There are about 16 000 desalination plants in the world and these discharge 142-million cubic metres of brine daily, which is well up on previous estimates and enough to cover KwaZulu-Natal in 30 cm of saturated salt water in a year.
What is needed is mining the salt and metals contained in the brine, which includes magnesium, gypsum, sodium chloride, calcium, potassium, chlorine, bromine and lithium – but mining companies have been slow to grasp this opportunity.
Much is made of the Witwatersrand being left with tonnes of acid mine drainage (AMD), which many would like to see cleaned up for reuse. But from a water recovery point of view, AMD is relatively tiny, compared with the saline groundwater opportunities of South Africa’s Karoo and north-west Cape. By pumping up 30 megalitres of it a day, South Africa could irrigate 2 200 ha of ground and create 15 000 jobs.
As has been previously pointed out by Mining Weekly, local technology has been developed that yields handsome profits through the conversion of AMD into valuable fertiliser materials, particularly potassium nitrate, and this technology has the potential to process South Africa’s large volumes of currently unusable brackish groundwater in arid regions.
But the growing unbeneficiated salt concentrations from desalination in mainly the Middle East and North Africa are what is worrying the United Nations (UN).
A UN-backed paper has found that 55% of global brine is produced by mainly Saudi Arabia (22%), the UAE (20.2%), Kuwait (6.6%) and Qatar (5.8%). Middle Eastern plants, which largely operate using seawater and thermal desalination technologies, typically produce four times as much brine for every cubic metre of clean water as plants where river water membrane processes dominate.
Of concern is that most of the untreated waste goes back into the marine environment, translating into ecological effects observable throughout the food chain.
With better technology, minerals like sodium, magnesium, calcium, potassium, bromine, boron, strontium, lithium, rubidium and uranium could also be recovered. All these are used by industry, in products, and in agriculture. The required technologies are immature, however, and the recovery of these resources is economically uncompetitive currently.
There is a need to convert an environmental problem into an economic opportunity, says Dr Manzoor Qadir, assistant director of UN University Institute for Water, Environment and Health, who points out that reject brine has been used for aquaculture, as well as to cultivate the dietary supplement, Spirulina.
Coauthor Dr Vladimir Smakhtin sees an urgent need to make desalination technologies more affordable and extend them to low-income and lower-middle-income countries.
With continuing technology refinement and improving economic affordability, much could be gained from successfully turning the brine waste to positive account.
Meanwhile, some mining companies are themselves getting in on the desalination act, with Chile poised to triple the use of seawater for mainly copper mining in the next decade, South32 opening a seawater desalination plant at its Hillside aluminium smelter, in Richards Bay, Sasol’s Synfuels operations, in Secunda, desalinating excess water from underground coal mines and Namibia building desalination plants for its uranium mines.