Stabilization of iron-arsenic deposits by encapsulation with montmorillonite inorganic gels

Encapsulation is recognized as an effective technique for enhancing the stability of hazardous waste by coating it with an inert material. In this work, an eco-friendly montmorillonite (Mt) inorganic gel with the characteristics of high viscosity, adsorption and easy preparation was developed and coated on the surface of iron-arsenic deposits (IAD) to restrain the release of arsenic (As). The encapsulation system investigated involves Mt/IAD mass ratio and aging temperature of the coated iron-arsenic deposits (C-IAD). The C-IAD was characterized by XRF, XRD, SEM-EDS, TEM, FTIR and BET. The results revealed that the IAD was completely encapsulated by the montmorillonite inorganic gel. From the experiment of stability, when IAD was coated with montmorillonite inorganic gel (Mt/IAD mass ratio 0.75) and aged at 25???, As release decreased from 3.15 mg/L to 0.64 mg/L at pH 5 after 24 h, and then dropped to 0.11 mg/L after 7 d. Furthermore, the results indicated that the IAD encapsulated with montmorillonite inorganic gel was effective in suppressing the release of As under both weakly acidic and alkaline conditions.