5,660,735
*Aug. 26, 1997
United States Patent [19]
Coltrinari et aI.
111111111111111111111111111111111111111111111111111111111111111111111111111
US005660735A
[11] Patent Number:
[45] Date of Patent:
37 Claims, 1 Drawing Sheet
FOREIGN PATENT DOCUMENTS
32891 3/1978 Japan 210/504
50439 4/1980 Japan 210/504
Primary Examiner-Neil McCarthy
Attorney, Agent, or Firm-Sheridan Ross P.C.
The present invention is a method to remove metals from
solutions by precipitating the metals and adding cellulosic
fiber to the solution. The precipitates attach to the cellulosic
fibers to form products. The products may be removed from
the solution by gravity separation techniques or by filtration.
The removed products may be dewatered and incinerated.
The method provides a simple and effective technique for
removing low concentrations of metals from high volume
solution streams.
[54] METHOD FOR REMOVING METALS FROM
WASTE SOLUTIONS
[75] Inventors: Enzo Coltrinari, Golden; Wayne C.
Hazen, Denver, both of Colo.
[73] Assignee: Hazen Research, Inc•. Golden, Colo.
[ *] Notice: The term of this patent shall not extend
beyond the expiration date of Pat. No.
5,536,416.
[21] Appl. No.: 683,530
[22] Filed: Jul. 15, 1996
Related U.S. Application Data
[63] Continuation of Ser. No. 332,536, Oct 31, 1994, Pat No.
5,536,416.
[51] Int. Cl.6 C02F 1/62
[52] U.S. Cl 210n23; 210/729; 2101730;
210/731; 2101747; 210/769; 210/911; 210/912;
210/913; 210/914; 210/734
[58] Field of Search 210/723, 769,
210/724,729,730,731,747,911,912,
913, 914, 734
[56] References Cited
U.S. PATENT DOCUMENTS
3,235,489 2/1966 Bell et aI 210/51
3,537,986 1111970 Watansbe et aI 210/15
Acid Mine
Drainage
[57]
4,324,667
4,559,143
4,710,298
4,758,414
4,764,281
4,800,024
4,909,944
4,980,071
4,999,116
5,006,262
5,078,900
5,164,095
5,262,064
5,283,123
4/1982 Konstantinov et aI 2101729
12/1985 Asada et aI 210m4
12/1987 Noda et aI. .. 210/505
7/1988 Gifford et aI 423/122
8/1988 Elfline 210/668
1/1989 Elffine 210/665
3/1990 Jackson 210/674
12/1990 Shuster et aI 2101725
3/1991 Bowers 2101709
4/1991 Weyls et aI 2101719
1/1992 Wegner 2101728
1111992 Sparapany et aI 2101735
1111993 El-Shall 2101728
2/1994 Carter et aI 210/504
ABSTRACT
Discrete Fibers
pH Adjustor
Precipitant
Flocculant
1
4
~
6 Fiber
----i Addition
8 17
----i Precipitate
Metal
10
----i
111
16 flocculate
-->
114
Thicken 18
Scrub
39
110 t 11
I
11 16
Fi Iter Dewater Combust ~
1
14
1
u.s. Patent
Acid Mine
Drainage
Aug. 26, 1997
FIG. 1
5,660,735
Discrete Fibers
pH Adjustor
Prec iPi tant
Flocculant
4
6 Fiber --. Addition
7
8
----+> Precipi tate
Metal
10
----+>
11 -
16 Flocculate --.
-
14
Thicken 18
Scrub
30
t 22
20
~ ~ ~ I
12 26
Fi Iter Dewater Combust 28
24
5,660,735
2
taining a metal. In a first step, a feed solution is provided
containing a metal precipitate. In a second step, discrete
fibers are dispersed in the feed solution. The precipitate
attaches to a discrete fiber to form a product. The product is
5 removed from the feed solution to form a treated solution
and a recovered product.
The precipitate preferably includes hydroxides, silicates,
sulfides, xanthates, phosphates, carbonates, cellulosederivatives,
and mixtures thereof. More preferably, the pre-
10 cipitate includes hydroxides, silicates, carbonates, and mixtures
thereof. In one embodiment, the precipitate is formed
by precipitating the metal from the feed solution using a
precipitant. The precipitant preferably includes a hydroxide,
silicate, sulfide, xanthate, phosphate, carbonate, hydroxy-
15 ethyl cellulose, and mixtures thereof. In an alternate
embodiment, the discrete fibers may include the precipitant.
In one embodiment, the product is removed from the feed
solution by filtering. The filtering step may be preceded by
a thickening step. In an alternate embodiment, the product is
20 removed from the feed solution by a density separation
method.
After product removal, the treated solution preferably has
a metal concentration that is less than the maximum con25
centrations for discharges into water resources under regulations
promulgated by the Environmental Protection
Agency.
The recovered product may be dewatered. The recovered
product preferably has a water content less than about 90%
30 by weight before dewatering. The dewatered product preferably
has a water content less than about 30% by weight.
The dewatered product may be combusted.
In an alternate embodiment, a method is provided for
concentrating the metals in the feed solution. In a first step,
35 the metals are precipitated from the feed solution. In a
second step, discrete fibers are dispersed in the feed solution
to form the product. The product is allowed to collect in a
portion of the feed solution by density separation techniques.
Various embodiments of the present invention offer
numerous advantages over existing methods and apparatuses.
First, one embodiment of the present invention provides
an inexpensive and simple method to purify large
quantities of contaminated water at high flow rates. The
45 product of the fibers and precipitates may be selected such
that the product is substantially larger than the precipitates
alone. The product size allows the present invention to
employ larger filter pore sizes and therefore higher filter
fluxes than is possible with conventional purification meth-
50 ods. The product size may be selected such that other
entrained particulate matter is smaller than the product and
passes through the filter while the product does not.
Second, another embodiment of the present invention
may economically purify solutions having low metal con-
55 centrations. Unlike conventional methods, which produce
smaller metal precipitates for lower metal concentrations,
the present invention employs fibers to collect the metal
precipitates before removal. The product of the fiber and
metal precipitates may then be rapidly and easily removed
60 by any number of methods known in the art.
Third, in another embodiment of the present invention,
high settling rates of product can be attained by appropriate
selection of product size and the use of settling aids. This
improvement permits the product to be removed more
65 rapidly by flocculation, thickening, and filtration of the feed
solution, than would otherwise be possible with the precipitate
alone.
1
METHOD FOR REMOVING METALS FROM
WASTE SOLUTIONS
This is a continuation of application Ser. No. 08/332,536,
filed Oct. 31, 1994, now U.S. Pat. No. 5,536,416.
FIELD OF THE INVENTION
The present invention is a method for removing metals
from a solution. More particularly, the present invention
embodies an improved approach for removing precipitates
containing such metals from an eflluent.
BACKGROUND OF THE INVENTION
SUMMARY OF THE INVENTION
In a preferred embodiment. the present invention relates
to a novel method for remediation of feed solutions con-
Discharges of metals into the environment are a major
problem worldwide. Metal discharges severely damage the
environment, being responsible each year for the contamination
of water resources and destruction of plant and
animal life.
Metal discharges into surface and ground water resources
(e.g., streams, rivers, ponds, lakes, and aquifers) pose the
greatest risk to wildlife and human health. Such discharges
may be either manmade, such as discharges by industrial
facilities, or natural, such as water runoff/from caves and
mines. Treatment of contaminated surface and ground water
resources is complicated not only by the large quantities of
water but also by the dilute concentrations of metals contained
in the resources.
Existing methods to remove metals from aqueous solutions
are poorly suited to remove dilute concentrations of
metals from large quantities of water to achieve the purity
levels mandated by state and federal laws. Existing metal
removal methods include the steps of precipitating the
metals and removing the precipitates from the solution by
filtering or by density separation techniques, such as by
settling.
The conventional filtering techniques are not only uneconomical
but also can fail to remove a significant portion of
the precipitates in many applications. The dilute (e.g., parts
per million) concentrations of metals in surface and ground
water resources cause very small metal precipitates to form. 40
As will be appreciated, such precipitates can form a thick
filter cake or gelatinous mass on the filter causing a large
pressure drop across the filter and a small filter flux. The
resulting flux is typically too low to handle economically the
large amounts of contaminated water. Many resources contain
particulate matter, other than the precipitates, that
further impedes the filtering step.
Another conventional technique to remove precipitates, is
by density separation, which is also not economical in most
cases. The most common density separation technique for
large quantities of water is a settling pond, where metal
precipitates settle out of solution. Settling ponds are typically
undesirable as they require large land areas that are
often not available, create a highly toxic sludge in the pond
bottom that is often difficult to dispose of, and often fail to
attain desired levels of purity in the pond overflow.
Other techniques to remove metal contaminants from
surface and groundwater resources require expensive components
and/or otherwise raise other operational complications.
Therefore, there is a need for a process to inexpensively
remove metals from surface and ground water resources
having low concentrations of metals.
5,660,735
FIG. 1 is a flow schematic of the subject invention.
illustrating the use of fibers to remove metal precipitates 15
from solution.
3
Fourth. recovered product of the present invention may
have a much smaller volume than the sludge produced by
conventional purification methods. Thus. subsequent handling
and disposal of such materials is relatively more
simple. For example. the recovered product may be incinerated
to an even smaller volume than the recovered product
The cinders from incineration may be disposed of or further
treated to recover the metals contained in the cinders. The
disposal of cinders is much easier and less expensive than
the cost to dispose of the sludge or filtrate produced by
conventional purification methods.
BRIEF DESCRIPTION OF TIIE DRAWINGS
DErAILED DESCRIPTION
A first embodiment of the present invention is a method
for remediation of a feed solution containing a metal. The
metal is contained in a precipitate. Discrete fibers are
dispersed in the feed solution to form a product including a
fiber and the precipitate. The product is removed from the
feed solution to form a treated solution and a recovered
product.
The feed solution may be any liquid containing a metal.
Preferably. the feed solution is aqueous. More preferably, the
feed solution is a portion of a stream. river, pond, lake, or
any other naturally occurring or manmade aqueous stream or
reservoir. The process of the present intention can be conducted
in a channel. reservoir, or other type of container.
Preferably, the feed solution is provided for remediation in
a channel, such as a sluice box, or in a stirred tank.
A preferred embodiment of the present invention purifies
a feed solution having a high rate of flow. The flow rate of
the feed solution is preferably greater than about 10 gallons
per minute. more preferably greater than about 100 gallons
per minute, and most preferably greater than about 500
gallons per minute. Such flow rates are in excess of the
amount of water that can be readily and effectively treated
by conventional methods.
The metal to be removed from the feed solution preferably
is a transition element (an element from Groups IB
through VIIB and Group vm of the Modem Periodic Table
of the Elements), an alkali metal (Group lA), an alkaline
earth metal (Group llA). aluminum, boron, lead. arsenic,
selenium. fluorine, compounds thereof, or mixtures thereof.
Most preferably, the metal is aluminum, arsenic, beryllium,
boron, cadmium, chromium, fluorine, nickel, selenium,
vanadium, lithium, molybdenum, barium, lead, mercury,
silver, copper, zinc, iron, manganese. compounds thereof, or
mixtures thereof.
The present invention is particularly suited to the removal
of low metal concentrations from the feed solution.
Surprisingly, the present invention may remove significant
portions of metal from feed solutions having metal concentrations
less than about 50 mg/l. The present invention
removes preferably at least about 75. more preferably at
least about 85. and most preferably at least 90% by weight
of metals from a feed solution having a concentration less
than about 50 mg/l.
The metal may be in the form of either an element or a
metal-containing compound (hereinafter collectively
referred to as ''metal''). In one embodiment of the present
invention. the metal is in the feed solution in the form of a
precipitate. As used herein. "precipitate" refers to any compound
containing the metal that is insoluble in the solution.
For aqueous solutions. the metal-containing compound
should be water insoluble. Preferably. the precipitate is a
4
hydroxide. silicate. sulfide. xanthate, phosphate, carbonate.
cellulose-derivatives, or mixtures thereof. More preferably.
the precipitate is environmentally benign. Most preferably,
the precipitate is a hydroxide, silicate. carbonate, or mixtures
5 thereof.
In an alternate embodiment of the present invention. the
metal is in a form that is soluble in the solution and is
precipitated from the feed solution to form the precipitate.
"Precipitated" or "precipitating" refers to any process that
10 causes a dissolved metal to form a precipitate. Preferably,
such a process includes a chemical reaction between the
soluble metal and a precipitant that produces a precipitate.
A precipitant may be introduced to the feed solution
before. concurrent with. or after the discrete fibers are
dispersed in the feed solution. As used herein, "precipitant"
refers to any element or compound capable of forming a
precipitate with the metal in the feed solution. Preferably. the
precipitant is selected such that the precipitant and the
precipitate containing the metal are each environmentally
benign. More preferably, the precipitant is a hydroxide,
20 silicate, sulfide, xanthate, phosphate, carbonate. hydroxyethyl
cellulose, or mixtures thereof. Most preferably, the
precipitant is Caco3 , NazC03• Ca(OH}z, NazSi03 , caS,
NaHS, H3P04 , CaHiP04}z. or mixtures thereof.
The precipitant may be contacted with the feed solution
25 either as a part of the discrete fibers or as a separate additive.
as desired. In the case of the precipitant as part of the fiber,
the precipitant may be attached to the discrete fibers by any
means known in the art to form functionalized fibers. The
functionalized fibers may form the metal-containing precipi-
30 tate either directly on the discrete fibers or in the feed
solution. For functionalized fibers, the precipitant is preferably
a phosphate, xanthate, or hydroxyethyl cellulose.
The desired concentration of the precipitant in the feed
solution is great enough to obtain acceptable reaction with
35 metal in the feed solution. The precipitant is preferably
present in the feed solution in at least stoichiometric
amounts relative to that amount of metal in feed solution to
be removed. More preferably, the precipitant is at least about
200% of the stoichiometric amount relative to the amount of
40 metal in the feed solution to be removed.
The time provided for reaction between the precipitant
and the metal in the feed solution between introduction of
the precipitant and removing product from the feed solution
is sufficient for substantial completion of the reaction.
45 Preferably, the residence time for substantial completion of
the reaction ranges between about 1 to about 120 minutes,
more preferably between about 1 to about 30 minutes, and
most preferably between about 1 to about 10 minutes.
As noted above. a discrete fiber is dispersed into the feed
50 solution to form a product with the precipitate. "Discrete
fibers" refer to fibers that are not attached to one another.
The fibers are preferably composed of cellulose, glass,
plastic, cotton, or wool. More preferably, the fiber is composed
of cellulose. "Cellulose" refers to a natural carbohydrate
polymer having anhydroglucose units joined by an
55 oxygen linkage to form long molecular chains. For example,
the discrete fibers may be in the form of shredded paper.
The fibers can be of varying sizes and shapes and typically
are elongated in at least one dimension. For example, a paper
fiber is a material having a size of less than about 3.0 mm,
60 more preferably less than about 2.5 mm.. and most preferably
less than about 2.0 mm.. Preferably. the median size of the
discrete fibers is less than about 2.5 mm. The size and
median size of the discrete fibers is measured based on the
longest dimension of the discrete fibers. As will be
65 appreciated. the size of the discrete fibers may be selected
either to yield a desired settling rate of product in the feed
solution or to permit the use of a desired filter pore size to
5,660,735
5
remove the product from the feed solution. The desired size
distribution of fibers can depend upon the application. Both
broad and narrow size distributions are within the scope of
the invention. Typically, the size distribution of the discrete
fibers will be directly proportional to the size distribution of
the product. Generally, the size of the product is not significantly
different from the size of the fiber from which the
product originated.
The settling rate of product may be further increased to a
desired rate by the use of settling aids with the fibers. As
used herein, a "settling aid" refers to a substance that
attaches to the product and causes the specific gravity of the
product and the settling aid to be greater than the specific
gravity of the product alone. Preferred settling aids are sand
and magnetite.
In one embodiment of the present invention, the discrete
fibers may be dispersed in the feed solution as part of an
aqueous slurry. In an alternative embodiment, dry discrete
fibers may be added directly to the feed solution. The
addition of the discrete fibers to the feed solution as a slurry
allows for more rapid dispersion of the fibers relative to the
addition of dry discrete fibers paper directly to the feed
solution.
The volume of the discrete fibers dispersed in the feed
solution can vary depending on process conditions and is
selected so as to achieve acceptable remediation. Preferably,
the concentration of the discrete fibers dispersed in the feed
solution is from about 10 to about 1000, more preferably
from about 50 to about 800, and most preferably from about
100 to about 500 mg/l.
The dispersion of the discrete fibers in the feed solution
may be accelerated by agitation. The agitation may be
induced passively by baffles or actively by mechanical
means, such as an impeller in a stirred tank.
It has been found that by operation of the present
invention, the discrete fibers attach to the precipitates to
form products. The attachment between the precipitate and
the fiber occurs whether the precipitant is attached to the
discrete fibers or added to the feed solution separately from
the fibers.
The time between the introduction of discrete fibers into
the feed solution and the removal of the product from the
feed solution is sufficient to achieve acceptable precipitation
of metals from the solution. Preferably, the time is sufficient
for a majority, more preferably at least 75%, and most
preferably at least 95% of the precipitate to form a product
with the discrete fibers.
The process of the invention can further include removing
the product from the feed solution to form a treated solution
and a recovered product. In one embodiment of the present
invention. the removing step includes filtering the feed
solution to remove the product. As used herein, "filtering"
includes screening as well as filtering. In the filtering step,
the feed solution is filtered to form the treated solution as the
filtrate and the recovered product as the cake. The filtration
of the feed solution may be accomplished by any continuous
or non-continuous filters known in the art. A preferred filter
is continuous. The more preferred filters are rotary drum and
rotary disk filters and the most preferred filters are rotary
drum filters. such as string filters and rotary belt filters.
The filter pore size is a function of the size distribution of
the discrete fibers and the size distribution of other particulate
matter in the feed solution. Thus. the filter pore size may
be selected based upon the size distribution of the discrete
fibers.
The filter pore size is preferably sufficient to retain
substantially all of the discrete fibers while passing substantially
all of the feed solution and other particulate matter
entrained therein. To remove entrained particulate matter
6
larger than the discrete fibers, it may be desirable to have
located upstream screens or secondary filters that have a
pore size sufficient to remove the entrained particulate
matter but large enough to pass substantially all of the
5 discrete fibers.
The filter pore size desirably retains at least about 80%,
more desirably at least about 90%, and most desirably at
least about 95% of the discrete fibers. To retain the desired
amount of the fibers, the filter pore size is desirably smaller
than the longest dimension of that portion of the size
10 distribution of the fibers that is sought to be recovered.
Preferably. the filter pore size ranges from no more than
about 2.0, more preferably no more than about 1.0 and most
preferably no more than about 0.5 mm.
As will be appreciated, density separation methods may
15 be employed to remove the product from the feed solution.
By way of example, the product may be allowed to settle
under gravity in settling ponds. As stated above, the size
distribution of the fibers may be selected to yield a desired
settling rate of the product in the feed solution. The upper
20 portion of the feed solution may be removed after settling of
the product is completed. Other methods to remove the
product include classifiers. centrifuges, and so forth.
In some embodiments, the feed solution is contacted with
a flocculant to concentrate the product in the feed solution or
25 to assist in fOrnIation of a product between a fiber and a
precipitate. As used herein, "flocculant" refers to any substance
that increases the cohesive forces among the discrete
fibers or among fibers and precipitates in the feed solution.
The flocculant assists in formation of product or removal of
the product from the feed solution by aggregating the
30 product into discrete domains in the feed solution. The
aggregated product more quickly settles under gravity to the
bottom of the feed solution than does the product in the
absence of the flocculant.
The flocculant may be a polyacrylamide. For example, a
35 suitable polyacrylamide flocculant is sold under the trademark
"PERCOL 351".
The desired concentration of flocculant in the feed solution
is a function of the concentration of the product (e.g.,
the concentration of the discrete fibers introduced into the
40 feed solution) in the feed solution. Preferably, the flocculant
concentration is less than about 1 mg/l and typically is from
about 0.1 to about 1 mg/l.
In a further alternative embodiment, which may be used
in combination with :flocculation, the feed solution, after
45 flocculation, may be treated by thickening techniques known
in the art to produce an overflow solution and slurry.
Thickening facilitates later filtration by reducing the volume
of solution that needs to be filtered to remove the product.
Thickening concentrates the product and the discrete fibers
50 in a lower portion of the flocculated solution, thereby
permitting an upper portion to be removed as the overflow
solution. In this embodiment, the slurry is preferably no
more than about V20, more preferably no more than about
1/50, and most preferably no more than about 1/100 of the
volume of the feed solution. The overflow solution prefer-
55 ably contains less than about 30% of product, more preferably
contains less than about 20% of product, and most
preferably is substantially free of product.
The treated solution formed from the process as broadly
described above preferably contains less than the concen-
60 trations allowed by applicable local, state or federal regulations.
For example, the United States Environmental Protection
Agency establishes allowable concentrations for
various metals of the present invention for agricultural and
domestic uses. Such standards are hereby incorporated by
65 reference.
The recovered product may be conveniently disposed of
by several techniques. In one embodiment, the recovered
5,660,735
7 8
EXAMPLE 1
TABLE 1
Analysis of Acid Mine Drainage
Concentration Concentration
(mgIL) Component (mgIL)
401 Cd .35
329 B 0.23
170 Ba 0.14
Pb 0.14
130 Li 0.05
128 Au <0.05
Se <0.05
104 As 0.03
91
14 Co 0.02
6.8 V 0.02
3.1 Be 0.008
2.1 Ge <0.008
1.4 Cr 0.004
1.1 Mo <0.003
Hg <0.002
Sr 0.38
Zn
Na
K
Si
AI
Cu
Ni
P
Mn
Fe
Mg
Ca
Mn
Component
A series of tests were run to illustrate that by using paper
fiber, a type offiber, sludge settling, filtering and compaction
is improved. Some of the tests were performed on an acid
mine drainage (AMD). An analysis of the AMD is shown
below in Table 1.
cinders 28. Waste gas 22 may be scrubbed with overflow
solution 18 to remove deleterious materials, including metals.
The scrubbing solution 30 may be added to feed solution
4 for purification. Cinders 28 may be disposed of or
5 recycled, as desired.
In each experiment in Table 2, the AMD sample was
spiked to 25 or 50 mgIL Cu with CuS04 and diluted (1 part
AMD to 3 parts demineralized H20).
The paper fiber, as a 2 weight percent slurry, was prepared
by shredding newspaper in water using a blender. The ash
content of the sample was less than 2%.
The tests were conducted in baffled 600 to 1000 ml
beakers using gentle mixing at room temperature (220 to 240
C.) for 7 to 10 minutes. A polyacrylamide flocculant was
used in some of the experiments as noted in Table 2. The
polyacrylamide flocculant employed is sold under the trademark
"PERCOL 351". After flocculation, the precipitate
and/or fibers were settled, decanted and the thickened slurry
was filtered through 48 or 65 mesh screens, or paper towel
filter.
The pH was maintained at 9.1 with 0.73 grams of
Na2C03• Hydrogen peroxide was added in the amount of 30
mg to oxidize manganese to Mn02• The solution temperature
was maintained at 230 C. for 10 minutes
Other experimental conditions or procedures are
described in Table 2.
As shown below in Table 2, with paper fiber added, the
precipitate settled roughly three times faster and was filterable
through a loose paper fiber filter. The supernatant
60 solution and filtrate were crystal clear. In those tests where
no paper fiber was employed, finer precipitates passed
through the filter to produce a less pure solution than was
obtained with paper fiber. Additionally, the volume of the
pressed cake and paper fiber is about a tenth as much as the
centrifuged precipitate when no paper fiber was employed
(which is analogous to the thickened sludge in a settling
pond of a conventional purification process).
product is dewatered. Before dewatering, the recovered
product has a water content of more than about 50%, more
typically more than about 75%, and most typically more
than about 90% by weight. The dewatered product has a
water content less than about 30%, more preferably less than
about 20%, and most preferably less than about 10% by
weight The recovered product may .be dewatered by any
means known in the art, including compaction or drying,
In another embodiment, the recovered product and
particularly, dewatered product may be incinerated to pro- 10
duce cinders and a waste gas. The waste gas may be
scrubbed with the overflow solution to remove deleterious
materials, including metals. The overflow solution after
scrubbing (e,g.. the scrubbing solution) is recycled. Before
recycle, it is possible to recover the metals from the scrub- 15
bing solution by standard techniques. The cinders may be
disposed of or recycled, as desired.
In an alternative embodiment of the present invention, the
metals may be concentrated in a solution by precipitating the
metal from the solution to form a precipitate; dispersing
discrete fibers in the solution to form a product containing a 20
discrete fiber and the precipitate; and allowing the product to
collect in a portion of the solution by density separation
techniques.
This embodiment is particularly applicable to large, stationary
bodies of water, such as lakes, reservoirs and ponds, 25
to concentrate metals in the bottom sediments of the body of
water in a form that is less harmful to aquatic life. It is often
not practical to remove the settled product from the bottom
sediments. The removal cost may be prohibitive due to the
cost to remove the bottom sediments, typically by dredging, 30
and to dispose of the removed material.
FIG. 1 depicts a preferred embodiment of the present
invention as applied to water runoff from a mine (hereinafter
called "acid mine drainage"). Discrete fibers 6 are introduced
into feed solution 4 by any means known in the art to 35
form a fiber-containing solution 7.
A precipitant 11 and, in some cases, pH adjustor 8 may be
contacted with fiber-containing solution 7 to form a
precipitate-containing solution 9. This step is desired if the
metal is in a water soluble form and must be precipitated. 40
The pH adjustor 8 may be an acid or base, as desired. In
some applications, the pH adjustor 8 is unnecessary sincepH
adjustment is provided by the precipitant The pH is adjusted
to provide the desired conditions in precipitate-containing
solution 9 for precipitant 10 to react with the metal to form 45
a precipitate. Preferably, pH adjuster 8 is an environmentally
benign compound. For acid mine drainage, to make the pH
more basic the preferred pH adjustor 8 is a hydroxide, such
as calcium hydroxide, or carbonate, such as calcium carbonate
and/or sodium carbonate. To make the pH more 50
acidic, the preferred pH adjustor 8 is sulfuric acid or
carbonic acid. The preferred pH in precipitate-containing
solution 9 ranges from about 4 to about 11 and more
preferably from about 6 to about 8.5.
Precipitate-containing solution 9 may be contacted with
flocculant 16 to concentrate the product in flocculated solu- 55
tion 14. In flocculated solution 14, the metal-containing
precipitate attaches to discrete fibers 6 to form a product in
the precipitate-containing solution 9. Flocculated solution
14 may be treated by any thickener known in the art to
produce an overflow solution 18 and slurry 20.
Overflow solution 18 may be used to scrub waste gas 22
in a conventional scrubber. The portion of overflow solution
18 that is not used to scrub waste gas 22 may be added to
treated solution 24.
Recovered product 12 may be dewatered. Dewatered 65
product 26 may be incinerated to form waste gas 22 and
5,660,735
9
TABLE 2
The Effect of Paper Fiber on the Separation of Heayy Metals Precipitate
10
Test Objective Test Conditions Results
Precipitating of Cu, Zn, Mn, Fe from diluted Paper fiber = 0.2 g Settling rate = 0.7 ftImin, thickened slurry =
AMD with Na2C03 plus paper fiber to Precipitate separated from solution by 50 ml in 10 min.
determine effect on thickening and filtration through 7.5 cm paper fiber clear supernatent solution
filtration. filter at 1" Hg vacuum. The moist cake Filtration = 65 mlJ20 sec (1.1 gpmlsq. ft.)
was pressed, dried at 85 C., and ignited at clear filtrate
700 C. Precipitate and fiber (pressed):
Precipitating of Cu, Zn, Mn, Fe from diluted Paper fiber = none
AMD with Na2C03 without paper fiber to Precipitate separated from solution by
determine precipitate filterability. filtration through 7.5 cm paper fiber
filter at 1" Hg vacuum.
Precipitating of Cu, Zn, Mn, Fe from diluted Paper fiber = none
AMD with Na2C03 without paper fiber to Precipitate separated from solution by
determine how much sludge is formed. centrifuge operating at 1000 rpm for 5
min.
EXAMPLE 2
The tests in Table 3 below were done according to the
same procedures as Example 1 with the exceptions enumer- 30
ated in Table 3 and the preparation of the solutions. For the
copper sulfide precipitation tests, solutions were made up
using reagent grade CuS04 and Na2S04 salts.
The data from the tests in Table 3 show the applicability
of paper fiber as a settling and filtration aid for precipitating 35
Cu as hydroxide, silicate, sulfide, and xanthate and Cu, Zn,
Fe and Mn (which is oxidized to precipitate out Mn02) as
hydroxides or carbonates.
TABLE 3
thickness = 0.1 mm
vol....fJ.7 cc
moist wt = 1.83 g
dry wt = 0.40 g, (21.9% solids)
ignited wt = 0.18 g
Settling rate = 0.2 ftImin, thickened slurry =
55 ml in 10 min.
supematemsomtioncon~d
suspended fibers
Filtration = fines passed through filter
Settling rate = 0.3 ftImin, thickened slurry =
40 ml in 10 min
supernatant solution contained
suspended fines
Centrifuged sludge volume = 9 cc
lest Objective
Heavy metal precipitation with Ca(OH)2
using paper fiber as settling and
filter aid
Cu precipitation as silicate with paper
fiber settling and filter aid
Cu precipitation as sulfide with paper
fiber as settling and filter aid
Probing Tests with Paper Fiber
Test Conditions
Feed som = 1.00 liter AMD
Mixture: Paper fiber = 0.23 g + Ca(OH)2 =
0.58 g mixed lime and paper fiber for
-15 min
pH = 8.9 adjusted with slight amount Ca(OH)2
H202 = added 30 mg after pH adjust to 8.9
Temp = 22 C., T1Ille = 15 min
'TERCOL 351" = 0.5 mg
SolidlLiquid Separation = settled, and filtered
through 65 mesh, 7.5 cm screen at 1"
vacuum
Feed som = 50 mgIL Cu + 1.3 gIL Na2S04, pH
2.9, 1.00 liter
Mixture
Paper fiber = 0.2 g
Na2Si03.Na20 soln = 0.3 ml 40-42 Be
soln (-150 mg)
pH = 7.8 with Ca(OH)2 or H2S04
Temp = 22 C., T1Ille = 5 min
'TERCOL 351" = 0.5 mg
SolidlLiquid Separation = Settled and filtered
through 7.5 cm, 65 mesh screen at 1"
vacuum
Feed soln = 50 mgIL Cu + 1.3 gIL Na2S04, pH
2.9, 1.00 liter
Results
Precipitate and fiber settled rapidly
Thickened slurry (200 cc) filtered in -3 min
giving a slimy cake
Gelatinous type mixture
Poor separation through 65 mesh screen
Precipitate and fiber settled rapidly
Very slight H2S odor
11
Test Objective
Cu precipitation as xanthate with paper
fiber as settling and filter aid
en snlfide precipitation from CuS04 +
Na2S04 soln using NallS and paper fiber
Cu snlfide precipitation from CUS04 +
Na2S04 soln using NallS and paper fiber
en snlfide precipitation from CUS04 +
Na2S04 soln using NallS and paper fiber
en snlfide precipitation from soln
using NallS and paper fiber - Tho stage
precipitation first with NallS at pH 5
to precipitate Cn, then with Na2C03 to
precipitate ZN, Fe, and Mn at pH 8.4
5,660,735
TABLE 3-continued
Probing Tests with Paper Fiber
Test Conditions
Mixture
Paper fiber = 0.2 g
CaS =90 mg
Activated carbon = 110 mg powder F400
pH = 8.0 with Ca(OH)2
Temp = 22 C., Tune = 6 min
''PERCOL 351" = 0.5 mg
SolidlLiquid Separation = thickened and
filtered through 7.5 cm, 65 mesh
screen at I" vacuum
Feed soln = 50 mgIL Cu + 1.3 gIL Na2S04,
pH 2.9, 1.00 liter
Mixture:
Paper fiber = 0.23 g
"KEX" = 280 mg
pH = 6.8 with Ca(OH)2
Temp = 22 C., TIme = 8 min
"PERCOL 351" = 0.3 mg
Flocculant = 0.5 mg "PERCOL 351"
SolidlLiquid Separation = thickened and
filtered through 7.5 cm, 65 mesh
screen at 1" vacuum
Feed soln = 50 mgIL Cu + 1.3 gIL Na2S04,
pH 2.9, 1.00 liter
Mixture:
NaHS added = 66 mg tech flake
Paper fiber = 0.2 g
"PERCOL 351" = 0.5 mg
pH = 7.2 with Na2C03
Temp = 22 C., Tune = 10 min
Flocculant = 0.5 mg "PERCOL 351"
SolidlLiquid Separation = thickened and
filtered through 7.5 cm, 65 mesh
screen at 1" vacuum
Feed soln = 50 mgIL Cu + 1.3 gIL Na2S04,
pH 2.9, 1.00 liter
Mixture:
NaHS = 66 mg tech flake
Paper fiber = 0.2 g
Na2C03 = 0.37 mg
pH =7.2
Temp = 22 C., Tune = 10 min
Flocculant = 0.5 mg "PERCOL 351"
SolidlLiquid Separation = thickened and
filtered through 7.5 cm, 65 mesh
screen at I" vacuum
Feed soln = 50 mgIL Cu + 1.3 gIL Na2S04,
pH 2.9, 1.00 liter
Mixture:
NaHS = 66 mg tech flake
Paper fiber = 0.2 g
pH = 7.1 with Na2C03
Temp = 22 C., Tune = 5 min
Flocculant = 0.5 mg "PERCOL 351"
SolidlLiquid Separation = thickened and
filtered through 7.5 cm, 48 mesh
screen at 1" vacuum
SlEPNO.l
Feed soln = Cu-spiked AMD,
1.00 liter
Mixture
NaHS added = 70 mg tech flake
Paper fiber = 0.2 g
pH = 5.4 with 140 mg Na2C03
Temp = 22 C., Tune = 5 min
Flocculant = 0.5 mg "PERCOL 351"
SolidlLiquid Separation = thickened and
12
Results
Screened OK
Precipitate and fiber settled rapidly
Very slight xanthate odor
Did not appear to "screen" as well as CaS!AC
Settled poorly, added another 0.5 mg "PERCOL
351" to flocculate, then solids settled
rapidly
Screened rapidly
Co=enl: Flocculan1 best added after
neutralization
Settled poorly, supemate = brownish
(colloidal CUS)
Co=ent: Best add NallS first then adjust pH
Settled rapidly
Filtered OK, clear filtrate
Assays (mgIL) en Zn Mn Fe
Feed soln 23 25 32 14
Treated soln 0.6 24 31 11
% precipitated 97 <10 <10 21
Settled rapidly
Filtered OK, clear filtrate
13
Test Objective
5,660,735
TABLE 3-continued
Probing Tests with Paper Fiber
Test Conditions
14
Results
filtered through 7.5 cm, 48 mesh
screen at 1" vacuum.
SlEPNO.2 Assays (mgIL) Cu Zn Mn Fe
Precipitate flocculated BUT settled slowly
Filtered OK through towel filter - sime fines
in filtrate
Co=ent: appears paper fiber collects sulfide
precipitate and makes settling and filtering
better
Assays (mgIL) Cu Zn Mn Fe
Cu sulfide precipitation without paper
fiber
Mn precipitation from spiked AMD using
Feed soln = NaHS filtrate from Step No. 1
Paper fiber = 0.2 g
pH = 8.4 with Na2C03
Temp = 22 C., Tune = 7 min
Flocculant = 0.5 mg "PERCOL 351"
SolidlLiquid Separation = thickened and
filtered through 7.5 cm, 48 mesh
screen at 1" vacuum
Feed soln = diluted, Cu spiked AMD
NallS added = 70 mgIL
Paper fiber = none
pH = 5.5 with Na2C03
Temp = 22 C., Tune = 7 min
Flocculant = 0.5 mg "PERCOL 351"
Feed soln = diluted, Cu spiked AMD
Feed soln (step 1) 23
NaHS filtrate (step 1) 0.6
Treated soln (step 2) <0.1
% precipitated >99
(total for steps 1 and 2):
Settled rapidly
Filtered OK, clear filtrate
25 32 11
24 31 11
0.9 22 <0.5
96 31 95
Feed soln 23 26 32 15
Treated soln <0.5 0.6 5.0 <0.2
% precipitated >'97 98 84 >'98
The fiber and precipitate settled rapidly and
filtered OK, clear filtrate.
Reagent addition (lb per 1000 gal):
5.5 Na2C03, 0.5 H202, 1.7 paper fiber;
1.7 sand, 0.004 flocculant
H202 to oxidize Mn to Mn02 at pH 8.5
Mn precipitation from simulated AMD by
H202 added = 1.8 mg per mg Mn
Paper fiber = 0.2 gIL as slurry
Sand = 0.2 gIL, -48 mesh
pH = 8.6 with Na2C03
Temp = 22 C., Tune = 12 min
Flocculant = 0.5 mg "PERCOL 351"
SolidlLiquid Separation = thickened and
filtered through 7.5 cm, 48 mesh
screen at 1" vacuum
Feed soln = diluted, Cu spiked AMD Assays min mgIL Mn % Precipitated
contacting with precipitated Mn02
Reaction of xanthated paper fiber with
Feed soln assay (mgIL) = 23 Cn, 26 Zn, 15 Fe,
31 Mn; pH 2.9
Mn02 added = -200 mgIL Mn02 as slurry
Paper fiber = 0.2 gIL
Sand = 0.2 gIL --48 mesh
pH = 8.6 with Na2C03
Temp = 22 C., Tune = 8 min
SolidlLiquid Separation = thickened and
filtered through 7.5 cm, 48 mesh
screen at 1" vacuum
Xanthating - Paper fiber = 5.0 g, H2O = 175 mI,
Feed soln 31
Treated soln 10 23 26
30 21 32
Settled fast, but some fines suspended
Filtered well, clear filtrate
Assays, mgIL Mn Zn Cu Fe
Feed soln 30 24 24 13
Treated soln 28 4.6 <0.1 2.8
Fiber and precipitate = 2.23 g moist
floc (e.g., the flocculated precipitate)
settled OK, light floc tended to flow
Filtered OK
dilutedAMD
'Ih:ated diluted AMD with impregnated
CS2 = 10 g, Ethanol = 6.0 g
Contact: Temp = 23 C., Tune = 18 hr
Diluted AMD = 250 mI AMD + 25 mg Cu to 1000
mI
Paper fiber (xanthated) = 8.2 g, pH rose from
2.8 to 7.1
Temp = 22 C., Tune = 9 min
Flocculant = 0.5 mg "PERCOL 351"
SolidlLiquid Separation = settled, and filtered
Impregnated Peat Mixture: Peat = 7.73 g, Assays, mgIL Mn Zn Cu Fe
DEHP(Ca) - Peat.
Test 1 = beaker contact
Treatment of AMD with paper fiber and
lime
''DEHPA''=
5.08 g, 6.2 acetone, mixed and
evaporated at 35 C.
Weight = 13.0 g
Diluted AMD = 25% AMD + 25 mgIL Cu;
1.ooL
DEPHA - peat mix = 1.33 g
pH = adjusted to 7.0 with 0.3.8 g Na2C03
Temp = 22 C., Tune = 10 & 24 min
SolidlLiquid Separation = added 0.22 g paper
fiber, stirred + 0.5 mg "PERCOL 351"
Feed soln = AMD + 50 mgIL Cu;
1000 mI
Paper fiber = 0.42 g paper as pulp + sand =
0.43 g --48 mesh
pH = maintained at 9.3 with 0.82 g Ca(0H)2
H202= 129 mg
Temp = 22 C., Tune = 10 min
SolidlLiquid Separation = +0.5 mg "PERCOL 351,"
settled and filtered through 7,5 cm
towel filter at 2" Hg vacuum
Feed soln 30 24 24 13
Treated soln, 10 min 27 16 3.5 <0.1
Treated soln, 24 min 26 13 2.6 <0.1
Floc (e.g., the flocculated precipitate)
settled fast
Filtered OK
Settling rate = 15 ftJhr
Thickened slurry (1 hr) = 1.6 wt % solids
Filter rate = 0.8 gpm/sq. ft.
Cake = 8.56 g moist, 1.62 g dry, 19% solids
15
lest Objective
'Ireatment ofAMD with paper fiber and
limestone and Na2C03
'Ireatment of diluted AMD with Portland
cement without paper filter
'l\"eatment of diluted AMD with Portland
cement plus paper fiber
Precipitating of Cu, Zn, Mn, Fe from
diluted AMD with Na2C03 plus paper
fiber - effect on thickening and
filtration
Precipitating of Cu, Zn, Mn, Fe from
diluted AMD with Na2C03 without paper
fiber - determine precipitate
filterability
Precipitating of Cll, Zn, Mn, Fe from
diluted AMD with Na2C03 without paper
fiber to determine how much sludge is
formed
"Blank" Test with paper fiber and
demineralized water
5,660,735
TABLE 3-continued
Probipg Tests with Paper Fiber
Test Conditions
Feed soln = AMD + 50 mgIL Cu;
1000 mI
Paper fiber = 0.23 g paper as pulp + limestone =
0.43 g powder
pH = maintained at 9.0 with 2.25 g Na2C03
H202 = 130 mg
Temp = 22 C., Tune = 8 min
Solicl!Liquid Separation = +0.5 mg "PERCOL 351,"
settled and filtered through 7.5 cm
towel filter at 2" Hg vacuum
Feed soln = 250 mI AMD + 50 mg Cu
diluted to 1000 mi.
Paper fiber = none
Portland cement = 0.71 g to pH 8.9
m02= 30mg
pH = maintained at 9.1 with 0.8 mg Ca(OH)2
Temp = 23 C., Tune = 10 min
Solicl!Liquid Separation = added 0.5 mg "PERCOL
351" to flocculated solids, settled,
decanted, and filtered through 7.5 cm
paper fiber filter at I" Hg vacuum
Feed soln = 250 mI AMD + 50 mg Cu
diluted to 1000 mi.
Paper fiber = 0.2 g
Portland cement = 0.55 g to pH 5.6
m02= 30mg
pH = maintained at 9.1 with 74 mg Ca(OH)2
Temp = 23 C., Tune = 10 min
Solicl!Liquid Separation = added 0.5 mg "PERCOL
351" to flocculated solids, settled,
decanted, and filtered through 7.5 cm
paper fiber filter at I" Hg vacuum,
pressed moist cake, dried at 85 C., and
iguited at 700 C.
Feed soln = 250 mI AMD + 50 mg Cu
diluted to 1000 mi.
Paper fiber = 0.2 g
m02 = 30mg
pH = maintained to 9.1 with 0.73 g Na2C03
Temp = 23 C., Tune = 10 min
Solicl!Liquid Separation = 0.5 mg "PERCOL
351" to flocculated solids, settled,
decanted, and filtered through 7.5 cm
paper fiber filter at I" Hg vacuum,
pressed moist cake, dried at 85 C., and
iguited at 700 C.
Feed soln = 250 mI AMD + 50 mg Cu
diluted to 1000 mi.
Paper fiber = none
H202=30 mg
pH = maintained to 9.1 with 0.73 g Na2C03
Temp = 23 C., Tune = 10 min
Solicl!Liquid Separation = added 0.5 mg "PERCOL
351" to flocculated solids, settled,
decanted, and filtered through 7.5 cm
paper fiber filter at I" Hg vacuum
Feed soln = 250 mI AMD + 50 mg Cu
diluted to 1000 m!.
Paper fiber = none
m02 = 30mg
pH = maintained to 9.1 with 0.73 g Na2C03
Temp = 23 C., Tune = 10 min
Solicl!Liquid Separation = added 0.5 mg "PERCOL
351" to flocculated solids, settled,
decanted, and centrifuged solids at
1000 rpm for 5 min
Feed soln = demineralized water only, 1000 mi.
Paper fiber = 0.3 g
H202 = IOmg
pH = maintained to 9.1 with Na2C03
Temp = 23 C., Tune = 10 min
Solicl!Liquid Separation = added 0.5 mg "PERCOL
16
Results
Settling rate = 7.5 ftJhr FINES SUSPENDED
Thickened slurry (1 hr) = 1.3 wt % solids
Filter rate = 0.1 gpmlsq. ft.
Cake = 6.28 g moist, 1.32 g dry, 21% solids
Settling rate = 0.17 ftlmin
Thickened slurry = 50 ml in 10 min
some fines in suspension
Filtration = fines passed through filter
Settling rate = 2 ftlmin
Thickened slurry = 50 ml in 10 min
clear supernatant solution
Filtering = 50 ml/8 sec (2.8 gpmlsq. ft.)
Precipitate and fiber (pressed):
thickness = 0.1 mm
moist wt = 2.58 g
dry wt = 0.77 g, (29.8% solids)
iguited wt =0.53 g
Settling rate = 0.7 ftlmin
Thickened slurry = 50 ml in 10 min
clear supernatant solution
Filtration =65 ml/20 sec (Ll gpmlsq. ft.)
Precipitate and fiber (pressed):
thickness = 0.1 mm
vol-D.7 cc
moist wt = 1.83 g
dry wt = 0.40 g, (21.9% solids)
iguited wt = 0.18 g
Settling rate = 0.2 ftlmin
Thickened slurry = 55 ml in 10 min
supernatant solution contained
suspended fibers
Filtration = fines passed through filter
Settling rate = 0.3 ftlmin
Thickened slurry = 40 ml in 10 min
supernatant solution coutained
suspended fibers
Centrifuged sludge volume = 9 cc
Paper fiber did NOT flocculate
Pressed fiber,
moist wt = 0.90 g
dried wt = 0.25 g
iguited wt = <0.002 g
5,660,735
17 18
TABLE 3-continued
Probing Tests with Paper Fiber
Test Objective Test Conditions Results
Precipitate CN from cyanide solution as
351" and filtered through paper fiber.
Pressed fiber, dried at 85 C., and
ignited at 600-700 C.
Feed scln = 0.5 gIL NaCN Assays (mgfL) CN, total
ferric ferrocyanide using paper fiber
as a filter aid
To 1000 m1 scln was added 0.1 g Na2S205, H2S04 Feed scln -260
to pH 5, added 0.3 g FeS04, and adjusted to pH Treated soln 36
8 with NaOH Flocculated and settled rapidly
Filtered well
Comment: colorless (n'": blue) filtrate was
obtained
45
11. The method, as claimed in claim 1, wherein said
removing step comprises separating said product from said
20 feed solution by a density separation method.
12. The method, as claimed in claim 1, wherein said feed
solution comprises water and said recovered product has a
water content less than about 90% by weight.
13. The method, as claimed in claim 1 wherein said
25 dewatered recovered product has a water content less than
about 30% by weight.
14. The method, as claimed in claim 1, wherein said
discrete fibers comprise a component selected from the
group consisting of cellulose, glass, plastic, cotton or wool.
30 15. The method, as claimed in claim 1, wherein said
discrete fibers are substantially composed of cellulose.
16. The method, as claimed in claim 15 further comprising:
contacting said feed solution with a flocculant after said
dispersing step.
17. The method, as claimed in claim 16 wherein said
flocculant is a polyacrylamide.
18. A method to remove a metal from an aqueous feed
solution, comprising:
40 continuously precipitating said metal from said feed solution
to form a precipitate selected from the group
consisting of hydroxides, peroxides, silicates, sulfides,
xanthates, phosphates, carbonates, cellulosederivatives
and mixtures thereof wherein said metal is
selected tom the group consisting of aluminum, arsenic,
beryllium, boron, cadmium, chromium, fluorine,
nickel, selenium, vanadium, lithium, molybdenum,
barium, lead, mercury, silver, copper, zinc, and compounds
thereof and mixtures thereof wherein the feed
solution has a rate of flow of more than about 100
gallons/minute;
(b) coutinuously mixing discrete cellulosic fibers in said
feed solution to form a product comprising a cellulosic
fiber and said precipitate; and
55 (c) continuously filtering said product from said feed
solution to form a recovered product and a treated
solution.
19. The method as claimed in claim 18 wherein said feed
solution is substantially free of solids before the precipitat60
ing step.
20. The method, as claimed in claim 18 wherein the
concentration of said discrete cellulosic fibers in said feed
solution is from about 10 to about 1,000 mgll.
21. The method, as claimed in claim 18 further compris65
ing compacting said recovered product.
22. A method for concentrating metals in a feed solution
comprising:
While various embodiments of the present invention have
been described in detail, it is apparent that modifications and
adaptations of those embodiments will occur to those skilled
in the art. However, it is to be expressly understood that such
modifications and adaptations are within the scope of the
present invention, as set forth in the following claims.
What is claimed is:
1. A method for remediation of aqueous feed solutions
containing a metal, comprising:
(a) precipitating the metal from a feed solution to form a
precipitate wherein said metal is selected from the
group consisting of aluminum, arsenic, beryllium,
boron, cadmium, chromium, fluorine, nickel, selenium,
vanadium, lithium, molybdenum, barium, lead,
mercury, silver, copper, zinc, compounds thereof and
mixtures thereof;
(b) dispersing discrete fibers in said feed solution to form
a product comprising a fiber and said precipitate;
35 (c) removing said product from said feed solution to form
a treated solution and a recovered product containing
the metal precipitate and discrete fibers; and
(d) separating the metal precipitate from the discrete
fibers in the product to recover the metal.
2. The method, as claimed in claim 1, wherein said feed
solution comprises a stream that has a rate of flow greater
than about 10 gallons/minute.
3. The method, as claimed in claim 1, wherein said metal
has a concentration in said feed solution of less than about
50 mgll.
4. The method, as claimed in claim 1, wherein said treated
solution has a concentration of said metal that is less than
about 1.0 mgll.
5. The method, as claimed in claim 1, wherein said
precipitate is selected from the group consisting of 50
hydroxides, silicates, sulfides, xanthates, phosphates,
carbonates, cellulose-derivatives and mixtures thereof.
6. The method, as claimed in claim 1 wherein a precipitant
is attached to the discrete fibers to precipitate said metal.
7. The method, as claimed in claim 1 wherein said
precipitant is selected from the group consisting of
hydroxides, silicates, sulfides, xanthates, phosphates,
carbonates, hydroxyethyl cellulose and mixtures thereof.
8. The method, as claimed in claim 1, wherein said
removing step comprises filtering said feed solution to form
said recovered product.
9. The method, as claimed in claim 8 wherein said
removing step comprises thickening said feed solution
before said filtering step.
10. The method, as claimed in claim 8 wherein the pore
size of the filter in said filtering step is sufficient to retain
substantially all of said discrete fibers.
5,660,735
10
19
(a) continuously precipitating said metals from said feed
solution to form a precipitate, the feed solution having
a rate of flow greater than about 100 gallons/minute;
(b) continuously dispersing discrete fibers in said feed
solution to form a product comprising a fiber and said 5
precipitate;
(c) contacting a flocculent with the feed solution;
(d) thickening the feed solution to form a thickened feed
solution;
(e) continuously filtering the thickened feed solution to
form a recovered product and a treated solution;
(f) dewatering the recovered product to form a dewatered
product;
(g) combusting the dewatered product to form a waste gas 15
containing the metal;
(h) scrubbing the waste gas with a scrubbing solution to
solubilize the metal therein; and
(i) removing the metal from the scrubbing solution. 20
23. The method, as claimed in claim 2, wherein the feed
solution is substantially free of solids before the precipitating
step.
24. The method, as claimed in claim 2, wherein said rate
of flow is greater than about 500 gallons/minute. 25
25. The method, as claimed in claim 1, wherein at lest
about 95% of the precipitate forms a product with the
discrete fibers.
26. The method, as claimed in claim 1. wherein the
concentration of the discrete fibers in the feed solution is 30
from about 100 to about 500 mg/L.
27. The method. as claimed in claim 2. wherein the rate
of flow is greater than about 100 gallons/minute.
28. The method, as claimed in claim 1. wherein the
recovered product comprises at least about 75% of the 35
precipitate in the feed solution.
29. The method, as claimed in claim 1, wherein the
recovered product comprises at least about 85% of the
precipitate in the feed solution.
20
30. The method. as claimed in claim 1, wherein the
recovered product comprises at least about 90% of the metal
precipitate in the feed solution.
31. The method. as claimed in claim 1. wherein at least
about 75% of the precipitate forms a product with the fibers.
32. The method, as claimed in claim 1, wherein the
precipitating step comprises:
contacting the feed solution with a precipitant, wherein
the amount of the precipitant contacted with the feed
solution is at least about 200% of the stoichiometric
amount relative to the amount of the metal to be
removed from the feed solution.
33. The method, as claimed in claim 18, wherein the
mixing step is done in the substantial absence of a flocculent.
34. The method, as claimed in claim 1, wherein the
separating step comprises:
(e) dewatering the product mass to form a dewatered
product having a water content less than about 30% by
weight.
35. The method, as claimed in claim 34, wherein the
separating step comprises:
(f) combusting the dewatered product to form a waste gas.
36. The method, as claimed in claim 35, wherein the
separating step comprises:
(g) scrubbing the waste gas with a scrubbing solution to
form a scrubbing solution comprising the metal; and
(h) recovering the metal from the scrubbing solution.
37. The method, as claimed in claim 18, further comprising
before the continuously filtering step:
(d) thickening the feed solution to form a thickened feed
solution;
(e) dewatering the recovered product to from a dewatered
product;
(f) combusting the dewatered product to form a waste gas
containing the metal; and
(g) recovering the metal from the waste gas.
* * * * *