Depressing Effect of Raising Pulp Temperature on Pyrite Flotation.

The depressing effect of raising pulp temperature on pyrite flotation have been investigated by using diethyl dithiophosphate (ethyl aerofloat, E. A. F.) as a collector. The mechanism of depression have been studied in terms of collector adsorption and changes in concentration of sulfate, hydroxide and iron ions in pulp during conditioning, and the surface products after conditioning identified by diffuse reflectance infrared fourier transform spectroscopy (DRIFTS) and X-ray photo-electron spectroscopy (XPS).The results obtained are as follows:The flotation recovery of pyrite at pH 6 was only slightly decreased by raising pulp temperature from25°C to °C in the presence of large amounts of collector, but it was significantly depressed in moderate collector addition of the order of 200-300 g/t.There was no difference between collector adsorption at 25 °C and that at 60°C in the collector addition less than 500 g/t. Accordingly, the depression of pyrite by raising pulp temperature can not be explained by the decrease of collector adsorption.From the changes of the concentration of sulfate, hydroxide and iron ions before and after conditioning at 25°C or 60°C, it was suggested that basic iron sulfate was precipitated on pyrite surface during conditioning at either pulp temperature, but the amount precipitated at 60 t was much larger than that at 25°C, because the oxidation reaction of pyrite surface took place at 60°.The existence of sulfate on the pyrite surface after conditioning at 60 t was detected by DRIFTS and XPS.From the above experimental results, it is concluded that pyrite depression by raising pulp temperature is mainly attributed to the formation of hydrophilic basic iron sulfate which offsets the hydrophobization effect with collector adsorption.