Sustainable development and the environmentRemediation

Basic options

• Prevent/control – minewater generation– Migration of contaminated minewater

• Collect and treat contaminated water

Controll at the site

• Prevent oxidation by eliminating– Processing rock containing reactive sulfide

• Use efficient extraction

– Segregate & isolate sulfide containing wastes– Exclude from oxygen and/or water– Control bacterial activity (if feasible, acceptable), temperature,

pH

• Sulphide removal or isolation– One of the key objectives to waste management

planning!• What would be the other objective of WM?

Exclusion of water

• Basal insulation• Prevention/reduction of infiltration by Dry

cover

– What are the conditions when basal insulation is needed/recommended for tailings?

7BEST PRACTICE ENVIRONMENTAL MANAGEMENT IN MINING

Soil Covers

• Materials– Imported materials e.g. clay, soil– Low-sulphide waste rock, if

compactable– Geotextile fabrics– Covers may require zones

• Base (main sealing) layer - high water retention, low permeability

• Middle layer - water reservoir (may have higher permeability)

• Surface layer (barrier zone) - erosion protection and/or substrate for plant growth

the dry and water cover of waste areas as far as such is possible (dusting and/or seepage quality reduction and improvement of quality).

Materials can be from organic soil layer from the site (temporarily stored)Peat (if not erosion risk)

8BEST PRACTICE ENVIRONMENTAL MANAGEMENT IN MINING

Isolation

Sulphidic waste

Top non-sulphidic waste layer

Basal layer

Revegetated and contoured cover material(surface capping and water storage medium)

Original ground surface

Freedumpednon-sulphidicwaste

Freedumpednon-sulphidicwaste

• In principle similar• Alkalinisation by

limestone, lime, fly ash• Vegetation to

evapotranspirate water, erosion prevention– Metabolism introduces

dissolved CO2, (bicarbonate ions)

Exclusion of oxygen

• Dry cover (soil cover) can aim also to prevent oxidation• Wet cover turned out effective way to reduce oxidation

– Diffusion rate of oxygen in water 1/10 000 times diffusion rate in air!

– Organic and certain inorganic reactions consume oxygen

Hammaslahti Zn mine

• Water layer reduces diffusion of oxygen

• Reduced conditions developed as oxygen is consumed

• Sulfate become stable phase

• (Vegetation organic layers can promote SRB)

Control of pH

• Increase of alkalinity– Reduces pH but is, in general

sufficient to induce precipitation of Cd, Zn, Ni and many other toxic metals

Enables other reactions and SRB

Control of bacterial action

• Nearly neutral conditions

• a prerequisite for SRB

• Bacterisides have been applied to eliminate sulfite oxydicing bacteria– Effective until bactericides are

consumed• Difficult to sustain• ”emergency” action?

Control of migration

• Controll of groundwater pollution by

• Reactive barrriers– Zero valent iron

• Extremely basic• U, Cr(IV), most metals

– Organic matter (suphate reaction)

• +SRB

• Continuos barriers

• Funnel and gate structures

Collection and treatment

• Neutralization (pH control)

• Removal of metals

• Active treatment– Requires continuous operation

maintenance• Pump and treat etc.

– Passive systems• Intended to be self sustaining

after initial start-up

Passive treatment

• Constructed wetlands

• Compositionally layers open pits (Hammaslahti mine)

• Successive alkalinity producing systems (SAPS)

• Limestone ditches/dams, open channels