Effect of Oxygen Content and Temperature On Stabilization of Arsenic in Copper Smelting System

Arsenic-bearing wastes from copper smelting system are usually disposed by trapping them in slag tailing. However, arsenic in slag tailing is not that stable, which can infiltrate into the groundwater, threatening the environment and human health. The solidification/stabilization (S/S) of arsenic is the only way to deal with arsenic contamination. The flash smelting method shows relatively high S/S ability of arsenic, but the process and mechanism remain unclear. In this paper, we aim at revealing the effect of atmosphere on the S/S process of arsenic owing to the different content of oxygen in reaction shaft and sedimentation tank in copper smelting system. Calcium arsenate, SiO2, Fe2O3 and iron powders were sintered at different temperature in air and argon to simulate the S/S reaction. The results show that the sintering product is Fe-Si oxide in air and fayalite in argon, and the fayalite possesses better capacity to solidify arsenic than that of Fe-Si oxide. The toxicity characteristic leaching procedure (TCLP) results reveal that the leached concentration of arsenic from fayalite fabricated at 1200 ℃ is only 2.916 mg L-1, which satisfies the identification standard for hazardous substances in China. Furthermore, the theoretical calculation reveals that AsO4 and SiO4 tetrahedrons can be connected by O atoms when sintered in argon, and the Si-O-As covalent bond can evidently inhibit the release of As atom from fayalite. This work can not only clarify the S/S mechanism of arsenic in flash smelting process, but also provide theoretical guidances to dispose arsenic-bearing waste harmlessly.

Numerical Investigation into Gas-Particle Inter-Phase Combustion and Reduction in the Flash Ironmaking Process

Despite the dominance of the blast furnace ironmaking process, more attention is being paid to the new technologies with lower energy consumption and carbon dioxide emissions. A novel flash ironmaking technology using pulverized coals and iron concentrates as raw materials, which is different from flash ironmaking with the reductive gas as the reducing agent, is studied. In order to obtain the flow patterns, temperature, and gas composition distribution, as well as particle trajectories in the reaction shaft of the flash ironmaking furnace, the Euler–Lagrangian model with a custom user defined function (UDF) code is used to simulate the processes of the fluid flow, heat and mass transfer, and chemical reactions, including the combustion reaction of pulverized coals and reduction reaction of iron concentrates. The results indicate that the flow patterns, temperature, and gas composition distributions present symmetrical distribution characteristics. The central oxygen expands rapidly after entering the reaction shaft and its distribution is approximately bell-shaped. The temperature distribution in the reaction shaft is wing-shaped. The maximum temperature, 2615 K, is reached at 5 m below the roof of the reaction shaft. The O2 is quickly consumed after entering the reaction shaft. At 6 m below the roof of the reaction shaft, the oxygen concentration becomes almost zero, with the CO concentration reaching the highest. The Fe2O3 and FeO in the iron concentrates are mostly reduced to Fe at 9 m below the roof of the reaction shaft, and more than 95 wt% iron particles could be obtained within 1.2–7.7 s.

A new mathematical model for copper concentrate combustion in flash smelting furnaces

A novel mathematical model for combustion of a single copper concentrate particle is presented. The model includes particle volatilization, fragmentation, smelting, and combustion phenomena. This model has been incorporated into a general computational fluid dynamics code to calculate flow field and particle trajectories needed to simulate the smelting process in flash furnaces. In this model, Lagrangian approach was used to handle solid particles and droplets of liquid fuel charged, while Eulerian framework was used to handle the gas phase flow field. The results show that the effect of particle fragmentation was remarkable in flash smelting process as compared with experimental data and should be considered in combustion modeling. Moreover, the flash smelting process simulation results show that the reaction shaft design should be optimized based on a combination of furnace dimension and type of concentrate burners.

CFD Simulation and Performance Analysis of CJD Burner for Intensified Flash Smelting Process

The flash smelting process has been widely acknowledged as a successful modern pyro-metallurgical technology because of its good production flexibility. In past decades, great efforts have been put on the equipment improvement in order to achieve a highly intensive and efficient flash smelting process. However, along with the increasing of the productivity and the intensification of the process, technical problems such as the un-smelted materials accumulated in the settler and the dust generation ratio going higher are found occurring more frequently than before. All these problems however indicate degeneration in the performance of the central jet distributor (CJD) burner. A study was then made on the combustion and reaction processes in the flash furnace equipped with a CJD burner. A steady-state turbulent model was developed and a discrete phase model was included to investigate the velocity and temperature changes of both the gaseous and particle phases in the reaction shaft. The deviation of the numerical model is estimated to be less than 6%. The simulation results reveal a serious delay in the ignition of concentrate particles after they are fed into the furnace. Minor modification was also made by CFD computation, attempting to improve the particle ignition speed, but it was found not so effective. The main reason for the decreased smelting efficiency is found to be the poor mixing between the gaseous and particle phases under the intensified condition. These appeal for a great improvement in the performance of the CJD burner.

Evaluation of Melting Temperature of the Freeze Slag in Reaction Shaft of Flash Smelting Furnace

According to the reaction shaft operation characteristics during the flash smelting process, 15 groups of slag samples containing high Fe3O4were prepared by some chemical reagents, and the slag melting temperatures were measured using a ZDHR-200 type intelligent test instrument for ash melting point by means of hemisphere point. Then, the mathematical formula between the melting temperature and the chemical composition of freeze slag were acquired by means of nonlinear regression analysis. The effects of the Fe/SiO2ratio (mFe/mSiO2), CaO/SiO2ratio (mCaO/mSiO2), Fe3O4content (ωFe3O4), Cu2O content (ωCu2O) and MgO content (ωMgO) on the slag melting temperature were also studied. Results show that the melting temperatures calculated by the regression formula reproduce the experimental data in molten freeze slag with high precision. The slag melting temperature ascends rapidly with increasing ωFe3O4when ωFe3O4>18%, and descends quickly when ωCu2Oraises from 3 % to 7 %, but descends slowly with increasing ωMgO. The melting temperature tend to go down first and then rise up with the increase of mFe/mSiO2and mCaO/mSiO2, arriving at the minimum when mFe/mSiO2=1.3 and mCaO/mSiO2=0.8, respectively.

Determination of Surface Tension of the Freeze Slag in Reaction Shaft of Flash Smelting Furnace

According to the reaction shaft operation characteristics during the flash smelting process, 15 groups of slag samples containing high Fe3O4were prepared by some chemical reagents, and then the slag surface tensions were measured using a RTW-10 type synthetic test instrument for melt physical property by means of suspension link. The effects of temperature ( T ), basicity ( B ), the Fe/SiO2ratio (mFe/mSiO2), Fe3O4content (ωFe3O4), Cu2O content (ωCu2O), MgO content (ωMgO) and CaO content (ωCaO) on the slag surface tension (δ) were also studied. Results show that δ fluctuate between 0.3N/m to 0.8 N/m, and is increased with the increase of T, B, mFe/mSiO2, ωCu2O, ωMgOand ωCaO, and with the decrease of ωFe3O4, under the range of slag contents: mFe/mSiO21.36~1.78, ωFe3O417.83%~21.18%,ωCu2O3.51%~8.34%,ωMgO2.21%~6.57%,ωCaO6.22%~9.87% and the temperature range of 1380°C to 1500°C. To make the freeze slag adhere to the reaction shaft inner wall easily, the Fe3O4content in freeze slag should be increased and the inner chamber temperature of reaction shaft should be controlled appropriately.