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RECEfVi:D <br />The primary requirements for acid generation are: <br />1. sulfide minerals in the overburden <br />2. water or a humid atmosphere <br />3. an oxidant {usually oxygen in the tone of Oz) <br />The primary factors which determine the rate of acid generation are: <br />1. pH <br />2. temperature <br />3. oxygen content of the gas phase, if saturation is less than 100% <br />4. oxygen concentration in the water phase <br />5. degree of saturation with water <br />8. chemical acttvily of Fe" <br />7. surface area of exposed metal sulfide <br />8. chemical activation energy required to initiate add generation <br />9. biological activity (such as iron oxidizing bacteria) <br />FEB 2 7 2007 <br />Division or reclamation, <br />Mining and Safety <br />Acid Producing Potential - In nature, exposed sulfide minerals read with oxygen and water to <br />produce add. A simplfied version of this reaction is <br />4 FeS=(.~ + 15 Oa,gr + 14 HZOr~r -- 4 Fe{OH)~.~ + 8 SOS'"r,or + 16 H'r.~r (1) <br />This reaction is too slow to observe in the latwrattxy. We will use a strong oxidant, hydrogen peroxide, <br />to increase the kinetics of the reaction. The H2Oz can be thought of as supptying the Oz and Hz0 in a <br />more reactive forth; in fad, the decomposition reaction (2 H2Oz -i OZ + ZH2O) does oxur naturally. <br />Substituting hydrogen peroxide into the balanced equation gives <br />4 F25Z(St + 30 H2O2(eQl ~ 4 Fe(OH)s,~ + 8 SO.Z (rar + 16 H'r+ar * 16 H=Orq (2) <br />Mine overburden material may also contain buttering capabilities in the forth of eaidum carbonates. <br />This woultl have a function of neutralizing the add pnxiudng potential of the sulfide minerals. A <br />simplified set of chemical equations showing this fs <br />CaCO~,~ + 2 H'(,q~ + S0,2'(„ r -i CaSOn,~ + H=COs.,~ (3) <br />H2CO~pr ++ HzO~,r + COaor (4) <br />Add production aril neutralization may be occurring at the same time in the mine tailings. Generally, <br />the rate of add production exceeds the rate of add neutralization. A common treatment fw add <br />produdng mine overburden is to amend it with lime (caldum carbonate). You will need to know the <br />add produdng potential of the overburden pile so you can determine how much ealdum carbonate to <br />add to the tailings pile. <br />To determine the neutralizing potential of a sample, a known amount of hydrochloric add is added to <br />the sample and heated. The amount of add neutralized by any carbonates in the sample is determined <br />by bads titration. <br />As you can imagine, there is a wmplex set of chemical and biological reactions and conditions that <br />ocau over time }n mine overburden which determine its potential pollutlon generating capabilities. )n <br />