TOXICS

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TOXICS MINING

• Mercury, Arsenic, Cyanide

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Mercury (Hg)

• What is it?
• How does it get into the environment?
• What is at risk?

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Mercury (Hg)

• What is it?
• Mercury (Hg) is a naturally occurring element -
  silvery white liquid also found as cinnabar
  (HgS)
• Mercury is used in the manufacture of electrical
  instruments, fungicides, pharmaceuticals,
  munitions, paper production, extraction of gold
  in mining

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Mercury (Hg)

• How does it get into the environment?
• Natural sources
• volcanoes
• volatilization from oceans
• erosion of natural deposits

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Mercury (Hg)

• How does it get into the environment?
• Human Activities
• estimated to be 1/3-2/3 of the total mercury
  released into the environment.
• Sources include
• stack losses from cinnabar roasting
• the working and smelting of metals
• coal fired power plants
• discharges from mines, refineries and factories
• combustion of coal and municipal wastes,
  industrial wastes and boilers
• medical waste incinerators
• pesticides
• runoff from landfills/croplands

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Mercury (Hg)

• What is at risk?
• Persistence
• can change form,
• cannot be destroyed
• Solubility
• Cinnabar (HgS) is insoluble (and resists
  weathering)
• liquid Hg is slightly soluble in water.

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Mercury (Hg)

• What is at risk?
• Bioaccumulation
• Hg methylation forms CH3Hg which is easily
  absorbed by organisms and biomagnifies from the
  bottom to the top of the food chain
• bioaccumulates (concentrates) in muscle and
  tissue of fish and other wildlife
• CH3Hg generally increases by a factor of ten or
  less with each step up the food chain

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Arsenic (As)

• What is it?
• How does it get into the environment?
• What is at risk?

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Arsenic (As)

• What is it?
• Arsenic rarely occurs in elemental form, but
  usually is found as a compound or dissolved ion
  widely distributed in earths crust
• found in the metal sulfides (e.g. Arsenopyrite
  FeAsS), and as oxides, and arsenates
• Persistence cannot be destroyed can only change
  its form
• Bioaccumulation by fish and shellfish

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Arsenic (As)

• What is it?
• the toxicity of inorganic arsenic (As) depends on
  its valence state (As-3, As3, or As5), and also
  on the physical and chemical properties of the
  compound in which it occurs
• trivalent (As3) compounds are generally more
  toxic than pentavalent (As5) compounds, but As5
  easily converts to As3 when ingested thus, this
  difference in toxicity is no longer considered
  that important
• Organic compounds (i.e., As in compounds combined
  with carbon and hydrogen) are less toxic than
  inorganic compounds (i.e., As combined with
  oxygen, chlorine, and sulfur).

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Arsenic (As)

• How does it get into the environment?
• Arsenopyrite (FeAsS) is the most common arsenic
  mineral in ores and is also a byproduct
  associated with copper, gold, silver, and
  lead/zinc mining.
• Arsenic trioxide (Fe2As3) is present in flue
  gases from copper ore roasting
• coal-fired power plants and incinerators also may
  release As into atmosphere.
• Water average concentration is 1 ppb, but can be
  gt 1,000 ppb in mining areas As5 most prevalent
  many compounds dissolve in water

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Arsenic (As)

• What is at risk?
• Arsenic is a human carcinogen
• In humans the primary target organs are the skin
  and vascular system
• birds, animals, plants, and freshwater fish can
  become contaminated
• Toxicity in water is determined by water
  temperature, pH, organic content, phosphate
  concentration, suspended soils, presence of
  oxidants, and speciation

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Cyanide (CN)

• What is it?
• How does it get into the environment?
• What is at risk?

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Cyanide (CN)

• What is it?
• Cyanide (CN) is a highly toxic carbon-nitrogen
  chemical compound
• may be combined with various organic and
  inorganic compounds,
• hydrogen cyanide (HCN), a colorless, flammable
  liquid or gas, or
• sodium cyanide (NaCN) and potassium cyanide
  (KCN), both solids

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Cyanide (CN)

• What is it?
• Cyanide has been used since the late 1800s for
  the recovery of gold, replacing the mercury
  amalgamation process.
• Two processes of cyanide leach mining, vat and
  heap-leaching, now process greater than 90 of US
  gold ores.
• CN is also used in small amounts to depress
  pyrite in the floatation processes of base metal
  ores (Cu, Ni, Pb, Zn, Mo)

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Cyanide (CN)

• What is it?
• Usually stored/transported in dry, solid form
• Usage
• Hydrogen cyanide is used in the manufacture of
  other cyanides for nylon, fibers, resins
• also used in herbicides, as chemical warfare
  agents, silver plating, dyes, and specialty
  products

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Cyanide (CN)

• How does it get into the environment?
• Can leach from landfills and cyanide-containing
  road salts as well as to the atmosphere from car
  exhaust (hydrogen cyanide gas - HCN).
• Some foods (almonds and lima beans) contain
  cyanides naturally
• It can be produced by some bacteria, fungi, and
  algae

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Cyanide (CN)

• How does it get into the environment?
• Spills Cyanide and other heavy metal pollutants
  overflowed a dam at Baia Mare, Romania,
  contaminating 250 miles of rivers, and killing
  millions of fish
• Most persistent in groundwater at higher pH

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Cyanide (CN)

• What is at risk?
• CN- oxidizes in the presence of sunlight and
  oxygen, forming Cyanate (CNO-), Thiocyanate
  (SCN-), ammonia (NH3), nitrate (NO3), and other
  compounds
• Cyanate (CNO-) and Thiocyanate (SCN-) compounds
  are more persistent than CN-, and do have
  significant toxicity

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Cyanide (CN)

• What is at risk?
• Oral lethal dose of KCN for an adult is 200 mg
• Airborne concentrations of 270 ppm is fatal
• Long term exposure to lower levels results in
  heart pains, breathing difficulties, vomiting,
  blood changes, headaches and thyroid gland
  enlargement
• CN does not bioaccumulate in fish

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Cyanide Facility Photos
Cyanide Isotainer
Cyanide Mixing Tank Impellor
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