Recovery of sulphuric acid from waste and process solutions using solvent extraction

Abstract

TEHA (tris-2-ethylhexylamine) was selected as the extractant in the current study due to high acid extraction and ease in stripping. An optimum organic system consisting of 50% TEHA, 40% octanol and 10% Shellsol A150 was determined. It was found that the acid extraction decreased with the increase in temperature. The change in enthalpy (ΔH) was −13.2kJmol−1, indicating exothermic extraction reaction. Both extraction and stripping kinetics was very fast. McCabe–Thiele extraction diagram showed that for a feed solution containing 200g/L H2SO4, three stages are required. McCabe–Thiele stripping diagram showed that three stages are required. Using slope analysis, it was found that the extracted species consisted of one acid molecule, one TEHA (A) molecule and two octanol (O) molecules with a formulae of H2SO4AO2¯.The optimised TEHA system was used to extracted acid from a synthetic process solution containing a number of metals. It was found that the system only extracted acid with a small amount of metals entrained. After scrubbing the loaded organic solution in a single contact, almost all entrained metals were removed. In the case that the mining waste solution contains low concentration of acid, membrane distillation (MD) technology can be used to recover the water and concentrate the acid and metals. Solvent extraction can be then used to recover the acid and metals. A conceptual process flowsheet has been developed using a combination of MD and SX.