Desalination plants worldwide discharge somewhere between 105 and 150 million cubic metres of concentrated brine every day, a volume expected to roughly double by mid-century. That reject stream carries sodium chloride, magnesium, bromine, and trace amounts of lithium, boron and strontium — minerals with genuine commercial value. The harder question the industry is now confronting is whether recovering them is actually profitable, or just a compelling slide in a pitch deck.
Brine disposal itself isn’t free, and the cost is rising. For a coastal seawater reverse osmosis (SWRO) plant using a conventional ocean outfall, disposal typically eats up 5–10% of operating expenditure. Inland plants relying on deep-well injection or evaporation ponds can see that climb to 15–25%, and zero-liquid-discharge systems can push it past a third of total costs. At the same time, regulatory scrutiny is tightening unevenly — Gulf states that produce roughly 55% of the world’s desalination brine still have no unified regional discharge standard, while California, Australia and Spain have moved toward stricter environmental limits tied to seagrass and marine-life protection.
The numbers behind the headline figures
A widely cited 2022 review estimated the theoretical gross mineral value of desalination brine at $11,000–18,000 per thousand cubic metres — a figure that, scaled globally, runs into the trillions. But that ceiling assumes full recovery and unconstrained markets, neither of which holds up in practice. Model a reference 100,000 m³/day plant selling every recoverable mineral at 2025 market prices, and the theoretical annual revenue comes out around $376 million. Adjust for what markets could realistically absorb — a single such plant’s salt output alone would be large enough to depress regional prices — and that figure falls to roughly $73 million. Subtract processing costs, and the plant is left with something closer to $18 million a year: a meaningful offset against typical SWRO operating costs of $23–29 million annually, but nowhere near the world-changing numbers often quoted.
Magnesium looks like the more credible near-term opportunity. SWRO brine typically runs 2–5 g/L of magnesium, recoverable at 90–100% efficiency via hydroxide precipitation, with industrial-grade product fetching $450–820 per tonne and high-purity flame-retardant grades reaching over $2,000. Given that China dominates global magnesium supply through processes Western regulators consider environmentally costly, magnesium recovery carries a supply-chain security argument that pure economics doesn’t fully capture. Bromine follows a similar logic: too dilute for direct extraction at typical brine concentrations, but viable once concentrated as a byproduct of salt crystallisation.
Policy is moving faster than commercial proof
Government incentives have shifted markedly in a short time. The US now offers a production tax credit for critical minerals recovered from brine under the Inflation Reduction Act’s Section 45X rules, while the EU’s Critical Raw Materials Act offers fast-track permitting for several minerals found in seawater reject streams. Capital has followed: water-tech firm Gradiant has reached unicorn status, and Rio Tinto’s multibillion-dollar acquisition of Arcadium Lithium signals growing investor interest in brine-adjacent assets, though most of that capital still targets geological and oilfield brines with far higher mineral concentrations than desalination reject.
Commercial-scale proof remains scarce. Saudi Arabia’s Saudi Water Authority is currently building two mineral-extraction plants at Ras Al Khair, targeting operations in early 2026 as part of a program with a reported $2.1 billion investment target and $266 million in projected annual revenue — figures that, as of this spring, remained unconfirmed by independent commissioning data. The most cautionary data point may be NEOM’s abandoned brine-mining complex at Oxagon, a joint venture between Enowa, Itochu and Veolia that was shelved in 2024 in favour of a conventional desalination plant with no mineral recovery component.
Industry consultant Christos Charisiadis, formerly brine innovation manager on the NEOM project, has argued the core chemistry is already understood — what’s missing is enough operating pressure on plant owners to justify the capital outlay. His own read on where the sector should focus: rather than attempting the full valorisation chain, operators are better served picking a small number of minerals worth extracting selectively.
For now, the sector’s fate likely hinges on a single proof point: whether Saudi Arabia’s Ras Al Khair plants can publish audited financials showing brine mining meaningfully offsetting operating costs at scale. If they do, brine valorization moves from theory to a repeatable business case. If they don’t, it stays where desalination itself once was — technically sound, but waiting for costs and policy to catch up.