Sustainable development and the environment Remediation

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?

7 BEST 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)

8 BEST PRACTICE ENVIRONMENTAL MANAGEMENT IN MINING Isolation

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/ 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