Continuous biocatalytic recovery of neodymium and europium

Abstract

Batch-grown cells and continuously-grown biofilm of a Serratia sp. were utilized to recover the rare earth elements (REEs) lanthanum and neodymium from solution.Selectivity was obtained for La(III) over Th(IV) using columns of polyacrylamide gelimmobilized cells challenged at a rapid flow rate, exploiting the different solution chemistries and behaviors of REEs(III) and Th(IV). Biofilm-grown cells had a tenfold higher activity of the mediating phosphatase, which promotes metal deposition as the corresponding metal phosphate, reflected as a correspondingly enhanced level of removal of Nd(III) (as NdPO 4 ) in flow-through columns utilizing biofilm on reticulated foam. The biofilms retained activity in the removal of Nd(III) for > 1 year, losing activity exponentially with a half life of 3 months. The flow rate giving 50% removal (FA 1/2 ) of Nd(III) by 3 month old biofilms at pH 5.5 was 272 and 275 mL/h using two independent biofilm preparations, equivalent to a FA 1/2 of 34 column volumes/h for fresh biofilms. The removal of Nd(III) was sustained at pH down to 3.5 with approx. 20% of the column activity lost upon return to pH 5.5. A similar result occurred in the presence of the common REE leaching agent ammonium sulfate (100 mM), this did not affect the ability of Serratia sp. to recover REEs. With a view to the potential for future biomanufacturing of Nd(III)-catalyst, the deposited material was identified as NdPO 4 by X-ray powder diffraction with a nanoparticle size of 14.5 nm, irrespective of the biofilm age.Key phrases: neodymium biorecovery, lanthanum biorecovery, selective rare earth biorecovery, continuous flow process, immobilized Serratia biofilm, nanocrystallite harvest.

Construction and evaluation of a modular biofilm-forming chamber for microbial recovery of neodymium and semi-continuous biofilm preparation. Tolerance of Serratia sp.N14 on acidic conditions and neutralized aqua regia

“…[38,43,45] Assay of inorganic phosphate Inorganic phosphate in the outflow solution of columns was determined by adding 0.97 mL of distilled water in a 2 mL cuvette, along with 0.6 mL of 2.5%(w/v) sodium molybdate in 1. hydrochloric acid). [22] The phosphate was visualized in the solution when adding the 0.4 mL stannous chloride and the blue complex was estimated at A = 720 nm 20min after mixing the reagents [21] and was compared to a calibration curve which was prepared using standards with phosphate concentrations from 0.5-5 mM and assayed in the same way. The spectrophotometer used was a Ultrospec 3300 pro UV/Visible Spectrophotometer, Amersham Biosciences.…”

“…Nd 3+ in the outflow solution was determined by adding 0.03 mL of the column outflow solution in 1.97 mL of assay solution 1 M ammonium acetate buffer-NH 4 Ac (pH 3.3). [22] (1M NH 4 Ac: 77.08 gr of NH 4 Ac were added in 500 mL distilled water, the pH was adjusted to 3.3 with hydrochloric acid (3 M) and the total volume was brought up to 1 L with distilled water. [21] The metal in the solution was visualized by adding 0.1 mL of 0.15% (w/v aq) arsenazo III (2,2 ′ -[1,8-dihydroxy-3,6-disulpho-2,7-naphthalene-bis(azo)] dibenzen-arsonic acid (stand for an hour and then filtered to remove the solids, stable for 3 months in the dark) in each cuvette and the purple complex was estimated at A = 652 nm compared to the calibration curve, which was prepared in the same way.…”

“…They were then left to dry out at room temperature prior to the analysis. [22] All samples were examined between 5 and 60 degrees 2θ, 0.02 degrees per step with a time per step of 1.1 seconds, for a total scan period of 53min for each sample. Acquired powder patterns were compared to a standard of NdPO 4 database (Joint Committee for Powder Diffraction Studies-JCPDS).…”

“…[19] The recovery by this strain was demonstrated and accurately modeled to take into account the pH and excess SO 2− 4 ion, using an acidic uranium mine wastewater. [17] Cells of this bacterium were immobilized as biofilm on a porous matrix and a process for the removal from solution of Cd 2+ initially [20] and then for various other metals, including uranium [21] and REEs [22], was shown. The metal phosphate produced on the polyurethane foams can be easily recovered by squeezing the foams.…”

“…Formation of NdPO 4 (1:1 ratio of Nd:P) was confirmed by a recent published work. [22] Also, since the FA 1/2 value is an observed 'lumped' parameter no information is conveyed about whether a change in this value is attributable to enzymatic, solution chemistry or metal desolubilization factors, or components of all three.…”