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A small fraction of zinc will exist in the aquatic phase as soluble inorganic zinc compounds (e.g., zinc <br />chloride, zinc sulfate). Soluble inorganic zinc compounds hydrolyze in solution, forming zinc hydroxide <br />precipitates. Hydrolysis may lower pH, but the buffering action present in most natural water prevents a <br />significant alteration in pH. The precipitation of zinc hydroxide and zinc carbonate was studied by <br />Patterson et al. (1977), who found that zinc hydroxide precipitates faster than zinc carbonate. Zinc <br />carbonate is soluble in pure water at 25 °C at concentrations of _ mg zinc /L. The hydroxide is soluble <br />only at concentrations of 50.2 mg zinc /L. As a result, some of the inorganic forms of zinc that are <br />expected to be present in water are basic carbonate (Zn2[OH]2CO3), hydroxide (Zn[OH]2), and silicate <br />(Zn2SiO4) (Florence 1980; NAS 1977). When the pH is A, most of these compounds will precipitate; <br />however, as the pH decreases, more and more of these compounds will dissolve and remain in the water <br />phase (EPA 1979d). <br />Zinc sorbs strongly onto soil particulates. Little water - soluble and exchangeable heavy metals were <br />found in soil irrigated with raw waste water (Schalscha et al. 1982). Although considerable amounts of <br />metals were added to the soil in soluble and exchangeable forms during waste -water irrigation, they were <br />converted into the less chemically active forms (i.e., organically bonded and inorganic precipitates). <br />Further examination showed that zinc accumulation in soil resulting from waste disposal occurred <br />primarily as inorganic precipitates. <br />Zinc is an active reducing agent for many metal ions such as iron (Fe +3) and <br />permanganate (Mn042) ions (Stokinger 1981). As a result of the reducing reactions, the manganese <br />oxides and ferric salts may precipitate and, in the process, may entrap soluble zinc in the precipitate, <br />thereby reducing the zinc concentration in the water phase. <br />1.2 Methods of lowering zinc in the mine water: <br />None of the data available shows exactly why the zinc levels are dropping in the mine water <br />channel, but it shows that the zinc levels do drop over time and distance. Because of this, Star Mine <br />Operations believes that the best methods for reducing the presence of zinc in the mine water <br />discharged from the tunnel are: a) encourage precipitation of zinc in the Revenue Tunnel mine <br />ditch, b) storage and dilution of mine water in a pond, and c) source control underground by sealing <br />off poor water quality contributions. <br />a) It is believed from the zinc solubility chemistry that the 3700 feet length from the Atlas drift <br />to the Revenue Mine portal can be enhanced with organic material, magnesium rich rocks <br />and other material which will encourage zinc precipitation. Much is already occurring, but <br />SMO can probably improve it by taking these steps. <br />Revenue Mine August 2012 T -6 <br />