REDUCTION OF TRACE-ELEMENT CONCENTRATIONS IN ALKALINE WASTE POREWATERS BY DEDOLOMITIZATION

Dolomite [CaMg(CO3)2] addition to alkaline waste materials, such as high lime content fly ash, is proposed as a method to reduce the concentrations of undesirable elements in leachate waters. The results of this study indicate that dolomite, in the presence of portlandite [Ca(OH)2], undergoes conversion to an assemblage of brucite [Mg(OH)2] and calcite (CaCO3) in unstirred pastes reacted for 8 months. Calcite coated the surfaces of reacted dolomite fragments while brucite occurred as individual acicular crystals. The generation of calcite can reduce porewater concentrations of certain trace elements through coprecipitation mechanisms. The results of experiments conducted in this study showed moderate uptake of B and Se by precipitating calcite. Arsenic was included in this evaluation, but the high pH of the reaction solution resulted in its immediate precipitation as basic calcium arsenate [Ca4(AsO4)2(OH)2.4H2O]. The potential of dedolomitization to reduce the concentrations of other undesirable elements in alkaline waste porewaters needs to be investigated. Dolomite is readily available in many areas of North America and can be easily processed to yield a fineness that is reactive when mixed with alkaline waste material.