REMOVAL OF LEAD AND CADMIUM FROM AQUEOUS WASTE STREAMS USING GRANULARACTIVATED CARBON (GAC) COLUMNS

The use of granular activated carbon (GAC) columns to treat metal-bear ing 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 (C(e) = 0. 03 C(o)). X/M values were as high as about 30 mg Pb/g carbon. For EDTA experime nts, C(e) was always > 0.03 C(o). The amount of metal not removed corr esponded to the amount that was complexed by EDTA. Column pH is the cr itical parameter influencing column performance. The increase in efflu ent metal concentration corresponded with the decrease in column pH. G AC 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 perf ormance was not adversely affected by regeneration. When the regenerat ion step was used on virgin carbon, a dramatic improvement in column p erformance was observed and was attributed to the increase in carbon s urface pH (pH almost-equal-to 11) and the deposition of OH- in the por e liquid. Possible removal mechanism are precipitation on the carbon s urface and in the pore liquid, and adsorption.