Algae-based sorbents for removal of gallium from semiconductor manufacturing wastewater

Removal of various soluble metallic impurities from wastewater in semiconductor fabrication plants is a critical issue facing the microelectronics industry. Considering the large volume of wastewater and a highly variable concentration of these contaminants, finding a robust adsorption process using a low-cost sorbent is of great value and interest to this industry. Of particular interest is the development of a flow-through abatement method for treating the process-tool effluent before it is mixed with other wastewaters. In this work, a strain of freshwater green algae (Chlorella sorokiniana), representing an algae-based sorbent, and a simulated wastewater, containing soluble gallium as the metallic impurity, are used as model compounds. The choice of gallium is based on its increased use, and the lack of related adsorption data compared to the information available for other metals such as copper and arsenic. Both batch and continuous-flow operations were used in this study. Comprehensive process models were developed and validated for both batch and flow systems. These models were found to be valuable for understanding the process steps as well as for obtaining the fundamental parameters that are needed for process design and scale-up. The sorbent was found to have high adsorption capacity even at low pH values (14.1 mg/g at pH of 2.3, and 38.5 mg/g at pH of 2.8). Based on the comparison of adsorption rate and capacity with data on previously studied and conventional sorbents, such as activated carbon and ion-exchange resins, the use of this algae-based sorbent is potentially an attractive option for the removal of gallium from the process-tool wastewater.