Metal Content,Leaching Characteristics And Environmental Risk Assessment Of Electronic Components On Waste Printed Circuit Boards

Waste printed circuit boards(WPCBs)have distinct resources and hazards,posing challenges to resource recovery and environmental protection.Overcoming this challenge requires combining the hazardous nature of WPCBs with the material composition of the electronic components(ECs).To this end,the paper systematically studies the metal composition and content of ECs,analyzes the toxicity distribution,and identifies the environment risks.The results provide theoretical information for the resources recycling and utilization in ECs,help to supervise the toxic and harmful substances,reduce the potential harm,and protect human health and the ecological environment.The main conclusions are as follows:(1)ECs contain a variety of metal resources,including base metals,precious metals,metalloids,and rare earth elements.The base metal with the highest content in ECs is Cu.,followed by Fe,with average contents of more than 100 g/kg;the average contents of Zn,Al,Ni,Sn is between 10-100 g/kg;the contents of other metals is low and distributed in 0-10 g/kg.As the base metal with the highest content,the total value of copper is about 700 million yuan.Precious metals include Ag(992 mg/kg),Au(303mg/kg),Pd(88 mg/kg)and Pt(3 mg/kg),with a total value of about 13.935 billion yuan,and gold is the mainstay.Rare earth elements(REEs)contain 17 kinds of elements.In2019,the REEs contents in the scrapped "four machines and one brain" is about 315.6tons,with a total value of about 240 million yuan.In short,ECs that concentrate a large amount of rare and precious metals in WPCBs have higher recycling value.(2)There are several environmental risks in ECs.First,the study found for the first time that As and Se have environmental risks,which two elements have not been paid attention to before;second,the risks of Pb and Cr have not been eliminated after the implementation of the Ro HS directive for many years;finally,Sn has strong bioavailability,with the highest proportion of acidic soluble state,which is easy to migrate and has great risks.All in all,the above elements are found in various ECs and bring risks such as leaching toxicity,bioavailability,human toxicity and ecotoxicity.(3)ECs are divided into 2 groups according to environmental risks.ECs classified as hazardous waste in relevant standards and specifications(CPU,graphics card,sound card,memory bank,capacitors with electrolyte,connectors containing precious metals such as gold)are included in the centralized supervision category,managing in accordance with hazardous waste to keep its environmental risks under control.The ECs that are not classified as hazardous wastes but have environmental risks(other ECs)are listed in the priority utilization category,and they shall be downgraded for utilization or recycled as secondary resources according to their resource attributes.But attention should be paid to the recycling process that environmental pollution problems of As,Se,Pb,Cr and Sn.