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Publication Date: 2017-Feb-28
Document File: 5 page(s) / 118K

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A process of ion-exchange treatment of the by-products of acid mine waste water for beneficiation is described. Removal of calcium and magnesium from the feed water results in more valued sodium salts in the cationic products. This thus results in reduction of reagent requirement along with increase in the valuable product yield, thereby improving the overall economics of the treatment. The process separates the ammonium chloride from the ammonium sulfate product. By separating ammonia from the ammonium chloride and recycling it, the process solves the problem of valuable ammonia going waste in the products.

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Acid mine drainage (AMD), sometimes referred to as Acid Rock Drainage  is a common effluent from the mines in which sulphidic minerals are present and which can form sulphuric acid and metal sulphates. Acid mine drainage (AMD) is low pH water arising from oxidation of iron and other sulfides to sulfuric acid.  There are a wide variety of such effluents from the metal mines or coal mines, highway construction and deep excavations and the composition of these effluents varies widely regarding the toxic constituents presents. If untreated AMD can seriously pollute water resources and land areas.

 Present methods of treating Acid Mine Drainage generally require extensive capital outlay, are expensive to operate and are specific in their application to a particular effluent. For this reason, Acid Mine Drainage is often only partially treated or left untreated in underground or open reservoirs. The water component from both partially treated effluent and untreated effluent is kept in open reservoirs and is allowed to evaporate. This is quite unsatisfactory in that the toxic constituents remain and often leak from the reservoirs, and in that much water is wasted in the process.

Currently Acid Mine Drainage is pre-treated using a high density separation (HDS) process producing a sludge product (stored in open reservoirs) and Neutralised mine drainage (NMD). Currently this Neutralised Mine Drainage is either discharged into rivers or used as agricultural water, neither of which is considered to be environmentally sustainable. Further processing the Neutralised Mine Drainage can be achieved through reverse osmosis (RO) or biological processes (both produce additional toxic waste) for use as potable or agricultural water. No other saleable products are produced in significant quantities.

Current Acid Mine Drainage treatment solutions are not economically viable. The operational cost of current High Density Separation technologies exceeds the revenue and this cost is exacerbated when used in combination with Reverse Osmosis and/or biological solutions to further treat the Neutralised Mine Drainage. All of the aforementioned treatment solutions are considered to be environmentally unsustainable as both produce a toxic waste to be stored in slimes dams and/or discharge a potentially hazardous liquid effluent into the environment.

Prior attempts were made to treat AMD by using Nanofiltration (NF) and eutectic crystallization. Ammonium chloride could be separated by ammonium sulfate by using nanofiltration. NF removes the monovalent ions from the divalent ions in the solution. However, NF does not remove the ions completely, and also it generates close to 50% of the feed solution as waste, and this needs to be disposed. Eutectic crystallization is used to separate the chlorides from the sulfates, but it is not a proven process.


As a potential treatment for acid mine draina...