Study Of Copper Slag Cleaning Process Based On DC Electric Field And C-H₂Mixed Reduction

In the modern copper smelting process, producing a high-grade matte throughoxidizing converting has increased the copper loss in the slag. The copper slagcleaning process is a necessary measure for high copper recoveries. The traditionalelectric furnace process for slag cleaning has the disadvantage of long operation time,high energy consumption, low recovery degree and the difficulty in treating the SO2.With the energy and resource shortage, the more efficient methods of copper slagcleaning should be developed.Combined with the previous research, the innovative copper slag cleaningmethod based on the electric field and slag reduction modification with mixed C-H2gas was provided in the study. The main research interests are focused on thefollowing aspects:(1) the physicochemical properties of FeOt-SiO2-CaO-Cu2O slags;(2) reduction and modification of molten slag using a mixed C-H2gas;(3) staticcleaning of molten copper slag under a DC electric field;(4) thermal simulation ofdynamic cleaning process under a DC electric field.Control and operation of slag properties become very essential in improving theseparation between slag and matte in copper slag cleaning process. The influence ofcomposition on the viscosities, electrical conductivities, densities and surface tensionsof FeOt-SiO2-CaO-Cu2O slags were studied in the paper. The slag should beconformed following the principle of low viscosity and density, high conductivity andsurface tension. The slag optimized area which was suitable to the slag cleaning wasobtained. On the phase diagram of FeOt-SiO2-CaO slag system, optimized phasecomposition is fayalite and tridymite.In the molten slag reduction process, the reduction rate increased with the higherH2content in the mixed gas. The viscosity of molten slag efficiently decreased duringthe molten reduction process. With the reduction of molten slag, the magnetite phasedecreased gradually while fayalite phase increased and metallic iron was gernerated. For the copper phase, the change sequence with the reduction was as follows:CuFe2O4â†'Cu2Oâ†'Cu0. The kinetic process of molten copper slag with mixed gas of60%CO-5%CH4-Ar was studied. The following conclusions were obtained: thereduction of the molten copper slag belonged to the first order reaction within thetemperature from1473K to1623K with the apparent activation energy58.8KJ·mol-1.The interfacial mass transfer between the gas and liquid phase is the rates limitingstep. The gas-liquid transfer process fits the penetration model. The overall masstransfer coefficient (kd) was obtained according to the dimensional analysis for thedispersion system with multiple gas bubbles with the experimental studies. A goodfitting effect was achieved with the help of the model. The application of the modelwas verified.Interfacial characteristics between copper matte particles and molten slagsprovided the possibility of utilization of electrocapillary phenomenon in slag cleaningprocess. The presence of a certain electric field accelerates the migration of copperdrops from anode to cathode and improves the copper slag cleaning. The settling rateunder an electric field of1.5V·cm-1is two or three times higher than the naturalsettling only under the gravity. The main force to accelerate the matte settling iselectrocapillary force rather than inertial force. The migration direction of microcopper matte particle in the molten slag is cathode whatever the matte composition is.The existing of electric field may promote the congregation and sedimentation of thecopper particles and also the reduction of CuxO and Fe3O4. But on the other hand, theelectrolysis action celebrates the corrosion of refractory as well.A thermal dynamic simulation experiment of copper slag cleaning under theelectric field was carried out in laboratory on a kilogram scale. The copper content ofthe slag was able to decrease below0.6wt%after two stage cleaning process in theconditions of1523K temperature,1.5V·cm-1electric field strength and15g·(10min)-1feeding rate. Although some laboratory conditions, such as fluidity of the molten slags,continuous feeding mode and stirring method et al, fell far from an ideal situation, the average level of electric furnace cleaning process was exceeded in above experiment.In conclusion, all key problems, such as slag optimization, slag reductionmodification process and the molten slag behaviors under the electric field wereinvestigated in the paper. The research can provide a complete theoretical andexperimental foundation for the further study of innovative copper slag cleaningprocess based on the DC electric field and slag modification with mixed C-H2gas.