AbstractRegeneration of spent sulphuric acid. Several processes are available for the regeneration of spent sulphuric acid. Generally, the dilute acids containing at least 20% of H2SO4are preconcentrated to 60 – 70% and then either further concentrated to over 90% or decomposed to SO2. Purifying operations can be combined with these steps. Spent sulphuric acid highly contaminated with inorganic and organic compounds can frequently only be regenerated after a prior purification step, e. g. by extraction of electrolysis. Dilute spent sulphuric acid containing less than 20% of H2SO4can also be regenerated, but the costs incurred by evaporation increase out of proportion with decreasing sulphuric acid concentratio