Process for removing heavy metals from aqueous solutions

A process for the removal of at least one heavy metal selected from the group consisting of arsenic, tin and lead from ground water initially substantially free of sulfuric acid and contaminated with dissolved said heavy metal, said process comprising forming a water-soluble salt of said heavy metal in solution at an acid pH by the addition to said groundwater of an inorganic water-soluble salt of a metal from Group Ib, IIb or VIII of the Periodic Table, and then adjusting the pH upward to precipitate said salt of said heavy metal, the salt formation and precipitation carried out at a temperature within the range from above 30.degree. C. to below the boiling point of the reaction solution, optionally, prior to forming the heavy metal salt, treating said groundwater with an oxidizing agent in an amount sufficient to convert any low valence said heavy metal to a higher valency and to oxidize any organic contaminants therein, before, during or after forming said water-soluble salt of said heavy metal adding a precipitation-enhancing agent selected from the group consisting of calcium sulfate, arsenic trioxide, calcium arsenate and cupric oxide to said groundwater in an amount sufficient to enlarge the average particle size of the heavy metal salt when precipitated, said precipitation-enhancing agent being present in the groundwater in crystalline form during the precipitation of said heavy metal salt, and separating the precipitate from said groundwater.