Bio-removal of PtCl₆^2- complex by Galdieria sulphuraria

Bio-removal of negative charged platinum complex is of great challenge owing to electrostatic repulsions between PtCl₆^2- and general extracellular polymeric substance (EPS) of microorganism. Galdieria sulphuraria (GS) are thermophilic and acidophilic microalga with specific metabolism, which subsequently lead to their unique cellular compositions such as EPS and phycocyanin, possibly providing a strategy to deal with negative charged metal complex. Accordingly, G. sulphuraria are employed to remove negative charged PtCl₆^2- complex with initial concentrations ranging from 0, 10, 20, 30, to 45 ppm. The growth rates of G. sulphuraria with microalgae named as GS-0, GS-10, GS-20, GS-30, and GS-45, respectively, and simultaneously bio-removal efficiencies of PtCl₆^2- are investigated. G. sulphuraria are independent to PtCl₆^2- within 0-30 ppm, while they are inhibited within 45 ppm of PtCl₆^2-. The PtCl₆^2- removal efficiencies of GS-10, GS-20, and GS-30 increase from 94.58%, 95.52%, to 95.92%, while decrease to 71.81% of GS-45. About 92.39%, 93.77%, 94.29%, and 75.21% of PtCl₆^2- adsorbed are accumulated within GS-10, GS-20, GS-30, GS-45, with few in EPS. The PtCl₆^2- complexes accumulated in EPS and algae cells are possibly decomposed to PtCl₄ according to the increasing zeta potentials of EPS and algae cells. The results indicate that PtCl₆^2- is efficiently removed by G. sulphuraria, achieving bio-removal of negative charged PtCl₆^2- complex from wastewater.