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A3 <br /> I <br /> and Morin, February 14-18 , 1982 ) . Since the rate of ground water <br /> flow is slow relative to the rate of calcite dissolution , the <br /> ,result is a slowly moving displacement acid front. <br /> 3 <br /> t <br /> Calcite dissolution may also take place by means of an anaerobic <br /> ` reaction wherein calcite reacts with ferrous iron to form ferric <br /> carborrate ( siderite) with the resultant liberation of calcium <br /> ion. By this means , calcite reacts with ferrous iron to remove <br /> iron from solution by the in place precipitation of ferric <br /> f carbonate. <br /> Geochemical precipitation pathways are , of course, reversible by <br /> dissolution , but in many instances. the chemical conditions <br /> necessary for the reversal (such as a pH of 2) are extremely rare <br /> or unlikely in natural geochemical environments (Wilson and <br /> Rouse, May 2 , 1980) . Precipitation of metal hydroxides as a <br /> result of increasing pH has been studied by a number of <br /> investigators. Rouse (October, 1976 ) presents a summarization of <br /> the process and notes that the various metals are sequentially <br /> removed as a result of elevated pH. Iron is the earliest metal <br /> hydroxide to be removed as a result of elevated pH values , <br /> followed in turn by aluminum, copper, zinc and finally manganese. <br /> In recent work in the Globe-Miami area of Arizona , several such <br /> sequential precipitation plumes have been identified downgradient <br /> of copper mining operations ( Envirologic Systems , Inc. , May <br /> 1983). Radiochemical pollutants tend to coprecipitate with the <br /> metal hydroxides. <br />