XANES study of Cr sorbed by a kitchen waste compost from water

A kitchen waste compost was used to sorb Cr for various times from water containing either Cr(NO3)3 or CrO3 in different concentrations. Scanning electron microscopy (SEM) results show that the composts have been partially oxidized by Cr(VI) during the sorption experiments. X-ray absorption near edge structure (XANES) simulation suggests that about 54.1-61.0% Cr sorbed on the compost is in form of organic Cr(III) through ionic exchange process with the rest being existent as Cr(NO3)3 in the Cr(III) sorption case; no Cr(OH)3 is observed or expected because the solution pH after sorption experiments is ⩽3.31. However in the Cr(VI) sorption cases, about 18.0-24.9% of the total sorbed Cr is in form of Cr(OH)3 precipitate due to the Cr(VI) chemical reduction by the compost and a contaminant increase in solution pH to ⩾5.94. Moreover, organic Cr(III) represents about 51.7-69.0% of the total sorbed Cr, and the rest (6.1-28.5%) is Cr(VI).