Reverse flotation of pyrite from a Zinc Sphalerite

There are several References [26, 27, 28] about the reverse flotation of pyrite from a zinc concentrate. The process treats a zinc concentrate of 40-50% having as main impurity: Pyrite. The first step is heat the pulp to 85-90^oC and adds sodium bisulphite. Reverse flotation requires destruction of the hydrophobic xanthate surface product which is most probably copper xanthate. Under the action of heat decomposition reactions of xanthate are int

ensified. After the conditioning the pulp can be diluted to about 35-40 % solids by cold water to about 50^oC in the reverse flotation circuit [27]. In these cells pyrite and sphalerite/pyrite intergrowths are floated and the sphalerite is depressed. Xanthate is added during flotation and frother is added only if the froth appearance needs to be improved.

In reference [29] is mentioned the use of nitrogen as flotation gas during reverse flotation of pyrite from a zinc concentrate from the Flin Flon concentrator (Canada). Xu et. al. used a portable miniflotation cell (see Fig. 9).

Fig. 9 Minicell circuit for pyrite flotation at Flin Flon (adapted from [29]).

During the test the zinc concentrate varied in composition from 50-55% Zn, 8-15% Fe, and 0.8-1.2% Cu (major sulphide minerals are sphalerite, pyrite and chalcopyrite). During sphalerite flotation was used amyl xanthate, DF 250, copper sulphate and lime; the pH of the zinc concentrate varied from 9 to 11. A combination of two levels of pH (pH 7 and 5.5 adjusted with SO2) and temperature (60oC and 80oC controlled by steam) in conditioning and three levels of gas composition (air, 95% N2, 100% N2) in flotation were tested. See Figures 10 and 11. For all conditions compared to the use of air, 95% or 100% N2 gave higher pyrite recovery. Taking 3% sphalerite loss to the float product as a base line, nitrogen increased pyrite recovery by about 10% even under the least severe conditions. Oxygen appears to be necessary in conditioning to deactivate sphalerite but its absence in flotation favors selective pyrite recovery.

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