Extent of environmental pollution is increased by technological development. Especially in industrialized areas, ecological equilibrium is affected by wastewater formed with industrial wastes. The more important pollutants for water are nitrogen compounds, which are threatening the human health. Ammonium removal from solution was investigated using Turkish sepiolite, having average particle dimension of 2.05 mm. Ammonium uptake experiments for two different adsorbent quantities were performed for the solutions having initial solution concentrations in the range of 8.333-222.23 mmol NH4+/1, and equilibrium isotherms were performed at 25 degreesC. Around 60% ammonium removal, of which 90% was achieved within 500 s, was observed. Maximum adsorbed amount was 3.50 mmol NH4+/g. The exponential decrease model for the variation of the solution concentration with time, gave reasonably good agreement with the experimental data. The effective diffusion coefficients were estimated around 1.4 x 10 (-10) m(2)/s. (C) 2002 Elsevier Science B.V. All rights reserved.