Metal adsorption and desorption by lyophilized Pseudomonas aeruginosa

Biosorption of nickel (Ni2+) and copper (Cu2+) by lyophilized Pseudomonas aeruginosa cells was investigated based on Freundlich isotherm. Bacterial biomass showed significant sorption of both Ni (265 mg g−1) or Cu (137.6 mg g−1), and was also superior over the cation exchanger, IRA 400 (98 mg Ni g−1 or 26.6 mg Cu g−1). Metal binding by the test organism was a fast saturating, pH-dependent process. The optimum pH for Cu adsorption was 7.0 and for Ni 8.0. X-ray diffraction studies revealed that both cations were deposited on the cell predominantly as phosphide crystals. The participation of carboxyl, carbonyl, and phosphoryl groups along with H-bonding in metal sorption was evident in IR spectra. Biomass pretreatment by agents like NaOH, NH4OH or toluene enhanced the metal loading capacity, whereas, oven heating (80°C), autoclaving (120°C, 15 lb (in.2)−1), acid, detergent and acetone treatments were inhibitory. In bimetallic combination, Na, K or Ca increased sorption of Ni as well as Cu in contrast to Cd or Pb. Mineral acids (HCl, H2SO4 and HNO3) and NTA could recover more than 75% (on average) Ni or Cu adsorbed on the biomass. Calcium carbonate (10 mM) was efficient in Ni desorption (71%) compared to Cu (57%). Noticeably sodium carbonate remained specific for Cu remobilization (88%) than Ni (21%). The data are in favour of deployment of the test biomass as an efficient metal removal/recovery system.