Lecture 21 resources 12

Question 1

What is Arsenic

Answer 1

Average concentration in the crust - 2ppm
- associated with gold and sulphide deposits
- main component of >200 minerals
Chemical forms As 3-, As0, As3+, As5+
forms organic compounds (e.g. arsenobetaine)
Acute poisoning above 100 grams per litre in blood (inorganic and metabolites)

Question 2

Sources of As

Answer 2

• abundant in many common rock types
• sulphide minerals (pyrite, galena sphalerite) these are common ore minerals and gangue minerals so mining releases As to environment
• coals can be extremely high in As.
• Fe formation.
  mine tailings

Question 3

What’s the toxicity of arsenic?

Answer 3

Toxicity varies with form (speciation) - bioactivity varies
Reduced forms (arsenide, organo-arsine) - extremely toxic
Arsenite (As111) As2O3 very toxic o.1g can be lethal
Arsenate (As5+) several times less toxic
Elemental arsenic - not considered poisonous

Question 4

What are the health effects of chronic exposure to Arsenic (mainly from groundwater)

Answer 4

• early studies in Taiwan, Argentina and Chile = cardiovascular disease
• skin lesions (few years of exposure)
• cancers of the skin, lung, liver and bladder (several decades of exposure)
• children’s intellectual function.

Question 5

Acid mine Drainage - when does it occur?

Answer 5

• results from oxidation of sulphide minerals (gets oxidised when exposed during mining)
• occurs wherever unstable sulphide minerals are oxidised but acidic effects may be neutralised by groundwater.

extraction decreases groundwater depth and natural filtration and increase the groundwater contamination.

Question 6

What to remember about pyrite weathering

Answer 6

Pyrite reacts with water to produce reduced (ferrous) iron, sulphate and acidity. produces H+ ions
- can produce sulphuric acid H2SO4 if oxidised by iron.

Question 7

How does acid generation and water work?

Answer 7

• dependant on weathering rates of iron sulphide phases (e.g. pyrite) and carbonate dissolution (neutralisation of acid)
• acid generation process consists of three phases: initiation, propagation and termination
  Initiation - pyritic material is exposed to an oxidising environment (acid load generate is low)
• propagation: pyrite weathering and acid production increases rapidly
• termination: Acid production gradually declines (depletion of pyrite source)
• peak acid load generally occurs 5-10 years after mining, followed by gradual decline over 20-40 years.

Question 8

What are the impacts of acid mine drainage

Answer 8

For every mole of pyrite dissolved, four H+ ions are released
- resulting low pH (1-2) waters are sufficiently acidic to result in dissolution of more toxic metals from other minerals.
- elements such as Cu, Zn, Pb, Hg and As may be highly enriched in acid mine drainage.
When acid waters meet high pH water bodies, those metals that are only soluble at very low pH will be deposited.
- Acid waters may also leach essential nutrients such as K, Na and Ca from soils.

Question 9

What is particulate release

Answer 9

smelting releases small particles of metal oxide and sulphides
- small size leads to relatively high solubility and bioavailability (enhances toxicity)
- So2 aerosols travel large distances and are deposited in rain -> acid rain
- most SO2 is derived from fossil fuel burning but smelting is also significant.

Question 10

What are the effects in sudbury canada (acid rain)

Answer 10

• lakes - no fish, acidic and endangered - they rectified the problem by reducing SO2 emissions.

Question 11

What is blasting

Answer 11

• particle velocity - most useful criteria to assess if a vibration is likely to cause damage.
• small explosive charge = low vibration, high frequency and low amplitude
• vibration causing peak particle velocity of 50mms-1 - safe (no structural damage
  50-100mms - requires caution
  more than 100 mms - high probability of damage.
  years of exposure correlates with loss of hearing.

Question 12

Problems of dust

Answer 12

can cause serious illnesses
- what is it? elements can become part of dust - lung problems etc.
- important to note size of fragment - the smaller may be more likely to end up in your body
i.e PM10 - can end up in the lungs (less than 10micro metres in size)

Question 13

What types of dust causes pnemoconiosis

Answer 13

• coal dust
• asbestos fibres
• silica
  -cotton dust (textile manufacturing)
• aluminium oxide, cobalt talc.

effect: scarring the lungs affecting transport of oxygen in the system.

Question 14

what is subsidence

Answer 14

the planned or unplanned result of removing material from the ground.
there is a scale of damage from very sight - cracks in plaster to complete rebuilding (very severe)

Question 15

What are sink holes

Answer 15

• associated with older mining districts.
• golf associated with carbonate reefs
• carbonate geology contained caverns infilled with unconsolidated sediments above the water table.
• water table lowered to improve access to ore-bearing rocks.
• unconsolidated material in caverns compacted and cavern arches collapsed.