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16 <br />• <br />SUMMARY OF WEATHERING <br />The dissolution of minerals to produce waters of high <br />Fe(II), S04 , and H+ contents and the recovery of the water <br />to natural conditions are probably as follows: <br /> A. In a rock with relatively low amounts of carbonate <br /> minerals and relatively high amounts of pyrite, the <br /> pyrite somehow dissolves, producing regions in which <br /> the water is below pH 3.5 and contains Fe(II). <br /> Oxygen has to be supplied for the dissolution. <br /> B. Bacteria begin to thrive in an environment caused by <br /> Step A and catalyze the reaction of 02 with FeS2 <br /> producing more dissolved Fe(II) and S04 and maintain- <br /> ing the pH between 2 and 3. Oxygen has to be supplied <br />• i <br />hi <br />2 <br />3 <br />b <br />h <br /> to <br />e w <br />t <br />n <br />as to <br />for this Step B and the pH <br /> for effective catalysis by microorganisms. <br /> C. If other base metal sulfides are present, their dis- <br /> solutions are accelerated by the joint action of the <br /> bacteria, H+ ions, S04ions, and the iron species. <br /> D. When the water starts flowing above ground, the <br /> action of bacteria and 02 oxidize Fe(II) to Fe(OH)3 <br /> and the pH is raised above 3.5. Most of the Fe is <br /> precipitated as well as Ag and Pb. Other base metals <br /> and S04 persist dissolved in the water. The pH of <br /> the water rises to 5=6 at this point. <br /> E. Interaction with C02 and carbonate minerals raises <br /> the pH of the water to 7-8 and the other base metals <br />• are removed from the water. Sulfate remains dissolved