Alkaline earth oxalates

The determination of calcium, strontium, and barium ions in the presence of one another has been carried out by thermogravimetry by Erdey et al. (35,36). The ions are precipitated in the form of mixed metal oxalate hydrates 

From the curve, it can be seen that the decomposition processes are going on independently of one another. Between 100 and 250CC, the water of hydration is evolved since each ion forms a metal oxalate l-hydrate. According to the curves of individual compounds, the water contents are lost in the 

After the loss of the water of hydration, the curve exhibited a horizontal mass level from 250-360°C, which corresponded to the composition for anhydrous metal oxalates. Decomposition of the three oxalates then took place simultaneously, the process being completed al about 500°G The anhydrous metal carbonates were then stable from about SOO-eKTG followed by strontium carbonate, which also began to decompose in this range and was completely decomposed at 1100°C, at which temperature barium carbonate began to decompose. 

From the mass-loss curve, then, the following data are obtained D, mass of dry precipitate at 100°C , mass of water of hydration F, mass of carbon monoxide formed by the decomposition of the anhydrous metal oxalates G, mass of carbon dioxide formed by the decomposition of calcium carbonate and L, the mass of carbon dioxide formed by the decomposition of strontium carbonate. From these data, the amounts of calcium, C, strontium, S, and barium, By can be calculated from 

Assuming that the amounts of C, S, and B are unity, the error of the determination was calculated as 

---

An excess of COs partially transposes the alkaline-earth oxalates, and vice versa, in accord with the Law of Mass Action ... 

Separation and Recovery of Rare-Earth Elements. Because rare-earth oxalates have low solubihty in acidic solutions, oxaUc acid is used for the separation and recovery of rare-earth elements (65). For the decomposition of rare-earth phosphate ores, such as mona ite and xenotime, a wet process using sulfuric acid has been widely employed. There is also a calcination process using alkaLine-earth compounds as a decomposition aid (66). In either process, rare-earth elements are recovered by the precipitation of oxalates, which are then converted to the corresponding oxides. 

Alkaline Earths Chlorides. lit) ee.. of the 1 20 aqueous solid ion should he nlTcofcd neither by ammonium oxalate Solid inn nor hy silver nitride solution. 

Heavy Metals and Alkaline Earths. —The solution of t gnu of potassium chloride in 50 cc. of water should not lie alT dal by ammonium oxalate solution nor hy sodium carbonate solution nor by ammonium sulphide solution. 

Alumina and Alkaline Earths, Dissolve 2 gin. of potassium chromate in 30 cc. of water, add 5 cc. of ammonium oxalate solution, and make slightly alkaline with ammonia water. No preeipitate should form within twelve hours. 

Alkaline Earths, and Heavy Metals. — The solution of 3 gm. uf sodium chloride in ftO ee. of water, heated to boiling,. sinnilil nut be nlTeeted by aiiunoiiiuin oxalate solution nor by sodium carbonate. solution nor by ammonium sulphide solution. 

I)Heavy metals. Acidify 25ml aliquot from opn D soln with 0. IN HC1 soln and bubble H2S gas thru the soln for ca 30 secs. No pptn or coloration should result ])Alkaline-earth metals. Alkalize 25ml aliquot from opn D with 1ml of 10% Amm hydroxide soln, add 5ml of 10% Amm oxalate soln and heat the mixt nearly to boiling. No ppt should be formed on cooling... 

Acetic acid-acetic anhydride, 85 Alkali azides, 79 Alkaline earth azides, 79 Alumino-oxalates, 36 Amalgams, 5 concentration of, 17 preparation of, 6 rare earth metal, 15 Ammonium nitrourethane, 69 Ammonium perrhenate, 177 Antimony oxyiodide, 105 Antimony triiodide, 104 Aquopentammino cobalti bromide, 187, 188... 

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. 

The classic method for the isolation of the rare earth group which is used for both qualitative and quantitative determination involves three methods. In the first method, rare earths are precipitated as fluorides in acidic medium. The elements precipitated include Mg, Cu, Fe, rare earths Th, Ca and Sr. The second method consists of precipitation as hydroxides resulting in the removal of alkaline-earth elements like calcium from the mineral. In the third method rare earths are precipitated as oxalates from moderately acidic solutions and the elements Ca, Zn, Pb, Cu, Cd, and Ag may be coprecipitated. In early times the above methods were repeated several times to isolate, the rare earth group in a relatively pure form. 

The three alkaline earth metals decompose water at different rates, forming hydroxides and hydrogen gas. Their hydroxides are strong bases, although with different solubilities barium hydroxide is the most soluble, while calcium hydroxide is the least soluble among them. Alkaline earth chlorides and nitrates are very soluble the carbonates, sulphates, phosphates, and oxalates are insoluble. The sulphides can be prepared only in the dry they all hydrolyse in water, forming hydrogen sulphides and hydroxides, e.g. 

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. 

The zinc reduction of Eu + to Eu +, followed by its precipitation as the sulfate, is a traditional step in the separation of europium from other lanthanides. In general, the solubilities of the inorganic compounds of the Ln + ions resemble those of the corresponding compounds of the alkaline earth metals (insoluble sulfate, carbonate, hydroxide, oxalate). Both europium and the Sm + and Yb + ions can also be prepared by other methods (e.g. electrolysis), although these solutions of the latter two metals tend to be short-lived and oxygen-sensitive in particular. Eu + is the only divalent aqua ion with any real stability in solution. Several divalent lanthanides can, however, be stabilized by the use of nonaqueous solvents such as HMPA and THE, in which they have characteristic colors, quite distinct from those for the isoelectronic trivalent ions on account of the decreased term separations. 

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. 

The oxalate hydrates of the alkaline earth metals, e.g. calcium, strontium and barium, are all insoluble. If a calcium salt made acidic with ethanoic acid is treated with sodium oxalate solution, a white precipitate of calcium oxalate... 

---