Modification of cemented paste backfill with calcined layered double hydroxides for lead-containing tailings disposal

Abstract

Cemented paste backfill (CPB) is the main way to treat tailings at present. Alternative binders are necessary due to the high cost and CO 2 emission of ordinary Portland cement . Besides, the heavy metals contained in the tailings should be immobilized effectively when being used in CPB. In the present work, calcined Mg-Al-layered double hydroxides (CMA) were used to modify the properties of high-volume fly ash (FA) cement to increase its performance in CPB. Isothermal calorimetric, X-ray diffraction, and thermogravimetric analysis were used to explore the reaction kinetics and phase assembles of the binder. The properties of CPB samples were then studied. In addition, the lead (Pb) immobilization effects in CPB samples were studied using toxicity characteristic leaching procedure and semi-dynamic leaching. The experimental results proved that CMA could accelerate binder reaction by providing additional nucleation sites for hydration gel formation. It then increased the compressive strength of CPB samples. Besides, the immobilization effects of Pb were enhanced when adding CMA due to the better immobilization capacity of regenerated LDHs. • CMA provided more nucleation sites for hydration gels formation. • CMA could increase the yield stress of fresh CPB slurry. • The presence of CMA increased Pb immobilization effects of CPB. • The leaching of Pb from CPB was controlled by diffusion.