Thorium chemical similarities with

Several hydrous oxides, such as those of aluminum, siTicon and, iron have been used to extract traces ions. Nevertheless, the sorption mechanism is not definitively established. Those oxides probably exhibit some ion exchange capacity among their properties and they can act as anionic or cationic exchangers and sometimes both. The separation of plutonium traces in the presence of HF by sorption onto an alumina column is based on its chemical similarities with thorium and lantanide elements reported by Abrao (2) In this case only thorium and rare earths are sorbed onto alumina from nitric acid-fluoride solutions while uranium remains in the effluent. 

Thorium is widely distributed in nature with an abundance in the Earth s crust of 12 mg/kg (i.e., ppm wt.), which is about four times greater than that of uranium and as abundant as lead and molybdenum. Owing to its chemical similarity with elements of group 1VB(4) such as zirconium, hafnium, and the other actinide uranium, thorium is usually associated in... 

The actinide elements are a group of chemically similar elements with atomic numbers 89 through 103 and their names, symbols, atomic numbers, and discoverers are given in Table 1 (1-3) (see Thorium and thorium compounds Uranium and uranium compounds Plutonium and plutonium compounds Nuclear reactors and Radioisotopes). 

The chemical similarity between lanthanide and actinide metals suggests that C2H I2 might also react with actinide metals. Preliminary experiments found no reaction between thorium or uranium metals and a THF solution of Plutonium and neptunium... 

The f-block elements comprise two series of inner transition elements which appear, firstly after lanthanum and secondly after actinium, in the Periodic Table. The elements from cerium to lutetium are known as the lanthanides and, because of its chemical similarity to these elements, lanthanum is usually included with them. Scandium and yttrium also show strong chemical similarities to the lanthanides, so that the chemistry of these elements is also often considered in conjunction with that of the lanthanide series. The second series of f-block elements, from thorium to lawrencium, is known as the actinide series and again it is usual to consider actinium together with this series. 

Tn reviewing the chemistry of the actinides as a group, the simplest approach is to consider each valence state separately. In the tervalent state, and such examples of the divalent state as are known, the actinides show similar chemical behavior to the lanthanides. Experimental diflB-culties with the terpositive actinides up to plutonium are considerable because of the ready oxidation of this state. Some correlation exists with the actinides in studies of the lanthanide tetrafluorides and fluoro complexes. For other compounds of the 4-valent actinides, protactinium shows almost as many similarities as dijSerences between thorium and the uranium-americium set thus investigating the complex forming properties of their halides has attracted attention. In the 5- and 6-valent states, the elements from uranium to americium show a considerable degree of chemical similarity. Protactinium (V) behaves in much the same way as these elements in the 5-valent state except for water, where its hydrolytic behavior is more reminiscent of niobium and tantalum. 

Tanthanide chemistry is approaching its 200th Anniversary, but except for data on thorium and uranium the chemistry of the actinides is a comparative youngster of some 30 years. However, the two chemistries are intimately associated because their elements are of the f transition type and thus formally comparable with each other and different from other elements. Indeed, these parallels made it possible to unravel actinide behavior in the early days of transuranium element production. In addition to their chemical similarities, the two series also share the properties of magnetism and radiant energy absorption and emission characteristic of /-electron species. However, important differences exist also, particularly in oxidation states, in bonding, and in complex-ion formation. 

Many of the actinoids are also separated by exploiting their redox behavior. Thorium is exclusively tetravalent and berkelium is chemically similar to cerium, so iodate precipitation of Th and extraction of Bk(IV) with bis(2-ethylhexyl)orthophos-phoric acid (HDEHP) are used to isolated these elements. The differing stabilities of the (III), (IV), (V), and (VI) states of U, Np, and Pu have be exploited in precipitation and solvent extraction separations of these elements from each other and from fission product and other impurities with which they are found. Because of its technical importance, the process chemistry to separate U and Pu in nuclear materials has been highly developed. Extraction of Bk(IV) with HDEHP is used to separate Bk from neighbouring elements. 

Thoriuin recovery processes. Because of the many elements in the solution, their chemical similarity, and the presence of phosphoric acid, separation of thorium from this acid solution has proved to be difficult. Wylie [WS] has reviewed the numerous separatirm processes that have been developed. Figure 6.5 shows the principal steps in seven of these processes and gives references for more details. Processes 4 and 6 appear to be the most economic when thorium, rare earths, and uranium all are to be recovered. Process 4, involving separation of thorium and rare earths from phosphate and uranium by precipitation with oxalic acid, is described next. Process 6, involving separation by solvent extraction with organic amines, is described in Sec. 8.6. 

The meta-elements of Crookes anticipated the idea of isotopes. The most readily available sources of separated stable isotopes are lead 206 from uranium minerals and lead 208 from thorium minerals, and it is interesting enough that before 1910 several successful chemical separations of radioactive isotopes of the same element were reported, involving both thorium 230 (ionium) and lead 210 (radium D). In otir opinion, this can only be due to kinetically metastable chemical nonequivalency in the mixture, for instance, due to colloidal or oligomeric complexes. The valuable conclusion of this story is that the chemical similarity of trivalent rare earths is so striking that doubts have been expressed whether they deserved more than one place in the Periodic Table, a situation isotopes later had to accept. Such a doubt has never been expressed for any other elements, not even for a pair of elements like vanadium and chromium, which were confused at the time of their discovery (7). Nevertheless, studies based on the possibility of metaelements continued rather late for instance, Debierne attempted to separate neo-radium from conventional radium 226 and to perform nuclear reactions on charcoal cooled with liquid helium (77). 

Periodic table of the elements. The lanthanide series ( rare earths ), beginning with lanthanum (57), and the actinide series, which begins with actinium (89) and includes thorium (90) and uranium (92), are chemically similar. Other families of elements read vertically down the table—at the far right, for example, the noble gases helium, neon, argon, krypton, xenon, radon. 

In fact, the classification of chemical elements is valuable only in so far as it illustrates chemical behaviour, and it is conventional to use the term transition elements in a mote restricted sense. The elements in the irmer transition series from cerium (58) to lutetium (71) are called the lanthanoids those in the series from thorium (90) to lawrencium (103) are the actl-noids. These two series together make up the /block in the periodic table. It is also common to include scandium, yttrium, and lanthanum with the lanthanoids (because of chemical similarity) and to include actinium with the actinoids. Of the remaining transition elements, it is usual to speak of three main transition series from titanium to copper from zirconium to silver and from hafnium to gold. All these elements have similar chemical properties that result from the presence of unfilled d-orbltals in the element or (in the case of copper, silver, and gold) in the ions. The elements from 104 to 109 and the undiscovered elements 110 and 111 make up a fourth transition series. The elements zinc, cadmium, and mercury have filled d-orbltals both in the elements and in compounds, and are usually regarded as nontransition elements forming group 12 of the periodic table. 

Dehierne started his work with a few hundreds kilograms of uranium ore extracting the active principle from it. After, he had extracted uranium, radium, and polonium he was left with a small amount of a substance whose activity was much higher than the activity of uranium (approximately, by a factor of 100 000). At first, Dehierne assumed that this highly radioactive substance was similar to titanium in its chemical properties. Then he corrected himself and suggested a similarity with thorium. Later, in spring of 1899 he announced the discovery of a new element and called it actinium (from the Greek for radiation). 

Gr. aktis, aktinos, beam or ray). Discovered by Andre Debierne in 1899 and independently by F. Giesel in 1902. Occurs naturally in association with uranium minerals. Actinium-227, a decay product of uranium-235, is a beta emitter with a 21.6-year half-life. Its principal decay products are thorium-227 (18.5-day half-life), radium-223 (11.4-day half-life), and a number of short-lived products including radon, bismuth, polonium, and lead isotopes. In equilibrium with its decay products, it is a powerful source of alpha rays. Actinium metal has been prepared by the reduction of actinium fluoride with lithium vapor at about 1100 to 1300-degrees G. The chemical behavior of actinium is similar to that of the rare earths, particularly lanthanum. Purified actinium comes into equilibrium with its decay products at the end of 185 days, and then decays according to its 21.6-year half-life. It is about 150 times as active as radium, making it of value in the production of neutrons. 

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