Dithiophosphate collectors – the class known generically as aerofloats – sit alongside xanthates as the two workhorses of sulphide flotation, but they are chosen for a different job. Xanthates are strong and cheap; dithiophosphates are weaker per molecule and considerably more selective. Knowing which one a circuit needs, and which alkyl chain length within the dithiophosphate family, is where most of the value sits.
What a dithiophosphate collector actually is
| Element |
Detail |
| Chemistry |
The sodium or potassium salt of a dialkyl dithiophosphoric acid – the acid form is the intermediate, the salt is the collector |
| Structure |
Two alkoxy groups and two sulphur atoms on a phosphorus centre; the anion chemisorbs through the sulphur |
| Hydrophobe |
The alkyl groups face outward from the mineral surface and provide the water-repellent layer |
| Commercial forms |
Aqueous solutions of the sodium or potassium salt, typically 40-60% active; also supplied as the acid for on-site neutralisation |
| Handling |
The salts are easier and safer to handle than the acid; the acid route suits plants that want to control the cation and the concentration themselves |
Dithiophosphate versus xanthate
| Property |
Dithiophosphate (aerofloat) |
Xanthate |
| Collecting strength |
Moderate |
Strong |
| Selectivity |
High – floats chalcopyrite, galena, sphalerite in preference to pyrite |
Lower – collects pyrite readily, which is a problem where pyrite rejection matters |
| Typical dose |
Higher per tonne for the same recovery |
Lower |
| pH tolerance |
Useful range but decomposes in strongly acidic or oxidising pulps |
Broad, though it also degrades outside its window |
| Cost per tonne of ore |
Higher |
Lower |
| Where it wins |
Cleaner concentrates, pyrite rejection, polymetallic separation, and as a secondary collector with a xanthate |
Bulk sulphide recovery, high-throughput roughing, cost-driven circuits |
The combination is common in practice: a xanthate does the roughing work and a dithiophosphate is added as a secondary or cleaner-stage collector to lift the grade. That is often more economic than pushing either reagent alone.
Choosing the alkyl group
| Alkyl group |
Hydrophobicity |
Behaviour |
Typical fit |
| Dimethyl |
Lowest |
Most polar, weakest collector, most selective |
Where selectivity dominates, or as a reagent for making other derivatives |
| Diethyl |
Low to moderate |
The general-purpose commercial grade |
Standard sulphide flotation, mixed with xanthate |
| Di-isopropyl |
Moderate |
Good balance of strength and selectivity; popular where froth control matters |
Copper and lead circuits |
| Di-isobutyl |
Moderate to high |
Stronger; used where a xanthate would over-collect |
Polymetallic separation |
| Cresyl / diaryl |
High, aromatic |
Very different solubility and surface behaviour |
Specific separations; often proprietary |
Longer and more branched chains increase hydrophobicity and collecting power, and reduce selectivity. The choice is therefore a trade between recovery and grade, which is exactly what a flotation test is for.
Circuit practice
| Point |
Typical practice |
What goes wrong |
| Addition point |
Conditioning tank with the collector and a frother, before flotation |
Added into the flotation cell itself, so conditioning is incomplete |
| Dose |
Set by test work; dithiophosphates commonly need more than a xanthate |
Scaling from a xanthate dose directly and concluding the reagent “does not work” |
| pH |
Matched to the mineralogy and to the depressant regime |
Running too acidic or too oxidising, which decomposes the collector |
| Combination |
Xanthate for roughing, dithiophosphate for cleaning or selectivity |
Adding both at the same point, so neither conditioning step is done properly |
| Water quality |
Process water chemistry affects the collector’s activity |
High hardness or oxidant levels in recycled water |
Handling the acid form
| Hazard |
Detail |
Control |
| Hydrogen sulphide |
The acid hydrolyses with water contact and evolves H2S, which is lethal at concentrations that no longer smell |
Ventilation, fixed gas detection, no confined-space entry without testing |
| Acidity |
Strongly acidic; attacks carbon steel |
PE, GRP or 316L stainless throughout |
| Neutralisation |
Exothermic when making the salt |
Controlled alkali addition with cooling |
| Storage life |
Degrades with heat and moisture |
Sealed, cool, dry, and order to consumption rate |
For the acid itself see dimethyl phosphorodithioate, and for the wider collector picture see mining reagents: flotation collectors and the xanthate pages starting with SIBX vs SIPX vs PAX.
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