Treatment of mercury in wastewter from condensate tank of petrochemical industry by ion exchange

Abstract

This study focuses on treatment of mercury in wastewater from condensate tank of petrochemical industry by ion exchange process in order to reduce mercury concentration in the wastewater to meet the regulatory requirement on effluent mercury level (5 ppb). In this study, optimal condition for ion exchange process, treatment efficiency, resin regeneration, design criteria for application in real operation and economic aspect were studied. Two types of resin were employed; weak acid cation exchange resin (Duolite C433) and mercury specific cation exchange resin (Amberlite IRC718). Batch study was carried out to determine equilibrium time, effect of pH, effect of exchange ion as well as adsorption isotherm. The optimal condition obtained from the batch test would be applied in the column study with varied bed depths. The results showed that Amberlite IRC718 had the capacity to reduce the mercury concentration in the wastewater down to 2.5 ppb. This is due to the fact its selectivity for mercury ions is 43,000 times higher than that for calcium ions. The optimal conditions was found at equilibrium time of 3 hours, pH 2, and resin dose of 200 grams/liter. Freundlich isotherm was unable to describe the ion exchange mechanism because of interference caused by competitive ion exchange with other ions in real wastewater. The continuous test showed that ion exchange process occurred rapidly. Although volume of resin in column was doubled, the ratio between volume of wastewater flowing through the column and volume of resin was still very low. The adsorption capacity of resin was low. This study concluded that Amberlite IRC718 was effective in reducing mercury level in the condensate wastewater to meet the 5 ppb standard.