About one-third of the copper currently produced in the world is derived from secondary materials e the copper scrap and waste described in the previous chapter. Secondary material is recycled in numerous ways. New scrap is often recycled directly back to the melting furnace, where it was produced in the first place. Old scrap and waste streams (and some new scrap) travel a more complex path. They can either be added to one of the furnaces used to produce primary copper e the smelters, converters, and anode furnace described in previous chapters. They can also be reprocessed by secondary smelters specifically designed to handle such material. This chapter looks at the different methods used to turn old scrap and waste back into new copper metal.
CHARACTERISTICS OF SECONDARY COPPER
Several factors determine what happens to copper-containing scrap and waste. These include:l The condition of the scrap. The different types of No. 1 scrap (see Table .1) contain very small levels of oxidation or impurities, and need only be remelted in a nonoxidizing environment. As a result, this scrap commands a higher price, and is more likely to be charged to furnaces requiring a purer grade of input material. No. 2 scrap is more oxidized, and requires refining. Heavily oxidized waste materials like plating sludges require remelting in a reducing environment to avoid copper loss. l Location. Copper scrap is often collected at locations which are very far from primary smelters. The cost of transporting it determines where it winds up. l Alloying elements. Impurity elements in secondary copper often have sufficient value to be recovered in their own right. This includes the gold and silver content of electronic scrap, the lead in copper drosses, and the lead, tin, and zinc in brass and bronze scrap. Recovering these elements often dictates recycling strategy. l Government regulations. Some governments place export tariffs on copper-containing scrap to encourage recycling at home. Restrictions on the exporting of some electronic scrap have also encouraged local reprocessing efforts. Restrictions on air emissions from processing plants have had an impact on processing strategy.
SCRAP PROCESSING IN PRIMARY COPPER SMELTERS
Secondary copper can be added at three locations in the primary coppermaking process. The most common is the converting furnace, but additions are also made in the smelting and anode furnaces.