| This work was supported by Natural Science Foundation of China (NO.51104182and NO.51234009) and State Science and Technology Supporting Plan (NO.2012BAC12B02).A new process to extracted antimony directly from stibnite concentrate by reductive sulfur-fixation smelting in sodium molten salt under low temperature has been presented, which is considered as a clean and efficient metallurgical process. Besides, several terrible problems could be avoided by this new process, which include the high smelting temperature, high energy and material consumption, high production costs, especially the low concentration SO2emission.In addition, volatile smelting and reduction smelting are mixed together by molten salt perfectly in this new process, which is different with the traditional process, in which volatile smelting would be performed firstly, and then the reduction smelting.Considering the reaction relationship between iron, zinc and antimony, the thermodynamic behaviors and conditions of ZnO, FeO and molten salt (Na2CO3-NaCl) in the process of reductive sulfur-fixation reactions were analysed. Then the reaction processes of ZnO, FeO and molten salt (Na2CO3-NaCl) were studied by using pure materials, the rules of phase structure about antimony, zinc, iron and sodium was revealed, and the fundamental of reaction mechanism was set up. On this basis, the new process of reductive sulfur-fixation smelting was studied.The results of thermodynamics investigation indicate that the reductive sulfur-fixation reactions can be carried out spontaneously when reaction temperatures are maintained between700K to1300K (427℃to1027℃) owing to their△GθT<0. Therefore, it can be concluded that Sb2S3could be reductive sulfur-fixed into Sb at reducing atmosphere, and the sulfur, which was included in concentrate, could be fixed in the slag.The thermodynamic of mechanism of melting process was calculated, there are four possible methods for reductive sulfur-fixation of stibnite. By comparing the△G9of each possible approaches, we found that Sb2S3occurred sulfur-fixation reaction with ZnO or FeO firstly, then reduced to the metal antimony was the most impossible reaction pathway.Research on the phase transformation of components in the reductive sulfur-fixation process in the pure materials system has been investigated. For Sb2S3-ZnO-C system and Sb2S3-FeO-C system, the sulfur-fixation reaction between SD2S3and ZnO or FeO to produce Sb2O3and ZnS or FeS was so rapid that the equilibrium of this process could be reached within5min, even at low temperatures. And then, Sb2O3could consecutively reduce to Sb by addition of reductive agent.For Sb2S3-Na2CO3-C system, the reaction between Sb2S3and Na2CO3was so complicated that some compounds, like sodium sulphide (Na2S, Na2S5), sodium thiosulfate (Na2S2O8, Na2S2O4), antimony matte (NaSbS2) and sodium antimonite (Na2Sb4O7), were obtained as the final products, whether reducing atmosphere or inert atmosphere.For Sb2S3-ZnO/FeO-Na2CO3-NaCl-C system, the reaction pathways could be changed by adding sulfur-fixing agent (ZnO/FeO), as a result, the reaction rate was improved shapely and the main reactions were carried out between Sb2S3and ZnO/FeO.Therefore, the sulfur-fixation reaction between Sb2S3and ZnO or FeO to produce ZnS and Sb2O3was occurred firstly, and then Sb2O3could consecutively reduce to Sb by addition of reductive agent. The results indicate that the reductive sulfur-fixation process occurs through the following consecutive reactions:STEP1: Sb2S3+3ZnO=Sb2O3+3ZnS Sb2S3+3FeO=Sb2O3+3FeSSTEP2: Sb2O3+3C=2Sb+3CO(g) Sb2O3+3CO(g)=2Sb+3CO2(g)A high-gold content stibnite concentrate, taken from Xikuangshan Co. Ltd, and a normal stibnite concentrate, taken from Shanxing Co. Ltd, were used in the thesis. The new process to extracted antimony directly from stibnite concentrate by reductive sulfur-fixation smelting in sodium molten salt has been presented.The results indicate that this new process is feasible, and SO2emission could be avoided completely owing to the sulfur contained in stibnite was fixed in the slag, and above95%sulfur-fixing rate could be obtained.When ZnO was used in this study as the sulphur-fixing agent, the optimum conditions were determined as follows:Wconcentrate:WSalt:WZnO:WC=100:400:66:40,1173K,120min. Under above mentioned optimum conditions, the average direct recovery ratio of antimony could reach85.25%, and the main chemical composition of obtained crude antimony is Sb89.30%, Zn3.54%, Pb1.86%, Fe0.85%.When Fe2O3was used in this study as the sulphur-fixing agent, the optimum conditions were determined as follows:Wconcentrate:WSalt:WFe2O3:WC=100:90:55:40, WNaCl. Wsalt=40%,1123K,60min. Under above mentioned optimum conditions, the average direct recovery ratio of antimony can reach91.48%, and the main chemical composition of obtained crude antimony is Sb95.99%, Fe2.85%, Pb0.54%.The gold in the stibnite concentrate, is recovered in the metal antimony, which is the final product in this process, and the recovery ratio of gold could reach90-plus percent. Above all, a good performance of this process in recovering valuable metal is demonstrated. |
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