Solidification/Stabilization of Heavy Metal-Loaded Red Muds and Fly Ashes

Red muds and fly ashes, used as immobilization agents for heavy metal ions in aqueous solution, were loaded to saturation with Pb(II), Cd(II) and Cu(II), and solidified by cement-based CFS technology to hard concrete blocks which should not pose any risk to the environment. The setting and hardening characteristics of mortars as well as the flexural and mechanical strengths of the solidified specimens were optimized with respect to the dosage of natural and metal-loaded solid wastes. The fixed metals essentially did not leach out into water over extended periods. The matrix-disrupting effect of lead was eliminated by adding NaAlO₂, Ca₃(PO₄)₂ or Ca₃(PO₄)₂+CaCl₂ at optimal dosages so as to improve the setting, hardening and mechanical properties of the final concrete block. © 1997 SCI.