BRINE AND METHOD FOR PRODUCING SAME

A method to produce a brine from mixed alum salts, the method comprising the steps of: (i) Dissolving or pulping alum salts (1) containing rubidium alum, cesium alum and/or potassium alum in water or a recycled liquor and adding a neutralising agent to precipitate (20) aluminium as aluminium hydroxide and some sulfate; (ii) Passing the product of step (i) to a solid liquid separation stage (21) to remove precipitated solids (5) from step (i); (iii) A decant or filtrate (6) from step (ii) is passed to a solvent extraction stage (24-27) whereby any contained cesium and rubidium is selectively extracted into the organic phase to form a loaded organic solution (16); (iv) Contacting the loaded organic solution (16) of step (iii) with a scrub solution (17), which is at a pH lower than the extraction pH, to effectively scrub co-loaded potassium from the organic phase; (v) Contacting the scrubbed organic (19) of step (iv) with formic acid (20) to strip cesium and rubidium from the organic, the stripped cesium and rubidium forming a cesium and/or rubidium sulfate brine (21); and (vi) Recycling the stripped organic (22) of step (v) to the extraction stage (24-27).