Vern. Lecture 3 Flashcards
Describe three sources of pollution
- Ore extraction - huge volumes of waste rock, e.g. Twin Buttes, Arizona, open pit Cu mine, 2 years sof stripping overburdem at 225k tonnes/day
- Oxidation of ore in mine and mine water rebound
- On site processing/enrichment: open pit dust, primary/secondary crushing and benefication
What is meant by the terms separation and beneficiation? What do they produce?
Separation: Ore separated from gangue
Beneficitaion: Increasing concentration of ore
Together they generate large quantities of wet and toxic waste (tailings)
What are tailings?
Fine grained slurries from ore washing.
Liquid waste and slime from various metal recovery processes.
Source of contamination for groundwater, surface water and soil.
Tailing need to be dammed. What two kinds of tailing dams are there?
- Earth fill dam
2. Raised embankment dam
What are spigotts?
They pump tailing slurry into dam. They must be moved regularly to avoid build up of coarse material in one place
How is water removed from tailings dams?
- Evaporation
- Removal of seepage water to effluent treatment system
- Surface level extraction
What systems are used to treat tailings effluent?
- Ultrafiltration and reverse osmosis: In reverse osmosis metals are retained on semipermeable membrane
- Vapour compression evaporation: condensor>expansion valve>evaporator>compressor
- AMD treatments
Cyanide used in gold extraction converts metals into water soluble cyanide complex. How can this be remediated?
Oxidation with hydrogen peroxide
Tailings must be stabilised on long term basis against erosion, environmental contamination and effects of natural run off entering the environment. How can we rehabilitate tailings?
Water runs out. Once dry the surface can be covered with topsoil and revegetated. Phytoremediation and phytostabilisation can be done
