Accumulation of zirconium by microalgae and cyanobacteria

The accumulation of zirconium (Zr) as [Zr4-(OH)8(H2O)16]8+ by cyanobacteria and microalgae has been characterized. In all the cyanobacterial and microalgal species examined, accumulation consisted of a single rapid energy-independent phase (''biosorp-tion'') and no energy-dependent accumulation was observed. Biosorption of Zr was concentration-dependent, followed a Freundlich adsorption isotherm, and was dependent on pH, showing decreased accumulation with decreased pH. Prior treatment with Na+, K+, Cs+, Ca2+, Mg2+ and Sr2+ (added as chlorides) also decreased Zr accumulation by cyanobacteria and microalgae, probably a result of competition between Zr ions and othecations, including H+, for available binding sites on the cell walls. Zr desorption from micoalgae and cyanobacteria was increased by increasing external cation concentrations or by decreasing the pH of the desorption agent. (orig.)