The highly soluble and toxic thallium compounds readily transported through aqueous routes into the environment. Thallium (Tl) is more toxic to humans than mercury, cadmium, lead, copper or zinc. Tl has been detected in base-metal mining effluents. The conventional methods of removal of heavy metals from wastewater have only limited applicability for thallium removal. Microorganisms especially fungi can remove heavy metals from aqueous solutions. The present study involved an investigation of pretreated fungal biomass of Aspergillus niger for the removal of thallium from aqueous solutions. Batch pH and kinetic studies were carried out to examine the effects of pH and contact time on the adsorption process. Among various pH values studied, the optimum pH for thallium adsorption was found to be between 4 and 5. The equilibrium time for Tl adsorption was observed to be 6 hours and the rate of Tl adsorption was rapid in the initial period. Both Lagergren's pseudo first order model and Ho's pseudo second-order model well described the reaction rate. Batch adsorption experiments conducted at room temperature (22 +/- 1°C) showed that the adsorption pattern followed the Freundlich isotherm model. Column studies using iron oxide-coated immobilized fungal biomass showed lower adsorption capacities for thallium, compared to batch studies.
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