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Cu0 + H2O2 + H2SO4 = Cu2+ + SO42− + 2H2O (2.1) Zn0 + H2O2 + H2SO4 = Zn2+ + SO42− + 2H2O (2.2) Oh et al. developed a leaching process for the recovery of valuable metals from waste printed circuit boards. In their study, PCB samples were first crushed to smaller than 1mm, and then separated by electrostatic separation and magnetic separation. The non-magnetic portion was treated by sulfuric acid. Under the conditions of 2M H2SO4, 0.2M H2O2, 85 °C for 12 hours, more than 95% of copper along with other base metals (Fe, Zn, Ni, Al) was dissolved (Oh et al., 2003). Yang et al. also used sulfuric acid to dissolve copper from waste printed circuit boards in the presence of hydrogen peroxide at room temperature (Yang et al., 2011). The results indicated that the particle size of shredded waste printed circuit boards was the key factor for sulfuric acid leaching, while the high agitation speed inversely affected the copper extraction. It could be attributed to the fact that the increasing stirring speed causes the H2O2 degradation (Birloaga et al, 2013). In acidic sulfate solutions, H2O2 is extensively used as the oxidant; however, H2O2 suffers from its relatively high cost and remarkably high consumption due to its decomposition. Ferric iron is served as an oxidant alternative because of its low cost and easy regeneration (Yazici et al, 2014). Yazici and Deveci (2014) demonstrated the feasibility of leaching copper as well as other metals (Ni, Ag and Pd) from PCBs in an acidic sulfate solution using Fe3+ as an oxidizing agent. High extractions of copper and nickel were readily achieved compared to 21.4% Ag and 69.4% Pd extractions. Moreover, the addition of chloride could improve the extraction of precious metals, silver and palladium. In addition to sulfuric acid leaching, other acids are also investigated. Kasper et al. used aqua regia to leach copper, followed by electrowinning. Approximately 95% of the copper purity was obtained on the cathodes (Kasper et al., 2011). Havlik et al. (2010) proposed a method in which hydrochloric acid was used as the leaching solution to leach thermally treated PCB samples. The thermal treatment was conducted by either pyrolysis or burning. The increased burning temperature improved the copper extraction. It could be explained by the fact that the burning treatment exposed copper and oxidized copper to copper oxide. On the other hand, the highest extraction of copper was achieved at the pyrolysis temperature of 900 °C (Havlik et al., 2010). Kim et al. (2011) were highly interested in electro-generated chlorine in a hydrochloric acid solution. Kim et al. investigated the effect of cuprous ions and leaching kinetics of copper from PCBs. It appeared that the depression of cuprous ions was helpful for increasing the leaching rate 15PDF Image | HYDROMETALLURGICAL TREATMENT OF E-SCRAP
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