Potash Production

Froth Flotation Applied surface science Oil sands Wastewater Mineral benefaction.

Waxing My Car (a hypothetical experiment)

Interactions of a submersed solid with an air bubble:

Flotation of Hydrophobic Materials Talc sulfur bitumen oil graphite

Collectors Selectively render surface of desired mineral hydrophobic. Surfactants Solid Surface Polar Non-polar Polar Non-Polar

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 pzc of quartz is 1.9

Various pzc values can lead to specificity

Chemisorption Bond formation between collector and mineral.

Other Flotation Chemicals Depressants Frothers Extenders

Depressants Inhibit flotation of undesired minerals Starch, guar depress flotation of clays in potash depression of copper with Na 2 S 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  C 6 - C 10 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 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 Mineralogy Composition: –NaCl: 55% –KCl:35-40% –KMgCl 3.6H 2 O :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 –CH 3 (CH 2 ) 17 NH 3 + –selectively coats KCl particles –exact mechanism unknown

Ore Conditioning Extender –heavy oil (fused aromatics) –added with the collector Frother –C 6 -C 10 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.

micron particles –rounded by abrasion –composites micron particles –complex microstructures –agglomerates 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.