2.3 COPPER INDUSTRY The copper industry consists of all establishments in the following SIC categories: SIC 3331 Primary Smelting and Refining of Copper - Establishments primarily engaged in smelting copper from the ore, and in refining copper by electrolytic or other processes. SIC 33412 Secondary Copper - Establishments primarily engaged in recovering copper from copper and copper- based alloy scrap by utilizing a variety of melting and refining methods. SIC 3351 Rolling, Drawing, and Extruding of Copper - Establishments primarily engaged in rolling, drawing, and extruding copper, brass, bronze, and other' copper- base alloy basic shapes, such as plate, sheet, strip, bar, and tubing. SIC 3362 Brass, Bronze, Copper, Copper Base Alloy Foundries (castings) - Establishments primarily engaged in manufacturing castings and die castings of copper and copper-base alloy. The domestic copper industry is segmented into primary and secondary sectors on the basis of whether the copper product has originated from mined copper (virgin ore) or from scrap. By this definition, firms in the primary sector preddinantly transform mined copper into refined copper; firms in the secondary sector either predominantly process scrap into secondary refined copper or prepare it for direct consumption in the form of unrefined copper scrap. The following sections detail these two divisions of the copper industry. 2.3.1 Primary Copper 2.3.1.1 Industry Structure. In 1979, nine companies operated 17 primary smelters with a smelting capacity of approximately 8.2 million tons of charge estimated to represent i.4 miilion tons of smelter product. Re- finery capacity totaled 2.6 million tons, of which 88 percent was electro- lytic refining and electrowinning capacity and 12 percent was fire-refining capacity (6) . According to the Bureau of Mines, 4,707,916 tons of copper was produced in mines, smelters, and refineries from domestic and foreign ores in 1979 (5). Mills are almost always located close to the mines to minimize transportation costs. The value of the concentrates is high enough to allow some flexibility in smelter location. With the major copper mines centered in the western states, most of the smelting capacity is in that region . The copper industry is highly concentrated. In 1979, four companies accounted for 63 percent of the domestic mine production. Twenty-five mines accounted for 94 percent of the U.S. output, the 5 largest produced 45 per- cent (6). 2.3.1.2 Process Description.* The three major steps in producing copper metal are roasting, smelting, and refining. Each is described below. Roasting. The object of roasting copper s fide ores and concentrates is to regulate the amount of sulfur so that the material can be efficiently I smelted and to remove certain volatile impurities such as antimony, arsenic, - and bismuth. Roaster gases are rich in so23 such that sulfuric acid can be produced in large quantities; some of the acid is used in the adjacent electrolytic re- finery. Some copper smelters do not roast prior to reverberatory furance smelt- ing but do make sulfuric acid from converter gases; some smelters do not have adjacent electrolytic copper refineries. Acid plant blowdown slurry effluent .yields a sludge which is not 100 .percent recycled, as will be discussed in a following section. Smelting. Roasted and unroasted materials are smelted after mixing with suitable fluxes in reverberatory furnaces. In this reducing or neutral atmosphere, copper and sulfur form copper sulfide and iron sulfide. The combination of the two sulfides known as copper matte collects in the lower area of the furnace and is removed. Mattes comonly contain 40 to 45 percent copper. Impurities such as sulfur, antimony, arsenic, iron, and precious metals are in the matte. The remainder of the molten mass containing most of the other impurities floats on top of the matte and is drawn off and dis- carded as a slag. A simplified flow diagram identifyfng solid waste sources and dis- posal is shown in Figure 2-4. The primary process steps comprise (1) roast- ing to reduce sulfur content, (2) reverberatory furnace smelting to form copper sulfide matte and a siliceous slag which is discarded, (3) oxidation * This section was derived from Reference 2. 38 i Copper Sulfide LIine Rock Silica Reverts Oust to ACID PLANT blowdarn Slurry Scrubber Slurries I41 scel lanrous Overflow To Tailings Pond (0lrsolv.d folldr Content 280 lbr. wr Short Ton Sopwr Productj Ann* capper Product Figure 2-4. PRIMARY COPPER SMELTING AND FIRE REFINING Source: Reference .2 (blowing) the molten sulfide matte to form molten “blister” copper and iron silicate slag which is returned to the reverberatory, and (4) furnace puri- fication (fire-refining) of the molten copper such that anodes suitable for electrolytic refining can be cast (or copper product that can be marketed directly). Converting is the final stage in the process of smelting and is accomplished by blowing thin streams of air through the molten matte in a refractory-lined converter to oxidize the ferrous sulfide to sulfur dioxide, to eliminate the sulfur as a gas, and also to form a ferrous slag containing trace metal impurities. When the converter cycle is finished, the converter is tilted to discharge the lighter slag and then the relatively pure copper metal, referred to as blister copper, into ladles in which it is transferred to a holding furnace and then to a poling furnace for fire-refining or cast- ing into anodes for electrolysis. The blister copper produced by smelting is too impure for most applications and requires refining before use. It may contain silver and gold, and other elements such as arsenic, antimony, bismuth, lead, seleuium, tellurium, and iron. Two methods are used for refining copper--fire refining and electrolysis. Fire Refining. The fire-refining process employs oxidation, fluxing, and reduction. The molten metal is agitated with compressed air. Sulfur di- oxide is liberated and some of the impurities form metallic oxides which com- bine with added silica to form slag. Sulfur, zinc, tin, and iron are almost entirely eliminated by oxidation. Lead, arsenic, and antimony can be removed by fluxing and skimming as a dross. Copper oxide in the melt is reduced to metal by inserting green wood poles below the bath surface (poling). Re- ducing gases, formed by ‘combustion of the pole convert the copper oxide in I:.. the bath to copper. If the original material does not contain sufficient gold or silver to warrant its recovery, or if a special purpose silver- Containing copper is desired, the fire refined copper is cast directly into forms for industrial use. If it is of such a nature as to warrant the recovery of the precious metals, the fire refining is not carried to completion but only far enough to insure homogeneous anodes for subsequent electrolytic refining. Electrolytic Refining. In the electrolytic refining step anodes and cathodes (thin copper starting sheets) are hung alternately in concrete electrolytic cells containing the electrolyte which is essentially a solu- tion of copper sulfate and sulfuric acid. When current is applied, copper is dissolved from the anode and an equivalent amount of copper plates out of solution on the cathode. Such impurities as gold, silver, platinum-group metals, and the selenides and tellurides of metal fall to the bottom of the i tank and form anode slime or mud. Arsenic, antimony, bismuth, and nickel enter the electrolyte. After the plating cycle is finished, the cathodes are removed from the tanks, melted, and cast into commercial refinery shapes. The copper produced has a minimum purity of 99.9 percent. Important auxiliary process steps are slimes recovery from the cell bottoms, and electrolyte purification to permit electrolyte reuse and to re- cover materials of value. The slimes tend to be rich in Se, Te, As, Ag, Au, and Pt such that their value is very high; the typical refinery ships the slimes filter cakes elsewhere for treatment to recover these metals. (Three of the existing electrolytic copper refineries in the U.S. treat slimes from their own operations and from other refineries.) Since slimes yield is only of the order of 0.002 short'ton pershort ton of copper refined, it is ap- parent that the slimes recovery "industry" in the U.S. is very small relative to copper production. Electrolytic purification consists of the following steps performed on the bleed stream of impure sulfuric acid containing copper and other ele- ments in solution: (1) copper removal by electrolysis with insoluble lead anodes in liberator cells; (2) filtration to remove an arsenical sludge; and (3) evaporation to precipitate nickel sulfate. A "black acid" product remains after nickel sulfate removal. This is marketed for acid recovery. Slags taken from the melting and refining furnace (and from the anode casting furnace at refineries wich cast anodes) are very rich in copper (50 percent Cu), i.e., immediate recycle to a copper smelter is dictated and practiced. 2.3.1.3 Waste Stream Characteristics.* ~e sources of solid waste at copper smelters include furnace slag, wet sludges, and in a few cases, collected particulates. Solid wastes at electrolytic copper refineries consist of only a few miscellaneous sludges and slurries; these occur in relatively small quantities because of the high purity of the material fed to the refinery process. Slag is the major solid waste from copper smelting. It is usually tapped from the furnace, transported molten to the slag pile, hot dumped, and allowed to solidify. At some copper smelters the slag is granulated as it is tapped from the furnace. Particulates are collected from the off-gases and are usually recycled to the process, although those with accumulations of impurities may need to be discarded. The furnace off-gas also contains sulfur dioxide.