Removal and Selective Recovery of Heavy Metal Ions from Industrial Waste Waters
The influence of hard-water components (calcium(ll) and magnesium(ll)) on metal-ion binding to different algal biomasses was investigated. Concentrations as high as 10,000 ppm of calcium and magnesium ions were virtually without effect on the binding of copper(ll), aluminum(lll), gold(lll), and mercury(ll) ions to harvested cells of Spirulina or Cyanidium. Slight inhibition of cadmium(ll), nickel(ll), and zinc(ll) ion binding was observed for both algal species.
Different algal-silica polymers showed good copper binding properties when exposed to an authentic copper-plating bath sample. However, various algal polymers exhibited substantial variations in performance under comparable conditions.
The algae, Spirulina and Cyanidium, were cultured under different nitrogen concentrations. Metal-ion binding experiments with the resultant biomass indicated that the nitrogen concentration present during growth of Spirulina had no impact on its metal-ion binding capacity. Conversely, the metal-ion binding capacity of Cyanidium was decreased in biomass grown at nitrogen levels below those found in the normal growth medium; however, growth medium nitrogen concentrations above normal may cause increased expression of high affinity gold binding sites. The copper binding capacity of Cyanidium biomass was found to increase, when cells were cultured in medium containing elevated levels of copper ion.
The mechanism of metal-ion binding to algae was studied by modifying algal chemical functional groups. These modifications showed that carboxyl groups are primary binding sites. Amino and sulfhydryl groups also play a role in algal metal-ion binding, but to a lesser extent.