Research On Gold Leaching And Recovery From Wasted PCB With Chlorine Dioxide

Electronic waste is one of the fastest growing streams of solid waste in the world. Wasted printed circuit boards cause people great concern because of its double characters that they are regarded as the potential environmental pollutant and one of the recycling sencondary resources. The studies on the harmlessness and resource of E-waste are also carried out worldwide.The author studies the separation of base and precious metals contained in wasted PCB, the leaching of gold by using chlorine dioxide as oxidation leaching reagent and the recovery of gold from the gold-containing liquor by selective reduction.The wasted PCB is crushed and then sepatated by physical density separation.The metals and non-metals components are effectively separated. The metals componets are enriched and the content of metals increases to 76.7%. To separate base and precious metals, the pretreated sample is leached by controlling the system potential from 380mV to 400mV with chlorine dioxide as oxidation reagent. The experiment shows that the leaching rate of Cu, Pb and Sn is 97.4%,96.2% and 97.2% respectively on the condition of the concentration of HCl 2mol/L, temperature of 80℃, the liquid/solid weight of 8:1 and the leaching time of 2.5h. The enrichment of Au and Ag is about 2.6 times and 2.3 times. The better condition of the experiment of the leaching of gold by chlorine dioxide is following: the ratio of liquid/solid weight of 6:1, the leaching time of 5h, temperature of 60℃,the concentration of HCl 2mol/L and the concentration of NaCl 1mol/L. The leaching rate of gold is up to 94.7%. The batch experiment shows the leaching rate of gold is 94.5%. With ferrous sulphate as reducing reagent, gold can be selecltively reduced and recoveried. On the condition of reaction time of 90min, pH of 3, temperature of 40℃and the concentration of FeSO₄·7H₂O 1.5g/L, the reducing rate of gold is 99.0%.Thermodynamically, the author analyzes the leaching behaviour of some metals at ClO₂-Cl^--H₂O system and obtains the potential-pH diagram under appropriate conditions. The result shows that chlorine dioxide as one of the environmental-friendly oxidation reagent can be used to recycle metals contained in wasted PCB.The result shows that chlorine dioxide has a strong ability of oxidization. The leaching rate of metals contained in PCB is high .The leaching velocity is fast. It is easy to separate the base and precious metals by controlling the system potential. The author puts forward to the hydrometallurgical process along with the use of chlorine dioxide which is environment-friendly green reagent and has a wide application. The process provides a new way to treat and reuse E-waste.