The processing of eWaste. Part 1: The preparation and characterization of a metallic alloy derived from the smelting of printed circuit boards

The disposal of waste electrical and electronic equipment—the so-called eWastes—has been recognized worldwide as an important issue. This is due to concerns about the leaching of hazardous metals such as chromium, mercury and cadmium from electronic and electric wastes in landfill. In more developed countries such as the United States of America and Western Europe the problem of eWaste has grown to the extent where legislation has been enacted, such as the Waste Electrical and Electronic Equipment (WEEE) legislation of the EU (European Union Directive 2002/96/EC). Worldwide there is also an increasing appreciation of the limited nature of economically exploitable primary metal resources1. Hence there is more pressure for reclaiming metal values from obsolete items through appropriate recycling. Such secondary sources have not, in general, featured strongly in the South African base metals industry. So far the country has had access to adequate primary ores especially in precious metals, but also in many base metals. In addition, while tonnages are relatively small, scrap material is often of unknown composition, and thus it requires additional chemical analysis, and possibly special treatment. Obsolete scrap is often complex, requiring disassembly and identification of component materials. For instance, as copper is an undesirable element in steel, wiring harnesses and small electric motors need to be stripped from scrapped cars before the steel can be smelted. Alternatively, scrapped items can be shredded complete, or after partial disassembly to provide adequate liberation of various materials. This makes the separation problem more difficult, however. In the case of electrical and electronic waste equipment it is necessary to remove items such as electrolytic capacitors which can contain dioxins when they have been in use, as well as batteries. Printed circuit boards (PCBs) can often be removed fairly intact after a simple disassembly process. This is worthwhile doing as they generally contain sufficient gold and other precious metals to make recovery economically viable. A typical PCB consists of a glass reinforced thermosetting epoxy resin base, or a sheet of phenolic resin impregnated paper material. These are normally impregnated with bromine based fire retardants that result in an off-gas handling problem if the base material is subjected to high temperatures. The board will have one or more layers of thin copper material defining the conductive interconnects between electronic components. Components of various types are connected to the copper tracks by soldered connections. The solders have generally been 60–40 tin-lead types. Due The processing of eWaste. Part 1: The preparation and characterization of a metallic alloy derived from the smelting of printed circuit boards