Trithiocarbonates as depressants in ore flotation

Polyhydroxytrithiocarbonates can be used as depressants in ore flotation.

In one aspect, this invention relates to novel compositions. In another 
aspect, the invention relates to the use of certain compositions. In 
another aspect this invention relates to the use of certain compositions 
in flotation processes for recovering minerals from their ores. In another 
aspect of the invention it relates to the use of flotation agents and 
flotation depressants in the recovery of minerals from their ores. 
Froth flotation is a process for concentrating minerals from ores. In a 
froth flotation process, the ore is crushed and wet ground to obtain a 
pulp. Additives such as collecting or mineral flotation agents and 
frothing agents are added to the pulp to assist in subsequent flotation 
steps in separating valuable minerals from the undesired portions of the 
ore. The pulp is then aerated to produce a froth at the surface. The 
minerals which adhere to the bubbles or froth are skimmed or otherwise 
removed and the mineral-bearing froth is collected and further processed 
to obtain the desired minerals. Frequently, other chemicals are added to 
the separated mineral-bearing froth to assist in subsequent separations 
particularly when significant proportions of two or more minerals are 
present in the separated mineral-bearing froth. Such chemicals are known 
as depressants. These materials are sometimes referred to more 
appropriately as deactivators and are used selectively to separate one 
type of mineral from another type of mineral. 
OBJECTS OF THE INVENTION 
It is one object of the invention to provide compositions which can be 
used, for example as flotation depressants in ore flotation processes. 
It is another object to provide a process for the recovery of substances 
from ores. 
It is still another object of this invention to provide ore separation 
process employing a treating agent. 
Other aspects and objects of this invention will become apparent upon 
reading this specification and the appended claims. 
DESCRIPTION OF THE INVENTION 
The novel compositions having a use as treating agents herein are believed 
to contain water soluble salts of polyhydroxy-substituted 
hydrocarbyltrithiocarbonates conforming to the general formula: 
##STR1## 
wherein R' is a C.sub.2-21 organic moiety; and Y is a Group IA or IIA 
metal ion or an ammonium ion, preferably ammonium or Group IA metal ion 
since Group IIA metal salts tend toward insolubility, and n is an integer 
of from 2 to 22. A preferred group of compositions are the salts of 
polyhydroxyhydrocarbyltrithiocarbonates conforming to the formula: 
##STR2## 
where R if present is a C.sub.0 -C.sub.20 organic moiety, Y has the above 
meaning and n is 0 to 20. 
Preferably, R is hydroxyalkyl having from 1 to 6 carbon atoms and n is 0 to 
3. 
One technique for preparing compositions according to the invention results 
from combining ingredients in an aqueous reaction medium in a manner 
represented by the equation: 
##STR3## 
wherein R' and Y have the designations recited above and n is an integer 
of from 2 to 22. 
The organic moiety, R' in the reagents of the invention can be any organic 
moiety containing up to about 22 carbon atoms containing a plurality of 
hydroxyl groups. Mixtures of the thus characterized treating agent are 
suitable for use in the invention. Preferably, R has an alkyl backbone and 
contains 2 to 15 carbon atoms and 2 to 4 hydroxyl groups. 
At least one Y substituent is associated with an anionic sulfur atom of the 
trithiocarbonate. While Y may be an ammonium ion or any Group IA or Group 
IIA metal ion, it is preferred that Y be a Group IA metal ion. Sodium is 
highly preferred. 
Exemplary compounds include but are not limited to such salts as 
sodium 2,3-dihydroxypropyltrithiocarbonate 
potassium 2,11,12-trihydroxydodecyltrithiocarbonate 
potassium tris(hydroxymethyl)methyltrithiocarbonate 
and the like and mixtures thereof. Sodium 
2,3-dihydroxypropyltrithiocarbonate is presently preferred because it has 
been tested and shown to be an effective depressant. 
These and similar compounds function as mineral sulfide depressants and are 
used with solid ores, concentrates or cleaners. The materials are 
basically depressants for Cu, Fe and Mo sulfides but other mineral 
sulfides such as those based on Pb, Zn, Ni, etc. are considered within the 
scope of this invention. Exemplary ores include the following: 
______________________________________ 
Molybdenum-Bearing Ores 
Molybdenum MoS.sub.2 
Wulfenite PbMoO.sub.4 
Powellite Ca(MO,W)O.sub.4 
Ferrimolybdite Fe.sub.2 Mo.sub.3 O.sub.12.8H.sub.2 O 
Copper-Bearing Ores 
Covallite CuS 
Chalcocite Cu.sub.2 S 
Chalcopyrite CuFeS.sub.2 
Bornite Cu.sub.5 FeS.sub.4 
Cubanite Cu.sub.2 SFe.sub.4 S.sub.5 
Valerite Cu.sub.2 Fe.sub.4 S.sub.7 or Cu.sub.3 Fe.sub.4 
S.sub.7 
Enargite Cu.sub.3 (As,Sb)S.sub.4 
Tetrahedrite Cu.sub.3 SbS.sub.2 
Tennanite Cu.sub.12 As.sub.4 S 
Stannite Cu.sub.2 S.FeS.SnS.sub.2 
Bournonite PbCuSbS.sub.3 
Lead-Bearing Ore: 
Galena PbS 
Antimony-Bearing Ore: 
Stibnite Sb.sub.2 S.sub.3 
Kermesite Sb.sub.2 S.sub.2 O 
Zinc-Bearing Ore: 
Sphalerite ZnS 
Silver-Bearing Ore: 
Argentite Ag.sub.2 S 
Stephanite Ag.sub.5 SbS.sub.4 
Polybasite 9Ag.sub.2 S.Sb.sub.2 S.sub.3 
Iron-Bearing Ore: 
Pyrite FeS.sub.2 
Pyrrohotite Fe.sub.5 S.sub.6 to Fe.sub.16 S.sub.17 
Arsenopyrite FeAsS 
Marmatite (ZnFe)S 
Nickel-Bearing Ore: 
Millerite NiS 
Pentlandite (FeNi)S 
Ullmannite NiSbS 
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The amount of trithiocarbonate treating agent employed as a depressant for 
one or more minerals can vary widely. Generally, the quantity used depends 
on the amount of flotation or collecting agent employed, the flotation 
technique used, and on the amount and kinds of minerals present in the 
ore. Generally, from 0.005 to 20 lbs of treating agent based on 
trithiocarbonate component per ton of ore is employed, usually from about 
0.01 to about 5 lbs per ton, preferably from about 0.1 to about 1 lb per 
ton. The treating agent is effective under both acidic and basic 
conditions such as over a pH range of 5 to 11. In one preferred embodiment 
of the instant invention trithiocarbonates are used to suppress the 
flotation of copper and iron from ores containing them. 
The aqueous treating agent obtained from the reaction of the metal salt of 
the thiol with CS.sub.2 is the preferred treating agent of the invention 
for use as a depressant composition in a flotation process. 
Generally, the flotation process comprises carrying out a minerals 
flotation with a depressant composition present, with the depressant 
composition being represented by the formula: 
##STR4## 
where n, R' and Y are previously defined. 
Generally, the flotation process will utilize a composition comprising the 
treating agent, water, and the mineral material. The depressants of the 
present invention can be used to depress iron, copper and/or lead in the 
presence of molybdenum. The depressants of the invention are also 
effective to depress sulfides in the presence of coal, and thus may also 
have utility in coal beneficiation. In ores, the metals are usually in a 
solid sulfided state and form a slurry, which can be finely divided, as in 
a pulp. For example, the invention can be employed to process an ore 
slurry containing high copper values. The invention can also be employed 
to process a concentrate, such as a concentrate which contains high 
molybdenum values. Generally, the solids to be processed will be present 
as a slurry in water which contains the treating agent with the treating 
agent being present in an amount of between about 0.005 and about 20 
pounds per ton of the solids. The slurry usually contains between about 10 
and 75 percent solids preferably in the range of 15-60 weight percent 
solids, depending on the processing stage. Preferably, the 
trithiocarbonate or derivative is present in the composition in an amount 
in the range of between about 0.01 to about 5 pounds per ton of solids. 
Even more preferably, the trithiocarbonate is present in an amount in the 
range of between about 0.1 and about 5 pounds per ton of the solids. 
The flotation process usually involves the steps of: 
(a) mixing crushed or ground mineral material with water and the treating 
agent defined above to establish a pulp, 
(b) aerating the pulp to produce a froth and a pulp, 
(c) separating the froth from the pulp and producing a concentrate product 
and a tail product, and 
(d) recovering minerals from the so separated concentrate and/or tail 
product. 
The depressant composition of the invention can also be employed with 
frothers and flotation agents. 
Examples of frothers that can be used in addition to the collector 
compositions defined above are polyoxyalkylene glycols and their 
corresponding methyl or ethyl ethers having broadly a molecular weight of 
about 400 to about 1000, and preferably a molecular weight in the range of 
about 420 to about 780. Particularly polypropylene glycols and their 
ethers having molecular weights of e.g., 400, 425, 750 or 900 can be used. 
Also polybutylene glycol and polypentylene glycol are useful materials. 
Examples of other frothers that may be used are alcohols such as methyl 
isobutyl carbinol, pine oil, phenols, fatty acids and cresylic acid. 
Examples of suitable flotation agents are organic xanthates, organic 
trithiocarbonates, amines, dithiocarbamates, fuel oils, aromatic oils and 
the like, generally in an amount of 0.005-0.5 pounds per ton of solids. 
Preferably frother and an oily flotation agent are used together. 
The inventive depressant can be used together with other depressant or 
depression steps if desired. For example, the depressant composition 
defined above can be used after a surface treatment of the solids, such as 
after heating or oxidation of a concentrate or with sulfuric acid, and/or 
with additional depressants, such as sodium cyanide, sodium ferrocyanide, 
lime and zinc sulfate, in the treatment of an ore. 
Any froth flotation apparatus can be used in this invention. The most 
commonly used commercial flotation machines are the Agitair (Galigher 
Co.), Denver D-2 (Denver Equipment Co.), and the Fagergren (Western 
Machinery Co.). Smaller, laboratory scale apparatus such as the Hallimond 
cell can also be used.

The instant invention was demonstrated in tests conducted at ambient room 
temperature and atmospheric pressure. However, any temperature or pressure 
generally employed by those skilled in the art is within the scope of this 
invention. 
EXAMPLE I 
This example describes the preparation of the inventive trithiocarbonate 
compound described herein. To a 3-neck glass flask fitted with a 
condenser, stirrer, thermometer and dropping funnel was added 96 
milliliters of water and 14 grams (0.35 mole) of sodium hydroxide. After 
cooling to below 50.degree. C., 36.1 grams (0.33 mole) of 
3-mercapto-1,2-propanediol was slowly added with stirring over a 10 to 20 
minute period. The mixture was cooled to below 45.degree. C. and 25.4 
grams (0.33 mole) of carbon disulfide was slowly added over a 30 minute 
period. The cloudy mixture was maintained with stirring at 45.degree. C. 
for about 1.5 hours at which time the solution became hazy and 
orange-colored. The solution was cooled to room temperature and bottled. 
The solution was estimated to be 40 weight percent of sodium 
3-(thiocarbonyldithio)-1,2-propanediol also referred herein as sodium 
2,3-dihydroxypropyltrithiocarbonate. 
EXAMPLE II 
This example discloses the use of the trithiocarbonate derivative described 
in Example I as an ore flotation reagent, particularly as a mineral 
sulfide depressant. To a 3 liter capacity Agitar LA 500 flotation cell was 
added 415 milliliters of a copper/molybdenum-containing agitated pulp 
(about 600 grams of solid-Anamax Mining Co.) and enough water to make 
about 30 weight percent aqueous mixture. The mixture had a natural pH of 
10.4. The depressant to be evaluated was then added and the mixture 
conditioned for about 2 minutes at 1200 rpm and then floated for 5 
minutes. The concentrate was filtered, dried and analyzed. The flotation 
was repeated except before the depressant was added there was enough 
sulfuric acid added to reduce the pH between 6.0 and 7.0. The evaluation 
listed in Table I was conducted in the absence of a depressant, in the 
presence of 3 depressants (including the inventive depressant), and in the 
presence of a Mo collector (Molyflo, an oily Mo collector from Phillips 
Petroleum Co.). The results indicate the inventive trithiocarbonate acts 
as a mineral sulfide depressant in either acid or basic conditions and 
appears to be superior in depression to any of the other reagents tested. 
TABLE I 
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Effect of Various Materials 
on Mineral Sulfide Depression 
% Recovery 
Run lb/ 
pH 6.0-7.0 
pH 10.4 
No. 
Reagent Ton 
Cu Fe Mo Cu Fe Mo 
__________________________________________________________________________ 
Control: 
1 None -- 5.1 
4.3 
82.5 
25.7 
23.5 
27.8 
2 Molyflo.sup.a 0.14 
6.3 
5.3 
84.8 
28.5 
28.2 
32.7 
3 Disodium Carboxymethyl 
0.8 
3.0 
4.0 
6.3 
3.4 
4.0 
57.9 
Trithiocarbonate, 
40 Wt. % Aq. 
4 Trisodium Succinyl 
0.8 
2.8 
3.3 
78.5 
3.0 
3.2 
72.1 
Trithiocarbonate,.sup.b 
40 Wt. % Aq. 
Invention: 
5 Sodium 2,3-Dihydroxy- 
0.8 
3.0 
2.9 
4.0 
3.8 
4.3 
10.0 
propyl Trithiocarbonate,.sup.b 
40 Wt. % Aq. 
__________________________________________________________________________ 
.sup.a An oily moly collector from Phillips Petroleum Co. 
.sup.b Also referred herein as sodium 
3(thiocarbonyldithio)-1,2-propanediol from Example I.