The differential flotation of polymetallic sulphide ores, including copper, lead and zinc, are a common practice where these metals are mined from the same ore deposit.

Although the physical parameters – circuit configuration, cell size and residence time – can still be improved, Johannesburg-based chemical reagents supplier and distributor Axis House tells Mining Weekly that these are relatively well established at plants that process these ore types.

The company primarily focuses on the chemical environment in the process by optimising the reagent type, dosage, pH and pulp potential. These, Axis House says, are all parameters that affect the floatability and separation efficiency in the various circuits.

While xanthates are still widely used as reagents, the company highlights that hazards and negative environmental impacts are associated with using the product, including spontaneous combustion and toxic and flammable decomposition products such as carbon disulphide.

These are common issues faced by Axis House customers when requesting xanthate alternatives. This has prompted the company to develop alternatives, providing the solution to customer concerns.

The Axis House range of specialised collector alternatives; TLQ2, DLQ2, TLQ2-DX and the PolyQ range for polymetallic ores can serve as more robust selective collectors.

Notably, in polymetallic processes, where one metal and/or mineral is recovered at a time in consecutive circuits, selective recovery is essential; thus, selective reagents are developed with a higher affinity for a specific mineral, and the process conditions are optimised to maximise the recovery of that particular mineral.

Axis House develops reagents by working with pure minerals and testing the affinity of certain specialised reagents to adsorb onto these minerals. Once this is accomplished, testwork is scaled up to complex ore samples before trialling it at full scale.

Subsequently, in addition to selectively floating the valuable metals, the rejection of gangue minerals, and the downstream effects, are also considered when developing a reagent suite. These liquid collectors can be applied over a wider pH range, at a lower dosage, and eliminate the need for solution preparation. Consequently, pH and pulp potential can be further optimised.

Through laboratory and on-site application, the specialised collectors have been classified based on ore mineralogy, ensuring that reagents can be selected based on the mineral type being mined.

These collectors have been trialled at operations in Zambia and Eritrea, where sulphide copper is recovered from sulphide gangue such as pyrite. Collectors, such as TLQ2 and TLQ2-DX, have been successfully introduced as selective collectors.

The company adds that the extensive work done also resulted in successful testing at copper, lead and zinc operations, in South Africa, and zinc operations, in Turkey.

At many of these operations, xanthates are used, but the improved selectivity of the PolyQ collector range, compared with the xanthate collectors, was reported during on-site work. Several trials are planned for mining operations in Turkey, Spain and South Africa for the remainder of 2020.

Axis House states that the initial feasibility of the PolyQ range has been proven through extensive laboratory-scale testing and these reagents have been approved for full-scale trials.

Moreover, the company acknowledges that there are other reagents in the market that are performing well, but that it always strives to develop alternatives or improved versions of its collectors.

To this end, reagent cost and consumption are also considered during the development stage.

This typically consists of finding the chemistry that can target the specific mineral, minimising the required dosage to recover the minerals, and finding the best possible solution to deliver and warehouse the product through a dedicated supply chain and logistics department.

All of these components, Axis House concludes, ultimately result in a lower production cost for the customer.