Abstract: For the past 40 years various approaches have been developed to treat acid waters coming from abandoned as well as operating mining operations. System designs have evolved to meet increasingly stringent discharge permit limits for treated water, as well as to provide solid disposal within economic constraints. A treatment system for remediation of acid mine drainage (AMD) or acid groundwater (AG) requires two main steps: 1. The addition of chemicals to precipitate dissolved metals contained in the waters, and if necessary, to coagulate the precipitated solids ahead of physical separation. 2. Physical separation of the precipitated solids from the water so the water can be lawfully discharged from the site. Choosing the appropriate technology and equipment results in the most efficient plant design, the lowest capital outlay, and minimum operating cost. The goal of these plants is to discharge liquids and solids able to meet standards. The separation of solids from liquids can be achieved through various means, including gravity settling, flotation, mechanical dewatering, filtration and evaporation. As important as the liquid solids separation unit operations are, they are driven by the chemistry of the water to be treated. The content of the dissolved solids will influence the quality and quantity of the solids produced during precipitation. Thus the two aspects must be integrated, with chemistry first, then mechanical engineering. This presentation will provide an overview of a number of liquid solids separation tools currently being used to treat AMD-AG at several sites in the USA. It will also discuss how their operations are impacted by the chemistry of their particular acid water feeds. The tools used include clarifier-thickeners, solids contact clarifiers, dissolved air flotation, polishing filters, membrane filters, and mechanical dewatering devices (belt and filter presses, vacuum filters, and driers).

Abstract: An array of techniques have been developed during the last several decades to abate or control pollution by acid mine drainage (AMD) from coal and metal mines. Although most of these techniques are successful in eliminating or decreasing the deleterious effects of AMD in some situations, they are unsuccessful in others. Due to the inherent variability between mines and environmental conditions, no one abatement or treatment technique is effective on all sites, and selection of the best method on each site is difficult given the array of methods available. The techniques also vary in the type and size of problem they are capable of handling. Their individual costs, effectiveness, and maintenance are also important considerations. Therefore, accurate information is needed to understand the limitations of the various methods and their response to various site variables. Continued research is imperative for field testing of existing technologies, as well as continued development of new technologies. At present, there is no authoritative guide or manual to assist in evaluating the best technique for a given situation. In order to continue to mine coal and other minerals without harming the environment, the best science and techniques must be identified and implemented in order to minimize the production of AMD. To accomplish this goal, the Acid Mine Drainage Technology Initiative (ADTI) was organized to promote communication among scientists and engineers dealing with AMD, and to develop a consensus on the identification and optimum usage of each method. The intent is to provide information on selection of appropriate techniques for specific problems that will ultimately lead to a higher level of success in avoidance of AMD and remediation of existing sources, at a savings in cost and staff time, and with greater assurance that a planned technique will accomplish its objective. This effort will result in enhancement of mine drainage quality, improvement in stream cleanup and its cost effectiveness, and development of a mechanism for technology transfer.