Rigorous controls on levels of mercury in drinking water and increased monitoring mandated by the Safe Drinking Water Act urged an investigation into practical treatment techniques for lowering mercury levels in water. Aqueous solutions of mercury were treated by various combinations of activated carbon, EDTA, tannic acid, citric acid, and calcium. Samples close to neutral pH allowed the most effective treatment; quite small additions of tannic acid dramatically increased treatment success, as did progressively higher concentrations of calcium ions.
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Thiem et al. (1976) studied this question.