process for recovering sulfuric acid and iron in the form of a residual oxide aqueous pickling liquor of sulfuric acid containing ferrous sulfate and sulfuric acid, lfree

摘要

H2SO4 and Fe2O3 are recovered from wast pickle liquor containing FeSO4 and dilute H2SO4 by evaporating below 250 DEG F., preheating the concentrated liquor with added carbonaceous fuel such as fuel oil, mineral oil, fuel gas or powdered coal in a closed space, atomizing the preheated concentrate in air and decomposing the atomized stream by heating it in an oxidizing atmosphere to such a high temperature (about 3000 DEG F.) that all the remaining water is converted to steam, the H2SO4 decomposed to SO3 and steam, and the FeSO4 into SO3, steam and solid Fe2O3 particles which are separated from the effluent gases. The SO3 is separated, too, and reacted with water from the earlier evaporation step to form H2SO4. The hot gases from the pyrodecomposition step can be used by heat exchange with triethylene glycol to provide heat for the earlier evaporation step, and steam from this step used to preheat air used in the thermal decomposition, to about 400 DEG F.