Citric Acid Functionalizing Wheat Straw as Sorbent for Copper Removal from Aqueous Solution

Abstract

A cationic sorbent, which bears carboxyl groups of citric acid (CA) derived from esterified wheat straw, was prepared using the solid-phase esterifying technique. Copper (Cu) removal from aqueous solution with modified wheat straw (MWS) was investigated to evaluate its capacities of cation exchange and metal chelation. The effects of various experimental parameters (e.g., solution pH, Cu concentration, sorbent dose, contact time, and presence of light metal) are studied in batch experiments. The maximum value of Cu removal appeared in the range of pH 4 to 5. The percentage of Cu removal decreased with increasing initial Cu concentration. The isothermal data of Cu sorption conformed well to the Langmuir model, and the maximum sorption capacity (Q_m) of MWS for Cuwas 78.13 mg/g. For 100 mg/l of Cu solution, a removal ratio of greater than 96% could be achieved with 2.0 g/l or more of MWS. The equilibrium of Cu removal was reached within 90 min. The presence of univalent and bivalent light metal ions (Na⁺, K⁺, Mg²⁺, and Ca²⁺) did not significantly interfere with Cu removal by MWS.