ammonium sorption rate by some soils series of golestan province

sorption reactions in many heterogeneous systems are important. adsorption is a time dependent process and knowing the adsorption rate is essential for designing, evaluating and recovering the adsorbents. at the present study, an ammonium adsorption kinetic experiment by some soils series of golestan provice, which is varying in mineralogical and textural properties was conducted using solution containing 100 mg/l of ammonium chloride at the times of 0.25 to 384 h. kinetic models were used to fit the experimental data, namely, zero-order, first-order, pseudo-second-order, simplified elovich, parabolic diffusion and power function models. the results of adsorption kinetic study showed that ammonium is adsorbed fast within the first hours, but with elapsing the time, it will be slow. the most ammonium adsorption was in karasou soil and the lowest one was observed in the houttan soil 2. according to coefficients of determination (r2) and standard errors of estimate (se) for equations, the rates of ammonium adsorption in all soils were described well by the pseudo second order, power function and simplified elovich equations. the constant of speed rate of second-order equation (kg mg−1 h−1) for soils varied from 0.0063 (kordkoy 2) to 0.0374 (houttan 2) with an avg. of 0.0179. ammonium uptake data plotted on a linear parabolic diffusion equation showed a discontinuity in slope at 8 hr. this could indicate the presence of two different mechanisms or different adsorption sites with different rate constants which are controlled adsorption process.