Hydrometallurgy recovers more than 90% of the lithium in a dead battery, and the smelting method it replaces cannot recover any

From black mass to battery grade salt

Black mass is the shredded powder left after a battery pack is torn apart, a mix of nickel, cobalt, manganese and lithium bound together with graphite. Hydrometallurgy is the chemical process that pulls those metals back out of black mass using acid instead of heat. The powder goes into a bath of sulfuric acid and hydrogen peroxide, which dissolves the metals into solution, then a series of chemical washes, called leaching, solvent extraction and precipitation, pulls each metal out on its own. What comes out at the end is nickel sulphate or hydroxide, cobalt sulphate or hydroxide, and lithium carbonate or hydroxide, battery grade material a factory can put straight into a new cathode. Lithium is the hardest of the 4 metals to pull out this way. The acid step has to swap a hydrogen ion for the lithium ion before lithium will dissolve, so lithium needs a stronger acid step than nickel or cobalt need.

What the older method leaves behind

Pyrometallurgy is the older method hydrometallurgy has been replacing, and it skips the chemistry bath entirely by smelting the pack at high temperature. 2 peer reviewed reviews agree on what that method costs. Cobalt and nickel recover well from a smelter, but lithium and manganese are left behind in the furnace slag, uneconomical to pull back out, and the graphite in the pack partially burns away as carbon dioxide rather than being recovered. That gap is why regulators still treat lithium as the hardest metal to recover, even as the newest hydrometallurgy plants report closing most of it. The European Union adopted a law on batteries and waste batteries on 12 July 2023 that sets the minimum share of each metal a recycler must recover from waste batteries collected in the union. By the end of 2027, recyclers only have to recover 50% of the lithium in those batteries, compared with 90% for cobalt, copper, lead and nickel, the clearest sign that lithium recovery is regarded as the harder problem industry wide.

2 plants that already claim to beat that target

Umicore in Belgium smelts the pack first, then runs a second hydrometallurgical stage that recovers lithium from the flue dust the smelter produces, by turning it into vapor and capturing it. The company now reports recovering cobalt, copper and nickel above 95%, and lithium above 90%, after recent process improvements.

Redwood Materials in Nevada skips smelting altogether. Its patented pretreatment step, called reductive calcination, uses the energy already inside a dead battery to free the metals without creating a slag, and the hydrometallurgy step that follows reclaims 95% of the lithium it takes in, the company states. Neither figure is independently audited within the sources for this article, each is the rate the company states for itself.

How big these plants are

Hydrometallurgy plants vary hugely in size. A 2023 review of the industry lists Duesenfeld in Germany processing 3,000 tonnes a year, Retriev Technologies in Canada 4,500 tonnes, Umicore 7,000 tonnes, and Brunp and CATL in China the largest at 30,000 tonnes a year.

Brunp and CATL also claims a metal recovery rate above 99%, but the review that reports the claim says it is difficult to verify, so this article states only the capacity of that plant, not the recovery number. A separate method, direct recycling, rebuilds the cathode structure without ever dissolving it into these salts, and sits outside what this article covers.