Synthesis of MnO2 on activated carbon and its potential application in the adsorption of As(V) and Pb(II) in aqueous solutions

Abstract

The conditions for the synthesis of a material with MnO₂ (OMD) on activated carbon (AC) were studied. These conditions were: reaction time, temperature, stirring speed, concentrations of AC, H₂SO₄, and O₃ in solution, and particle size. Agglomerates on AC were observed by means of scanning electron microscopy (SEM) and microanalysis by energy dispersive spectroscopy (EDS) and revealed the presence of OMD deposited on the surface. The activation energy and the factor of frequency for the reaction were determined as E_a = 1.2 kcal/mol and A = 2.2. The value of E_a indicates that the precipitation of OMD on the AC was controlled by mass transfer in aqueous solution and the order of reaction was zero.

The adsorption capacities of AC were q = 14 mg Pb(II)/g AC and q = 9.1 mg As(V)/g AC. Whereas, for the OMD/AC obtained in the following conditions: [AC] 1 or 2 g/L, particle size of AC of +0.59 mm, [H₂SO₄] 1 or 2 mol/L, 25 °C, stirring speed 600 rpm, and [O₃] 1.35 mol/L, the adsorption capacities were q = 90.5 mg Pb(II)/g OMD/AC and 25.4 mg As(V)/g OMD/AC. Therefore, the fixing of OMD on the surface of the AC greatly improved the removal of both Pb(II) and As(V)from aqueous solutions.