JSE-listed diversified mining company Sibanye-Stillwater has built various innovative water treatment plants and is researching and developing new technologies to treat water, as well as extract valuable materials from the water it treats, Sibanye-Stillwater South Africa mine water treatment specialist Quinton Paulse said this week.
During a seminar hosted by industry organisation the Southern African Institute of Mining and Metallurgy, he gave an overview of some of the plants the company operates, including zero-liquid discharge plants that are producing, as by-products, various chemicals that the company is using internally, such as calcium carbonate, besides others.
"A large mining operation, such as one with more than 10 000 people on site on 8 500 ha of land, can use more than 21 Mℓ/d of water.
“Some of the main water uses are for reclamation surface mining and water is a critical component to transport ore, as well as in cooling underground mines and to cool equipment, among others," he illustrated.
For example, one plant on such a large mining operation can use 1.5 Mℓ/d of potable water.
"Given the high water consumption, it is important for us to identify alternative sources and implement water management and reuse [strategies], and increase our efficiency of use, which will bring down our municipal potable water demand," Paulse said.
While any water treatment projects Sibanye pursues must be financially viable and sustainable, he noted that the company also aimed to reduce waste generation and ensure it can create more value.
"Mine water typically has lots of dissolved metals and we can produce calcium carbonate and fertilisers, among others. A recent project we started is also looking at extracting rare earth minerals.
"So, there are lots of opportunities and, if we can find a suitable technology and the project makes financial sense, then we can ensure we gain additional value from our resources and put that into the economy," he said.
For example, one of the company's oldest water treatment plants treats 25 Mℓ/d of water to potable standards. It is fed with water from underground that is partially contaminated with solids and has elevated levels of salts. It is a zero-liquid discharge system that produces calcium carbonate and magnesium carbonate.
"We are looking at using some of the carbonates as part of our tailings projects, but we are producing so much that we could give it to local farmers," noted Paulse.
However, this requires permits and, while the company was looking at how it could sell excess products from its plants, it was currently using the various chemicals and fertilisers internally in its own operations, he added.
Meanwhile, in response to questions, Paulse noted that Sibanye wanted to sell potable water where it could. Municipal water costs range from R15/m3 to R27/m3 of potable water, while the miner was producing potable water from some of its plants at about R10/m3, albeit from relatively simple water bodies.
"We work in three of the nine water catchment management areas in South Africa. On one of our mines, local water costs are around R27/ m3 and our plant at this mine is running below R10/m3, which means we achieve a significant saving.
“This level seems to be a sweet spot, as plants pay themselves off in a relatively short time after which the mine realises savings," he noted.
TREATMENT AND RECOVERY
Meanwhile, Paulse praised Sibanye's approach to stimulating research and development (R&D), and said he and other engineers at the company were able to explore a range of technologies and applications.
"We are allowed to play with various technologies to see whether they make commercial sense for a mine.
"If a mine becomes water-independent, this makes more municipal water available for the rest of the local communities and the country at large," he said.
Following on from these steps to secure its own water sources and conduct the required treatment prior to discharge, Sibanye is focusing on the recovery of precious metals, rare earths and chemicals, besides others, from these water projects.
Value recovery from water treatment can also help, especially in a post-closure environment, as value recovery can potentially alleviate post-closure costs, he said.
Meanwhile, Paulse outlined two R&D projects that the company was piloting. One of them was looking at using the high levels of ammonia found in North-West platinum group metal (PGM) mines' water bodies.
"At these levels, ammonia is volatile and can lead to health and safety issues. We have not found a good way to manage this challenge. However, a new system that will be commissioned in the next four weeks is generating a lot of positive results. This system uses an innovative way to remove nitrates and ammonia in a circulating water body," he noted.
Another potential solution the company was investigating, to solve the ammonia challenge, would look at using in-earth biological processes, but this remained in the investigation phase, he added.
Further, Sibanye was also working on a zero-liquid discharge project that would produce ammonium sulphate and potassium sulphate, as well as rare earth elements, from solid waste and produce water to potable standards, Paulse highlighted.
The company has done testing on gold and PGMs water bodies and initial indications are that the project makes financial sense and should achieve a return on investment within a few years, after which it will be able to produce significant value and products that can be sold onto a secondary market.
"If we are able to realise plants such as this, then doing water treatment in a post-closure environment would be much easier from a financial point of view, as a company would not be stuck with a financial liability until the end of time."
Paulse said the team was aiming to develop a large-scale 5 Mℓ/d pilot plant by the end of 2023, after which it hoped to progress past the pilot phase.