Lanmodulin as protein-based platform for the separation of light rare earth elements from acidic leachate

This study investigates the model light rare earth element, Lanthanum (La) removal from synthetic acidic leachate using a novel lanthanide-dependent crude lanmodulin (LanM) protein produced by Methylorubrum extorquens. The effect of adding succinate and methanol as dual substrates on the biomass growth was first examined. The results revealed that 0.5% v/v methanol and 0.4% w/v succinate are optimum for maximum biomass growth of M. extorquens in the presence of 1 µM lanthanum. The maximum La sorption capacity of 70 mg La/g protein at 100 mg/L initial lanthanum concentration and lower 49.8 mg La/g at 50 mg/L with 54% removal efficiency was observed. The optimum solution pH for La sorption was observed to be 5 (pH_PZC − 5.8) and an equilibrium time of 90 minutes. The sorption kinetics and isotherm indicated chemisorption, along with other mechanisms were involved with monolayer adsorption capacity as high as 181.97 mg/g for La(III) sorption (50 mg/L, pH 5, 318K). Thermodynamic parameters revealed spontaneous exothermic chemisorption at 298K and a minimum randomness of the process (∆G° = -0.29 kJ/mol; ∆H° = -88.70 kJ/mol; ∆S° = -249.9 J/mol). This is the first study on using LanM protein from M. extorquens proposing a potential mechanism for light rare earth element recovery.