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 usingAcidithiobacillus caldus (DSM 8584) using elemental sulphur, achieving H₂SO₄concentration 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  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.

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

Abbreviation

Nomenclature:, Desorption rate constant (min^-1); L, ion-exchange column length (m); OUR, oxygen uptake rate (g/L.day); dP/dt, sulphuric acid production rate (g/L.day), S_e, amount of lithium in the resin at exit port (mg/L); S, concentration of lithium in the resin (mg/L), S_o, ⁷Li⁺ capacity on a 30 ml degraded lithiated resin (mg/L);dS°/dt, sulphur utilisation rate (g/L.day); u_z, axial eluent flow rate at the entry (L/min);t, time (min); Y_p/s, product yield based on substrate consumption; Y_x/s, biomass yield based on substrate consumption; Y_p/x, product yield based on biomass generation; e,porosity; α, Inverse of the product yield based on biomass generated.