Stabilization of Scorodite by Aluminum Silicate Microencapsulation

Abstract

Crystalline scorodite (FeAsO4·2H2O) is a common arsenic-(As-)containing solid waste produced from nonferrous metallurgical processes. Its stability is the key factor to determine environmental risks. Scorodite is stable in the mildly acidic environment, while in a neutral to weakly alkaline environment, it can easily decompose and release As into solutions. In this work, scorodite was microencapsulated with an aluminum silicate gel for improving its stability. The effect of Si/As molar ratios on the stability of microencapsulated scorodite was investigated. A short-term stability environmental testing of 10 days indicated that a coating formed at a Si/As molar ratio of 0.2 inhibited As release at pH 4 and 6. A coating formed at a Si/As molar ratio of 1.5 was proportionately more successful at preventing As release at pH 6 and 8. The morphology and elemental composition were analyzed using a scanning electron microscope (SEM) and energy dispersive spectrometer (EDS), respectively. Raman spectroscopy and attenuated total reflectance Fourier-transform infrared spectroscopy (ATR-FTIR) were employed for characterization of encapsulated scorodite (E-scor). The results showed that aluminum silicate was uniformly coated on the surface of scorodite and the coating still adhered to the surface of scorodite after short-term stability testing performed at pH 4, 6, and 8. These findings have significant implications for the stabilization of the arsenic-containing solid waste in the hydrometallurgical industry and reducing its environmental risks.