SOLIDIFICATION STABILIZATION OF A SYNTHETIC ELECTROPLATING SLUDGE IN CEMENTITIOUS BINDERS CONTAINING NAOH

Solidification/stabilization of a highly concentrated synthetic electr oplating waste sludge by cementitious mixtures containing NaOH was stu died. The sludge contained 86.2 mg/g Ni, 84.1 mg/g Cr, 18.8 mg/g Cd, a nd 0.137 mg/g Hg and before mixing was dewatered to 25% solids. It was stabilized by ordinary Type I portland cement (OPC), an OPC/Class F f ly ash mixture (referred to as CFA), and a lime/Class C fly ash mixtur e (referred to as LFA). Mix ratios of OPC: sludge of 0.3:1, OPC:fly as h:sludge of 0.2:0.5:1, and lime:fly ash:sludge of 0.3:0.5:1 were used, respectively. NaOH was added to each mix at 0 (control sample), 2, 5 and 8% by weight of solidified binder. A set of binder samples without sludge, but containing 8% NaOH, was also prepared. The microstructure , microchemistry, and component phases present in the binders after cu ring were determined by scanning electron microscopy, energy dispersiv e X-ray spectroscopy, and X-ray diffractometry. The chemical species p resent in the sludge were not significantly affected by the high pH pr oduced by NaOH; the sample showing the least effect was CFA/sludge. Et tringite was formed in CFA/sludge samples containing up to 5% NaOH, an d in CFA/sludge and LFA/sludge containing up to 2% NaOH. NaOH reacted with the binders to produce phases containing Na plus minor amounts of Cr and Ni.