[Adsorption of Pb²⁺ and Cd²⁺ from Aqueous Solution Using Vermicompost Derived from Cow Manure and Its Biochar]

Using vermicompost (CV) as raw material, its biochar (CVC350) was prepared at 350℃ and then their physio-biochemical properties were characterized. Furthermore, adsorption studies were performed in a batch system for removing Pb²⁺ and Cd²⁺ ions from solution. The characterization results revealed much higher surface area, smaller pore size, greater aromaticity and nonpolarity of CVC350 as compared to CV. Batch adsorption experiments revealed that both the adsorption of Pb²⁺ and Cd²⁺ onto CV or CVC350 fitted Langmuir isotherm model very well, and the maximum adsorption capacity of Pb²⁺ was in the order of CVC350>CV, but no difference was observed for the adsorption capacity of Cd²⁺ between CV and CVC350. The desorption studies showed that both CV and CVC350 had much higher adsorption rate for Pb²⁺ than that for Cd²⁺, and the Cd²⁺ adsorbed could be more easily desorbed from CV and CVC350 compared with that for the Pb²⁺ adsorbed. Both the dynamic adsorption process of Pb²⁺ onto CV and CVC350 was a rapid process, however, the adsorption process of Cd²⁺ onto CV and CVC350 could be separated into the first rapid step and the second slower step. The adsorption capacity of Pb²⁺ or Cd²⁺ onto CV and CVC350 was only affected by the much lower initial pH of the solution, besides, the adsorption capacity of Cd²⁺ onto CV and CVC350 was relatively more influenced by the initial pH compared with that of Pb²⁺. Moreover, FTIR analysis showed that the adsorption of Pb²⁺ and Cd²⁺on CV depended on the active sites such as aliphatic alcohol, aliphatic acid,carbonates as well as phosphate while that on CVC350 mainly relied on aromatic alcohol, aromatic acid and carbonates.