Polymeric ore agglomeration aids

Low grade gold and silver ores are leached by spraying barren cyanide solution onto a large heap of ore. As the solution percolates through the heap, the precious metal is dissolved out of the ore. The resulting pregnant solution is then collected for further processing. A major problem is segregation of fines in building the heap and migration of fines during percolation which results in channeling and/or blinding. To overcome the problem, the U.S. Bureau of Mines developed a process in which the ore is agglomerated with 5-20 lbs/ton cement binder and about 12% water or barren solution. Liquid is sprayed onto the tumbling ore-cement mixture. This tumbling action causes the coarse ore particles, fine particles, and cement to form balls or agglomerates. After curing for about 72 hours, the cement sets up and binds the agglomerates--thus preventing channeling and migration. Tumbling of the ore is obtained in practice with rotary agglomerators, pug mills, belt transfer points, or ore cascading down the side of the heap.
Even though the above process is beneficial it does not totally solve the problem leading to long leach cycles and/or slow percolation rates. In this invention a high molecular weight water-soluble vinyl addition polymer is inverted and added to the agglomerating liquid. As the data will show, the polymer increases the flow through the column and reduces the tendency of the fines to migrate and reduce the flow. The Bureau of Mines used a high molecular weight polyethyleneoxide (PEO) in a similar manner. However, this PEO does not achieve as high a flow rate and the agglomerates break down more rapidly than the polymers of this invention. A proposed mechanism is that the polymer helps tie up the fines in the agglomerating step enabling the cement, when it is used as a co-agglomerating agent, to better contact and bind the fines.
For a more detailed description of heap leaching and the agglomeration of ore fines with either lime or Portland cement, see "Silver and Gold Recovery from Low-Grade Resources" by G. E. McClelland and S. D. Hill Mining Congress Journal, 1981, pages 17-23.

BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1-8 are a series of SEM pictures showing the interaction of polymer with inorganic agglomerating agents
FIG. 1 is an electron photomicrograph of untreated ore,
FIG. 2 is an electron photomicrograph of ore and Composition 1.sup.1 polymer,
.sup.1 See glossary
FIG. 3 is an electron photomicrograph of ore and cement,
FIG. 4 is an electron photomicrograph of ore, cement and Composition 1,
FIG. 5 is higher magnification of FIG. 3,
FIG. 6 is higher magnification of FIG. 4,
FIG. 7 is an electron photomicrograph of ore and lime, and,
FIG. 8 is an electron photomicrograph of ore, lime and Composition 1.
FIG. 9 is a graph showing the percolation improvement using the practice of the invention.

THE INVENTION
The invention comprises an improved process for heap leaching gold and silver ores of the type wherein the ore fines are agglomerated with an agglomeration agent, formed into a heap and then leached by percolating through the heap a cyanide solution which extracts the precious metal from the agglomerated ore for subsequent recovery, the improvement which comprises using as the agglomerating agent a water-soluble vinyl polymer having a molecular weight of at least 500,000.
THE HIGH MOLECULAR WEIGHT WATER-SOLUBLE VINYL ADDITION POLYMERS
General:
The water-soluble vinyl addition polymers are illustrated by acrylamide polymers which include polyacrylamide and its water-soluble copolymeric derivatives such as, for instance, acrylic acid, methacrylic acid, itaconic acid, acrylonitrile, and styrene. Other monomers with which acrylamide may be copolymerized include those which are cationic such as dimethyl amino ethyl methacrylate and its water-soluble quaternary salts, as well as anionic materials such as, for instance, sulfonate-containing vinyl monomers and carboxyl-containing monomers. These copolymers will generally contain from 5-95% by weight of acrylamide and will be water soluble.
Cationics:
Polymers of this type include polymers of acrylamide and dimethyl amino ethyl methacrylate and its water-soluble quaternary derivatives, polydimethyl amino ethyl methacrylate and its water-soluble quaternary derivatives and polymers and copolymers of diallyl dimethyl ammonium chloride (DADMAC) such as that described in U.S. Pat. No. 3,288,770 and further described in water-in-oil emulsion form in U.S. Pat. No. 3,920,599, the disclosures of which are incorporated herein by reference. These polymers are advantageously employed as copolymers of acrylamide. Another group of cationic polymers are the DADMAC polymers.
DADMAC:
The polymers or copolymers utilized in the water-in-oil emulsions of this invention are cationically charged polymers or copolymers of allyl amines. A preferred example of a material of this type is diallyl dimethyl ammonium chloride such as that described in U.S. Pat. No. 3,288,770 which is further described in water-in-oil emulsion form in U.S. Pat. No. 3,920,599. Also useful are polydiallyl dimethyl ammonium fluoride and bromide.
Anionics:
The anionic polymers and copolymers are anionically charged and water soluble. Examples of materials of this type include polymers of acrylic and methacrylic acid and copolymers of acrylic and methacrylic acid with other non-ionic or anionic water-soluble monomers such as acrylamide or sulfomethylated polyacrylamide. This latter type of polymers are described in European Patent Application No. 0225 596 and U.S. Pat. No. 4,703,092, the disclosures of which are incorporated herein by reference.
A preferred class of anionic polymers are the acrylamide copolymers containing sulfonate groups. Illustrative of such polymers are those described in Hoke, U.S. Pat. No. 3,692,673, European Patent Application No. 0225 596, U.S. Pat. No. 4,703,092, and U.S. Pat. No. 4,704,209, the disclosures of which are incorporated herein by reference.
These sulfonated acrylamide terpolymers contain in their structure, in addition to acrylamide:
(A) at least 1 mole % of acrylic acid; and
(B) at least 1 mole % of an alkyl/aryl sulfonate substituted acrylamide.
In a preferred embodiment (A) is present in the copolymer in amounts ranging between 1-95 mole % with a preferred range being 5-70 mole %. (B) is present in the copolymer in amounts ranging between 1-50 and most preferably 5-30 mole %.
The alkyl/aryl group of the alkyl/aryl sulfonate substituted acrylamide contains between 1-10 carbon atoms with a preferred embodiment being an alkyl group of from 1-6 carbon atoms. Most preferably, the sulfonate is substituted on an alkyl group, which can be linear or branched, and contains from 1-6 carbon atoms, preferably 1-4 carbon atoms.
As indicated, the molecular weight of the polymers used in the invention should have a molecular weight of at least 500,000. Preferably, the molecular weight is at least 1 million and most preferably is at least 5 million or more. These molecular weights are weight average molecular weights.
The most preferred polymers used in the invention are the acrylamide polymers described above and most preferably are anionic acrylamide polymers which contain sulfonate groups. As previously mentioned, one preferred class are the acrylamide polymers which have been reacted with 2-AMPS.sup.1. The polymers of this type contain preferably between 5% up to about 50% by weight of the AMPS groups.
.sup.1 2-AMPS is a trademark of Lubrizol Corporation: 2-acrylamido, 2-methyl propane sulfonic acid.
It should be pointed out tht the anionically charged or modified polymers and copolymers which are utilized in this invention need only to be slightly anionically charged and must be water soluble. It will be seen by those skilled in the art that many permutations and combinations of water-soluble vinyl addition polymers can be employed.
METHOD OF PREPARING THE SULFONATED ACRYLAMIDE-CONTAINING TERPOLYMERS
The terpolymers are prepared by the transamidation reaction of an acrylamide homopolymer or an acrylamide copolymer which contains at least 1 mole % of acrylic acid with an amino alkyl sulfonate. The alkyl group of the amino alkyl sulfonate contains 1-6 and preferably 1-4 carbon atoms. Examples of the preferred starting amino alkyl sulfonates are amino methyl sulfonic acid or amino ethyl sulfonic acid, (taurine). The acrylamide polymer or copolymer is reacted with the amino alkyl sulfonate under following reaction conditions:
I. a reaction temperature of at least 100.degree. C., and preferably at least 110.degree. C.;
II. a reaction time of at least 1/4 hour and preferably at least 1/2 hour;
III. a mole ratio of chemical reactant to polymer ranging between about 2:1 to about 1:50;
IV. a pressure ranging from atmospheric pressure to 35 times atmospheric pressure, or more; thereby achieving the synthesis of the sulfonate polymers described above.
V. in a compatible solvent or solvent admixture for the reactants, preferably, water, or aqueous solvents containing water miscible cosolvents, such as for example, tetrahydrofuran, polyethylene glycols, glycol, and the like.
If the starting polymer is a homopolymer of acrylamide such that no other pendant functional group is present, the condition of the reaction is such that some degree of amide hydrolysis occurs in those reactions in which water or a water containing solvent is utilized. In such cases, a carboxylate functional group is also obtained in addition to the sulfonate modified amide and any unreacted starting amide groups from the starting polymer.
When the alkyl group of the alkyl sulfonate substituted acrylamide present in the terpolymer is a methyl group, a preferred method of preparing such polymers resides in the reaction of the acrylamide polymer or acrylamide acrylic acid copolymer with formaldehyde and a bisulfite. Specifically, these polymers are prepared from acrylamide-containing polymers with sodium formaldehyde bisulfite (or formaldehyde and sodium bisulfite) in from about 1/4 to about 8 hours at temperatures of at least about 100.degree. C. and at a pH of less than 12, preferably at temperatures higher than 110.degree. C. and at a pH of 3 to 8. Under these reaction conditions, sulfomethylamide readily forms in high conversion, based on the sodium formaldehyde bisulfite charged. Sulfite salts may be substituted for the bisulfite salts in this reaction.
WATER-IN-OIL EMULSIONS OF THE WATER-SOLUBLE VINYL ADDITION POLYMERS
It is known that acrylamide and acrylamide acrylic acid polymers as well as other water-soluble vinyl monomers may be polymerized using a so-called inverse emulsion polymerization technique. The finished product of such a polymerization process is a water-in-oil emulsion which contains the water-soluble polymer present in the aqueous phase of the emulsion. When a water-soluble surfactant is added to these emulsions, they dissolve rapidly in water and provide a convenient method for preparing aqueous solutions of these polymers.
The preparation of these emulsions is discussed in Vanderhoff, U.S. Pat. No. 3,284,393. The addition thereto of a water-soluble surfactant to permit rapid dissolution of the polymer into water is described in Reissue Pat. No. 28,474, the disclosures of which are incorporated herein by reference.
The transamidation and sulfomethylation reactions described above may be performed on the water-in-oil emulsions of the acrylamide or acrylamide-acrylic acid copolymers to provide the acrylamide terpolymers used in the invention.
Methacrylamide and methacrylic acid may be substituted for acrylamide or methacrylamide acid used in the preparation of the polymers described herein. Similarly, the acrylic acid and the starting sulfonates may be either prepared or used in the form of the free acids or as their water-soluble salts, e.g. sodium, potassium or ammonium and such forms are considered to be equivalents.
The preferred method of preparing any of the polymers of the present invention resides in the utilization of the water-in-oil emulsion polymerization technique described above.
Also, as indicated in Pat. Reissue No. 28,474, when such emulsions are added to water in the presence of a water-soluble surfactant, rapid solubilization of the polymer contained in the emulsion occurs. This represents a convenient and preferred method of preparing solutions of the polymers used as agglomerating aids.
THE USE OF THE WATER-SOLUBLE VINYL ADDITION PRODUCTS AS AGGLOMERATING AGENTS
The polymers may be used alone to agglomerate the ore fines or they may be used in conjunction with known inorganic agglomerating agents such as lime, Portland cement or clays. When the polymers are used alone, a typcial dosage range is with the weight percentage range of 0.05 to 0.5 pounds per ton based on the weight of the ores treated.
When the polymers are used in conjunction with an alternative inorganic agglomerating agent such as cement, the inorganic is added in the range of 5 to 20 pounds per ton of ore and the polymer is in the range of 0.05 to 0.5 pounds per ton of ore.
Dosage cannot be set forth with any degree of precision since it depends upon the polymer and the particular ore treated.
EVALUATION OF THE INVENTION
The invention was evaluated using a variety of aggregating agents which are set forth below in the Glossary.
______________________________________GlossaryCom-positionNo.______________________________________1 NaAMPS-acrylamide 12/88.sup.1 MW - 5-10,000,0002 polyethylene oxide - MW 1,000,0003 latex polyacrylamide - MW 5 MM4 latex polyacrylamide - MW 10 MM5 latex acrylamide/Na acrylate, 92/8 - MW 15 MM6 latex acrylamide/Na acrylate, 65/35 - MW 3-4 MM7 latex acrylamide/Na acrylate, 65/35 - MW 10-12 MM8 latex acrylamide/Na acrylate, 65/35 - MW 20 MM9 dry acrylamide/Na acrylate, 65/35 - MW 10-12 MM10 latex acrylamide/Na AMPS, 88/12 - MW 8-10 MM11 latex acrylamide/Na AMPS, 82/18 - MW 8-10 MM12 latex acrylamide/Na AMPS, 50/50 - MW 8-10 MM13 cross linked TX-429914 latex Na AMPS/acrylamide/Na acrylate, 10/10/8015 latex SO.sub.3 /CO.sub.2 /NH.sub.2, 9.5/28.0/62.516 latex SO.sub.3 /CO.sub.2 /NH.sub.2, 10/42/4817 latex DMAEM Quat/acrylamide MW 500,000______________________________________ .sup.1 Mole ratio: Sodium acrylamido, 2methyl propane sulfonic acid/acrylamide = 12/88
The test method was as follows:
Procedure
1. Screen ore to -4 mesh.
2. Mix ore and cement on a rotating disc for five minutes.
3. Spray water on the cascading mixture to form the agglomerates.
4. The composition to be tested is added to the spray water to get good mixing throughout the ore.
5. 1000 g of agglomerates are added to 21/2" diameter percolation column.
6. Water is added at the top of the column to give an overflow and constant head.
7. Flow rate through the column is measured over time at the bottom exit tube.
The above test method was utilized to screen the additives of the invention as gold ore aggregating agents either alone or with cement. The results are set forth below in Tables I to VI and FIGS. 1 to 9.
The results presented in Table VII are a pilot plant run using the following procedure:
1. -1/4" ore.
2. Mix ore and cement in a small cement mixer.
3. Spray water on the cascading mixture to form the agglomerates.
4. The composition to be tested is added to the spray water to get good mixing throughout the ore.
5. Agglomerates are added to 4" diameter leach column.
6. Sodium cyanide solution is pumped to the bottom of the column, flows up through the ore and out exit tube at the top of the column.
TABLE I__________________________________________________________________________AGGLOMERATION TESTS ON GOLD ORE IFLOW RATE (GPH/FT.sup.2 Cement (20 lbs/ton) Cement (20 lbs/ton) Cement (20 lbs/ton)Time Cement Comp. 2 Comp. 7 Comp. 17(hr) Blank 20 lbs/ton (0.1 lb/ton) (0.5 lb/ton) (0.5 lb/ton)__________________________________________________________________________0 0 133 193 226 1261 0 53 70 163 722 0 32 44 149 513 0.32 32 63 -- --4 -- 27 42 135 355 0.29 26 37 -- --6 -- 22 36 128 --7 0.29 21 32 -- --8 -- 19 30 133 --1 day 0.29 -- -- 110 --3 days -- 3.6 4.3 -- 3.24 days 7.27 days 4.0__________________________________________________________________________
TABLE II__________________________________________________________________________PERCOLATION TESTS ON GOLD ORE ICEMENT (20 LBS/TON)FLOW GPH/FT.sup.2Time No. Comp. 10 Comp. 10 Comp. 10 Comp. 10 (0.5 lb/ton) Comp. 13 Comp. 14 (0.5 lb/ton)(hr) Polymer (0.12 lb/ton) (0.25 lb/ton) (0.5 lb/ton) No cement (0.5 lb/ton) No cement__________________________________________________________________________0 149 212 209 265 237 91 2090.5 hr 107 170 205 264 182 63 1771 91 142 172 261 151 48 1442 77 116 154 252 93 31 1003 70 112 151 237 65 24 775 58 105 149 196 42 16 467 53 -- 142 186 32 18 461 day 28 72 112 193 14 14 322 -- -- 74 -- 7.2 10 --3 12 37 46 172 6.9 4.3 --4 11 28 -- 175 10.85 8.3 20 16 1756 13 11 1657 9.4 1548 4.7 --9 --10 3011 1912 1313 8.714 6.515 --16 --17 3.6__________________________________________________________________________
TABLE III______________________________________PERCOLATION TESTS ON GOLD ORE ICEMENT = 20 LBS/TONSOLUTION pH TO 11.5 WITH CaOFLOW RATE (GPH/FT.sup.2) Comp. 4 Comp. 5 Comp. 10 Comp. 14 (0.5 (0.5 (0.5 (0.5Time lb/ton) lb/ton) lb/ton) lb/ton) (No polymer)______________________________________0 209 363 233 223 1493 hr 142 270 182 165 707 hr 116 252 177 151 531 day 86 193 175 130 282 58 137 172 116 --3 -- -- -- -- 124 -- -- -- -- 115 32 65 130 68 8.36 26 58 128 647 23 46 116 538 20 37 109 409 19 28 93 3910 -- -- -- --11 -- -- -- --12 -- -- -- --13 11 15 30 1414 5.0 5.0 19 8.315 2.3 13 5.416 1717 --18 --19 9.720 1121 7.922 1523 524 --25 4.7______________________________________
TABLE IV__________________________________________________________________________PERCOLATION TESTS ON GOLD ORE IIFLOW RATE (GPH/FT.sup.2) Cement Cement Cement Cement Cement Cement (20 lb/ton) (20 lb/ton) (20 lb/ton) (20 lb/ton) (20 lb/ton) (20 lb/ton) Cement Comp. 10 Comp. 11 Comp. 12 Comp. 6 Comp. 7 Comp. 8 Comp. 10Time Blank (20 lb/ton) (0.5 lb/ton) (0.5 lb/ton) (0.5 lb/ton) (0.5 lb/ton) (0.5 lb/ton) (0.5 lb/ton) (0.5 lb/ton)__________________________________________________________________________0 217 252 522 559 503 242 559 568 2523 hr 114 242 428 -- -- -- -- -- 1677 hr 30 198 398 -- -- -- -- -- 1281 day 17 179 377 373 413 163 326 302 682 3.6 -- -- 382 379 149 307 298 353 -- -- -- 345 358 133 265 271 284 -- 163 302 349 335 114 242 247 --5 .94 158 298 340 312 107 234 236 196 1.6 135 289 -- -- -- -- -- 177 137 215 -- -- -- -- -- 198 133 228 261 261 79 170 191 169 -- -- 247 237 77 161 161 1310 135 149 252 228 77 154 167 1311 133 161 --12 130 165 --13 126 136 9.414 105 13315 105 11916 -- --17 -- --18 74 681920__________________________________________________________________________
TABLE V__________________________________________________________________________PERCOLATION TESTS ON GOLD ORE IIIFLOW RATE (GPH/FT.sup.2) Cement (10 lb/ton) plus No Water Cement Comp. 7 Comp. 9 Comp. 15 Comp. 16 Comp. 10Time Agglomeration Agglomeration 10 lb/ton 0.4 lb/ton 0.18 lb/ton .5 lb/ton 0.5 lb/ton 0.5 lb/ton__________________________________________________________________________0 -- -- -- 466 205 77 552 2800.5 hr -- -- -- 130 51 -- 67 731 hr 0.62 0.47 2.8 99 37 18 56 5118 hr 0.093 0.14 1.4 28 20 4.2 20 161 day -- -- 1.2 23 14 2.8 18 172 days 0.093 0.093 0.82 19 12 2.3 19 125 days 0.058 0.058 0.93 5.1 3.3 3.7 7.5 3.36 days 0.186 0.056 0.77 2.8 1.9 16.3 4.2 1.97 days 0.12 0.056 0.56 3.7 2.8 8.4 4.2 3.58 days 0.43 1.4 1.9 7.5 1.6 1.49 days 0.43 1.9 1.4 2.6 2.3 1.412 days 0.47 1.0 1.8 0.84 2.2 0.8413 days 0.58 0.7 1.0 0.70 1.9 1.214 days 0.42 1.0 1.0 1.2 1.9 0.93__________________________________________________________________________
TABLE VI______________________________________Percolation Tests on Gold Ore IIICement (10 lb/ton) Flow Rate GPH/FT.sup.2 Comp. 4 Comp. 3Time (0.5 lb/ton) (0.5 lb/ton)______________________________________0 380 4641 hr. 224 4032 hr. 212 2351 day 39 202 day 30 176 day 17 107 day 17 3.7______________________________________
TABLE VII______________________________________Pilot Column Leach Tests on aCommerical Ore (0.05 oz/ton Au) Mineral Recovery (%)______________________________________Cement (lb/ton 15 1Comp. 10 (lb/ton) -- 0.25Based on head assayAu 59.7 70.5Ag 9.5 10.0Based on calculated headAu 62.1 72.1Ag. 12.0 13.8______________________________________
The invention may be practiced with an inverse flow, that is, a downflow (Tables VIII-X) rather than an upflow of leaching solution. Silver as well as gold may be leached either way.
Additional data show improved recovery as the amount of agglomerating agent of the present invention (e.g. Comp. 1 in water) per ton of ore is increased, compared to the blank; an increase in yield compared to the blank may also be achieved with less volume of cyanide solution if the concentration of cyanide is increased. Percents are weight of course.
Test Procedure: Downflow
1. Screen ore to -1/2".
2. Mix ore and cement in a small cement mixer.
3. Spray NaCN solution onto the cascading mixture to form the agglomerates.
4. The composition to be tested is added to the spray water to get good mixing throughout the ore.
5. Agglomerates are added to 6" diameter leach column.
6. Sodium cyanide solution is pumped to the top of the column and allowed to percolate down through the ore.
7. Pregnant solution is collected from an exit tube at the bottom of the column and analyzed for mineral values.
TABLE VIII__________________________________________________________________________PILOT COLUMN LEACH TESTS ON COMMERCIAL ORE A0.005 gpm/FT.sup.2 Flow Rate10 lb/ton Cement Agglomerating Liquid:Agglomerating Liquid: 12% of 0.1% NaCN 6% of 0.2% NaCN Blank 0.25 lb/ton Comp 1 0.5 lb/ton Comp 1 0.25 lb/ton Comp 1 Au Au Au AuDay Recovery (%) Recovery (%) Recovery (%) Recovery (%)__________________________________________________________________________1 43.0 52.9 53.3 45.02 47.3 62.0 67.2 55.83 48.0 63.9 68.5 57.44 50.9 67.4 70.8 59.8__________________________________________________________________________
TABLE IX______________________________________PILOT COLUMN LEACH TESTSON COMMERCIAL ORE B12.3% Agglomerating Liquid0.005 GPM/ft.sup.2 Flow Rate Composition 1 0.25 lb/tonCement 12 lb/ton Cement 5 lb/tonRecovery (%) Recovery (%)Day Au Ag Au Ag______________________________________1 25.4 11.3 32.0 19.72 58.3 15.5 69.4 24.53 61.8 18.1 71.8 27.34 67.0 21.8 74.8 30.95 24.3 33.1______________________________________
TABLE X______________________________________PILOT COLUMN LEACH TESTSON COMMERClAL ORE B8.8% Agglomerating Liquid0.015 GPM/ft.sup.2 Flow Rate Composition 1 0.25 lb/tonCement 12 lb/ton Cement 5 lb/tonWt. sol. Recovery (%) Wt. sol. Recovery (%)Day Wt. ore Au Ag Wt. ore Au Ag______________________________________ 0.19 38.0 11.8 0.17 52.6 20.2 0.34 45.9 16.6 0.31 60.6 24.61 0.65 52.6 20.8 0.58 65.7 28.1 0.88 22.3 0.80 29.62 1.36 24.9 1.23 31.9 1.58 25.8 1.42 32.83 1.91 27.0 1.75 34.1 2.06 27.8 1.88 34.9______________________________________

Number	Name	Date
RE28474	Anderson et al.	Jul 1974
3284393	Vanderhoff et al.	Nov 1966
3288770	Butler	Nov 1966
3692673	Hoke	Sep 1972
3920599	Hurlock et al.	Nov 1975
4256705	Heinen et al.	Mar 1981
4256706	Heinen et al.	Mar 1981
4703092	Fong	Oct 1987
4704209	Richardson et al.	Nov 1987

Polymeric ore agglomeration aids

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INTRODUCTION

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