Effect of ultrasound intensity on the size and morphology of synthesized scorodite particles

Abstract

The effect of different ultrasound intensities (11.6, 8.4, 5.3, 2.1, and 0W) on the size and morphology of synthesized scorodite particles was investigated under O2 gas flow at 70°C. The higher ultrasound intensity promoted the oxidation of Fe(II) in the reaction solution. Therefore, higher values of oxidation–reduction potential (ORP) in the solution and the yield of the precipitate were obtained for higher ultrasound intensities. Large scorodite particles (>10μm) were successfully synthesized using ultrasound irradiation. The particle morphology was related to the ultrasound intensity, with the particles synthesized with low intensity showing rough surfaces and those with high intensity showing faceted surface. The higher ultrasound intensity generated a larger amount of fine oxygen bubbles during ultrasound irradiation under O2 gas flow. This increased the area of the interface between the gas phase (oxygen bubbles) and the liquid phase [Fe(II) solution] and promoted the oxidation. Additionally, ultrasound enhanced the transfer of the solutes [Fe(III), As(V)] from the solution to the nuclei with the jet flow by collapsing of the bubbles and the physical stirring by ultrasound irradiation. These characteristics of ultrasound irradiation contributed to the crystal growth of scorodite.