Modeling fixed bed column for cadmium removal from electroplating wastewater

摘要

Removal of cadmium by xanthated chitosan was investigated in a packed bed up-flow column. The experiments were conducted to study the effect of important design parameters such as bed height and flow rate. At a bed height of 9 cm and flow rate of 3 ml min~(-1), the metal-uptake capacity of xanthated chitosan and plain chitosan flakes for cadmium was found to be 132.3 ±1.5 and 40.1 ±0.5 mgg~(-1) respectively. The bed depth service time (BDST) model was used to analyze the experimental data. The computed sorption capacity per unit bed volume (N0) was 2.19 and 14.6 gl~(-1) for plain and xanthated flakes respectively. The rate constant (K_a) was recorded as 0.5514 and 0.04181 mg~(-1) h~(-1) for plain and xanthated chitosan respectively. In flow rate experiments, the results confirmed that the metal-uptake capacity and the metal removal efficiency of plain and xanthated chitosan decreased with increasing flow rate. The Thomas model was used to fit the column sorption data at different flow rates and model constants were evaluated. The column regeneration studies were carried out for two sorption-desorption cycles. The eluant used for the regeneration of the sorbent was 0.01 N H2SO4. A decreased breakthrough time and an increased exhaustion time were observed as the regeneration cycle progressed, which also resulted in a broadened mass transfer zone. The column was successfully applied for the removal of cadmium from electroplating wastewater. Three hundred sixty-seven bed volumes of electroplating wastewater were treated in column experiments using this adsorbent, reducing the concentrations of Cd(II) from 10 to 0.1 mgl~(-1).