Removal of zinc using foundry sand waste in packed columns

Abstract

The released of heavy metals such as zinc in wastewater is of significant effect due to its potential to cause environmental and human health problems. The USEPA has classified zinc as one of the most common metal of concern at superfund site. This metal is also present in streams from industrial processes at concentration of 7.2-1500 mg/1 which is well above the USEPA standard of 5 mg/1. The objectives of this study were to investigate the column performance of foundry sand as medium for zinc removal in a continuous flow system and to generate a set of data that can be used for column design. Foundry sand was investigated as a new sorbent for zinc removal in aqueous solutions. It was collected from local foundry factories in Saraburi province, Thailand, and was packed at density between 1.04-1.05 g/cm3 in a column with the depth and diameter of 300 and 25 mm, respectively. The results of the column study indicated that the removal capacities of various bed heights 25, 21.5, 18, and 14.5 cm at flow rate of 6 ml/min were 0.61, 0.66, 0.5 and 0.48 mg/g, respectively. A bed height of 25 cm and flow rate of 6 ml/min resulted in maximum zinc removal. Studies carried out to investigate the effect of flow rates (6, 11, and 15 ml/min) at the optimum bed height of 25 cm indicated removal capacities to be 0.61, 0.45, and 0.48 mg/g respectively. It was found that the change in concentration affected breakthrough time and exhaustion time but posed no effect of column capacities of foundry sand. An initial concentration of 60 mg/1 caused shorter breakthrough and exhaustion times than 30 mg/1. The study on the effect of pH to the removal capacity of foundry sand indicated that at pH 5 removal was higher than a pH 3 (0.66, and 0.29 mg/g of initial pH 5 and 3, respectively). Finally, the study showed that mode of column operation, up-flow and down-flow, resulted in almost the same removal capacity; however, down-flow mode had shorter breakthrough time.