Research On Top-blown Redution Depleted Technology For Copper Smelting Slag With Diesel-Nitrogen

China is a super-country with scarcity of copper resources. Run of Mine （ROM） mining grade of large domestic copper mines has generally dropped below 0.5% Cu. Copper smelting enterprises have to import large amount of copper concentrates from abroad every year in order to meet their production requirements. To decrease Cu content in discard slag and improve comprehensive utilization of resources for copper smelting enterprises, they have become the issues of common concern both to academic world and industrial world. It is a valuable and meaningful work as these issues concerning National Strategic Resources. There have been more and more applications of Oxygen-Enriched Intensive Smelting Technology in copper smelting enterprises. Also it brings some new problems to be studied and solved while both improvement of energy conservation & emission reduction and better production benefit are achieved. Large amount of Fe₃O₄ is produced during intensive smelting and converting under high oxygen potential atmosphere. High Fe₃O₄ content in slag results in high slag viscosity and high melting point of Slag Cleaning Electric Furnace, and diaphragm is formed due to Fe₃O₄ enrichment. Therefore, obviously this affects settling and separation of valuable elements （including Cu, Au and Ag）, it also causes incomplete separation of copper and slag, high Cu in discard slag （up to 0.7-1% Cu）, loss of valuable elements （such as Au, Ag and so on） with discard slag carry-over, and low resources recovery.In view of characteristics of copper smelting slag under high oxygen potential, this thesis proposed that directional adjustment and control for slag chemistry can be achieved by changing valence state of iron oxides contained in copper smelting slag, Fe₃O₄ Content in molten slag can be decreased by means of top-blown intensive reduction by mixture of diesel oil and nitrogen gas. In this paper, the author provided a new approach for an efficient separation of copper and slag by forming composite oxides of Fe₂SiO₄ as much as possible to improve migration and enrichment of copper.Firstly, the author investigated mechanisms of copper loss in slag and reduction/cleaning of copper smelting slag, carried out thermodynamic calculation and experimental research by high temperature pyrolysis with diesel oil and reduction of Fe₃O₄ in slag. This paper verified the effect of reduction temperature and reduction time on reduction of Fe₃O₄ in copper smelting slag, demonstrated the technological feasibility of reduction of Fe₃O₄ in copper slag by diesel oil in the presence of N₂ in Slag Cleaning electric Furnace. Furthermore, based on the law of Gibbs Free Energy, model of Fe₃O₄ reduction by diesel oil in the presence of N2 was constructed. Calculation shows conversion from pyrolysis products of diesel oil into CO₂, H₂O and small amount of CO. It also shows big equilibrium constant between Fe₃O₄ and pyrolysis products of diesel oil, and high degree of reaction. The abovementioned mechanisms provides theory basis for technology research and development of top-blown slag cleaning by mixture of diesel oil and nitrogen gas.Secondly, the author of this paper established three-dimensional mathematical model for two-phase flow of top-blown intensive mixing by oil-gas mixture, made mutual authentication of model calculation results and water modeling experiment results, revealed coupling mechanism of flow pattern evolution and intensive mixing effect of top-blown intensive mixing by oil-gas mixture. That’s to say; effect of injection and reduction was subject to flow pattern evolution in gas-liquid mixing & top-blown pipe due to gas-liquid ratio. There was swirling flow caused by the change from bubble flow to annular flow in pipe, so intensive injection and mixing were achieved accordingly. And in this way, one new-type of top-blown reduction lance with mixture of diesel oil and nitrogen gas was invented.Finally, combined with the aforementioned research results of theory and model calculation results, industrial test of top-blown reduction & cleaning technology by mixture of diesel oil and nitrogen gas was performed in this study. The diaphragm, mainly contained Fe₃O₄ in lower part of the slag, can be reduced efficiently under control of 700-950mm of thickness of slag layer in Slag Cleaning Electric Furnace,3/5 of lance insertion degree into slag layer and 1:17.5 of oil-to-gas ratio. Compared to the original top-blown smelting technology with diesel oil, the top-blown reduction technology by mixture of diesel oil and nitrogen gas increased contact area between diesel oil and slag layer of Slag Cleaning Electric Furnace. Lance life extended 5-6 times, production efficiency of reduction improved, Fe₃O₄ content in slag dropped 39.26%, and unit consumption of diesel oil per ton slag decreased 56.58%. By considering of 450,000 tpa of electric furnace slag produced,1,044,000 L of diesel oil can be saved each year, that is equivalent to 1,247.38 tons of standard coal for energy conservation, and Cu in discard slag decreased 11.67%. By considering of 450,000 tpa of electric furnace slag produced,405 tpa of additional copper can be recovered. Moreover, Au and Ag contained in slag can be recovered from copper matte entrained by copper matte making and Au capture process. Ag in discard slag has decreased 49.23%,1.44 tpa of additional Ag can be recovered each year. Au in discard slag has decreased 60.34%,15.75 kg of additional Au can be recovered every year.This research results have been applied successfully in commercial operations. Significant benefits have been achieved from energy conservation and emission reduction. And this technology has been promoted to use in the related copper smelting enterprises.