Pollution Prevention and Abatement Handbook WORLD BANK GROUP Effective July 1998 Copper Smelting Industry Description and Practices ISA-SMELT and KIVCET, which replace roasting and smelting. For converting, the Pierce-Smith Copper can be produced either pyrometallur- and Hoboken converters are the most common gically or hydrometallurgically. The hydromet- processes. allurgical route is used only for a very limited The matte from the furnace is charged to con- amount of the world’s copper production and is verters, where the molten material is oxidized in normally only considered in connection with in- the presence of air to remove the iron and sulfur situ leaching of copper ores; from an environmen- impurities (as converter slag) and to form blister tal point of view, this is a questionable produc- copper. tion route. Several different processes can be used Blister copper is further refined as either fire- for copper production. The traditional process is refined copper or anode copper (99.5% pure cop- based on roasting, smelting in reverbatory fur- per), which is used in subsequent electrolytic naces (or electric furnaces for more complex ores), refining. In fire refining, molten blister copper is producing matte (copper-iron sulfide), and con- placed in a fire-refining furnace, a flux may be verting for production of blister copper, which is added, and air is blown through the molten mix- further refined to cathode copper. This route for ture to remove residual sulfur. Air blowing re- production of cathode copper requires large sults in residual oxygen, which is removed by amounts of energy per ton of copper: 30–40 mil- the addition of natural gas, propane, ammonia, lion British thermal units (Btu) per ton cathode or wood. The fire-refined copper is cast into an- copper. It also produces furnace gases with low odes for further refining by electrolytic processes sulfur dioxide (SO2) concentrations from which or is cast into shapes for sale. the production of sulfuric acid or other products In the most common hydrometallurgical pro- is less efficient. The sulfur dioxide concentration cess, the ore is leached with ammonia or sulfuric in the exhaust gas from a reverbatory furnace is acid to extract the copper. These processes can about 0.5–1.5%; that from an electric furnace is operate at atmospheric pressure or as pressure about 2–4%. So-called flash smelting techniques leach circuits. Copper is recovered from solution have therefore been developed that utilize the by electrowinning, a process similar to electrolytic energy released during oxidation of the sulfur in refining. The process is most commonly used for the ore. The flash techniques reduce the energy leaching low-grade deposits in situ or as heaps. demand to about 20 million Btu/ton of produced Recovery of copper metal and alloys from cathode copper. The SO2 concentration in the off copper-bearing scrap metal and smelting resi- gases from flash furnaces is also higher, over 30%, dues requires preparation of the scrap (e.g., re- and is less expensive to convert to sulfuric acid. moval of insulation) prior to feeding into the (Note that the INCO process results in 80% sul- primary process. Electric arc furnaces using scrap fur dioxide in the off gas.) Flash processes have as feed are also common. been in use since the 1950s. In addition to the above processes, there are a Waste Characteristics number of newer processes such as Noranda, Mitsubishi, and Contop, which replace roasting, The principal air pollutants emitted from the pro- smelting, and converting, or processes such as cesses are sulfur dioxide and particulate matter. 291 292 PROJECT GUIDELINES: INDUSTRY SECTOR GUIDELINES The amount of sulfur dioxide released depends ges from wastewater treatment processes that on the characteristics of the ore—complex ores require reuse/recovery or appropriate disposal. may contain lead, zinc, nickel, and other metals— The main portion of the solid waste is dis- and on whether facilities are in place for captur- carded slag from the smelter. Discard slag may ing and converting the sulfur dioxide. SO2 contain 0.5–0.7% copper and is frequently used emissions may range from less than 4 kilo- as construction material or for sandblasting. grams per metric ton (kg/t) of copper to 2,000 Leaching processes produce residues, while ef- kg/t of copper. Particulate emissions can range fluent treatment results in sludges, which can be from 0.1 kg/t of copper to as high as 20 kg/t of sent for metals recovery. The smelting process copper. typically produces less than 3 tons of solid waste Fugitive emissions occur at furnace openings per ton of copper produced. and from launders, casting molds, and ladles car- rying molten materials. Additional fugitive par- Pollution Prevention and Control ticulate emissions occur from materials handling and transport of ores and concentrates. Process gas streams containing sulfur dioxide are Some vapors, such as arsine, are produced in processed to produce sulfuric acid, liquid sulfur hydrometallurgy and various refining processes. dioxide, or sulfur. The smelting furnace will gen- Dioxins can be formed from plastic and other erate process gas streams with SO2 concentrations organic material when scrap is melted. The prin- ranging from 0.5% to 80%, depending on the pro- cipal constituents of the particulate matter are cess used. It is important, therefore, that a pro- copper and iron oxides. Other copper and iron cess be selected that uses oxygen-enriched air (or compounds, as well as sulfides, sulfates, oxides, pure oxygen) to raise the SO2 content of the pro- chlorides, and fluorides of arsenic, antimony, cad- cess gas stream and reduce the total volume of mium, lead, mercury, and zinc, may also be the stream, thus permitting efficient fixation of present. Mercury can also be present in metallic sulfur dioxide. Processes should be operated to form. At higher temperatures, mercury and ar- maximize the concentration of the sulfur diox- senic could be present in vapor form. Leaching ide. An added benefit is the reduction of nitro- processes will generate acid vapors, while fire- gen oxides (NOx). refining processes result in copper and SO2 emis- Closed-loop electrolysis plants will contribute sions. Emissions of arsine, hydrogen vapors, and to prevention of pollution. acid mists are associated with electrorefining. Continuous casting machines should be used Wastewater from primary copper production for cathode production to avoid the need for contains dissolved and suspended solids that mold release agents. may include concentrations of copper, lead, cad- Furnaces should be enclosed to reduce fugi- mium, zinc, arsenic, and mercury and residues tive emissions, and dust from dust control equip- from mold release agents (lime or aluminum ox- ment should be returned to the process. ides). Fluoride may also be present, and the ef- Energy efficiency measures (such as waste heat fluent may have a low pH. Normally there is no recovery from process gases) should be applied liquid effluent from the smelter other than cool- to reduce fuel usage and associated emissions. ing water; wastewaters do originate in scrubbers Recycling should be practiced for cooling wa- (if used), wet electrostatic precipitators, cooling ter, condensates, rainwater, and excess process of copper cathodes, and so on. In the electrolytic water used for washing, dust control, gas scrub- refining process, by-products such as gold and bing, and other process applications where wa- silver are collected as slimes that are subsequently ter quality is not a concern. recovered. Sources of wastewater include spent Good housekeeping practices are key to mini- electrolytic baths, slimes recovery, spent acid mizing losses and preventing fugitive emissions. from hydrometallurgy processes, cooling water, Such losses and emissions are minimized by en- air scrubbers, washdowns, stormwater, and slud- closed buildings, covered or enclosed conveyors Copper Smelting 293 and transfer points, and dust collection equip- of World Bank Group assistance. Any devia- ment. Yards should be paved and runoff water tions from these levels must be described in routed to settling ponds. Regular sweeping of the World Bank Group project documentation. yards and indoor storage or coverage of concen- The emissions levels given here can be con- trates and other raw materials also reduces ma- sistently achieved by well-designed, well- terials losses and emissions. operated, and well-maintained pollution control systems. Treatment Technologies The guidelines are expressed as concen- trations to facilitate monitoring. Dilution of air Fabric filters are used to control particulate emis- emissions or effluents to achieve these guidelines sions. Dust that is captured but not recycled will is unacceptable. need to be disposed of in a secure landfill or other All of the maximum levels should be achieved acceptable manner. for at least 95% of the time that the plant or unit Vapors of arsenic and mercury present at high is operating, to be calculated as a proportion of gas temperatures are condensed by gas cooling and annual operating hours. removed. Additional scrubbing may be required. Effluent treatment by precipitation, filtration, Air Emissions and so on of process bleed streams, filter back- wash waters, boiler blowdown, and other The air emissions levels presented in Table 1 streams may be required to reduce suspended should be achieved. and dissolved solids and heavy metals. Residues The EA should address the buildup of heavy that result from treatment are sent for metals re- metals from particulate fallout in the vicinity of covery or to sedimentation basins. Stormwaters the plant over its projected life. should be treated for suspended solids and heavy metals reduction. Liquid Effluents Slag should be landfilled or granulated and sold. The effluent emissions levels presented in Table Modern plants using good industrial practices 2 should be achieved. should set as targets total dust releases of 0.5–1.0 kg/t of copper and SO2 discharges of 25 kg/t of Ambient Noise copper.