Resource reuse of spent pickle acid by mineralization process

The spent pickle acid was collected from metal surface treatment factory. The pH of spent pickle acid was lower than 1.0, and the total concentration of ferrous ion was 186 g/L. Firstly, the lower activity of metal in the spent pickle acid solution was displaced by cementation process (pre-treatment). After cementation scraped iron, the coagulant agent (poly aluminum chloride (PAC)) was added to the solution. Then, the pH of the solution was adjusted to 4.5 by ammonia to remove SiO₂, P, and other impurities. Finally, the mineralization process was proceeded at pH 4.0 and 60°C with H₂O₂. X-ray diffraction (XRD) analysis shows that the mainly crystalline phase of the mineral product was γ-FeOOH. The high purity of Fe₂O₃ has been obtained by calcination from mineral product. Additionally, the economic evaluation results also show that the mineralization process was economic feasible. Therefore, this method could be applied to the metal surface treatment industry and printed circuit board manufacturing for recycling waste acid lotion.