Ultrasound enhances the removal of V5+ in wastewater by ball-milled zero-valent iron: Effects and mechanisms

Abstract

Vanadium is considered to be a harmful industrial pollutant that poses a serious threat to health. In this study, the effect of ultrasonic-enhanced ball milling zero-valent iron removal of vanadium in wastewater was investigated and the basic mechanism of this process was elucidated. The results of the study confirmed that the ultrasonic intervention significantly accelerated the vanadium removal rate and greatly shortened the time required to achieve equilibrium. Under certain experimental conditions, the removal efficiency of vanadium under ultrasonic conditions is 99.1 %, which is 1.4 times higher than that of the traditional constant-temperature water bath device (70.86 %). Analytical techniques such as electron paramagnetic resonance (EPR) and ultraviolet (UV) spectroscopy have confirmed that ultrasonic-induced cavitation and microjet phenomena actively stimulate the formation of more H radicals and Fe2+. The key role of Fe2+ in the removal reaction was further explored and confirmed by a quenching experiment. Through fitting the experimental data of different isothermal adsorption models and reaction kinetics, it is concluded that the adsorption process conforms to the pseudo-second-order kinetics and the Langmuir isothermal model. The adsorption process is dominated by chemisorption, and the maximum adsorption capacity is 153.033 mg·g−1. X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and other analyses show that under the action of ultrasonic waves, V5+ is rapidly reduced to its lower oxidation state through reduction within the first 10 min of the reaction. Secondly, as the reaction progresses and the pH value increases, electrostatic adsorption and coprecipitation are involved in the removal reaction.