Dissolved rare earth

Gadolinium is produced from both its ores, monazite and bastnasite. After the initial steps of crushing and beneficiation, rare earths in the form of oxides are attacked by sulfuric or hydrochloric acid. Insoluble rare earth oxides are converted into soluble sulfates or chlorides. When produced from monazite sand, the mixture of sand and sulfuric acid is initially heated at 150°C in cast iron vessels. Exothermic reaction sustains the temperature at about 200 to 250°C. The reaction mixture is cooled and treated with cold water to dissolve rare earth sulfates. The solution is then treated with sodium pyrophosphate to precipitate thorium. Cerium is removed next. Treatment with caustic soda solution fohowed by air drying converts the metal to cerium(lV) hydroxide. Treatment with hydrochloric or nitric acid sol-... 

Byrne, R. H. Kim, K.-H. 1993. Rare earth precipitation and coprecipitation behavior The limiting role of PC>4 on dissolved rare earth concentrations in seawater. Geochimica et Cosmochimica Acta, 57, 519-526. 

Shiller A. M. (2002) Seasonality of dissolved rare earth elements in the lower Mississippi River. Geochem. Geophys. Geosys. 3(11), 1068. 

Dissolve into water = dissolved rare earth cations. 

Nozaki Y, Alibo DS, Amakawa H, Gamo T, and Hasumoto H (1999) Dissolved rare earth elements and hydrography in the Sulu Sea. Geochimica et Cosmochimica Acta 63 2171-2181. 

I In the first of a series of papers on rare earth calorimetry, Bommer and Hohmann [12] noted that the combustion-calorimetry results of these three research teams were unusually exothermic, probably because of the poor purity of the metal samples. Bommer and Hohmann determined enthalpies of formation of rare earth aquo-ions by dissolving rare earth metals in dilute acids. The rare earth oxides from which they prepared metals were well separated from other rare earths. The enthalpies of formation of Bommer and Hohmann are now known to be far too exothermic because the metals were prepared by reduction with potassium, and... 

Solvent extraction or liquid-liquid solvent extraction uses two immiscible or partially immiscible solvents containing dissolved rare earths. The two liquids ate mixed, the solutes ate allowed to distribute between the two phases until equilibrium is established, and then the two liquids are separated. The concentrations of the solutes in the two phases depend upon the relative affinities for the two solvents. According to convention, the product (liquid) that contains the desired solute is called the extract, while the residue left behind in the othca- phase is called the raffinate. (Encyclopedia Britannica 2015a). 

In order to dissolve rare earths from phosphors under mild condition, a mechanochemical treatment using a planetary mill was applied by Zhang and Saito s group (Zhang and Saito, 1998 Zhang et al., 2000). The mechanochemical treatment was shown to cause disordering of the crystal structures of the phosphor and thus enabled the leaching under mild conditions yttrium. 

On the other hand, a leaching experiment was performed on larger scale by digesting 50 g ore sample with 250 ml of 9M sulfuric acid concentration in order to remove the rare earth from one liter leach liquor. Table (2) shows the concentration of elements of interest in the leach liquor. The dissolved rares earth in the leach liquor is given in the Table (3). 

The third method was based upon dissolution of the rare earth in nitric acid followed by conversion to the oxide by calcination of the nitrate. Carefully controlled aliquots of standard preparations may be added to the dissolved rare earth samples to adjust spectral intensities to optimum levels. Comparisons of similar rare earths by this means of standard preparation provided relative reproducibilities of 7 percent. 

The classical preparative method of dissolving rare earth oxides or carbonates in diluted sulfuric acid (3 M or lower) and evaporating at room temperature (e.g., Wendlandt, 1958 Brauer, 1980) yields the octahydrated sulfate for all rare earths... 

Thus, the main series of selenates, the octahydrates R2(Se04)3-8H20 (R = Pr-Lu,Y), is isostructural with the corresponding sulfate series (Rosso and Perret, 1970 Hiltunen and Niinisto, 1976a,b). The preparation of the crystalline compounds can be carried out by similar methods, viz. dissolving rare earth oxide, hydroxide, carbonate or chloride in selenic acid and letting the solution evaporate at room temperature. 

Mona.Zlte, The commercial digestion process for m on a site uses caustic soda. The phosphate content of the ore is recovered as marketable trisodium phosphate and the rare earths as RE hydroxide (10). The usual industrial practice is to attack finely ground m on a site using a 50% sodium hydroxide solution at 150°C or a 70% sodium hydroxide solution at 180°C. The resultant mixed rare-earth and thorium hydroxide cake is dissolved in hydrochloric or nitric acid, then processed to remove thorium and other nonrare-earth elements, and processed to recover the individual rare earths (see... 

Opa.nte. There are two methods used at various plants in Russia for loparite concentrate processing (12). The chlorination technique is carried out using gaseous chlorine at 800°C in the presence of carbon. The volatile chlorides are then separated from the calcium—sodium—rare-earth fused chloride, and the resultant cake dissolved in water. Alternatively, sulfuric acid digestion may be carried out using 85% sulfuric acid at 150—200°C in the presence of ammonium sulfate. The ensuing product is leached with water, while the double sulfates of the rare earths remain in the residue. The titanium, tantalum, and niobium sulfates transfer into the solution. The residue is converted to rare-earth carbonate, and then dissolved into nitric acid. 

In order to make an efficient Y202 Eu ", it is necessary to start with weU-purifted yttrium and europium oxides or a weU-purifted coprecipitated oxide. Very small amounts of impurity ions, particularly other rare-earth ions, decrease the efficiency of this phosphor. Ce " is one of the most troublesome ions because it competes for the uv absorption and should be present at no more than about one part per million. Once purified, if not already coprecipitated, the oxides are dissolved in hydrochloric or nitric acid and then precipitated with oxaflc acid. This precipitate is then calcined, and fired at around 800°C to decompose the oxalate and form the oxide. EinaHy the oxide is fired usually in air at temperatures of 1500—1550°C in order to produce a good crystal stmcture and an efficient phosphor. This phosphor does not need to be further processed but may be milled for particle size control and/or screened to remove agglomerates which later show up as dark specks in the coating. 

Some nut trees accumulate mineral elements. Hickory nut is notable as an accumulator of aluminum compounds (30) the ash of its leaves contains up to 37.5% of AI2O2, compared with only 0.032% of aluminum oxide in the ash of the Fnglish walnut s autumn leaves. As an accumulator of rare-earth elements, hickory greatly exceeds all other plants their leaves show up to 2296 ppm of rare earths (scandium, yttrium, lanthanum, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium). The amounts of rare-earth elements found in parts of the hickory nut are kernels, at 5 ppm shells, at 7 ppm and shucks, at 17 ppm. The kernel of the Bra2d nut contains large amounts of barium in an insoluble form when the nut is eaten, barium dissolves in the hydrochloric acid of the stomach. 

Anhydrous ammonium oxalate is obtained when the monohydrate is dehydrated at 65°C. The monohydrate is a colorless crystal or white powder, and dissolves in water at 0°C up to 2.17 wt %, and 50°C up to 9.63 wt %. It is slightly soluble in alcohol and insoluble in ether. It is used for textiles, leather tanning, and precipitation of rare-earth elements. 

In most uranium ores the element is present in several, usually many diverse minerals. Some of these dissolve in sulfuric acid solutions under mild conditions, while others may require more aggressive conditions. Thus, while it may be comfortable to recover 90-95% of the uranium present, it may be tough or impractical to win the balance amount of a few percent economically. Some of the most difficult uranium minerals to leach are those of the multiple oxide variety, most commonly brannerite and davidite. These usually have U(IV) as well as U(VI), together with a number of other elements such as titanium, iron, vanadium, thorium, and rare earths. To extract uranium from these sources is not as easy as other relatively simpler commonly occurring sources. 

In the case of molten salts, the functional electrolytes are generally oxides or halides. As examples of the use of oxides, mention may be made of the electrowinning processes for aluminum, tantalum, molybdenum, tungsten, and some of the rare earth metals. The appropriate oxides, dissolved in halide melts, act as the sources of the respective metals intended to be deposited cathodically. Halides are used as functional electrolytes for almost all other metals. In principle, all halides can be used, but in practice only fluorides and chlorides are used. Bromides and iodides are thermally unstable and are relatively expensive. Fluorides are ideally suited because of their stability and low volatility, their drawbacks pertain to the difficulty in obtaining them in forms free from oxygenated ions, and to their poor solubility in water. It is a truism that aqueous solubility makes the post-electrolysis separation of the electrodeposit from the electrolyte easy because the electrolyte can be leached away. The drawback associated with fluorides due to their poor solubility can, to a large extent, be overcome by using double fluorides instead of simple fluorides. Chlorides are widely used in electrodeposition because they are readily available in a pure form and... 

The rare earth oxides of lanthanum, samarium and gadolinium were converted into soluble nitrate salts by dissolving them in the minimum amount of concentrated nitric acid. Then two sets were prepared by adding 2.0 ml of aqueous solution of La(N03)3.6H20 [0.2 M] and 0.01 ml of (n-BuO)4Ti to 25 ml of aqueous solution of Cu(N03)2 [1.0 M]. Similarly, two sets were prepared with Co(N03)3. Same procedures were followed for Sm(N03)3 [0.2 M] and Gd(N03)3 [0.2 M], One set of all these solutions were sonicated under ultrasonic bath (Model - Meltronics, 20 kHz, 250 W) for half an hour. The solutions prepared in normal and sonicated conditions were kept in muffle furnace (Model - Deluxe Zenith) first at 100°C for 2 h and then the temperature of the furnace was raised up to 900°C and calcined for 2 h. The solid composites prepared were then cooled to room temperature and treated as catalyst for phenol degradation. 

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