Potash Production

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Potash Production
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Froth Flotation

• Applied surface science
• Oil sands
• Wastewater
• Mineral benefaction.

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Waxing My Car (a hypothetical experiment)
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Interactions of a submersed solid with an air
bubble
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Flotation of Hydrophobic Materials

• Talc
• sulfur
• bitumen
• oil
• graphite

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Collectors

• Selectively render surface of desired mineral
  hydrophobic.
• Surfactants

Non-Polar
Polar
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Mechanisms of Collector Adsorption

• Poor basic understanding
• Mechanisms
• Physical Adsorption
• Chemisorption
• Weak Electrostatic Interaction
• Neutral Molecule Adsorption.

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Physical Adsorption

• dipole-dipole interactions
• hydrogen bonding
• electrostatic attraction

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Point of Zero Charge (PZC)

• Surface charge often a function of pH

• pzc of quartz is 1.9

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• Various pzc values can lead to specificity

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Chemisorption

• Bond formation between collector and mineral.

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Other Flotation Chemicals

• Depressants
• Frothers
• Extenders

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Depressants

• Inhibit flotation of undesired minerals
• Starch, guar depress flotation of clays in potash
• depression of copper with Na2S or NaHS for
  molybdenum recovery

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Frothers

• Stabilize air bubbles so they dont burst
• formation of a foam layer
• small chain alcohols
• coat air bubbles - lower air/water ?
• C6 - C10 alcohols used in potash

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Extenders

• Improve recovery of desired mineral
• non-polar liquids
• in potash, use heavy oil (fused ring aromatics)
• extenders improve recovery of larger particles
• mechanism unknown

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Potash Processing

• Saskatchewan has immense reserves of potash
• nameplate capacity of 20 M tonnes/year
• 10 plants
• 7 plants use flotation

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Rocanville, Sask.
Sussex, N.B
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Devonian Period, -350 Ma

• Sea water concentrated
• Chloride salts crystallized in sequence
• Now buried by 1000 m of sediments

• Seas covered continent
• Mountain uplift, then cutoff
• Solar evaporation concentrated brine

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Ore Mineralogy

• Composition
• NaCl 55
• KCl 35-40
• KMgCl3.6H2O 1-5
• Insolubles 1-8
• Size Range of Natural Crystals in Ore
• 1-10 mm

3 mm
Discrete KCl/NaCl/insoluble particles
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Crushing Grinding

• Dry crushed to - 8 mm
• crushing with hammer mills
• crushed ore passed through screens
• wet grinding in rod mills or cage mills
• ground ore classified by screen or cyclone
• Ground to lt 4 mm
• Ground to the liberation size
• closed circuits

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Desliming

• series of agitated tanks (scrubbers)
• clays scrubbed from ore surface
• insolubles separated by cyclone or flotation
• dirty brine sent to thickener
• clean brine recycled
• U/F discarded

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Ore conditioning

• Depressants
• inhibit flotation of residual clays.
• Starch, guar, carboxymethylcellulose (CMC)
• conserves amine
• Collector
• CH3(CH2)17NH3
• selectively coats KCl particles
• exact mechanism unknown

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Ore Conditioning

• Extender
• heavy oil (fused aromatics)
• added with the collector
• Frother
• C6-C10 aliphatic alcohols
• stabilizes the product froth

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Ore Conditioning

• Ore slurry is mixed to provide good coverage of
  reagents.
• Frother added just prior to flotation.

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Flotation Equipment

• Conditioned feed, 20-40 solids
• 3 to 6 cells in series forms one bank
• each cell has an agitator, air injection
• froth collected from top by paddles
• gangue flows through cells

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Bubble-solid interactions

• agitation zone
• bottom of the cell
• bubbles dispersed by agitator
• bubbles adhere to surface of desired mineral.
• quiescent zone
• intermediate depths
• agitation is less vigorous.
• air bubbles carry the desired mineral up
• unfloated material flows on to the next cell

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Bubble-solid interactions

• concentration zone
• top of the cell
• froth enriched in the desired mineral
• product collected by paddles
• flows into a collection launder

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Mineral Flotation Cell
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Flotation

• Amine-treated KCl collected from top of cells
• product is 95 KCl
• waste salt flows through cells and is discarded.

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Product Treatment

• Product slurry debrined by centrifuge (3-5
  moisture)
• dried in rotary kiln or fluidized bed driers
• sized by screen

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Drying and Screening

• Potash from flotation is dried and sized to
  produce fertilizer-grade products.
• Finished product is screened into Granular (SGN
  285) and Standard (SGN 95).
• Undersize sent to crystallization or compaction.

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Compaction

• Granular product is produced by compacting the
  dust from screening.
• Compaction fuses (sinters) the dust into a flake
  in compactors under moderate temperature and high
  pressure.
• Flake is then crushed and screened to produce
  more Granular product.

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Toshiba 2000 HP VFD Drive
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Crystallization

• Widely used
• potash
• salt
• ammonium sulfate
• sugar
• chemicals
• Can be thermal or evaporative

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Crystallization

• Potash dust is dissolved in hot brine. Purified
  KCl is then produced as it cools.
• KCl is much more soluble in a hot brine than a
  cool brine.
• Dust from screening is dissolved in hot (100C)
  brine.

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Crystallization (contd)

• The hot, saturated brine is sent through a
  thickener to remove colored impurities.
• Clear brine is pumped to a series of
  crystallizers.
• In the crystallizers, the brine cools to 40C and
  precipitates purified KCl.
• The grade of the product is regulated by
  controlling the sodium chloride content of the
  circuit.

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• 600-1200 micron particles
• rounded by abrasion
• composites
• 300-425 micron particles
• complex microstructures
• agglomerates
• 150-212 micron particles
• primary KCl cubes
• some agglomerates

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Crystallization (contd)

• Solid product is debrined by centrifuge and dried
  in rotary kiln dryers.
• Sold for industrial and pharmaceutical uses.

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