PYRITE DEPRESSION BY PHOSPHATES IN COAL FLOTATION

The selective depression of pyrite from the Kentucky No. 9 coal seam w as systematically examined using various kinds of inorganic and organi c chemicals. Most of the organic chemicals rested showed little select ivity in pyrite depression. It was found that both orthophosphate and pyrophosphate were effective for the selective depression of coal pyri te in coal flotation using fuel oil as a collector. At substantially l ow concentrations of pyrophosphate, the flotation of coal pyrite was c ompletely depressed over-a wide pH range, while the coal flotation rem ained unaffected. The mechanism of the selective depression of pyrite by phosphates was explained with the help of thermodynamic calculation s of iron-phosphate-water systems and zeta-potential measurements. It was shown that pyrophosphate reacts strongly with the iron ions of pyr ite to form stable hydrophilic ir-on pyrophosphate complexes on pyrite surfaces.