
invention further employ a precipitate product of the carbonate
compound precipitation conditions as a building material, e.g., a
cement. Also provided are systems configured for use in methods of
the invention.
[0011] Before the present invention is described in greater detail,
it is to be understood that this invention is not limited to
particular embodiments described, as such may, of course, vary. It
is also to be understood that the terminology used herein is for
the purpose of describing particular embodiments only, and is not
intended to be limiting, since the scope of the present invention
will be limited only by the appended claims.
[0012] Where a range of values is provided, it is understood that
each intervening value, to the tenth of the unit of the lower limit
unless the context clearly dictates otherwise, between the upper
and lower limit of that range and any other stated or intervening
value in that stated range, is encompassed within the invention.
The upper and lower limits of these smaller ranges may
independently be included in the smaller ranges and are also
encompassed within the invention, subject to any specifically
excluded limit in the stated range. Where the stated range includes
one or both of the limits, ranges excluding either or both of those
included limits are also included in the invention.
[0013] Certain ranges are presented herein with numerical values
being preceded by the term "about." The term "about" is used herein
to provide literal support for the exact number that it precedes,
as well as a number that is near to or approximately the number
that the term precedes. In determining whether a number is near to
or approximately a specifically recited number, the near or
approximating unrecited number may be a number which, in the
context in which it is presented, provides the substantial
equivalent of the specifically recited number.
[0014] Unless defined otherwise, all technical and scientific terms
used herein have the same meaning as commonly understood by one of
ordinary skill in the art to which this invention belongs. Although
any methods and materials similar or equivalent to those described
herein can also be used in the practice or testing of the present
invention, representative illustrative methods and materials are
now described.
[0015] All publications and patents cited in this specification are
herein incorporated by reference as if each individual publication
or patent were specifically and individually indicated to be
incorporated by reference and are incorporated herein by reference
to disclose and describe the methods and/or materials in connection
with which the publications are cited. The citation of any
publication is for its disclosure prior to the filing date and
should not be construed as an admission that the present invention
is not entitled to antedate such publication by virtue of prior
invention. Further, the dates of publication provided may be
different from the actual publication dates which may need to be
independently confirmed.
[0016] It is noted that, as used herein and in the appended claims,
the singular forms "a", "an", and "the" include plural referents
unless the context clearly dictates otherwise. It is further noted
that the claims may be drafted to exclude any optional element. As
such, this statement is intended to serve as antecedent basis for
use of such exclusive terminology as "solely," "only" and the like
in connection with the recitation of claim elements, or use of a
"negative" limitation.
[0017] As will be apparent to those of skill in the art upon
reading this disclosure, each of the individual embodiments
described and illustrated herein has discrete components and
features which may be readily separated from or combined with the
features of any of the other several embodiments without departing
from the scope or spirit of the present invention. Any recited
method can be carried out in the order of events recited or in any
other order which is logically possible.
Methods
[0018] As summarized above, aspects of the invention include
desalination method, where an aspect of the methods is that a
carbonate compound precipitation process is performed at one or
more times during the overall desalination protocol, e.g., where
the feed water and/or waste brine is subjected to carbonate
compound precipitation conditions. Embodiments of the methods
include: (a) subjecting a feed water to carbonate compound
precipitation conditions one or more times to produce a carbonate
compound precipitate and an alkali-earth-metal-ion-depleted water;
and (b) desalinating the alkali-earth-metal-ion-depleted water to
produce a product water. Embodiments of the methods include: a)
desalinating salt water to produce desalinated water and waste
brine; b) subjecting the waste brine to mineral precipitation
conditions to produce a precipitated mineral composition and
depleted (i.e., treated) brine; and c) separating the mineral
composition from said depleted brine. In certain embodiments, these
steps may involve several sequential processes of step a-c,
resulting in near zero, or discharge following the processing. In
certain of the above embodiments, the methods include charging the
water with carbon dioxide from an exogenous source, such as the
flue gases from and electrical power plant, to increase the
efficiency and yield of the process.
[0019] The salt water that is desalinated in embodiments of the
invention may be from any convenient saltwater source. The term
"saltwater" is employed in its conventional sense to refer a number
of different types of aqueous fluids other than fresh water, where
the term "saltwater" includes brackish water, sea water and brine
(including man-made brines, e.g., geothermal plant wastewaters,
etc), as well as other salines having a salinity that is greater
than that of freshwater. Brine is water saturated or nearly
saturated with salt and has a salinity that is 50 ppt (parts per
thousand) or greater. Brackish water is water that is saltier than
fresh water, but not as salty as seawater, having a salinity
ranging from 0.5 to 35 ppt. Seawater is water from a sea or ocean
and has a salinity ranging from 35 to 50 ppt. The saltwater source
from which the saltwater feedwater is obtained may be a naturally
occurring source, such as a sea, ocean, lake, swamp, estuary,
lagoon, etc., or a man-made source. In certain embodiments, the
saltwater source is an ocean or sea and the saltwater feedwater is
seawater. Saltwaters of interest are ones which contain one or more
alkaline earth metals, e.g., magnesium, calcium, etc, such that
they may be viewed as alkaline-earth-metal-containing waters.
Examples of such waters are those that include calcium in amounts
ranging from 50 ppm to 20,000 ppm, such as 200 ppm to 5000 ppm and
including 400 ppm to 1000 ppm. Waters of interest include those
that include magnesium in amounts ranging from 50 ppm to 40,000
ppm, such as 100 ppm to 10,000 ppm and including 500 ppm to 2500
ppm.
[0020] Any convenient protocol may be employed in desalinating
saltwater. Desalination (i.e., desalinization or desalinization)
refers to any of several processes that remove excess salt and
other minerals from water. In desalination, water is desalinated in
order to be converted to fresh water suitable for animal
consumption or irrigation, or, if almost all of the salt is
removed, for human consumption. Desalination methods of interest
include, but are not limited to: distillation methods, e.g.,
Multi-stage flash distillation (MSF), Multiple-effect evaporator
(MED|ME), Vapor-compression evaporation (VC) and
Evaporation/condensation; Ion exchange methods; Membrane processes,
e.g., Electrodialysis reversal (EDR), Reverse osmosis (RO),
Nanofiltration (NF), Forward osmosis (FO), Membrane distillation
(MD); etc.
[0021] As summarized above, at some point during the overall
desalination process, e.g., before and/or after desalination, a
carbonate compound precipitation step is performed, such that a
water is subjected to carbonate compound precipitation conditions.
As such, a feedwater and/or waste brine of the desalination process
is subjected carbonate compound precipitation conditions. Carbonate
precipitation conditions of interest include contacting a water of
interest, e.g., feedwater and/or waste brine, with CO.sub.2 to
produce a CO.sub.2 charged water and then subjecting the CO.sub.2
charged water to carbonate compound precipitation conditions.
[0022] Contact of the water with the source CO.sub.2 may occur
before and/or during the time when the water is subject to CO.sub.2
precipitation conditions, e.g., as described in greater detail
below. Accordingly, embodiments of the invention include methods in
which the volume of water is contacted with a source of CO.sub.2
prior to subjecting the volume of water to precipitation
conditions. Embodiments of the invention include methods in which
the volume of water is contacted with a source of CO.sub.2 while
the volume of water is being subjected to carbonate compound
precipitation conditions. Embodiments of the invention include
methods in which the volume of water is contacted with a source of
a CO.sub.2 both prior to subjecting the volume of water to
carbonate compound precipitation conditions and while the volume of
water is being subjected to carbonate compound precipitation
conditions.
[0023] The source of CO.sub.2 that is contacted with the volume of
water in these embodiments may be any convenient CO.sub.2 source.
The CO.sub.2 source may be a liquid, solid (e.g., dry ice) or
gaseous CO.sub.2 source. In certain embodiments, the CO.sub.2
source is a gaseous CO.sub.2 source. This gaseous CO.sub.2 may vary
widely, ranging from air, industrial waste streams, etc. This
gaseous CO.sub.2 is, in certain instances, a waste product from an
industrial plant. The nature of the industrial plant may vary in
these embodiments, where industrial plants of interest include
power plants, chemical processing plants, and other industrial
plants that produce CO.sub.2 as a byproduct. By waste stream is
meant a stream of gas (or analogous stream) that is produced as a
byproduct of an active process of the industrial plant, e.g., an
exhaust gas. The gaseous stream may be substantially pure CO.sub.2
or a multi-component gaseous stream that includes CO.sub.2 and one
or more additional gases. Multi-component gaseous streams
(containing CO.sub.2) that may be employed as a CO.sub.2 source in
embodiments of the subject methods include both reducing, e.g.,
syngas, shifted syngas, natural gas, and hydrogen and the like, and
oxidizing condition streams, e.g., flue gases from combustion.
Particular multi-component gaseous streams of interest that may be
treated according to the subject invention include: oxygen
containing combustion power plant flue gas, turbo charged boiler
product gas, coal gasification product gas, shifted coal
gasification product gas, anaerobic digester product gas, wellhead
natural gas stream, reformed natural gas or methane hydrates, and
the like.
[0024] In embodiments of the invention, the CO.sub.2 source may be
flue gas from coal or other fuel combustion, which is contacted
with the volume of saltwater with little or no pretreatment of the
flue gas. In these embodiments, the magnesium and calcium ions in
the alkali-earth-metal-containing water react to form CaSO.sub.4
and MgSO.sub.4 and other compounds, as well as CaCO.sub.3 and
MgCO.sub.3 and other compounds, effectively removing sulfur from
the flue gas stream without additional release of CO.sub.2 from the
desulfurization step. In certain embodiments, the desulfurization
step may be staged to coincide with the carbonate compound
precipitation step, or may be staged to occur before this step. In
certain embodiments therefore there are multiple sets of reaction
products collected at different stages, while in other embodiments
there is a single reaction product collected.
[0025] In addition to magnesium and calcium containing products of
the precipitation reaction, compounds of interest include those
based on silicon, aluminum, iron, boron and other elements.
Chemical composition and morphology of the products resulting from
use of these reactants may alter reactivity of cements resulting
from the process, or change the nature of the properties of cured
cements and concretes made from them. In embodiments of the
invention, ash (as described in greater detail below) is added to
the reaction as one source of these additional reactants, to
produce carbonate mineral precipitates which contain one or more
components such as amorphous silica, crystalline silica, calcium
silicates, calcium alumina silicates, or any other moiety which may
result from the reaction of ash in the carbonate mineral
precipitation process.
[0026] The volume of water may be contacted with the CO.sub.2
source using any convenient protocol. Where the CO.sub.2 is a gas,
contact protocols of interest include, but are not limited to:
direct contacting protocols, e.g., bubbling the gas through the
volume of saltwater, concurrent contacting means, i.e., contact
between unidirectionally flowing gaseous and liquid phase streams,
countercurrent means, i.e., contact between oppositely flowing
gaseous and liquid phase streams, and the like. Thus, contact may
be accomplished through use of infusers, bubblers, fluidic Venturi
reactor, sparger, gas filter, spray, tray, or packed column
reactors, and the like, as may be convenient.
[0027] In methods of the invention, a volume of CO.sub.2 charged
water, e.g., produced as described above, is subjected to carbonate
compound precipitation conditions sufficient to produce a
precipitated carbonate compound composition and an alkaline-earth
metal depleted water, which in the context of the precipitation
step may be viewed as the mother liquor (i.e., the part of the
water that is left over after precipitation of the carbonate
compound composition from the water). Any convenient precipitation
conditions may be employed, which conditions result in the
production of a carbonate-containing solid or precipitate from the
CO.sub.2 charged water.
[0028] Precipitation conditions of interest include those that
modulate the physical environment of the CO.sub.2 charged water to
produce the desired precipitate product. For example, the
temperature of the CO.sub.2 charged may be raised to an amount
suitable for precipitation of the desired carbonate compound to
occur. In such embodiments, the temperature of the CO.sub.2 charged
may be raised to a value from 5 to 70.degree. C., such as from 20
to 50.degree. C. and including from 25 to 45.degree. C. As such,
while a given set of precipitation conditions may have a
temperature ranging from 0 to 100.degree. C., the temperature may
be raised in certain embodiments to produce the desired
precipitate. In certain embodiments, the temperature is raised
using energy generated from low or zero carbon dioxide emission
sources, e.g., solar energy source, wind energy source,
hydroelectric energy source, etc. In certain embodiments the
temperature may be raised utilizing heat from flue gases from coal
or other fuel combustion.
[0029] Aspects of the invention include raising the pH of the
CO.sub.2 charged water to alkaline levels for precipitation. The pH
may be raised to 9 or higher, such as 10 or higher, e.g., 11 or
higher.
[0030] In embodiments of the invention, ash is employed as a pH
modifying agent, e.g., to increase the pH of the CO.sub.2 charged
water. The ash may be used as a as the sole pH modifier or in
conjunction with one or more additional pH modifiers.
[0031] Of interest in certain embodiments is use of a coal ash as
the ash. The coal ash as employed in this invention refers to the
residue produced in power plant boilers or coal burning furnaces,
for example, chain grate boilers, cyclone boilers and fluidized bed
boilers, from burning pulverized anthracite, lignite, bituminous or
sub-bituminous coal. Such coal ash includes fly ash which is the
finely divided coal ash carried from the furnace by exhaust or flue
gases; and bottom ash which collects at the base of the furnace as
agglomerates. Use of ashes as an alkaline source is further
described in U.S. Provisional Application 61/073,319 filed on Jun.
17, 2008, the disclosure of which is herein incorporated by
reference.
[0032] In embodiments of the invention, slag is employed as a pH
modifying agent, e.g., to increase the pH of the CO.sub.2 charged
water. The slag may be used as a as the sole pH modifier or in
conjunction with one or more additional pH modifiers. Slag is
generated from the processing of metals, and may contain calcium
and magnesium oxides as well as iron, silicon and aluminum
compounds. The use of slag as a pH modifying material may provide
additional benefits via the introduction of reactive silicon and
alumina to the precipitated product. Slags of interest include, but
are not limited to, blast furnace slag from iron smelting, slag
from electric-arc or blast furnace processing of steel, copper
slag, nickel slag and phosphorus slag.
[0033] In certain embodiments, a pH raising agent may be employed,
where examples of such agents include oxides, hydroxides (e.g.,
calcium oxide, potassium hydroxide, sodium hydroxide, brucite
(Mg(OH.sub.2), etc.), carbonates (e.g., sodium carbonate),
serpentine, chrysotile, and the like. The addition of serpentine,
also releases silica and magnesium into the solution, leading to
the formation of silica containing carbonate compounds. The amount
of pH elevating agent that is added to the water will depend on the
particular nature of the agent and the volume of water being
modified, and will be sufficient to raise the pH of the water to
the desired value. Alternatively, the pH of the water can be raised
to the desired level by electrolysis of the water. Where
electrolysis is employed, a variety of different protocols may be
taken, such as use of the Mercury cell process (also called the
Castner-Kellner process); the Diaphragm cell process and the
membrane cell process. Where desired, byproducts of the hydrolysis
product, e.g., H.sub.2, sodium metal, etc. may be harvested and
employed for other purposes, as desired. In certain embodiments,
the pH level of the carbonate precipitation supernatant is
increased via electrolysis and then returned to the reaction vessel
along with seawater or desalination brine to participate in further
carbonate precipitation. The removal of calcium, magnesium and
other cations in these embodiments prior to electrolysis can make
using the electrolysis process to raise the solution pH more
efficient
[0034] Additives other than pH elevating agents may also be
introduced into the water in order to influence the nature of the
precipitate that is produced. As such, certain embodiments of the
methods include providing an additive in water before or during the
time when the water is subjected to the precipitation conditions.
Certain calcium carbonate polymorphs can be favored by trace
amounts of certain additives. For example, vaterite, a highly
unstable polymorph of CaCO.sub.3 which precipitates in a variety of
different morphologies and converts rapidly to calcite, can be
obtained at very high yields by including trace amounts of
lanthanum as lanthanum chloride in a supersaturated solution of
calcium carbonate. Other additives beside lathanum that are of
interest include, but are not limited to transition metals and the
like. For instance, the addition of ferrous or ferric iron is known
to favor the formation of disordered dolomite (protodolomite) where
it would not form otherwise.
[0035] In certain embodiments, additives are employed which favor
the formal of precipitates characterized by larger sized particles,
e.g., particles ranging in size from 50 to 1000 .mu.m, such as 100
to 500 .mu.m, and/or of an amorphous nature. In certain
embodiments, these additives are transition metal catalysts.
Transition metal catalysts of interest include, but are not limited
to: soluble compounds of Zn, Cr, Mn, Fe, Co, and Ni or any
combination thereof. Specific compounds of interest include, but
are not limited to: CoCl.sub.2 or NiCl.sub.2. The amount of such
transition metal catalysts, when employed, may vary, ranging in
certain embodiments from 10 ppb to 2000 ppm, such as 100 ppb to 500
ppm. Inclusions of such additives may be employed to provide for
amorphous products where otherwise crystalline products are
obtained without such additives and/or to obtain larger particle
sizes in the precipitate as compared to precipitates produced in
the absence of such additives.
[0036] The nature of the precipitate can also be influenced by
selection of appropriate major ion ratios. Major ion ratios also
have considerable influence of polymorph formation. For example, as
the magnesium:calcium ratio in the water increases, aragonite
becomes the favored polymorph of calcium carbonate over
low-magnesium calcite. At low magnesium:calcium ratios,
low-magnesium calcite is the preferred polymorph.
[0037] Rate of precipitation can also be modulated to control the
nature of the compound phase formation. The most rapid
precipitation can be achieved by seeding the solution with a
desired phase. Without seeding, rapid precipitation can be achieved
by rapidly increasing the pH of the sea water, which results in
more amorphous constituents. When silica is present, the more rapid
the reaction rate, the more silica is incorporated with the
carbonate precipitate. The higher the pH is, the more rapid the
precipitation is and the more amorphous the precipitate is. In
certain embodiments, the rate of precipitation is chosen to produce
large aragonite crystals of higher purity, e.g., crystals of
agglomerated structures ranging from 20 to 50 .mu.m, made up of
individual structures ranging from 10 to 15 .mu.m, e.g., as
described in Example II, below.
[0038] Accordingly, a set of precipitation conditions to produce a
desired precipitate from a water include, in certain embodiments,
the water's temperature and pH, and in some instances the
concentrations of additives and ionic species in the water.
Precipitation conditions may also include factors such as mixing
rate, forms of agitation such as ultrasonics, and the presence of
seed crystals, catalysts, membranes, or substrates. In some
embodiments, precipitation conditions include supersaturated
conditions, temperature, pH, and/or concentration gradients, or
cycling or changing any of these parameters. The protocols employed
to prepare carbonate compound precipitates according to the
invention may be batch or continuous protocols. It will be
appreciated that precipitation conditions may be different to
produce a given precipitate in a continuous flow system compared to
a batch system.
[0039] Following production of the carbonate compound precipitate
from the water, the resultant precipitated carbonate compound
composition is separated from the mother liquor to produce a
product water, e.g., alkaline-earth-metal-depleted water that can
be used for feedwater for desalination or treated brine. Separation
of the precipitate from the product water can be achieved using any
convenient approach, including a mechanical approach, e.g., where
bulk excess water is drained from the precipitate, e.g., either by
gravity alone or with the addition of vacuum, mechanical pressing,
by filtering the precipitate from the mother liquor to produce a
filtrate, etc. Separation of bulk water produces a wet, dewatered
precipitate.
[0040] In certain filtration embodiments, the size of the
precipitate particles are controlled to provide for efficient and
non-energy intensive filtration, e.g., where precipitated particles
are produced having a size ranging from 50 to 1000 .mu.m, such as
100 to 500 .mu.m. As such, in some embodiments of the current
invention, the size and composition of the precipitated material is
controlled to reduce or eliminate the need for high energy
mechanical filtration of the feedstock prior to reverse
osmosis.
[0041] With the use of certain transition metal catalysts in
carbonate and carbonate/silicate precipitation processes, it is
possible to attain amorphous precipitates where crystalline
structures are typically observed. The transition metal catalysts
that can be used comprise soluble compounds of Zn, Cr, Mn, Fe, Co,
and Ni or any combination of. For instance, CoCl.sub.2 or
NiCl.sub.2 added at concentration anywhere from 10 ppb to 2000 ppm,
including 100 ppb to 500 ppm, will result in the precipitation of
an amorphous structure where a completely crystalline structure
would typically be observed.
[0042] The rate of formation of the precipitate is enhanced by the
use of these catalysts, resulting in a larger particle size, a more
amorphous structure, or a combination thereof. In those embodiments
producing larger particle sizes, the removal of the precipitate
from the feedstock can be accomplished by lower energy means, such
as gravity settling.
[0043] In contrast with seeding approaches to precipitation,
methods of invention do not generate CO2 during the precipitation
process. As such, embodiments of methods of the invention may be
viewed as CO.sub.2-generation-free precipitation protocols.
[0044] FIG. 1 provides a schematic flow diagram of a carbonate
precipitation process according to an embodiment of the invention.
In FIG. 1, water from a water source 10, which may be feedwater for
a desalination plant and/or waste brine from a desalination plant,
is subjected to carbonate compound precipitation conditions at
precipitation step 20. In the embodiment depicted in FIG. 1, the
water from water source 10 is first charged with CO.sub.2 to
produce CO.sub.2 charged water, which CO.sub.2 is then subjected to
carbonate compound precipitation conditions. As depicted in FIG. 1,
a CO.sub.2 gaseous stream 30 is contacted with the water at
precipitation step 20. The provided gaseous stream 30 is contacted
with a suitable water at precipitation step 20 to produce a
CO.sub.2 charged water, as reviewed above. At precipitation step
20, carbonate compounds, which may be amorphous or crystalline, are
precipitated. As reviewed above, CO.sub.2 charging and carbonate
compound precipitation may occur in a continuous process or at
separate steps. As such, charging and precipitation may occur in
the same reactor of a system, e.g., as illustrated in FIG. 1 at
step 20, according to certain embodiments of the invention. In yet
other embodiments of the invention, these two steps may occur in
separate reactors, such that the water is first charged with
CO.sub.2 in a charging reactor and the resultant CO.sub.2 charged
water is then subjected to precipitation conditions in a separate
reactor.
[0045] Following production of the carbonate precipitate from the
water, the resultant precipitated carbonate compound composition is
separated from the alkaline-earth-metal-depleted water, i.e., the
mother liquor, to produce separated carbonate compound precipitate
product, as illustrated at step 40 of FIG. 1. Separation of the
precipitate can be achieved using any convenient approach,
including a mechanical approach, e.g., where bulk excess water is
drained from the precipitated, e.g., either by gravity alone or
with the addition of vacuum, mechanical pressing, by filtering the
precipitate from the mother liquor to produce a filtrate, etc.
Separation of bulk water (which is to be employed as treated feed
water for desalination or treated brine, as described above and
indicated as 42) produces a wet, dewatered precipitate.
[0046] In the embodiment shown in FIG. 1, the resultant dewatered
precipitate is then dried to produce a product, as illustrated at
step 60 of FIG. 1. Drying can be achieved by air drying the
filtrate. Where the filtrate is air dried, air drying may be at
room or elevated temperature. In yet another embodiment, the
precipitate is spray dried to dry the precipitate, where the liquid
containing the precipitate is dried by feeding it through a hot gas
(such as the gaseous waste stream from the power plant), e.g.,
where the liquid feed is pumped through an atomizer into a main
drying chamber and a hot gas is passed as a co-current or
counter-current to the atomizer direction. Depending on the
particular drying protocol of the system, the drying station may
include a filtration element, freeze drying structure, spray drying
structure, etc. Where desired, the dewatered precipitate product
from the separation reactor 40 may be washed before drying, as
illustrated at optional step 50 of FIG. 1. The precipitate may be
washed with freshwater, e.g., to remove salts (such as NaCl) from
the dewatered precipitate. Used wash water may be disposed of as
convenient, e.g., by disposing of it in a tailings pond, etc. In
certain embodiments, the resultant product is further processed,
e.g., to produce an above ground storage stable carbon
sequestration material, to produce a building material, etc., as
described in greater detail below. For example, in the embodiment
illustrated in FIG. 1, at step 70, the dried precipitate is further
processed or refined, e.g., to provide for desired physical
characteristics, such as particle size, surface area, etc., or to
add one or more components to the precipitate, such as admixtures,
aggregate, supplementary cementitious materials, etc., to produce a
final product 80.
[0047] In certain embodiments, a system is employed to perform the
above methods, where such systems include those described below in
greater detail.
[0048] The product water of the process illustrated in FIG. 1,
i.e., the alkaline-earth-metal-depleted water, is either subjected
to desalination and/or disposed of in a suitable manner, e.g.,
depending on whether the input water of the carbonate compound
precipitation reaction is feedwater or waste brine, as indicated by
element 42.
[0049] In those embodiments where input water of the carbonate
compound precipitation process is desalination feedwater, the
product alkaline-earth-metal-depleted water is then subjected to a
desalination process. As reviewed above, any convenient protocol
may be employed in desalinating saltwater. Desalination (i.e.,
desalinization or desalinization) refers to any of several
processes that remove excess salt and other minerals from water. In
desalination, water is desalinated in order to be converted to
fresh water suitable for animal consumption or irrigation, or, if
almost all of the salt is removed, for human consumption.
Desalination methods of interest include, but are not limited to:
distillation methods, e.g., Multi-stage flash distillation (MSF),
Multiple-effect evaporator (MED|ME), Vapor-compression evaporation
(VC) and Evaporation/condensation; Ion exchange methods; Membrane
processes, e.g., Electrodialysis reversal (EDR), Reverse osmosis
(RO), Nanofiltration (NF), Forward osmosis (FO), Membrane
distillation (MD); etc.
[0050] Of interest in certain embodiments are membrane desalination
processes, e.g., reverse osmosis. Reverse osmosis (RO) is a
separation process that uses pressure to force a feedwater through
a membrane(s) that retains a solute(s) on one side and allows water
molecules to pass to the other side. As such, it is the process of
forcing water molecules from a region of high solute concentration
through a membrane to a region of low solute concentration by
applying a pressure in excess of the osmotic pressure. Membranes
employed in RO processes are semipermeable, such that they allow
the passage of water but not of solute(s). The membranes used for
reverse osmosis have a dense barrier layer in the polymer matrix
where most separation occurs. In certain embodiments, the membrane
is designed to allow only water to pass through this dense layer
while preventing the passage of solutes (such as salt ions).
Embodiments of RO employ a high pressure that is exerted on the
high concentration side of the membrane, such as 2-17 bar (30-250
psi) for brackish water, and 40-70 bar (600-1000 psi) for seawater.
RO processes and systems with which the present invention may be
employed include, but are not limited to, those described in U.S.
Pat. Nos. 6,833,073; 6,821,430; 6,709,590; 6,656,362; 6,537,456;
6,368,507; 6,245,234; 6,190,556; 6,187,200; 6,156,680; 6,139,740;
6,132,613; 6,063,278; 6,015,495; 5,925,255; 5,851,355; 5,593,588;
5,425,877; 5,358,640; 5,336,409; 5,256,303; 5,250,185; 5,246,587;
5,173,335; 5,160,619; RE 34,058; 5,084,182; 5,019,264; 4,988,444;
4,886,597; 4,772,391; 4,702,842; 4,473,476; 4,452,696; 4,341,629;
4,277,344; 4,259,183; the disclosures of which are herein
incorporated by reference.
[0051] As summarized above, in certain embodiments the water
subjected to carbonate compound precipitation conditions is a waste
brine. Desalinating salt water produces desalinated water and waste
brine. The desalinated water may be further employed in any
convenient manner, e.g., for irrigation, for animal and human
consumption, for industrial use, etc.
[0052] Waste brine produced by desalination is then processed to
produce treated brine. In the subject methods, the waste brine is
subjected to carbonate compound precipitation conditions, as
described above. In some cases, it may be desirable to remove the
chloride and sodium from the initial brine concentrate before the
brine is treated to produce depleted brine. For instance, following
the initial desalting step where freshwater is produced, and the
initial brine concentrate is formed, chlorine, caustic soda, and
halite (table salt) may be produced via a chlor-alkali process or
the like, before the carbonate and hydroxide minerals are
precipitated from the brine. In these cases, a near-zero, or zero
discharge depleted brine, of only fresh, or near-fresh water is
produced.
[0053] Following production of the precipitate from the waste
brine, the resultant precipitate is separated from the remaining
liquid, which is referred to herein as treated or depleted brine.
Separation of the precipitate can be achieved as described above.
The resultant treated brine may then be further processed and/or
returned to the environment as desired. For example, the treated
brine may be returned to the source of the water, e.g., ocean, or
to another location. In certain embodiments, the treated brine may
be contacted with a source of CO.sub.2, e.g., as described above,
to sequester further CO.sub.2. For example, where the treated brine
is to be returned to the ocean, the treated brine may be contacted
with a gaseous source of CO.sub.2 in a manner sufficient to
increase the concentration of carbonate ion present in the treated
brine. Contact may be conducted using any convenient protocol, such
as those described above. In certain embodiments, the treated brine
has an alkaline pH, and contact with the CO.sub.2 source is carried
out in a manner sufficient to reduce the pH to a range between 5
and 9, e.g., 6 and 8.5, including 7.5 to 8.2.
[0054] The resultant treated brine of the reaction may be disposed
of using any convenient protocol. In certain embodiments, it may be
sent to a tailings pond for disposal. In certain embodiments, it
may be disposed of in a naturally occurring body of water, e.g.,
ocean, sea, lake or river. In certain embodiments, the treated
brine is returned to the source of feedwater for the desalination
process, e.g., an ocean or sea.
[0055] Practice of the methods of the invention results in the
production of a carbonate containing precipitate product. As the
precipitates are derived from a water source, they will include one
or more components that are present in the water source, e.g., sea
water, brine, brackish water, and identify the compositions that
come from the water source, where these identifying components and
the amounts thereof are collectively referred to herein as a water
source identifier. For example, if the water source is sea water,
identifying compounds that may be present in the carbonate compound
compositions include, but are not limited to: chloride, sodium,
sulfur, potassium, bromide, silicon, strontium and the like. Any
such source-identifying or "marker" elements are generally present
in small amounts, e.g., in amounts of 20,000 ppm or less, such as
amounts of 2000 ppm or less. In certain embodiments, the "marker"
compound is strontium, which may be present in the precipitated
incorporated into the aragonite lattice, and make up 10,000 ppm or
less, ranging in certain embodiments from 3 to 10,000 ppm, such as
from 5 to 5000 ppm, including 5 to 1000 ppm, e.g., 5 to 500 ppm,
including 5 to 100 ppm. Another "marker" compound of interest is
magnesium, which may be present in amounts of up to 20% mole
substitution for calcium in carbonate compounds. The saltwater
source identifier of the compositions may vary depending on the
particular saltwater source employed to produce the
saltwater-derived carbonate composition. In certain embodiments,
the calcium carbonate content of the cement is 25% w/w or higher,
such as 40% w/w or higher, and including 50% w/w or higher, e.g.,
60% w/w. The carbonate compound composition has, in certain
embodiments, a calcium/magnesium ratio that is influenced by, and
therefore reflects, the water source from which it has been
precipitated. In certain embodiments, the calcium/magnesium molar
ratio ranges from 10/1 to 1/5 Ca/Mg, such as 5/1 to 1/3 Ca/Mg. In
certain embodiments, the carbonate composition is characterized by
having an water source identifying carbonate to hydroxide compound
ratio, where in certain embodiments this ratio ranges from 100 to
1, such as 10 to 1 and including 1 to 1.
[0056] In certain embodiments, the product precipitate may include
one or more boron containing compounds. Boron containing compounds
that may be present include, but are not limited to: boric acid;
borates and borate polymers, e.g., Borax (i.e., sodium borate,
sodium tetraborate, or disodium tetraborate), Colemanite
(CaB.sub.3O.sub.4(OH).sub.3.H.sub.2O); Admontite (or Admontit or
Admontita (MgB.sub.6O.sub.10.7H.sub.2O)); etc. In addition, the
precipitates may include organics, e.g., polyacrylic acid,
trihalomethane precursors, pesticides, algae and bacteria, Asp,
Glu, Gly, Ser rich acidic glycoproteins, and other highly charge
moieties
[0057] The dried product may be disposed of or employed in a number
of different ways. In certain embodiments, the precipitate product
is transported to a location for long term storage. Such
embodiments find use where CO2 sequestration is desired, since the
product can be transported to a location and maintained as a
storage stable above ground CO.sub.2 sequestering material. For
example, the carbonate precipitate may be stored at a long term
storage site adjacent to the power plant and precipitation system.
In yet other embodiments, the precipitate may be transported and
placed at long term storage site, e.g., above ground, below ground,
etc. as desired, where the long term storage site is distal to the
desalination plant (which may be desirable in embodiments where
real estate is scarce in the vicinity of the desalination plant).
In these embodiments, the precipitate finds use as an above-ground
storage stable form, so that CO.sub.2 is no longer present as, or
available to be, a gas in the atmosphere. As such, sequestering of
CO.sub.2 according to methods of the invention results in
prevention of CO.sub.2 gas from entering the atmosphere and long
term storage of CO.sub.2 in a manner that CO.sub.2 does not become
part of the atmosphere. By above-ground storage stable form is
meant a form of matter that can be stored above ground under
exposed conditions (i.e., open to the atmosphere) without
significant, if any, degradation for extended durations, e.g., 1
year or longer, 5 years or longer, 10 years or longer, 25 years or
longer, 50 years or longer, 100 years or longer, 250 years or
longer, 1000 years or longer, 10,000 years or longer, 1,000,000
years or longer, or even 100,000,000 years or longer. As the
storage stable form undergoes little if any degradation while
stored above ground under normal rain water pH, the amount of
degradation if any as measured in terms of CO.sub.2 gas release
from the product will not exceed 5%/year, and in certain
embodiments will not exceed 1%/year. The above-ground storage
stable forms are storage stable under a variety of different
environment conditions, e.g., from temperatures ranging from
-100.degree. C. to 600.degree. C. humidity ranging from 0 to 100%
where the conditions may be calm, windy or stormy.
[0058] In certain embodiments, the carbonate compound precipitate
produced by the methods of the invention is employed as a building
material. An additional benefit of certain embodiments is that
CO.sub.2 employed in the process which may be obtained from a
gaseous waste stream is effectively sequestered in the built
environment. By building material is meant that the carbonate
mineral is employed as a construction material for some type of
manmade structure, e.g., buildings (both commercial and
residential), roads, bridges, levees, dams, and other manmade
structures etc. The building material may be employed as a
structure or nonstructural component of such structures. In such
embodiments, the precipitation plant may be co-located with a
building products factory.
[0059] In certain embodiments, the precipitate product is refined
(i.e., processed) in some manner prior to subsequent use.
Refinement as illustrated in step 80 of FIG. 1 may include a
variety of different protocols. In certain embodiments, the product
is subjected to mechanical refinement, e.g., grinding, in order to
obtain a product with desired physical properties, e.g., particle
size, etc. In certain embodiments, the precipitate is combined with
a hydraulic cement, e.g., as a supplemental cementitious material,
as a sand, as an aggregate, etc. In certain embodiments, one or
more components may be added to the precipitate, e.g., where the
precipitate is to be employed as a cement, e.g., one or more
additives, sands, aggregates, supplemental cementitious materials,
etc. to produce a final product, e.g., concrete or mortar, 90.
[0060] In certain embodiments, the carbonate compound precipitate
is utilized to produce aggregates. Such aggregates, methods for
their manufacture and use are described in co-pending U.S.
Application Ser. No. 61/056,972, filed on May 29, 2008, the
disclosure of which is herein incorporated by reference.
[0061] In certain embodiments, the carbonate compound precipitate
is employed as a component of a hydraulic cement. The term
"hydraulic cement" is employed in its conventional sense to refer
to a composition which sets and hardens after combining with water.
Setting and hardening of the product produced by combination of the
cements of the invention with an aqueous fluid results from the
production of hydrates that are formed from the cement upon
reaction with water, where the hydrates are essentially insoluble
in water. Such carbonate compound component hydraulic cements,
methods for their manufacture and use are described in co-pending
U.S. application Ser. No. 12/126,776 filed on May 23, 2008; the
disclosure of which application is herein incorporated by
reference.
Utility
[0062] The subject methods find use in any situation where it is
desired to treat desalinate water. Practice of methods of the
invention can provide numerous advantages for desalination
protocols. For example, practice of the methods can be used to
increase desalination efficiency, e.g., by reducing membrane
fouling and scaling. Embodiments of the invention results in
decreased membrane scaling as compared to control processes in
which a carbonate compound precipitation step is not employed.
Membrane scaling may be assessed using the protocols described in
Rahardianto et al., Journal of Membrane Science, (2007)
289:123-137. For example, membrane scaling may be assessed by flux
decline measurements and post-operation membrane surface image
analysis, e.g., as described in Rahardianto et al., supra. Practice
of embodiments of the subject methods results in flux decline over
a 24 hour test period of 25% or less, such at 15% or less,
including 10% or even 5% or less, and in certain embodiments
results in substantially no, if any, flux decline. Practice of the
methods of invention can provide water recovery rates of 90% or
more, such as 95% or more, including 98% or more, e.g., 99% or
more. Waste brines that may be treated according to methods of the
invention include those having a salinity ranging from 45,000 to
80,000 ppm. Embodiments of the methods produce treated brines
having salinities of 35,000 ppm or less. As such, the methods of
the invention find use in treating brines so that they are
environmentally acceptable, less toxic, etc., than their
non-treated waste brine counterparts. Such protocols can result in
less environmental deleterious impact, easier compliance with
governmental regulations, etc.
[0063] In addition, embodiments of the methods result in CO.sub.2
sequestration. By "sequestering CO.sub.2" is meant the removal or
segregation of CO.sub.2 from a source, e.g., a gaseous waste
stream, and fixating it into a stable non-gaseous form so that the
CO.sub.2 cannot escape into the atmosphere. By "CO.sub.2
sequestration" is meant the placement of CO.sub.2 into a storage
stable form, such as an above-ground storage stable form, so that
it is no longer present as, or available to be, a gas in the
atmosphere. As such, sequestering of CO.sub.2 according to methods
of the invention results in prevention of CO.sub.2 gas from
entering the atmosphere and long term storage of CO.sub.2 in a
manner that CO.sub.2 does not become part of the atmosphere.
Systems
[0064] Aspects of the invention further include systems, e.g.,
processing plants or factories, for treating desalination waste
brine, as described above. Systems of the invention may have any
configuration which enables practice of the particular method of
interest.
[0065] In certain embodiments, the systems include a source of
saltwater, e.g., in the form of a structure having an input for
salt water. For example, the systems may include a pipeline or
analogous feed of saltwater. Where the saltwater source that is
desalinated by the system is seawater, the input is in fluid
communication with a source of sea water, e.g., such as where the
input is a pipe line or feed from ocean water to a land based
system or a inlet port in the hull of ship, e.g., where the system
is part of a ship, e.g., in an ocean based system.
[0066] Also present in systems of the invention is a desalination
station or reactor that produces desalinated water and waste brine
from saltwater. The desalination station may be configured to
perform any of a number of different types of desalination
protocols, including, but not limited to, the desalination
protocols mentioned above, such as reverse osmosis and multi stage
flash distillation protocols.
[0067] In addition, the systems will include a carbonate compound
precipitation station or reactor that subjects feed water for the
desalination station and/or salt waste brine produced by the
desalination station to carbonate compound precipitation
conditions, e.g., as described above, and produces a precipitated
carbonate compound composition and alkaline-earth-metal depleted
water, e.g., softened feedwater for the desalination plant or
treated brine from the desalination plant. Systems of the invention
may further include a separator for separating a precipitate from a
mother liquor. In certain embodiments, the separator includes a
filtration element.
[0068] The system may also include a separate source of carbon
dioxide, e.g., where the system is configured to be employed in
embodiments where the saltwater and/or mother liquor is contacted
with a carbon dioxide source at some time during the process. This
source may be any of those described above, e.g., a waste feed from
an industrial power plant, etc.
[0069] In certain embodiments, the system will further include a
station for preparing a building material, such as cement, from the
precipitate. This station can be configured to produce a variety of
cements from the precipitate, e.g., as described in U.S.
application Ser. No. 12/126,776 filed on May 23, 2008; the
disclosure of which applications is herein incorporated by
reference.
[0070] The system may be present on land or sea. For example, the
system may be land based system that is in a coastal region, e.g.,
close to a source of sea water, or even an interior location, where
water is piped into the system from a salt water source, e.g.,
ocean. Alternatively, the system bay a water based system, i.e., a
system that is present on or in water. Such a system may be present
on a boat, ocean based platform etc., as desired.
[0071] The following examples are put forth so as to provide those
of ordinary skill in the art with a complete disclosure and
description of how to make and use the present invention, and are
not intended to limit the scope of what the inventors regard as
their invention nor are they intended to represent that the
experiments below are all or the only experiments performed.
Efforts have been made to ensure accuracy with respect to numbers
used (e.g. amounts, temperature, etc.) but some experimental errors
and deviations should be accounted for. Unless indicated otherwise,
parts are parts by weight, molecular weight is weight average
molecular weight, temperature is in degrees Centigrade, and
pressure is at or near atmospheric.
EXPERIMENTAL
I. P00099 Precipitate
[0072] In the following example, the methodology used to produce a
carbonate precipitate from seawater (i.e., the P00099 precipitate),
as well as the chemical and physical characteristics of the
generated precipitate, are described. In addition, the compressive
strengths and shrinkage properties of a blended cement made up of
80% ordinary Portland cement (OPC) and 20% P00099 are reviewed. The
following examples demonstrate that water may be softened in a
reaction that employs CO.sub.2 gas and the product precipitate
finds use as a building material.
A. Precipitation Reaction
[0073] The following protocol was used to produce the P00099
precipitate. 380 L of filtered seawater was pumped into a
cylindrical polyethylene 60.degree.-cone bottom graduated tank.
This reaction tank was an open system, left exposed to the ambient
atmosphere. The reaction tank was constantly stirred using an
overhead mixer. pH, room temperature, and water temperature were
constantly monitored throughout the reaction.
[0074] 25 g of granulated (Ca,Mg)O (a.k.a., dolime or calcined
dolomite) was mixed into the seawater. Dolime that settled to the
bottom of the tank was manually re-circulated from the bottom of
the tank through the top again, in order to facilitate adequate
mixing and dissolution of reactants. A second addition of 25 g of
dolime was performed in an identical manner, including a manual
recirculation of settled reactant. When the pH of the water reached
9.2, a gas mixture of 10% CO.sub.2 (and 90% compressed air) was
slowly diffused through a ceramic airstone into solution. When the
pH of the solution fell to 9.0, another 25 g addition of dolime was
added to the reaction tank, which caused the pH to rise again. The
additions of dolime were repeated whenever the pH of the solution
dropped to 9.0 (or below), until a total of 225 g were added. A
manual recirculation of settled reactant was performed in between
each dolime addition.
[0075] After the final addition of dolime, the continuous diffusion
of gas through the solution was stopped. The reaction was stirred
for an additional 2 hours. During this time, the pH continued to
rise. To maintain a pH between 9.0 and 9.2, additional gas was
diffused through the reaction when the pH rose above 9.2 until it
reached 9.0. Manual re-circulations of settled reactant were also
performed 4 times throughout this 2 hour period.
[0076] 2 hours after the final addition of dolime, stirring, gas
diffusion and recirculation of settled reactant was stopped. The
reaction tank was left undisturbed for 15 hours (open to the
atmosphere).
[0077] After the 15 hour period, supernatant was removed through
the top of the reaction tank using a submersible pump. The
remaining mixture was removed through the bottom of the tank. The
collected mixture was allowed to settle for 2 hours. After
settling, the supernatant was decanted. The remaining slurry was
vacuum filtered through 11 .mu.m pore size filter paper, in a
Buchner funnel. The collected filter cake was placed into a Pyrex
dish and baked at 110.degree. C. for 24 hours.
[0078] The dried product was ground in a ball mix and fractioned by
size through a series of sieves to produce the P00099
precipitate.
B. Materials Analysis
[0079] Of the different sieve fractions collected, only the
fraction containing particles retained on the 38 .mu.m-opening
sieve and passing through the 75 .mu.m-opening sieve was used.
1. Chemical Characteristics
[0080] The P00099 precipitate used for the blend were analyzed for
elemental composition using XRF. Results for the main elements are
reported for the Quikrete type I/II Portland cement used in this
blend as well as for the P00099 precipitate. In Table 1, below.
TABLE-US-00001 TABLE 1 XRF analysis of the type I/II portland
cement and P00099-002 used in this blend Na.sub.2O MgO
Al.sub.2O.sub.3 SiO.sub.2 P.sub.2O.sub.5 SO.sub.3 Cl K.sub.2O CaO
Fe.sub.2O.sub.3 Sr CO.sub.3 Sample % % % % ppm % % % % % ppm %
diff. OPC1 2.15 1.95 4.32 20.31 2336 2.54 0.072 0.36 62.88 3.88
1099 0.002 P00099 1.36 3.44 0.14 0.083 462 0.65 1.123 0.04 45.75
0.12 3589 46.82
The XRD analysis of this precipitate indicates the presence of
aragonite and magnesium calcite (composition close to
Mg.sub.0.1Ca.sub.0.9CO.sub.3) and in minor amounts, brucite and
halite (Table 2).
TABLE-US-00002 TABLE 2 Magnesium Sample Aragonite Calcite Brucite
Halite P00099 79.9 17.1 2.8 0.2
The total inorganic carbon content measured by coulometry is in
fair agreement with the same value derived from the XRD Rietveld
estimated composition coupled with XRF elemental composition. Table
3 provides a coulometric analysis of P00099 compared to % C derived
from XRD/XRF data
TABLE-US-00003 TABLE 3 Total C from Total C derived from coulometry
other analytical data 10.93 .+-. 0.16% 11.5%
2. Physical Characteristics
[0081] SEM observations on the precipitate confirm the dominance of
aragonite (needle-like) as well as the size of the particle
agglomerates. The determined BET specific surface areas ("SSA") of
the Portland cement and the P00099 precipitate are given in Table
4.
TABLE-US-00004 TABLE 4 Type I/II Quikrete Portland cement P00099
1.18 .+-. 0.04 m.sup.2/g 8.31 .+-. 0.04 m.sup.2/g
[0082] The particle size distribution was determined after 2 min of
pre-sonication to dissociate the agglomerated particles.
C. OPC/P00099 Blended Cement
[0083] The P00099 precipitate was blended with ordinary Portland
cement (OPC) by hand for approximately two minutes just before
mixing the mortar. The blended cement comprised 20% (w/w) P00099
and 80% (w/w) OPC.
1. Compressive Strengths
[0084] The compressive strength development was determined
according to ASTM C109. Mortar cubes of 2'' side were used for the
compression tests. A replacement level of 20% was investigated for
this precipitate and compared to plain Portland type I/II cement
mortars and to Portland type I/II cement substituted by fly ash F.
The water/cement ratio was adjusted to 0.58 to meet the flow
criterion of 110%+/-5% (value: 107%).
[0085] 6 cubes were prepared for the blends. Changes to the ASTM
C511 storage conditions were as follows: [0086] The cubes were
cured under a wet towel for 24 hours (estimated relative humidity
of 95%) [0087] After demolding, the cubes were stored in the
laboratory at a relative humidity of 30-40% instead of the lime
bath.
[0088] Data for a 5% replacement level was also investigated with a
duplicate precipitate (P00100, BET specific surface area of ca. 11
m.sup.2/g). The water/cement ratio was adjusted to 0.54 to meet the
110% flow requirement. At a 5% level of replacement, the strength
development is similar to that of plain portland cement. The
results are summarized in the Graph provided in FIG. 2.
2. Shrinkage
[0089] The drying shrinkage of mortar bars at a replacement level
of 5% and 20% was investigated for the P00099 precipitate following
ASTM C596. It was compared to similar bars made with Portland
cement type I/II only or a blend of Portland cement and fly ash F.
The water/cement ratio was adjusted to 0.50 to meet the flow
criterion of 110%+/-5% (value: 107%), and in one set of specimens a
Daracem plasticizer was added to achieve a water/cement ratio of
0.45. Changes to the ASTM C596 storage conditions were as follows:
the relative humidity in the lab is closer to 30-40% than the 50%
recommended by ASTM C596, increasing the drying potential. The
results are summarized in Table 6 below.
TABLE-US-00005 TABLE 6 Mix Cement composition Duration (weeks)
description W/C OPC SCM FA Flow 1 2 3 4 6 100% OPC 0.40 100% 0% 0%
105% 0.034% 0.052% 0.056% 0.075% baseline 80% OPC-20% 0.40 80% 0%
20% 118% 0.034% 0.054% 0.067% FAF1-1 80% OPC-20% 0.5 80% 20% 0%
118% 0.043% 0.080% 0.099% 0.104% P00099 80% OPC-20% 0.45 80% 20% 0%
108% 0.050% 0.110% 0.198% 0.207% P00099 + Daracem
II. Production of Large Aragonite Crystals of High Purity
A. Precipitate P00143:
[0090] 390 L of seawater (source: Long Marine Lab, UCSC, Santa
Cruz, Calif.) (Water temperature=23.5-24.5.degree. C. Initial
pH=7.72) was pumped into a cone-bottom plastic tank. 1 M NaOH
solution was slowly added to the seawater using an automated pH
controller, while continuously stirring, until the pH was raised to
9.10. A gas mixture of 10% CO.sub.2 and 90% air was diffused
through the seawater, acidifying the seawater and increasing the
dissolved carbon. The pH controller was set to automatically add
small amounts of NaOH solution, countering the acidifying effects
of the gas mixture, to maintain a pH between 9.00 and 9.10. The gas
mixture and NaOH solution were continuously added over a period of
about 4 hours, until a total of 12.0 kg of NaOH solution had been
added.
[0091] Stirring was stopped, and the water was allowed to settle
for 15 hours. Most of the (.about.380 L) supernatant was pumped out
of the tank. The remaining supernatant and settled precipitate was
removed from the tank as a slurry. The slurry was vacuum filtered
using 11 .mu.m pore size filter paper. The filter cake was dried in
a 110.degree. C. oven for 6 hours.
[0092] The dried product was a fine off-white powder. Analysis by
SEM, EDS, XRD and carbon coulometry indicated that the product was
over 99% aragonite (CaCO.sub.3). SEM showed two major aragonite
morphologies present: smaller spikey "stars" and larger "broccoli"
shapes, either as individuals or agglomerations. "Stars" were
typically 5 .mu.m in diameter. Individual "broccoli" were typically
10-15 .mu.m in length. Agglomerated "broccoli" sizes ranged widely,
but were in the range of 20-50 .mu.m in diameter.
B. Precipitate P00145:
[0093] (Water temperature=24.0-25.7.degree. C. Initial pH=7.84) 390
L of seawater (source: Long Marine Lab, UCSC, Santa Cruz, Calif.)
was pumped into a cone-bottom plastic tank. 2 M NaOH solution was
slowly added to the seawater using an automated pH controller,
while continuously stirring, until the pH was raised to 9.10. A gas
mixture of 10% CO2 and 90% air was diffused through the seawater,
acidifying the seawater and increasing the dissolved carbon. The pH
controller was set to automatically add small amounts of NaOH
solution, countering the acidifying effects of the gas mixture, to
maintain a pH between 9.00 and 9.10. The gas mixture and NaOH
solution were continuously added over a period of about 5 hours,
until a total of 12.4 kg of NaOH solution had been added. Stirring
was stopped, and the water was allowed to settle for 65 hours. Most
of the (.about.380 L) supernatant was pumped out of the tank. The
remaining supernatant and settled precipitate was removed from the
tank as a slurry. The slurry was vacuum filtered using 11 .mu.m
pore size filter paper. The filter cake was dried in a 110.degree.
C. oven for 6 hours.
[0094] The dried product was a fine off-white powder. Analysis by
SEM, EDS, XRD and carbon coulometry indicated that the product was
over 99% aragonite (CaCO3). SEM showed that the solid was
predominately composed of "broccoli" agglomerations. Agglomerated
"broccoli" sizes ranged widely, but were in the range of 20-50
.mu.m in diameter.
III. Control of Precipitate Particle Size with Nickel Catalysis of
Carbonate Precipitation
A. Experimental Procedure for P00140,
1. Methods:
[0095] 1 L Seawater dosed with 15 ppm NiCl.sub.2 [0096] 1. 1 L of
Seawater, Starting pH=8.10 T=21.4.degree. C. [0097] 2. Add 15 ppm
of NiCl.sub.2 to Seawater [0098] 3. Titrate 55 ml of 1M NaOH
countered by CO.sub.2 gas to maintain a pH range between 8.0-10.2,
including a pH range between 8.8-9.8 [0099] Final pH=9.73 T=22.0.
Duration of experiment: 19 minutes. Filter using vacuum filtration
on 11 .mu.m filter paper. Settling Time before filtration: 15
minutes. Oven Dried at 110.degree. C. for 24 hours
2. Results
[0100] The above protocol yields 1.14 g of Precipitate. The
resultant precipitate has particle sizes ranging up to 500 .mu.m
(control experiments with no nickel produce particle size ranging
from 5-20 .mu.m), as illustrated in SEM micrographs, shown in FIGS.
3A to 3C. Fully Amorphous Crystal Structure observed, as
illustrated in FTIR (See FIG. 4). Ca:Mg ratio's of 4:1 and 3:1 in
precipitate.
[0101] In precipitative softening of feedstock water for
desalination processes, the particle sizes of the precipitates are
generally very fine, and require substantial mechanical filtration
to prevent clogging of the reverse osmosis membranes. In
embodiments of the current invention, the size and composition of
the precipitated material is controlled to reduce or eliminate the
need for high energy mechanical filtration of the feedstock prior
to reverse osmosis, e.g., by including a transition metal catalyst
as described above.
[0102] These results contrast with the results achieved without a
Nickel catalyst, e.g., as described for P00143 and P00145,
above.
IV. Identification of Boron in Carbonate Compound Precipitate
[0103] Precipitate P00144 was prepared according to the same
procedure as that employed for the preparation of P00143, described
above. Precipitate P00144 was analyzed for Boron content via
inductively coupled plasma-mass spectrometry. Boron was found to
present in the precipitate at an amount of 109 .mu.g/g. This
finding equates to 0.109 mg/L Boron in ppt (assuming 1 g/L ppt).
Noting that there is 0.00042 mol B/.about.L[SW]*10.8 g/mol->4.5
mg B/L in Seawater, it was determined that approximately 2.5% of
the B in seawater is being taken in by the ppt.
[0104] Although the foregoing invention has been described in some
detail by way of illustration and example for purposes of clarity
of understanding, it is readily apparent to those of ordinary skill
in the art in light of the teachings of this invention that certain
changes and modifications may be made thereto without departing
from the spirit or scope of the appended claims.
[0105] Accordingly, the preceding merely illustrates the principles
of the invention. It will be appreciated that those skilled in the
art will be able to devise various arrangements which, although not
explicitly described or shown herein, embody the principles of the
invention and are included within its spirit and scope.
Furthermore, all examples and conditional language recited herein
are principally intended to aid the reader in understanding the
principles of the invention and the concepts contributed by the
inventors to furthering the art, and are to be construed as being
without limitation to such specifically recited examples and
conditions. Moreover, all statements herein reciting principles,
aspects, and embodiments of the invention as well as specific
examples thereof, are intended to encompass both structural and
functional equivalents thereof. Additionally, it is intended that
such equivalents include both currently known equivalents and
equivalents developed in the future, i.e., any elements developed
that perform the same function, regardless of structure. The scope
of the present invention, therefore, is not intended to be limited
to the exemplary embodiments shown and described herein. Rather,
the scope and spirit of present invention is embodied by the
appended claims.
* * * * *