Preparation of sodium manganate from low-grade pyrolusite by alkaline predesilication-fluidized roasting technique

Low concentration alkaline leaching was used for predesilication treatment of low-grade pyrolusite. The effects of initial NaOH concentration, liquid-to-solid ratio, leaching temperature, leaching time and stirring speed on silica leaching rate were investigated and the kinetics of alkaline leaching process was studied. The results show that silica leaching rate reached 91.2% under the conditions of initial NaOH concentration of 20%, liquid-to-solid ratio of 4：1, leaching temperature of 180 ℃, leaching time of 4 h and stirring speed of 300 r/min. Shrinking-core model showed that the leaching process was controlled by the chemical surface reaction with activation energy Ea of 53.31 k J/mol. The fluidized roasting conditions for preparation of sodium manganate were optimized by the orthogonal experiments using the desiliconized residue. The conversion rate of sodium manganate was obtained to be 89.7% under the conditions of silica leaching rate of 91.2%, NaOH/MnO2 mass ratio of 3：1, roasting temperature of 500 ℃ and roasting time of 4 h, and it increased with the increase of silicon leaching rate.

Characterization of fluidized reduction roasting of nickel laterite ore under CO/CO_(2)atmosphere

Fluidized reduction roasting is an efficient metallurgical technique.However,its application to nickel laterite ore has rarely been reported.In this paper,the effects of reduction temperature,reduction time,CO concentration,and material particle size on the roasting characteristics of ferronickel fluidization reduction were investigated.Combined with X-ray diffraction,scanning electron microscopy-energy dispersive spectrometry(SEM-EDS)characterization,the mineral phases and microscopic morphology of nickel laterite ore and its roasted ores were analyzed in depth.The results indicated that under the condition of a CO/CO_(2)ratio of 1:1,a reduction temperature of 800℃,and a reduction roasting time of 60 min,a nickel-iron concentrate with a nickel grade of 2.10%and an iron content of 45.96%was produced from a raw material with a nickel grade of 1.45%,achieving a remarkable nickel recovery rate of 46.26%.XRD and SEM-EDS analysis indicated that nickel in the concentrate mainly exists in the form of[Fe,Ni],while the unrecovered nickel in the tailings is primarily present in the form of[Fe,Ni]and Ni_(2)SiO_(4)in forsterite.This study established a theoretical foundation for further exploration of fluidized reduction roasting technology.

Characterization and Pyrometallurgical Removal of Arsenic from Copper Concentrate Roasting Dust

This paper describes the experimental results of removing arsenic from the dust collected in electrostatic precipitators of a fluidized bed roasting furnace (RP dust). The fluidized bed roasting process generates 600 kilotons of copper concentrate per year with 3 - 6 wt% of concentration of arsenic, producing a roasted product with a low content of arsenic below 0.3 wt%. The process generates 27 kilotons of RP dust per year with a concentration of arsenic of the order of 5 wt% and copper concentration of around 20 wt%. Subsequently, the dust collected in the electrostatic precipitators is treated by hydrometallurgical methods allowing the recovery of copper, and the disposition of arsenic as scorodite. This work proposes to use a pyrometallurgy process to the volatilization of arsenic from RP dust. The obtained material can be recirculated in copper smelting furnaces allowing the recovery of valuable metals. The set of experiments carried out in the roasting of the mixture of copper concentrate/RP dust and sulfur/RP dust used different ratios of mixtures, temperatures and roasting times. By different techniques, the characterization of the RP dust determined its size distribution, morphology, and chemical and mineralogical composition. RP dust is a composite material of small particles (<5 μm) in 50 μm agglomerates, mostly amorphous, with a complex chemical composition of sulfoxides. The results of the roasting experiments indicated that for a 75/25 weight ratio of the mixture of the copper concentrate/PR dust under 700℃, 15 minutes of roasting time with injection of air, the volatilization of arsenic reached 96% by weight. The arsenic concentration after the roasting process is less than 0.3% by weight. For a 5/95 mixture of sulfur/RP dust, at 650℃, the volatilization of arsenic reached a promissory result of 67%. Even that this study was carried out for a particular operation, the results have the potential to be extended to dust produced in the roasting of concentrates of nickel, lead-zinc, and gold.