Copper smelting slag usually contains 1–6 wt% copper, which can be recovered by pyrometallurgical and flotation processes. However, the tailing slags still consist of 0.3–0.7 wt% Cu and 35–45 wt% Fe equivalents to those in the copper and iron ores, respectively. Most of the research was focused on the recovery of iron from the tailing slags. Copper can increase the mechanical strength, corrosion resistance and antibacterial property of some steels. A new process to recover copper and iron directly and fully from hot copper smelting slag is proposed to produce Cu-Fe alloy for steel production. Effects of flux, temperature, reaction time, reductant type and addition on the recovery of copper and iron were investigated by high-temperature experiments and thermodynamic calculations. It was found that, with 5% CaO and 13–16% carbon additions, most of the copper and iron can be recovered from copper smelting slag at 1350–1400 °C. The copper and iron contents of the reduced slag are lower than 0.1% and 0.5%, respectively, at optimum condition. The new process has the advantages of low energy consumption, low flux addition and high recovery of copper and iron.

To determine slag properties and the factors influencing these properties for optimization of operating conditions in the copper flash smelting process, the composition and microstructures of the quenched smelting and converting slags have been analyzed. Thermodynamic software FactSage 8.2 has been used to investigate the effects of matte grade, SO₂ partial pressure, and the Fe/SiO₂ ratio on the liquidus temperature and the copper content of the smelting slag. The possibility to recover valuable metals from the smelting and converting slags through pyrometallurgical reduction by carbon is also discussed. It was found that the flash smelting slag temperature is usually higher than its liquidus temperature and the copper (1.2% Cu) is mainly present in the slag as dissolved copper. In the copper flash smelting process, the copper content in the slag can be decreased by decreasing the Fe/SiO₂ ratio and temperature. In pyrometallurgical slag reduction, most Cu, Mo, and Ni can be recovered as an alloy. The conditions of recovery such as the ratio of smelting slag to converting slag, temperature, and reduction extent have been discussed.

Arsenic content in copper concentrates is continuously increasing worldwide. It is desirable to remove arsenic from copper in the earlier stages of copper making due to the deposition of arsenic to cathode copper during the electrorefining process. Effects of temperature, flux, and oxygen on the distribution of arsenic during copper converting and fire refining processes were studied using FactSage 8.2. The results showed that arsenic can be effectively removed by proper selection of converting and refining slags. The decrease in Fe/SiO₂ or Fe/CaO ratio in the converting slag is favorable for arsenic distributed to slag. CaO is more effective than SiO₂ in decreasing the liquidus temperature of the slag and arsenic content in the blister copper during the converting process. Na₂O or CaO as a flux is effective to remove arsenic in the fire refining process.

Pyrometallurgy is the primary technique for the production of many nonferrous metals such as copper, lead, and zinc. The phase equilibrium information of smelting slags plays an important role in the efficient extraction of metals and energy consumption. The experimental technologies used in phase equilibrium studies are compared. The presentation and applications of the pseudo-ternary and pseudo-binary phase diagrams are demonstrated in the Fe–Si–Ca–Zn–Mg–Al–Cu–S–O system. Experimental results are also compared with the predictions of FactSage to evaluate the accuracy of the current thermodynamic database. This review paper provides comprehensive information for the operation of nonferrous metals and optimization of the thermodynamic database.