acid neutralization and oxidation and precipitation of the resulting metal flocs. Before selecting an appropriate treatment technology, the AMD conditions and chemistry must be characterized. Flow, acidity and alkalinity, metal, and dissolved oxygen concentrations are critical parameters. This paper reviews the current state of passive system technology development, provides results for various system types, and provides guidance for sizing and effective operation.Keywords Anoxic limestone drains · Bioreactors · Limestone leach beds · Low-pH Fe oxidation channels · Open limestone channels · Wetlands
Acid Mine DrainageOxidation of pyritic materials during and after mining produces sulfuric acid and metal ions. These products react with host rock and surface and groundwater to create a range of water chemistries from pH 2 to 8 and elevated ion concentrations. Such waters have traditionally been called acid mine drainage (AMD) and alkaline mine drainage. I n this paper, we use AMD when the water is acidic and state clearly in the text when the water being referred to is not acidic. When AMD enters surface water bodies, biotic impairment often occurs through direct toxicity, habitat alteration by metal precipitates, nutrient cycle alterations, or other mechanisms, and the water often becomes unsuitable for domestic, agricultural, and industrial uses. The process of pyrite oxidation and its effects on water resources have been known for centuries (Nordstrom 2011;Seal and Shanks 2008) and AMD is a worldwide concern (Younger and Wolkersdorfer 2004). Damaging effects of AMD have been described by researchers in Asia (David 2003; Wei Abstract When appropriately designed and maintained, passive systems can provide long-term, efficient, and effective treatment for many acid mine drainage (AMD) sources. Passive AMD treatment relies on natural processes to neutralize acidity and to oxidize or reduce and precipitate metal contaminants. Passive treatment is most suitable for small to moderate AMD discharges of appropriate chemistry, but periodic inspection and maintenance plus eventual renovation are generally required. Passive treatment technologies can be separated into biological and geochemical types. Biological passive treatment technologies generally rely on bacterial activity, and may use organic matter to stimulate microbial sulfate reduction and to adsorb contaminants; constructed wetlands, vertical flow wetlands, and bioreactors are all examples. Geochemical systems place alkalinity-generating materials such as limestone in contact with AMD (direct treatment) or with fresh water upgradient of the AMD. Most passive treatment systems employ multiple methods, often in series, to promote 1 3Mine Water Environ (2017) 36:133-153
Benzoic acid, sorbic acid, and sodium lauryl sulfate at low concentrations (5 to 10 mg/liter) each effectively inhibited bacterial oxidation of ferrous iron in batch cultures of Thiobacillusferrooxidans. The rate of chemical oxidation of ferrous iron in low-pH, sterile batch reactors was not substantially affected at the tested concentrations (5 to 50 mg/liter) of any of the compounds.
US government regulations require that all effluents from industrial operations, including mining, meet certain water quality standards. Constructed wetlands have proven to be useful in helping to attain those standards. Application of this biotechnology to mine water drainage can reduce water treatment costs and improve water quality in streams and rivers adversely affected by acidic mine water drainage from abandoned mines. Over 400 constructed wetland water treatment systems have been built on mined lands largely as a result of research by the US Bureau of Mines. Wetlands are passive biological treatment systems that are relatively inexpensive to construct and require minimal maintenance. Chemical treatment costs are reduced sufficiently to repay the cost of construction in less than a year. The mine waste water is typically treated in a series of excavated ponds that resemble small marsh areas. The ponds are engineered to facilitate bacterial oxidation of iron. Ideally, the water then flows through a composted organic substrate supporting a population of sulphate‐reducing bacteria which raises the pH. Constructed wetlands in the USA are described ‐ their history, functions, construction methodologies, applicabilities, limitations and costs.
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