Selective recovery of nickel from stainless steel pickling sludge with NH3-(NH4)2CO3 leaching system

The recovery of valuable metals from stainless steel pickling sludge(SSPS) has great economic and environmental benefits. In this study, a new method is proposed for selective recovery of nickel from SSPS by NH3-(NH4)(2)CO3 ammonia leaching system. The Eh-pH diagram was used to analyze Ni, Fe, Cr leaching behavior during the ammonia leaching process. Nickel can be leached as the complex [Ni(NH3)(n)](2+), whereas Fe and Cr remain as precipitates in the leaching slag. The effects of NH3 center dot H2O concentration, liquid-solid ratio, reaction temperature, and reaction time on the leaching efficiency of nickel in the ammonia leaching system were analyzed and optimized by single-factor study and response surface analysis, and the kinetics were analyzed. The optimal conditions for Ni leaching were found to be 28.28 min, 54.07 degrees C, a liquid-solid ratio of 23.7:1, and NH3 center dot H2O concentration of 5.10 mol/L. Each factor had a greater effect on the rate of Ni leaching in the following order: liquid-solid ratio > NH3 center dot H2O concentration > leaching time > leaching temperature. The ammonia leaching recovery system was controlled by chemical reaction and the activation energy was 58.17 KJ/mol. The results of scanning electron microscopy-energy dispersion spectrum (SEM-EDS), x-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) show that the leaching slag was in granular form with agglomerated particles and particle size of approximately 2.8 mu m The major components of the leaching slag were Fe(OH)(3), Fe2O3, Fe(OH)(2), Cr(OH)(3), and Cr2O3. Therefore, this study provides a new and effective way of using the resources of SSPS.