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

Options for Management of Wastes and Residues

6.1 Considerations for Recovery
6.1.1 Leachate Test
6.1.2 Barriers to Re-use
6.2 General Management Methods
6.3 Slags
6.3.1 Recycle
6.3.2 Re-use
6.3.3 Disposal
6.4 Drosses and Skimmings
6.4.1 Recycle
6.4.2 Re-use
6.4.3 Disposal
6.5 Spent Linings and Refractories
6.5.1 Recycle
6.5.2 Re-use
6.5.3 Disposal
6.6 Wastes/Residues of Air Pollution Abatement Systems
6.6.1 Recycle
6.6.1.1 Dust
6.6.1.2 Filter Material
6.6.2 Re-use
6.6.3 Disposal
6.7 Wastes and Residues from Liquid Effluent Treatment
6.7.1 Recycle
6.7.2 Re-use
6.7.3 Disposal
6.8 Wastes and Residues from Hydrometallurgical Processes
6.8.1 Recycle
6.8.2 Re-use
6.8.3 Disposal

For the purposes of this report, two broad categories have been developed for the management of wastes and residues, these are:

  • Recovery (i.e., recycle or re-use); and
  • Disposal.

Definitions can be found in the Introduction Section of this report.

Also note 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 Base Metals Smelting Sector uses many residues through internal recycle streams or as raw materials for other processes.

Material that is not recovered is considered a waste. Disposal should only be considered when there are no possibilities for recycle or re-use. Some wastes may be disposed of directly, while others will require some form of treatment prior to disposal.

Some general considerations which may impact on the ability to recover Base Metals Smelting residues are presented. General management methods are then described and, for each of the major types of wastes and residues, the possibilities for recycling, re-use and disposal are presented.


6.1 Considerations for Recovery

6.1.1 Leachate Test

The characteristics of the material (e.g., metals content, impurities) determines the feasibility of recycle, re-use or disposal of the residue.

For some potential re-uses of residues, it is a requirement that the residue pass a leachate test prior to being deemed acceptable for re-use. A leachate test predicts whether a material is likely to leach contaminants, specifically metals, at levels of concern.

The Federal Transportation of Dangerous Goods Act, the Export and Import of Hazardous Wastes Regulations, the Inter-provincial Movement of Hazardous Waste Regulations and Ontario and Alberta regulations determine the leachate characteristic using the Toxicity Characteristic Leaching Procedure (TCLP).15 The material is subjected to an extraction fluid (e.g. a basic or buffered solution) and then the resulting extract is analyzed and compared to a leachate criteria list. If the resulting concentration is equal to or in excess of the concentration specified for that contaminant in the applicable schedules, the material is considered leachate toxic and may not be suitable for recovery. In addition, the material may require treatment to eliminate or reduce the leaching potential prior to disposal or may require disposal in a secure, hazardous waste landfill.

6.1.2 Barriers to Re-use

The Minerals and Metals Policy of the Government of Canada16 recognizes that recycled minerals and metals constitute an important source of secondary materials for industry, and generate environmental benefits. The policy states that "As a consequence, the Government will work to: enhance the efficiency and effectiveness of regulations; promote a more efficient metals recycling industry in Canada; advance recycling as a feature of product design; and at the international and domestic levels, promote common approaches to the definition of waste (including a distinction between metal-bearing recyclables destined for recovery and wastes destined for final disposal)."

In May 1996, a multi-stakeholder Issue Table (IT) for the BMSS Strategic Options Process (SOP) was convened to identify and evaluate options and provide advice to the Ministers of Environment and Health. The SOP culminated in the development of a Strategic Options Report (SOR).17

Recommendation #6 of the Strategic Options Report concerned recycling. It was recommended that the federal government, within its jurisdictional responsibilities and resources, should, among other things:

  • Work with provinces and territories, industry, and other stakeholders to enhance the efficiency and effectiveness of regulations and remove unnecessary impediments to metal recycling; and
  • Encourage development of products that take into account recyclability in their design.

It was also recommended that efforts should continue to identify and address barriers to recycling. Such barriers may include regulatory mechanisms or inequities in the tax system.

The SOR noted the efforts led by the National Round Table on the Environment and the Economy (NRTEE). This group was discussing in a multi-stakeholder forum how best to eliminate existing barriers and market concerns regarding recycling.

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6.2 General Management Methods

Table 16 lists some general management methods for wastes and residues from the Base Metals Smelting Sector.

Table 16: Overview of Wastes/Residues and Available Management Options18
SourceAssociated MetalsWaste/ResidueAvailable Options
Raw materials handling

All metals

 

Dust, Sweepings

 

Feed for main process

 

Smelting furnace

 

All metals

 

Slag

 

Construction material after slag treatment, abrasive industry, refractory material, mine backfill. Slag dump
Converting furnaceCopperSlagRecycle to smelter
Refining furnacesCopperSlagRecycle to smelter
 LeadSkimmingsRecovery of other valuable metals
 Precious metalsSkimmings and slagInternal recycle

Slag treatment

 

Copper and Nickel

 

Cleaned slag

 

Construction material, abrasives, mine back fill. Matte produced in treatment recycled. Slag dump
Melting furnaceAll metalsSkimmingsRecycle to process after treatment.
  Slag and salt slagMetal recovery, recovery of salt and other material
Electro-refiningCopperElectrolyte bleedRecovery of Nickel
  

Anode scrap

 

Recycle to smelter if contaminated, to melting furnace if clean
  Anode slimeRecovery of precious metals

Electro-winning

 

Zinc, Nickel, Cobalt, Precious MetlasSpent electrolyteRe-use in leaching process
LeachingZincIron wastesSafe disposal, re-use of liquor
 CopperWastesSafe disposal
 Nickel/CobaltCopper/Iron Wastes/residuesRecovery, disposal
Sulphuric acid plantAll metalsCatalystRegeneration
  Acid sludgesSafe disposal
  Weak acidNeutralization, safe disposal of sludge, discharge of water
Furnace liningsAll metalsRefractoryUsed as slagging agent, disposal
PicklingCopperSpent acidRecovery
Dry abatement systemsMost-using fabric filters or ESPsFilter dustRecycle to process, recovery of other metals
Wet abatement systemsMost-using scrubbers or wet ESPsFilter sludgeReturn to process or recovery of other metals (mercury). Disposal
Wastewater treatment sludgeMostHydroxide or sulphide sludgeRecycle or Safe disposal

 

6.3 Slags

6.3.1 Recycle

In an effort to further recover the valuable metals contained in slags, facilities might recycle the slag directly to a previous stage or process slags in slag cleaning or fuming furnaces to remove the valuable metals. The metals removed from the slag are recycled back into the process.

For example, molten slag from the converter has a high copper content and is returned to the smelter. The slag leaving the smelter has its copper removed in a slag cleaning furnace. The resulting matte from the slag cleaning furnace is recycled back to the converter. This internal recycling of slag is shown in Figure 4.


Figure 4: Internal recycling of slag

Figure 4: Internal Recycling of Slag


Slag from the converter at Falconbridge Kidd’s Copper Smelter is granulated, dried and recycled back to the smelting furnace.

At Inco Copper Cliff’s Smelter, the slag from the converter is recycled back to the Flash Furnaces for metals recovery.

The slag containing iron and zinc from Cominco’s Lead Plant is charged into the slag fuming furnace where fine coal and air is injected into it. The injection generates more heat and causes the zinc to vaporize and form a mainly zinc oxide fume (also contains residual lead and silver, cadmium, indium and germanium) which is collected in a baghouse and further treated in the leaching area to recover the zinc, indium, germanium and cadmium.

The value of the recoverable metals content in the slag must be sufficient to warrant the slag processing costs.

One constraint to the recycling of slag to recover the metals is that fine materials may have to be pelletized or briquetted prior to recycling.


6.3.2 Re-use

The resulting clean slag with low metal content in the above example is either granulated to produce abrasives or cooled slowly and broken into lumps for filling or construction material. The use of final slag as a construction material is only possible if the amount of leachable metal compounds is low. Slag that cannot be used as an abrasive or in civil engineering and construction is sent for ultimate disposal.

Cleaned slags from copper production are sometimes used in the construction industry, as ballast in highway and railroad building, and in granulated form, for sand blast use. Copper slags are generally too heavy to be used as aggregate in cement.

Some slags can be used as blasting sands. Granulated slag has an average grain size between 0 and 5 mm. It has to be ground and sieved, as blasting sands need a grain size range between 0.25 and 2.8 mm. Fine dusts cannot be used. The heavy metal load as well as toxic organic compound content have to be considered in determining if the specific slag is appropriate for this re-use.

Some slag exhibits pozzolanic behaviour and can be added to Portland cement and used for solidifying flotation tailings for mine backfill. Finely ground, rapidly cooled slags can replace up to 70% of Portland cement clinker. Slags can be used with Portland cement as mine backfill.

Slag can also be used for filling large mined out pits as part of a site rehabilitation plan.

Slags can be used in the manufacture of ceramics and they could be used for production of insulating wool.

The main barriers to reuse are the quantities of impurities in the material being re-used. For instance, slags used for road construction must pass leachate tests prior to use.

6.3.3 Disposal

Slags that do not pass leachate tests as described in Section 6.1.1 or where commercial markets are readily available cannot be re-used and need to be disposed of in secure landfills.

Slags are typically disposed of on smelter sites. Often, in order to obtain environmental approvals, any leachate from slag disposal areas must be collected and treated.

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6.4 Drosses and Skimmings

6.4.1 Recycle

The metals content in drosses and skimmings is relatively high (between 20% and 80%) and can, therefore, be recycled to the main process or used as a secondary raw material to other base metals facilities.

For example, drosses are treated at Noranda Brunswick at the Silver Refinery for silver recovery.

6.4.2 Re-use

Drosses and skimmings which have high metals contents can be used as a secondary raw material to other base metals facilities.

6.4.3 Disposal

After treatment for metals recovery, the resulting materials are disposed.

6.5 Spent Linings and Refractories

6.5.1 Recycle

Typically, the following practices are used for furnace linings:

  • Treatment in a smelter to form an inert slag; or
  • Use as a component in the tap-hole block.

Refractories are recycled in primary and secondary copper smelting after grinding as a flux to adjust slag composition. For example, spent refractories are used as a flux at the Inco Copper Cliff Nickel Refinery converter plant.

A tap-hole block is like a stopper or cork to prevent material from spilling out of the furnace through the tap-hole until the furnace is ready to be tapped. The block is removed prior to tapping. Use of furnace linings as a component of the tap-hole block is not used in practice in Canada as more sophisticated systems are used to minimize and simplify maintenance of the tap-hole.

6.5.2 Re-use

Refractories can sometimes be reused for construction purposes after the metals content has been separated from the material by milling or grinding. The metals content can be recycled to the smelter or supplied to other non-ferrous metals facilities.

6.5.3 Disposal

Inert linings can be landfilled if no other use can be found. Linings from all copper and nickel smelters are landfilled, unless it is economic to re-cycle.

6.6 Wastes/Residues of Air Pollution Abatement Systems

6.6.1 Recycle

6.6.1.1 Dust

Most off-gas dusts collected in gas cleaning systems are returned directly to the smelting furnaces. The dusts must be collected through a system separate from impurities. For example, the dusts may be collected from a baghouse or ESP but should not be allowed to be combined with other materials during transfer. Dust removed in a wet system (e.g., scrubber) forms a sludge which must typically be dewatered (e.g., dried, filtered) prior to recycling.

For example, Falconbridge Kidd recycles dust from the waste heat boilers and cyclones at the copper smelter back to the concentrate dryer to be recycled to the smelting furnace. The dust from the electrostatic precipitator in the Copper Smelter is processed in the Zinc Plant to produce a copper residue, a lead/silver residue and a zinc solution. Indium is separated by solvent extraction, recovered by cementation, refined by electrolysis and cast into bars.

Fine dusts may need to be pelletized or agglomerated prior to recycling.

One of the barriers to this process may be if the dust contains volatile toxic compounds. The return of dust repeatedly to the smelting furnace may result in the build-up of a recycle load. Some dust may need to be bled from the system to avoid this build-up.

Another barrier is the transportation of dust back to the furnace. Ideally, this should occur in a manner which does not result in increased workplace exposure or generation of fugitive emissions. For instance, closed conveying systems are preferred over open systems.

6.6.1.2 Filter Material

When off-gas cleaning takes place in a fabric filter (e.g., baghouse), the filter material occasionally needs to be replaced. The filters contain metal compounds and particles from the process. These filter materials can be recycled to the pyrometallurgical process as a secondary feed. If this is not possible, they are sent for disposal.

6.6.2 Re-use

Some residues from air pollution abatement systems are processed on site and sold as by-products.

For example, many of the Canadian Base Metals Smelting facilities produce sulphuric acid (H2SO4) in an acid plant, utilizing SO2 rich off-gases from roasters, smelters and/or converters. The acid is used for chemical processing, paper, fertilizer, textile, leather, and other industries.

Liquid Sulphur Dioxide can also be produced in an acid plant and is used in chemical processing.

Mercury removed from the gas stream prior to the acid plant can be used as a feed material for mercury production.

Commercial markets must be readily available for these materials to be produced and sold.

Dusts that are not internally recycled can be supplied as a raw material for further metals recovery in other facilities. For example, the zinc-rich dust from a converter or slag-cleaning furnace at a copper process can be treated and re-used as a raw material in a zinc recovery plant.

Acid sludge can be neutralized with limestone to yield a gypsum sludge which, depending on its physical characteristics and chemical stability, has the potential to be used as a tailings cover.

6.6.3 Disposal

Some sludges have a lower valuable metals content that does not justify the additional costs to recycle or recover the metals. For example, some sludges from wet-based air pollution abatement systems (e.g., wet scrubbers) are disposed of into a landfill.

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6.7 Wastes and Residues from Liquid Effluent Treatment

6.7.1 Recycle

Water is typically used in pyrometallurgical operations for direct or indirect cooling of furnaces, lances and casting machines. This water is treated to settle out solids which are recycled to the process.

If wet scrubbers are used for off-gas cleaning, wastewater is generated. The sludge from scrubbers is recycled to the process if the metal content is high enough.

The main wastes and residues from hydrometallurgical effluent treatment systems are gypsum (CaSO4) and metal hydroxides and sulphides. The sludge can sometimes be recycled to the main production process when the neutralization is not required to bleed a minor element.

Some sludges from liquid effluent treatment can be recycled back to the process. For example, the zinc hydroxide sludge from Hudson Bay Mining and Smelting’s waste water treatment plant is recycled to the gypsum removal and iron removal steps to be used for neutralizing.

The residue from the Effluent Treatment Plant at Cominco’s Zinc Plant is recycled to the Lead Plant.

The composition of the sludge determines whether it can be recycled for metals recovery or other purposes.

6.7.2 Re-use

Gypsum can be sold if there is a market available such as for wall board and the quality of the gypsum meets the users’ requirements. These requirements may include metals content as determined by leachate test.

In Canada, however, most wall board manufacturers use quarried feed or recyclable desulphogypsum (DSG). DSG is gypsum produced as a by-product of a sulphur dioxide removal process used by particular coal-fired thermal electric generating stations. The market for gypsum from Base Metals Smelters may be quite limited due to the metals content.

6.7.3 Disposal

Some wastes/residues from liquid effluent treatment cannot be recycled or reused and require disposal.

For example, the sludge from the effluent treatment plant at Noranda CEZ is disposed of at the on-site impoundment area.

6.8 Wastes and Residues from Hydrometallurgical Processes

6.8.1 Recycle

The leaching and purification process and the electrolysis processes generate metals-rich solids. These can be recycled to the production process or sent for metals recovery to other base metals facilities (e.g., for the production of precious metals, lead, copper, and cadmium).

Sludges from hydrometallurgical processes are not typically recycled.

6.8.2 Re-use

Anode slimes produced in electrolytic cells in copper production tank houses are processed for recovery of the precious metals and other valuable metals. This recovery may occur on the site where the slimes were generated or at another metals facility.

Noranda CEZ commissioned a market study19 to identify the potential market for iron residues, including jarosite. No commercial use for jarosite was identified.

6.8.3 Disposal

Iron wastes (e.g., jarosite) from leaching processes are often classified as hazardous waste due to the leaching of elements such as cadmium, arsenic and lead. These residues require disposals in a hazardous waste facility, or in on-site residue areas or tailings ponds.

Sludges produced in the leaching process are normally disposed in specially sealed lagoons.

Jarosite disposal in Quebec is an example of a waste requiring treatment prior to disposal. Noranda has developed the Jarofix process in which jarosite is mixed with about 15% Portland cement to give a concrete-like material. The Quebec Ministry of the Environment has approved the resulting material as inert which can be landfilled. It should be noted that while the metals do not leach when the waste is fixed, the process does increase the volume of waste produced.


15 United States Environmental Protection Agency (EPA), SW-846, "Method 1311, Toxicity Characteristic Leaching Procedure", July 1992, in "Test Methods for Evaluating Solid Waste, Volume 1C: Laboratory Manual, Physical/Chemical Methods", Third Edition, SW-846, November 1986.

16 The Minerals and Metals Policy of the Government of Canada - Partnerships for Sustainable Development, June 1996, www.nrcan.gc.ca/mms/sdev/policy-e.htm

17 Strategic Options for the Management of Toxic Substances from the Base Metals Smelting Sector Report of Stakeholders consultations, Environment Canada, June 23, 1997, www.ec.gc.ca/toxics/docs/sor/bms/en/toc.cfm

18 Source: Table 2.27 Residues and potential uses, IPPC BREF

19 Iron Disposal Options at Canadian Electrolytic Zinc, L.I. Rosato and M.J. Agnew, published in Iron Control and Disposal, Second International Symposium on Iron Control in Hydrometallurgy, 1996

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