Enrichment of minerals by flotation and collector agents employed for this purpose

Process of enrichment of minerals by flotation by means of a collector comprising a thio-compound, the thio-compound being a straight or branched dialkyl or dialkenyl polysulphide.

The present invention relates to the enrichment of minerals by flotation 
with organic collectors constituted by thio-compounds. It relates more 
particularly to the treatment of minerals based on oxides and sulphides of 
heavy metals. 
Compounds containing sulphur in their molecules have been successfully 
employed in the flotation technique: this is particularly the case with 
the alkali metal alkyl xanthates, which are among the best collectors 
known at present. However, alkyl mercaptans are also regarded as good 
collectors, particularly C.sub.12 to C.sub.16, which--despite their low 
solubility in water--have been advantageously utilized, when emulsified 
with surfactant compounds. 
The present invention is based on the discovery that the collector 
properties of a thio-compound can be intensified by a certain accumulation 
of sulphur atoms in the molecules of these compounds. Thus, it has been 
found that dialkyl polysulphides can give better results than the 
corresponding mercaptans; this is theoretically surprising, because 
polysulphides have a molecular structure containing two lipophilic chains. 
This fact is all the more unexpected as the alkyl polysulphides higher 
than C.sub.8 are even less soluble in water than the mercaptans. 
The process according to the invention consists in effecting the flotation 
of the mineral or minerals in a general manner known per se, but with at 
least one di-hydrocarbyl polysulphide as a collector or in conjunction 
with a collector of the known type, the one or more polysulphides being 
represented by the formula: 
EQU R-S.sub.x -R' 
where R and R' are the same or different and are alkyl or alkenyl groups, 
which can carry substituents, and x is a number having an average value of 
2 to 8. 
The substituents of the hydrocarbon groups R and/or R' can be other 
aliphatic, cyclo-aliphatic or aryl radicals, halogens, nitriles or 
functional groups, for example OH, -COOH, NO.sub.2, CONH.sub.2, esters, 
carbonyls etc. Functional substituents giving affinity with water are 
particularly favourable. 
In practice, the groups R and/or R' are generally C.sub.1 to C.sub.18, 
straight or branched, and particularly C.sub.4 to C.sub.12. 
A mode of preparation of such polysulphides is known, which consists in 
treating for example the corresponding mercaptan with sulphur, in the 
presence of an amine as catalyst, according to the reaction: 
EQU 2RSH+(x-l)S amine RS.sub.x R+H.sub.2 S 
This process in fact provides a mixture of polysulphides having various 
numbers of S atoms, x thus being an average of these numbers. 
Although starting with C.sub.8, the polysulphides according to the 
invention are practically insoluble in water, they can be introduced into 
the mineral pulp to be treated in the form of a solution in a solvent, or 
as an emulsion or as an extremely fine dispersion. Thus, the polysulphide 
can be employed in solution in alcohol, carbon disulphide, dimethyl 
sulphoxide, benzene, kerosene, oil or other appropriate solvent. The 
emulsion can be produced by mixing with a surfactant liquid, such as a 
polyol or a polyethoxylated alkyl-phenol, a petroleum sulphonate, a 
polyalkoxylated mercaptan, an ester of a polyoxyalkylene fatty acid or of 
sorbitan, etc. As regards the aqueous or other dispersion, it can be 
obtained by wet mircronisation. 
The molar proportions of the new collectors according to the invention 
employed in flotation are the same as those of the known technique, that 
is generally about 0.05 to 1.5 and, more particularly, 0.1 to 0.25 mole 
per tonne of mineral.

The Examples which follow illustrate the invention non-limitatively. 
EXAMPLES 1 to 6 
A series of flotation tests is effected with a sulphide mineral of copper 
obtained from the South African mine at Palabora, containing 0.45 to 0.48% 
Cu. 600 g of this mineral is ground to a fineness such that 76% of the 
powder passes through a screen having 148 micron meshes. 
After adding the necessary adjuvants, the product is subjected to flotation 
for 20 minutes at pH 7.5, in a 2.5 liter laboratory cell of the Minemet M 
130 type, in the presence of methyl-isobutyl-carbinol as a wetting agent 
added at the rate of 25 g per tonne of mineral. 
The collectors are introduced in the form of mixtures of 57.5% by weight of 
the thio-compounds with 42.5% of the surfactant, polyoxyethylene nonyl 
phenol, known commercially under the name "SIMULSOL 730". They are, on the 
one hand, (Examples 1 and 2) the mercaptans usually used in flotation and, 
on the other hand, (Examples 3 to 6) polysulphides according to the 
invention; their proportion in millimoles per tonne of mineral is 
indicated in the results Table which follows. The last two columns in this 
Table indicate the percentage Cu content in the concentrate obtained, as 
well as the percentage of Cu recovered. 
______________________________________ 
Ex. Millimoles 
Conc. % Cu 
No. Collector per tonne % Cu recovered 
______________________________________ 
1 n-dodecyl-mercaptan 
173 10.4 30.4 
2 tert.dodecyl-mercap- 
" 9.4 61.0 
tan 
3 di-tert.dodecyl- 
" 14.5 66.7 
pentasulphide 
4 di-tert.dodecyl- 
124 13.3 48.0 
pentasulphide 
5 di-tert.dodecyl-tri- 
173 13.7 20.5 
sulphide 
6 di-tert.nonyl-tri- 
" 11.6 19.7 
sulphide 
7 di-tert.nonyl-penta- 
" 12.7 58 
sulphide 
______________________________________ 
Thus the concentrations of Cu obtained are always better with the 
polysulphides than those given by known collectors. Also, in equal molar 
proportions, the pentasulphides permit a recovery of copper comparable or 
superior to that of the mercaptans. 
EXAMPLES 7 to 14 
Flotation tests are effected with each of the minerals designated in the 
results Table by: 
CHAL. --for chalcopyrite, 
GAL. --for galena 
BL. --for blende and 
PYR. --for pyrites. 
265 ml of water, 1 g of fine powder of the mineral and 3.times.10.sup.-4 g 
of the collector to be tested, per liter, are introduced into a cell; this 
collector is utilized in the form of a 1% solution in ethanol. 
The Table below gives the percentage of each mineral recovered as the 
product of the flotation. 
______________________________________ 
Ex. % of mineral recovered 
No Collector CHAL. GAL. BL. PYR. 
______________________________________ 
8 Dihexyl-disulphide 
94 88 84 90 
9 Lauryl-ethyl-di- 
92 -- 91 -- 
sulphide C.sub.12 H.sub.25 SSC.sub.2 H.sub.5 
10 Dilauryl-disulphide 
88 -- 89 87 
C.sub.12 H.sub.25 SSC.sub.12 H.sub.25 
11 Dihexyl-trisulphide 
92 87 76 88 
C.sub.6 H.sub.13 SSSC.sub.6 H.sub.13 
12 Dilauryl-trisulphide 
95 91 73 84 
C.sub.12 H.sub.25 SSSC.sub.12 H.sub.25 
13 Dilauryl-pentasulphide 
88 93 69 79 
C.sub.12 H.sub.25 S.sub.5 C.sub.12 H.sub.25 
14 n-Dodecyl-mercaptan 
81 87 64 73 
______________________________________ 
It can be seen that the polysulphides of Examples 8 to 13 give bettwer 
results than those given by n-dodecyl mercaptan (Example 14) currently 
employed at the present time. 
EXAMPLES 15 to 20 
Assey on chalcopyrite with 3.times.10.sup.-4 g/l of collector. 
______________________________________ 
Ex. Results % 
No. Collector pH 7 8 9 10 
______________________________________ 
15 C.sub.6 H.sub.13 S.sub.2 C.sub.6 H.sub.13 
46% 45% 45% 42% 
16 C.sub.12 H.sub.25 S.sub.2 C.sub.12 H.sub.25 
54% 49% 47% 46% 
17 C.sub.12 H.sub.25 S.sub.2 C.sub.2 H.sub.5 
44% 44% 44% 37% 
18 C.sub.6 H.sub.13 S.sub.3 C.sub.6 H.sub.13 
48% 43% 41% 40% 
19 t C.sub.12 H.sub.25 S.sub.3 tC.sub.12 H.sub.25 
88% 86% 86% 88% 
20 t C.sub.12 H.sub.25 S.sub.5 tC.sub.12 H.sub.25 
85% 85% 85% 85% 
______________________________________ 
It can be seen that when the collector has two S atoms and six or less 
carbon atom alkyl groups, the results are poorer.