Coppers Melting

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Multilateral Investment Guarantee Agency

Environmental Guidelines for

Copper Smelting

Industry Description and Practices In addition to the above processes there are anumber of newer processes such as theNoranda, Mitsubishi, and Contop whichreplaces or was intended to replace roasting,smelting and converting, or processes such as

ISA-SMELT and KIVCET which replacesroasting and smelting. For converting thePierce-Smith and Hoboken converters are themost common processes.

Copper can be produced eitherpyrometallurgically or hydrometallurgically.The hydrometallurgical route is used only for a

very limited amount of the worlds copperproduction and normally only considered inconnection to in-situ leaching of copper ores;from an environmental point of view this is aquestionable production route. Several differentprocesses can be used for copper production.The old traditional process is based on roasting,smelting in reverbatory furnaces or electricfurnaces for more complex ores, producingmatte and converting for production of blistercopper which is further refined to cathodecopper. This route for production of cathode

copper requires large amounts of energy per tonof copper (30-40 million Btu per ton cathodecopper). It also produces furnace gases with lowsulfur dioxide concentrations from which theproduction of sulfuric acid or other products isless efficient. The sulfur dioxide concentrationin the exhaust gas from a reverbatory furnace isabout 0.5-1.5% and from an electric furnace isabout 2-4%. So called flash smelting techniqueshave therefore been developed which utilize theenergy released during oxidation of the sulfurin the ore. The flash techniques reduce theenergy demand to about 20 million Btu/ton of

produced cathode copper. The sulfur dioxideconcentration in the off gases from flashfurnaces is also higher, over 30%, and lessexpensive to convert to sulfuric acid (note: theINCO process results in 80% sulfur dioxide inthe off gas). Flash processes have been in usesince the 1950s.

The matte (copper-iron sulfide) from thefurnace is charged to converters where themolten material is oxidized in the presence ofair to remove the iron and sulfur impurities (asconverter slag) and to form blister copper.

Blister copper is further refined as either fire-refined copper or anode copper (99.5% purecopper), which is used in subsequent

electrolytic refining. In fire-refining, moltenblister copper is placed in a fire-refiningfurnace, a flux may be added and air is blownthrough the molten mixture to remove residualsulfur. Air blowing results in residual oxygenwhich is removed by the addition of naturalgas, propane, ammonia or wood. The fire-refined copper is cast into anodes for furtherrefining by electrolytic processes or is cast intoshapes for sale.

In the most common hydrometallurgicalprocess the ore is leached with ammonia orsulfuric acid to extract the copper. These

processes can operate at atmospheric pressureor as pressure leach circuits. Copper isrecovered from solution by electrowinning aprocess similar to electrolytic refining. Theprocess is most commonly used for leachinglow grade deposits in situ or as heaps.

Recovery of copper metal and alloys fromcopper bearing scrap metal and smelting

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residues requires preparation of the scrap (suchas removal of insulation, etc.) prior to feedinginto the primary process. Electric arc furnacesusing scrap as feed are also common.

Waste Characteristics

Principal air pollutants emitted are sulfurdioxide (SO2) and particulate matter from theprocesses. The amount of sulfur dioxidereleased from the process will depend on thecharacteristics of the orecomplex ores maycontain lead, zinc, nickel and other metalsandwhether facilities are in place for capturing andconverting the SO2. Sulfur dioxide emissionsmay range from less than 4 kilograms permetric ton (kg/t) copper to 2,000 kg/t copper.Particulate emissions can range from 0.1 kg/t

copper to as high as 20 kg/t copper.Fugitive emissions occur at furnaceopenings, from launders, casting molds, andladles carrying molten materials. Additionalfugitive particulate emissions occur frommaterials handling and transportation of oresand concentrates.

Some vapors, as arsine, are produced inhydrometallurgy and various refiningprocesses. Dioxins can be formed from plasticand other organic material during melting ofscrap. The principal constituents of theparticulate matter are copper and iron oxides.

Other copper and iron compounds as well assulfides, sulfates, oxides, chlorides and/orfluorides of arsenic, antimony, cadmium, lead,mercury and zinc may also be present. Mercurycan also be present in metallic form. At highertemperatures, mercury and arsenic could bepresent in vapor form. Leaching processes willgenerate acid vapors while fire-refiningprocesses result in copper and sulfur dioxideemissions. Emissions of arsine, hydrogenvapors and acid mists are associated withelectrorefining.

Wastewater from primary copper

production contains dissolved and suspendedsolids that may include: concentrations ofcopper, lead, cadmium, zinc, arsenic andmercury, and residues from mold release agents(lime or aluminum oxides). Fluoride may alsobe present and the effluent may have a low pH.Normally there is no liquid effluent from the

smelter other than cooling water; waste watersdo originate in scrubbers (if used), wetelectrostatic precipitators, cooling of coppercathodes, etc. In the electrolytic refining process,by-products such as gold and silver arecollected as slimes which are subsequentlyrecovered. Sources of wastewater include spentelectrolytic baths, slimes recovery, spent acidfrom hydrometallurgy processes, cooling water,air scrubbers, washdowns, stormwater andsludges from wastewater treatment processesthat require reuse/recovery or appropriatedisposal.

The major portion of the solid waste isdiscarded slag from the smelter. Discard slagmay contain 0.5-0.7% copper and is frequentlyused as construction material or forsandblasting. Leaching processes produce

residues while effluent treatment results insludges which can be sent for metals recovery.The smelting process typically produces lessthan three tons of solid waste per ton of copperproduced.

Pollution Prevention and Control

Process gas streams containing SO2 areprocessed to produce sulfuric acid, liquid sulfurdioxide, or sulfur. The smelting furnace willgenerate process gas streams with SO2concentrations ranging 0.5-80% percent

depending on the process used. It is important,therefore, that a process be selected which usesoxygen enriched air (or pure oxygen) to raisethe sulfur dioxide content of the process gasstream and reduce the total volume of thestream, thus permitting efficient fixation ofsulfur dioxide. Processes should be operated tomaximize the concentration of the SO2. Anadded benefit is the reduction of nitrogenoxides (NOx).

Closed loop electrolysis plants willcontribute to prevention of pollution.

Continuous casting machines should be used

for cathode production to avoid the need formold release agents.

Furnaces should be enclosed to reducefugitive emissions, and dust from dust controlequipment should be returned to the process.


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Emission GuidelinesUse energy efficiency measures (such aswaste heat recovery from process gasses) toreduce fuel usage and associated emissions. Emission levels for the design and operation of

each project must be established through theEnvironmental Assessment (EA) process, basedon country legislation and the PollutionPrevention and Abatement Handbook as applied tolocal conditions. The emission levels selectedmust be justified in the EA and acceptable toMIGA.

Recycle cooling waters, condensates,rainwater, and excess process water forwashing, for dust control, for gas scrubbing,and for other process applications where waterquality is not of concern.

Good housekeeping practices are key tominimizing losses and preventing fugitiveemissions. Such losses and emissions areminimized by enclosed buildings, covered orenclosed conveyors and transfer points, anddust collection equipment. Yards are paved andrun-off water is routed to settling ponds.Regular sweeping of yards, and indoor storageor coverage of concentrates and other rawmaterials also reduce material losses and

emissions.

The following guidelines present emissionlevels normally acceptable to the World BankGroup in making decisions regarding provisionof World Bank Group assistance, includingMIGA guarantees; any deviations from theselevels must be described in the World BankGroup project documentation.

The guidelines are expressed as

concentrations to facilitate monitoring. Dilutionof air emissions or effluents to achieve theseguidelines is unacceptable.Treatment Technologies

All of the maximum levels should beachieved for at least 95% of the time that theplant or unit is operating, to be calculated as aproportion of annual operating hours.

Fabric filters are used to control particulateemissions. Dust that is captured but notrecycled will need to be disposed in a securelandfill or other acceptable manner.

Air EmissionsVapors of arsenic and mercury present athigh gas temperatures are condensed by gascooling removed. Additional scrubbing may berequired.

For copper smelters the following air emissionslevels should be achieved:

Effluent treatment by precipitation, filtration,

etc. of process bleed streams, filter backwashwaters, boiler blowdown, and other streamsmay be required to reduce suspended anddissolved solids and heavy metals. Residuesthat result from treatment are either sent formetals recovery or sent to sedimentation basins.Storm waters should be treated for suspendedsolids and heavy metals reductions.

Emissions from Copper Smelting

Parameter

Maximum valuemilligrams per

normal cubic meter(mg/Nm3)

SO2 1,000

Arsenic 0.5

Cadmium 0.05

Copper 1

Lead 0.2

Mercury 0.05

Particulates - smelter 20Particulates - othersources

50

Slag should be landfilled or granulated andsold.

Modern plants using good industrialpractices should target on meeting releases fortotal dust of 0.5-1.0 kg/t copper and a discharge

for SO2 of 25 kg/t copper.The double contact double absorption plant

should emit no more than 0.2 kg of sulfurdioxide per ton of sulfuric acid produced (basedon a conversion efficiency of 99.7%).

The environmental assessment shouldaddress the build-up of heavy metals from


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particulate fall-out in the vicinity of the plantover its projected life.

Liquid Effluents

For copper smelters the following effluentemissions levels should be achieved:

Effluents from Copper Smelting

Parameter

Maximum valuemilligrams per

liter (mg/L)

pH 6-9

Total suspended solids 50

Arsenic 0.1

Cadmium 0.1

Copper 0.5

Iron 3.5

Lead 0.1

Mercury (total) 0.01

Zinc 1.0

Total metals 10

Temperature increase less than orequal to 30C1

1The effluent should result in a temperature increase ofno more than 3 degrees Celsius at the edge of the zonewhere initial mixing and dilution take place. Where thezone is not defined, use 100 meters from the point of

discharge.

Note: Effluent requirements are for directdischarge to surface waters.

Ambient Noise

Noise abatement measures should achieveeither the following levels or a maximumincrease in background levels of 3 dB(A).Measurements are to be taken at noise receptorslocated outside the project property boundary.

Ambient Noise

Maximum Allowable Leq(hourly), in dB(A)

Receptor Daytime

07:00 - 22:00

Nightime

22:00 - 07:00

Residential;institutional;educational

55 45

Industrial;commercial

70 70

The emission requirements given here can beconsistently achieved by well-designed, well-operated and well-maintained pollution controlsystems.

Monitoring and Reporting

Frequent sampling may be required duringstart-up and upset conditions. Once a record ofconsistent performance has been established,sampling for the parameters listed above shouldbe as detailed below.

Air emissions should be monitoredcontinuously for SO2 and particulate matter.Other air emission parameters should bemonitored annually.

Liquid effluents should be monitored dailyfor pH and total suspended solids and at leastmonthly for all other parameters.

Monitoring data should be analyzed andreviewed at regular intervals and comparedwith the operating standards so that anynecessary corrective actions can be taken.Records of monitoring results should be kept inan acceptable format. These should be reportedto the responsible authorities and relevantparties, as required, and provided to MIGA ifrequested.

Key Issues

The following box summarizes the keyproduction and control practices that will leadto compliance with emissions requirements:

Give preference to processes that are energyefficient and which produce high SO2concentrations (e.g., flash smelting).

Use oxygen for enrichment of SO2.

Use the double contact double absorptionprocess for sulfuric acid production.

Reduce effluent discharge by maximizingwastewater recycling.

Maximize the recovery of dust and sludges.


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Minimize fugitive emissions byencapsulation of process equipment and useof covered or enclosed conveyors.

Give preference to dry dust collectors overwet scrubbers.

Further Information

The following are suggested as sources ofadditional information (these sources areprovided for guidance and are not intended tobe comprehensive):

Bounicore, A.J. and W.T. Davis. 1992. AirPollution Engineering Manual. New York: VanNostrand Reinhold.

Environment Canada. April 1980. A Study of

Sulphur Containment Technology in the Non-Ferrous Metallurgical Industries. Report EPS 3-AP-79-8.

World Bank, Environment Department. 1996.Pollution Prevention and Abatement: CopperSmelting. Technical Background Document.

Technical Note on Best Available TechnologiesNot Entailing Excessive Costs for Heavy MetalEmissions from Non-Ferrous Industrial Plants,May 1991, European Commission

Study on the Technical and Economical Aspectsof Measures to Reduce the Pollution of Waterand Other Environmental Areas fro the Non-Ferrous Metal Industry, August 1993, EuropeanCommission..

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Coppers Melting