Ultrasonic-enhanced selective arsenic removal and sulfide conversion from iron slag

Abstract

There are numerous valuable metals and the hazardous element arsenic in the iron slag produced in the zinc hydrometallurgy. The arsenic must be removed for comprehensive recovery of valuable elements. Generally, the alkaline arsenic removal produces large amounts of iron hydroxide colloids and iron slag agglomeration. Here, ultrasonic enhancement of NaOH–Na2S system is proposed to selectively remove arsenic from iron slag. Ultrasound destroys the agglomeration and encapsulation of zinc-containing iron slag and promotes the liquid-solid interfacial reaction. The arsenic removal percentage is 92.24% under ultrasonic power of 400 W, which is 12.14% higher than the conventional alkaline arsenic removal. The apparent activation energy of ultrasonic-enhanced alkali leaching for arsenic removal is calculated to be only 8.84 kJ/mol by kinetic experiments. Diffusion is proved to be the limiting link in the ultrasonic-enhanced leaching process for arsenic removal. This study proves that ultrasonic-enhanced Na2S–NaOH system has a good prospect for selective removal of arsenic from iron slag.