Study On A Novel Technology Of Interactive Roasting Between Bismuth Sulfide Ore And Pyrolusite

To solve the disadvantage of high smelting temperature, high energy consumption and pollution of low concentration of SO2and so on, which exist in the domestic pyrometallurgical processes for bismuth, and problems brought by strong corrosive of oxidizers in hydrometallurgy for bismuth, a novel technology of interactive roasting between bismuth sulfide ore and pyrolusite-selectively leaching-purification-pure BiOCl was put forward. Focusing on the core issues of sulfur capture, sulfur conversion in interactive roasting and iron removal in leaching, the thermodynamic theory and optimum experiment of interactive roasting are systematically investigated. The virgin BiOCl powders are obtained as raw material by water leaching, acid leaching, reducing, first hydrolysis and secondary hydrolysis. The research accomplisinments in this paper are as follows:The calculation of the thermodynamic theory of interactive roasting system was conducted according to the probable reactions occurring in the interactive roasting process. The pourbaix diagrams of Bi-Mn-S-O, Fe-Mn-S-O, Cu-Mn-S-O system were drawn by thermodynamic calculation software FactSage6.2. The thermodynamic analysis results show that pyrolusite could directly or indirectly promote the oxidative decomposition of bismuth sulfide ore according to the very negative standard Gibbs free energy of the interactive roasting reaction to obtain MnSO4, Bi2O3, Bi28032(SO4)10and the corresponding impurities metal oxide existing in the raw materials. The formation of MnSO4play significance role of sulfur fixing. The interactive roasting technology is entirely feasible in theory.The conditions of the interactive roasting between bismuth sulfide ore and pyrolusite are addressed in detail including the roasting temperature, roasting time, ratio of n(MnO2)/n(S), ventilation rate, the bismuth sulfide ore particle size and mixture way of raw material. The optimum conditions are as follows:uniformly mixing between bismuth sulfide ore and pyrolusite for raw material,600-650℃for roasting temperature,1.5-2h for roasting time,1.3-1.6for n(MnO2)/n(S) ratios,80-140L/h for ventilation rate and bismuth sulfide ore particle size was200-250mesh, the sulfur capture ratio is more than97%and sulfur conversion rate is up to94%. The experimental results showed the desulfurization efficiency of pyrolusite is outstanding, and the sulfur capture ratio increase with the increase of ratio of n(MnO2)/n(S). Under T=650℃, t=2h and n(MnO2)/n(S)≥1.6, sulfur capture ratio is up to99%above, the vast majority of S in bismuth sulfide ore is transformed into MnSO4, and sulfur conversion rate are all up to90%above. The X-ray diffraction analysis of calcined product showed Bi2S3was mainly converted into Bi2O3, and a small amount was presented into Bi28O32(SO4)10, and other sulfide phase disappeared. The experimental results confirmed the accuracy of the thermodynamic analysis.The sulfur capture mechanism of pyrolusite was proposed preliminarily. The analysis results showed that sulfur capture mechanism is indirect sulfur capture by the following reactions MeS+1.5O2=MeO+SO2MnO2+SO2=MnSO4The separation of MnSO4from the calcined product was investigated in detail just by one step using weak acid leaching method. The results showed that in the condition of4.8-5.0for leaching pH value by dilute sulfuric acid,40℃for temperature,1.5h for leaching time,5for L/S ratio and300rad/min for stirring rate, the leaching rate was up to97.5%and the total yield of Mn reached about69%. The leaching residue was leached by hydrochloric acid, and under the condition of40℃for leaching temperature,5mol/L for initial c(HCl),5for L/S ratio,2.0h for leaching time,and600rad/min for stirring rate, the leaching ratio of bismuth reaches97.2%. leaching solution was reduced. Preliminary product of relatively pure BiOCl was obtained directly by reduction, first hydrolysis and secondary hydrolysis of hydrochloric acid leaching solution.The pollution of low concentrations of SO2in process of bismuth smelting could be solved by this novel technology of interactive roasting. In addition, Mn in the pyrolusite can be comprehensively utilizated. Oxidizers can be avoided in leaching process and the preliminary product of relatively pure BiOCl obtained from the process can be used in the next step for preparation of ultrafine Bi2O3powders. In a word, it is of great significance for development of metallurgy in bismuth. The number of figures35, the number of tables14, the number of references72.