Mercury removal from aqueous solutions by complexation–ultrafiltration

The separation of mercury from aqueous solutions by complexation–ultrafiltration was investigated. Polyethylenimine (PEI) was used as polymeric complexing agent. Effects of pH and chloride ions concentration on mercury retention were studied. Mercury retention depends strongly on both pH and chloride ions concentration. For neutral solutions mercury retention values close to 100% were obtained. A process allowing mercury separation and concentration was studied. It couples two ultrafiltration stages: the first one concentrates mercury/PEI complex and the second one enables mercury separation and polymer recycling. This process was experimentally tested. Results showed that it is possible to concentrate mercury ten fold while a permeate with very low mercury concentration is collected. Recycling of PEI does not modify operation performance.

In acidic medium the mercury retention strongly depends on pH and chloride ion concentration. The zero retention pH varies in the range from 1 without chloride ions and up to 5 for a 1 mol L–1 chloride ion concentration. For neutral pH, mercury retention is not affected by chloride ion concentration and the retention reaches values higher than 95%. Mercury retention close to 100% can be obtained for pHe ≥ 7 if the PEI solution is previously filtered. A process allowing mercury separation and concentration was studied. It couples two ultrafiltration steps: the first step concentrates mercury/PEI complex and the second one enables mercury separation and polymer recycling. This process was experimentally tested. In the chosen conditions, adsorption does not affect the mercury concentration step while polymer recycling is accompanied by a nonnegligible quantity of metal. Nevertheless, a concentrated solution of mercury (about 10 fold the feed concentration) is obtained in the second stage and a depleted stream is obtained from the first step.