Oxalic acid earths

Uses of oxalic acid ia each region are summarized in Table 5 (58). The demand for agrochemical/pharmaceutical production and for separation/recovery of rare-earth elements in each region has been increasing. The use for marble polishing in western Europe is unique to the region. 

The tetrahydropyranyl ether, prepared from a phenol and dihydropyran (HCl/EtOAc, 25°, 24 h) is cleaved by aqueous oxalic acid (MeOH, 50-90°, 1-2 h). Tonsil, Mexican Bentonite earth, HSZ Zeolite, and H3[PW,204o] have also been used for the tetrahydropyranylation of phenols. The use of [Ru(ACN)3(triphos)](OTf)2 in acetone selectively removes the THP group from a phenol in the presence of an alkyl THP group. Ketals of acetophenones are also cleaved. ... 

Nuryono, Huber, C. G., and Kleboth, K., Ion-exchange chromatography with an oxalic acid-alpha-hydroxyisobutyric acid eluent for the separation and quantitation of rare-earth elements in monazite and xenotime, Chromatograph-ia, 48, 407, 1998. 

Insoluble silica residues are removed by filtration. The solution now contains beryllium, iron, yttrium, and the rare earths. The solution is treated with oxalic acid to precipitate yttrium and the rare earths. The precipitate is calcined at 800°C to form rare earth oxides. The oxide mixture is dissolved in an acid from which yttrium and the rare earths are separated by the ion-exchange as above. Caustic fusion may be carried out instead of acid digestion to open the ore. Under this condition sihca converts to sodium sihcate and is leached with water. The insoluble residue containing rare earths and yttrium is dissolved in an acid. The acid solution is fed to an ion exchange system for separating thuhum from other rare earths. 

If the starting material is gadolinite, ore is digested with hydrochloric or nitric acid. Rare earths dissolve in acid. The solution is treated with sodium oxalate or oxalic acid to precipitate rare earths as oxalates. For euxenite, ore is opened either by fusion with potassium bisulfate or digestion with hydrofluoric acid. If monazite or xenotime is extracted, ore is either heated with sulfuric acid or digested with caustic soda solution at elevated temperatures. 

Rare-earth elements - [RADIOPROTECTIVEAGENTS] (Vol20) -recovery with oxalic acid [OXALIC ACID] (Vol 17)... 

The filtrate from the double sulphate precipitation contains the other half of the thorium and small amounts of the heavy rare earth double sulphates. This solution is heated to—90°, and oxalic acid is added. The precipitates contain phosphato-oxalates of thorium and rare earths (heavy). 

Oxalic acid is used in various industrial areas, such as textile manufacture and processing, metal surface treatments leather tanning, cobalt production, and separation and recovery of rare-earth elements. Substantial quantities of oxalic add are also consumed in the production of agrochemicals, pharmaceuticals, and other chemical derivatives... 

The culture liquid obtained above was adjusted to phi 3.0 with a saturated oxalic acid solution and the precipitate formed therein collected by filtration. The filtrate was added to 50.0 g each of kaolin and Celite 545 powder (diatomaceous earth), and stirred for 15 h at 4°C and after chromoprotein was allowed to adsorb as much as possible, it was filtered. The resulting filtrate was divided and placed in cellophane bags dry air was blown on them at 27°C for 24 h condensing them to about 600 ml. This concentrated solution at 4°C was desalted by cellophane dialysis for 24 h in distilled water. The yield of desalted concentrated solution from the culture liquid was approximately 80% (867 mkg/ml, 600 ml). 

The first of these, utilized by Yoder, McCalip and Seibert,34 and by Balch, Broeg and Ambler,37 provides for the extraction of the aconitic acid from the sample being investigated, usually with diethyl ether, and the subsequent isolation of the acid from the solvent. In dealing with solid samples, e.g. alkaline earth aconitates, evaporator scale, etc., the prescribed procedure is to dissolve the material in aqueous mineral acid and to extract the acid solution exhaustively with ether. The ether extract is then evaporated under reduced pressure, the dried residue titrated with standard alkali and the titratable acid calculated as aconitic acid. In dealing with such solid samples it is often necessary to make an additional determination for oxalic acid which otherwise would be assumed to be aconitic acid.37 The aconitic acid in liquid samples is usually precipitated as the insoluble lead salt which is separated and treated as any other solid sample. In some cases this procedure is unnecessary and the liquid samples are merely acidified with a mineral acid and then extracted with ether.37 This method for the determination of aconitic acid, however, requires a considerable amount of time and is further complicated by the interference of ether-soluble waxes and non-volatile acids. 

Action of heat All oxalates decompose upon ignition. Those of the alkali metals and of the alkaline earths yield chiefly the carbonates and carbon monoxide a little carbon is also formed. The oxalates of the metals whose carbonates are easily decomposed into stable oxides, are converted into carbon monoxide, carbon dioxide, and the oxide, e.g. magnesium and zinc oxalates. Silver oxalate yields silver and carbon dioxide silver oxide decomposes on heating. Oxalic acid decomposes into carbon dioxide and formic acid, the latter being further partially decomposed into carbon monoxide and water. 

Oxalic acid is a precipitation agent for rare earth ions. The solubility of rare earth oxalates range from 10 to lO" mol in neutral solutions. The precipitate usually contains coordinated and/or lattice water molecules, RE2(C204)3 n H2O, where = 10 for lanthanum to erbium and yttrium while n = 6 for holmium, erbium, thulium, ytterbium to lutetium and scandium. 

An emulsion liquid membrane (ELM) system has been studied for the selective separation of metals. This system is a multiple phase emulsion, water-in-oil-in-water (W/O/W) emulsion. In this system, the metal ions in the external water are moved into the internal water phase, as shown in Fig. 3.4. The property of the ELM system is useful to prepare size-controlled aiKl morphology controlled fine particles such as metals, carbonates/ and oxalates.Rare earth oxalate particles have been prepared using this system, consisting of Span83 (sorbitan sesquioleate) as a surfactant and EHPNA (2-ethyl-hexylphospholic acid mono-2-ethylhexyl ester) as an extractant. In the case of cerium, well-defined and spherical oxalate particles, 20 - 60 nm in size, are obtained. The control of the particle size is feasible by the control of the feed rare earth metal concentration and the size of the internal droplets. Formation of ceria particles are attained by calcination of the oxalate particles at 1073 K, though it brings about some construction of the particles probably caused by carbon dioxide elimination. 

Uranium minerals may be obtained in solution, in a suitable condition for estimation, by the following process. The ore is dissolved in aqua regia, or, if necessary, fused with alkali bisulphate and extracted mth hot hydrochloric acid. After evaporation to drjmess, the residue is taken up with dilute hydrochloric acid, and the solution saturated with hydrogeir sulphide in order to remove any copper, lead, bismuth, arsenic, antimony, or any other metal yielding an insoluble sulphide. The filtrate is concentrated and treated with ammonium carbonate, which precipitates the carbonates of the alkaline earths, iron, and most of the rare earths. The filtrate is neutralised by hydrochloric acid, evaporated to dryness, and the residue ignited to drive off ammonium salts, and then redissolved in dilute acid. The remaining rare earths, and particularly thorium, are next precipitated by the addition of oxalic acid. The filtrate, which contains the uranium in the uranyl condition, may now be precipitated by any of the methods described above. 

Use Making oxalic acid and organic oxalates, glazes, rare-earth-metal separations. 

Fig. 3-134. Separation of alkaline-earth metals on a silica-based cation exchanger. - Separator column Nucleosil 5 SA eluent 0.0035 mol/L oxalic acid + 0.0025 mol/L ethylenediamine + 50 mL/L acetone, pH 4.0 flow rate 1.5 mL/min detection direct conductivity injection volume 100 pL solute concentrations 2.5 ppm magnesium, 5 ppm calcium, 20 ppm strontium, and 40 ppm barium.

The precipitation of thorium oxalate with calcium as collector is a much favoured separation method [3]. In a weakly acid medium (pH 1-4) it can be precipitated with oxalic acid. Rare-earth metals and U(IV) are also precipitated, but many metals (e.g., Fe, Al, Ti, Zr, Nb, and Mo) remain in solution as soluble oxalate complexes. 

The solution of rare earth salts is saturated with hydrogen sulfide to remove lead, copper, bismuth, molybdenum, etc, and the rare earths precipitated by adding oxalic acid solution. Separation from the common elements is somewhat more effectively accomplished if both the solutions are boiling hot, the oxalic acid being added slowly while stirring. The crude oxalates are filtered and thoroughly washed. 

Thorium oxalate, ThfCjOdi 611 0, Is precipitated as a while amorphous powder when oxalic acid is adtled to a solution of n thorium salt. It dissolves readily in solutions of ammonium ourhunate uud ammonium oxalate, but is less Roluble in sulfuric, acid than tho ran earth oxalates and is insoluble in nitric acid. Double alkali oxalates, acid oxalates, and mixed salts have been prepared. 

A volumetric method is based on the fact that ammonium molybdate precipitates thorium as the normal molybdate but has no action on the rare earth elements.3 The mixed nitrates are dissolved in 1 15 acetic acid to which a little sodium acetate has been added. This solution is titrated cold with ammonium molybdate, using diphenylcarbazide as an outside indicator. The end point is the appearance of a deep rose color which fades quickly. Another volumetric method 4 precipitates thorium from a mixed nitrate solution with hot oxalic acid let stand, filter, wash, and add the precipitate to hot water, then add 1 1 sulfuric acid and titrate with decinormal permanganate. 

The rare earths are removed hy adding oxalic acid to a hot solution and filtering off the run earth oxalate. To decompose the excess oxalic acid in the filtrate, evaporate to dryness, ignite, and take up the residue with Il( l, If necessary any insnluhle residue may Is brought into solution by fusion with KHSt... 

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. 

Precipitation with oxalic acid. Figure 6.6 shows the principal steps in the process for separating the sulfuric acid solution of monazite into a thorium concentrate, a rare earth concentrate, and a uranium concentrate developed at the Ames, Iowa, Laboratory of the U.S. Atomic Energy Commission [Bl]. 

The solution of monazite in sulfuric acid containing about 50 to 60 g of thorium and rare earths per liter is diluted with about 4.5 volumes of water and brought to a pH of 1.5 by addition of NH4OH. Oxalate ion is added in the form of recycle sodium oxalate, plus sufficient oxalic acid in 10% aqueous solution to provide 110% of the oxalate ion needed to precipitate thorium and rare earth oxalates. The precipitate is filtered and washed with 1 % oxalic acid in... 

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