Desorption of cadmium from FeCd and recycle of Fe0: Experimental and mechanism study

Zero valent iron (Fe0) has been proven to be a highly efficient adsorption material for cadmium in wastewater. However, how to deal with Fe0 after cadmium adsorption, restricts its industrialization. In this paper, we attempted to desorb cadmium from the post-adsorption material (FeCd) through ammoniacal leaching and recycle the Fe0. Desorption experiments, Infrared and SEM-EDS results showed leaching with (NH4)2SO4 and NH3·H2O can effectively desorb cadmium from FeCd. Based on Ultraviolet spectrum, solution chemistry and quantum chemical analysis, cadmium on FeCd can combine with free ammonia and form Cd-NH3 complexes. Then the complexes are transferred into the leached solution, achieving the desorption of cadmium. Subsequently, cadmium in leached solution was precipitated into Cd(OH)2, a high-grade cadmium product. Finally, the cadmium adsorption capability of regenerated Fe0 was roughly investigated, and the results showed that it has a better capability for cadmium adsorption than initial Fe0, which further guaranteed the recycle of Fe0.