Influence of sodium chloride on leaching behavior of fly ash stabilized with carbide lime

Abstract

Fly ash (FA) stabilized with carbide lime (CL) and sodium chloride (NaCl) can possess excellent mechanical properties within a short curing period. However, potential leachability of undesirable chemical constituents from FA, CL and their combinations under different proportions, densities, curing temperatures, sodium chloride and curing periods has not been investigated. In this study, acid digestion and water leaching batch tests were conducted to determine the total and water leachable chemical constituents in FA and CL. Batch tests results showed that FA could have water leachable concentrations of arsenic (As), chromium (Cr) and selenium (Se) above the drinking water limits, but CL did not contain any leachable metal concentrations. Furthermore, several series of column leaching tests were conducted with blends of FA, CL and NaCl under different conditions, using deionized water as permeant to assess the leachability of chemical constituents. The results from the column tests showed that the hydraulic conductivity (k) varies depending on the blend composition, density and curing conditions. The addition of NaCl in the mixtures affects the retention capacity of some metals (e.g., Se, Cr, and Al) in the cementitious matrix, resulting in higher concentrations of these metals in the leachate. The variation in time and temperature of curing, amount of carbide lime, and density influenced the concentration of chromium in the column leach extract. The stabilization/solidification technique allowed the reduction of the release of heavy metals.