acid for reaction to obtain an acidic solution having metal sulphates including ferrous sulphate cobalt sulphate nickel sulfate etc therein the sulphuric acid has a density of 5 u02dc 30 weight percents wt c crystallizing 3 the acidic solution obtained after reaction is crystallized through convection with a cooling water to obtain crystals of the metal sulphates containing crystallization water therein the crystallization is processed at a temperature of 2 u02dc 8 celsius degrees u00b0 c d separating crystals 4 solid liquid separation is processed to separate crystals of the metal sulphates from the acidic solution for obtaining a purer fluoroborate acid thus a novel method of recycling a radioactive waste acid is obtained the above steps of removing solid objects 1 adding sulphuric acid 2 crystallizing 3 and separating crystals 4 are processed with a device of purifying and recycling a waste acid 5 the device of purifying and recycling a waste acid 5 comprises a collecting tank 51 for containing the fluoroborate waste acid a filter 52 connected with the collecting tank 514 for removing solid objects in the fluoroborate waste acid a dispensing tank 53 connected with the filter 52 for containing a sulphuric acid and the fluoroborate waste acid obtained after the solid objects are removed a pre crystallizing tank 54 connected with the dispensing tank 53 a crystallizing tank 55 connected with the pre crystallizing tank 54 a purifying tank 56 connected with the crystallizing tank 55 a recycling tank 57 connected with the purifying tank 56 a low temperature recycling water tank 58 connected with the purifying tank.