Effect of the mole ratio of Mn/Fe composites on arsenic (V) adsorption

Highlights: • Synthesis of new adsorbent media for the removal of arsenic (V) in water • Study of changes in the properties of synthesized materials by adding Mn to the goethite structure • Evaluate changes in adsorbent media and their influence on the removal of arsenic (V) in water • Evaluate removal arsenic (V) rates and adsorption capacities of adsorbent media in model water and real well water • Removal of high (10 mg/L) and low (5 mg/L) arsenic (V) concentrations -- Abstract: Iron and manganese have been studied as a proposal for new materials that could be used for the adsorption of arsenic (V) (As (V)), in order to remove this contaminant. The objective of this work was to study the effect of the molar ratio of three Mn/Fe + Mn composites (X = 0.17, 0.32, 0.47) on the properties of adsorbent media, and to determine their influence on arsenic removal by comparing them with two metallic oxyhydroxides, that are commonly used as adsorbents of As(V) in aqueous solution (goethite and birnessite). These media were synthesized by chemical precipitation while controlling particle size. They were characterized using X-ray diffraction (XDR), scanning electron microscopy with X-ray dispersive energy spectrometry (SEM-EDS), surface area analysis by the BET method, Fourier transform infrared spectroscopy (FTIR), and isoelectric point analysis (IEP). The surface area (286 m²/g) of the composite with a molar ratio of X = 0.17 was larger than that of the other media. The adsorption kinetics and isotherms were fitted to the mathematical models, specifically, the pseudo-second order and Langmuir, respectively. The X = 017 composite had an adsorption capacity of 3.28 mg/g and removed 99% of As(V) with an initial concentration of 0.5 and 97% with an initial concentration of 10 mg/L, at 180 min, 25 °C, and pH 7. The five adsorbent media were tested with well water with an initial As(V) concentration of 0.075 mg/L, and the best behavior was exhibited with a molar ratio of X = 0.17 at 90 min, resulting in 100% removal of As(V). The results suggest that this material is an effective and viable alternative to remove this contaminant from water.