Reclamation of Sedimented Ash Deposit by Chemical Columns

Abstract

This research focuses on the potentiality of calcium hydroxide (Ca(OH)2) and sodium hydroxide (NaOH) columns in augmenting the geoengineering and geoenvironmental properties of sedimented ash beds. Model ash beds were prepared and stabilized with NaOH and Ca(OH)2 of 9 M concentration. The bearing resistance, collapse potential, hydraulic conductivity, pore characteristics, concentration of elements, and pH of the pore fluid were measured. The strength contours formed around chemical columns were found to be bell-shaped. The magnitude of strength development in the Ca(OH)2 column was relatively insignificant and limited to the peripheral region of the column, whereas it spread to a greater extent in a NaOH-treated ash bed. Calcium-based hydration compounds were found in a Ca(OH)2 column-treated ash bed whereas an ash bed column treated with NaOH displayed both geopolymeric as well as calcium-based hydration compounds. The encapsulation of leached elements in the reaction matrix reduced their concentrations in leachate. The concentration of elements in leachate was identified to be influenced by the pH value and stabilization period. Both the chemical columns were found to be effective. However, the NaOH column showed a significant improvement in bearing resistance and in situ dry unit weight along with reducing the hydraulic conductivity, collapsibility, and migration of leachable elements.