PAX in Gold and Copper Flotation

Potassium amyl xanthate (PAX, CAS 2720-73-2) is the longest-chain common xanthate and the strongest collector. Where the priority is maximising recovery of sulphide minerals – gold-bearing sulphides, copper rougher circuits – PAX is often the collector of choice. This page covers how PAX is used and how it fits with the more selective xanthates.

1. Why PAX

Property	Consequence in the circuit
Longest common chain (C5)	Strongest collecting power
Lower selectivity	Tensor to co-float other sulphides than SIPX/SIBX
Fast kinetics	Good recovery in short flotation times (rougher/scavenger)
Potassium salt	Higher solubility than sodium xanthates of similar chain – convenient solution make-up

2. Gold flotation

Where gold is locked in sulphides (pyrite, arsenopyrite and other hosts), the aim is to float the sulphide host and carry the gold into the concentrate. PAX is well suited to this:

Gold-bearing sulphide flotation – PAX floats the sulphide host with strong kinetics for high gold recovery.
Gold-copper ores – PAX recovers both the copper sulphide and the gold-bearing sulphide in a bulk circuit.
Free / gravity gold fines – contributes to recovering the finer gold fraction in flotation.

The trade-off is selectivity: a strong collector can co-float unwanted sulphides (for example pyrite in a copper circuit). That is managed by pH control, depressants and staged addition, not by using PAX everywhere.

3. Copper flotation

Stage	Typical role of PAX
Rougher	Strong collector to maximise copper sulphide recovery
Scavenger	Recovers the last of the copper – often the best place for PAX
Cleaner	Usually a more selective collector (SIPX/SEX), or PAX at low addition

A common pattern is PAX in the rougher/scavenger, SIPX in the cleaner: strong collecting to pull the values out, selective collecting to clean the concentrate.

4. Dosage

Stage	Typical dosage (starting point)
Rougher / scavenger	Higher addition to drive recovery
Overall	Commonly about 10 – 100 g per tonne of ore, set by ore and circuit

PAX is usually dosed as a solution (made up on site) to conditioning or the grinding circuit. Because it is strong, small changes in dosage can change selectivity – optimise on the actual ore.

5. Practical notes

Stage the addition. Dose the rougher first, then add to the scavenger; do not over-dose the cleaner.
Control pH and depressants. Lime and depressants keep the extra collecting power from pulling unwanted sulphides.
Watch the froth and grade. A strong collector changes froth character – adjust frother and circuit.
Degradation. Like all xanthates, PAX decomposes with moisture, heat and time – make up solutions fresh and use stock within its shelf life.

6. PAX vs SIBX vs SIPX

Collector	Strength	Best for
PAX (C5)	Strongest	Rougher/scavenger recovery of gold and copper sulphides
SIBX (C4)	Strong	General-purpose sulphide flotation (Cu, Pb-Zn, Ni, Au)
SIPX (C3)	Selective	Cleaner concentrates; lead-zinc separation

See the SIBX vs SIPX vs PAX comparison and the xanthate selection chart.

Frequently Asked Questions

What is PAX used for?

As a strong sulphide collector – especially in gold and copper circuits, where it is used in the rougher and scavenger stages to maximise recovery.

Is PAX better than SIBX?

PAX is stronger and less selective than SIBX. Use PAX where recovery is the priority; use SIBX where a balance with selectivity is needed – confirm on the ore.

How much PAX is used?

Commonly about 10-100 g/t, split between stages and set by flotation testing; because it is strong, dosage changes affect selectivity.

Should PAX be used in the cleaner?

Usually not on its own – cleaners are better served by a selective collector (SIPX/SEX). Use PAX in the rougher/scavenger.