mineral processing and storing waste underground Flashcards
in situ leaching
boreholes drilled into ore body and opened up. Leaching solutions sent down and pumped back up through second borehole.
heap leaching
Ore crushed and placed on impermeable liner. Leaching solution added and allowed to leach through. Dissolved minerals then collected in pond.
froth floatation
separates water repelling minerals from water loving minerals.
describe how froth floatation is carried out
Ore crushed and mixed with water to form slurry. Target mineral made hydrophobic by adding a chemical. Floatation cell aerated to make bubbles, hydrophobic material attach to bubbles, rise to surface as froth. Floatation tailing removed.
what’s an advantage of froth floatation?
can yield a significant amount of metal from a low grade ore
leaching
uses chemical solutions to dissolve the ore from the rock
what are the two types of leaching
in situ
heap
smelting
the extraction of elemental metal from the ore using a blast furnace
historically how were crushings and tailings disposed of?
surface ponds, underground, rivers or sea
How does Acid Mine Drainage (AMD) form?
void left from mining allows water and oxygen to get in = formation of sulphuric acid underground. This leaches toxic metal directly out of rock, creating AMD which can percolate through rocks in to drinking water supplies.
what are the environmental consequences of heap leaching?
leachate is acidic and contains toxic metals which may enter river systems posing a risk to ecosystems
what is an environmental consequence of smelting?
carbon dioxide is released, which is a greenhouse gas, causing atmospheric pollution.
why is heavy metal contamination of soils a threat to human health?
heavy metal are toxic, if they contaminate soils they could enter groundwater sources, leading to contaminated drinking water.
carbon sequestration
a process where CO2 is removed from the atmosphere and held in an alternative form, either solid or liquid.
pollution plume
zones of contamination, usually in an aquifer or water source. Can be from various sources
leachate
the liquid that drains or leaches from a landfill site
what is a ground improvement strategy to improve a site for landfill waste disposal?
impermeable geomebrane or clay seal can be laid down to help prevent leakage out of the site
what can affect the stability of a landfill site? x3
saturated clays- undergo plastic flow=collapse of sides
joints= blocks fall from sides
dip of bed= bedding plane slip +landslides
what causes groundwater leakage in and out of landfill sites? x4
water table high= quarry flooded= leachate move into water table
leakage down fault lines, joints +permeable rocks
seepage from porous rocks that form quarry sides
flooding if an aquifer is excavated
what are the 4 criteria nuclear waste disposal must meet?
isolation for at least 250,000 years
secure from entry
safe from natural disasters
no chance of leakage
name 3 new ideas for nuclear waste disposal
launching into space
burying in subduction zones
placing in Antarctica
name 4 long term problems of waste disposal
landfill gases
chemical reactions
contamination of surface or ground water
may take decades for reactions to end
what types of rock are unsuitable for a landfill site?
unconsolidated materials e.g. sands and gravels are often full of water and have very high permeability
what will happen if the rock forming the quarry floor is permeable?
leachate will escape and may contaminate water table
how does leachate form?
waste is very permeable. Rainwater falling on waster percolates through gradually becoming contaminated
