Design and scaling up of fixed bed adsorption columns for lead removal by treated laterite

Abstract

Laterite (rocky soil, rich in iron and aluminium) was treated using hydrochloric acid (6 M) and sodium hydroxide (4 M) to increase its uptake capacity for lead species present in water. Process parameters, like, bed depth, flow rate and feed concentration of lead were varied and the corresponding changes in outlet concentration were observed. The depth of mass transfer zone was increased from 1.4 cm to 2.2 cm as bed volume increases from 39 cm3 to 137 cm3. Total lead removal efficiency of the bed was increased from 68% to 74% for the same increase in bed volume. Increase in inlet flow rate from 10 ml/min to 20 ml/min decreased the interaction time between adsorbent and adsorbate, resulting in marginal reduction of adsorbed amount (2.5 mg/g to 2 mg/g). However, the extent of adsorption was increased from 2.5 mg/g to 5.4 mg/g as inlet concentration increases from 3 mg/L to 15 mg/L due to enhanced driving force. Delayed breakthrough was observed for higher bed depth, while faster breakthrough was achieved for enhanced flow rate and inlet concentration. Efficiency of various fixed bed models (Adams-Bohart, Thomas, Yoon-Nelson and pore diffusion-adsorption model) was tested. Analysis for scaling up was also provided to observe the filter performance at a higher throughput. Performance of the filter using lead spiked pond water was also assessed.