zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA A study was conducted to evaluate two chemical models of iron oxidation. The first model was proposed by U. S. EPA in 1983 for use in the design of acid mine drainage (AMD) treatment systems. This model expresses the oxidation rate as a function of ferrous iron, oxygen concentrations, and pH. The second model was proposed by the U. S. Bureau of Mines and expresses the oxidation rate as a function of a treatment system's oxygen transfer rate. The findings of the study were that the model based on oxygen transfer was accurate in predicting oxidation rates over a wide range of initial ferrous iron concentrations. The predictions of the EPA model were inaccurate in modeling iron oxidation.zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Water Environ. Res., 64, 817 (1992).

A pipeline treatment system, previously used to treat coal mine drainage, was tested at pilot-and full-scale to determine its effectiveness in treating a copper-zinc bearing metal mine drainage in northern California. The 37.85 liters per minute (L/min) (10 gpm) system consisted of a jet pump and static mixer, arranged in series. Three alkaline reagents were each evaluated at four treatment pH values. An additional reagent mixture was evaluated at one treatment pH value. Initial copper, zinc, and cadmium concentrations were 100, 450, and 1.7 milligrams per liter (mg/L), respectively. Post-treatment concentrations for these metals were below detection limits for soluble metals using the inductively-coupled plasma spectroscopy (ICP) method, regardless of reagent used, when the treatment pH was in the 9.0 to 10.0 standard unit range. A full-scale version of the pipeline system was constructed and operated at 1,136 L/min (300 gpm) for approximately 5 months. Calcium hydroxide slurry was introduced at the jet pump to achieve a pH of 9.5 to 10.0 standard units. The system removed between 97% and 99% of copper, zinc, cadmium. Based on these studies, it was concluded that 1) pipeline treatment is a viable approach to metal mine drainage treatment, 2) establishing a treatment pH in the 9.0 to 10.0 standard unit range was critical for metals removal, and 3) treatment in the In-Line System (ILS) may involve coprecipitation mechanisms.Additional

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