Bioleaching of lanthanum from nickel metal hydride dry battery using siderophores produced by Pseudomonas sp

Abstract

There is still much to be learned about the properties of siderophores and their applications. This study was designed to characterize and optimize the production of the siderophore produced by a marine bacterium Pseudomonas sp. strain ASA235 and then evaluate their use in bioleaching of rare earth elements (REEs) from spent Nickel-metal hydride (NiMH) batteries. The results of both Tetrazolium and Arnow's tests indicated that the test organism produces a mixed-type siderophore of pyoverdine family, a result that was confirmed by FT-IR and MALDI-TOFF analyses. Optimization of pH, temperature, incubation period, and iron concentration for siderophore production led to a noticeable shift from 44.5% up to 91% siderophore unit when the test bacterium was incubated at 28 °C and pH 7 after 72 h in the absence of iron. The purified siderophore showed the ability to bleach about 14.8% of lanthanum from the anode of the NiMH battery along with other elements, although in lower amounts. This data put siderophores in distinct focus for further prospective studies intending the bioleaching of such precious elements. The scaling up of this process and optimization would make a big difference in such a green bioleaching strategy, allowing us to recover such precious elements in an environmentally friendly way.

Keywords: Pseudomonas; Bioleaching; Lanthanum; Nickel metal hydride battery; Optimization; Siderophores..

Fig. 1

Phylogenetic tree of the bacterial strain used in this study based on 16S rRNA sequence displaying its position to the closely related species of the genus Pseudomonas. The tree was constructed using MEGA X software based on the maximum likelihood method. E. coli.JCM_1649_LC069032.1 was used as an external reference

Fig. 2

(A) CAS agar assay showing the production of siderophores by Pseudomonas sp. and the change of the blue color of CAS-agar medium to the yellow color. (B1) The formation of the deep red color of the bacterial siderophore indicates a positive tetrazolium test, while (B2) is a negative control showed no color change. (C1) The formation of the deep yellow-brown color of the bacterial siderophore indicating a positive Arnow´s test, while (C2) is a negative control. (D) UV–VIS spectrum of siderophore alone (connected line) and siderophore-iron complex (dashed line) showing the characteristic maximum absorbance at 410 nm and 468 nm, respectively. E) The developed siderophore with lemon green pigment

Fig. 3

Effect of different pH degrees on the growth of Pseudomonas sp. and its productivity of siderophore. The results were expressed as mean of triplicates ± standard error (S.E). According to Duncan’s test, different letters in small and capital styles indicate significant differences in growth and SU%, respectively, in response to different pH values (p-value ≤ 0.05)

Fig. 4

Color contour plot showing the interaction between the tested variables (temperature and incubation time) for optimum responses of (A) siderophore production and (B) bacterial growth

Fig. 5

Influence of different concentrations of FeCl₃ on the production of siderophore and growth of Pseudomonas sp. The results were expressed as mean of triplicates ± standard error (S.E). Duncan’s test revealed that different letters differ significantly from each bar (p-value ≤ 0.05). Different letters in small and capital styles indicate the significant differences between different values of growth and SU%, respectively, according to Duncan’s test

Fig. 6

Chemical characterization of the purified siderophore where (A) FT-IR spectrum of the purified siderophore and (B) MALDI-TOF MS analysis of the purified siderophore