Evaluation of the Kinetics of Acid Drainage by Fly Ash Grouts

摘要

The possibility of control and abatement of acid mine drainage (AMD) by Fly Ash-Lime Grout Injection (FGI) into underground mines is investigated. Lab-scale studies are completed that both demonstrate the potential of the fly-ash-lime grout to neutralize AMD and bracket the important parameters that affect the efficacy of the neutralization processes. Experimental results indicate that the fly ash-lime grout may be an effective means of ameliorating AMD. However, the long term potential of the grout may be adversely affected due to the armoring of the grout by Fe(0H)_3(s), Al(0H)_3(s) and CaSO_4). As pH of the AMD increases to approximately 8, most of the metals including manganese, aluminum, iron, barium, zinc, and magnesium precipitate. The precipitation of manganese at a relatively low pH·may be attributed to the formation of a solid-solid solution between MnCO_3 and carbonate phases of the grout, physical removal of the Mn species by iron and aluminum hydroxide flocs, and adsorption of the Mn species on the grout. Unlike other metals, sodium, potassium and strontium concentrations in the AMD increase with time. However, no trace metals are leached from the fly ash in excess of current regulatory limits. The effectiveness of the FGI technology is shown to depend on the reactive surface area of the grout, surface area to AMD-volume ratio, residence time of the AMD, lime content of the grout, and influent pH, acidity and metal concentrations of the AMD. Higher reactive surface area, lower surface area to AMD-volume ratio, and higher lime content speed up the neutralization kinetics. Higher initial iron or aluminum concentration slows down the neutralization process, as precipitation of Fe(OH)_3(s) and Al(OH)_3(s) produces acidity.