Abstract
The viability of utilizing Reclaimed Limestone Residual RLR (Modified Steel Slag) to remove hexavalent chromium Cr(VI) from the aqueous phase was investigated. A physical characterization of RLR showed that it is composed of various minerals some of which can reduce and others adsorb Cr(VI). Preliminary results showed that RLR significantly reduced the concentration of Cr(VI) from the aqueous phase. Adsorption competition tests with orthophosphate (HP04(2-)) and sulfate (SO4(2-)) showed that Cr(VI) was still effectively reduced from solution regardless of the competing anions present. Kinetic tests based on the relationship d[Cr(VI)]/dt = kCr[RLR]alpha[Cr(VI)]beta showed that under initially neutral to basic conditions kCr = 3.45+/-(0.25) x 10(-4) mg0.4 L(-0.4) h(-1), alpha = 0.9, and beta = -0.3, while under initially acidic conditions kCr = 5.65+/-(1.055) x 10(-1) mg(-0.4) L0.4 h(-1), alpha = 2.2, and beta = -0.8. Stirred batch tests with RLR in deionized water showed significant drops in the redox potential (Eh), and in the presence of oxygen Eh values dropped to between 50 and 100 mV while in the absence of oxygen Eh values as low as -200 mV were observed. These results lead to the conclusion that redox mechanisms were responsible for the reduction of hexavalent chromium by RLR.
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