Waste printed circuit boards (PCBs) are the focal point for handling electronic waste. Discarded PCBs are a heterogeneous mix of organic materials, metal, and glass fiber, and consume a large quantity of resources during their production. Mechanical techniques which employ crushing and separation processes to recycle valuable metals from PCBs are becoming more in favor. In general, after the multi-level crushing step, magnetic, electric, air classification or shaking table separation techniques are used to recover metallic materials from the waste PCBs. However, above mechanical combination technologies need fine particles of crushed materials. These provide a high degree of liberation, but separation is difficult. Moreover, there are other problems associated with the crushing process, such as the dust and noise pollution, and serious abrasion of the crushing machine’s cutting tools. Fortunately, rapid temperature change (cooling or heating) could alter the interfacial and mechanical physical properties of an object. Thermal shock may result in structural and mechanical changes of PCBs. Thus, taking into consideration these materials intrinsic characteristics, a preprocessing of waste PCBs by a thermal shock technique is designed, to change the physical performance of PCBs materials, with the aim of simplifying the mechanical technology system and achieving the maximum efficiency for the recovery of metal substances (see figure 5).

The results showed that for a 2mm mesh of a single-level shear-crushing machine, the passed-sieves fraction reached an aggregated degree of liberation of 100% at 250°C, which was an improvement from 13.6% without thermal shock pretreatment. The new-designed equipment for PCB thermal shock was showed in figure 6.