Effect of pH, flow rate and concentration on the sorption of Pb and Cd on montmorillonite: I. Experimental

Continuous column adsorption of lead (Pb) and cadmium (Cd) was studied usin g pH adjustment and calcium-saturated montmorillonite in a short stainless steel column. Changing either pH or flow rate, while keeping inlet concentr ation of the ions constant, led to considerable changes in effluent concent rations and breakthrough curves (BTCs). At low pH values (2-4), H+ ions com peted strongly with lead and cadmium ions; at intermediate pH (4-6), ionic size played the major role in adsorption and ion exchange and at high pH (6 -9) precipitation was the major process taking place especially for lead so rption. At low flow rates less than 0.5 cm(3) min(-1), sorption of both lea d and cadmium increased due to the long retention time in the column. When both lead and cadmium ions were present in the feed, adsorption remained th e same while that of cadmium decreased compared with single ion experiments . (C) 1999 Society of Chemical Industry.