Hafnium separation from rare earths

Solvent extraction is often applied to separate two chemically similar metals such as nickel/ cobalt, adjacent rare earths, niobium/tantalum, zirconium/hafnium, etc. For the purpose of elaboration, the example of the separation of two chemically similar elements such as zirconium and hafnium from their nitrate solution, using TBP as an extractant is considered. The solvent extraction process in this case is chemically constant (K) is given by ... 

In the extraction and separation of zirconium from hafnium in a nitric acid system, using TBP, the system operates best if run at about 10% less than saturation [56]. As saturation of the solvent is approached, a zirconium compound precipitates in the presence of the solvent, causing cruds and emulsions. This problem is also encountered in rare earth circuits using DEHPA. 

Assay of beryllium metal and beryllium compounds is usually accomplished by titration. The sample is dissolved in sulfuric acid. Solution pH is adjusted to 8.5 using sodium hydroxide. The beryllium hydroxide precipitate is redissolved by addition of excess sodium fluoride. Liberated hydroxide is titrated with sulfuric acid. The beryllium content of the sample is calculated from the titration volume. Standards containing known beryllium concentrations must be analyzed along with the samples, as complexation of beryllium by fluoride is not quantitative. Titration rate and hold times are critical therefore use of an automatic titrator is recommended. Other fluoride-complexing elements such as aluminum, silicon, zirconium, hafnium, uranium, thorium, and rare earth elements must be absent, or must be corrected for if present in small amounts. Copper—beryllium and nickel—beryllium alloys can be analyzed by titration if the beryllium is first separated from copper, nickel, and cobalt by ammonium hydroxide precipitation (15,16). 

The use of solvating extractants in the recovery of gold and platinum-group metals (PGM) was described in the previous section. These extractants have also found some specialized applications in the extractive metallurgy of base metals. For example, they have been used in the recovery of uranium, the separation of zirconium and hafnium, the separation of niobium and tantalum, the removal of iron from solutions of cobalt and nickel chlorides, and in the separation of the rare-earth metals from one another. 

Lutecium is the heaviest, rarest, and most expensive lanthanoid element. The lanthanoids elements make up Row 6 of the periodic table between barium and hafnium. The periodic table is a chart that shows how chemical elements are related to one another. The lanthanoids are usually shown as a separate row at the bottom of the table. They are also called the rare earth elements. That name does not fit very well for most lanthanoids. They are not really so rare, but were once difficult to separate from each other. However, lutetium is both rare and difficult to separate from the other lanthanoids. 

Differences in the extraction coefficients with different cations may be utilised in the separation of uranium, transition metals and rare earths. This is a well-established method for the extraction of U in the processing of nnclear fuels. Hafnium ean also be separated from zirconium by this technique, using TBP. 

The separation of the rare earth metals by liquid extraction is a most useful application, since by this method the tedious recrystallizations usually necessary are avoided. The work of Asselin and Comings (7) on the separation of neodymium and thorium, and the extensive work of Templeton (159, 160) and Fischer (48, 49) on separations of lanthanum and neodymium, zirconium and hafnium, and scandium from its accompanying elements has confirmed the success of this technique. 

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