CA1319452C - Recovery of gold using diisobutyl and disec. butyl monothiophosphinates - Google Patents

Abstract

30,033 TITLE OF THE INVENTION
IMPROVED RECOVERY OF GOLD USING DIISOBUTYL
AND DISEC. BUTYL MONOTHIOPHOSPHINIC
ACIDS AND THEIR SALTS
ABSTRACT OF THE DISCLOSURE
Diisobutyl and disec. butyl monothiophosphinic acids and their salts are used, in conjunction with sodium mercaptobenzothiazole, as collectors for the recovery of gold from gold-bearing minerals.

Description

BACKGROUND O~ T~iE INVENTION
30'033 The present invention relates to a froth flotation process for the recovery of gold from gold-bearin~ min-erals. More particularly, it relates to new and novel collectors comprising mixtures o~ diisobutyl or disec.
butyl monothiophosphinic acids or their salts and sodium mercaptobenzothiazole.
Froth flotation is one of the most widely used processes for the recovery of values. It is especially used for separating finely ground values from their associated gangue or for separating values from one another. The process is based on the affinity of suitably prepared valuable mineral surfaces for air bubbles. In froth flotation, a froth or a foam is formed by introducing air into a agitated pulp of the finely ground ore and water containing a frothing or a foamingagent. A chief advantage of separation by froth flotation is that it is a relatively efficient operation at a substantially lower cost than many other processes.
Current theory and practice state that the success of the flotation process depends to a great degree on reagents called collectors that impart selective hydro-phobicity to the values which have to be separated. Thus, the flotation separation of one value from another depends upon the relative wettability of these value surfaces by water. Typically, the surface free energy is purportedly lowered by the adsorption of heteropolar collectors. The hydrophobic coating thus provided, acts, in this explana-tion, as a bridge so that the values may be attached to an air bubble. The practice of this invention is not, however, limited by this or other theories of flotation.
In addition to the collector, several other re-agents are usually necessary. Among these are the frothing agents used to provide a stable flotation froth, persistent enough to facilitate value separation, but not so per-sistent that it cannot be broken down to allow subsequent processing. The most commonly used frothing agents include creosote, cresylic acid and alcohols such as 4-methyl-2-pentanol, polypropylene glycols and ethers, etc.
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Moreover, certain other important reagents, sueh as modi~iers, are also largely responsible for the success of flotation separation of values. Modifiers include all reagents whose principal function is neither collecting nor frothing, bu~ one ofmodifying the surface of the values so that a collector either adsorbs to it or does not.
~odifying agents may thus be considered as depressants, activators, pH regulators, dispersants, deactivators, etc.
Often, a modifier may perform several functions simultan-eously. Current theory and practice of flotation again state that the effectiveness of all classes of flotation agents, depends to a large extent on the degree of alka-linity or acidity of the ore pulp. As a result, modifiers that regulate the pH are of great importance. The most commonly used pH regulators are lime, soda ash and, to a - lesser extent, caustic soda and sulfuric acid or mineral acids.
Alkyl and aralkyl dithiosphosphoric salts have been used as collectors for many years. However, organo-phosphorus compounds wherein there is a direct bond between the phosphorus and carbon thereof, have not been as widely used. In U.S. 3,355,017, for example, it is disclosed that diisobutyldithiophosphinate may be used as the collector to provide superior collector activity, in comparison with the correspondingdithiophosphates. These collectors have, indeed, shown superior collecting properties in a variety of ores. One problem, however, is that they do not perform satisfactorily in acid, neutral or mildly alkaline cir-cuits.
In U.S. 2,919,025, a reagent containing a mixture of mono and dithiophosphates is disclosed to overcome the shortcomings of the dithiophosphate collectors. This re-agent has been successfully used as an acid circuit col-lector, e.g., at pH values of from 3.5 to 6.0, for copper.
The major drawback of this reagent is the difficulty of preparation to yield a consistent product from batch to 1 3 ~ 2 batch. Moreover, the reagent still contains a substantial quantity of the dithio compound which exhibits poor col-lector strength in acid, neutral or mildly alkaline cir-cuits. The efficacy of this reagent is therefore lowered, even though it is still better than a reagent comprising only the corresponding straight dithiophosphate. This re-agent, however, did provide evidence to indicate that diethylmonothiophosphate was superior in collector be-havicr in an acid environment as compared with diethyl dithiophosphate.
In a related system, the collector properties of diisobutyldithiophosphinate are known, although not as well as, those of the dithiophosphates. The collector pro-perties of a corresponding diisobutylmonothiophosphinate are not known in the literature. The Soviet authors, P~M.
- Solozhenkin, et al, in an article entitle, "Flotation Pro-perties of Sulfur-Containing Phosphorus Derivatives," ap-pearing in Dokl. Akad. Nauk Tadzh. SSR 13, No. 4, 26-30 (1970), disclose collector properties for diethylmono-thiophosphinate. These authors also disclose a method for the synthesis of a diethylmonothiophosphinate compound. A
mention is made of diphenylmonothiophosphinic acid, but its collector property has not been studied. These authors compared the flotation collector properties of diethyl-monothiophosphate/phosphinate and diethyl dithiophos-phate/phosphinate. The results of their study indicate that the dithiophosphinate is better than the monothio-phosphinate. The authors state that the increase in the flotability observed upon transition from phosphorous mo-nothio acids to dithio acids is related to the effect of electron donor substituents on an increase in the effective negative charge on the sulfur atoms responsible for the reaction with the metal cation. Their results clearly indicated that the dithiophosphinate was a much better collector than the monothiophosphinate. The article pro-vides no trends or definite theory of the collector pro-~31~2 5 61109-748g perties of these materials and therefore any prediction of their flotation properties on other minerals such as gold, for example, cannot be determined. Applicant in contradis~inction to the work of the Soviet authors, has discovered that for ~old flotations, the monothiophosphinate compounds are far superior to the dithiophosphinates especially in conjunction with sodium mercaptobenzothiazole.
Accordingly, it is an ohjec~ of the present invention to provide a new and improved sulfide collector and flotation process for the beneficiation of gold ores employing froth flotation methods.
SUMMARY OF THE INVENTION
The present invention, in one embodiment, provides a new and improved collector composition for beneficiating gold from gold-bearing minerals, said collector composition comprising 1) ~rom about 5 to 95%, by weight, based on the total weight o~ 1) and 2), of diisobutyl or disec. butyl monothiophosphinic acids or their salts and 2) from about 95~ to 5%, by weight, same basis, of sodium mercaptobenzothiazole.
In particular, the present invention provides a collector composition for the recovery of gold from gold bearing minerals comprising 1) from about 5 to 95~, by weight, based on the total weight of (1) and (2), of a compound having the formula (R)2-P-O X
wherein R is isobutyl or sec. butyl, and ~ is hydrogen, an alkali metal or N(Rl) 4 wherein each Rl is, individually, hydrogen, a Cl-C8 alkyl radical or a C6-C10 aryl radical, and 2) from about IB

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5a 61109-7489 95% to 5%, by weight, same basis, of sodium mercaptobenzothiazole.
Generally, and without lim:Ltation, the new and improved collectors of this invention may be used in amounts of from about 1 to 500 grams/metric ton of minerals (0.002 to 1.0 lb/ton of minerals) and preferably from about 5 to 150 yrams/metric ton of minerals (0.01 to 0.3 lb/ton of minerals~, ~o effectively selectively recover gold values from gold-containing minerals.
The new and improved collectors of this invention may yenerally be employed independently of the pH of the pulp slurries. Again, without limitation, ~hese collectors may be employed at pH values of from about 3.5 to 11.0, and preferably from about 4;0 to 10Ø
In accordance with another embodiment, the present invention provides a new and improved process for bene-1.~

1 3 ~ 2 ficiating gold-containing minerals said process compri-sing: grinding said ore to provide particles of flotation size, slurrying said particles in an aqueous medium, con-ditioning said slurry with effective amounts of a frothing agent and a metal collector, and frothing the desired gold-containing minerals by froth flotation procedures; said collector comprising4) from about 5-100%, by weight, based on the total weight of 4) and 5) of diisobutyl or disec.
butyl monothiophosphinic acids or their salts and 5) from about 95% to 0%, by weight, same basis, of sodium mercap-tobenzothiazole.
The present invention therefore provides a new class of collectors and a new and improved process for froth flotation of gold-containing minerals. The collectors and the process of the present invention unexpectedly provide `~ superior metallurgical recovery in froth flotation separ-ations as compared with conventional sulfide collectors, even at reduced collector dosages, snd are effective under conditions of acid, neutral or mildly alkaline pH.
Other objects and advantages of the present inven-tion will become apparent from the following detailed description and illustrative working examples.

DETAILED DESCRIPTION OF THE INVENTION
In accordance with the present invention, gold values are recovered by froth flotation methods in the presence of a novel collector, said collector comprising a mixture of diisobutyl or disec. butyl monothiophosphinic acids or their salts and sodium mercaptobenzothiazole in the concentrations expressed above.
The diisobutyl and disec. butyl monothiophosphinic acids or their salts used in the present invention may be prepared by several different methods. In one method, a corresponding diisobutyl or disec~ butyl thiophosphoryl chloride is hydrolyzed to provide the monothiophosphinate, in accordance with the following equation:

~ 3 ~ 2 1~ 11 R / ¦ C1 + XOH ~ R ¦ O X + HC1 R R

wherein R is isobutyl or sec. butyl and X+ is hydrogen, an alkali metal such as sodium, potassium, lithium, etc., or N(R1)4 wherein each R1 is, individually, hydrogen, a C1-C8 alkyl radical or a C6-C10 aryl radical-Another method of making the monothiophosphinic acids useful in the present invention is by a Grignard synthesis, such as that described by Solozhenkin e~ al in the ahove cited article, and summarized by the equation:

PC13 + 3ROH ~ (RO)2 PlO)H ;
S _ _ (RO)2 P(I)H + RMgX __~ R2PIOMgX
S
~ R2IOMgX ~ ~ R2P \

Although the above-described methods may be useful for preparing the monothiophosphinic acids and their salts used in the present invention, they are not very practical.
An especially preferred method for making the monothiophosphinic acids and their salts compounds used in the present invention is in accordance with the method taught in U.S.
Patent No. 4,555,368. More particularly, in ~, accordance with this pre~erred method, the corresponding dissobutyl or disec. butyl phosphine is oxidized, in the presence of air or hydrogen peroxide, to form the correspon-ding phosphine oxide, which is thereafter reacted with sulfur in the presence of an alkali or alkaline earth metal hydroxide or ammonium hydroxide or an amine in accordance with the equation:

R/ R R I R (etc) R /1\ OX

R R
wherein R and X are as above defined.
Further details of the reaction conditions used and concentration of reagents employed may be found in said application.
In accordance with the present invention, the above-described diisobutyl and disec. butyl monothiophos-phiphinic acids and their salts are employed as collectors in a new and improved froth flotation process which provides a method for enhanced beneficiation of gold values from gold-bearing minerals.
In accordance with the present invention, the new and improved process for the beneficiation of gold values comprises, firstly, the step of size-reducing the mineral to provide particles of flotation size. As is apparent to those skilled in this art, the particle size to which a mineral must be size-reduced in order to liberate gold values i.e., liberation size, will vary and may depend on several fac-tors, such as, for example, the geometry of the minerals. In any event, as is common in this art, a determination that particles have been size-reduced to liberation size may be made by microscopic examination. Generally, and without limitation, suitable particle size will vary from between about 50 mesh to about 400 mesh sizes. Preferably, the mineral wil] be size-reduced to provide flotation sized - particles of between about +65 mesh and about -200 mesh.

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Size-reduction of the ores may be per~ormed in accordance with any method known to those skilled in this art. For example, the mineral can be crushed to -10 mesh size followed by wet grinding in a steel ball mill to specified mesh size, or autogenous or semi-autogenous grinding or pebble milling may be used. The procedure employed in size-reducing is not critical to the method of this invention, as long as particles of effective flotation size are provided.
Preadjustment of pH is conveniently performed by addition of the modifier to the grind during the size reduction step.
The pH of the pulp slurry may be pre-adjusted to any desired value by the addition of either acid or base, and typically sulfuric acid or lime may be used for this purpose, ~ respectively.
The size-reduced mineral is thereafter slurried in aqueous medium to provide a flotable pulp. The aqueous slurry or pulp of flotation sized particles, typically in a flotation apparatus, is adjusted to provide a pulp slurry which contains from about 10 to 60%, by weight, of pulp solids, preferably 25 to 50%, by weight, and especially preferably from about 30% to about 40%, by weight, of pulp solids.
In accordance with a preferred embodiment of the process of the present invention, the flotation of gold is performed at a pH of less than or equal to 10.0 and pre-ferably less than lO.û. In this preferred process, sulfuric acid is used to bring the pH of the pulp slurry to less than or equal to 10.0, if necessary.
In any event and for whatever reason, the pH of the pulp slurry may be pre-adjusted if desired at this time by any method known to those skilled in the art.

~ ol 3 ~ 2 After the pulp slurry has been prepared, the slurry is conditioned by adding effective amounts of a frothing agent and the collector. By "effective amount" is me~nt any amount of the respective components which provides a desired level of beneficiation of the gold.
More particularly, any known frothing agent may be employed in the process of the present invention. By way of illustration, such frothing agents as straight or branched chain low molecular weight hydrocarbon alcohols, such as C6 to C8 alkanols, 2-ethyl hexanol and 4-methyl-2-pentanol, also known as methyl isobutyl carbinol (MIBC) may be em-ployed, as well as, pine oils, cresylic acid, polyglycol or monoethers of polyglycols and alcohol ethoxylates. Gener-ally, and without limitation, the frothing agent(s) will be added in conventional amounts and amounts of from about 0.01 ~ to about 0.2 pound of frothing agent per ton of mineral treated are suitable.
Thereafter, in accordance with the process of the present invention, the conditioned slurry, containing an effective amount of frothing agent and an effective amount of collector is subjected to a frothing step in accordance with conventional froth flotation methods to collect the gold values in the froth concentrate.
The following examples are set forth for purposes of illustration only and are not to be construed as limitations on the present invention except as set forth in the appended claims. All parts and percentages are by weight unless otherwise specified.
In each of the following Examples, the following general preparation and testing procedures are used:
The ore used is South African consisting princi-pally of silica and silicates with minor amounts of gold, uranium and carbon. The gold value is approximately 0.6.
gram/ton and sulfur is 1.2%. About 1000 g of the previously ground solid is repulped to 50% solids yielding a slurry of size distribution of about 80% -200 mesh (74 microns). The slurry is conditioned for 30 minutes using sodium hydroxide 13~3 L~ 2 -- ], 1 or sul~uric acid to achieve the desired pH. A turbine impeller is used at 300 rpm. The slurry is then transfered to a Denver D12 flotation cell and the volume adjusted to 2650 ml, 32% solids with the slurry level 2 cm below the lip.
Frother, a polyglycol ether type, and the collector(s) are added and conditioned for 1.5 minutes at 1300 rpm. A modi-fier, copper sulphate, is added to all tests and conditioned for 0.5 minutes. Air is introduced at 8 lpm from a com-pressed air cylinder and a first concentrate collected for 0-1.5 minutes and a second concentrate collected for 1.5-10 minutes. The three products are processed using accepted means and analyzed for gold. A mass balance for the products is completed and values for the rate and overall recovery of gold calculated.
TABLE I

-TEST SERIES ~1-COLLECTOR GRAMS/TON GOLD RECOVERY
_ CT%

B 00 37.5 B 4 43.2 B 15 46.0 B 19 49.4 B 23 42.8 B 38 42.9 - 12~ 9L~

-TEST SERIES #2-A 38 34.6 B l9 50.6 C 19 48.2 X* 13 20.5 A l9 Y' l9 40.8 -TEST SERIES #3-Cl% C2% CT%
A 38 30.8 40.4 53.9 B 15 49.8 58.0 67.2 -TEST SERIES #4-C1% CT%
A 38 10.4 16.4 B 4 16.6 22.5 B 8 21.8 32.7 Code for Table 1 A = Sodium Mercaptobenzothiazole B = Ammonium Diisobutyl Monothiophosphinate C = Ammonium Disec. butyl Monothiophosphinate CT% a Concentrate (total) percent Cl% = Concentrate percent after 0 - 1.5 minutes C2% = Concentrate percent after 0 - 10 minutes X = Sodium Diisobutyl Dithiophosphonate Y = Ammonium Diisobutyl Dithiophosphinate -' = Comparative ~ 3 ~

Substitution of the following compounds for those listed as B & C, above, results in substantially indentical achievement of gold recovery.
l. Diisobutyl monothiophosphinic acid.

2. Sodium diisobutylmonothiophosphinate.

3. Trimethylamino disec. butyl monothiophosphinate.

4. Disec. butyl monothiophosphinic acid.

5. Diphenylamino diisobutyl monothiophosphinate.

6. Potassium disec butyl monothiophosphinate.

Claims (6)

1. A collector composition for the recovery of gold from gold bearing minerals comprising 1) from about 5 to 95%, by weight, based on the total weight of (1) and (2), of a compound having the formula (R)2-?-O X
wherein R is isobutyl or sec. butyl, and X is hydrogen, an alkali metal or N(R1)4 wherein each R1 is, individually, hydrogen, a C1-C8 alkyl radical or a C6-C10 aryl radical, and 2) from about 95% to 5%, by weight, same basis, of sodium mercaptobenzothiazole.

2. A collector according to Claim 1 wherein 1) is ammonium diisobutylmonothiophosphinate.

3. A collector composition according to Claim 1 wherein 1) is ammonium disec. butylmonothiophosphinate.

4. A process for the recovery of gold from gold-bearing minerals which comprises:
a) providing an aqueous slurry of finely divided, liberation-sized gold-bearing mineral particles, b) conditioning said pulp slurry with ef-fective amounts of a frothing agent and a collector composition comprising 4) from about

5% to 100%, by weight, based on the total weight of 4) and 5), of a compound having the formula:

(R)2-?-O X

wherein R is isobutyl or sec. butyl and X is hydrogen, an alkali metal or N(R1)4 wherein each R1 is, individually, hydrogen, a C1-C8 alkyl radical or a C6-C10 aryl radical, and 5) from about 95 % to 0 %, by weight, same basis, of sodium mercaptobenzothiazole, c) thereafter collecting the gold by froth flotation mineral particles.

5. A process according to Claim 4 wherein said collector contains ammonium diisobutylmonothiophosphinate.

6. A process according to Claim 4 wherein said collector contains ammonium disec.butylmonothiophosphinate.