Applications of biological processes in mineral processing

Biological processes have been attracting attention in mineral processing recently due to lower operating costs and their possible applications in processing low-grade ores that are not easily concentrated using conventional processes. Adhesion of microbes to particle surfaces can alter the hydrophobicity of minerals markedly. Such surface modification to impart hydrophobicity or hydrophilicity is used in flotation of sulfide as well as nonsulfide minerals. Microbes are also able to assist dissolution of precious metals from insoluble solids. In some systems they also cause excellent flocculation of fine particles. In addition, certain microbes possess the ability to adsorb toxic heavy metal ions, and hence are finding applications for environmental protection. These processes (microbially induced flotation, flocculation and biosorption) are examined in this paper. While certain microbes will adhere to some surfaces and not to others, others will adhere to all and some to none. Interestingly, even the same microbe, with fimbriae which are its discriminating tethers, can undergo marked changes in its preference to adhere to surfaces upon selectively removing some of the fimbriae. In this regard, the role of changes in surface properties brought onto microorganisms and the minerals due to microbe-mineral interactions also needs to be recognized. Clearly, understanding the mechanisms involved in all these processes will prove useful for developing new and improved biomineral processing techniques. (C) 1998 Elsevier Science B.V.