Optimal sulphuric acid production using Acidithiobacillus caldus (DSM 8584): Bioprocess design for application in ion-exchange

Abstract

An optimised bioprocess was designed for the optimal production of sulphuric acid for application in an isotope recovery ion-exchange process. Firstly, the production of sulphuric acid (H₂SO₄) was optimised in aerated batch bioreactors using Acidithiobacillus caldus (DSM 8584) using elemental sulphur, achieving H2SO4 concentration of >0.4 to ~0.5 M (0.45 M average) with the following bioprocess parameters: product yield of 3.06 (Y_p/s), oxygen uptake rate of 1.35 g/L.day (OUR), 52% sulphur conversion at a rate of 0.83 g/L.day (dS°/dt), achieving a sulphuric acid production rate of 2.76 g/L.day (dP/dt), while the oxidation of elemental sulphur per dissolved oxygen consumed was 0.67 g S°/g O2. Secondly, after 80% (v/v) moisture loss from the recovered biological H₂SO₄ titres, the acid solution was used for the recovery of nuclear grade lithium 7 (⁷Li⁺) from a degraded resin, achieving >80% recovery rate within two bed volumes (60 ml) at an averaged desorption rate K¯ of 0.1829 min ^-1 and eluent rate of 6.65 ml.min^-1 in comparison to the ~60% ⁷Li⁺ recovery rate using a commercial grade mineral H₂SO₄ using similar operational ion-exchange reactor parameters. The designed bioprocess proved to be an effective and environmentally friendly bioprocess for the recovery of valuable metals adsorbed onto ion-exchange resin.

Keywords: Acidithiobacillus caldus, sulphuric acid, ion-exchange, desorption, lithium 7 isotope