Removal of lead and cadmium from aqueous waste streams using granular activated carbon (GAC) columns

Abstract

The use of granular activated carbon (GAC) columns to treat metal-bearing wastewaters was investigated. Synthetic wastewaters containing Pb and Cd (10 or 50 mg/L), acetic acid (0.001 N) or EDTA (1:0.1 or 1:1 Me:EDTA molar ratios) were studied. For metal-only and metal-acetic acid experiments, significant quantities (as high as 325 bed volumes (BV)) of wastewater were treated prior to breakthrough (Ce = 0.03 Co). X/M values were as high as about 30 mg Pb/g carbon. For EDTA experiments, Ce was always > 0.03 Co. The amount of metal not removed corresponded to the amount that was complexed by EDTA. Column pH is the critical parameter influencing column performance. The increase in effluent metal concentration corresponded with the decrease in column pH. GAC columns were successfully regenerated using a 1 L (≈ 8 BV) 0.1 N HNO3 rinse followed by a 1 L 0.1 N NaOH rinse. Column performance was not adversely affected by regeneration. When the regeneration step was used on virgin carbon, a dramatic improvement in column performance was observed and was attributed to the increase in carbon surface pH (pH ≈ 11) and the deposition of OH− in the pore liquid. Possible removal mechanism are precipitation on the carbon surface and in the pore liquid, and adsorption.