Interaction of Inorganic Leachate with Compacted Pozzolanic Fly Ash

Abstract

This paper presents results of a study on the feasibility of using pozzolanic western coal fly ash, either by itself or mixed with sand, as a construction material for waste‐containment liners and impermeable covers. Liners can be constructed from pozzolanic fly ash or fly ash‐sand mixtures to meet the usual requirement for the permeability to be 10-7cm/s or less. This paper reports an investigation of the effects of long‐term permeation of inorganic leachate solutions on such liner materials. The effluent leachate was tested to determine changes in chemical composition (in particular pH, boron, and heavy metals) due to leaching from the liner. The inorganic solution had no detrimental effect on liner permeability; in fact, the permeability decreased over time. The main chemical change in the permeate solution is an increase in pH, because the fly ash is highly alkaline. This had the beneficial effect of precipitating the heavy metals within the liner, so heavy metals in the effluent were minimal. Overall, the use of compacted pozzolanic fly ash as a liner material appears to be feasible in terms of its physical properties and chemical attributes.