A comparison between TEHA and Cyanex 923 on the separation and the recovery of sulfuric acid from aqueous solutions

In this study, the separation of sulfuric acid with TEHA and Cyanex 923 from acidic solutions by solvent extraction method was investigated. Extraction of sulfuric acid with TEHA and Cyanex 923 is an exothermic reaction and the enthalpy changes of the reaction were found to be − 6.34 and − 2.24 kJ, respectively. Comprehensive study on determining the stoichiometric coefficients of sulfuric acid in the extraction equation, using slope analysis method, lead to a new approach for this procedure. This study showed that when organic phase extracts more than 100 g/L sulfuric acid, the number of extracted sulfuric acid molecules by TEHA, n, is estimated to be 1. While, each mole of TEHA extracts 2 mol of sulfuric acid when organic phase extracts less than 100 g/L sulfuric acid. In addition, the value of n, using Cyanex 923 as extractant, is estimated to be 1. Using McCabe–Thiele diagram results showed that after 4 stages, sulfuric acid concentration in aqueous phase was reduced from the initial value of 200 to the values of 30 and 5 g/L when octanol concentration in organic phase was 20 and 40%vol, respectively. While, using Cyanex 923 as extractant, 5 stages were needed to reduce the sulfuric acid concentration from 100 to 5 g/L.