Removal of zinc and cadmium from an aqueous solution using sawdust as a low-cost adsorbent: application of Plackett-Burman design

In this study, the sawdust was used as an abundant and inexpensive material for the removal of two heavy metals simultaneously from an aqueous solution. In order to evaluate the adsorbent potential of the sawdust, the effects of many operating parameters were studied. The metals considered were zinc and cadmium. The experiments were organized according to a well defined window of a statistical design of experiments. Starting from a large number of operating parameters (type, source, size and quantity of sawdust, temperature, pH, contact time, stirring speed, initial concentrations of cadmium, zinc and salt), a Plackett-Burman design was used to identify the most influential factors on the elimination performance of zinc and cadmium simultaneously with a minimum number of experiments. Effects of these factors were deduced from an interesting statistical treatment of experimental responses. For Zn sorption, the most important factors are mass of sawdust, initial concentration of zinc and time; while for Cd sorption, the most important factors are initial concentrations of zinc and cadmium, pH, mass, type and size of sawdust. The presence of cadmium decreased the removal of zinc considerably and the inverse did not happen. These effects were more remarkable for cadmium (sorption varied from 0 to 80%) than for zinc (sorption varied from 0 to 50%). These results allowed to choose the most important parameters which could be optimized using another designs of experiments, such as Box Behnken or full factorial, and response surface methodology to obtain the best performance of metals sorption.