Suppression of floatability of pyrite in coal processing by carrier microencapsulation

Carrier microencapsulation, CME, is a technique to form a thin layer of metal oxide or hydroxide on pyrite surface using a water soluble organic carrier combined with metal ions. The present study investigated the effect of CME using a tris-catecholato complex of Si4+, Si(cat)32− on pyrite-coal separation by dynamic bubble pick-up experiments and Hallimond tube flotation experiments using coal, pyrite, and a coal–pyrite mixture. The mineral samples were treated in 0–5 mol m− 3 Si(cat)32− solutions at pH 4–9 at treatment times of 1–24 h. Dynamic bubble pick-up experiments showed that CME treatment converted the pyrite surface from hydrophobic to hydrophilic but did not affect coalʹs hydrophobic surface. The results of the Hallimond tube flotation experiments of a coal–pyrite mixture at pH 7–9 in the presence of kerosene as a collector showed that pyrite floatability was selectively suppressed after 1 h CME treatment with 0.5 mol− 3 Si(cat)32− while both coal and pyrite were floated without the treatment. This indicates that CME treatment is effective in suppressing pyrite floatability in coal–pyrite flotation.