Impact of thermal pretreatment process on recycled copper purity

Recent research has focused on improving the copper refining process to meet the stringent purity standards required by industries such as aerospace. This research builds on our previous study, which identified 1120 °C as the minimum melting temperature required to achieve optimum copper purity from recycled copper scrap. In this phase, we are investigating the effects of thermal pretreatment of copper scrap samples at specific temperatures prior to melting and casting at 1120 °C. The initial thermal pretreatment process involved continuous heating with isothermal holds at six target temperatures (200, 300, 500, 700, 850 and 950 °C). For each test, the duration of the isothermal hold at each temperature was fixed at 5, 10, 15 or 20 minutes, depending on the selected refining sequence. This method significantly improved the purity of the cast copper, increasing it from 99.9230 to 99.9714 wt. %. However, significant mass losses were noticed when holding times exceeded 10 minutes, mainly due to the thermal degradation and fragmentation of thin copper wires. To overcome this, alternative thermal pretreatment techniques were investigated using different holding times. One of the most effective refinements, consisting of a holding time sequence of 5 – 5 – 10 – 10 – 15 – 5 minutes at selected isothermal stages, increased the purity to 99.9716 wt. % and achieved a thermal conductivity of approximately 362 W/mK, while reducing the total refining time to 94 minutes. These findings help to optimise the copper refining process by reducing both costs and mass losses while improving overall efficiency.