Temperature-Dependent Speciation Analysis of Chromium Immobilized in Calcium Hydroxyapatite Matrix

Abstract

To develop a green, rapid and energy-efficient route for the toxic waste immobilization, chromium was captured from aqueous system and subsequently solidified using calcium hydroxyapatite (HA) powder. The effect of sintering temperatures on the inter-conversion of Cr(III/VI) species in the HA matrix was investigated by synchrotron X-ray absorption fine structure spectroscopy. The results of X-ray absorption near edge structure showed the gradual transformation of Cr(III) to Cr(VI) oxides from similar to 0 to similar to 100% at sintering temperatures of 100-1150 degrees C. The extended X-ray absorption fine structure results revealed a typical Cr(III) oxide as the dominant structure at a temperature lower than 500 degrees C and Cr(VI) oxide structure at higher temperatures. Thus, the oxidation behavior of Cr(III) is strongly dependent on sintering temperatures. Therefore, this study will help to design a waste management route for toxic wastes including Cr(VI) to reduce its leaching from the waste matrix. Rapid oxidation of Cr(III) inside HA matrix may be avoided by adopting low-temperature sintering techniques. [GRAPHICS] .