mineral processing and storing waste underground

Question 1

in situ leaching

Answer 1

boreholes drilled into ore body and opened up. Leaching solutions sent down and pumped back up through second borehole.

Question 2

heap leaching

Answer 2

Ore crushed and placed on impermeable liner. Leaching solution added and allowed to leach through. Dissolved minerals then collected in pond.

Question 3

froth floatation

Answer 3

separates water repelling minerals from water loving minerals.

Question 4

describe how froth floatation is carried out

Answer 4

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.

Question 5

what’s an advantage of froth floatation?

Answer 5

can yield a significant amount of metal from a low grade ore

Question 6

leaching

Answer 6

uses chemical solutions to dissolve the ore from the rock

Question 7

what are the two types of leaching

Answer 7

in situ

heap

Question 8

smelting

Answer 8

the extraction of elemental metal from the ore using a blast furnace

Question 9

historically how were crushings and tailings disposed of?

Answer 9

surface ponds, underground, rivers or sea

Question 10

How does Acid Mine Drainage (AMD) form?

Answer 10

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.

Question 11

what are the environmental consequences of heap leaching?

Answer 11

leachate is acidic and contains toxic metals which may enter river systems posing a risk to ecosystems

Question 12

what is an environmental consequence of smelting?

Answer 12

carbon dioxide is released, which is a greenhouse gas, causing atmospheric pollution.

Question 13

why is heavy metal contamination of soils a threat to human health?

Answer 13

heavy metal are toxic, if they contaminate soils they could enter groundwater sources, leading to contaminated drinking water.

Question 14

carbon sequestration

Answer 14

a process where CO2 is removed from the atmosphere and held in an alternative form, either solid or liquid.

Question 15

pollution plume

Answer 15

zones of contamination, usually in an aquifer or water source. Can be from various sources

Question 16

leachate

Answer 16

the liquid that drains or leaches from a landfill site

Question 17

what is a ground improvement strategy to improve a site for landfill waste disposal?

Answer 17

impermeable geomebrane or clay seal can be laid down to help prevent leakage out of the site

Question 18

what can affect the stability of a landfill site? x3

Answer 18

saturated clays- undergo plastic flow=collapse of sides
joints= blocks fall from sides
dip of bed= bedding plane slip +landslides

Question 19

what causes groundwater leakage in and out of landfill sites? x4

Answer 19

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

Question 20

what are the 4 criteria nuclear waste disposal must meet?

Answer 20

isolation for at least 250,000 years
secure from entry
safe from natural disasters
no chance of leakage

Question 21

name 3 new ideas for nuclear waste disposal

Answer 21

launching into space
burying in subduction zones
placing in Antarctica

Question 22

name 4 long term problems of waste disposal

Answer 22

landfill gases
chemical reactions
contamination of surface or ground water
may take decades for reactions to end

Question 23

what types of rock are unsuitable for a landfill site?

Answer 23

unconsolidated materials e.g. sands and gravels are often full of water and have very high permeability

Question 24

what will happen if the rock forming the quarry floor is permeable?

Answer 24

leachate will escape and may contaminate water table

Question 25

how does leachate form?

Answer 25

waste is very permeable. Rainwater falling on waster percolates through gradually becoming contaminated