This article discusses how membrane technology was used to optimise nickel sulphate recovery from a waste stream at a Platinum Group Metals (PGM) company and achieve downstream process dilution.

A current global trend is a growing value attached to raw materials utilised in the manufacture of batteries. High purity nickel sulphate is a raw material for the manufacture of rechargeable lithium-ion batteries, the global market for which is expected to generate revenue of around $46 billion by 2022.

Lithium-ion batteries, used in electric and hybrid-electric vehicles, consist of 80% nickel. Nickel has additional applications in energy storage batteries, rechargeable battery devices and the more traditional nickel-plating market. A by-product of the PGM company is a crude nickel sulphate stream.

An opportunity exists to purify the crude nickel to a grade suitable to market to the lithium-ion battery industry.

Presence of nickel sulphate in high-value waste streams

During the metallurgical processing of the crude nickel, various waste streams are generated, some of which are regarded as high-value streams as they contain entrained nickel sulphate.  A secondary waste stream containing high levels of sodium sulphate is also generated.

The waste streams cannot be re-introduced back into the process as this may cause dilution and return a portion of the impurities. The options to manage these streams are to either recover them via a separate process or dispose of them using an external third-party disposal company.

The cost of waste disposal is a key factor limiting the economic viability of the crude nickel beneficiation process as disposal costs are charged per mass of waste trucked. The ideal situation was to reduce the waste stream volumes as low as possible, thereby minimising the mass of waste generated and the associated cost of disposal.

Watercare Mining designed, built and commissioned a membrane plant to integrate into the nickel sulphate purification plant.

Membrane plant for nickel sulphate recovery

The plant was designed to purify the nickel sulphate, at the same time addressing the challenges associated with the generation of the waste streams. The nickel purification plant comprises a reverse osmosis water treatment package, consisting of 3 reverse osmosis (RO) plants, designed and built by Watercare Mining. The RO plants include pre-treatment for solids removal.

RO Plant 1 (diagram below) is the nickel reverse osmosis circuit (Ni RO), configured to include upfront primary and secondary filtration followed by reverse osmosis. It recovers and upgrades nickel sulphate from dilute solutions to be processed further through the nickel purification plant.

The nickel is upgraded more than 2.5 times into the concentrate stream, important for the minimisation of downstream dilution of the main nickel concentrate stream feeding the crystalliser.

RO Plant 2 (diagram below) treats the sodium bearing solutions to minimise the volume and hence, disposal costs. The sodium reverse osmosis circuit is configured to include primary filtration and secondary filtration followed by reverse osmosis.  The major role of the sodium RO circuit is to concentrate the sodium as much as possible, reducing the volume of concentrate required to be disposed of.

RO Plant 3 is the final RO unit fed from the nickel (RO Plant 1) and sodium reverse osmosis permeate streams (RO Plant 2) to produce ultra-pure process water for re-use in the plant with no pre-treatment. RO Plant 3 produces water to recycle thereby optimising water usage.

Benefits of the nickel purification plant project

The results have been that the nickel purification plant has generated:

• Increased recovery of purified nickel per month
• A reduction in sodium sulphate solution volume that needs to be transported from the plant for disposal
• Recovery of ultrapure water for re-use, offsetting the municipal consumption

The associated benefits of the project have been:

• Maximising nickel recovery for the production of high purity nickel suitable for sale to the lithium-ion battery industry. The high purity product commands a higher market value.
• A significant reduction in the volume of waste required to be disposed of, decreasing waste removal costs.
• A reduction in municipal water consumption, and costs, resulting from the generation of ultra-pure water that is recycled back into the process.
• The creation of an additional potential revenue stream as sodium sulphate is a raw material for other industries such as the paper, board, glass, detergent and chemical industries.

Conclusion

In conclusion, this case study demonstrates Watercare Mining’s membrane technology capabilities.

The CEO of a well-known mining house in South Africa commented: “This nickel purification plant is a flagship black industrialist project . . . such initiatives are key for beneficiation in South Africa and market extension for our by-product streams.”