GB1433338A - Process for obtaining a more concentrated solution of a compo nent using ion exchange beds - Google Patents

Abstract

1433338 Ion-exchange; chromic acid ECOTEC Ltd 25 April 1973 [2 May 1972] 19526/73 Heading C1A In a process for concentrating a solution of a component A by (1) absorbing A from a relatively dilute first solution on to a first ion-exchange bed, (2) removing A from the bed by passing through it a relatively concentrated second solution containing B exchangeable with with A and also containing C of opposite charge to A, (3) passing the second solution (now containing A and C) through a second ionexchange bed capable of retaining C and (4) then rinsing both beds, the improvement comprising (a) passing the second solution directly from the first to second bed (i.e. without an intervening reservoir) and (b) passing the rinse solution through the second bed directly to the first bed in a direction countercurrent to the flow of second solution. The solution to be concentrated may be chromic acid or a nickel salt solution, formed as spent liquor in plating processes and to be recycled to the plating path, component A being chromiumcontaining anions or nickel cations. In one such process for recovering and concentrating chromic acid (Fig. 1), the dilute chromic acid solution, obtained by passing rinse water through cation exchanger 5, is fed to the concentrator 6 (Fig. 2). Chromium-containing anions are absorbed by passing the solution downwardly via valve 26 through anion exchanger 20, pure water being recycled at 11. Aqueous NaOH (the second solution) is then passed upwardly through the bed and thence via line 22. The sodium chromate solution issuing from the top of 20 is then passed directly via line 22 and valve 24 upwardly through H+-form cationic exchanger 21 where Na<SP>+</SP> exchanges with H<SP>+</SP> to form concentrated chromic acid for recycle to plating bath 3. Both 20 and 21 are then rinsed by passing water from 19 downwardly through 21 and then 20 and thence via line 15 to NaOH reservoir. Dilute chromic acid, solution (diverted from line 9) may also be used as rinse liquid. In order to avoid undue dilution of the NaOH, valve 25 may be adjusted to divert the rinse to waste. On completion of rinsing, the first step of the process is repeated by feeding further dilute chromic acid to anion exchanger 20, via cation bed 9, and at the same time, cationic exchanger 21 is regenerated to H<SP>+</SP>-form by passing in H 2 SO 4 . NaOH solution is then passed through both beds as before. In example chromic acid containing 44À2-78À9 g./l. CrO 3 litre is obtained from rinse water containing 0À316-7À74 g./l. CrO 3 .