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Guidance Document for Management of Wastes from the Base Metals Smelting Sector

Base Metals Smelting Sector Waste Generation and Management

3.1 Key Wastes
3.2 Wastes from Copper Production
3.3 Wastes from Nickel Production
3.4 Wastes and Residues from Lead Production
3.5 Wastes and Residues from Zinc Production

This section describes the wastes generated by the Base Metals Smelting (BMS) Sector. For the purposes of this report, the BMS sector includes smelters, refineries and hydrometallurgical processors.

Wastes and residues are site-specific and depend on many factors such as feed composition and process facilities. The determination of what is a waste and what can be recovered will vary from facility to facility depending upon a number of technical, environmental and economic factors.

The section begins with a description of generic wastes and residues, then presents wastes and residues specific to copper, nickel, lead and zinc production. For each of the specific processes, the types of wastes and residues generated are presented along with the process source and the average quantity generated per tonne of metal product. The management of these wastes and residues and potential uses are also presented.

3.1 Key Wastes

The production of non-ferrous metals from primary and secondary material results in the generation of a wide variety of wastes and residues. They are a result of the metals separation that is necessary for the production of pure metals from complex sources. These wastes and residues arise from the different stages of processing as well as from the off-gas and water treatment systems. The key wastes and residues which result from the production of non-ferrous metals are:

  • Slag;
  • Drosses and skimmings;
  • Spent linings and refractories;
  • Wastes/residues/by-products of air pollution abatement systems;
  • Liquid effluent treatment wastes and residues; and,
  • Wastes and residues from hydrometallurgical processes.

Slag is produced by the reaction of slag-forming elements (e.g., iron) in the ore with added fluxes. In the smelting process, the slag is liquid and has a different density than the melted metal and separates on top of the metal-rich matte. The slag can, therefore, be tapped off separately. It is either rapidly quenched with water to form granules that can be re-used or discarded or alternatively, the slag is transported in a liquid state to a cleaning operation or slag dump.

Drosses and skimmings result from the oxidation of metals at the bath surface or by reactions with fireproof material used as furnace linings.

Spent linings and refractories result when refractory material falls out of the furnace linings or when the furnace lining has to be replaced completely.

Pollution abatement systems wastes and residues include flue gas dust and sludge recovered from the air pollution control equipment as well as other solid materials like spent filter material. Sulphuric acid and liquid sulphur dioxide are also wastes/residues from pollution abatement systems.

Liquid effluent treatment wastes and residues result from treatment of waste water streams. Process water from processing usually requires cleaning in a wastewater treatment plant. The cleaning takes place by neutralization and precipitation of specific ions. The main wastes/residues from these effluent treatment systems are gypsum (CaSO4), and metal hydroxides and sulphides.

Hydrometallurgical wastes and residues include sludge generated in the leaching process, while purification and electrolysis processes can generate metal rich solids such as anode slime.

Other wastes and residues typically produced are oils and greases and industrial scrap such as steel and wood wastes.

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3.2 Wastes from Copper Production

Primary copper may be produced from primary concentrates and other materials by pyrometallurgical or hydrometallurgical routes. Concentrates contain various amounts of other metals besides copper and the processing stages are used to separate these and recover them as much as possible.

The major stages in the pyrometallurgical route are smelting, converting, refining and electrolytic refining.

Typically in copper production, all copper-bearing materials are recycled back to the production process, this includes ladle skulls, scrap and flue dusts. Almost 100% of new or processed copper scrap is recycled and according to some studies it has been estimated that 95% of old copper scrap that becomes available is also recycled.

Slags contain varying amounts of copper and many are re-used or treated to recover the metal content. Slags with high copper content, such as converter slags, are returned to the smelting process to recover the copper metal.

Slags with lower copper content (e.g., smelter slag) may be processed by mineral dressing techniques or in slag cleaning furnaces to increase the amount of copper recovered. In a slag cleaning furnace, the copper in the slag is removed and recycled back to the process. The resulting slag is referred to as cleaned slag. Sometimes low copper content slags are disposed of without additional processing to recover the copper.

Many of the final slags produced by copper slag treatment processes contain very low levels of leachable metals and are stable. These slags have excellent mechanical properties and can be sold as products for the abrasive and construction industries. However, if the slag does not pass leachate tests, as described in Section 6.1.1, or if the market for re-use is not available, it is disposed of in a secure landfill, lagoon or tailings pond.

When a furnace requires relining due to wear, some of the existing furnace linings may have been significantly penetrated by copper. These linings could be used as a secondary feed into the copper converter, in other cases the linings are disposed.

Flue dusts from copper production are typically recycled to the smelting furnaces. Dust from the bag filters and metals precipitated in the waste water treatment plant are also fed to flash smelting furnaces as secondary materials.

Wastes destined for disposal from copper production are kept to a minimum and mainly consist of acid slimes/sludges from the sulphuric acid plants and furnace linings. Acid slimes/sludges are formed when the scrubbing liquid used in the wet scrubber of the off-gas treatment system is bled from the scrubber and treated in an effluent treatment plant. This weak acid effluent stream is neutralized with lime to form insoluble gypsum and precipitate metals as metal hydroxides. The hydroxides and gypsum are settled in a thickener. These solids are removed from the bottom of the thickener and are usually disposed of in a tailings pond or an HDPE-lined impoundment area.

In some cases, another waste stream is tailings from the processing of smelter or converter slag by flotation. After the slag is cooled and crushed, it is processed in a flotation column where the floating material is high in copper and is returned to the process. The tailings (i.e., the material at the bottom) are typically disposed of on-site or at the mine site if it is near the smelter.

Table 2 is a listing of wastes and residues which may result from copper production, typical quantities generated and potential end uses. The example quantities of residues generated by the primary copper processes shown in Table 2 is data from the Norddeutsche Affinerie and was presented in the IPPC BREF document. The annual cathode production of this plant is 220,000 tonnes per year of copper.

Table 2: Typical Wastes and Residues from Copper Production11
Ammount Generated
Ammount Generated
(kg/t Copper)
End Use
Smelting (Flash) FurnaceSlag400 0001800Internal recycle (e.g., slag cleaning furnace)
 Furnace linings  Recovered or disposed



Slag150 000680Internal recycle (to smelter)
 Furnace linings  Recovered or disposed
Slag furnaceCleaned slag400 000 Abrasive, construction material, disposal
 Furnace linings  Recovered or disposed
Refining (anode) furnaceSlag20 00090Internal recycle (to smelter)
 Furnace linings  Recovered or disposed
Pollution Abatement systemCollected dusts (from fabric filters, ESPs, cyclones etc.)  Internal recycle (to smelter) or recovery of lead, zinc and other metals

Sludges (from scrubbers, etc.)


  Recycled to process, metals recovery or disposal
 Mercury compounds from mercury removal equipment  Raw material for mercury production

Spent catalysts


  Sent to chemical industry for regeneration
 Sulphuric Acid656 0003000By-product sold
 Liquid SO2  By-product sold

Weak acid


  Neutralization, sludges to disposal
Waste Water TreatmentWaste water sludge (wet weight)15007Internal recycle (to smelter)

Tank house


Electrolyte bleed


  Nickel, salts, copper recovery, acid recovery or other uses

Anode scrap


  Internal recycle (converter or anode furnace)
 Anode slimes (wet weight)300014Precious metals recovery
Hydrometallurgical processingDepleted electrolyte  Leaching
GeneralOils and Greases  Oil recovery

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3.3 Wastes from Nickel Production

In Canada, nickel is produced from sulphide ore or purchased secondary materials. Sulphide ores are usually smelted under oxidizing conditions to oxidize the iron sulphides, which with other gangue materials forms an iron silicate slag. The matte is then treated in a converter and the converter matte is processed by electrorefining, and chemical reduction or vapo-metallurgy to produced refined nickel.

Stainless steel and other nickel bearing alloys are the primary sources of secondary nickel. It is estimated that around 80% of nickel is recycled from new and old stainless steel scrap and returns to that end use. Other nickel bearing materials such as precipitates and residues are recycled to primary production.

Copper and cobalt, and several other valuable metals are present in Canadian ores. Most of these are recovered as by-products in nickel production.

Slag from the smelting step usually contains very low concentrations of leachable materials and is, therefore, suitable for use in construction.

Dust or sludge from the treatment of gases is recycled to the smelter step.

Gypsum waste (CaSO4) and metal hydroxides result from the treatment of liquid effluent are either recycled or sent for disposal.

Table 3 lists wastes and residues which typically arise from nickel production in Canada and the potential uses.

Table 3: Wastes and Residues from Nickel Processes
Process SourceResiduePotential End Use
SmeltingSlagInternal recycle (e.g., slag cleaning furnace)
 Furnace liningsRecovered or disposed
ConverterSlagInternal recycle (to smelter)
 Furnace liningsRecovered or disposed
Slag furnaceCleaned slagAbrasive, construction material, disposal
 Furnace liningsRecovered or disposed
Refining (anode) furnaceSlagInternal recycle (to smelter)
 Furnace liningsRecovered or disposed
Pollution abatement systemCollected dusts (from fabric filters, ESPs, cyclones etc.)Internal recycle (to smelter) or recovery of lead, zinc and other metals
 Sludges (from scrubbers, etc.)Recycled to process, metals recovery or disposal
 Mercury compounds from mercury removal equipmentRaw material for mercury production or disposed
 Spent catalystsSent to chemical industry
 Sulphuric AcidBy-product sold
 Liquid SO2By-product sold
 Weak acidNeutralization, sludges to disposal
Waste water treatmentWaste water sludge (wet weight)Internal recycle (to smelter)
Tank houseElectrolyte bleedNickel, salts, copper recovery, acid recovery or other uses
 Anode scrapInternal recycle (converter or anode furnace)
 Anode slimes (wet weight)Precious metals recovery
GeneralOils and GreasesOil recovery

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3.4 Wastes and Residues from Lead Production

There are two basic pyrometallurgical processes available for the production of lead from lead concentrates: sintering/smelting or direct smelting. These processes may also use secondary raw materials.

Table 4 and Table 5 list the wastes and residues, quantities generated and end uses from the sinter/blast furnace and direct smelting processes, respectively.

Table 4: Typical Wastes and Residues from Lead Production – Sinter/Blast Furnace12
Process SourceWaste ResidueAmount Generated
(kg/t Lead)
Potential End Use
Sinter MachineCollected dustup to 100Return to sinter after cadmium leach
 Return sinterup to 3000Return to sinter
Acid PlantSulphuric Acid
600By-product for sale
 Calomel (mercury chloride) Sale or controlled disposal
 Acid sludge Disposal
Cadmium plantCadmium-Zinc (CdZn) precipitate Sale
Shaft furnaceSlag500-600Disposal
 Collected dustup to 80Return to sinter
Waste water treatmentSludge3Return to sinter


Table 5: Typical Wastes and Residues from Lead Production – Direct Smelting13
Process SourceWaste ResidueAmount Generated
(kg/t Lead)
Potential End Use
Sinter MachineCollected dustup to 100Return to sinter after cadmium leach
 Return sinterup to 3000Return to sinter
Acid PlantSulphuric Acid
600By-product for sale
 Calomel (mercury chloride) Sale or controlled disposal
 Acid sludge Disposal
Cadmium plantCadmium-Zinc (CdZn) precipitate Sale
Shaft furnaceSlag500-600Disposal
 Collected dustup to 80Return to sinter
Waste water treatmentSludge3Return to sinter

Recycling of lead is normally conducted whenever appropriate and economic. Batteries which resulted in 52% of the lead consumption in the EU in 1994, were recycled with more than 90% efficiency.

Newer processes, such as Kivcet, generate lower amounts of slag per tonne of refined lead or lead bullion, versus the older sinter/blast furnace process. Slags from blast furnaces have low metals concentrations in the leachate and can be used in the construction industry.

The feed for the sinter plant recycles dusts and sludges which are blended with concentrates and secondaries.

Drosses and solids from the lead processes contain metals that are suitable for recovery, if economic.

3.5 Wastes and Residues from Zinc Production

Zinc can be produced from primary raw materials by pyrometallurgical or hydrometallurgical methods.

Zinc and zinc containing products can be largely recycled, if economic. Estimates based on historical consumption and product life cycles indicate that a recovery rate of 80% of recoverable zinc has been reached.

Direct smelting furnaces generate slags. The slag output is between 10% and 70% of the weight of the metal produced depending on the raw materials used. Dust or sludge result from the treatment of gases.

The hydrometallurgical production of zinc generates relatively large quantities of iron based solids (i.e., jarosite or goethite) from the leaching process. jarosite and goethite may be classified as hazardous waste in some jurisdictions if the leachate test exceeds the regulatory limits for the leachable elements such as cadmium (Cd), lead (Pb) and arsenic (As).

The main waste stream from the treatment of liquid effluents is gypsum (CaSO4) and metal hydroxides that are produced at the waste water neutralization plant.

Typical residues from zinc processes, quantities and potential end uses are shown in Table 6.

Table 6: Typical Wastes and Residues from Zinc Production14
Process SourceWaste ResidueAmmount generated (kg/t Zinc)Potential End Use
Roaster/sulphuric acid plantSulphuric acid1750By-product for sale
 Acid sludge<0.5Recycle to Roast or controlled disposal
Leaching plantNatural leach residue500-600To hot acidic leach, ISF or Waelz Kiln
 Goethite or Jarosite350-650Controlled disposal
 Lead-Silver (PbAg) concentrate40-120Silvery recovery
 Final residue (Pb/Ag removed)150Controlled disposal
PurificationCadmium2-4By-product for sale
 Copper cementateup to 10Sale
Wastewater treatmentPrecipitated sludge10Disposal

11 Source: adapted from Table 3.17: Intermediate products, by-products from the production of copper and Table 3.18: Example of the quantity of residues produced by a complex primary and secondary installation IPPC BREF.

12 Source: adapted from Table 5-29: Residues from lead process, IPPC BREF

13 Source: adapted from Table 5.30: Residues from direct smelting lead processes, IPPC BREF

14 Source: adapted from Table 3.28 Residues from zinc processes, IPPC BREF

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