Leaching of Major and Trace Elements from Ash Beds Treated with Chemical Columns

Abstract

The efficacy of chemical columns in attenuating leaching of major and trace elements from sedimented ash beds was presented. Sedimented ash beds were formed and treated with a centrally installed sodium hydroxide (NaOH) column of 18 M concentration. After specified curing periods, leachate specimens were extracted and analyzed for elements such as Na, Ca, Mg, Fe, Ni, Pb, Zn, Cu, Cr, As, and Hg. The concentration of elements was found to be a function of the pH of the pore fluid, stabilization period, and location of the specimens. At initial days of curing, the concentration of elements increased marginally; subsequently, a considerable reduction in concentration occurred. The reaction products encapsulated the elements in matrix structures, reducing their concentration. The contamination potential ratio (CPR) was found to be a function of hydraulic conductivity, microstructure, pH of the pore fluid, stabilization period, and location. A decline in CPR value with stabilization period was primarily due to the reduction in hydraulic conductivity, encapsulation of metals in the reaction matrix, and precipitation of metal hydroxides in a highly basic environment.