Weathering and Leaching Characteristics of a Fixated Scrubber Sludge Cap at an Abandoned Mine Site in Pike County, Indiana

摘要

In 1996 an abandoned mine site containing a coal refuse pile, ash-filled highwall lake, and spoil was capped with fixated scrubber sludge (FSS) obtained from a nearby coal- fired power generation station. The FSS is a blend of flue-gas desulfurization sludge from an oxygen-inhibited scrubber unit, fly ash, and lime. Core samples of the FSS cap were collected and lysimeters were placed above and below the cap near monitoring wells screened in the refuse and ash fill. Mineral compositions of cores were determined, and samples of weathered and unweathered FSS were subjected to laboratory leaching experiments of 3-week duration. The experiments employed ultrapure water, synthetic regional groundwater, and synthetic acid mine drainage. Mineralogical analysis of core samples determined that the primary weathering indicators are increases in gypsum and calcite coinciding with decreases in hannebachite (CaSO3·0.5H2O), the dominant sulfur-capture mineral phase generated in an oxygen-inhibited flue gas scrubber from which the bulk of the FSS is derived. Weathering appears to be minimal since the 1996 emplacement and confined to the top of the capping material. Laboratory studies demonstrate that weathered FSS leachate generated more sulfate, boron, molybdenum, and arsenic than unweathered FSS leachate, and less aluminum, barium, nickel, and selenium. Both synthetic solutions enhanced calcium, sulfate, nickel, and boron, and suppressed aluminum, arsenic, and selenium in leachate. Weathering characteristics observed for the FSS cap after 15 years suggest negligible water interaction based on comparisons of field data with laboratory leaching potential from continuous exposure to synthetic equivalents of locally present water.