Reverse flotation of pyrite from a zinc-concentrate using nitrogen

A mobile flotation facility, based on two 5 L minicells equipped with on-line monitoring of pH, dissolved oxygen and pulp potential, was used to study flotation of pyrite from zinc concentrate (i.e. reverse flotation) at the Trout Lake circuit of Hudson Bay Mining and Smelting Co. Ltd., Flin Flon, Manitoba. A combination of 2 levels of pH (pH 7 and 5.5 adjusted with sulphur dioxide) and temperature (60°C and 80°C controlled by steam) in conditioning and 3 levels of gas composition (air, 95% N2, 100% N2) in flotation were tested. 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% (absolute) even under the least severe conditions (pH 7 and 60°C). In contrast, the flotation of chalcopyrite was retarded when using nitrogen. onitoring of the pulp chemistry, oxygen appears to be necessary in conditioning to de-activate sphalerite but its absence in flotation favours selective pyrite recovery. The use of sulphur dioxide in conditioning may help oxygen achieve these conflicting roles: the sulphur dioxide/oxygen combination gives initially strong oxidizing conditions but finally results in consumption of the oxygen. The use of nitrogen in flotation effectively maintains the low pulp potential and dissolved oxygen levels achieved in conditioning permitting less severe conditioning to be used.