5,536,416 Method for removing metals from a solution

Patent Number/Link:

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

6 Fiber

-----+ Addition

-----+ Prec ipitate

Metal

-----+

16 Flocculate

-----+

Thicken 18 30

Scrub

20 t 22

Fi Iter

12 26 Oewater 28 Combust ~

u.s. Patent Jul. 16, 1996 5,536,416

FIG. 1

Acid Mine

Drainage

6 Fiber ----. Addition

8 ----. Precipitate

Metal

----'I

16 Flocculate

----'I

Thicken 18 30 Scrub

20 f 22

Fi Iter

12 26 28

Dewater Combust

Flocculant

pH Adjustor

Precipitant

Discrete Fibers

5,536,416

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

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

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

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.

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

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"

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

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

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

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

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.

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

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,

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

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

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

Zn Mn Fe

25 32 14

24 31 11

<10 <10 21

min mgfLMn

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

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

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

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

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

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

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

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.

* * * * *