Mark E. Schlesinger’s research while affiliated with Missouri University of Science and Technology and other places

About one-third of the copper currently produced in the world is derived from secondary materials. 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. It can either be added to one of the furnaces used to produce primary copper—the smelters, converters, and anode furnace described in previous chapters. It 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.

This chapter describes production of secondary copper—recovery of copper from scrap. It emphasizes the scrap recycling in general, major sources and types of scrap, and physical beneficiation techniques for isolating copper from its coatings and other contaminants. The purest copper scrap is simply re-melted and recast in preparation for manufacture and use. Less pure copper scrap is re-smelted and re-refined. Alloy scrap is usually recycled directly to make new alloy. Considerable scrap must be physically treated to isolate its copper from its other components. An important example of this is recovery of copper from wire and cable. It is done by: chopping the wire and cable into small pieces to liberate its copper; physically isolating its copper by means of a specific gravity separation (air table). Copper recovery from used automobiles and electronic devices follows a similar pattern, i.e.: Liberation by size reduction (shredding); isolation of copper by magnetic, specific gravity, and eddy-current separation. The copper from these processes is then re-smelted and re-refined. Old (obsolete) scrap is often discarded in landfills. There is, however, an increasing tendency to recycle this material due mainly to the increased cost and decreased availability of landfill sites.

This chapter discusses production and use of copper around the world. It gives production, use, and price statistics, and identifies and locates the world's largest copper producing plants. Copper is produced around the world. About 40% is mined in the western mountain region of South America. Concentrators and leach/solvent extraction/electrowinning plants are located near their mines. Smelters and refineries, on the other hand, are increasingly being located on sea coasts so that they can receive concentrates from mines around the world. Copper's most exploited property is its high electrical conductivity, in conjunction with its excellent corrosion resistance, formability, and joinability. Its high thermal conductivity and corrosion resistance are also exploited in many heat transfer applications. Worldwide, about 22 million tons of copper come into use per year. About 18 million tons of this comes from new mine production and about 4 million tons from recycled end-of-use objects and manufacturing wastes.

This chapter focuses on the Outotec flash smelting, which accounts for around half of all Cu matte smelting. It is also used in three locations for direct-to-copper smelting and in two locations for continuous converting. It blows a well-dispersed mixture of oxygen, air, dried concentrate, flux, and particulate recycle materials into a hot reaction shaft. Smelting reactions are extremely fast under these conditions. Outotec flash furnaces smelt equals to 4000 tonnes of new concentrate per day. Modern Outotec flash furnaces operate with high oxygen blast and very little hydrocarbon fuel. Most of the energy for heating and melting comes from Fe and S oxidation. This operation also gives strong SO2 offgas from which SO2 can be captured efficiently as sulfuric acid. Outotec flash furnaces are operated under automatic control to give constant temperature, constant composition products at a rapid rate and with minimum energy consumption. Matte and slag compositions are controlled by adjusting the ratios of O2 input rate to concentrate feed rate, and of flux input to concentrate input. Product temperatures are controlled by adjusting the N2/O2 ratio of the input blast and the hydrocarbon fuel combustion rate. Wide adoption of Outotec flash smelting is due to its efficient capture of SO2, its rapid production rate, and its small energy requirement. Its only limitation is its inability to smelt scrap.

The processing of byproduct streams is a significant activity at copper concentrators, smelters, and refineries. The treatment of several common byproducts is the subject of this chapter. MoS2 occurs in economic quantities in many porphyry Cu deposits. It is recovered to MoS2 flotation concentrates by: floating MoS2 and Cu–Fe–S minerals together in a bulk Cu–Mo concentrate, then; depressing Cu–Fe–S minerals and floating MoS2 in a Mo–Cu flotation separator plant. Typical Mo recovery to final MoS2 concentrate is ∼70% (80% to the bulk concentrate and 90% of that to the final MoS2 concentrate). Other byproducts from copper production include the slime from electrorefining, dust recovered from bag houses and electrostatic precipitators, and smelting slag. All of these can be treated to recover their copper content, and the remaining material is also valuable. The slime, in particular, contains significant levels of gold, silver, selenium, and tellurium. The recovery of these metals has a significant impact on the profitability of copper production facilities.

This chapter describes production of Cu-rich sulfide concentrate (∼30% Cu) from finely ground ore. Copper sulfide ores must be concentrated before they can be economically transported and smelted. The universal technique for this concentration is froth flotation of finely ground ore. Froth flotation entails attaching fine Cu-sulfide mineral particles to bubbles and floating them out of a water–ore mixture. The flotation is made selective by using reagents, which make the Cu-sulfide minerals water-repellant (hydrophobic) while leaving the other minerals wetted (hydrophilic). Typical Cu sulfide recoveries to concentrate are 85–90%. Typical concentrate grades are 30% Cu (higher with chalcocite, bornite, and native copper mineralization). Column flotation cleaner cells are particularly effective at giving a high Cu grade in the concentrate. Modern concentrators are automatically controlled to give maximum Cu recovery, maximum % Cu in the concentrate, and maximum ore throughput rate at minimum cost. Expert control systems help to optimize the performance of flotation plants. On-stream particle size and on-stream X-ray fluorescence analyses are key components of this automatic control.

This chapter describes the production of high-grade concentrate from low-grade ore. Processing of sulfide minerals is emphasized because these minerals account for virtually all Cu concentration. Copper ores typically contain 0.5–2% Cu. They must be concentrated to ∼30% Cu before smelting. The universal concentration technique is froth flotation of finely ground ore particles. The feed to froth flotation is produced by comminution, which includes: Blasting ore fragments from the mine walls (∼0.1 m diameter); crushing these fragments in eccentric and roll crushers (∼0.01 m diameter); grinding the crushed ore in rotating tumbling mills (<100 mm diameter). The resulting finely ground particles are then sent continuously to froth flotation. A recent development is the formation of finer more uniform fragments during blasting by means of larger explosive loadings in blast holes. This increases crushing rate and lowers crushing electricity requirements. It has been aided by: Automatic ore toughness measurements during blast hole drilling and continuous measurement of fragment sizes by electronic imaging of blasted ore during delivery to crushing.

This chapter describes the investment and production costs of producing copper metal from ore and discusses how these costs are affected by such factors as ore grade, process route, and inflation. The total direct plus indirect cost of producing electrorefined copper from ore by conventional mining/concentration/smelting/refining is in the range of 3–6 per kg of copper. The total direct plus indirect cost of producing electrowon copper cathodes from oxide and chalcocite ores (including mining) is 1–2 per kg of copper. Copper extraction is distinctly profitable when the selling price of copper is above $6/kg. It is unprofitable for some operations when the selling price falls below$3/kg. At the former price, the industry tends to expand. At the latter, it begins to contract. The selling price of copper in mid-2011 was ∼$9/kg. Virtually all existing operations are profitable and the industry is expanding.

This chapter describes operation and control of various types submerged-tuyere smelting. Teniente and Noranda smelting are submerged-tuyere smelting processes where Fe and S are oxidized by blowing oxygen-enriched air through submerged tuyeres into a matte-slag bath. The principal product is super high-grade matte, 72–74% Cu. Both use horizontal refractory-lined cylindrical furnaces with a horizontal line of submerged tuyeres. The furnaces are rotatable so that their tuyeres can be rolled out of the liquids when blowing must be interrupted. Concentrate feed is dried and blown into the matte-slag bath through dedicated tuyeres or charged moist onto the bath surface. Tuyere injection is increasing due to its even concentrate and heat distributions, high-thermal efficiency and small dust evolution. Submerged blowing of blast causes violent stirring of the matte/slag bath. This results in rapid melting and oxidation of the furnace charge. It also prevents excessive deposition of solid magnetite in the furnace even under highly oxidizing conditions. The violent stirring also permits extensive smelting of scrap and reverts. Teniente and Noranda smelting furnaces account for about 15% of world copper smelting. They are the dominant smelting method in Chile and are used in several other countries. Installation rate has slowed appreciably during the last decade. A third submerged tuyere copper smelting technology is Vanyukov smelting. It uses stationary furnaces and is used in Russia and Kazakhstan.

This chapter focuses on the top-lancing technology suitable for a variety of pyrometallurgical applications including smelting and converting of sulfide concentrates. This technology is known generically as top submerged lance technology. It is now licensed by two separate organizations, Isasmelt and Ausmelt. Smelting is done in vertically aligned cylindrical furnaces 3.5–5 m diameter and 12–16 m high. The smelting entails: dropping moist concentrate, flux, and recycle materials into a molten matte/slag bath in a hot furnace; blowing oxygen-enriched air through a vertical lance into the matte/slag bath. Most of the energy for smelting is obtained from oxidizing the Fe and S in the concentrate. The principal product of the furnace is a matte/slag mixture. It is tapped into a hydrocarbon-fired or electric settling furnace. The products after settling are 60% Cu matte and 0.7% Cu slag. The main advantages of the process are: its small footprint, which makes it easy to retrofit into existing smelters, its ability to process a variety of feed materials, and small evolution of dust. Further, Mitsubishi Process also performs smelting and converting in a molten bath. It uses three interconnected furnaces to continuously smelt copper concentrates, settle, and separate matte from discard slag, and convert the matte to blister copper. When performing properly, continuous processing solves many of the problems created by more traditional copper smelting technology, most notably the elimination of ladle transfer of molten matte, the fugitive emissions associated with Peirce–Smith converting, and the uneven SO2 offgas content that results from batch processing of copper concentrates.