Beneficiation of printed wiring boards with gravity concentration

Abstract

With the ever-increasing problem of addressing end-of-life electronics, more emphasis is being placed on recycling and reuse. Between the years 1997 and 2007, experts estimate that we will have more than 500 million obsolete computers in the United States. Companies are seeking new ways to make recycling of electronic scrap more profitable while reducing environmental impacts. Scrap printed wiring boards (PWBs) found in electronic components contain a significant amount of high-value metals and alloys. However, the complexity of PWB material, chemically and physically, creates a significant challenge in the recycling and asset recovery of the different metals and materials. One popular method used to recover the copper (Cu) and precious metals is primary smelting. Demanufacturers and recyclers who send PWB material to Cu smelters will sometimes perform bulk separation and concentration of PWB material in order to reduce shipment volume and make the smelting process more economical. However, concentrated PWB material still typically contains 70-75 percent nonmetals. In primary metal production, the concentration of metals and metal compounds that are found naturally in ore bodies are typically too low to make their recovery and refining cost-effective. As a result, ores are typically mined and the metal compounds are liberated and separated from nonmetals before metal recovery and refining. The ability to economically liberate and separate the metals from the nonmetals found in PWB material before smelting has the potential to make smelting more economical and reduce environmental impacts associated with smelting nonmetals. As part of an electronics scrap recycling study, ground PWB material was processed on concentrating tables to separate metals from nonmetals. The tables exploit the differences in specific gravity and particle size to achieve separation. Results indicate that concentrating tables have the ability to effectively separate the metals from the nonmetals within a specified size distribution. In support of the concentration tables, additional separation equipment testing has begun to determine their ability to produce purer metallic and nonmetallic fractions.