Sorption performance of cysteine-modified bentonite in heavy metals uptake

A local clay, bentonite (N-Ben), was modified by the biologically- -based ligand, cysteine (Cys), through a simple sorption technique. The modi- fied sorbent (Cys-Ben) demonstrated affinity for soft and moderately soft heavy metal ions (HMI), such as Cd(II) and Pb(II), probably as a result of the soft basic character of the thiol ligand side chains. The resulting modified system was effective for metal binding with capacities of 0.503 and 0.525 mmol g -1 , for Pb(II) and Cd(II), respectively. Comparative batch experiments were per- formed for removing lead and cadmium from aqueous solutions. The sorption parameters were derived from a Langmuir fit to the sorption isotherms of the studied ions. The study showed that the sorption capacity of Cys-Ben was higher than that of N-Ben for these ions. The effect of pH was examined over the range 2.0-6.0. The sorption capacities of Cys-Ben showed that this modified clay is a good sorbent for the examined heavy metal ions.