The vitrification of arsenic-rich residue using iron phosphate glass

Iron phosphate glass was applied to vitrify arsenic-rich residue (ARR). Different ARR contents had been added into the iron phosphate based glass. X-ray diffraction (XRD) and USEPA toxicity characteristic leaching procedure (TCLP) tests were used to analyze phases and arsenic leaching concentration of ARR and glasses, respectively. The results indicated that arsenic existed in the ARR in the form of arsenate, which resulted in high arsenic leaching concentration in TCLP test. While the glasses were x-amorphous and all arsenic leaching concentrations of glasses were below the US standard. Viewed by scanning electron microscope (SEM), the surface of the ARR was rough, with porous structure; while the glasses showed a regular and homogeneous surface with a shiny external surface. High arsenic immobilization ratios were achieved during the vitrification, which was verified by EDX analysis. The glass structure and thermal stability were examined by Raman spectra and differential thermal analysis (DTA). The results showed that arsenic formed chemical bonds with PO₄ tetrahedron via bridging oxygen. The high (T_c–T_g) value was observed in the DTA test, which indicated the thermal stability of the glasses had been improved.