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Extraction of rare earths from monazine sand, rare earth residues Ball, Robert William 1927

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EXTRACTION OF RARE EARTHS FROM MONAZITE SAND RARE EARTH RESIDUES by ROBERT WILLIAM BALL EXTRACTION OF RARE EARTHS FROM MOl RARE EARTH RESIDUES by ROBERT WILLIAM BALL A Thesis submitted, for the Degree of MASTER OF ARTS in the Department of Chemistry The University of British Columbia April, 192 7. m EXTRACTION OF RARE EARTHS FROM MONAZITE SAND RARE EARTH RESIDUES. Introductory. More than three thousand tons of monazite sand are decomposed annually in order to obtain the thorium necessary for the manufacture of incandescent gas mantles. Since monazite is primarily a phosphate of the cerium group metals of the rare earths and as the percentage of thoria is usually quite low, very large quantities of com-pounds of this group are annually produced during the pro-cess of extraction of thorium. Such compounds are known as monazite residues, and are usually in the form of double carbonates or double sulphates. These residues have been extensively used by rare earth workers as a source of cerium group elements. Although they are widely used, little information is avail-able as to the methods of extraction of rare earths from them» A little more is known regarding the decomposition of the original ores, although these are not nearly so widely used as are the residues. James, in his "A Scheme for the Separation of Rare Earths,"W suggests the following method for the de-composition of an ore:- The mineral is decomposed either « by hydrochloric acid, sulphuric acid, potassium bisulphate, 2 sodium hydroxide or hydrofluoric acid. When hydrochloric acid is used, the whole is evaporated to dryness to render the silica insoluble, and then warmed with a little con-centrated hydrochloric acid, after which the mass is treated with water and filtered. The filtrate may then be precipi-tated either by oxalic acid or anmonium oxalate. When sul-phuric acid or potassium bisulphate has been used to break up the mineral, it is necessary to stir with cold water to obtain solution of the desired elements. JAision with sodium hydroxide and washing with water gives a residue of oxides. These are dissolved in hydrochloric acid. Hydrofluoric acid decomposes many minerals in the cold, giving a residue of rare earth fluorides. The insol-uble fluorides are decomposed by means of sulphuric acid. The sulphate or,chloride solutions are then precipitated either by anmonium oxalate or oxalic acid. U) James has digested euxenite with strong sul-phuric acid. He has decomposed fergusonite and samarskite with hydrofluoric acid, or with concentrated sulphuric acid containing po tassium sulphate to raise the temperature. He fused columbates for two hours with twice its weight of sodium hydroxide, while he digested yttrotitanite and gado-linite with hydrochloric acid and ytterspar with an equal weight of sodium hydroxide' plus half its weight of water. Prandtl and Io8oh^) attacked monazite earth with concentrated nitric acid. Wenger and Christin^) recommend concentrat4d sulphuric acid for this purpose. - 3 -(5) Chesneau^ ' fused monazite with sodium potassium carbonate. ( 6) Hicks used sulphur monochloride for opening up rare earth minerals containing columbium, tantalum, titanium, etc. Travers''' fused one gram of finely powdered zirconium mineral with ten grams of sodium pero-xide. On the other hand, the only available reference to the decomposition of monazlte residues is that of Hopkins and Kremers^ . They advise boiling double sulphates for a few hours with a fifty per cent sodium hydroxide solution, until they are completely disintegrated. The mass is then diluted and the resulting hydroxides filtered and washed with boiling water until free from sulphates. The hydro-xides are then dissolved in nitric acid, and the rare earths precipitated from hot solution by means of oxalic acid. It is noteworthy, however, that in no case has any quantitative work been conducted in order to ascertain which method of extraction would yield the maximum possible results. Since, therefore, the monazite residues formed the source of so much material used in the cerium group rare earth work, and in as much as the presence of illinium was first detected in such residues, (cf. Harris-Hopkinsv ' ) , and as this is the first of a series of investigations re-garding the concentration of this element, it was deemed advisable to investigate Quantitatively, methods that would 4 -yield maximum extraction of all rare earths present. Analysis. The materials used in this work were finely powdered sodium cerium-group sulphates. In order to check the efficiency of the various methods of extraction, the material was analyzed, first according to a method proposed "by W.F. Hillebrand and then by a method which was de-vised and foljLnd to "be more adaptable. Both methods are given below. Two gram samples of the material were fused with exeess sodium carbonate, the melt digested with water con-taining a few drops of methyl alcohol, filtered, and the pre cipitate washed with water until the filtrate did not affect red litmus paper;. The precipitate was washed into a beaker with 100 c.c. of dilute sulphuric acid, digested on the hot plate and filtered through the original filter paper. The filter paper and undissolved precipitate were then ignited. The resulting oxides were fumed with hydrofluoric and con-centrated sulphuric acids, dissolved in dilute sulphuric acid and the solution filtered. The two filtrates thus obtained were made alkaline with potassium hydroxides to precipitate the rare earths and ferric and titanic oxides (if any) while retaining the silica and alumina in solution. The precipitate was allowed to settle; the liquor poured off and the precipitate washed by decantation, filtered and again washed slightly on the filter paper. The precipitate - 3 -was then washed from the paper into a small platinum dish, treated with hydrofluoric acid and the liquid evaporated nearly to dryness. A little water with a few drops of hydrofluoric acid was added and the insoluble rare earth fluorides (crude) were collected on a small filter paper held by a waxed funnel* The precipitate was washed into a small platinum dish and evaporated to dryness with sulphuric aoid, the paper being burned and added before expulsion of the acid. The sulphates were dissolved in dilute hydro-chloric acid, the rare earth hydroxides precipitated by ammonium hydroxide, redissolved in hydrochloric aoid, the solution evaporated to dryness and the residue heated with a few cubic centimeters of oxalic acid* The mixture was filtered, the precipitate ignited and the resulting oxides weighed. -O.7880 grams rare earth oxide were extracted from 2.0000 grams of the original material by the above method of Hillebrand. In another determination, the method of analysis used was as follows: After precipitating the soluble sul-phates with potassium hydroxide, the resulting hydroxides were transferred to a platinum dish, the filter paper ignited and added, and the whole fumed with concentrated sulphuric acid. The sulphates were dissolved in dilute sulphuric aoid, the rare earth, hydroxides precipitated by ammonium hydroxide, dissolved in hydrochloric acid, the solution evaporated to « dryness and the residue heated with a few cubic centimeters - 6•-of oxalic acid. The mixture was filtered, the precipitate ignited and the resulting oxides weighed. Two samples were analyzed "by the above method. In the first, 0*3944 grams were extracted from 1*0000 gram, and in the second, 0*7860 grams of rare earth oxide were extracted from 2.0000 grams of the original material. Results of analysis. Method of Wt. of Wt. of Wt. R 0 per Monazite E G 100 grafts Analysis residue d * monazite residue Hillebrand 2.0000 grams O.788O grams 39.40 grams Modified 1.0000 " 0.3944 » 39.44 " Modified 2.0000 H O.786O " 39.30 " The modified method is less troublesome, and from the above figures appears to be quite as accurate as the longer one. Acid Extraction. Although one would not expect maximum results by means of acid extraction, it was thought that it would be interesting to compare the efficiency of the mineral acids as extractants. Accordingly, two gram samples of the original residues were digested with nitric, hydrochloric and sulphuric acids. In each case the two gram sample was digested with 25 c.e. of concentrated acid, evaporated to 5 c.c, taken up in 250 c.c. water, boiled and filtered. - 7 -The sulphuric acid solution was cooled before filtering. In addition, two gram samples were digested with excess saturated sodium hydroxide solution as in the method of Hopkins and Kremers^ . The resulting hydroxides were boiled with 50 c.c. of concentrated nitric acid, evaporated to 10 c.c, taken up in 600 c.c. water, boiled and filtered. Concentrated oxalic acid was added to each of the above filtrates. The resulting oxalates were filtered off, ignited and weighed as the oxide. The following table shows the weights of rare earth oxide thus obtained. Digested Sample Wt. R«0_ wlth d * HNO. HC1. H 2S0 4 NaOH I II I II I II I II from 2 g. 0,3146 grams 0.2252 " O.58I4 grams O.507O " 0.7975 grams O.687O " 0.7778 grams 0.7595 " Wt. oxide extracted per 100 grams monazite re si due. 15*73 grams 11.26 » 29.07 grams 25.35 " 39.87 grams 34.35 w 38.89 grams 37.98 From these values it appears that there is little difference between sodium hydroxide and sulphuric acid on small samples. - 8 -Application of the above methods to large amounts of material, however, showed that none of the acid extrac-tions were applicable, giving widely varying results, and two weeks digestion with acid served to remove only a very small portion of the material present. Extraction with sodium hydroxide solution was also not very satisfactory. I483 grams of rare earth material were boiled with excess concentrated sodium hydroxide solution. The resulting hydroxide precipitate was fumed with concentrated sulphuric aeid and the soluble sulphates dissolved in water. Concen-trated oxalic acid was added to the sulphate solution and the precipitated rare earth oxalates dried and weighed. Two gram samples of the dried oxalate were ignited and weighed and from this value, the weight of rare earths as the oxides calculated , Results of HaOH digestion. Wt. monazite residue decomposed 1483 grams Wt. rare earth oxalate obtained ,544 " Wt. oxide from 2 g. oxalate 1.0000 " Wt. Ro0 extracted per 100 g. monazite residue 18.34 w 2 3 Fusion Methods. It was then decided to try out the efficiency of fusion methods, using alkali fusions as being the most likely to be successful. Sodium hydroxide and sodium car-- 9 -bonate were the two fusion reagents used. Four two gram samples of the original material were fused with four grams of sodium hydroxide. The melt was boiled with 200 c.c. of water and filtered. Sample (1). The oxide residue was digested with 12.5 c.c, of dilute nitric acid, made up to 600 c.c. with water, boiled and filtered. The undissolved nitrate residue was digested with concentrated nitric acid, diluted with water, boiled and filtered. Sample (2). This oxide was digested with 125 c.c. of concentrated nitric acid, dilated to 600 c.c. with water, boiled and filtered. The undissolved residue was again digested with concentrated nitric acid. Sample (3), This oxide was digested with 125 c.c. of dilute sulphuric acid, made up to ?00 c.c. with water and filtered. The undissolved sulphate residue was fumed with concentrated sulphuric acid, taken up in water, boiled, cooled and filtered. Sample (4). This oxide residue was digested with 125 c.c. of concentrated sulphuric acid, evaporated almost to dryness, taken up in 500 c.c. of water, boiled, cooled and filtered. The sulphate residue was digested with 400 c.c. of water and the residue from this treatment again fumed with sulphuric acid and taken up in 800 c.c. of water. 1 - 10 -Excess concentrated oxalic acid was added to the nine filtrates from the above treatments and the insoluble rare earth oxalates filtered off, ignited and weighed. Below are the weights of rare earth oxides obtained in this manner. Wt. oxide Wt. oxide from ext. per Sample 2 g. residue lOOg. resi-due. I. Digestion of oxide with dil. HUO O.36II g. 18.05 g. 3 Digestion of above residue with cone. HUO 0.2880 g. 14.40 g. * Total Oxide 0.6491 g. 32.45 g. II. Digestion of oxide with conc.HHO^ O.598I g, 29.90 g. Digestion of above residue with cone. KIJ0, 0,1281 g. 6.41 g. p Tota,l Oxide O.7262 g, 36.31 g. III. Digestion of oxide with dil. H2S04 0.4948 g. 24.74 g. Digestion of above residue with cone. H2S0 0.1816 g. 9*08 g. Total Oxide O.6764 g. 33*82 g, IV.. Digestion of oxide with cone. H SO 0,5121 g. 25.61 g. Digestion of above residue with water O.23O4 g. 11*52 g. Digestion of above residue with cone. H SO O.O387 g. 1.93 g. 2 4 *—*• "-Total Oxide O.78I2 g. 39.06 g. * - 11 -Two two gram samples were fused with four grams of sodium carbonate (anhydrous). The melt was digested with 200 c.c. of water, filtered and washed, ignited with the filter paper, fumed with concentrated sulphuric acid, taken up in 400 c.c. of water, "boiled, cooled and filtered. The soluble rare earth sulphates were precipitated "by oxalic acid, filtered, ignited and weighed. Results of Ha CO fusion. Wt. oxide from Wt. oxide extraction 2 g. residue per 100 g. residue Sample (l) 0,5951 grams 29.76 grams Sample (2) 0.6154 n 3O.77 » The above values from the sodium carbonate fusion are probably lower,than they would have been if the pre-cipitate from the water digestion had not been ignited. This lowering is due to the fact that ignited rare'earth oxides containing cerium are difficultly soluble in any acid. The following method of extraction was finally tried on a larger scale and found to be most satisfactory:-Equal weights of monazite residue and soda ash are mixed, poured into a Battersea crucible, fused in a muffle furnace and while still molten, poured into water. The crucible is immediately charged again, placed in the furnace and the operation repeated. The molten mass is completely disintegrated by the sudden cooling. It is filtered, and washed with water until 12 -the filtrate does not affect red litmus paper. The pre-cipitate is dried on a steam hath, made up to a thin paste with concentrated sulphuric acid and evaporated almost to dryness, when copious white fumes begin to come off. The resultant sticky mass is digested with water and the sol-uble sulphates precipitated as oxalates by oxalic acid. The residue is digested with more water and the soluble sulphates precipitated as oxalates. This is repeated until only a minute quantity of oxalate is precipitated from 5 litres of the solution. From time to time a few drops of auiphuric acid are added to the sulphate material to keep the solution slightly acid. In the first run, 872 grams of original material were fused with 1474 grams of UagCO . H 0 and 580 grams of dried rare earth,oxalates were extracted. In the second run, 2000 grams of monazlte residue were mixed with 2000 grams of soda ash. The material was fused, washed and heated with concentrated sulphuric acid until it became quite pasty. Five litres of water were added and the mixture heated and stirred. The liquor was decanted and filtered. The filtrate was deep red in colour and was marked filtrate (1). Another five litres of water were added to the residue and again a red filtrate was ob-tained. The filtrates from the third and succeeding wash-ings were quite colourless. In all, the residue was washed twelve times and filtrates (l) - (12) obtained. Five litres of water were then added to the residue which was • - 13 -s e t a s ide for n ine weeks, water being added to make up for l o s s "by evapora t ion . I t was then f i l t e r e d and the co lour less s o l u t i o n marked f i l t r a t e ( 1 3 ) . Excess concentra ted o x a l i c a c i d was added t o the f i l t r a t e s and the i n so lub l e ra re ea r th oxa la tes p r e c i p i t a t e d , f i l t e r e d d r i ed and weighed. Oxalates (3) - (12) were u n i t e d . Oxalate (1) was decidedly pink. The red co loura t ion g radua l ly decreased i n i n t e n s i t y from oxala te (1) to oxala te (13) which was almost pure white* Two gram samples of t he oxa la te s were i g n i t e d to oxides and weighed, and from t h i s the weight of r a re ea r ths ca l cu l a t ed as t h e ox ide . Below i s a t a b l e of the values ob-t a ined from the e x t r a c t i o n of 2000 grams of monazite r e s i d u e s . Oxalate Wt. Oxalate Wt. oxide Average w t . Tota l wt . of from 2 g. from 2 g. oxide from oxa la te oxala te oxalate I 376.33 g . 0.9333 g. 0.9342 g. 179.8 g. 0.9338 g. II 851.60 g. O.9813 g. O.9830 g. 433.3 g. 0.9847 g. Ill 66.00 g. 1.1173 g. 1.1137 g. 36.8 g. 1.1142 g. IV 16.93 g. 1.1279 g. 1.1274 g. 9.6 g. 1.1270 g. V-XII 73.40 g . 1.0247 g. 1.0262 g. 38.7 g. 1.0277 g. 1111 17.28 g. 0.9400 g. 0.9400 g. 8.1 g. 1433.7b grams 706.3 grams 1 - 14 -Summary. Method of Extraction. Wt. oxide extracted per 100 grams mona-zite residue. Analysis hy HillebrandTs method Analysis by modified method (l) Digestion 2 g. residue with cone. HNO^ (l) Digestion 2 g. residue with cone. HCl (l) Digestion 2 g. residue with cone. HpSO^ (1) 81 Digestion 2 g. residue with cone. KaOH Fusion 2 g. residue with KaoC0_ (l) 2 3 (2) Fusion 2 g. r e s idue with UaOH and ( l ) Diges t ion oxide with fl.il. HUO, - 18.05 grams Diges t ion above res idue with cone. 39.40 g . 39.44 g. 39.30 g . 15.73 g. 11.26 g. 29.07 g . 23.35 g. 39.87 g. 34.35 g. 38.89 g. 37.98 g. 29.76 g . 30.77 g. HNO; - 14.40 (2) Digestion oxide with oonc. HKO, - 29.90 Digestion above residue with cone. mro_ - 6.41 3 (3) Digestion oxide with dil. HpS04 - 24.74 Digestion above residue with - 9.08 cone. HpSO. -32.45 g. r36.31 g. -33.82 g. (4) Digestion oxide with oonc. HpSO* - 25.6l Digestion above residue with water - 11.52 Digestion above residue with eonc. H2SO4 - 1.93 -39.06 g. - 13 -Extraction per 100 grams monazite residue of Oxalate Oxide 36.68 g. 18.34 g. 66.^1 g. 71.69 g. 33.32 g. The values obtained in the present invest igat ion c lear ly show tha t fusion with sodium carbonate i s the most e f f i c ien t method of extraction of rare earths from sulphate res idues . This method i s not only most ef f ic ient but i s a lso quite inexpensive, sodium carbonate and sulphuric acid being two of our cheapest chemicals. Since monazite residues are the source of nearly a l l cerium group rare earth elements, t h i s research has /uncovered a method of extract ion that should be of great value to a l l workers in th i s f i e ld . The above research was suggested by Dr. J . Allen Harris and carr ied out under h is d i rect ion. I take th i s opportunity of thanking Dr. Harris for the great personal i n t e r e s t he has shown in the progress of t h i s invest igat ion. Digestion 1483 g. residue with UaOH Fusion 872 g. residue with IfeuCO, Fusion 2000 g. residue with Ka?C0, * - 16 -Bibliography. J. Am. Chem. Soe. 30, 979-92 (1908.) Chem. News. 97, 203-9 (1908). J. Am. Chem. Soc. 33, 1332 (1911). C. A. 17 2401 (1923). 2. anorg. Allgem, Chem. 127, 209-14 (1923). C. A. 16: 383O (1922). Ann. chim. anal. chim. appl. 4, 231-2 (1922). C. A. 3 : 3776 (1911) . Compt. rend . 133: 429-31 (1911) . J . Am. Chem. Soc. 33 , 1492-6 (1911). C. A. 1 3 : 1802-03 (1919) . Chimie & i n d u s t r i e 2 , 383-92 (1919). Bur. of S tandards , S c i . Papers , 421 , 3 1 8 - 3 1 ( 1 9 2 1 ) . J . Am. Chem. Soc. 4 8 , 1583 (1926) . IT. S. Geological Survey, Bulletin 700. 


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