Recovery and Separation of Rare Earth Elements Using Salmon Milt

Abstract

Recycling rare earth elements (REEs) used in advanced materials such as Nd magnets is important for the efficient use of REE resources when the supply of several REEs is limited. In this work, the feasibility of using salmon milt for REE recovery and separation was examined, along with the identification of the binding site of REEs in salmon milt. Results showed that (i) salmon milt has a sufficiently high affinity to adsorb REEs and (ii) the adsorption capacity of the milt is 1.04 mEq/g, which is comparable with that of commercial cation exchange resin. Heavier REEs have higher affinity for milt. A comparison of stability constants and adsorption patterns of REEs discussed in the literature suggests that the phosphate is responsible for the adsorption of REE in milt. The results were supported by dysprosium (Dy) and lutetium (Lu) LIII-edge extended x-ray absorption fine structure (EXAFS) spectroscopy. The REE-P shell was identified for the second neighboring atom, which shows the importance of the phosphate site as REE binding sites. The comparison of REE adsorption pattern and EXAFS results between the milt system and other adsorbent systems (cellulose phosphate, Ln-resin, bacteria, and DNA-filter hybrid) revealed that the coordination number of phosphate is correlated with the slope of the REE pattern. The separation column loaded with milt was tested to separate REE for the practical use of salmon milt for the recovery and separation of REE. However, water did not flow through the column possibly because of the hydrophobicity of the milt. Thus, sequential adsorption–desorption approach using a batch-type method was applied for the separation of REE. As an example of the practical applications of REE separation, Nd and Fe(III) were successfully separated from a synthetic solution of Nd magnet waste by a batch-type method using salmon milt.

Worker Safety in the Rare Earth Elements Recycling Process From the Review of Toxicity and Issues

“…Adsorption-based technology, such as acid leaching, is currently used for recovering REEs from mine wastes and environmental samples; but the use of electrochemical, membrane filtration, oxidation, photocatalyst, biological treatment, or a combination thereof is necessary for the efficient recovery of REEs in the future [45]. Innovative recycling research has been actively conducted in Japan, and a low-cost, high-efficiency, environment-friendly technology was reported, which used salmon milt containing phosphate that has high adsorption affinity for REEs [51]. The Comet Traitements of Belgian company also developed biohydrometallurgical technology with Liège University to recover valuable metals from metal scraps.…”

Rare Earth Element Distribution in the NE Atlantic: Evidence for Benthic Sources, Longevity of the Seawater Signal, and Biogeochemical Cycling

“…It is noted that fish milt accomplishes a very similar effect by an almost identical mechanism to bacteria, with preferential HREE complexation to external phosphate functional groups confirmed in salmon milt (Takahashi et al, 2014). Fish milt is also likely to be present in the pelagic waters of the Rockall Trough (e.g., blue whiting are known to spawn in this region, Hátún et al, 2009).…”

“…As an addendum to this section about the biological effects on dissolved REE fractionation, we mention the growing evidence for REE involvement in bacterial processes (Martinez-Gomez et al, 2016, and references therein) and the recent observations of seawater LREE depletion associated with methanotrophy following the Deepwater Horizon incident (Shiller et al, 2017). The role of LREE (particularly La) in these biological processes is an active one, rather than the apparently more passive complexation of HREE by phosphate functional groups on bacterial cell or fish milt surfaces (e.g., Takahashi et al, 2010Takahashi et al, , 2014. Thus far, LREE depletions have been identified in bacteria associated with methanotrophy, and appear to be essential or superior to Ca in the catalysis of enzymes in methanotrophs (Pol et al, 2014).…”

There's more to Fish than Just Food: Exploring the Diverse Ways that Fish Contribute to Human Society

“…Recent research has demonstrated the potential of salmon milt (semen) as an adsorbent to recycle rare earth elements (REE) used in various advanced materials, including catalysts, alloys, magnets, optics, and lasers (Takahashi et al. ). Solvent extraction has long been an effective method to recover REEs from ore waste, but this expensive process involves the use of toxic and sometimes radioactive chemicals that often are released into the environment.…”

“…To address this problem, a team of Japanese scientists demonstrated that dried salmon semen, which could be sourced from a vast fishing industry, was a viable replacement and was very effective in extracting expensive elements (Takahashi et al. ). Fish scales have also been used as a natural adsorbent for treatment of organic pollution, such as to remove carotenoid pigment from wastewater in the seafood industry (Stepnowski et al.…”