Recovery and Separation of Rare Earth Elements Using Columns Loaded with DNA-filter Hybrid

Abstract

Given that the supply of several rare earth elements (REEs) is sometimes limited, recycling REEs used in various advanced materials, such as Nd magnets, is important for realizing efficient use of REE resources. In the present work, the feasibility of using DNA for REE recovery and separation was examined, along with the identification of the binding site of REEs in DNA. In particular, a DNA-cellulose filter paper hybrid was prepared so that DNA-based materials can be used for the separation of REEs using columns loaded with DNA. N,N′-Disuccinimidyl was used as a cross-linker reagent for the fixation of DNA onto a fibrous cellulose filter. The results showed that (i) the DNA-filter hybrid has a sufficiently high affinity to adsorb REEs; (ii) the adsorption capacity was 0.182 mg/g for Nd; and (iii) the affinity of REEs for DNA was stronger for REEs with larger atomic numbers. The difference of the affinity among REEs in the third result was compared with the adsorption patterns of REEs discussed in the literature. The comparison suggests that phosphate in the DNA-filter paper hybrid was responsible for REE adsorption onto the hybrid. The results were supported by the Nd, Dy, and Lu LIII-edge EXAFS; the REE-P shell was identified for the second neighboring atom, showing the importance of the phosphate site as REE binding sites. The difference in the affinity among REEs suggest that group separation of REEs (such as La, Ce, (Pr and Nd), (Ho, Dy, and Er), (Tb and Gd), (Sm, Eu), Tm, Yb, and Lu) is possible, although complete isolation of each REE from a solution containing all REEs may be difficult. For practical applications, Nd and Fe(III) were successfully separated from a synthetic solution of Nd magnet waste using columns loaded with the DNAfilter hybrid.

Recovery and Separation of Rare Earth Elements Using Salmon Milt

“…The REE pattern of K d (solid–water distribution coefficient, L/g) was larger at heavy REE part (HREE) such as Tm, Yb, and Lu. This pattern is similar to those observed for REE adsorption onto bacterial cell surfaces [10] and DNA (DNA–filter hybrid) [9] , as shown in Fig. 1a (for comparison, the REE patterns of K d for Ln-resin, CP, and CMC are shown in Fig.…”

“…EXAFS spectra were recorded for Dy and Lu adsorbed onto the milt to confirm the binding site of REEs on the milt. A similar experiment has been reported by Takahashi et al (2010, 2012) [9] , [12] . The sample for the milt was prepared at constant concentration of each REE (Dy and Lu) as 1×10 −7 mol/mg milt.…”

“… (a) salmon milt (pH 4, 3, and 2), bacteria ( B. subtilis ) [10] , and DNA-filter paper hybrid [9] ; (b) CP, CMC, and Ln-resin [9] , [10] . …”

“…For DNA, researchers have conducted various studies on the removal of inorganic and organic substances using DNA-based materials [14] – [17] . Our previous studies on the interaction of REEs with bacteria and DNA suggest high affinities of REEs to phosphate sites in bacterial cell surfaces or DNA [9] – [12] . Based on these findings, we considered that milt also has high affinity to REEs through the phosphate sites.…”

“…DNA attached to cellulose (DNA-filter hybrid) has been successfully employed for the recovery and separation of REEs through column method, where the binding site of REEs is the phosphate within the DNA [9] . The high affinity of REEs for phosphate has also been found in adsorption studies of REEs on bacteria [10] – [12] .…”