Potassium amyl xanthate — almost universally shortened to PAX — is the heavy hitter of the xanthate collector family. Where ethyl and butyl xanthates deliver selectivity, PAX delivers power: its longer five-carbon chain gives it the strongest collecting action of the common xanthates, which is exactly what gold and copper concentrators need when valuable minerals are fine-grained, partially oxidised, or slow to float. This guide explains what PAX is, how it differs from the other xanthate grades, and where it earns its place in a reagent scheme.
What Is Potassium Amyl Xanthate?
Potassium amyl xanthate is the potassium salt of amyl xanthic acid, with the general formula C5H11OCSSK. The “amyl” group is a five-carbon alkyl chain — the longest of the commercially common xanthate grades — and the potassium salt is preferred over the sodium form because of its greater solubility and handling convenience.
The reagent is manufactured by reacting amyl alcohol with carbon disulfide and potassium hydroxide. It appears as a pale yellow to yellow-green powder or pellet, with the characteristic pungent odour shared by all xanthates, and it is readily soluble in water at the concentrations used in plant reagent preparation.
Why Chain Length Matters
The behaviour of any xanthate is dominated by one structural fact: the length of its hydrocarbon chain. A longer chain makes the collector more hydrophobic and therefore more aggressive at attaching mineral particles to air bubbles. The trade-off is selectivity — the same aggressiveness that lifts valuable minerals also lifts more of the unwanted sulphides.
Within the standard family, this produces a clear ranking of collecting power, from weakest to strongest: ethyl (SEX), isopropyl (SIPX), butyl and isobutyl (SBX, SIBX), isobutyl-amyl blends, then amyl grades such as PAX and SIAX. Practical circuits exploit this ordering: a selective grade floats the target mineral in the rougher, while a strong grade such as PAX handles the scavenger stages where the remaining values must be recovered even at lower concentrate grade.
Applications: Gold, Copper, and Polymetallic Ores
PAX is the collector of choice in several situations:
- Gold ores: free gold and gold associated with pyrite float readily with PAX, and its strength helps recover fine and coarse gold that weaker collectors leave in the tailings.
- Copper ores: chalcopyrite and other copper sulphides respond strongly, particularly in scavenger circuits or where the ore is partially oxidised.
- Polymetallic and gold-silver ores: PAX is often blended with dithiophosphates or thionocarbamates to combine bulk pulling power with the selectivity needed in cleaning stages.
Because PAX floats fast, circuits using it typically operate with shorter conditioning times — but they also need disciplined control of the depressant regime (lime to hold pyrite back, or zinc sulfate and related reagents in lead-zinc flowsheets) so that the extra power does not drag the whole sulphide suite into the concentrate.
PAX versus SIAX: Two Amyl Grades
Two amyl xanthates are sold commercially — potassium amyl xanthate (PAX, normal five-carbon chain) and sodium isoamyl xanthate (SIAX, branched chain). Both are strong collectors, and both are widely used in gold and base-metal flotation. In practice, the branched SIAX structure tends to give somewhat better selectivity in certain ores, while PAX is the more established and widely available grade; most concentrators settle the choice with comparative locked-cycle tests on their own feed rather than on general rules.
Dosage, Handling, and Specification
PAX is typically dosed in the range of tens of grams per tonne, adjusted by ore type and stage — rougher and scavenger additions are usually higher than cleaner additions. Three practical points govern its use and purchase:
- Stability: xanthates hydrolyse and decompose faster in acidic conditions; reagent solutions should be prepared fresh and stored under alkaline, cool conditions, and powdered product must be kept dry and out of direct sunlight.
- Safety and packaging: the product has a strong odour and is moisture- and heat-sensitive, so sealed, waterproof packaging and clear labelling matter for both quality and workplace safety.
- Specification: commercial PAX is specified by effective content (commonly 90% or above) and moisture; buying on effective content rather than gross weight keeps dosage calculations honest, and a certificate of analysis per batch is the only reliable way to confirm it.
Conclusion
Potassium amyl xanthate (PAX) is the strong, fast collector that gold and copper circuits reach for when a selective xanthate cannot deliver the recovery they need. Its long five-carbon chain gives it the highest collecting power of the common xanthate grades, making it a natural fit for scavenging duty and for ores where values are fine, locked, or partly oxidised. Use it with a disciplined depressant regime, blend it where cleaning stages demand selectivity, and specify it by effective content. To compare it against the other amyl grade, see our guide to sodium isoamyl xanthate (SIAX), and for the wider context of collector selection in base-metal circuits, see xanthate collectors for copper and lead-zinc ores.