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8 <br />from the other weather reactions is that it generates hydrogen <br />• ions making the water more acidic. The other weathering <br />reactions work towards buffering the water; reaction 12 works <br />in the opposite direction. Precipitation of goethite will <br />keep the water at a pH of around 5 rather than 7 (6, 8, 16). <br />Pyrite is a mineral which contains Fe(II) and sulfur as <br />S22 The weathering reaction 13 shows that S22 is oxidized <br />to S04 when pyrite dissolves. Hydrogen ions are also <br />released when this reaction occurs. In addition, it is found <br />that Fe(III) will also react to dissolve pyrite. <br />FeS2 + 14 Fe 3+ + 8H20 -} 15 Fe 2+ + 2SO4 + 16 H (14) <br />The complete model for the dissolution of pyrite was proposed <br />by Stumm and Morgan (6) and is shown below: - <br />Fe(II) + S22 <br />+02 (g) a? <br />FeS z (s) + 02 ( g) a --- ? S04 + Fe(II) + H+ <br />+02(g) b d + FeS2(s) <br />slow fast <br />Fe(III) f Fe(OH)3(s) + H+ <br />c <br />The immediate results of this weathering mechanism are two <br />possible types of water: <br />A. Fe(III) water of a pH about 5 which is in association <br />with Fe(OH)3 sediment. <br />B. Fe(II) sulfate water of a pH of 3 or less. <br />0