Experimental Research On Comprehensive Recovery Of Valuable Metals By Reduction And Smelting Of Circuit Boards

With the increase in the use and update rate of electronic products,the variety and amount of e-waste have risen sharply.E-waste has the characteristics of large quantity,great harm,and high content of valuable metals.It is not only a dangerous solid waste but also a typical"urban mine".Circuit boards are the core components of electronic products,and the non-ferrous metal content accounts for more than 30%,which is a high-quality"non-ferrous metal secondary resource".Based on the national environmental protection and hazardous solid waste management regulations,research on environmentally friendly,safe,and cost-effective disposal technologies is an urgent requirement for the circuit board recycling industry.This paper takes waste circuit boards as the research object,and proposes a fire reduction smelting process for waste circuit boards based on the FeO-SiO₂-Al₂O₃-CaO slag system.Through relevant literature and metallurgical principles,the slag composition and structure regulation are analyzed theoretically based on the feasibility of the process,reducing metal loss in slag and controlling performance.On this basis,relevant experiments were carried out,focusing on the effect of flux addition,holding time,smelting temperature,and slag composition on the metal recovery rate,and the optimal smelting process conditions and slag type were determined based on FeO-SiO₂-Al₂O₃-CaO slag type smelting.The production process and heat utilization have been mastered by metallurgical calculations;The circuit board recycling process has been understood and the rules of element migration has been explored through industrial production practice;Environmental protection measures in industrial production are preliminarily analyzed.The main research results are as follows:（1）A FeO-SiO₂-Al₂O₃-CaO slag type suitable for smelting circuit boards is proposed.The phase diagram of liquid phase region of the slag system is simulated by thermodynamic software Fact Sage,and the effect of slag composition on slag viscosity is calculated.The results show that the suitable melting temperature of the slag system is 1400℃,the iron-silicon ratio in the slag composition should be controlled at 0.8-1.1,the alumina content in the slag should be less than 15 wt%,and the calcium oxide content in the slag should be controlled within 8 wt%.（2）Aiming at the reduction smelting process of waste circuit boards based on the FeO-SiO₂-Al₂O₃-CaO slag system,the slag composition and structure are regulated and tested from the perspective of reducing metal loss in the slag and controlling performance.The results show that,under the conditions of 30%flux as raw material,smelting temperature of 1450℃,75 min holding time,FeO/SiO₂=1,and 8%CaO content in the slag,the recovery rate of Cu and Sn in the circuit board can reach 91.98%and 86.30%,and the contents of precious metals Au,Ag and Pt in alloy phase can reach67.41 g/t,1020.74 g/t,54.75 g/t,which proves that the process of reducing and smelting waste circuit boards based on this slag system is feasible.（3）Based on metallurgical calculations,the production process and heat utilization has been mastered;Through the practice of industrial production,the process flow of circuit board recycling and the environmental protection measures in industrial production are understood,and then the migration law of elements is explored,and the methods or ways of harmless treatment and comprehensive utilization of products are put forward.（4）Part of the research results have been applied in the production of industrial processing circuit boards of Shaanxi Jinguo Environmental Protection Company.The results indicate that the process flow is short,the comprehensive utilization and the level of environmental protection are high,the economic benefits are good as well.Therefore,it can be promoted and applied in the hazardous waste treatment industry.