Problem-1 An industry generating wastewater that contains both ionic silver (Ag+) and ionic mercury (Hg2+) is considering two
options for discharge of the wastewater after treatment. The first option is to discharge the water through an ocean outfall (pH 8.0), in which case the initial dilution is predicted to yield concentrations of 0.04 mg/L TOTHg and 2.5 mg/L TOTAg. The second option is to discharge the treated wastewater to a large river (pH 7.0), in which the dilution would be faster and more extensive to yield concentrations of 0.003 mg/L TOTHg and 0.205 mg/L TOTAg.
??It is believed that both silver and mercury are considerably more toxic when present in solution as free metal ions (Ag+ and Hg2+) than when bound to different ligands, forming metal complexes. The major complexing ligands in the two potential receiving waters mentioned above are chloride or Cl? (19,400 mg/L in the ocean, 35 mg/L in the river) and sulfate or SO42? (2710 mg/L in the ocean, 12 mg/L in the river).
Using MINTEQ without balancing the charge difference, and a step-by-step problem solving approach: (i) determine which one of these two disposal options you would recommend, and (ii) using a few sentences (feel free to cite the literature), say why?