Rice husk was converted into activated carbon (AC) as a byproduct of agricultural waste in an electric furnace at 700 °C and chemically activated using three distinct processes: NaOH AC(C), acetic acid AC(C-1), phosphoric acid AC(C-2), and carbonization AC(C-3) without any chemical activation. To characterize the activated carbon and the removal efficiencies of Fe(III) and Mn(II) from aqueous solutions, various analytical tools were used. The results revealed that the capacities of the four adsorbents to adsorb Fe(III) or Mn(II) from an aqueous solution differ significantly. AC(C-3) was chosen for additional research. The impact of different operational factors, including pH, contact time, adsorbent dosage, starting metal ion concentration, interfering ions, and temperature, were investigated. The optimum pH values for Fe(III) and Mn(II) adsorption were found to be pH 3 and pH 6, respectively. The results obtained were utilized to assess the kinetics and thermodynamics of the adsorption process. The sorption of Fe(III) and Mn(II) ions was found to be a pseudo-second-order kinetic process, and the equilibrium data were fitted with the Langmuir isotherm. Additionally, the evidence suggests that an endothermic mechanism governs the adsorption process. The maximum adsorption capacities of Fe(III) and Mn(II) were 28.9 and 73.47 mg/g, respectively.

Activated carbon (AC) has been prepared from rice husk (RH) as an agricultural by-product. Different analytical instruments characterized the prepared activated carbon. Fe 3+ and Mn 2+ were extracted from the aqueous solution. The effects of many different variables namely, pH effect, reaction time, adsorbent amount, starting concentration of metal ions, interfering ions and temperature on the adsorption of ions were evaluated. The optimal adsorption of Fe 3+ and Mn 2+ was 3 and 6, respectively. The optimal contact time was determined to be 2 hours for both Fe 3+ and Mn 2+ ions. The kinetic and thermodynamic of adsorption process was found to be a pseudo-second order for both Fe 3+ and Mn 2+ ions. The equilibrium data was applicable to Langmuir, and Freundlich isotherm. The correlation coefficient (R 2 ) of both isotherms were 0.99 & 0.89 for Fe 3+ , respectively and 0.99 & 0.77 for Mn 2+ , respectively. The obtained data predicted also that; the endothermic system governs the adsorption process. Furthermore, the maximum adsorption capacities for Fe 3+ and Mn 2+ were 72.2 & 49.6 mg/g, respectively and the removal of metal ions were 90.12 & 83.42 %, respectively. Finally, the results revealed that the adsorption process of the two metal ions is consistent with the pseudo-second-order kinetics.