ADSORPTION OF METAL-IONS BY RHIZOPUS-ARRHIZUS BIOMASS - CHARACTERIZATION STUDIES

Freeze-dried, oven-dried, and nonmetabolizing live Rhizopus arrhizus biomass were tested for their capacity to adsorb the test ions, Sr2+, Cd2+, and Cu2+, over the pH range 4-6. Metal uptake values for each biomass type were found to increase in the order Cu2+ > Cd2+ > Sr2+. Freeze-dried biomass proved to be the most efficient biomass type for metal adsorption, followed in order by oven-dried and five biomass for Sr2+ systems, and live and oven-dried biomass for Cd2+ and Cu2+ systems. Each test ion displaced constant levels of Ca2+ and Mg2+ ions from the three biomass types, indicating that biomass pretreatment had no apparent effect on the ion-exchange capacity of Rhizopus arrhizus. Similarly, the levels of H+ displacement resulting from test ion adsorption were unaffected by pretreatment but were found to increase in the order Cu2+ > Cd2+ > Sr2+. Linear reciprocal Langmuir and Scatchard transformation plots reflected the predominantly ion-exchange mechanism of Sr2+ and Cd2+ adsorption, and a curved Scatchard transformation plot reflected the more covalent nature of Cu2+ adsorption.