Acid recovering and iron recycling from pickling waste acid by extraction and spray pyrolysis techniques

Abstract

Acid recovering and iron recycling from pickling waste acid are the desired goal of the steel mills for current ecological requirements and economic benefit. This study proposed a novel method to treatment the pickling waste acid using extraction separation of ferric chloride and hydrochloric acid, following by the spray pyrolysis of ferric chloride stripping liquor. Comparing the Ruthner method, the significant technical advantages of this method is the lower treatment load and operating costs for the spray pyrolysis process, attributing to the reuse of most hydrochloric acid without iron powder neutralizing. Different extractants (TBP, CYC, IA, OA, and PA) are compared to extract ferric ion from high-concentration hydrochloric acid solution and the optimum conditions are researched. Spectroscopic analysis is performed to characterize iron state in extractants. For the stripped solution, spray pyrolysis is employed to produce high-purity Fe2O3 fine particles, meanwhile hydrochloric acid is recovered for following pickling procedure. The results showed that the effect of CYC under lower O/A ratio was better than that of TBP, and the opposite occurred at higher ratios. Three-stage extraction efficiency can reach over 80% at O/A = 2:1. The final O/A ratio of 1:1 was chosen for the stripping of iron-loaded extractants. Raman and UV–visible found that it was [FeCl4]- anion that existed in Fe-loaded TBP and CYC. Spray pyrolysis at 1000 °C can obtain fine pure Fe2O3 and hydrochloric acid. Eventually, a feasible technological process was put forward to recycle all chemicals and achieve zero emission of water and solid waste in the whole process.