Feasibility and Environmental Compatibility of Concrete using Chromium Bearing Wastewater

Abstract

The effluents of chrome plating industry seepage contain toxic hexavalent chromium generally in the range of 100 to 300 mg/L. The said values of chromium are not advisable to dispose to surface water bodies or land and the treatment process of this wastewater is quite expensive. Herein, we found a course of action to reuse the wastewater in cement matrix in manufacturing concrete work. The M-30 grade concrete samples were casted with portland slag cement (PSC) at wastewater to binder ratio of 0.45. The technical compatibility of concrete specimen i.e. the chromium immobilization and other properties are well satisfied nevertheless a small decrease in hardened concrete values also observed. XRD study revealed that the hydration product Ca(OH)2 is replaced by more insoluble CaCrO4. Scanning electron microscopy study (SEM) with energy dispersive spectrum (EDS) study exhibited the immobilization of chromium and quantification of chromium content. The mortar samples from concrete after 56 days of air curing were subjected to toxicity characteristic leaching procedure (TCLP) test at pH 2.88. In addition, two days’ short tank leaching test was conducted with the concrete samples as a whole. The leachability of toxic Cr6+ found in the range 0.03-0.09 mg/L and the total chromium (TCr) values in the range 0.12 -0.17 mg/L, which are less than discharge standard as per EP Act (1986), India. All these leaching test results comply with the discharge norms to land and inland surface water, respectively. Thus, the concrete specimens using aforesaid wastewater satisfy the technical aspects and fulfil the environmental requirement.