Hydrochloric acid regeneration in hydrometallurgical processes: a review

Hydrochloric acid regeneration has become a vital stage in most chloride process flowsheets. Pyrohydrolysis has been the traditional method of regenerating hydrochloric acid from a variety of chloride solutions, including magnesium, iron and nickel brines, however, its high thermal requirements renders it uneconomic in most processing flowsheets. Hydrochloric acid being an expensive acid, it is vital to the continued development of chloride processes to develop an economically favourable and environmentally sound method to recycle the lixiviant back to the process. This paper seeks to review the latest research in this area, including the use of electrowinning, solvent extraction, metal sulphate salt crystallisation and hydrolytic distillation to regenerate leaching lixiviants. Metal sulphate salt crystallisation is the most promising method included in this review; with significant research having been conducted to date and favourable economics having been shown. Industrial application of this method depends on careful design and operational control due to sensitive parameter control being needed.