Tributyl phosphate rare earths

Lanthanum also may be separated from aqueous solutions of rare-earth nitrates by liquid-hquid extraction using a suitable water-immiscible organic hquid such as tributyl phosphate or another complexing agent dissolved in it. 

Thorium sulfate, being less soluble than rare earth metals sulfates, can be separated by fractional crystallization. Usually, solvent extraction methods are applied to obtain high purity thorium and for separation from rare earths. In many solvent extraction processes, an aqueous solution of tributyl phosphate is the extraction solvent of choice. 

Finely-ground monazite is treated with a 45% NaOH solution and heated at 138°C to open the ore. This converts thorium, uranium, and the rare earths to their water-insoluble oxides. The insoluble residues are filtered, dissolved in 37% HCl, and heated at 80°C. The oxides are converted into their soluble chlorides. The pH of the solution is adjusted to 5.8 with NaOH. Thorium and uranium are precipitated along with small quantities of rare earths. The precipitate is washed and dissolved in concentrated nitric acid. Thorium and uranium are separated from the rare earths by solvent extraction using an aqueous solution of tributyl phosphate. The two metals are separated from the organic phase by fractional crystallization or reduction. 

In one acid digestion process, monazite sand is heated with 93% sulfuric acid at 210°C. The solution is diluted with water and filtered. Filtrate containing thorium and rare earths is treated with ammonia and pH is adjusted to 1.0. Thorium is precipitated as sulfate and phosphate along with a small fraction of rare earths. The precipitate is washed and dissolved in nitric acid. The solution is treated with sodium oxalate. Thorium and rare earths are precipitated from this nitric acid solution as oxalates. The oxalates are filtered, washed, and calcined to form oxides. The oxides are redissolved in nitric acid and the acid solution is extracted with aqueous tributyl phosphate. Thorium and cerium (IV) separate into the organic phase from which cerium (IV) is reduced to metalhc cerium and removed by filtration. Thorium then is recovered from solution. 

Warp [54] was the first to report a preferential extraction of Ce4 into tributyl phosphate (TBP) from a nitrate solution of other rare earths. In a system equilibrated between the aqueous phase containing nitrate ion and TBP, the extraction process may be represented by eq. (3). 

Rare earths separation has been achieved by formation of species of the formula Ln(NC>3)3 -3TBP, where TBP is tributyl phosphate. This process is solvent extraction which is widely used at present in the production of rare earths in pure form. 

Fundamental studies have been reported using the cationic liquid ion exchanger di(2-ethylhexyl) phosphoric acid in the extraction of uranium from wet-process phosphoric acid (H34), yttrium from nitric acid solution (Hll), nickel and zinc from a waste phsophate solution (P9), samarium, neodymium, and cerium from their chloride solutions (12), aluminum, cobalt, chromium, copper, iron, nickel, molybdenum, selenium, thorium, titanium, yttrium, and zinc (Lll), and in the formation of iron and rare earth di(2-ethylhexyl) phosphoric acid polymers (H12). Other cationic liquid ion exchangers that have been used include naphthenic acid, an inexpensive carboxylic acid to separate copper from nickel (F4), di-alkyl phosphate to recover vanadium from carnotite type uranium ores (M42), and tributyl phosphate to separate rare earths (B24). 

Tributyl phosphate (TBP) is the traditional and still most widely used neutral organophosphorus extractant . The light trivalent rare earths can be separated in 10-14 extraction stages. Liquid-liquid extraction is used commercially to separate the lanthanoids. ... 

Neutral extractants constitute the third important class of solvent extraction reagents for the rare-earth elements. Since they have no charge, neutral extractants only extract neutral complexes or charge-balanced ion pairs. They also tend to extract ion-paired acid molecules such as HNO3. Solvating extractants may be dissolved in an organic diluent, or they may be the organic diluent itself (e.g., diethylether, methylisobutylketone, tributyl-phosphate). Phase transfer is accomplished by solvation of the complex by the extractant, and a typical equilibrium can be written as... 

The tributyl phosphate purification process- 73, 74 developed by the U.K. Atomic Energy Authority can accept feed solutions containing thorium which have been produced in a number of ways. - Monazite may be broken with sulphuric acid, the thorium selectively precipitated as oxalate from the major part of the rare earth constituents and dissolved in... 

Purification or refining of rare earths. The separation of rare earths from thorium can be performed in different ways depending on the production scale. Small laboratory-scale methods used first the fractional crystalhzation of nitrates, followed by the fractional thermal decomposition of nitrates. Pilot-scale separation can be achieved by ion exchange. Large commercial-scale separation is based only on the solvent-extraction process of an aqueous nitrate solution with n-tributyl phosphate (TBP) dissolved in kerosene. 

Purification or refining of thorium. Thorium produced previously is too impure to be used as nuclear fuel. In fact, impurities such as rare earths and uranium, owing to their elevated thermal neutron cross sections, are objectionable. Hence, the objective of the thorium refining process is to remove these impurities until concentrations below gg/kg (i.e., ppb wt.) are reached. Solvent extraction of an aqueous thorium nitrate solution with n-tributyl phosphate (TBP) in kerosene is a common procedure to perform the refining of thorium. At the end of the purification process, the thorium is recovered in the form of an aqueous solution of thorium nitrate or crystals of hydrated thorium nitrate. 

The primary industrial extractants in use for the separation of rare earths by solvent extraction are di-2-ethylhexyl phosphoric acid (HDEHP), tributyl phosphate (TBP), carboxylic acids, and amines. Many other extractants have been examined and reported in the literature in the search for improving the extraction and separation of individual rare earths. This chapter discusses several of these extractants for their interesting chemistry and potential future development, in addition to the available industrial extractants now in use and proposed for the separation of rare earths. 

Warf (1949) was the first to report the use of tributyl phosphate (TBP) as an extractant for the preferential extraction of Ce(IV) with respect to La(III) in 8—10 F HNO3. The extractability of rare earths from an aqueous HCl phase and from an aqueous phase 8 to 15.6 M HNO3 by diluted and pure TBP was studied by Peppard et al. (1953, 1957) and was shown to increase with increasing atomic number. 

Isol. as amine salt. Extractant for transuranic and rare earth elements. Metab. of Tributyl phosphate, T-00211. pK, 1.89 pi, 2 6.84 (H2O, 25°). 

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