Synthesis of LDH-Type Clay Substituted With Fe and Ni Ion for Arsenic Removal and Its Application to Magnetic Separation

Syntheses of LDH (layered double hydroxides) substituted with Fe³⁺ and Ni²⁺ were attempted by a co-precipitation method and their products were characterized by X-ray diffraction (XRD), Fourier transform infrared (FT-IR), and X-ray absorption fine structure (XAFS). XRD and FT-IR results indicated that obtained products were composed of a single phase of LDH with CO₃ ^2- anions at interlayer, suggesting the successful syntheses of various modified LDH, Mg-Fe/LDH and Ni-Fe/LDH. In addition, XAFS measurements of Mg-Fe/LDH indicated that substituted Fe³⁺ located at octahedral site in LDH structure. For the application to water purification, these modified-LDH substituted with Fe³⁺ and Ni²⁺ as an adsorbent material were used for the magnetic separation system. As a results, these modified-LDH possessed the higher removal ability for As ions than ordinary Mg-Al/LDH and FeOOH, and furthermore were able to collect with high gradient magnetic separations. In addition, after As removal the existence conditions of As ions in LDH were examined by XANES.