Solidification/stabilization of a synthetic electroplating waste in lime-fly ash binder

Abstract

A synthetic electroplating sludge was solidified in a binder which was a mixture of lime and Class C fly ash (LFA). The sludge contained 86.2, 84.1, 18.8 and 0.137 mg/g of nickel, chromium, cadmium, and mercury, respectively. The binder contained lime and Class C fly ash in the ratio 3:5, and the waste to binder ratio was 1.0:0.8. The microstructure and microchemistry of the solidified samples were studied by scanning electron microscopy, energy dispersive x-ray microanalysis, and x-ray diffractometry. The sludge was composed of impure, complex species of the heavy metals. The microstructure and phase composition of LFA were not affected by sludge. The sludge/LFA mixtures were simple mechanical mixtures of the binder and sludge. The heavy metals existed as large particles embedded in the binder, and uniformly mixed in the matrix at low concentrations, and with particle sizes smaller than those resolvable by the microscope under the conditions dictated by the specimen type and form. Fly ash spheres acted as sites of adsorption for the heavy metals.