| Nickel converter slag, a typical kind of non-ferrous metallurgy slag, is recently disposed to extract valuable metals by the industry with reduction and sulfidization processes. Most of the metal values are transferred to an intermediate sulfide product which is then treated by ore dressing after slow cooled or/and acid leaching. However, huge quantities of slag are dumped due to low recovery efficiency, environmental pollution, and high energy consumption, posing a potential environmental threat and economic problem. In this paper, high pressure oxidative leaching of nickel converter slag with sulfuric acid solution was studied to develop a kind of clean and effective hydrometallurgical method. The optimum conditions of extracting cobalt, nickel and copper from the slag was obtained and optimized by response surface methodology. The influence mechanism of filtration of slurry, conversion behavior of silicon and iron, and kinetics of cobalt dissolution were investigated as well.The study suggests that high pressure oxidative leaching of nickel converter slag with sulfuric acid solution is a suitable technology for base metal recovery. Extractions of>95%for cobalt and nickel,>93% for copper,<0.4 for iron and<2% silicon were successfully achieved under the conditions of-150+74 μm particle size, 0.3 mol/L sulfuric acid concentration,7 mL/g liquid/solid (L/S) ratio and 600 kPa oxygen partial pressure at 200℃ for 80 min. The filtration rate of the leaching slurry was as high as 433.73 Lm·h-1. It was found that the decrease of sulfuric acid concentration is capable of hindering the dissolution of hematite and hydrolysis of SiO2, and favors the solid-liquid separation characteristics of the leach slurry. Extractions of cobalt, nickel and copper increases significantly with increasing temperature. As the temperature rises, iron in the residue tends to transform y-Fe2O3 to α-Fe2O3 causing more even residue particle, and therefore easier solid-liquid separation of the slurry. The residue consists mainly of hematite (y-Fe2O3 and a-Fe2O3) and contains less than 0.1% base metals and virtually zero sulfur.The optimization of process of high pressure oxidative acid leaching of nickel converter slag using response surface methodology shows that the model has a high fit degree and can predict suitably experimental results. The optimized parameters for the converter slag leaching are:temperature 208 C, sulfuric acid concentration 0.35 mol/L and L/S ratio 5.4 mL/g. Under the above conditions, more than 98% of Co and Ni and more than 96% Cu were extracted into solution together with less than 0.3% Fe, the leaching slurry performed a good filter performance, and the fitration rate was more than 550 L·m-2·h-1.Kinetics of cobalt dissolution from nickel converter slag by high pressure oxidative leaching with sulfuric acid shows that the dissolution rate of cobalt increased with increasing temperature (165～225℃) and oxygen partial pressure (350-650 kPa) and with decreasing particle size (210～53 μm), but stirring speeding above 600 r/min, and sulfuric acid concentration of more than 0.4mol/L were found to have very little effect on it. The kinetics of cobalt dissolution follows the shrinking core model. The leaching process is controlled by the chemical reaction during its early stage, then gradually switches to the diffusion control through a surface product layer. The activation energy was reported to be 44.43 kJ/mol in the stage of surface-reaction control and 10.49 kJ/mol in the diffusion controlled stage. In the stage controlled chemical reaction, the reaction orders with respect to sulfuric acid concentration, oxygen partial pressure and particle size are 0.79,0.83 and-0.94 respectively, and an empirical equation of cobalt dissolution rate was established as:...
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