Synthesis, characterization, and property test of crystalline polyferric sulfate adsorbent used in treatment of contaminated water with a high As(III) content

A crystalline polyferric sulfate (PFS) adsorbent was synthesized by oxidizing and precipitating ferrous ions in air atmospheric conditions. The morphology, structure, specific surface area (SSA), and adsorptive efficacy of the adsorbent to As(III) were characterized by scanning electron microscope (SEM) and transmission electron microscopy (TEM) images, X-ray diffraction (XRD) patterns, Fourier- transform infrared (FTIR) spectra, BET SSA analyses, and adsorption experiments. The adsorbent showed a near-spherical aggregate structure and had good crystallinity. A significant amount of α-goethite co-precipitated with PFS in the case of the initial ferrous concentration of 1 mol/L and increased SSA of the adsorbent. The stability region of ferric compounds in the process was drawn and applied to analyze the iron behavior during the synthesis. The adsorption of As(III) in high As(III)-containing solutions fitted the Langmuir isotherm model adequately. The absorbent with co-precipitation of α-goethite showed good adsorbability for As(III) and good filtering performance in the high As(III)-containing solution of 10–100 mg/L under acidic, neutral, and alkaline conditions (pH 2.09–9.01). After the adsorption process, the stability of the residues bearing As(III) was evaluated by toxic characteristic leaching procedure (TCLP) tests. The results indicated that the residues were extremely stable, and the concentrations of arsenic in the leaching solutions were less than 0.01 mg/L.