Optimization of the Adsorption of Cadmium and Copper Ions from an Aqueous Solution by Alum Sludge

This work aims to reuse waste from drinking water treatment plants that use alum, called alum sludge (AS). By calcining alum sludge (CAS) at 550 °C for two hours, then using it to adsorb the heavy metals copper and cadmium from their aqueous solutions with the batch adsorption method. The ability of CAS to remove Cd (II) and Cu (II) was studied under the influence of several factors (i.e., initial concentration of metal ions, contact time and CAS dosage) by using Box-Behnken experimental designs (BBD) for the response surface methodology (RSM) and with statistical analysis (ANOVA). Then, identify the optimal conditions that produce the maximum removal. The AS, which has been dried and ground was characterized by chemical method analysis (SEM, XRD, and EDX). At optimum conditions, the maximum removal percentages of Cu and Cd reached 92.5% and 98.8%, respectively. The adsorption isotherms for Cu data followed the Langmuir model, while the Cd data fitted well with the Freundlich and the Langmuir models. For each Cd (II) and Cu (II), the maximum monolayer adsorption capacity was 29.101 and12.45 mg/g, respectively. The pseudo-second-order kinetic model provided a good match to the kinetic data. It was found that water treatment sludge is a good source from which to create an inexpensive adsorbent to remove heavy metal ions from wastewater.