Using shell-type tuyeres at Pierce–Smith horizontal converters of the Nadezhda Metallurgical Plant

Since 2015 the processing capacity reconfiguration at the Polar Branch of MMC Norilsk Nickel (hereinafter PB) sets new goals for conventional pyrometallurgical processes of smelting and converting. The design flowsheet of Kolesnikov Nadezhda Metallurgical Abstract: Plant (hereinafter NMP) provided for «cross-converting» when copper matte was first processed in one converter to produce blister copper followed by nickel matte processing to yield copper-nickel converter matte bypassing the discharge of dry coagulated slag. This flowsheet allowed for converter heat balance optimization, decreasing the formation of refractory reverts and significant extension of the converter campaign. PB Nickel Plant shutdown resulted in copper processing elimination at NMP and switching the converters to the conventional nickel converting flowsheet. In turn, it gave rise to the need for solutions to extend converter campaign while maintaining the possibility to process large amounts of nickel slag from the second converting stage at the PB Copper Plant. For this purpose the series of lab experiments were carried out to develop the technology and design documentation for the system to supply oxygen-enriched air (up to 45 %) to horizontal converters using shell-type tuyeres. In addition, literature data were analyzed on this topic along with the experience of smelters in this area. Process design calculations were done. The efforts were taken in cooperation with the PB engineering personnel and Laboratory of Pyrometallurgy of LLC «Gipronickel Institute». The use of reduced diameter shell-type tuyeres to inject the oxygen-air mixture was found to decrease the converter blowing and off-gas volumes. The decline in off-gas quantity leads to reduced heat load on the converter mouth and flue duct system, as well as to lowered converter dust entrainment. The use of oxygen-enriched blowing implies the higher smelt heating rate. Excess heat compensation requires timely charging of cold reverts and flux. In emergencies (if cold reverts are not available) the oxygen content of the blowing has to be reduced until switching over to air blowing. The series of the above efforts will offer a possibility to use the shell-type tuyeres keeping the converter off-gas temperature at the current level. Thus continuous monitoring and efficient control will ensure the off-gas temperature and volume at the inlets of gas cooling and cleaning systems not exceeding the limiting values. The introduction of the reduced diameter shell-type tuyeres for air-oxygen mixture injection does not require any upgrade of the existing gas cooling and cleaning systems. Moreover, switching to these tuyeres will reduce gas load on the flue duct system and heat load on the water-cooled dust cap, lower dust entrainment and non-recoverable dust losses after the gas cleaning system.

Influence of Desulfurization with Fe2O3 on the Reduction of Nickel Converter Slag

Generally in the nickel converter slag, metals are mainly in the form of sulfides, which are difficult to separate from slag. Although metal oxides in the slag, such as NiO, CoO, and Cu2O, are easily reduced into metal using carbon, the presence of sulfur inhibits the reduction reaction. In this study, the addition of Fe2O3 to nickel converter slag produced desulfurized slag, which enhanced the carbothermal reduction process. Increasing the desulfurization rate promoted the conversion of sulfides into oxides in slag, which significantly increased the activity of NiO, Cu2O, and Fe2O3. However, the residual sulfur content had no significant effect on the activity of FeO and CoO, due to the high initial FeO content and cobalt existing mainly in the form of oxides. The optimum addition of Fe2O3 was 15.0 g per 100 g nickel slag, while the desulfurization ratio was 36.84% and the rates of nikel, cobalt and copper recovery were 95.33%, 77.73%, and 73.83%, respectively.

Recovery of the valuable metals from complex converter slag at elevated temperature with sulfuric acid solution

The aim of this paper was exploring the effective utilization of nickel converter slag by means of the methodology of pressure oxidative leaching. The central composite design of response surface methodology was employed to optimize controlling conditions for the leaching of more valuable metals such as nickel, cobalt, and copper, while dissolution of iron was curbed. XRD, SEM-EDS were performed for characterizing the structure of leach residues for analyzing the mechanism of selective leaching. Experimental results demonstrate that the effects of temperature and sulfuric acid concentration on the metals extraction and filtration rate are significant, followed by liquid/solid (L/S) ratio. The optimized conditions for the leaching of converter slag are: temperature 208 ?C, sulfuric acid concentration 0.35 mol/L, and L/S ratio 5.4 mL/g. Under these conditions, 99.60% Co, 99.20% Ni, and 96.80% Cu were extracted into solution together with only 0.21% Fe, and the filtration rate of leach slurry reached 576.86 L?m?2?h?1. The mechanism for achieving selective leaching of nickel, cobalt, and copper against iron dissolution and good filtration performance of the leach slurry was enabled by iron that dissolved in the solution, decomposed, and hydrolyzed mainly to form hematite (?-Fe2O3 and ?-Fe2O3), and letting silicic acid form precipitated SiO2 in the leach residue.