University of Alicante

To address the previously described problems, an extractant mixture has been developed consisting of a process ionic liquid TSIL (see the chemical formula in Figure 1) dissolved in an ionic liquid IL (see the chemical formula in Figure 2).

Figure 1: TSIL compound

This extractant mixture is characterised by allowing the selective liquid liquid extraction of the rare earth metals, uranium and thorium in samples that contain other s, p and/or d series metals.

The procedure for preparing the aforementioned TSIL compound is carried out in a very simple manner from the antibiotic ciprofloxacin using conventional functional group transformations. The synthesis of this compound takes place in three stages conducted under mild reaction conditions (temperature between 0°C–25°C, atmospheric pressure, etc.).

Stage 1: N-alkylation of ciprofloxacin with 1 bromopropane in the presence of excess N,N-diisopropylethylamine to generate the following intermediate (see Figure 3) with a yield of 88%:

Figure 3: Reaction intermediate

Stage 2: Amidation of the previous compound using an excess of N,O-dimethylhydroxylamine in the presence of thiourea chloride to obtain the following Weinreb amide (see Figure 4) with a yield of 86%:

Figure 4: Weinreb's amide

Stage 3: Alkylation of the previous compound by adding an excess of 1 iodononane and subsequent ion exchange with lithium bis(trifluoromethanesulfonyl)amidate to obtain the previously indicated TSIL molecule (see Figure 1) with a yield of 92%.

On the other hand, the selective extraction procedure for rare earth metals, uranium and thorium from a sample containing metals from this block together with other s, p and/or d series metals is as follows:

1) Prepare the extractant mixture (B) consisting of the TSIL compound from Figure 1 and the ionic liquid CYPHOS NTf₂ from Figure 2.

2) Introduce the sample to be separated (A) into a test tube; it contains one or more f-block metals and other metals from the s, p and/or d series. Adjust the pH to 6.

3) Add the extractant mixture (B) to the sample to be separated (A).

4) Stir for at least 3 minutes.

5) Wait until two liquid–liquid phases of different densities separate.

6) Separate both phases, with the organic phase corresponding to the extractant mixture (B) that contains the f-block metal(s) initially present in the sample to be separated (A) (see Figure 5).

Figure 5: Scheme of the selective extraction process

7) Add to the recovered organic phase (B) an acidified solution at pH=0.5 (C) (see Figure 6).

8) Stir.

9) Wait until two liquid–liquid phases of different densities separate.

10) Separate the two phases, where the organic phase corresponds to the metal-free extractant mixture (B) and the aqueous phase (C) contains the f-block metal(s) (see Figure 6).

Figure 6: Scheme of the extractant mixture recovery process

The extractant mixture (B) can be reused in successive new extraction cycles without loss of selectivity or effectiveness.

ADVANTAGES OF THE TECHNOLOGY

This novel extraction procedure has the following advantages:

1) Allows the selective extraction of internal transition metals (f-block), especially those classified as rare earths, uranium and thorium, against metals belonging to the s, d and/or p blocks of the periodic table in a highly effective manner.

2) The extractant mixture is reusable: once the extraction procedure is complete, it is possible to fully recover the metal(s) complexed, allowing the extractant mixture to be used in new extraction cycles.

3) The extractant mixture has a low affinity for metals from the s, d and p series of the periodic table, so metals from these series are extracted with a low or negligible percentage.

4) The recovery percentage of the extractant mixture is, at least, 95%, so it can be reused in new extraction cycles once the extracted metals have been released.

5) The extraction procedure is environmentally friendly.

6) The procedure is carried out under mild reaction conditions (temperature between 0°C–25°C and atmospheric pressure).

7) Both the TSIL compound and the solvent CYPHOS NTf₂ are commercially affordable (or can be easily prepared via a simple ion exchange).

8) The procedure is industrially scalable, able to be adapted and implemented to meet the company's needs. It efficiently and sustainably recovers, separately, rare earth metals, uranium and thorium, and produces high purity gypsum.

In summary, the new extractant mixture is a revolutionary technology that significantly improves current methods for extracting rare earth metals, uranium and thorium from waste generated in the phosphoric acid industry (phosphogypsum).

INNOVATIVE ASPECTS OF THE TECHNOLOGY

This novel chemical composition allows selective and efficient extraction of rare earth metals, uranium and thorium against other metals from the s, d and/or p series of the periodic table. In this sense, the primary interaction of internal transition metals with the TSIL, which acts as a selective chelator, occurs through the 1,3 dicarbonyl region.

Furthermore, once the extracted metals have been separated, the original extractant mixture is recovered with a yield exceeding 95%, allowing its subsequent use in new extraction cycles, making it a sustainable and environmentally friendly procedure. No other extraction system with these characteristics is available on the market that is reusable.

This methodology adapts exceptionally well to a separation process of rare earths, uranium, thorium and high quality gypsum from waste derived from the fertilizer industry that generates phosphoric acid (impurified phosphogypsum).

The trials conducted have shown very promising results. Below is a table with the distribution coefficient of the analyte (K), which is the ratio of the metal concentration in the organic phase to its concentration in the aqueous phase after the extraction procedure (see Table 1).

With these trials, the high efficiency and great selectivity of the extractant mixture have been demonstrated, as a higher distribution coefficient (K) of the analyte corresponds to greater extraction efficiency.

Table 1: The distribution coefficient (K) values obtained for the f-block metals, as well as for other metallic elements of the periodic table that may be present with them, at pH=6.

This novel composition can selectively extract internal transition metals against other metals of the periodic table at pH=6.

The main application sectors for this novel technology are:

• Fertiliser industry that generates phosphoric acid.

• Mining.

• Nuclear chemistry.

• Nuclear medicine.

• Nuclear waste treatment.

• Scientific research.

With this technology, the problem of selective separation of the chemical elements belonging to rare earths, uranium and thorium, some of which are used as fuels in nuclear power plants, is solved. The selective separation of these metals relative to the rest of the metals collected in the periodic table is crucial, both in the extraction process of the initial phosphogypsum waste and in the treatment of nuclear waste products. Its application in various industrial sectors can have a positive impact on the environment and can contribute to improving global energy sustainability.

Companies interested in acquiring this technology for commercial exploitation through patent licence agreements are sought.

Desired company profile:

• Phosphoric acid derived industry.

• Mining.

• Chemical industry.

• Nuclear industry.

• Nuclear medicine.

• Nuclear waste treatment.

The present invention is protected through patent application:

• Patent title: "Compuesto TSIL, procedimiento de preparación y procedimiento para la extracción selectiva de elementos de transición interna frente a metales de las series s, d y p empleando el compuesto TSIL ".

• Application number: P202330797.

• Application date: 25^th September 2023.