Functionalized Mesoporous Silicas For Selective Adsorption Of Precious Metals From Scrap Printed Circuit Boards

The rapid development of economy drives the electronic products updating and the printed circuit boards(PCBs)are the essential parts in it,resulting a lot of electronic junk which is difficult to deal with.Metallic and non-metallic materials contained in PCBs show a very high economic value.Toxic wastes that produce in traditional processing method for PCBs cause serious potential harm and resources losing.A scheme with three processes to recycle scrap printed circuit boards was proposed in this paper.The first process of preprocess technology contains disassembly,mechanical disruption and enrichment of metals.The second process which containing extract copper and gold is a key step.Other metals in leaching residu were extracted by electrochemical process in the last step.The first and third processes were not discussed because they have been realized in the industrialization of the industrialization of current technologies.Leaching copper in PCBs,then leach and adsorb gold with functionalized mesoporous silica was designed.The functionalized mesoporous silica with ordered hexagonal pore structure was fabricated by a one-step synthesis pathway.The selective adsorption for precious metals was investigated using single and binary component adsorption solutions.In this work,two methods to recover copper and gold from the printed circuit boards were researched.NH3-NH4C1-NH2(CH2)2NH2 and NaS2O3-NH3 solutions served as the systems of hydrometallurgical process.The functionalized mesoporous silica with ordered porous structure and well-formed hexagonal pore array were prepared by a one-step synthesis pathway.The capacity and selectivity of the adsorbents for precious metals were analyzed in relation to the physicochemical and adsorption properties.The results demonstrated that 92.39%copper extracted in the leaching of NH3-NH4C1-NH2(CH2)2NH2 system,80.65%and 51.61%gold extracted in the leaching of NH3-NH4C1-NH2(CH2)2NH2 system and NaC1O3-HCl system,respectively.Both functionalities and morphology of functionalized periodic helical mesostructured silicas(AFMS and TFMS)were controlled by the cocondensation of tetraethoxysilane and hydrophobic organoalkoxysilane using achiral surfactants as templates utilize a one-step synthetic pathway.We use the synthesized materials as adsorbent for removal and recovery of high-purity gold and platinum from binary mixtures containing copper,nickel and iron.The adsorption capacity and selectivity of adsorbents were analyzed in relation to the physicochemical and adsorption properties of the mesoporous adsorbent.The adsorption capacity reached more than 4.2 mmol/g in the optimum conditions.After the desorption experiments,the adsorbent was recovered completely by elution with 5 M HC1 or 0.7 M thiourea-2 M HC1,and released the precious metal nearly 100%.Finally,functionalized mesoporous silica was applied in extracting gold in PCBs and got good results.In this paper,we use a leaching method to collect copper and gold in PCBs,and AFMS and TFMS were fabricated by a one-step synthesis pathway.The selective adsorption for precious metals was investigated by single and binary component adsorption experiments.The precious metal in PCBs is extracted effectively and it has a high economic benefits.