Biocoagulation as part of a new technology for separation of fine particles
Jana Pinka
Technical University Berlin, Mechanical Process Engineering & Solids Processing
Microbes can enrich or degrade particles due to different charges of particles and microbes. This fact is exploited in microbiological separation processes like bioaccumulation, bioprecipitation and biosorption. Such processes are used to recover metals, either valuable or nuisance, from bleeds and effluents from bioleaching operations and other hydrometallurgical treatments. Still, the transport of particles by microbes is not well-investigated [1]. Biocoagulation new technology for making extremely fine-grained particles collectible, and differs from well-known processes like biosorption [2], bioaccumulation and biotransformation: In biocoagulation the particles are very small and solid. For the other processes, the minerals dissolve and the ions are adsorbed or accumulated.
The investigations follow three major directions (figure 1): Firstly, the different behaviour of particles, minerals and microbes, in electrolytes is used. Between the electrolyte and the particle surface, a transition of charge carriers (electrons, ions) often takes place. Thereby the charge carriers can migrate into the liquid phase or vice versa - adsorb to the solid phase. Because of the enrichment of charge carriers, an electrochemical bilayer originates consisting of a relatively fixed layer (Stern Layer) and a more diffuse layer (Gouy-Chapman-Layer). The potential of the shearing layer in direction to the neutral solution is called zeta-potential. Different zeta-potentials at the surfaces of minerals and microbes are connecting the minerals and microbes into clusters.
Measurements of the zeta-potential were performed to find the best conditions for coagulation of the model minerals Galena and Sphalerite and the yeasts Saccharomyces cerevisiae and Yarrowia lipolytica. The yeasts were cultivated, gathered and provided for coagulation tests. Microscopic studies demonstrate the adhesion of the sulphidic minerals onto the yeasts’ surface.
[1] Bowen et al. (2001) J Colloid Interface Sci. 1, 237, 54-61
[2] Strouhal et.al. (2003) Bioelectrochemistry 60, 29-36
24.01.2007