BACKGROUND: In this study three natural Yemeni zeolites (NZ1, NZ2 and NZ3) having major minerals such as clinoptilolite and mordenite, were evaluated as low cost sorbents for the removal and recovery of ammonium ions. RESULTS: The zeolite samples, with pH(PZC) = 9.1 +/- 0.2, 7.9 +/- 0.2 and 7.4 +/- 0.2 for NZ1, NZ2 and NZ3, respectively, showed high ammonium sorption capacities. At pH8, for treated waste waters: (i) with low NH4+ levels (from 25 to 100 mgNH(4)/L); and (ii) for concentrated NH4+ side streams generated from the anaerobic digestion of sewage sludge (from 400 up to 1500 mg L-1), maximum loading capacities of 27 to 51 mgNH(4) g(-1) were measured for the studied zeolites. Measured sorption isotherms, in the concentration range 0.05 to 5 g L-1, were well described by the Langmuir isotherm. The ammonium sorption kinetics was controlled by particle diffusion and was well described by both the homogeneous diffusion (HPDM) and shell progressive (SPM) models. CONCLUSION: Comparison of the equilibrium data with results for natural and synthetic zeolites demonstrate the higher performance of the studied zeolites providing low residual ammonium values <1 mgNH(4) g(-1) and <10 mgNH(4) g(-1) when treating both diluted and concentrated-NH4+ streams, respectively. (C) 2017 Society of Chemical Industry