Abstract: A method for passivating sulfidic iron-containing rock comprising: contacting sulfidic iron-containing rock with a magnesium-containing substance, a manganese-containing substance, and a calcium-containing substance; and adjusting the pH of the system to below about 11, is provided. The method can be used to prevent acid rock drainage of metal-bearing rocks or to produce a pretreated ore or rock which can be contacted with a lixiviating agent to extract metals from the pretreated ore or rock.

Abstract: A method for removing a selected heavy metal ion from an aqueous solution is provided herein. Said method comprises contacting the solution with collophane at a pH effective for capture of the selected heavy metal ion by the collophane. Heavy metal ions include Sb.sup.2+, As.sup.3+, Cd.sup.2+, Cr.sup.3+, Co.sup.2+, Cu.sup.2+, Fe.sup.3+, Pb.sup.2+, Mn.sup.2+, Hg.sup.2 +, UO.sub.2.sup.2+ or Zn.sup.2+, preferably Fe.sup.3+, Pb.sup.2+, and Hg.sup.2+, As.sup.3+ and UO.sub.2.sup.2+. The process is pH-sensitive and selective removal of desired heavy metal ions may be achieved by varying pH and other conditions to favor removal of the desired ions and leave other heavy metal ions whose removal is inhibited under such conditions in solution.