What to do with the battery industry’s sodium sulfate waste?

In fall 2012, an employee conducting a routine inspection at Talvivaara Mining Company’s nickel mine in a forested part of central Finland discovered that the site’s 60 hectare wastewater pond had sprung a leak. Crews built emergency dams to contain the spill, but within a few days, water containing heavy metals and sulfates flowed into the local watershed.

It took 10 days to plug the leak, which ultimately released more than 3,000 metric tons (t) of sulfates into the environment. Scientists from the University of Helsinki found that this spill, and another one just a few months later, caused a “massive ecological disruption” in Lake Kivijärvi, located a few kilometers southwest of the mine.

Dense, sulfate-rich water sank to the bottom of the lake. Oxygen stopped circulating from the surface to the lake bed, killing insects, mussels, snails, and other organisms living there.

That had ripple effects throughout the ecosystem, according to Jaakko Leppänen, an aquatic ecologist who assessed the spill’s impact. “When the bottom is dead, there’s no food for fish,” he says.

Since the spill, the demand for nickel, and other metals used to make lithium-ion batteries, has exploded, driven by the adoption of electric vehicles. Companies are now racing to build mines, battery material plants, and recycling facilities. But like Talvivaara’s mine, these facilities generate sulfate waste, usually ammonium sulfate or sodium sulfate.

Most battery materials are made in China, where firms often sell their sodium sulfate as a raw material for other products. But the number of battery projects planned in Europe and North America, which don’t have industries to absorb this waste, is growing quickly. Some industry leaders worry that plans by these developers for discharging sulfate waste won’t pass muster with environmental agencies. “Eventually, the volumes get so big that you can’t deal with them anywhere outside of China,” says Dan Blondal, CEO of Nano One Materials, a start-up developing a sulfate-free manufacturing process for battery cathodes.

To avoid the risk of delays and community backlash against their plants, battery material firms are experimenting with new technologies. Several hope to recycle sulfates into fertilizers or regenerate them into needed raw materials. Others claim to have new processes for manufacturing battery materials that don’t generate sulfates.

But these new approaches could increase costs at a time when the battery industry wants to make its products cheaper. “There are companies aware of the issue and trying to do something to fix it,” says Robert Baylis, principal of the battery industry consulting firm Carding Mill. “But it takes longer to bring in these new technologies than it does to ramp up the scale of existing stuff.”

Sulfur cycle

Most of the metals in a lithium-ion battery came from rocks. In the case of lithium, which can also be extracted from brine, miners dig lithium ore out of the ground, crush it, and blast it with heat to concentrate the lithium. The concentrated ore is roasted with sulfuric acid, leached with water, and then neutralized to produce lithium sulfate. After removing impurities, refineries treat lithium sulfate with sodium hydroxide, yielding lithium hydroxide, a raw material used to make battery cathodes. The by-product is sodium sulfate.

Other metals also go through a sulfate step before they are used in batteries. Companies that make a precursor for nickel-based battery cathodes, a product called pCAM, dissolve sulfates of nickel, manganese, and cobalt into a solution. Then they use sodium hydroxide to strip off sulfate molecules and form a mixed-metal hydroxide, generating sodium sulfate. For iron-based cathodes, companies react ammonium phosphate with iron sulfate to make the precursor iron phosphate, creating ammonium sulfate as a by-product.

Similar chemistry happens in battery recycling, where firms use sulfuric acid to leach key metals out of shredded batteries.

Sodium sulfate isn’t particularly toxic and exists naturally in seawater. “Although we have a big issue where there’s just way too much of it, it’s not the worst waste product,” says Rob Pell, the founder of Minviro, a consultancy that assesses the environmental impact of clean technology projects.

At current production levels, sulfate waste isn’t a big hazard, according to a 2022 report from RWTH Aachen University and the consulting firm Roland Berger. But the authors anticipate that battery material factories could be discharging almost 6 million t of sodium sulfate—nearly an eightfold increase over 2022 levels—by the end of the decade.

Existing battery plants, and those in other industries that produce sodium sulfate, such as pulp and paper, have a few options for disposing of this waste. Some facilities pump the salt into the ocean, where it is diluted. In China, firms often sell powdered sodium sulfate, which becomes a slippery, soapy gel when mixed with water, to makers of dry laundry detergents. But in many of the countries now trying to establish battery industries, consumers prefer liquid detergents, which don’t contain sodium sulfate, according to Baylis.

Some upcoming battery projects are taking these conventional approaches to waste management. The chemical firm Albemarle hopes to sell 200,000 t of sodium sulfate from a lithium refinery it’s building in Australia to detergent makers in China. During the commissioning phases, the sulfate waste will go to a specialized dump.

A joint venture between CNGR Advanced Material and Finnish Minerals Group, which now owns the Talvivaara nickel mine, wants to discharge the sodium sulfate from a planned Finnish pCAM plant into the Baltic Sea.

With careful management, pumping sodium sulfate into the ocean can be a reasonable waste disposal approach, Leppänen says. Sulfates would mostly be diluted into a huge body of water that is already saline, and ocean currents would help prevent the formation of a dense layer of sulfate-rich water. While there might be impacts where the sulfates are discharged, he says this is a much better option than disposing of sulfates into freshwater lakes or rivers, as other facilities have proposed.

A Finnish court forced BASF to delay the start-up of an inland pCAM plant because the original wastewater management plan entailed releasing sodium sulfate into a local river, the Kokemäenjoki. Environmental groups in Finland opposed that plan and a subsequent proposal to truck sodium sulfate to the coast and release it into the ocean. BASF is considering building a crystallizer that would remove sodium sulfate from wastewater, but construction could take 18 months. The firm is now threatening to lay off workers at the stalled plant.

Pell says the firms making battery materials have to weigh the low cost of dumping sulfates into oceans and lakes against the risk of regulatory hurdles or pushback from nearby communities. “The waste management approach for sodium sulfate completely depends on your context, about where you are,” he says.

Recycle

Some companies building new pCAM facilities in Europe and North America are hoping to circumvent disposal issues by turning their waste into something they can sell.

One option is to convert sodium sulfate into potassium sulfate, a high-value fertilizer. Potassium is most commonly applied to fields as potassium chloride. Potassium sulfate is more expensive, but the presence of sulfur, a necessary nutrient, makes it an appealing option for some crops.

In May, Cinis Fertilizer started up a plant in Örnsköldsvik, Sweden, that will react potassium chloride with sodium sulfate to form 100,000 t of potassium sulfate–containing fertilizer per year. The facility is already using sodium sulfate from the Northvolt battery manufacturing plant located about 200 km to the north.

CEO Jakob Liedberg say Cinis’s process, which has been known for decades, is cheaper and less energy-intensive than the more common approach of reacting potassium chloride and sulfuric acid at high temperature.

Cinis is planning to build its its next fertilizer plants adjacent to battery materials manufacturers that will generate lots of sodium sulfate waste. The company is planning one site by Northvolt’s Swedish plant, another near Ascend Elements’ battery recycling operation in Kentucky, and three other projects. Liedberg says a commitment to recycle waste should help battery plants to open successfully. “The more environmentally friendly you can be, the more likely you will be to get the permit,” he says.

CNGR has a permit to discharge sodium sulfate into the ocean, but Thorsten Lahrs, CEO of the company’s European subsidiary, says the firm may opt to recycle waste into fertilizer if it wants to expand. “It’s obviously desirable to make valuable products out of certain molecules,” he says.

Not all of the battery industry’s waste can be diverted into fertilizers, and several companies argue that sodium sulfate should be recycled back into battery raw materials. These firms are developing electrolyzers that can convert sodium sulfate into sulfuric acid and sodium hydroxide, the chemicals from which it originated.

In 2022, Adven formed a joint venture with Finnish Minerals Group to scale up such a system with the help of a $17.3 million grant from the Finnish government. Adven is currently testing an industrial-scale pilot at a customer’s plant in Finland.

In June, Aepnus Technology raised $8 million in seed funding for a similar process. CEO Lukas Hackl says the company previously hoped to use electrolyzers to separate lithium salts from brine. But while talking to lithium executives, he learned about the sodium sulfate waste problem and realized his technology could provide a solution. “It became clearer and clearer that it wasn’t processing the lithium but dealing with the chemical by-products that was more of an issue,” he says.

One challenge to this approach is that electrolyzers yield dilute sulfuric acid and sodium hydroxide. Increasing the concentration requires a costly evaporation step. But Hackl says battery manufacturers may be able to reuse these products at fairly low strength.

Reduce

Instead of recycling sulfates, several firms are trying to avoid them altogether with technologies that make battery materials without generating sulfate waste.

The battery start-ups Novonix, Sylvatex, and Nano One hope to produce nickel, manganese, and cobalt cathode materials from metal oxides or hydroxides, rather than sulfates. Sylvatex CEO Virginia Klausmeier argues that sulfate-free manufacturing processes will make it easier to build large plants in places with strict environmental regulations.

“You don’t have any sodium sulfate waste,” she says. “That completely mitigates the environmental issue that is becoming an increasingly big thorn in the growth of cathode manufacturing in Europe and North America.”

Metal sulfates are soluble, and can be mixed relatively easily, in water. But metal oxides and hydroxides usually aren’t soluble in water, which makes them hard to combine uniformly.

Sylvatex and Nano One overcome this challenge with additives that encourage metal hydroxides to combine homogeneously. Novonix uses heat and mechanical force to mix the materials. “We’ve developed techniques to combine these materials, break them down, and then rebuild them,” says Chris Burns, CEO of Novonix.

These start-ups all claim that their processes will lower the cost of cathode manufacturing once they are scaled up, but they have yet to build commercial plants.

Similarly, the Finnish technology firm Metso is trying to deploy a sulfate-free process for lithium refining. Instead of roasting concentrated lithium ore with sulfuric acid, the company treats the ore with sodium carbonate in a high-temperature, high-pressure reactor, producing lithium carbonate, a material that can be used to make batteries. Sodium aluminum silicate is the by-product, which Metso says could be sold as an input for cement manufacturing.

The vast majority of lithium ore is refined in China, and Marika Tiihonen, who manages lithium-processing technology for Metso, argues that her company’s approach will make it easier to open lithium chemical plants in other places. “Developing a minerals processing and chemicals plant. . . takes years and years,” she says. “One of the reasons is the environmental permitting issues.”

Several companies, including Sibanye-Stillwater, EV Metals Group, Avalon Advanced Materials, and Piedmont Lithium have announced they will use the Metso process at plants they are planning in Finland, Saudi Arabia, Canada, and Tennessee.

Even with new technologies, the battery industry won’t eliminate every potential environmental impact, or even all of its sulfate waste. For example, nickel and cobalt refineries use sulfuric acid to extract the metals out of ore. But Pell, from the environmental impact assessment firm Minviro, points out that failing to scale up battery manufacturing has consequences as well. “The bigger risk would be to continue in a fossil fuel economy,” he says.