A novel tannin–formaldehyde resin was synthesized from Acacia nilotica fruit extract. The experimental factors controlling the resin synthesis were investigated and the obtained resin was characterized by Fourier transform infrared spectroscopy and scanning electron microscopy analyses. The adsorption of manganese as Mn(II) was firstly demonstrated in distilled water solution. The subjected parameters studied for Mn(II) removal by using the resin were the effects of contact time, an initial Mn(II) concentration and the resin dose. The Mn(II) adsorption preceded very fast, and within 3 min the amount of adsorbed Mn(II) for three different initial manganese concentrations (5, 10, and 20 mg/L) approached 60–76% of the maximal uptake potential under the equilibrium conditions. The pseudo second-order equation explained the kinetic data well and the obtained adsorption isotherm data fitted the Langmuir isotherm model which gave high Langmuir capacity (15.54 mg/g) value. The mean adsorption energy (11.04 kJ/mol) computed from the Dubinin–Radushkevich isotherm suggested the ion exchange mechanism for Mn(II) adsorption. Results of the resin application for treatment of natural ground water samples (Bani Mor and El-Fath areas, Assiut, Egypt) showed that reducing the Mn(II) level to minimum and the complete removal depended on the resin dose.

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