Immobilization of hazardous Cr(VI)in blended cement: XRD and leaching studies
- Vol.28(4), Oct-Dec
- Pune NICMAR 2013
- 51-60p.
Marble dust from gang saw industries is generated as waste in million tonnes and is an environmental hazard due to disposal problems. The marble dust is a filler material having similar properties like limestone and takes part in early hydration reactions due to the presence of high amount of calcium carbonate. In the present study, 40 % of marble dust (CM) blended with Portland cement (C0) has been utilized to immobilize (solidify) hazardous Cr (VI) (1000-3000 mg/l) and the effect on parameters like setting time, compressive strength and leachability of Cr (VI) has been investigated as a function of curing time. It is observed that the initial and final setting times of these cements increase with increase in Cr (VI) concentration. The effect of Cr (VI) addition on the physical, chemical and engineering properties of solidified samples (C0 and CM with Cr (VI)) were studied and the results revealed that the compressive strength reduced with addition of Cr (VI). The samples of C0 and CM containing Cr (VI) were also tested for leachability of Cr (VI) in acidic solution (pH=~3) using Toxicity Characteristics Leaching procedure (TCLP) tests. The leached Cr (VI) concentration was under the allowable limit (5 mg/l) of U.S. EPA at lower initial concentration. The hydration chemistry of the solidified samples has been studied by XRD which shows the formation of various phases like ettringite, Cr-ettringite, tobermorite, monocarboaluminate etc. The morphology of the hydration products was studied by Scanning Electron Microscopy (SEM) which also supports the formation of various hydrations phases as observed during XRD in the solidified Cementitious binders.