potash production. froth flotation applied surface science oil sands wastewater mineral benefaction
TRANSCRIPT
Potash Production
Froth Flotation
• Applied surface science• Oil sands• Wastewater• Mineral benefaction.
Mineral Annual Production (MTonnes)
Copper 8 Zinc 6 Lead 4 Nickel 0.7 Potash 35 Coal 2 500
Waxing My Car (a hypothetical experiment)
Interactions of a submersed solid with an air bubble:
Flotation of Hydrophobic Materials
• Talc• sulfur• bitumen• oil• graphite
Dispersed Air Flotation
Cleaned Water
Oil Phase
Collectors
• Selectively render surface of desired mineral hydrophobic.• Surfactants
Solid Surface
Polar
Non-polar
Polar
Non-Polar
Collector Type Structure Applications Xanthates
S R-O-C
S Na+
Pb, Cu, Zn, Ag, Co …
Dithiophosphates
R O S P R O S M+
Cu, Zn, Ag, Cu
Carboxylic Acids
O R-C O - H
Iron ore, chromite
Amines
R1 + H N R2 H
Potash, SiO2
Mechanisms of Collector Adsorption
• Poor basic understanding• Mechanisms:
– Physical Adsorption– Chemisorption– Weak Electrostatic Interaction– Neutral Molecule Adsorption.
Physical Adsorption
• dipole-dipole interactions• hydrogen bonding• electrostatic attraction
Point of Zero Charge (PZC)
• Surface charge often a function of pH
+ H Si O Si O H + H+ Si O + H+ Equ. (33) H
• pzc of quartz is 1.9
Mineral Formula pzc Anthracite 8.1 Biotite K(Mg Fe)3(AlSi3O10)(OH)2 2.1 Chrysotile Mg3Si2O5(OH)8 10.5 Fayerite Fe2SiO4 4 - 5 Feldspar, orthoclase K(AlSi3O8) 4.8 Molybdenite MoS2 1.0 Muscovite KAl2(AlSi3O10)2(OH)2 4.0 Quartz SiO2 1.9 Pyrophyllite Al2(OH)2Si4O10 1.7 Sulfur S 2.0
• Various pzc values can lead to specificity
Chemisorption
• Bond formation between collector and mineral.
S S PbS + 2O2 + R O C Pb S C OR + SO4
= Equ. (34)
S
Other Flotation Chemicals
• Depressants• Frothers• Extenders
Depressants
• Inhibit flotation of undesired minerals• Starch, guar depress flotation of clays in potash
• depression of copper with Na2S or NaHS for molybdenum recovery
Frothers
• Stabilize air bubbles so they don’t burst• formation of a foam layer• small chain alcohols• coat air bubbles - lower air/water • C6 - C10 alcohols used in potash
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
Potash Processing
• Saskatchewan has immense reserves of potash• nameplate capacity of 20 M tonnes/year• 10 plants• 7 plants use flotation
Rocanville, Sask. Sussex, N.B
Devonian Period, -350 MaDevonian Period, -350 Ma
• Seas covered continent
• Mountain uplift, then cutoff
• Solar evaporation concentrated brine
• Sea water concentrated
• Chloride salts crystallized in sequence
• Now buried by 1000 m of sediments
Ore MineralogyOre 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
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 < 4 mm• Ground to the “liberation size”• closed circuits
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
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
Ore Conditioning
• Extender– heavy oil (fused aromatics)– added with the collector
• Frother– C6-C10 aliphatic alcohols
– stabilizes the product froth
• Ore slurry is mixed to provide good coverage of reagents. • Frother added just prior to flotation.
Ore Conditioning
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
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
Bubble-solid interactions
concentration zone: - top of the cell- froth enriched in the desired mineral- product collected by paddles- flows into a collection launder
Mineral Flotation Cell
Flotation
• Amine-treated KCl collected from top of cells• product is 95% KCl• waste salt flows through cells and is discarded.
Product Treatment
• Product slurry debrined by centrifuge (3-5% moisture)• dried in rotary kiln or fluidized bed driers• sized by screen
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.
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.
Toshiba
2000 HP VFD
Drive
Crystallization
• Widely used:– potash– salt– ammonium sulfate– sugar– chemicals
• Can be thermal or evaporative
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 (100°C) brine.
Crystallization (cont’d)
• 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 40°C and precipitates purified
KCl.• The grade of the product is regulated by controlling the sodium
chloride content of the circuit.
• 600-1200 micron particles– rounded by abrasion– composites
• 300-425 micron particles– complex microstructures– agglomerates
• 150-212 micron particles– primary KCl cubes
– some agglomerates
Crystallization (cont’d)
• Solid product is debrined by centrifuge and dried in rotary kiln dryers.• Sold for industrial and pharmaceutical uses.
Vapour Vapour Vapour Vapour
External Coolant
Cool Liquor1 2 3 4Hot
Feed
Product