This study aimed to find optimal conditions for the recovery of nickel (Ni) from spent catalyst wastewater via the sulfidation method with low processing and environmental loads. Simulated Ni catalyst wastewater was used, which contained high concentrations of chloride ions and methanol. It was found that preliminary neutralization is crucial to suppress the overdose of sulfidation reagents. The gasification ratio of sulfur (S) and the recovery ratio of Ni were experimentally determined and then simulated with the numerical fitting. Results indicated that the presence of methanol expanded the range of pH and S/Ni molar ratio in which safe and complete Ni recovery can be achieved, showing the effectiveness of the sulfidation method on Ni recycling from Ni catalyst wastewater.

In this study, we employed the Discrete Element Method (DEM) incorporating liquid bridging forces and a coarse-grained model, to analyze the influence of rotation speed on particle behavior within a pan-type pelletizer. We compared simulation results for particle layers in the pan at three different rotation speeds to comprehend their impact. The findings indicate that the average particle velocity increases depending on the degree of coarsening. This phenomenon is attributed to a reduction in the relative collision frequency among particles with an increase in coarsening, leading to a presumed elevation in the overall velocity of coarse particles due to diminished energy attenuation from collisions. Consequently, for future studies with even higher coarsening rates than those in this study, it is suggested to introduce a novel energy attenuation model that considers the relative decrease in collision frequency among particles.

Volatile organic compounds (VOC) such as trichloroethene (TCE) and tetrachloroethene (PCE) cause the contamination of groundwater and soil pollution around the world. It is well-known that persulfate oxidation process activated by ferrous ion has been utilized for the treatment of organic pollutant. In this study, degradation of TCE using persulfate oxidation process with tartaric acid and iron ion was investigated. Tartaric acid accelerated the rate of TCE degradation more than other organic acids used in the experiment. Tartaric Acid/Fe/Persulfate/TCE molar ratio of 2/5/20/1 is the most efficient for TCE degradation. The complex of ferric ion and tartaric acid plays an important role in the reaction of TCE degradation.