base metal and iron

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Multilateral Investment Guarantee Agency

Environmental Guidelines forBase Metal and Iron

Ore Mining

Industry Description and Practices

This document addresses the mining of base

metal ores (copper, lead and zinc) and iron ores.The mining of precious metals, bauxite, and coalare covered in separate documents.

Major phases in mine development are:(a) exploration; (b) mine development;(c) extraction (underground and open pit) andmine operation; (d) ore beneficiation; (e) storageand transport of ore; and (f) mine closure andreclamation. Fires may result from the oxidationof sulfide-bearing materials and these canpresent a significant hazard. This documentfocuses on the development, operation andclosure phases. Further processing of these oresis covered in separate documents.

Waste Characteristics

The volume of solid waste generated (includingtailings from processing) is one of the mainconcerns. Removal of overburden to access theore can pose major problems in storage andreclamation. The overburden ratio for surfacemining of metal ores generally ranges from 2:1to 8:1 (waste:ore) depending on local conditions.Solid wastes from underground mining are

typically 0.2:1. Where concentration or otherprocessing of the ore occurs on-site, then thetailings generated also have to be managed.Ores with a low metal content, for example, ofless than 0.4 percent, generate significantquantities of tailings.

In certain mines with ores with high sulfurcontent, drainage from mine workings and

waste heaps can become highly acidic andcontain dissolved high concentrations of heavymetals. This Acid Mine Drainage (AMD) can

have a pH of 3 or lower; sulfate levels of 800-1800 milligrams per liter (mg/L); copper levelsup to 50 milligrams per liter (mg/L); iron levelsup to 1000 milligrams per liter (mg/L); leadlevels up to 12 milligrams per liter (mg/L); zinclevels up to 1700 mg/L, and cadmium levels ofseveral milligrams per liter depending on thecontents of the ore. The tailings pond effluentmay also contain concentrations of chromium ofseveral milligrams per liter. Base metal miningtailings decant may also contain highconcentrations of thiosalts. Chemicals used inmetal concentration (floatation and other)processes could also pose toxicity whenreleased in effluents.

Surface runoffs may also pose significantenvironmental problems through erosion andcarry-over of tailings and other mining residues.Explosives, such as ammonium nitrate, mayalso be present in surface runoff. Contaminationof surface water can also occur from transportof mined material and from machinerymaintenance and repair.

Significant levels of dust, above to 3kilogram per ton (kg/t) (with a range of 0.003 to

27 kg/t) of ore mined, may be generated. Thisdust can be generated by extraction activities,crushing, ore beneficiation, transportation andtraffic, and by wind borne losses. Significantreleases of metal (including mercury)containing dust may result from the drying ofthe ore concentrate.

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324 Base Metal and Iron Ore Mining

Pollution Prevention and Control

The critical factors in good environmentalperformance for mining are adequate planning,effective management and implementation.Specific responsibilities should be assigned forthe implementation and monitoring ofenvironmental measures. Before mining begins,a mining plan and a mine closure andreclamation plan must be prepared andapproved. These plans should be updatedregularly as mining progresses.

Development Plans

These plans define the sequence and nature ofextraction operations and detail the method tobe used in closure and restoration. At a

minimum, the plans must address thefollowing: Removal, proper storage and management

of topsoil. Early restoration of worked-out areas and

of spoil heaps to minimize the extent of openareas. Identification of potential areas for AMD

generation and planning for successiveremediation of pyrites to reduce AMDgeneration. A water management plan focusing on the

effective use of mine water for operations (and

recirculation of process water) and post-closure. Extraction methods in relation to

subsidence and to surface use. Development of suitable restoration and

vegetation methods, appropriate to the specificsite conditions. Blasting methods which minimize noise

and vibrations.The Development Plan would normally have

specific sections dealing with:

Erosion and Sediment Control

An erosion and sediment control plan should beprepared and should include measures ormethods appropriate to the situation tointercept, divert, or otherwise reduce thestormwater runoff from exposed soil surfaces,tailings dams, and waste rock dumps. Bothvegetative and non-vegetative soil stabilizationmeasures should be an integral part of the

erosion control plan. Sediment controlstructures (for example, detention/retentionbasins) should be provided to intercept andtreat surface runoff prior to discharge. Allerosion control and sediment containmentfacilities must receive proper maintenanceduring the project life.

Tailings Disposal

Tailings must be managed to optimize humansafety and environmental protection. On-landtailings impoundment systems must bedesigned and constructed in accordance withinternationally recognized engineeringpractices, local seismic conditions, andprecipitation conditions (to accommodatesurface run-on). These should address the

structural integrity of the tailingsdams/deposits even during post-closure. On-land disposal systems should be designed toisolate acid leachate-generating material fromoxidation and percolating water. Marine andriverine discharges are normally not acceptableand should be considered only when on-landdisposal would pose an environmental risk andit can be demonstrated that such discharges willnot have a significant adverse effect ondownstream coastal or riverine resources.Riverine discharges are only acceptable when

justified based on the environmental analysis of

alternatives, and effects on aquatic resourcesand downstream users of riverine resources.

The design of the tailings managementsystem must address post-closure issues suchas: (a) long-term geotechnical stability of theimpoundment; (b) chemical stability of thetailings; (c) long-term surface and groundwatermanagement, including the provision for long-term spillway capacity requirements; and (d)restoration requirements.

Mine Closure and Restoration Plan

The plan should include reclamation of tailingsdeposits, waste rock deposits, any open pitareas, sedimentation basins, and abandonedmine, mill, and camp sites. Mine reclamationplans should incorporate the following: Return of the land to conditions capable of

supporting prior land use, equivalent uses, orother acceptable uses.


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Diverting and managing leachates fromwaste heaps to avoid contact with, andcontamination of, surface and groundwater.

Elimination of significant adverse effectson adjacent water resources. Use of waste rock for backfill and topsoil

(or other acceptable materials) for reclamationto the extent feasible.

Minimizing fresh water intake; recyclingtailings decant water and wastewater from theconcentration process to minimizecontaminated discharges to the extent feasible.

Contouring of slopes to minimize erosionand runoff.

Collect leachates from tailings pond andtreat before discharge. Provide sufficientresidence time in the tailings pond to ensurethiosalt oxidation. Provide buffer capacity forraining season.

Planting of native and other species ofvegetation which are environmentallyacceptable to prevent erosion and to encourageself-sustaining development of a productiveecosystem on the reclaimed land.

Divert surface runoff away from tailingponds using ditches.

Post-closure and management of AMDand tailings. Reduce AMD formation by sealingof pyrite containing waste from oxidation andpercolating water.

Using dust suppression measures such as:wetting of work areas, roads, and storage piles;installing equipment covers; minimizing dropdistances by using adjustable height conveyors;

and using dust hoods and shields.

Budget and schedule for pre- and post-abandonment reclamation activities.

Upon mine closure, all shaft openings andmine adits should be sealed or secured. Collecting and recycling waste oils andlubricants.There is a need to reserve money over the

life of the mine to cover the costs associatedwith mine closure. The amount of money andthe type of financing required will depend on anumber of factors such as the projected life ofthe mine, the nature of the operations, thecomplexity of environmental issues, thefinancial and environmental managementcapacity of the borrower/project sponsor, andthe jurisdiction in which the mine is located.The mine reclamation and closure plan, the

timing of its submission, and its financingshould be discussed and agreed with theborrower/sponsor as early as possible.

Minimizing chemical (includingammonium nitrate, if used in blastingoperations) spills. Providing appropriate storage areas for

chemicals and fuels. Avoid the use of toxic floatation agents. Controlling noise through the use of berms

and mufflers; controlling noise and vibrationsby sequenced blasting.

Treatment Technologies

Filters for cushers, grinding mills, and driers areused to control dust emissions.

Operating Measures Treatment of AMD and wastewaterstypically includes physical-chemical treatmenttechniques such as neutralization, precipitation,flocculation, coagulation, settling, and filtration.In some cases, cyanide oxidation and ionexchange may also have to be performed.Chrome reduction may be needed for floatationwater.

Other recommended pollution preventionmeasures include: Using progressive backfilling to minimize

land disturbances. Use dust control equipment on dryers. Use

pressure-air driers instead of fuel-baseddrumdriers for the drying of concentrations.

Emission Guidelines Provide covers or control devices forcrushing and milling to avoid the generation ofdust. 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 selected

Minimizing generation of AMD byreducing disturbed areas and isolating drainagesystems.


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Key Issues

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

Develop a comprehensive environmentaland mine management plan to include:

- Restoration and rehabilitation of disturbedareas.

- Identification and management of AMDsources.

- Water management for operations andpost-closure conditions.

- Management and sealing of tailings.

Develop and implement a post-closure plan

to include:

- Restoration of disturbed areas.

- Long-term geotechnical and chemicalstability of tailings.

- Adequate spillway capacity for the tailingspond overflow.

- Management of AMD, water drainage, andsurface runoff.

Further Information

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

United Nations Environment Programme(UNEP). 1993. Environmental Management ofNickel Production. Technical Report No. 15.

UNEP. 1991. Environment Aspects of SelectedNon-ferrous Metals (Cu, Ni, Pb, Zn, Au) OreMining. Technical Report Series No. 5.

Warhurst, Alyson. 1994. EnvironmentalDegradation from Mining and Mineral Processing

in Developing Countries: Corporate Responses andNational Policies. Organisation for Economic Co-operation and Development, Paris.

World Bank, Environment Department. 1996."Pollution Prevention and Abatement: BaseMetal and Iron Ore Mining. TechnicalBackground Document.

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