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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 Sze 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 />FeSz + 14 Fe 3+ + 8H2O -} 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 />• <br />Fe(II) + S22- <br />+12(g) at <br />a _ + <br />FeS2(s) + 02(g) S04 + Fe(II) + H <br />+02 (g) b d + FeSz (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.