Removal of lead (Pb²⁺) from aqueous medium by using chars from co-pyrolysis

The effectiveness of chars from the co-pyrolysis of pine, used tires and plastic wastes for the removal of lead (Pb²⁺) from aqueous medium, was investigated. The chars were predominantly of macroporous nature, but the introduction of tires in the pyrolysis feedstock enhanced their mesoporous content as well as surface area. Pb²⁺ sorption with the chars was a slow and unstable process in which sorption-desorption seems to be competing. The highest Pb²⁺ removal (88%) was attained by the char resulting from the pyrolysis of a mixture composed by equal mass ratios of used tires and plastics, at 48h of contact time. This char was also the one with the overall better performance for Pb²⁺ sorption, achieving almost 100% of Pb²⁺ removal on the study of the effect of adsorbent dose. Mixing the three raw materials for pyrolysis had no advantage for the resulting char concerning the removal efficiency of Pb²⁺. The sorption mechanisms varied according to the pyrolysis feedstock: in chars from feedstock with pine, chemisorption involving complexation with oxygenated surface functional groups followed by cation exchange was the presumable mechanism. In tire rubber derived chars, cation exchange with Ca²⁺, K⁺, and Zn²⁺ played the major role on Pb²⁺ sorption.