In the production of ground calcium carbonate (GCC) for the paper industry, pyrrhotite dramatically
reduces the GCC brightness and the removal of pyrrhotite through froth flotation is essential. The present
study aims to study the effect of pyrrhotite oxidation on flotation recoveries during typical GCC flotation
(i.e. alkaline pH, CaCO3 saturation, amine collector). EDTA extraction and measurements of Eh (redox
potential) showed a significant difference in pyrrhotite surface oxidation state when comparing exposure
times of 40 and 60 min, the latter being significantly more oxidised. Microflotation results show that
when pyrrhotite is exposed to air extending for more than 5 min at pH 8, the recoveries drop signifi-
cantly. At higher pH, recoveries were generally low at all exposure times tested. Flotation recoveries
showed strong correlation with zeta potential measurements. Bench scale flotation experiments on a
sulphide bearing marble, confirmed that pyrrhotite oxidation significantly lower the GCC quality at
low collector concentrations. By increasing the amine concentration, the flotation performance became
independent of pH and exposure time.