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

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 (H 2 SO 4 ) 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 H 2 SO 4 titres, the acid solution was used for the recovery of nuclear grade lithium 7 ( 7 Li + ) 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% 7 Li + recovery rate using a commercial grade mineral H 2 SO 4  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