Removal of heavy metal ions from aqueous solutions by a local dairy sludge as a biosorbant

In this work, the removal of lead and cadmium from an aqueous solution by a local dairy sludge was investigated in a batch system. Biosorption of these heavy metals was studied as a function of solution initial pH, equilibrium time, temperature, biosorbent dose, biosorbent particle diameter and initial metal ion concentration. Maximum sorption was observed at a pH value of 5 and a temperature of 40 °C. Equilibrium uptake increased with increasing metal ion concentration for both metals with a maximum sorption capacity of a 148.6 mg/g for Pb (II) and 66.7 mg/g for Cd(II). The Langmuir model was found to better describe the sorption of lead ions with a correlation factor of 0.99 while Freundlich and Temkin models were better for Cd(II) sorption. The temperature increase from 20 to 40 °C enhanced the uptake of Pb(II) by 20% and Cd(II) by 5%. The sorption kinetics were compatible with the pseudo-second order model for the systems investigated. SEM micrographs were determined before and after sorption. Nitric and hydrochloric acids were used for the metals desorption. Pb(II) was better desorbed by nitric acid whereas Cd(II) was eluted slightly better by chlorhydric acid.