塩化揮発法を利用した廃電子基板からの金属回収と揮発挙動の検討

抄録

  Printed circuit boards of discarded personal computers, televisions, mobile phones and so forth contain many valuable metals. With the aim of recycling the valuable metals contained in printed circuit board waste (PCBW), the effect of temperature on the chlorination-volatilization of metals under chlorine gas flow was investigated. The experimental samples used consisted of two types of powder: crushed PCBW made from PCs and other machines and roasted PCBW, made by roasting PCBW at 700℃. The principal element in crushed PCBW and roasted PCBW was copper, with contents of about 13 mass% and 20 mass%, respectively. Crushed PCBW contained elemental metals such as copper, tin and lead. In contrast, roasted PCBW consisted of oxides such as copper oxide, tin dioxide and silicon dioxide. The two types of sample were heated at temperatures ranging from 300℃ to 900℃ in chlorine gas. It was found that copper in crushed PCBW began to volatilize at 600℃ and was almost completely volatilized at 700℃ by chlorination-volatilization, whereas in roasted PCBW, copper started to volatilize at 600℃ and reached 100% volatilization at 800℃. For crushed PCBW, zinc reached about 85% volatilization at 500℃, while for roasted PCBW, zinc volatilization reached a maximum of only about 80% at 600℃. Lead and nickel also exhibited similar behavior. Consequently, the volatilization rate of crushed PCBW is higher than that of roasted PCBW, and the temperature dependence of the volatilization rate was verified for copper, lead, zinc, nickel, antimony and chromium. The volatilization rate of these metals increased with the temperature. It is thought that chlorination-volatilization is accelerated by the effect of carbon, which is included in crushed PCBW. In this study, the volatilization behavior of some of the valuable metals in PCBW in chlorine gas was observed.