XAS study of the residual copper after desorption from rice husk ash

Rice husk ash is a good sorbent to remove copper ions from industrial wastewater. To recover the sorbed copper, two reagents (nitric acid and sodium thiosulfate) were used to desorb copper from the rice husk ash. XAS was used to investigate speciation of the residual copper in the rice husk ash after desorption. XANES simulation indicates that the copper species distributions in all pre-desorbed and post-desorbed solid samples are 40-45% CuSO4 + 41-52% CuO + 7-16% Cu(OH)2. On the other hand, in the liquid phase collected from desorption by Na2S2O3, Cu2O accounts for 48% of the total copper. Formation of Cu2O is attributed to the chemical reduction of Cu(II) with Na2S2O3 that is a reductant.