Lead removal in fixed-bed columns by zeolite and sepiolite

The removal efficiency of zeolite (clinoptilolite) and sepiolite from lead containing aqueous solutions was investigated. A series of experiments were conducted in batch-wise and fixed-bed columns. Synthetic wastewaters containing lead (50 mg l^-1) and acetic acid (0.001 N) along with untreated and regenerated clinoptilolites and sepiolites were used in the adsorption studies. Batch tests were mainly conducted to isolate the magnitude of lead precipitation from real adsorption. Adsorption isotherms for both abstraction and adsorption were constructed. The removal of lead is found to be a sum of adsorption induced by ion exchange and precipitation of lead hydroxide. The breakthrough curves were obtained under different conditions by plotting the normalized effluent lead concentration (C/C₀) versus bed volume (BV). The ion exchange capacity of sepiolite and clinoptilolite for lead removal showed good performance up to approximately 100 and 120 BV where the C/C₀ remained below 0.1, respectively. The lead removal capacity of clinoptilolite bed from wastewater containing only lead yielded 45% higher performance compared to that of acetic acid partly due to a decrease in the effluent pH and consequently in precipitation. Also, the presence of acetic acid in the sepiolite column decreased the bed volumes treated by about 40%. Removal efficiency of lead-acetic system both in untreated clinoptilolite and sepiolite columns was found higher than that in regenerated columns.