Enhancing phosphate adsorption by novel calcium-silicate composites: batch and column studies

Abstract

This paper presents two new kinds of calcium-silicate composites adsorbents KMnO4 modified alkali-treated calcium silicate composite (KASC and Fe3O4@KASC) to investigate adsorption capacity of adsorbing phosphate. The synthesized adsorbents were studied systematically by X-ray fluorescence analysis, nitrogen absorption-adsorption analyzer, X-ray diffraction, zeta potential analyzer, scanning electron microscopy and Fourier-transform infrared spectroscopy (FTIR) spectrophotometer. Factors affecting phosphate adsorption including kinetics, isotherm, pH, coexistent anions, and adsorbent dosage were investigated in batch experiments. The adsorption processes were best described by pseudo-second-order and Langmuir model, and the amount of adsorbed phosphate calculated using Langmuir model was 182 mg g–1 for KASC and 145 mg g–1 for Fe3O4@ KASC. Besides, Fe3O4@KASC also contained magnetic property. Adsorption of phosphate by KASC and Fe3O4@KASC were also performed by fixed-bed column experiments and the results were well described by Yoon-Nelson model and Thomas model. Almost all the adsorbed phosphorus could be recovered by 2% citric acid solution. The phosphate fractionation and FTIR spectra analysis indicated that (CaO)2PO2 was generated during the phosphate adsorption process.