Stabilization of Sludge Produced by Ferrite Treatment of Wastewater Containing Cadmium Ion

Abstract

Leached test was used to evaluate the safety of the ferrite sludge formed by the heat treatment after conventional or two-step treatment with pH adjustment of wastewater. Simultaneously, the concentrations of Cd and Fe ions in the treated water were measured before the leached test. The effect of the heat treatment on the concentrations of Cd (C_Cd) and Fe (C_Fe) in the elute was discussed by comparing the ferrite sludge formed without heat treatment.
The C_Cd of ferrite sludge formed by the heat treatment with the two-step treatment was remarkably lower than that by conventional or two-step treatments in relation to Cd(OH)₂ on the surface of ferrite particles. XPS measurement of the sludge formed by conventional and two-step treatments indicated the existence of Cd(OH)₂ on the surface of ferrite particles. XPS measurement of the sludge formed by the heat treatment indicated no existence of Cd(OH)₂ on the surface of ferrite particles. The measurement after Xe⁺ sputtering showed that the Cd(OH)₂ is absent not only on the surface but also in the bulk of the particles formed by heat treatment.
The heat treatment after two-step treatment stabilizes the sludge and is favorable for steady operation of the ferrite process, industrial utilization of the sludge and good quality of the treated water.