The flotation separation behavior of apatite from calcite using carboxymethyl chitosan as depressant

The separation of apatite from calcite has been recognized as one of the most difficult subjects in mineral processing owing to their similar surface properties, thus finding high-efficiency depressants become the key for the separation. In this paper, carboxymethyl chitosan was tested as a potential selective depressant in the separation of apatite and calcite using sodium oleate (NaOL) as a collector. Contact angle measurements, adsorption tests, zeta potential tests, FTIR analysis and XPS analysis were performed to explain the selective depression mechanism of carboxymethyl chitosan. The micro-flotation experiment indicated that carboxymethyl chitosan had significantly depression effect on calcite but had a little influence on apatite at pulp pH 9. A series of mechanism tests show that the carboxymethyl chitosan adsorption quantity on calcite surface more than that on apatite surface, which is due to that carboxymethyl chitosan adsorbed on apatite surface by hydrogen bonding, while absorbed on calcite surface mainly through chemical chelating between Ca on mineral surface and -COO- on the depressant. Moreover, both apatite and carboxymethyl chitosan are negatively charged, strong electrostatic repulsive force and steric hindrance between carboxymethyl chitosan and apatite also make the carboxymethyl chitosan adsorb on apatite surface more difficult. These adsorption differences lead to the flotation separation of the two minerals.