by Ina King (Potgieter) July 31, 2019
Minerals aren’t only found in ore deposits. They are also dissolved, in naturally occurring surface or groundwater brines and seawater across the world. In Africa, where industries such as potash are new and exciting prospects in the central, eastern and northern parts of the continent, technologies including evaporation and crystallisation are positioning ‘brine mining’ as an increasingly commercially viable venture. But it may also have another important role to play in African mining. ProjectsIQ Managing Director Ina King discusses …
Brine mining, the process of extracting desirable materials and minerals naturally dissolved in salt solutions, is practiced across the world in recovering lithium, potash, zinc, salt, and many other minerals.
While natural evaporation has been used to separate salt from seawater for millennia, today commercial brine mining is driven by technologies like controlled evaporation, crystallisation, reverse osmosis, ion exchange and membrane distillation.
As these modern technologies have become dramatically more energy-efficient, with a far lower physical and environmental footprint, mining mineral-rich brines – whether as surface or groundwater bodies or even seawater – is a lucrative business across the world, particularly in North and South America, Asia and Australasia.
And they may soon play a significant role in Africa’s mining landscape as well.
Key focus areas for African brine mining
Brine mining is already the most common method of recovery for one key strategic mineral of the future, lithium, with subsurface brines containing up to 4 000 mg of the valuable element per litre.
Yet another critically important resource may also be found in significant quantities in brines across Africa: potash. Over 90 million tonnes of these potassium-containing salts are mined every year, with their primary application as agricultural fertiliser. However, this is still not enough to meet the demand, and it is estimated that the world production of potash would have to double to meet the present day population.
In Africa, current farming methods are removing potassium from the soils faster than it is being replaced. On average, African farmers are replacing only approximately 10 percent of the potassium that is removed during each harvest. Potash deficiencies are especially pronounced across otherwise rich arable land in East Africa, with Uganda, for example, estimated to have a nutrient deficiency of about 35 kilograms per acre. The lack of availability of potash has been a significant factor contributing to famine and malnutrition across the continent.
This has placed even greater strategic importance on Africa’s deposits of potash, including the Danakil Depression in Ethiopia and Eritrea, an area with abundant and accessible potash reserves, and the Kola potash deposit in the Republic of Congo. Relative newcomer African Potash Ltd. is among the African miners involved in this exciting mineral industry, which is being supported by the Doraleh Container Terminal in Djibouti for the export market.
With the global supply of potash falling some way short of demand, brine mining for potash in Africa is likely to be a lucrative industry in the future.
Recovering minerals from industrial brines
Evaporation and crystallisation technologies are also being deployed to extract valuable dissolved minerals in brines generated by mining and industry, harvesting a variety of saleable products to create additional revenue streams and limit hazardous effluent waste discharge to the environment.
At Ambatovy mine in Madagascar – one of the world’s largest nickel mines, producing 60 000 tonnes of nickel and 5 600 tonnes of cobalt each year – high-tech evaporation technologies are used in the treatment of the mine’s effluent, and produce over 200 000 tonnes of ammonium sulphate each year, that is then sold to the agricultural industry as a high-grade fertiliser. Apart from agricultural products, minerals used in the explosives industry are also commonly found in many industrial effluents. What was previously hazardous waste is now a valuable source of economically important resources.
In this regard, the technologies of brine and solution mining are likely to play an increasingly critical role in addressing the current and historical environmental issues associated with mine effluent.
Indeed, they are likely to form the kind of long-term solution that will enable the South African mining industry to deal with the removal of salts following the treatment of over 220 ML of acid mine water at the Western Basin, Central Basin and Eastern Basin treatment plants on the Witwatersrand.
Whether in naturally occurring or industrial brines, modern technologies enabling us to profitably extract elements and compounds from saline solutions is opening up a new dimension to mining in Africa.
