Adhesion of two bacteria onto dolomite and apatite: their effect on dolomite depression in anionic flotation

Bacteria can adhere to mineral surfaces and affect subsequent flotation of the minerals. In the present study, the adhesion of Bacillus subtilis and M ycobacterium phlei onto dolomite and apatite was studied by sorption measur ements and scanning electron microscopy. The effect of the microorganisms o n the oleate flotation of the minerals was then compared at several differe nt pH values. It was found that both B, subtilis and M. phlei adhered to do lomite more readily than onto apatite at acidic and near neutral pH values. At more basic pH values B. subtilis adheres more readily onto and remains a better depressant for dolomite than for apatite. However, at basic pH val ues, M. phlei adsorbs more onto apatite than onto dolomite with the result that it is a weaker depressant for dolomite, but a stronger depressant for apatite than B, subtilis. The differences in adsorption characteristics are attributed to the different surface characteristics of the two bacteria sp ecies and of the two minerals. Both possess acidic isoelectric points. Howe ver, B. subtilis has a greater affinity for Mg(II) ions than does M. phlei, Thus, B. subtilis should adsorb more strongly onto dolomite through Mg sit es than M. phlei. M. phlei, however, has a more hydrophobic surface. The re sult is that both species adsorb onto dolomite and function as dolomite dep ressants and also function as apatite depressants, albeit as weaker depress ants. The net results show that, while both function as depressants in anio nic collector flotation of dolomitic phosphate ores. B. subtilis functions as the stronger depressant, especially for dolomite. Implications in the an ionic flotation of apatite from dolomite are discussed. (C) 2001 Elsevier S cience B.V. All rights reserved.