MERCURY REMOVAL FROM CHLORO-ALKALI PLANT WASTE-WATERS BY ION-EXCHANGE

Equilibrium and kinetic studies of mercury extraction by ionic exchang e with Lewatit MP 64 (anionic resin) and Lewatit TP 214 (cationic resi n) were carried out in batch tests, using Erlenmeyer flasks and an orb ital shaker. Synthetic solutions were used to simulate the composition of waste waters produced in chloro-alkali plants. The influence of te mperature, stirring level, chloride and sulphate concentration on equi librium and on kinetics were studied. Equilibrium tests were carried o ut using different amounts of resin for the same volume of solution wi th different chloride and sulphate concentrations. In kinetic studies, the influence of stirring and temperature was studied. The results sh ow that for a stirring speed lower than 250 rpm, the rate of mercury e xtraction is affected by the level of stirring, and the kinetic proces s depends on the diffusion in solution. However, for higher stirring s peeds, the process is also controlled by the diffusion inside the resi n grains. Using the kinetic data, the effective diffusivities of mercu ry species in solution and inside the resin grains were estimated. The increase in temperature affects favourably the kinetics of the proces s, 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 we re, respectively, 8.1 and 9.3 kJ mol(-1).