USE OF GRANULAR ACTIVATED CARBON COLUMNS FOR LEAD REMOVAL

The use of granular activated carbon (GAC) columns to treat lead wastewaters was investigated. Synthetic wastewaters containing Pb (10 or 50 mg/L), acetic acid (0.001 N) or EDTA (1:0.1 or 1:1 Pb:EDTA molar ratios) were studied. For lead-only and lead-acetic acid experiments significant quantities [70 to 325 bed volumes (BV)] of wastewater were treated prior to breakthrough (C(e) = 0.03C(o)); X/M-values were as high as about 30 mg Pb/g carbon. For EDTA experiments, C(e) was always >0.03C(o). The amount of lead not removed corresponded to the amount that was complexed by EDTA. Column pH is the critical parameter influencing column performance. The increase in effluent Pb concentration corresponded with the decrease in column pH. GAC columns were successfully regenerated using a 1 L (almost-equal-to 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 almost-equal-to 11) and the deposition of OH - in the pore liquid. Possible removal mechanisms are precipitation of lead on the carbon surface, precipitation in the pore liquid, and adsorption (surface complexation).