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Laboratory study of the coating method to control ARD generation Jia, Weiyi

Abstract

This study proposed a new approach in preventing ARD generation by coating rock surfaces to exclude moisture and oxygen. Four market-available materials, two of them epoxy based, one aromatic based, and the other silicon based, were tested with five different test conditions and techniques. Six ARD generation tests were carried out to study the characteristics of the rock samples. The rock samples showed a strong ARD generating potential. The pH value and metal concentrations of the rock samples were near these observed in field measurements. The water to rock ratio influenced ARD generation significantly. The higher the rock to water ratio, the lower the pH value, and the higher the metal concentrations. Five testing methods and techniques were carried out to study the coating material's ability to prevent ARD generation. In the coating capacity test, coating materials, epoxy-41, epoxy-43, and aromatic-W were tested with the agitation of water circulation. There was no significant difference amongst the three samples in pH and metal concentration. The freezing and thawing test was designed to study the performance of materials during and after freezing and thawing cycles, the heating and cooling test for heating and cooling cycles. No significant alterations were identified on the surface of the coating materials during the tests. The freezing and thawing, and heating and cooling had no influence on the material capacity tests. However, silicone-S showed a much greater value of metal concentrations and much lower values of pH than the other three. The bonding capacity test was designed to study a material's ability to adhere to the rock surface and hold adjacent, rocks together. All three materials, epoxy-41, epoxy-43, and acetone-W, showed a high performance, in which acetone-W was the best. The thin section technique was used to visually observe the coating layers on the rock surface. Ten thin section samples coated with all four coating materials (epoxy-41, epoxy-43, acetone-W, silicone-S) under different test conditions (coating capacity test, freezing and thawing test, and heating and cooling test) were observed. No significant difference among the coating materials was found. Through the above-mentioned tests and analysis, this preliminary study evaluated the performance of coating materials in preventing ARD generation using the coating method. The recommended coating materials in order of performance were acetone-W > epoxy-43 > epoxy-41. Silicone-S was not an appropriate material for the coating method.

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