GB630979A - Improvements in or relating to the recovery of salts from dilute solution - Google Patents

Abstract

In obtaining a relatively concentrated solution of a salt of a strong acid from a relatively dilute solution of the same salt or another salt having the same cation, the dilute solution is passed through hydrogen-ion-exchange material, a solution of the acid of which the salt is to be obtained is passed through the material, more acid is added to the effluent and the resultant solution is passed through one or more beds of hydrogen-ion-exchange material which have taken up cations from the initial solution, the last two steps being repeated if desired. In one embodiment the dilute solution is passed through a number of beds of exchange material in series followed by the acid solution, the initial concentration of which is restored during its passage between each bed and the next by the addition of acid; in a modification the regeneration may be effected with two different portions of acid solution, the acid concentration of each being restored after each passage through a bed and the second solution being used again as the first solution in a subsequent process after the beds have been again treated with the dilute salt solution. The material used for removal of the displacing acid from the final effluent may be one which will not exchange hydrogen for metal ions in solution with strong acid anions but will do so when these are in solution with weak acid anions. A similar material may be used for an initial solution which contains the salt of a weak acid, and for an initial solution which contains a mixture of salts of strong and weak acids, e.g. potassium sulphate and acetate; while this material is being saturated the effluent contains unchanged potassium sulphate which can be absorbed by material capable of exchanging for hydrogen ions the potassium ions from salts of strong acids, e.g. a cation exchange material having replaceable hydrogen ions forming part of sulphonic acid groups; the saturated material on regeneration results in a solution containing potassium sulphate and free sulphuric acid from which the latter may be removed by passage through exchange material already saturated with potassium ions or by neutralization with potassium hydroxide or carbonate.ALSO:In obtaining a relatively concentrated solution of a salt of a strong acid from a relatively dilute solution of the same salt or another salt having the same cation, the dilute solution is passed through hydrogen-ion-exchange material, a solution of the acid of which the salt is to be obtained is passed through the material, more acid is added to the effluent and the resultant solution is passed through one or more beds of hydrogen-ion-exchange material which have taken up cations from the initial solution, the last two steps being repeated if desired. In one embodiment the dilute solution is passed through a number of beds of exchange material in series followed by the acid solution, the initial concentration of which is restored during its passage between each bed and the next by addition of acid; in a modification the regeneration may be effected with two different portions of acid solution, the acid concentration of each being restored after each passage through a bed and the second solution being used again as the first solution in a subsequent process and the second solution being used again with dilute salt solution. The material used for removal of the displacing acid from the final effluent may be one which will not exchange hydrogen for metal ions in solution with strong acid anions but will do so when these are in solution with weak acid anions. A similar material may be used for an initial solution which contains the salt of a weak acid and for an initial solution which contains a mixture of salts of strong and weak acids, e.g., potassium sulphate and acetate; while this material is being saturated, the effluent contains unchanged potassium sulphate which can be absorbed by material capable of exchanging for hydrogen ions the potassium ions from salts and strong acids, e.g., a cation exchange material having replaceable hydrogen ions forming part of sulphonic acid groups; the saturated material on regeneration results in a solution containing potassium sulphate and free sulphonic acid from which the latter may be removed by passage through exchange material already saturated with potassium ions or by neutralization with potassium hydroxide or carbonate.