Steel making slags, byproducts of steel making processes, have been largely reused as construction materials such as land banking and road bases. However, one of main constituents of slags, CaO, in particular, free CaO, often generates highly alkaline leachates (pH ~ 13) when exposed to water. When the reused slags are in contact with soils, the generated highly alkaline leachates may have adverse effects on living organisms in soil, groundwater, and even surface water. Therefore, an appropriate treatment should be applied prior to slags reuse. We have been investigating the applicability of biotic and/or abiotic treatments for the prevention of alkaline leachates. For the biotic treatment, CaCO3-forming alkalophilic bacteria, Bacillus pseudofirmus, were considered. The bacteria were incubated with slags in an attempt to convert free CaO into CaCO3. Our preliminary study showed approximately 83% reduction of free CaO was achieved when B.pseudofirmus was sprayed (108 CFU/ml) on the slags every six hours for 48 hours. The effect of bacterial inoculation on the biomineralization of free CaO into CaCO3 is being studied. The changes in the leachate pH after the biotic treatment are to be monitored to determine the effectiveness of biotic treatment for pH reduction. The abiotic treatment involved mixing of aluminum (Al) salts with slags to capture hydroxide ions generated from the exposure of free CaO to water, which is expected to result in Al(OH)3 precipitates. Studies on different types of Al salts are being carried out to determine appropriate Al salts. Development of both the biotic and abiotic treatment methods for preventing alkaline leachates generation will assure environmentally safe reuse of steel making slags.

Biotic and abiotic treatment methods for alkaline leachates from steel slags

249th National Meeting (2015)

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