FACTORS THAT FAVOR THE DEVELOPMENT OF FERRUGINOUS COATINGS FROM ACID MINE DRAINAGE

Acid Mine Drainage, AMD, is mine water discharge characterized by low pH and a high concentration dissolved metals. These conditions are created by the oxidation of sulfur bearing minerals in coal. A typical feature of AMD is the precipitation of Fe(III) oxyhydroxides called “yellowboy.” Iron oxyhydroxides, FeO(OH), can occur as either a surface coating or as suspended colloidal material. The objective of this study is to identify the factors that favor the formation of ferruginous coatings and examine the physical, chemical, and biological controls in the formation of iron hydroxide surface coatings. Blocks of various lithologies and surface textures were placed in five areas of AMD at an abandoned coal mine in Strasburg, Tuscawaras County, Ohio. The site is characterized by both AMD from an underground coal mine and surface runoff from a spoil pile. Chemical analysis was conducted on water samples from the five areas of the site. The pH ranged from 1.80 to 6.64, dissolved oxygen ranged from 0.6 to 9.71 mg/L, and conductivity ranged from 2.91 to 3.70 mS. The blocks remained in situ for one to three months. After collection, the blocks were inspected to determine which lithology types and textures the precipitate best adheres to. A qualitative investigation was also carried out to identify the biologic organisms present and their potential influence on the precipitate. Initial results indicate precipitate adsorption is greater on rough, silica-rich surfaces. The coatings were best developed in the areas characterized by acidic surface runoff. Algae, specifically species of Mougeotia, are associated with areas of high iron hydroxide precipitation. The results of this study could lead to the development of new AMD remediation methods. Surface coatings are preferred over colloidal suspension because they can more readily be removed from the environment. Also, it may provide a possible avenue for the recovery of valuable metallic ions.