5,660,735 Method for removing metals from waste solutions

Patent Number/Link:

5,660,735

*Aug. 26, 1997

United States Patent [19]

Coltrinari et aI.

111111111111111111111111111111111111111111111111111111111111111111111111111

US005660735A

[11] Patent Number:

[45] Date of Patent:

37 Claims, 1 Drawing Sheet

FOREIGN PATENT DOCUMENTS

32891 3/1978 Japan 210/504

50439 4/1980 Japan 210/504

Primary Examiner-Neil McCarthy

Attorney, Agent, or Firm-Sheridan Ross P.C.

The present invention is a method to remove metals from

solutions by precipitating the metals and adding cellulosic

fiber to the solution. The precipitates attach to the cellulosic

fibers to form products. The products may be removed from

the solution by gravity separation techniques or by filtration.

The removed products may be dewatered and incinerated.

The method provides a simple and effective technique for

removing low concentrations of metals from high volume

solution streams.

[54] METHOD FOR REMOVING METALS FROM

WASTE SOLUTIONS

[75] Inventors: Enzo Coltrinari, Golden; Wayne C.

Hazen, Denver, both of Colo.

[73] Assignee: Hazen Research, Inc•. Golden, Colo.

[ *] Notice: The term of this patent shall not extend

beyond the expiration date of Pat. No.

5,536,416.

[21] Appl. No.: 683,530

[22] Filed: Jul. 15, 1996

Related U.S. Application Data

[63] Continuation of Ser. No. 332,536, Oct 31, 1994, Pat No.

5,536,416.

[51] Int. Cl.6 C02F 1/62

[52] U.S. Cl 210n23; 210/729; 2101730;

210/731; 2101747; 210/769; 210/911; 210/912;

210/913; 210/914; 210/734

[58] Field of Search 210/723, 769,

210/724,729,730,731,747,911,912,

913, 914, 734

[56] References Cited

U.S. PATENT DOCUMENTS

3,235,489 2/1966 Bell et aI 210/51

3,537,986 1111970 Watansbe et aI 210/15

Acid Mine

Drainage

[57]

4,324,667

4,559,143

4,710,298

4,758,414

4,764,281

4,800,024

4,909,944

4,980,071

4,999,116

5,006,262

5,078,900

5,164,095

5,262,064

5,283,123

4/1982 Konstantinov et aI 2101729

12/1985 Asada et aI 210m4

12/1987 Noda et aI. .. 210/505

7/1988 Gifford et aI 423/122

8/1988 Elfline 210/668

1/1989 Elffine 210/665

3/1990 Jackson 210/674

12/1990 Shuster et aI 2101725

3/1991 Bowers 2101709

4/1991 Weyls et aI 2101719

1/1992 Wegner 2101728

1111992 Sparapany et aI 2101735

1111993 El-Shall 2101728

2/1994 Carter et aI 210/504

ABSTRACT

Discrete Fibers

pH Adjustor

Precipitant

Flocculant

6 Fiber

----i Addition

8 17

----i Precipitate

Metal

----i

111

16 flocculate

-->

114

Thicken 18

Scrub

110 t 11

11 16

Fi Iter Dewater Combust ~

u.s. Patent

Acid Mine

Drainage

Aug. 26, 1997

FIG. 1

5,660,735

Discrete Fibers

pH Adjustor

Prec iPi tant

Flocculant

6 Fiber --. Addition

----+> Precipi tate

Metal

----+>

11 -

16 Flocculate --.

Thicken 18

Scrub

t 22

~ ~ ~ I

12 26

Fi Iter Dewater Combust 28

5,660,735

taining a metal. In a first step, a feed solution is provided

containing a metal precipitate. In a second step, discrete

fibers are dispersed in the feed solution. The precipitate

attaches to a discrete fiber to form a product. The product is

5 removed from the feed solution to form a treated solution

and a recovered product.

The precipitate preferably includes hydroxides, silicates,

sulfides, xanthates, phosphates, carbonates, cellulosederivatives,

and mixtures thereof. More preferably, the pre-

10 cipitate includes hydroxides, silicates, carbonates, and mixtures

thereof. In one embodiment, the precipitate is formed

by precipitating the metal from the feed solution using a

precipitant. The precipitant preferably includes a hydroxide,

silicate, sulfide, xanthate, phosphate, carbonate, hydroxy-

15 ethyl cellulose, and mixtures thereof. In an alternate

embodiment, the discrete fibers may include the precipitant.

In one embodiment, the product is removed from the feed

solution by filtering. The filtering step may be preceded by

a thickening step. In an alternate embodiment, the product is

20 removed from the feed solution by a density separation

method.

After product removal, the treated solution preferably has

a metal concentration that is less than the maximum con25

centrations for discharges into water resources under regulations

promulgated by the Environmental Protection

Agency.

The recovered product may be dewatered. The recovered

product preferably has a water content less than about 90%

30 by weight before dewatering. The dewatered product preferably

has a water content less than about 30% by weight.

The dewatered product may be combusted.

In an alternate embodiment, a method is provided for

concentrating the metals in the feed solution. In a first step,

35 the metals are precipitated from the feed solution. In a

second step, discrete fibers are dispersed in the feed solution

to form the product. The product is allowed to collect in a

portion of the feed solution by density separation techniques.

Various embodiments of the present invention offer

numerous advantages over existing methods and apparatuses.

First, one embodiment of the present invention provides

an inexpensive and simple method to purify large

quantities of contaminated water at high flow rates. The

45 product of the fibers and precipitates may be selected such

that the product is substantially larger than the precipitates

alone. The product size allows the present invention to

employ larger filter pore sizes and therefore higher filter

fluxes than is possible with conventional purification meth-

50 ods. The product size may be selected such that other

entrained particulate matter is smaller than the product and

passes through the filter while the product does not.

Second, another embodiment of the present invention

may economically purify solutions having low metal con-

55 centrations. Unlike conventional methods, which produce

smaller metal precipitates for lower metal concentrations,

the present invention employs fibers to collect the metal

precipitates before removal. The product of the fiber and

metal precipitates may then be rapidly and easily removed

60 by any number of methods known in the art.

Third, in another embodiment of the present invention,

high settling rates of product can be attained by appropriate

selection of product size and the use of settling aids. This

improvement permits the product to be removed more

65 rapidly by flocculation, thickening, and filtration of the feed

solution, than would otherwise be possible with the precipitate

alone.

METHOD FOR REMOVING METALS FROM

WASTE SOLUTIONS

This is a continuation of application Ser. No. 08/332,536,

filed Oct. 31, 1994, now U.S. Pat. No. 5,536,416.

FIELD OF THE INVENTION

The present invention is a method for removing metals

from a solution. More particularly, the present invention

embodies an improved approach for removing precipitates

containing such metals from an eflluent.

BACKGROUND OF THE INVENTION

SUMMARY OF THE INVENTION

In a preferred embodiment. the present invention relates

to a novel method for remediation of feed solutions con-

Discharges of metals into the environment are a major

problem worldwide. Metal discharges severely damage the

environment, being responsible each year for the contamination

of water resources and destruction of plant and

animal life.

Metal discharges into surface and ground water resources

(e.g., streams, rivers, ponds, lakes, and aquifers) pose the

greatest risk to wildlife and human health. Such discharges

may be either manmade, such as discharges by industrial

facilities, or natural, such as water runoff/from caves and

mines. Treatment of contaminated surface and ground water

resources is complicated not only by the large quantities of

water but also by the dilute concentrations of metals contained

in the resources.

Existing methods to remove metals from aqueous solutions

are poorly suited to remove dilute concentrations of

metals from large quantities of water to achieve the purity

levels mandated by state and federal laws. Existing metal

removal methods include the steps of precipitating the

metals and removing the precipitates from the solution by

filtering or by density separation techniques, such as by

settling.

The conventional filtering techniques are not only uneconomical

but also can fail to remove a significant portion of

the precipitates in many applications. The dilute (e.g., parts

per million) concentrations of metals in surface and ground

water resources cause very small metal precipitates to form. 40

As will be appreciated, such precipitates can form a thick

filter cake or gelatinous mass on the filter causing a large

pressure drop across the filter and a small filter flux. The

resulting flux is typically too low to handle economically the

large amounts of contaminated water. Many resources contain

particulate matter, other than the precipitates, that

further impedes the filtering step.

Another conventional technique to remove precipitates, is

by density separation, which is also not economical in most

cases. The most common density separation technique for

large quantities of water is a settling pond, where metal

precipitates settle out of solution. Settling ponds are typically

undesirable as they require large land areas that are

often not available, create a highly toxic sludge in the pond

bottom that is often difficult to dispose of, and often fail to

attain desired levels of purity in the pond overflow.

Other techniques to remove metal contaminants from

surface and groundwater resources require expensive components

and/or otherwise raise other operational complications.

Therefore, there is a need for a process to inexpensively

remove metals from surface and ground water resources

having low concentrations of metals.

5,660,735

FIG. 1 is a flow schematic of the subject invention.

illustrating the use of fibers to remove metal precipitates 15

from solution.

Fourth. recovered product of the present invention may

have a much smaller volume than the sludge produced by

conventional purification methods. Thus. subsequent handling

and disposal of such materials is relatively more

simple. For example. the recovered product may be incinerated

to an even smaller volume than the recovered product

The cinders from incineration may be disposed of or further

treated to recover the metals contained in the cinders. The

disposal of cinders is much easier and less expensive than

the cost to dispose of the sludge or filtrate produced by

conventional purification methods.

BRIEF DESCRIPTION OF TIIE DRAWINGS

DErAILED DESCRIPTION

A first embodiment of the present invention is a method

for remediation of a feed solution containing a metal. The

metal is contained in a precipitate. Discrete fibers are

dispersed in the feed solution to form a product including a

fiber and the precipitate. The product is removed from the

feed solution to form a treated solution and a recovered

product.

The feed solution may be any liquid containing a metal.

Preferably. the feed solution is aqueous. More preferably, the

feed solution is a portion of a stream. river, pond, lake, or

any other naturally occurring or manmade aqueous stream or

reservoir. The process of the present intention can be conducted

in a channel. reservoir, or other type of container.

Preferably, the feed solution is provided for remediation in

a channel, such as a sluice box, or in a stirred tank.

A preferred embodiment of the present invention purifies

a feed solution having a high rate of flow. The flow rate of

the feed solution is preferably greater than about 10 gallons

per minute. more preferably greater than about 100 gallons

per minute, and most preferably greater than about 500

gallons per minute. Such flow rates are in excess of the

amount of water that can be readily and effectively treated

by conventional methods.

The metal to be removed from the feed solution preferably

is a transition element (an element from Groups IB

through VIIB and Group vm of the Modem Periodic Table

of the Elements), an alkali metal (Group lA), an alkaline

earth metal (Group llA). aluminum, boron, lead. arsenic,

selenium. fluorine, compounds thereof, or mixtures thereof.

Most preferably, the metal is aluminum, arsenic, beryllium,

boron, cadmium, chromium, fluorine, nickel, selenium,

vanadium, lithium, molybdenum, barium, lead, mercury,

silver, copper, zinc, iron, manganese. compounds thereof, or

mixtures thereof.

The present invention is particularly suited to the removal

of low metal concentrations from the feed solution.

Surprisingly, the present invention may remove significant

portions of metal from feed solutions having metal concentrations

less than about 50 mg/l. The present invention

removes preferably at least about 75. more preferably at

least about 85. and most preferably at least 90% by weight

of metals from a feed solution having a concentration less

than about 50 mg/l.

The metal may be in the form of either an element or a

metal-containing compound (hereinafter collectively

referred to as ''metal''). In one embodiment of the present

invention. the metal is in the feed solution in the form of a

precipitate. As used herein. "precipitate" refers to any compound

containing the metal that is insoluble in the solution.

For aqueous solutions. the metal-containing compound

should be water insoluble. Preferably. the precipitate is a

hydroxide. silicate. sulfide. xanthate, phosphate, carbonate.

cellulose-derivatives, or mixtures thereof. More preferably.

the precipitate is environmentally benign. Most preferably,

the precipitate is a hydroxide, silicate. carbonate, or mixtures

5 thereof.

In an alternate embodiment of the present invention. the

metal is in a form that is soluble in the solution and is

precipitated from the feed solution to form the precipitate.

"Precipitated" or "precipitating" refers to any process that

10 causes a dissolved metal to form a precipitate. Preferably,

such a process includes a chemical reaction between the

soluble metal and a precipitant that produces a precipitate.

A precipitant may be introduced to the feed solution

before. concurrent with. or after the discrete fibers are

dispersed in the feed solution. As used herein, "precipitant"

refers to any element or compound capable of forming a

precipitate with the metal in the feed solution. Preferably. the

precipitant is selected such that the precipitant and the

precipitate containing the metal are each environmentally

benign. More preferably, the precipitant is a hydroxide,

20 silicate, sulfide, xanthate, phosphate, carbonate. hydroxyethyl

cellulose, or mixtures thereof. Most preferably, the

precipitant is Caco3 , NazC03• Ca(OH}z, NazSi03 , caS,

NaHS, H3P04 , CaHiP04}z. or mixtures thereof.

The precipitant may be contacted with the feed solution

25 either as a part of the discrete fibers or as a separate additive.

as desired. In the case of the precipitant as part of the fiber,

the precipitant may be attached to the discrete fibers by any

means known in the art to form functionalized fibers. The

functionalized fibers may form the metal-containing precipi-

30 tate either directly on the discrete fibers or in the feed

solution. For functionalized fibers, the precipitant is preferably

a phosphate, xanthate, or hydroxyethyl cellulose.

The desired concentration of the precipitant in the feed

solution is great enough to obtain acceptable reaction with

35 metal in the feed solution. The precipitant is preferably

present in the feed solution in at least stoichiometric

amounts relative to that amount of metal in feed solution to

be removed. More preferably, the precipitant is at least about

200% of the stoichiometric amount relative to the amount of

40 metal in the feed solution to be removed.

The time provided for reaction between the precipitant

and the metal in the feed solution between introduction of

the precipitant and removing product from the feed solution

is sufficient for substantial completion of the reaction.

45 Preferably, the residence time for substantial completion of

the reaction ranges between about 1 to about 120 minutes,

more preferably between about 1 to about 30 minutes, and

most preferably between about 1 to about 10 minutes.

As noted above. a discrete fiber is dispersed into the feed

50 solution to form a product with the precipitate. "Discrete

fibers" refer to fibers that are not attached to one another.

The fibers are preferably composed of cellulose, glass,

plastic, cotton, or wool. More preferably, the fiber is composed

of cellulose. "Cellulose" refers to a natural carbohydrate

polymer having anhydroglucose units joined by an

55 oxygen linkage to form long molecular chains. For example,

the discrete fibers may be in the form of shredded paper.

The fibers can be of varying sizes and shapes and typically

are elongated in at least one dimension. For example, a paper

fiber is a material having a size of less than about 3.0 mm,

60 more preferably less than about 2.5 mm.. and most preferably

less than about 2.0 mm.. Preferably. the median size of the

discrete fibers is less than about 2.5 mm. The size and

median size of the discrete fibers is measured based on the

longest dimension of the discrete fibers. As will be

65 appreciated. the size of the discrete fibers may be selected

either to yield a desired settling rate of product in the feed

solution or to permit the use of a desired filter pore size to

5,660,735

remove the product from the feed solution. The desired size

distribution of fibers can depend upon the application. Both

broad and narrow size distributions are within the scope of

the invention. Typically, the size distribution of the discrete

fibers will be directly proportional to the size distribution of

the product. Generally, the size of the product is not significantly

different from the size of the fiber from which the

product originated.

The settling rate of product may be further increased to a

desired rate by the use of settling aids with the fibers. As

used herein, a "settling aid" refers to a substance that

attaches to the product and causes the specific gravity of the

product and the settling aid to be greater than the specific

gravity of the product alone. Preferred settling aids are sand

and magnetite.

In one embodiment of the present invention, the discrete

fibers may be dispersed in the feed solution as part of an

aqueous slurry. In an alternative embodiment, dry discrete

fibers may be added directly to the feed solution. The

addition of the discrete fibers to the feed solution as a slurry

allows for more rapid dispersion of the fibers relative to the

addition of dry discrete fibers paper directly to the feed

solution.

The volume of the discrete fibers dispersed in the feed

solution can vary depending on process conditions and is

selected so as to achieve acceptable remediation. Preferably,

the concentration of the discrete fibers dispersed in the feed

solution is from about 10 to about 1000, more preferably

from about 50 to about 800, and most preferably from about

100 to about 500 mg/l.

The dispersion of the discrete fibers in the feed solution

may be accelerated by agitation. The agitation may be

induced passively by baffles or actively by mechanical

means, such as an impeller in a stirred tank.

It has been found that by operation of the present

invention, the discrete fibers attach to the precipitates to

form products. The attachment between the precipitate and

the fiber occurs whether the precipitant is attached to the

discrete fibers or added to the feed solution separately from

the fibers.

The time between the introduction of discrete fibers into

the feed solution and the removal of the product from the

feed solution is sufficient to achieve acceptable precipitation

of metals from the solution. Preferably, the time is sufficient

for a majority, more preferably at least 75%, and most

preferably at least 95% of the precipitate to form a product

with the discrete fibers.

The process of the invention can further include removing

the product from the feed solution to form a treated solution

and a recovered product. In one embodiment of the present

invention. the removing step includes filtering the feed

solution to remove the product. As used herein, "filtering"

includes screening as well as filtering. In the filtering step,

the feed solution is filtered to form the treated solution as the

filtrate and the recovered product as the cake. The filtration

of the feed solution may be accomplished by any continuous

or non-continuous filters known in the art. A preferred filter

is continuous. The more preferred filters are rotary drum and

rotary disk filters and the most preferred filters are rotary

drum filters. such as string filters and rotary belt filters.

The filter pore size is a function of the size distribution of

the discrete fibers and the size distribution of other particulate

matter in the feed solution. Thus. the filter pore size may

be selected based upon the size distribution of the discrete

fibers.

The filter pore size is preferably sufficient to retain

substantially all of the discrete fibers while passing substantially

all of the feed solution and other particulate matter

entrained therein. To remove entrained particulate matter

larger than the discrete fibers, it may be desirable to have

located upstream screens or secondary filters that have a

pore size sufficient to remove the entrained particulate

matter but large enough to pass substantially all of the

5 discrete fibers.

The filter pore size desirably retains at least about 80%,

more desirably at least about 90%, and most desirably at

least about 95% of the discrete fibers. To retain the desired

amount of the fibers, the filter pore size is desirably smaller

than the longest dimension of that portion of the size

10 distribution of the fibers that is sought to be recovered.

Preferably. the filter pore size ranges from no more than

about 2.0, more preferably no more than about 1.0 and most

preferably no more than about 0.5 mm.

As will be appreciated, density separation methods may

15 be employed to remove the product from the feed solution.

By way of example, the product may be allowed to settle

under gravity in settling ponds. As stated above, the size

distribution of the fibers may be selected to yield a desired

settling rate of the product in the feed solution. The upper

20 portion of the feed solution may be removed after settling of

the product is completed. Other methods to remove the

product include classifiers. centrifuges, and so forth.

In some embodiments, the feed solution is contacted with

a flocculant to concentrate the product in the feed solution or

25 to assist in fOrnIation of a product between a fiber and a

precipitate. As used herein, "flocculant" refers to any substance

that increases the cohesive forces among the discrete

fibers or among fibers and precipitates in the feed solution.

The flocculant assists in formation of product or removal of

the product from the feed solution by aggregating the

30 product into discrete domains in the feed solution. The

aggregated product more quickly settles under gravity to the

bottom of the feed solution than does the product in the

absence of the flocculant.

The flocculant may be a polyacrylamide. For example, a

35 suitable polyacrylamide flocculant is sold under the trademark

"PERCOL 351".

The desired concentration of flocculant in the feed solution

is a function of the concentration of the product (e.g.,

the concentration of the discrete fibers introduced into the

40 feed solution) in the feed solution. Preferably, the flocculant

concentration is less than about 1 mg/l and typically is from

about 0.1 to about 1 mg/l.

In a further alternative embodiment, which may be used

in combination with :flocculation, the feed solution, after

45 flocculation, may be treated by thickening techniques known

in the art to produce an overflow solution and slurry.

Thickening facilitates later filtration by reducing the volume

of solution that needs to be filtered to remove the product.

Thickening concentrates the product and the discrete fibers

50 in a lower portion of the flocculated solution, thereby

permitting an upper portion to be removed as the overflow

solution. In this embodiment, the slurry is preferably no

more than about V20, more preferably no more than about

1/50, and most preferably no more than about 1/100 of the

volume of the feed solution. The overflow solution prefer-

55 ably contains less than about 30% of product, more preferably

contains less than about 20% of product, and most

preferably is substantially free of product.

The treated solution formed from the process as broadly

described above preferably contains less than the concen-

60 trations allowed by applicable local, state or federal regulations.

For example, the United States Environmental Protection

Agency establishes allowable concentrations for

various metals of the present invention for agricultural and

domestic uses. Such standards are hereby incorporated by

65 reference.

The recovered product may be conveniently disposed of

by several techniques. In one embodiment, the recovered

5,660,735

7 8

EXAMPLE 1

TABLE 1

Analysis of Acid Mine Drainage

Concentration Concentration

(mgIL) Component (mgIL)

401 Cd .35

329 B 0.23

170 Ba 0.14

Pb 0.14

130 Li 0.05

128 Au <0.05

Se <0.05

104 As 0.03

14 Co 0.02

6.8 V 0.02

3.1 Be 0.008

2.1 Ge <0.008

1.4 Cr 0.004

1.1 Mo <0.003

Hg <0.002

Sr 0.38

Component

A series of tests were run to illustrate that by using paper

fiber, a type offiber, sludge settling, filtering and compaction

is improved. Some of the tests were performed on an acid

mine drainage (AMD). An analysis of the AMD is shown

below in Table 1.

cinders 28. Waste gas 22 may be scrubbed with overflow

solution 18 to remove deleterious materials, including metals.

The scrubbing solution 30 may be added to feed solution

4 for purification. Cinders 28 may be disposed of or

5 recycled, as desired.

In each experiment in Table 2, the AMD sample was

spiked to 25 or 50 mgIL Cu with CuS04 and diluted (1 part

AMD to 3 parts demineralized H20).

The paper fiber, as a 2 weight percent slurry, was prepared

by shredding newspaper in water using a blender. The ash

content of the sample was less than 2%.

The tests were conducted in baffled 600 to 1000 ml

beakers using gentle mixing at room temperature (220 to 240

C.) for 7 to 10 minutes. A polyacrylamide flocculant was

used in some of the experiments as noted in Table 2. The

polyacrylamide flocculant employed is sold under the trademark

"PERCOL 351". After flocculation, the precipitate

and/or fibers were settled, decanted and the thickened slurry

was filtered through 48 or 65 mesh screens, or paper towel

filter.

The pH was maintained at 9.1 with 0.73 grams of

Na2C03• Hydrogen peroxide was added in the amount of 30

mg to oxidize manganese to Mn02• The solution temperature

was maintained at 230 C. for 10 minutes

Other experimental conditions or procedures are

described in Table 2.

As shown below in Table 2, with paper fiber added, the

precipitate settled roughly three times faster and was filterable

through a loose paper fiber filter. The supernatant

60 solution and filtrate were crystal clear. In those tests where

no paper fiber was employed, finer precipitates passed

through the filter to produce a less pure solution than was

obtained with paper fiber. Additionally, the volume of the

pressed cake and paper fiber is about a tenth as much as the

centrifuged precipitate when no paper fiber was employed

(which is analogous to the thickened sludge in a settling

pond of a conventional purification process).

product is dewatered. Before dewatering, the recovered

product has a water content of more than about 50%, more

typically more than about 75%, and most typically more

than about 90% by weight. The dewatered product has a

water content less than about 30%, more preferably less than

about 20%, and most preferably less than about 10% by

weight The recovered product may .be dewatered by any

means known in the art, including compaction or drying,

In another embodiment, the recovered product and

particularly, dewatered product may be incinerated to pro- 10

duce cinders and a waste gas. The waste gas may be

scrubbed with the overflow solution to remove deleterious

materials, including metals. The overflow solution after

scrubbing (e,g.. the scrubbing solution) is recycled. Before

recycle, it is possible to recover the metals from the scrub- 15

bing solution by standard techniques. The cinders may be

disposed of or recycled, as desired.

In an alternative embodiment of the present invention, the

metals may be concentrated in a solution by precipitating the

metal from the solution to form a precipitate; dispersing

discrete fibers in the solution to form a product containing a 20

discrete fiber and the precipitate; and allowing the product to

collect in a portion of the solution by density separation

techniques.

This embodiment is particularly applicable to large, stationary

bodies of water, such as lakes, reservoirs and ponds, 25

to concentrate metals in the bottom sediments of the body of

water in a form that is less harmful to aquatic life. It is often

not practical to remove the settled product from the bottom

sediments. The removal cost may be prohibitive due to the

cost to remove the bottom sediments, typically by dredging, 30

and to dispose of the removed material.

FIG. 1 depicts a preferred embodiment of the present

invention as applied to water runoff from a mine (hereinafter

called "acid mine drainage"). Discrete fibers 6 are introduced

into feed solution 4 by any means known in the art to 35

form a fiber-containing solution 7.

A precipitant 11 and, in some cases, pH adjustor 8 may be

contacted with fiber-containing solution 7 to form a

precipitate-containing solution 9. This step is desired if the

metal is in a water soluble form and must be precipitated. 40

The pH adjustor 8 may be an acid or base, as desired. In

some applications, the pH adjustor 8 is unnecessary sincepH

adjustment is provided by the precipitant The pH is adjusted

to provide the desired conditions in precipitate-containing

solution 9 for precipitant 10 to react with the metal to form 45

a precipitate. Preferably, pH adjuster 8 is an environmentally

benign compound. For acid mine drainage, to make the pH

more basic the preferred pH adjustor 8 is a hydroxide, such

as calcium hydroxide, or carbonate, such as calcium carbonate

and/or sodium carbonate. To make the pH more 50

acidic, the preferred pH adjustor 8 is sulfuric acid or

carbonic acid. The preferred pH in precipitate-containing

solution 9 ranges from about 4 to about 11 and more

preferably from about 6 to about 8.5.

Precipitate-containing solution 9 may be contacted with

flocculant 16 to concentrate the product in flocculated solu- 55

tion 14. In flocculated solution 14, the metal-containing

precipitate attaches to discrete fibers 6 to form a product in

the precipitate-containing solution 9. Flocculated solution

14 may be treated by any thickener known in the art to

produce an overflow solution 18 and slurry 20.

Overflow solution 18 may be used to scrub waste gas 22

in a conventional scrubber. The portion of overflow solution

18 that is not used to scrub waste gas 22 may be added to

treated solution 24.

Recovered product 12 may be dewatered. Dewatered 65

product 26 may be incinerated to form waste gas 22 and

5,660,735

TABLE 2

The Effect of Paper Fiber on the Separation of Heayy Metals Precipitate

Test Objective Test Conditions Results

Precipitating of Cu, Zn, Mn, Fe from diluted Paper fiber = 0.2 g Settling rate = 0.7 ftImin, thickened slurry =

AMD with Na2C03 plus paper fiber to Precipitate separated from solution by 50 ml in 10 min.

determine effect on thickening and filtration through 7.5 cm paper fiber clear supernatent solution

filtration. filter at 1" Hg vacuum. The moist cake Filtration = 65 mlJ20 sec (1.1 gpmlsq. ft.)

was pressed, dried at 85 C., and ignited at clear filtrate

700 C. Precipitate and fiber (pressed):

Precipitating of Cu, Zn, Mn, Fe from diluted Paper fiber = none

AMD with Na2C03 without paper fiber to Precipitate separated from solution by

determine precipitate filterability. filtration through 7.5 cm paper fiber

filter at 1" Hg vacuum.

Precipitating of Cu, Zn, Mn, Fe from diluted Paper fiber = none

AMD with Na2C03 without paper fiber to Precipitate separated from solution by

determine how much sludge is formed. centrifuge operating at 1000 rpm for 5

min.

EXAMPLE 2

The tests in Table 3 below were done according to the

same procedures as Example 1 with the exceptions enumer- 30

ated in Table 3 and the preparation of the solutions. For the

copper sulfide precipitation tests, solutions were made up

using reagent grade CuS04 and Na2S04 salts.

The data from the tests in Table 3 show the applicability

of paper fiber as a settling and filtration aid for precipitating 35

Cu as hydroxide, silicate, sulfide, and xanthate and Cu, Zn,

Fe and Mn (which is oxidized to precipitate out Mn02) as

hydroxides or carbonates.

TABLE 3

thickness = 0.1 mm

vol....fJ.7 cc

moist wt = 1.83 g

dry wt = 0.40 g, (21.9% solids)

ignited wt = 0.18 g

Settling rate = 0.2 ftImin, thickened slurry =

55 ml in 10 min.

supematemsomtioncon~d

suspended fibers

Filtration = fines passed through filter

Settling rate = 0.3 ftImin, thickened slurry =

40 ml in 10 min

supernatant solution contained

suspended fines

Centrifuged sludge volume = 9 cc

lest Objective

Heavy metal precipitation with Ca(OH)2

using paper fiber as settling and

filter aid

Cu precipitation as silicate with paper

fiber settling and filter aid

Cu precipitation as sulfide with paper

fiber as settling and filter aid

Probing Tests with Paper Fiber

Test Conditions

Feed som = 1.00 liter AMD

Mixture: Paper fiber = 0.23 g + Ca(OH)2 =

0.58 g mixed lime and paper fiber for

-15 min

pH = 8.9 adjusted with slight amount Ca(OH)2

H202 = added 30 mg after pH adjust to 8.9

Temp = 22 C., T1Ille = 15 min

'TERCOL 351" = 0.5 mg

SolidlLiquid Separation = settled, and filtered

through 65 mesh, 7.5 cm screen at 1"

vacuum

Feed som = 50 mgIL Cu + 1.3 gIL Na2S04, pH

2.9, 1.00 liter

Mixture

Paper fiber = 0.2 g

Na2Si03.Na20 soln = 0.3 ml 40-42 Be

soln (-150 mg)

pH = 7.8 with Ca(OH)2 or H2S04

Temp = 22 C., T1Ille = 5 min

'TERCOL 351" = 0.5 mg

SolidlLiquid Separation = Settled and filtered

through 7.5 cm, 65 mesh screen at 1"

vacuum

Feed soln = 50 mgIL Cu + 1.3 gIL Na2S04, pH

2.9, 1.00 liter

Results

Precipitate and fiber settled rapidly

Thickened slurry (200 cc) filtered in -3 min

giving a slimy cake

Gelatinous type mixture

Poor separation through 65 mesh screen

Precipitate and fiber settled rapidly

Very slight H2S odor

Test Objective

Cu precipitation as xanthate with paper

fiber as settling and filter aid

en snlfide precipitation from CuS04 +

Na2S04 soln using NallS and paper fiber

Cu snlfide precipitation from CUS04 +

Na2S04 soln using NallS and paper fiber

en snlfide precipitation from CUS04 +

Na2S04 soln using NallS and paper fiber

en snlfide precipitation from soln

using NallS and paper fiber - Tho stage

precipitation first with NallS at pH 5

to precipitate Cn, then with Na2C03 to

precipitate ZN, Fe, and Mn at pH 8.4

5,660,735

TABLE 3-continued

Probing Tests with Paper Fiber

Test Conditions

Mixture

Paper fiber = 0.2 g

CaS =90 mg

Activated carbon = 110 mg powder F400

pH = 8.0 with Ca(OH)2

Temp = 22 C., Tune = 6 min

''PERCOL 351" = 0.5 mg

SolidlLiquid Separation = thickened and

filtered through 7.5 cm, 65 mesh

screen at I" vacuum

Feed soln = 50 mgIL Cu + 1.3 gIL Na2S04,

pH 2.9, 1.00 liter

Mixture:

Paper fiber = 0.23 g

"KEX" = 280 mg

pH = 6.8 with Ca(OH)2

Temp = 22 C., TIme = 8 min

"PERCOL 351" = 0.3 mg

Flocculant = 0.5 mg "PERCOL 351"

SolidlLiquid Separation = thickened and

filtered through 7.5 cm, 65 mesh

screen at 1" vacuum

Feed soln = 50 mgIL Cu + 1.3 gIL Na2S04,

pH 2.9, 1.00 liter

Mixture:

NaHS added = 66 mg tech flake

Paper fiber = 0.2 g

"PERCOL 351" = 0.5 mg

pH = 7.2 with Na2C03

Temp = 22 C., Tune = 10 min

Flocculant = 0.5 mg "PERCOL 351"

SolidlLiquid Separation = thickened and

filtered through 7.5 cm, 65 mesh

screen at 1" vacuum

Feed soln = 50 mgIL Cu + 1.3 gIL Na2S04,

pH 2.9, 1.00 liter

Mixture:

NaHS = 66 mg tech flake

Paper fiber = 0.2 g

Na2C03 = 0.37 mg

pH =7.2

Temp = 22 C., Tune = 10 min

Flocculant = 0.5 mg "PERCOL 351"

SolidlLiquid Separation = thickened and

filtered through 7.5 cm, 65 mesh

screen at I" vacuum

Feed soln = 50 mgIL Cu + 1.3 gIL Na2S04,

pH 2.9, 1.00 liter

Mixture:

NaHS = 66 mg tech flake

Paper fiber = 0.2 g

pH = 7.1 with Na2C03

Temp = 22 C., Tune = 5 min

Flocculant = 0.5 mg "PERCOL 351"

SolidlLiquid Separation = thickened and

filtered through 7.5 cm, 48 mesh

screen at 1" vacuum

SlEPNO.l

Feed soln = Cu-spiked AMD,

1.00 liter

Mixture

NaHS added = 70 mg tech flake

Paper fiber = 0.2 g

pH = 5.4 with 140 mg Na2C03

Temp = 22 C., Tune = 5 min

Flocculant = 0.5 mg "PERCOL 351"

SolidlLiquid Separation = thickened and

Results

Screened OK

Precipitate and fiber settled rapidly

Very slight xanthate odor

Did not appear to "screen" as well as CaS!AC

Settled poorly, added another 0.5 mg "PERCOL

351" to flocculate, then solids settled

rapidly

Screened rapidly

Co=enl: Flocculan1 best added after

neutralization

Settled poorly, supemate = brownish

(colloidal CUS)

Co=ent: Best add NallS first then adjust pH

Settled rapidly

Filtered OK, clear filtrate

Assays (mgIL) en Zn Mn Fe

Feed soln 23 25 32 14

Treated soln 0.6 24 31 11

% precipitated 97 <10 <10 21

Settled rapidly

Filtered OK, clear filtrate

Test Objective

5,660,735

TABLE 3-continued

Probing Tests with Paper Fiber

Test Conditions

Results

filtered through 7.5 cm, 48 mesh

screen at 1" vacuum.

SlEPNO.2 Assays (mgIL) Cu Zn Mn Fe

Precipitate flocculated BUT settled slowly

Filtered OK through towel filter - sime fines

in filtrate

Co=ent: appears paper fiber collects sulfide

precipitate and makes settling and filtering

better

Assays (mgIL) Cu Zn Mn Fe

Cu sulfide precipitation without paper

fiber

Mn precipitation from spiked AMD using

Feed soln = NaHS filtrate from Step No. 1

Paper fiber = 0.2 g

pH = 8.4 with Na2C03

Temp = 22 C., Tune = 7 min

Flocculant = 0.5 mg "PERCOL 351"

SolidlLiquid Separation = thickened and

filtered through 7.5 cm, 48 mesh

screen at 1" vacuum

Feed soln = diluted, Cu spiked AMD

NallS added = 70 mgIL

Paper fiber = none

pH = 5.5 with Na2C03

Temp = 22 C., Tune = 7 min

Flocculant = 0.5 mg "PERCOL 351"

Feed soln = diluted, Cu spiked AMD

Feed soln (step 1) 23

NaHS filtrate (step 1) 0.6

Treated soln (step 2) <0.1

% precipitated >99

(total for steps 1 and 2):

Settled rapidly

Filtered OK, clear filtrate

25 32 11

24 31 11

0.9 22 <0.5

96 31 95

Feed soln 23 26 32 15

Treated soln <0.5 0.6 5.0 <0.2

% precipitated >'97 98 84 >'98

The fiber and precipitate settled rapidly and

filtered OK, clear filtrate.

Reagent addition (lb per 1000 gal):

5.5 Na2C03, 0.5 H202, 1.7 paper fiber;

1.7 sand, 0.004 flocculant

H202 to oxidize Mn to Mn02 at pH 8.5

Mn precipitation from simulated AMD by

H202 added = 1.8 mg per mg Mn

Paper fiber = 0.2 gIL as slurry

Sand = 0.2 gIL, -48 mesh

pH = 8.6 with Na2C03

Temp = 22 C., Tune = 12 min

Flocculant = 0.5 mg "PERCOL 351"

SolidlLiquid Separation = thickened and

filtered through 7.5 cm, 48 mesh

screen at 1" vacuum

Feed soln = diluted, Cu spiked AMD Assays min mgIL Mn % Precipitated

contacting with precipitated Mn02

Reaction of xanthated paper fiber with

Feed soln assay (mgIL) = 23 Cn, 26 Zn, 15 Fe,

31 Mn; pH 2.9

Mn02 added = -200 mgIL Mn02 as slurry

Paper fiber = 0.2 gIL

Sand = 0.2 gIL --48 mesh

pH = 8.6 with Na2C03

Temp = 22 C., Tune = 8 min

SolidlLiquid Separation = thickened and

filtered through 7.5 cm, 48 mesh

screen at 1" vacuum

Xanthating - Paper fiber = 5.0 g, H2O = 175 mI,

Feed soln 31

Treated soln 10 23 26

30 21 32

Settled fast, but some fines suspended

Filtered well, clear filtrate

Assays, mgIL Mn Zn Cu Fe

Feed soln 30 24 24 13

Treated soln 28 4.6 <0.1 2.8

Fiber and precipitate = 2.23 g moist

floc (e.g., the flocculated precipitate)

settled OK, light floc tended to flow

Filtered OK

dilutedAMD

'Ih:ated diluted AMD with impregnated

CS2 = 10 g, Ethanol = 6.0 g

Contact: Temp = 23 C., Tune = 18 hr

Diluted AMD = 250 mI AMD + 25 mg Cu to 1000

Paper fiber (xanthated) = 8.2 g, pH rose from

2.8 to 7.1

Temp = 22 C., Tune = 9 min

Flocculant = 0.5 mg "PERCOL 351"

SolidlLiquid Separation = settled, and filtered

Impregnated Peat Mixture: Peat = 7.73 g, Assays, mgIL Mn Zn Cu Fe

DEHP(Ca) - Peat.

Test 1 = beaker contact

Treatment of AMD with paper fiber and

lime

''DEHPA''=

5.08 g, 6.2 acetone, mixed and

evaporated at 35 C.

Weight = 13.0 g

Diluted AMD = 25% AMD + 25 mgIL Cu;

1.ooL

DEPHA - peat mix = 1.33 g

pH = adjusted to 7.0 with 0.3.8 g Na2C03

Temp = 22 C., Tune = 10 & 24 min

SolidlLiquid Separation = added 0.22 g paper

fiber, stirred + 0.5 mg "PERCOL 351"

Feed soln = AMD + 50 mgIL Cu;

1000 mI

Paper fiber = 0.42 g paper as pulp + sand =

0.43 g --48 mesh

pH = maintained at 9.3 with 0.82 g Ca(0H)2

H202= 129 mg

Temp = 22 C., Tune = 10 min

SolidlLiquid Separation = +0.5 mg "PERCOL 351,"

settled and filtered through 7,5 cm

towel filter at 2" Hg vacuum

Feed soln 30 24 24 13

Treated soln, 10 min 27 16 3.5 <0.1

Treated soln, 24 min 26 13 2.6 <0.1

Floc (e.g., the flocculated precipitate)

settled fast

Filtered OK

Settling rate = 15 ftJhr

Thickened slurry (1 hr) = 1.6 wt % solids

Filter rate = 0.8 gpm/sq. ft.

Cake = 8.56 g moist, 1.62 g dry, 19% solids

lest Objective

'Ireatment ofAMD with paper fiber and

limestone and Na2C03

'Ireatment of diluted AMD with Portland

cement without paper filter

'l\"eatment of diluted AMD with Portland

cement plus paper fiber

Precipitating of Cu, Zn, Mn, Fe from

diluted AMD with Na2C03 plus paper

fiber - effect on thickening and

filtration

Precipitating of Cu, Zn, Mn, Fe from

diluted AMD with Na2C03 without paper

fiber - determine precipitate

filterability

Precipitating of Cll, Zn, Mn, Fe from

diluted AMD with Na2C03 without paper

fiber to determine how much sludge is

formed

"Blank" Test with paper fiber and

demineralized water

5,660,735

TABLE 3-continued

Probipg Tests with Paper Fiber

Test Conditions

Feed soln = AMD + 50 mgIL Cu;

1000 mI

Paper fiber = 0.23 g paper as pulp + limestone =

0.43 g powder

pH = maintained at 9.0 with 2.25 g Na2C03

H202 = 130 mg

Temp = 22 C., Tune = 8 min

Solicl!Liquid Separation = +0.5 mg "PERCOL 351,"

settled and filtered through 7.5 cm

towel filter at 2" Hg vacuum

Feed soln = 250 mI AMD + 50 mg Cu

diluted to 1000 mi.

Paper fiber = none

Portland cement = 0.71 g to pH 8.9

m02= 30mg

pH = maintained at 9.1 with 0.8 mg Ca(OH)2

Temp = 23 C., Tune = 10 min

Solicl!Liquid Separation = added 0.5 mg "PERCOL

351" to flocculated solids, settled,

decanted, and filtered through 7.5 cm

paper fiber filter at I" Hg vacuum

Feed soln = 250 mI AMD + 50 mg Cu

diluted to 1000 mi.

Paper fiber = 0.2 g

Portland cement = 0.55 g to pH 5.6

m02= 30mg

pH = maintained at 9.1 with 74 mg Ca(OH)2

Temp = 23 C., Tune = 10 min

Solicl!Liquid Separation = added 0.5 mg "PERCOL

351" to flocculated solids, settled,

decanted, and filtered through 7.5 cm

paper fiber filter at I" Hg vacuum,

pressed moist cake, dried at 85 C., and

iguited at 700 C.

Feed soln = 250 mI AMD + 50 mg Cu

diluted to 1000 mi.

Paper fiber = 0.2 g

m02 = 30mg

pH = maintained to 9.1 with 0.73 g Na2C03

Temp = 23 C., Tune = 10 min

Solicl!Liquid Separation = 0.5 mg "PERCOL

351" to flocculated solids, settled,

decanted, and filtered through 7.5 cm

paper fiber filter at I" Hg vacuum,

pressed moist cake, dried at 85 C., and

iguited at 700 C.

Feed soln = 250 mI AMD + 50 mg Cu

diluted to 1000 mi.

Paper fiber = none

H202=30 mg

pH = maintained to 9.1 with 0.73 g Na2C03

Temp = 23 C., Tune = 10 min

Solicl!Liquid Separation = added 0.5 mg "PERCOL

351" to flocculated solids, settled,

decanted, and filtered through 7.5 cm

paper fiber filter at I" Hg vacuum

Feed soln = 250 mI AMD + 50 mg Cu

diluted to 1000 m!.

Paper fiber = none

m02 = 30mg

pH = maintained to 9.1 with 0.73 g Na2C03

Temp = 23 C., Tune = 10 min

Solicl!Liquid Separation = added 0.5 mg "PERCOL

351" to flocculated solids, settled,

decanted, and centrifuged solids at

1000 rpm for 5 min

Feed soln = demineralized water only, 1000 mi.

Paper fiber = 0.3 g

H202 = IOmg

pH = maintained to 9.1 with Na2C03

Temp = 23 C., Tune = 10 min

Solicl!Liquid Separation = added 0.5 mg "PERCOL

Results

Settling rate = 7.5 ftJhr FINES SUSPENDED

Thickened slurry (1 hr) = 1.3 wt % solids

Filter rate = 0.1 gpmlsq. ft.

Cake = 6.28 g moist, 1.32 g dry, 21% solids

Settling rate = 0.17 ftlmin

Thickened slurry = 50 ml in 10 min

some fines in suspension

Filtration = fines passed through filter

Settling rate = 2 ftlmin

Thickened slurry = 50 ml in 10 min

clear supernatant solution

Filtering = 50 ml/8 sec (2.8 gpmlsq. ft.)

Precipitate and fiber (pressed):

thickness = 0.1 mm

moist wt = 2.58 g

dry wt = 0.77 g, (29.8% solids)

iguited wt =0.53 g

Settling rate = 0.7 ftlmin

Thickened slurry = 50 ml in 10 min

clear supernatant solution

Filtration =65 ml/20 sec (Ll gpmlsq. ft.)

Precipitate and fiber (pressed):

thickness = 0.1 mm

vol-D.7 cc

moist wt = 1.83 g

dry wt = 0.40 g, (21.9% solids)

iguited wt = 0.18 g

Settling rate = 0.2 ftlmin

Thickened slurry = 55 ml in 10 min

supernatant solution contained

suspended fibers

Filtration = fines passed through filter

Settling rate = 0.3 ftlmin

Thickened slurry = 40 ml in 10 min

supernatant solution coutained

suspended fibers

Centrifuged sludge volume = 9 cc

Paper fiber did NOT flocculate

Pressed fiber,

moist wt = 0.90 g

dried wt = 0.25 g

iguited wt = <0.002 g

5,660,735

17 18

TABLE 3-continued

Probing Tests with Paper Fiber

Test Objective Test Conditions Results

Precipitate CN from cyanide solution as

351" and filtered through paper fiber.

Pressed fiber, dried at 85 C., and

ignited at 600-700 C.

Feed scln = 0.5 gIL NaCN Assays (mgfL) CN, total

ferric ferrocyanide using paper fiber

as a filter aid

To 1000 m1 scln was added 0.1 g Na2S205, H2S04 Feed scln -260

to pH 5, added 0.3 g FeS04, and adjusted to pH Treated soln 36

8 with NaOH Flocculated and settled rapidly

Filtered well

Comment: colorless (n'": blue) filtrate was

obtained

11. The method, as claimed in claim 1, wherein said

removing step comprises separating said product from said

20 feed solution by a density separation method.

12. The method, as claimed in claim 1, wherein said feed

solution comprises water and said recovered product has a

water content less than about 90% by weight.

13. The method, as claimed in claim 1 wherein said

25 dewatered recovered product has a water content less than

about 30% by weight.

14. The method, as claimed in claim 1, wherein said

discrete fibers comprise a component selected from the

group consisting of cellulose, glass, plastic, cotton or wool.

30 15. The method, as claimed in claim 1, wherein said

discrete fibers are substantially composed of cellulose.

16. The method, as claimed in claim 15 further comprising:

contacting said feed solution with a flocculant after said

dispersing step.

17. The method, as claimed in claim 16 wherein said

flocculant is a polyacrylamide.

18. A method to remove a metal from an aqueous feed

solution, comprising:

40 continuously precipitating said metal from said feed solution

to form a precipitate selected from the group

consisting of hydroxides, peroxides, silicates, sulfides,

xanthates, phosphates, carbonates, cellulosederivatives

and mixtures thereof wherein said metal is

selected tom the group consisting of aluminum, arsenic,

beryllium, boron, cadmium, chromium, fluorine,

nickel, selenium, vanadium, lithium, molybdenum,

barium, lead, mercury, silver, copper, zinc, and compounds

thereof and mixtures thereof wherein the feed

solution has a rate of flow of more than about 100

gallons/minute;

(b) coutinuously mixing discrete cellulosic fibers in said

feed solution to form a product comprising a cellulosic

fiber and said precipitate; and

55 (c) continuously filtering said product from said feed

solution to form a recovered product and a treated

solution.

19. The method as claimed in claim 18 wherein said feed

solution is substantially free of solids before the precipitat60

ing step.

20. The method, as claimed in claim 18 wherein the

concentration of said discrete cellulosic fibers in said feed

solution is from about 10 to about 1,000 mgll.

21. The method, as claimed in claim 18 further compris65

ing compacting said recovered product.

22. A method for concentrating metals in a feed solution

comprising:

While various embodiments of the present invention have

been described in detail, it is apparent that modifications and

adaptations of those embodiments will occur to those skilled

in the art. However, it is to be expressly understood that such

modifications and adaptations are within the scope of the

present invention, as set forth in the following claims.

What is claimed is:

1. A method for remediation of aqueous feed solutions

containing a metal, comprising:

(a) precipitating the metal from a feed solution to form a

precipitate wherein said metal is selected from the

group consisting of aluminum, arsenic, beryllium,

boron, cadmium, chromium, fluorine, nickel, selenium,

vanadium, lithium, molybdenum, barium, lead,

mercury, silver, copper, zinc, compounds thereof and

mixtures thereof;

(b) dispersing discrete fibers in said feed solution to form

a product comprising a fiber and said precipitate;

35 (c) removing said product from said feed solution to form

a treated solution and a recovered product containing

the metal precipitate and discrete fibers; and

(d) separating the metal precipitate from the discrete

fibers in the product to recover the metal.

2. The method, as claimed in claim 1, wherein said feed

solution comprises a stream that has a rate of flow greater

than about 10 gallons/minute.

3. The method, as claimed in claim 1, wherein said metal

has a concentration in said feed solution of less than about

50 mgll.

4. The method, as claimed in claim 1, wherein said treated

solution has a concentration of said metal that is less than

about 1.0 mgll.

5. The method, as claimed in claim 1, wherein said

precipitate is selected from the group consisting of 50

hydroxides, silicates, sulfides, xanthates, phosphates,

carbonates, cellulose-derivatives and mixtures thereof.

6. The method, as claimed in claim 1 wherein a precipitant

is attached to the discrete fibers to precipitate said metal.

7. The method, as claimed in claim 1 wherein said

precipitant is selected from the group consisting of

hydroxides, silicates, sulfides, xanthates, phosphates,

carbonates, hydroxyethyl cellulose and mixtures thereof.

8. The method, as claimed in claim 1, wherein said

removing step comprises filtering said feed solution to form

said recovered product.

9. The method, as claimed in claim 8 wherein said

removing step comprises thickening said feed solution

before said filtering step.

10. The method, as claimed in claim 8 wherein the pore

size of the filter in said filtering step is sufficient to retain

substantially all of said discrete fibers.

5,660,735

(a) continuously precipitating said metals from said feed

solution to form a precipitate, the feed solution having

a rate of flow greater than about 100 gallons/minute;

(b) continuously dispersing discrete fibers in said feed

solution to form a product comprising a fiber and said 5

precipitate;

(d) thickening the feed solution to form a thickened feed

solution;

(e) continuously filtering the thickened feed solution to

form a recovered product and a treated solution;

(f) dewatering the recovered product to form a dewatered

product;

(g) combusting the dewatered product to form a waste gas 15

containing the metal;

(h) scrubbing the waste gas with a scrubbing solution to

solubilize the metal therein; and

(i) removing the metal from the scrubbing solution. 20

23. The method, as claimed in claim 2, wherein the feed

solution is substantially free of solids before the precipitating

step.

24. The method, as claimed in claim 2, wherein said rate

of flow is greater than about 500 gallons/minute. 25

25. The method, as claimed in claim 1, wherein at lest

about 95% of the precipitate forms a product with the

discrete fibers.

26. The method, as claimed in claim 1. wherein the

concentration of the discrete fibers in the feed solution is 30

from about 100 to about 500 mg/L.

27. The method. as claimed in claim 2. wherein the rate

of flow is greater than about 100 gallons/minute.

28. The method, as claimed in claim 1. wherein the

recovered product comprises at least about 75% of the 35

precipitate in the feed solution.

29. The method, as claimed in claim 1, wherein the

recovered product comprises at least about 85% of the

precipitate in the feed solution.

30. The method. as claimed in claim 1, wherein the

recovered product comprises at least about 90% of the metal

precipitate in the feed solution.

31. The method. as claimed in claim 1. wherein at least

about 75% of the precipitate forms a product with the fibers.

32. The method, as claimed in claim 1, wherein the

precipitating step comprises:

contacting the feed solution with a precipitant, wherein

the amount of the precipitant contacted with the feed

solution is at least about 200% of the stoichiometric

amount relative to the amount of the metal to be

removed from the feed solution.

33. The method, as claimed in claim 18, wherein the

mixing step is done in the substantial absence of a flocculent.

34. The method, as claimed in claim 1, wherein the

separating step comprises:

(e) dewatering the product mass to form a dewatered

product having a water content less than about 30% by

weight.

35. The method, as claimed in claim 34, wherein the

separating step comprises:

(f) combusting the dewatered product to form a waste gas.

36. The method, as claimed in claim 35, wherein the

separating step comprises:

(g) scrubbing the waste gas with a scrubbing solution to

form a scrubbing solution comprising the metal; and

(h) recovering the metal from the scrubbing solution.

37. The method, as claimed in claim 18, further comprising

before the continuously filtering step:

(d) thickening the feed solution to form a thickened feed

solution;

(e) dewatering the recovered product to from a dewatered

product;

(f) combusting the dewatered product to form a waste gas

containing the metal; and

(g) recovering the metal from the waste gas.

* * * * *