GB815841A - Separation of guanidine values - Google Patents

Abstract

Guanidine values are recovered from an aqueous mixture comprising a guanidine salt, ammonium salts and melamine by a modification of the method described in the parent Specification which comprises the steps of adding to said mixture borate ions and an excess of ammonium ions to provide a crystalline precipitate of substantially pure guanidine tetraborate and separating said precipitate. The borate ions may be provided by the addition of boric acid and the ammonium ions by passing gaseous ammonia through the aqueous mixture. The guanidine tetraborate may be converted to other guanidine salts by treatment with the appropriate acid, e.g. the sulphate using dilute sulphuric acid, and the boric acid recovered may be re-used. The products of fusion of ammonium thiocyanate, comprising guanidine thiocyanate, ammonium thiocyanate, thiourea and melamine, in 2 to 80 per cent, preferably 20 to 60 per cent, solution may be treated with 0.1 to 2.1 mols. of boric acid per mol. of guanidine, the mixture heated to 70 DEG C. while ammonia is passed through until a pH of 7.5 is attained and the solution then cooled slowly to 15 DEG C. and the white crystalline solid centrifuged and washed with water at 70 DEG C. The process may be also used where the hydrochloride, sulphate, sulphamate or carbamate of guanidine is present with ammonium salts. Detailed examples of the recovery of guanidine tetraborate from ammonium thiocyanate fusion products by the above method are given.