Mercury Removal from Chloro-Alkali Plant Waste Waters by Ion Exchange

Abstract

Equilibrium and kinetic studies of mercury extraction by ionic exchange with Lewatit MP 64 (anionic resin) and Lewatit TP 214 (cationic resin) were carried out in batch tests, using Erlenmeyer flasks and an orbital shaker. Synthetic solutions were used to simulate the composition of waste waters produced in chloro-alkali plants. The influence of temperature, stirring level, chloride and sulphate concentration on equilibrium and on kinetics were studied. Equilibrium tests were carried out using different amounts of resin for the same volume of solution with different chloride and sulphate concentrations. In kinetic studies, the influence of stirring and temperature was studied. The results show that for a stirring speed lower than 250 rpm, the rate of mercury extraction is affected by the level of stirring, and the kinetic process depends on the diffusion in solution. However, for higher stirring speeds, the process is also controlled by the diffusion inside the resin grains. Using the kinetic data, the effective diffusivities of mercury species in solution and inside the resin grains were estimated. The increase in temperature affects favourably the kinetics of the process, but decreases the final equilibrium concentration. Considering the values of effective diffusivities in the resin grains, the calculated activation energy for diffusion with the MP 64 and the TP 214 resin were, respectively, 8.1 and 9.3 kJ mol−1.