21 Sept 2026 · Process notes
Choosing a lithium extractant for brine and recycle streams
Lithium sources differ in sodium, magnesium and sulphate background, and that background decides the reagent route far more than the lithium grade alone.
Start from the stream, not the grade
Two lithium streams with the same lithium concentration can behave very differently in solvent extraction. A salt-lake brine arrives with a high sodium background and often a significant magnesium load, while a recycling liquor carries residual nickel, cobalt, manganese and fluoride species. Those differences change the pre-treatment sequence before the reagent is even considered.
In practice the first question is not which extractant loads lithium, but which ions will compete for the organic phase and how much scrub capacity the circuit can afford. A high magnesium feed usually needs softening or a selective pre-step; a recycling liquor needs the transition metals removed first so that the lithium strip stays clean.
Set the extraction window
Lithium extractants work inside a defined acidity and phase-ratio window. Move outside it and either the loading drops or co-extraction of sodium rises. The window is confirmed on the actual feed, because published values for a synthetic brine rarely reproduce the behaviour of a concentrated plant stream.
Phase ratio is the other lever. A higher organic-to-aqueous ratio raises lithium transfer per pass but increases the load on stripping and on the solvent inventory. Most circuits settle the ratio with a small number of stages in a mini-plant rather than a single shake-out test.
Match the strip route to the product
Stripping produces a lithium chloride or sulphate stream, and the choice depends on whether the plant is heading for carbonate or hydroxide. Chloride routes need attention to chloride carry-over in later stages; sulphate routes need the sulphate balance to stay inside the crystalliser design.
Where the product specification is tight, a polishing stage after stripping is normal. It is cheaper to design that stage in at the start than to add it after the circuit is running.
