Phosphate removal from aqueous solutions by adsorption using ferric sludge

► The ferric sludge has the largest adsorption capacity at pH 5.5. ► The adsorption process is well described by the M-Langmuir isotherm model. ► The maximum phosphate adsorption amount computed by M-Langmuir isotherm is 36.67 mg/g. ► The adsorption by Ferric Sludge is an inner-sphere complexation process.