Prospects for using the effect of selective oriented drift of cationic aquacomplexes in elementary enrichment technology

This chapter discusses electrophysical and electrochemical methods used in elemental and isotopic enrichment substances such as electrodialysis, ionic mobility method. An unconventional approach to solving the problem of processing is presented.

Problem state

As a result of processing ore containing thorium, chemical concentrates are obtained in the form of phosphates, hydroxides, oxalates. They contain from 40 to 70% ThO,, significant quantities of rare earth elements, as well as impurities of uranium, titanium, iron, silicon and others. For example, for thorium concentrates secreted during alkaline treatment of monazite, the following chemical composition is typical, mass. %: Th02 (50-60); P,05 (1.0-2.5); (REE),03 (9.2-15); SiO, (9.1-30); Fe,03 (2-5); U03 (1.5-2.5); TiO, (0.1-1.0) - insoluble in the acids of the residue.

The final products of the purification of thorium concentrates - hydroxide and thorium dioxide - should be suitable for use in nuclear engineering. Various methods are used to clean thorium. In this case, thorium concentrates dissolve in sulphuric, nitrogen or hydrochloric acid depending on the method chosen for further cleaning up. If the concentrate contains sparingly soluble compounds of the thorium type phosphates or oxalates, then the concentrate initially treated with a solution of alkali to convert thorium to hydroxide and then dissolving it in acid.

When cleaning thorium compounds, particular attention is paid to the removal of rare earths that have a large cross section of the neutron capture. For cleaning, mainly two groups of methods are used. The first group includes selective precipitation or dissolution methods

  • • stepwise neutralization;
  • • selective precipitation of thorium compounds, less soluble,

than the corresponding REE salts;

• selective dissolution based on the formation of thorium by

soluble complexes with alkali oxalates and carbonates of alkali

metals and ammonium.

The second group consists of methods of selective extraction with organic solvents. Currently, the extraction method is of great importance. The methods of the first groups also have not lost their role in industry.

Extraction purification of thorium compounds has great advantages over the methods based on the difference in hydrolytic properties or different solubility, since it allows to carry out deep purification of thorium from most impurities.

Figure 4.1 presents one of the schemes for the extraction purification of thorium [159]. The circuit contains three column type extractors. The supply solution (thorium nitrate solution with a concentration of thorium of approximately 170 g/1, rare earth elements, uranium) is fed into the first extract in which uranium is extracted with a 5% solution of TBF in xylene.

Thorium is extracted from the raffinate of the first extractor in the second extractor with a 40% solution of TBF in xylene. Rare earth elements remaine in the aqueous solution (raffinate). In the third extractor of the circuit, thorium is re-extracted with a solution of 0.02M E1N03. The concentration of thorium in the reextract is approximately 60 g/1. General extraction of thorium according to this scheme from the initial solution reaches 99.8%.

The aqueous raffinate containing REE nitrates is a valuable raw material for the extraction of the required elements.

Schematic diagram of the extraction purification of a solution of nitrate thorium

Fig. 4.1. Schematic diagram of the extraction purification of a solution of nitrate thorium.

Electrophysical and electrochemical methods in elemental and isotopic enrichment

 
Source
< Prev   CONTENTS   Source   Next >