Factors Associated with the Optimal Resource Recovery of Mine Drainage Precipitates From a Passive Remediation Wetland System.

Acid mine drainage (AMD) from coal mines pollutes over 3000 km of Pennsylvania streams. These discharges currently produce at least 20,000 tons per year of iron-rich precipitates that either pollute streams or are collected in constructed ponds and wetlands. Traditionally considered to be a waste product, these precipitates can be recycled for use as pigments, soil amendments and toxic metal sorbents. We are investigating the relationship between the geochemistry of AMD and its precipitates within a constructed wetland system to properties such as color variation and metal sorbent capacity. Samples were obtained from a passive treatment system near Lowber, western Pennsylvania. The remediation system, constructed in 2006, employs six ponds and a wetland. Dissolved oxygen, pH, temperature and alkalinity were measured in waters; thermogravimetric analysis, surface area, and micromorphology were determined for the precipitates. Elemental analysis was performed on waters and precipitates. Our preliminary results indicate that the AMD precipitates can contain iron concentrations greater than or equal to those in commercial pigments, and can produce pigment of uniform color and purity over the life of the treatment system. Some trace metals in the precipitates, such as arsenic, decrease in concentration from the first pond to the final wetland. Crystal morphology and iron oxide surface area changes throughout the treatment system. The goal is to employ these parameters to optimize production of commercially useful products. This will aid in developing new wetland system designs to increase the value of AMD residuals, and/or methods to improve pigment quality or sorbent properties of previously unmarketable AMD precipitates. If successful, mine water treatment could, in some cases, be self-sustaining.