| Mercury (Hg) is widely used in industries and manufacturing processes. Unfortunately, mercury vapor during industrial processes, mercury-containing wastes, and leakage from waste treatment systems have transported mercury into the environment. In the environment, microorganisms methylize inorganic mercury into organic mercury, such as methylmercury. Methylmercury ingested by humans through food sources such as contaminated fish and shellfish can cause liver, kidney, and blood cell damage, and accumulate in the central nerve systems.; Mercury is hydrophobic, associating with solids in natural waters. A series of carefully controlled laboratory experiments in this research were conducted to find the relationship between the mercury adsorption and pH and total chloride concentration. A strong relationship was found and formulated as a set of predictive equations for estimating adsorption under specific conditions.; The resulting model equations describe the effects of pH and total chloride concentration on the mercury adsorption well. They confirm many findings of other researchers, and establish a conceptual model of the affinity between the mercuric species and the solids adsorbents. The equations further reveal how the hydroxide and chloride ions compete with each other for mercuric ion complexation as a result of adsorption change. Through competitive complexation, the degree of mercuric hydroxide complexation with respect to mercuric adsorption is defined. The results show that lightly hydroxide complexed mercury, e.g., HgOH+ and Hg2(OH)3+, increase as the maximum mercuric adsorption moves toward its peak value due to the change in chloride and hydroxide ion concentrations. pH reductions observed in the experimental data further support that hydroxide ions are involved with the adsorption.; Graphical depictions of the empirical formulations allow simple estimation of mercuric partition coefficients under various pH and total chloride concentrations. The resulting partition coefficients can be used in suspended solids transport models to estimate mercury distribution. Since the empirical models focused on only two of the important environmental parameters that control adsorption, studies of other factors such as oxidation-reduction potential and organic content are necessary to expand and increase the utility of the empirical models. |
