Factors affecting the selective flocculation of hydroxyapatite from quartz and/or calcite mixtures

This work presents results on some physical and chemical factors involving the selective flocculation of hydroxyapatite from mixtures with calcite and quartz. These factors were the selective adsorption of an anionic polyacrylamide, the separation of flocculated from dispersed fractions, and the process sensitivity to feed grade and grinding conditions. High selectivity was obtained with an anionic polyacrylamide as the flocculant, and sodium silicate and/or sodium polyacrylate as dispersants for quartz and calcite, respectively. Multistage treatment was more efficient than elutriation as a cleaner-upgrading process for the flocculated hydroxyapatite (29% P2O5 and 85% recovery after 5 redispersion flocculation stages). These results were highly dependent on feed grade and on grinding conditions (surface contamination). Results are discussed in terms of the interfacial phenomena involved and the physical aspects of floc-formation and cleaning.