Abstract

In this work, a novel strategy based on evaporation and crystallization unit operations, capable of producing hydrochloric acid solution, iron(II) chloride and magnetic iron oxide from waste pickling acid (WPA), is proposed to be an eco-friendly alternative to the methods available in the literature. The suggested approach took into account both the partial recovery of the unused HCl by evaporation/condensation and iron(II) chloride by crystallization at room temperature. It was possible to obtain chemicals with yields above 80 wt% and purity above 97 wt%. Magnetic iron oxide presented magnetic saturation of 70.1 emu/g, magnetic retentivity of 4.3 emu/g and magnetic coercivity of 44.5 Oe, as well as an undetectable level of contamination by metals other than iron and agglomeration of its nanoparticles. The HCl solution presented less than 35 mg/L of iron and zinc. The evapo-crystallization method showed potential to be a mild form of treating WPA and generating three chemicals in the same process.

Graphic Abstract