5,536,416
Jul. 16, 1996
[11]
[45]
111111111111111111111111111111111111111111111111111111111111111111111111111
USOO5536416A
Patent Number:
Date of Patent:
[19]
Coltrinari et al.
United States Patent
[73] Assignee: Hazen Research, Inc., Golden, Colo.
[54] METHOD FOR REMOVING METALS FROM
A SOLUTION
[75] Inventors: Enzo Coltrinari, Golden; Wayne C.
Hazen, Denver, both of Colo.
References Cited
ABSTRACT
1/1989 Ellline 210/665
3/1990 Jackson et aI 210/674
12/1990 Schuster et aI 210/725
3/1991 Bowers 21On09
4/1991 Weyls et aI 2101719
111992 Wegner 21On28
11/1992 Sparapany et aI' 21On35
11/1993 El-ShaIl 210n28
2/1994 Carter et aI 210/504
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
26 Claims, 1 Drawing Sheet
[57]
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.
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 & McIntosh
1111970 Watansbe et aI 210/15
4/1982 Konstantinov et al. 21On29
12/1985 Asada et aI 210n14
12/1987 Noda et aI' 210/505
7/1988 Gifford et aI 423/122
8/1988 Ellline 210/668
u.s. PATENT DOCUMENTS
Appl. No.: 332,536
Filed: Oct. 31, 1994
Int. CI.6 C02F 1/62
U.S. CI 210n23; 210/729; 210/730;
2101731; 210/747; 210/911; 210/912; 210/913;
210/914; 210/734
Field of Search 210/727, 734,
210/503,504,505,729, 730, 731, 723,
912, 913, 914, 747, 911
3,537,986
4,324,667
4,559,143
4,710,298
4,758,414
4,764,281
[56]
[21]
[22]
[51]
[52]
[58]
Acid Mine
Drainage
Discrete Fibers
pH Adjustor
Precipitant
Flocculant
4
6 Fiber
-----+ Addition
7
8
-----+ Prec ipitate
10
Metal
-----+
11
16 Flocculate
-----+
14
Thicken 18 30
Scrub
20 t 22
I
Fi Iter
12 26 Oewater 28 Combust ~
24
u.s. Patent Jul. 16, 1996 5,536,416
FIG. 1
Acid Mine
Drainage
4
6 Fiber ----. Addition
7
8 ----. Precipitate
10
Metal
----'I
11
16 Flocculate
----'I
14
Thicken 18 30 Scrub
20 f 22
l
Fi Iter
12 26 28
Dewater Combust
24
Flocculant
pH Adjustor
Precipitant
Discrete Fibers
5,536,416
2
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
removed from the feed solution to form a treated solution
5 and a recovered product.
The feed solution may have high rates of flow of more
than about 500 gallons/minute. The feed solution may also
have low metal concentrations less than about 50 parts per
million by volume. The metals removed by the present
10 invention may include aluminum, arsenic, beryllium, boron,
cadmium, chromium, fluorine, nickel, selenium, vanadium,
lithium, molybdenum, barium, lead, mercury, silver, copper,
zinc, manganese, iron compounds thereof and mixtures
thereof.
15 The precipitate preferably includes hydroxides, silicates,
sulfides, xanthates, phosphates, carbonates, cellulose-derivatives,
and mixtures thereof. More preferably, the precipitate
includes hydroxides, silicates, carbonates, and mixtures
thereof. In one embodiment, the precipitate is formed
by precipitating the metal from the feed solution using a
20 precipitant. The precipitant preferably includes a hydroxide,
silicate, sulfide, xanthate, phosphate, carbonate, hydroxyethyl
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
25 solution by filtering. The filtering step may be preceded by
a thickening step. In an alternate embodiment, the product is
removed from the feed solution by a density separation
method.
After product removal, the treated solution preferably has
30 a metal concentration that is less than the maximum concentrations
for discharges into water resources under regulations
promulgated by the Environmental Protection
Agency.
The recovered product may be dewatered. The recovered
35 product preferably has a water content less than about 90%
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 40
concentrating the metals in the feed solution. In a first step,
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
45 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 pro-
50 vides an inexpensive and simple method to purify large
quantities of contaminated water at high flow rates. The
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
55 employ larger filter pore sizes and therefore higher filter
fluxes than is possible with conventional purification methods.
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 concentrations.
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
by any number of methods known in the art.
SUMMARY OF THE INVENTION
1
METHOD FOR REMOVING METALS FROM
A SOLUTION
FIELD OF THE INVENTION
In a preferred embodiment, the present invention relates 65
to a novel method for remediation of feed solutions containing
a metal. In a first step, a feed solution is provided
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.
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 60
remove metals from surface and ground water resources
having low concentrations of metals.
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 effluent.
BACKGROUND OF THE INVENTION
5,536,416
3
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
rapidly by flocculation, thickening, and filtration of the feed
solution, than would otherwise be possible with the precipitate
alone.
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 THE DRAWINGS
FIG. 1 is a flow schematic of the subject invention,
illustrating the use of fibers to remove metal precipitates
from solution.
DETAILED 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 invention 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 VIII 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
4
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
5 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.
10 For aqueous solutions, the metal-containing compound
should be water insoluble. Preferably, the precipitate is a
hydroxide, silicate, sulfide, xanthate, phosphate, carbonate,
cellulose-derivatives, or mixtures thereof. More preferably,
the precipitate is environmentally benign. Most preferably,
15 the precipitate is a hydroxide, silicate, carbonate, or mixtures
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.
20 "Precipitated" or "precipitating" refers to any process that
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
25 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
30 precipitate containing the metal are each environmentally
benign. More preferably, the precipitant is a hydroxide,
silicate, sulfide, xanthate, phosphate, carbonate, hydroxyethyl
cellulose, or mixtures thereof. Most preferably, the
precipitant is CaC03, NazC03' Ca(OH)2' NazSi03' CaS,
35 NaHS, H3P04, CaHiP04)z, or mixtures thereof.
The precipitant may be contacted with the feed solution
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
40 means known in the art to form functionalized fibers. The
functionalized fibers may form the metal-containing precipitate
either directly on the discrete fibers or in the feed
solution. For functionalized fibers, the precipitant is preferably
a phosphate, xanthate, or hydroxyethyl cellulose.
45
The desired concentration of the precipitant in the feed
solution is great enough to obtain acceptable reaction with
metal in the feed solution. The precipitant is preferably
present in the feed solution in at least stoichiometric
50 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
metal in the feed solution to be removed.
The time provided for reaction between the precipitant
55 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. Preferably,
the residence time for substantial completion of the
reaction ranges between about 1 to about 120 minutes, more
60 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
solution to form a product with the precipitate. "Discrete
fibers" refer to fibers that are not attached to one another.
65 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 carbohy5,536,416
5
drate polymer having anhydroglucose units joined by an
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,
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 rom. The size and
median size of the discrete fibers is measured based on the
longest dimension of the discrete fibers. As will be 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 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 ofthe 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.
Tbe 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 mgll.
The dispersion of the discrete fibers in the feed solution
may be accelerated by agitation. The agitation may be
induced passively by baffies 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"
6
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
5 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
10 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
15 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
larger than the discrete fibers, it may be desirable to have
located upstream screens or secondary filters that have a
20 pore size sufficient to remove the entrained particulate
matter but large enough to pass substantially all of the
discrete fibers.
The filter pore size desirably retains at least about 80%,
more desirably at least about 90%, and most desirably at
25 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
distribution of the fibers that is sought to be recovered.
Preferably, the filter pore size ranges from no more than
30 about 2.0, more preferably no more than about 1.0 and most
preferably no more than about 0.5 rom.
As will be appreciated, density separation methods may
be employed to remove the product from the feed solution.
By way of example, the product may be allowed to settle
35 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
portion of the feed solution may be removed after settling of
the product is completed. Other methods to remove the
40 product include classifiers, centrifuges, and so forth.
In some embodiments, the feed solution is contacted with
a fiocculant to concentrate the product in the feed solution or
to assist in formation of a product between a fiber and a
precipitate. As used herein, "flocculant" refers to any sub-
45 stance that increases the cohesive forces among the discrete
fibers or among fibers and precipitates in the feed solution.
The fiocculant assists in formation of product or removal of
the product from the feed solution by aggregating the
product into discrete domains in the feed solution. The
50 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
55 suitable polyacrylamide fiocculant is sold under the trademark
"PERCOL 351".
The desired concentration of fiocculant in the feed solution
is a function of the concentration of the product (e.g.,
the concentration of the discrete fibers introduced into the
60 feed solution) in the feed solution. Preferably, the fiocculant
concentration is less than about 1 mg/l and typically is from
about 0.1 to about 1 mgll.
In a further alternative embodiment, which may be used
in combination with flocculation, the feed solution, after
65 flocculation, may be treated by thickening techniques known
in the art to produce an overflow solution and slurry.
Thickening facilitates latcr filtration by reducing the volume
5,536,416
7 8
A series of tests were run to illustrate that by using paper
fiber, a type of fiber, 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.
In each experiment in Table 2, the AMD sample was
spiked to 25 or 50 mglL Cu with CuS04 and diluted (l 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 m1
beakers using gentle mixing at room temperature (220 to 240
C.) for 7 to 10 minutes. A polyacrylamide flocculant was
EXAMPLE 1
TABLE 1
Analysis of Acid Mine Drainage
Concentration Concentration
(mglL) Component (mglL)
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
0.38
Component
Mn
Fe
Sr
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 car-
S bonate and/or sodium carbonate. To make the pH more
acidic, the preferred pH adjustor 8 is sulfuric acid or
carbonic acid. The preferred pH in precipitate-containing
solution 11 ranges from about 4 to about 11 and more
preferably from about 6 to about 8.5.
Precipitate-containing solution 11 may be contacted with
flocculant 16 to concentrate the product in flocculated solution
14. In flocculated solution 14, the metal-containing
precipitate attaches to discrete fibers 6 to form a product in
the precipitate-containing solution 11. Flocculated solution
15 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
20 treated solution 24.
Recovered product 12 may be dewatered. Dewatered
product 26 may be incinerated to form waste gas 22 and
cinders 28. Waste gas 22 may be scrubbed with overflow
25 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
recycled, as desired.
of solution that needs to be filtered to remove the product.
Thickening concentrates the product and the discrete fibers
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 1/20, 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 preferably
contains less than about 30% of product, more preferably
contains less than about 20% of product, and most 10
preferably is substantially free of product.
The treated solution formed from the process as broadly
described above preferably contains less than the concentrations
allowed by applicable local, state or federal regulations.
For example, the U.S. Environmental Protection
Agency establishes allowable concentrations for various
metals of the present invention for agricultural and domestic
uses. Such standards are hereby incorporated by reference.
The recovered product may be conveniently disposed of
by several techniques. In one embodiment, the recovered
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 produce 30
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 scrubbing solution 35
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 40
discrete fibers in the solution to form a product containing a
discrete fiber and the precipitate; and allowing the product to
collect in a portion of the solution by density separation Mg
techniques. Ca
45 Mn
This embodiment is particularly applicable to large, stationary
bodies of water, such as lakes, reservoirs and ponds,
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 Zn
not practical to remove the settled product from the bottom 50 Na
sediments. The removal cost may be prohibitive due to the K
cost to remove the bottom sediments, typically by dredging, Si
and to dispose of the removed material. ~~
FIG. 1 depicts a preferred embodiment of the present Ni
invention as applied to water runoff from a mine (hereinafter 55 P
called "acid mine drainage"). Discrete fibers 6 are introduced
into feed solution 4 by any means known in the art to
form a fiber-containing solution 7.
A precipitant 10 and, in some cases, pH adjustor 8 may be
contacted with fiber-containing solution 7 to form a precipi- 60
tate-containing solution 11. This step is desired if the metal
is in a water soluble form and must be precipitated. The pH
adjustor 8 may be an acid or base, as desired. In some
applications, the pH adjustor 8 is unnecessary since pH
adjustment is provided by the precipitant. The pH is adjusted 65
to provide the desired conditions in precipitate-containing
solution 11 for precipitant 10 to react with the metal to form
5,536,416
9
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 5
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 23° C. for 10 minutes. 10
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 filter- 15
able through a loose paper fiber filter. The supernatant
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 20
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).
TABLE 2
The Effect of Paper Fiber on the Separation of Heavy Metals Precipitate
10
Test Objective
Precipitating of Cu, Zn, Mn, Fe
from diluted AMD with Na2C03
plus paper fiber to
dctennine effect on
thickening and filtration
Precipitating of Cu, Zn, Mn, Fe
from diluted AMD with Na2C03
without paper fiber to
determine precipitate filterability.
Precipitation of Cu, Zn, Mn, Fe
from diluted AMD with Na2C03 without
paper fiber to
detennine how much sludge is formed.
EXAMPLE 2
Test Conditions
Paper fiber = 0.2 g
Precipitate separated from solution by
filtration through 7.5 em paper fiber
filter at 1" Hg vacuum. THe moist cake
was pressed, dried at 85 c., and ignited at
700C.
Paper fiber = none
Precipitate separated from solution by
filitration through 7.5 em paper fiber
filter at 1- Hg vaenum.
Paper fiber = none
Precipitate separated from solution by
eentrifuge operation at 1000 rpm for 5
min.
50
Results
Settling rate =0.7 ftlmin, thickened slurry =
50 ro1 in 10 min.
clear supernatant solution
Filtration = 65 ro1I20 sec (1.1 gpmlsq.lft.)
clear filtrate
Precipitation and fiber (pressed):
thickness = 0.1 rom
vol- 0.7 cc
moist wt = 1.83 g
dry wt = 0040 g, (21.9%) solids)
ignited wt = 0.18 g
Settling rate =0.2 ftlmin, thickened slurry =
55 ro1 in 10 min.
supernatant solution contained
suspended fibers
Filtration = fines passed through filter
Settling rate =0.3 ftlmin, thickened slurry =
40 ro1 in 10 min.
supernatant solution contained
suspended fines
Centrifuged sludge volume = 9 cc
60
The tests in Table 3 below were done according to the 55
same procedures as Example 1 with the exceptions enumerated
in Table 3 and the preparation of the solutions. For the
eopper sulfide precipitation tests, solutions were made up
using reagent grade CuS04 and Na2S04 salts.
The data from the tests in Table 3 show the applieability
of paper fiber as a settling and filtration aid for precipitating
Cu as hydroxide, silicate, sulfide, and xanthate and Cu, Zn,
65
Fe and Mn (which is oxidized to precipitate out Mn02) as
hydroxides or carbonates.
Test Objective
Heavy metal
precipitation
with Ca(OH)2
using paper
fiber as settling
and filter aid
Cu precipitation
as silicate
with paper
fiber as settling
and filter aid
Cu precipitation as
sulfide with paper
fiber as settling
and filter aid
Cu precipitation
as zanthate
with paper
fiber as settling
and filter aid
Cu sulfide
precipitation
from CuS04 +
NaS04 soln
using NaHS
and paper fiber
Cu sulfide
precipitation
from CuS04 +
NaZS04 soln using NaHS
and paper fiber
Cu sulfide
precipitation from
CuS04 + NaZS04
soln using NaHS
and paper fiber
5,536,416
11
TABLE 3
Test Conditions
Feed soln = 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, Time =15 min
"PERCOL 351" = 0.5 mg
Solid/Liquid Separation = settled, and filtered
through 65 mech, 7.5 em screen at I"
vacuum
Feed soln = 50 mglL Cu + 1.3 gil NaZS04, pH
2.9, 1.00 liter
Mixture - Paper fiber = 0.2 g
- NaZSi03.NaZ) soln = 0.3 ml 4Q-42 Be
soln (- 150 mg)
pH = 7.8 with Ca(OH)2 or H2S04
Temp =22 C, Time =5 min
"PERCOL 351" = 0.5 mg
Solid/Liquid Separation = Settled and filtered
through 7.5 em, 65 mesh screen at I"
vacuum
Feed soln = 50 mglL Cu + 1.3 gil NaZS04, pH
2.9, 1.00 liter
Mixture - Paper fiber = 0.2 g
- caS = 90 mg
- Activated carbon = 110 mg powder F-
400
pH = 8.0 with Ca(OH)2
Temp =22 C, Time =6 min
"PERCOL 351" = 0.5 mg
Solid/Liquid Separation = Settled and
filtered through 7.5 em, 65 mesh screen
at I" vacuum
Feed soln = 50 mglL Cu + 1,3 gIL NaZS04,
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"
Solid/Liquid Separation = thickened and
filtered through 7.5 em, 65 mesh
screen at I" vacuum
Feed soln = 50 mglL Cu + 1.3 gIL NaZS04,
pH = 2.9, I liter
Mixture: NaHS added = 66 mg tech flake
Paper fiber = 0.2 g
"PERCOL 351" = 0.5 mg
pH = 7.2 with NaZC03
Temp =22 C, Time =10 min
Flocculant = 0.5 mg "PERCOL 351"
Solid/Liquid Separation = thickened and
filtered through 7.5 em, 65 mesh
screen at I "vacuum
Feed soln = 50 mglL Cu + 1.3 gIL NaZS04,
pH 2.9, 1.00 liter
Mixture: NaHS = 66 mg tech flake
Paper fiber = 0.2 g
NaZC03 = 0.37 mg
pH = 7.2
Temp =22 C., Time =10 min
Flocculant = 0.5 mg "PERCOL 351"
Solid/Liquid Separation = thickened and
filtered through 7.5 em, 65 mesh
screen at I" vacuum
Feed soln = 50 mglL Cu + 1.3 gIL NaZS04,
pH 2.9, 1.00 liter
Mixture: NaHS = 66 mg tech flake
Paper fiber = 0.2 g
pH = 7.1 with NaZC03
Temp = 22 C., Time = 5 min
Flocculant = 0.5 mg "PERCOL 351"
Solid/Liquid Separation = thickened and
filtered through 7.5 em, 48 mesh
screen at I" vacuum
12
Results
Precipitate and fiber settled rapidly
Thickened slurry (200 cc) filtered in - 3 min
giving a slime cake
Gelatinous type mixture
Poor separation through 65 mesh screen
Precipitate and fiber settled rapidly
Very slight H2S odor
Screened OK
Precipitate and fiber settled rapidly
Very slight xanthate odor
Did not appear to "screen" as well as CaSlAC
Settled poorly, added another 0.5 mg "PERCOL
351" to flocculate, then solids settled
rapidly
Screened rapidly
Comment: Flocculant best added after
neutralization
Settled poorly, supernate = brownish
(colloidal CuS)
Comment: Best add NaHS first then adjust pH
Settled rapidly
Filtered OK, clear filtrate
5,536,416
13 14
TABLE 3-continued
Test Objcctive Test Conditions Results
Settling rate = 15 ft/hr
Thickened slurry (I hr) = 1.6 wt % solids
Filter rate = 0.8 gpmlsq. ft.
Cake = 8.56 g moist, 1.62 g dry, 19% solids
Assays, mglL Mn Zn Cu Fe
Feed soln 30 24 24 13
Treated soln 28 4.6 <0.1 2.8
Fiber and preeipitate = 2.23 g moist
floc (e.g., the flocculated precipitate)
settled OK, light floc tended to flow
Filtered OK
Assays, mglL Mn Zn Cu Fe
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
Assays (mglL) Cu Zn Mn Fe
Feed soln (step I) 23 25 32 11
NaHS filtrate (step I) 0.6 24 31 11
Treated soln (step 2) <0.1 0.9 22 <0.5
% precipitated >99 96 31 95
(total for steps
I and 2):
Settled rapidly
Filtered OK, clear filtrate
Precipitate flocculated BUT settled slowly
Filtered OK through towel filter - some fines
in filtrate
Comment: appears paper fiber collects sulfide
precipitate and makes settling and filtering
better
Assays (mgfL) Cu Zn Mn Fc
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,
I.7 sand, 0.004 f10cculant
% Precipitated
26
32
Zn Mn Fe
25 32 14
24 31 11
<10 <10 21
min mgfLMn
31
10 23
30 21
Settled fast, but some fines suspended
Filtered well, clear filtrate
Assays
Feed soln
Treated soln
Assays (mglL) Cu
Feed soln 23
Treated soln 0.6
% precipitated 97
Settled rapidly
Filtered OK, clear filtrate
STEP NO. I
Feed soln = Cu_spiked AMD,
1.00 liter
Mixture - NaHS = 70 mg tech flake
- Paper fiber = 0.2 g
pH = 5.4 with 140 mg Na2C03
Temp = 22 C., Time = 5 min
Flocculant = 0.5 mg "PERCOL 351"
Solid/Liquid Separation = thickened and
filtered through 7.5 cm, 48 mcsh
screen at 111 vacuum
STEP NO. 2
Feed soln = NaHS filtrate from Step No. I
Papcr fibcr = 0.2 g
pH = 8.4 with 140 mg Na2C03
Temp = 22 C., Time = 7 min
Flocculant = 0.5 mg "PERCOL 351"
Solid/Liquid Separation = thickened and
fi Itered through 7.5 cm, 48 mesh
screen at III vacuum
Feed soln = diluted, Cu spiked AMD
NaHS added = 70 mglL
Paper fiber = none
pH = 5.5 with Na2C03
Temp = 22 C., Time = 7 min
Flocculant = 0.5 mg "PERCOL 351"
Feed soln = diluted, Cu spiked AMD
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., Time =12 min
Flocculant =0.5 tug "PERCOL 351"
Solid/Liquid Separation = thickened and
filtered through 7.5 cm, 48 mesh
screen at 1" vacuum
Feed soln = diluted, Cu spiked AMD
Feed soln assay (mglL) = 23 Cu, 26 Zn, 15 Fe,
31 Mn; pH 2.9
Mn02 added = -200 mglL Mn02 as slurry
Paper fiber = 0.2 gil
Sand = 0.2 gIL -48 mesh
pH = 86 with Na2C03
Temp = 22 C., Time = 8 min
Solid/Liquid Separation = thickened and
filtered through 7.5 cm, 48 mesh
screen at 1" vacuum
Xanthating - Paper fiber = 5.0 g, H20 = 175 ml,
CS2 = 10 g, Ethanol = 6.0 g
- Contact: Temp = 23 c., Time = 18 hr
Diluted AMD = 250 ml AMD + 25 mg Cu to 1000
ml
Paper fiber (xanthated) = 8,2 g, pH rose from
2.8 to 7.1
Temp =22 c., Time =9 min
Flocculant = 0.5 mg "PERCOL 351"
Solid/Liquid Separation = settled, and filtered
Impregnated Peat mixture: Peat = 7.73 g,
"DEMPA"=
5.08 g, 6.2 acetone, mixed and
evaporated at 35 C.
Weight = 13.0 g
Diluted AMD = 25% AMD + 25 mgfL Cu;
DEHPA - peat mix = 1.33 g
pH = adjusted to 7.0 with 0.38 g Na2C03
Temp = 22 C., Time = 10 & 24 min
Solid/Liquid Separation = added 0.22 g paper
fiber, stirred + 0.5 mg "PERCOL 351"
Feed soln = AMD + 50 mglL Cu;
1000 ml
Paper fiber = 0.42 g paper as pulp + sand =
0.43 g -48 mesh
pH = maintained at 9.3 with 0.82 g Ca(OH)2
H202 = 129 mg
Temp = 22 c., Time = 10 min
Solid/Liquid Separation = +0.5 mg "PERCOL
351" settled and filtered through 7.5 cm
Mn precipitation
from
spiked AMD using
H202 to oxidize
Mn to Mn02 at pH 8.5
Treatment ofAMD with
paper fiber and lime
Mn precipitation from
simulated AMD by
contacting with
precipitated Mn02
Treat diluted AMD
with impregnated
DEHP(Ca) - Peat.
Test I = beaker contact
Reaction of xanthated
paper fiber with
dilutedAMD
Cu sulfide
prccipitation
without paper fiber
Cu Sulfide
precipitation from soln
using NaHS and paper
fiber - Two stage
precipitation first
with NaHS at pH 5
to precipitate
Cu, then with
Na2C03 to precipitate
Zn, Fe, and Mn at pH 8.4
5,536,416
15 16
TABLE 3-continued
Test Objective Test Conditions Results
Settling rate = 0.17 ftJmin
Thickened slurry = 50 mI in 10 min
some fines in suspension
Filtration = fines passed through filter
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 dyr, 21% solids
Settling rate = 0.2 ftJmin
Thickened slurry = 55 mI in 10 min
supernatant solution contained
suspended fibers
Filtration = fines passed through filter
Paper fiber did NOT flocculate
Pressed fiber,
moist wt = 0.90 g
dried wt = 0.25 g
ignited wt = <0.002 g
Assays (mglL) CN, total
Settling rate = 2 ftImin
Thickening slurry = 50 mI 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)
ignited wt = 0.53 g
Settling rate = 0.3 ftJmin
Thickened slurry = 40 mI in 10 min
supernatant solution contained
suspended fibers
Centrifuged sludge volume = 9 cc
Settling rate = 0.7 ftJmin
Thickening slurry = 50 mI in 10 min
clear supernatant solution
Filtering = 65 ml/20 sec (1.1 gpmlsq. ft.)
Precipitate and fiber (pressed):
thickness = 0.1 mm
vol = 0.7 cc
moist wt = 1.83 g
dry wt = 0.40 g, (21.9% solids)
ignited wt = 0.18 g
towel filter at 2" Hg vacuum
Feed soln = AMD + 50 mglL 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., Time = 8 min
SolidlLiquid 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
H202 = 30 mg
pH = maintained at 9.1 with 0.8 mg Ca(OH)2
Temp = 23 C., Time = 10 min
SolidlLiquid 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
H202 = 30 mg
pH = maintained at 9.1 with 74 mg Ca(OH)2
Temp = 23 C., Time = 10 min
SolidlLiquid 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
ignited at 700 C.
Feed soln = 250 mI AMD + 50 mg Cu
diluted to 1000 mi.
Paper fiber = 0.2 g
H202 = 30 mg
pH = maintained at 9.1 with 0.73 mg Ca(OH)2
Temp = 23 C., Time = 10 min
SolidlLiquid 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
ignited 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, Time '2 10 min
SolidlLiquid 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 = none
H202 = 30 mg
pH = maintained to 9.1 with 0.73 g Na2C03
Temp = 23 C, Time '2 10 min
SolidlLiquid 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 = OJ g
H202= 10 mg
pH = maintained to 9.1 with Na2C03
Temp = 23 C., Time = 10 min
SolidlLiquid Separation = added 0.5 mg "PERCOL
351" and filtered through paper fiber.
Pressed fiber, dried at 85 C., and
ignited at 600-700 C.
Feed soln = 0.5 gIL NaCN
Treatment of diluted AMD
with Portland cement
without pape~ fiber
Precipitation of Cu,
Zn, Mn, Fe from
diluted AMD with Na2C03
without paper fiber dctermine
precipitate
filterability
Treatment ofAMD with
paper fiber and
limestone and Na2C03
Precipitate CN from
Precipitation of
Cu, An, Mn, Fe from
diluted AMD with
Na2C03 without paper
fiber to determine how
much sludge is formed
"Blank" Test
with paper fiber and
dcmineralized water
Treatment 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
5,536,416
17 18
TABLE 3-continued
Test Objective Test Conditions Results
eyanide solution as
ferric ferro cyanide
using paper fiber
as a filter aid
To 1000 m1 soln was added 0.1 g Na2S205, H2S04
to pH 5, added 0.3 g FeS04, and adjusted to pH
8 with NaOH
Feed soln -260
Treated soln 36
Flocculated and settled rapidly
Filtered well
Comment: colorless (uo blue) filtrate was
obtained
25
65
50
60
40
said discrete fibers in said feed solution is from about 100 to
about 500 mgfl.
14. The method, as claimed in claim 4, wherein said rate
15 of flow is greater than about 100 gallons/minute.
15. The method, as claimed in claim 1, wherein said
recovered product comprises at least about 75% of said
metal precipitate in said feed solution.
16. The method, as claimed in claim 1, wherein said
20 recovered product comprises at least about 85% of said
metal precipitate in said feed solution.
17. The method, as claimed in claim 1, wherein said
dewatered recovered product has a removed product comprises
at least about 90% of said metal precipitate in said
feed solution.
18. 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.
19. The method, as claimed in claim 1, wherein at least
about 75% of said metal precipitate forms a product with
30 said fibers.
20. The method, as claimed in claim 1, further comprising:
contacting said feed solution with a flocculent after said
dispersing step.
21. The method, as claimed in claim 1, wherein said
precipitating step comprises:
contacting said feed solution with a precipitant, wherein
the amount of said precipitant contacted with said feed
solution is at least about 200% of the stoichiometric
amount relative to the amount of said metal to be
removed from said feed solution.
22. A method to remove a metal from a feed solution that
includes water runoff from a mine, comprising:
(a) precipitating said metal from said feed solution to
form a metal precipitate selected from the group consisting
of hydroxides, peroxides, silicates, sulfides,
xanthates, phosphates, carbonates, cellulose-derivatives
and mixtures thereof 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, manganese,
iron, and compounds thereof and mixtures
thereof wherein said metal has a concentration in said
feed solution before the precipitation step of less than
50 mgfl;
(b) mixing discrete cellulosic fibers in said feed solution
to form a product comprising a cellulosic fiber and said
metal precipitate; and
(c) filtering said product from said feed solution to form
a recovered product and a treated solution, wherein the
concentration of said metal in said treated solution is no
more than about 25% by weight of the metal concentration
in said feed solution.
23. The method, as claimed in claim 22, wherein said feed
solution is substantially free of solids before said precipitating
step.
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 feed solutions containing
a metal, comprising:
(a) precipitating a metal from a feed solution comprising
acid mine drainage to form a metal precipitate;
(b) dispersing discrete fibers in said feed solution to form
a product comprising afiber and said metal precipitate;
and
(c) removing said product from said feed solution to form
a treated solution and a recovered product containing
the metal precipitate.
2. The method, as claimed in claim 1, wherein said feed
solution is substantially free of solids before said precipitating
step.
3. The method, as claimed in claim 1, wherein said metal
is selected from the group consisting of aluminum, arsenic,
beryllium, boron, cadmium, chromium, fluorine, nickel,
selenium, vanadium, lithium, molybdenum, barium, lead, 35
mercury, silver, copper, zinc, manganese, iron, compounds
thereof and mixtures thereof.
4. 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.
5. The method, as claimed in claim 1, wherein said metal
has a concentration in said feed solution of less than about
50 mgfl.
6. The method, as claimed in claim 1, wherein said treated
solution has a concentration of said metal that is less than 45
about 1.0 mgfl.
7. The method, as claimed in claim 1, wherein said
precipitate is selected from the group consisting of hydroxides,
silicates, sulfides, xanthates, phosphates, carbonates,
cellulose-derivatives and mixtures thereof.
8. The method, as claimed in claim 2, wherein said
discrete fibers comprise a precipitant to precipitate said
metal.
9. The method, as claimed in claim 2, wherein said
precipitant is selected from the group consisting of hydrox- 55
ides, silicates, sulfides, xanthates, phosphates, carbonates,
hydroxyethyl cellulose and mixtures thereof.
10. The method, as claimed in claim 1, wherein said
removing step comprises filtering said feed solution to form
said recovered product.
11. The method, as claimed in claim 4, wherein said rate
of flow is greater than about 500 gallons/minute.
12. The method, as claimed in claim 1, wherein at least
about 95% of said metal precipitate forms a product with
said discrete fibers.
13. The method, as claimed in claim 1, further comprising
combusting said dewatered wherein the concentration of
5,536,416
19
24. The method, as claimed in claim 22, wherein the
concentration of said discrete cellulosic fibers in said feed
solution is from about 10 to about 1,000 mg/l.
25. The method, as claimed in claim 22, wherein said
mixing step is done in the substantial absence of a ftocculent. 5
26. A method for concentrating a number of different
types of metals derived from acid mine drainage and contained
in a feed solution comprising:
(a) precipitating at least about 75% by weight of said
metals from said feed solution to form a precipitate, 10
said feed solution having a rate of ftow greater than
20
about 10 gallons/minute and a concentration of said
metals of less than about 50 mg/l;
(b) dispersing discrete fibers in said feed solution to form
a product comprising a fiber and said precipitate; and
(c) removing said product from said feed solution to form
a treated solution, wherein said metals have a concentration
in said treated solution that is less than about
75% by weight of the metals concentration in said feed
solution.
* * * * *