Porous Carbon Materials For Selective Adsorption Of Precious Metals From Scrap Printed Circuit Boards

The rapid technological innovation and development of economy accelerate the replacement of electronic products,which results in a large amount of e-wastes,such as printed circuit boards(PCBs).The waste PCBs contain a large amount of metals and metalloids,about 130 kg of copper,20 kg of tin,24 kg of lead,18 kg of nickel,and 0.45 kg of gold are available in each ton of the PCBs.It is well worth recovering metal resources from the waste PCBs.On the other hand,waste PCBs contain many harmful materials like brominated flame retardant and heavy metals which are highly toxic to the environment.Toxic wastes that produce in traditional processing method for PCBs cause serious potential harm and resources losing.Therefore,the green recycling process of PCBs is an important subject not only from the point of environmental protection but also from the economic point of view.In our work,two key factors to recover copper and gold from the printed circuit boards were researched.In the first place,NE3·H2O-NH4C1-NH2(CH2)2NH2 solutions served as the systems of copper extraction,NaS2O3-NH3·H2O-NaCl and HC1 solutions served as the systems of gold extraction,respectively.On the other hand,the ordered mesoporous carbon(OMC)and banana peel carbon(BPC)materials were prepared by the use of hard templates and carbonization methods.The selectivity adsorption properties and the reaction condition of the adsorbents for precious metals were analyzed.In addition,we explored the gold desorption of HCl solution adsorption on carbon materials.The results displayed that 94.10%copper extracted in the leaching of NH3·H2O-NH4Cl-NH2(CH2)2NH2 system,90.79%and 90.92%gold extracted in the leaching of NaS2O3,NH3·H2O-NaCl system and HCl system,respectively.Physicochemical property of OMC and BPC were characterized by BET,TEM,micro-IR and XRD,and the functional groups(-OH,-NH2)were founded on the carbon materials.The adsorption performance for precious metals was investigated using single and multi-component adsorption solutions.The single component adsorption results of OMC showed its high adsorption capacities of 1306.20 mg/g for Au(Ⅲ)at pH 2.5,99.32 mg/g for Pt(Ⅳ)at pH 1.0 when the temperature was 25℃,which are important for recovery high purity precious metal(gold and platinum)from PCBs resources.The adsorption results of BPC showed its adsorption capacity reached 801.70 mg/g,at pH 1.0 when the temperature was 25 ℃.Both OMC and BPCs displayed excellent selectivity for Au(Ⅲ)in the multi-component adsorption.After the desorption experiments,these two adsorbents were recovered completely by elution with HC1 solutions,and released the precious metal nearly 90%.Finally,BPCs was applied in extracting precious metal gold from PCBs.In this paper,we use a step by step leaching method to extract copper and gold from PCBs and BPC that containing functional groups were fabricated by a simple carbonization process.The selective adsorption for precious metals was investigated by single and multi-component adsorption experiments.The above technology is available for its simple operation,friendly environment and high recovery rate for metals.This waste treatment technology can not only contribute to solid electronic waste,but also realize the recycling of agricultural waste,which benefit greatly in economic,environment and social aspects.