Diffusion of ammonia and ammonium ions in sulphonic acid cation exchangers (gel Purolite SGC 100 x 10 MBH and macroporous Purolite C 160 MBH) from the solutions, representing the composition of "caustic condensate" (waste of nitrogen fertilizers production) is affected by pH of initial solution and structure of the matrix of cation exchanger. In get matrix the effective intraparticle diffusivity (D-ef) depends greatly on the solution pH because of shrinkage in alkaline and swelling in acidic medium: on decreasing the initial concentration of ammonia from 0.214 to 0.003 and increasing that of ammonium nitrate from 0 to 0.214 mol l(-1) instead, the effect of ion exchange leads to a decrease in pH, resulting in swelling and increase in D-ef from 0.1 to 0.34 x 10(-10) for gel Purolite SGC 100 x 10 MBH and variation of 0.18-0.11 x 10(-10) m(2) s(-1) for macroporous Purolite C 160 MBH (resistant to shrinkage and swelling). In Purolite C 160 MBH both macropore diffusivity (0.07-0.29 x 10(-10) m(2) s(-1)) and gel (solid phase) diffusivity (0.06-0.19 x 10(-10) m(2) s(-1)) are higher than micropore diffusivity (0.28-0.56 x 10(-18) m(2) s(-1)). With respect to the effective intraparticle diffusivity, resistance to nitric acid, used for the regeneration, and high concentration of ammonium nitrate in eluate (up to 110 g l(-1)), Purolite C 160 MBH has been installed for the conversion of ammonia and ammonium ions to ammonium nitrate reusable in the fertilizers production. This allows minimizing the economic loss and preventing the environmental contamination. (c) 2005 Elsevier B.V. All rights reserved.