) _‘-‘" If“ \t‘f‘fi‘mg fig“ 0"; :,' \;'0'1-LJ:‘4‘.3’:‘: Rx. 1‘. : “RIMENa-ll JON C)"; ”‘ ‘T {0223‘} M Thesis {or flu Degree of M. S. MICHIGAN STATE COLLEGE Raipfi J. Berto!acinsi 1951 This is to certifg that the thesis entitled "The Hypophosphate Method for the Volumetric Determination of Thorium" presented bg Ralph J. Bertolaeini has been accepted towards fulfillment of the requirements for M.S. Chemistry degree in (5W Major prolesmg Date May 16: 1951 0-169 I '51. fl: , . _ - ".Iz‘ g. ,- .. . _ _ . ”or . _ . _ Kr J ‘- ‘ - ' " ' . . . ._ _- .‘3’\ ’ '__ — .:_.V ‘ v, 3' '7.:: -' ’ ‘ \. , ' ‘ .' . afi" . 2': - ’.'- - r U-—4 2‘ - _ “I. fig ’. .a‘i’. _- 2 ._ 3:33- i‘~. In "3‘ ‘,-_r.'~'fi. L’ ’IO .:'_II ‘4; 3')..l"y_‘ - ‘V.I' ‘ ‘ I_- . .}' I pa ? ‘ : ' - 4": N,‘ s ‘__'. 1'. .L ' ' ' ' ,0 . ' _ ~ _‘ x"- .. < _' ‘ _ ‘r_‘ ' . 4%. '~ 4'.-.H""-Vh L2" - “' ’ L ."IV ‘01 ‘ ‘ ~": . gvv " I,“ '- _ . - .A ' -.4- ~._ ‘1- . .- n: #5 l - _ ‘ » 1.x .1 - or '- - . ‘r‘: - I . . ~ _ . ' , -‘ _ ‘< -'- . .’." ‘ " . . ~‘.. . t - _ 3" A . .. - . -‘ ‘ H, i l . ‘— '_”‘ _I I - l..- :.: . VA A - . . - . 4 V'-_ V. F?” ’7 _." _ ',_‘. ‘l fl Ir ' \' I A '. ' .51. ~ '_ . g-:_ I" 15 i' J.- . n. - ' “ . \ ”\J \l Il.’ l ‘ 'a , . I .3} I; m fit”; I; (6:11:11; (9 v a '1‘!” mt, \ g I if; .._. ‘1‘} WI, 1"? 23'1".“ V" P . ’3 ‘li’ k. (2;; "I .' ‘::' 0‘. ' Rat-- 'l ‘ ‘9 I: ‘ l I } KN if}? " '. fist“?! h.) r til: . r a ..l ._' V. ‘_ ,‘Vfi‘l .I mm HYPOP’LZC'SKIATE 115131013 .L.LA__J FOR THE VOLUfiETRIC DSTfiifilUATION OF THORIUH BY Ralph J. Bertolacini U) F—l (/1 A THE School of Graduate Studies of Nichigan of Agriculture and Applied Science fulfillment of the requirements for the degree of Submitted to the State College in partial ""3 ER 03‘ SCIEITCE 14L Department of Chemistry 1951 CHEWSTRY DEPT- 7545 ( .3? 5f .4 I/ 21/ ACKI‘TC“. "JLE‘DGT Call“? '1‘ The writer wishes to express his sincere appreciation to Doctor Elmer Leininger, Professor of Chemistry, for his assistance and guidance during the course of this work. The writer also is indebted to the Lindsay Light and Chemical Company of'Nest Chicago, Illinois, for providing the analyzed Brazilian monazite sand. ********** ******** ****** **** ** * 255896 TREES CF CCfmflfTS Iii-1310:)??(1T1Cl37000.0000...00....OOOOOOOOOOOOOOOOOIOOOOOOOOOOOOOOOOO 2:1:3TO;::ICAIJOOOOOOI0.0.0...OOOOOOOOOOCOOOOOOOOOOOOOIOOOOOOOOOOO... fi‘*"DP“I’V’?”:‘m',L .L'J»'..L_.J.--.J...A.JL .0..............0.0.000.0.0.0....00....0...‘........ A. :?.ea€ent8000000000ooooooooooocoo.co.ocococoon-000000.000. B. Factors Influencing the Apparent Tilliequivalent Weight. 1. Acidity of ”edium and'Iash Solution................ 2. Effect of Varying Amounts of Thorium.on.the Tilli- equivalent Weight................................ 3. Effect of Cerium on the Tilliequivalent Height..... 4. Effect of Acidity in the Presence of Interferences. 5. Effect of Thoriuererium Ratio on the Factor....... C. Dete‘mination of Thorium in Ionazite Sand............... DISCTTSSIC" i’ivD CCT'ZCLTTSICI‘TOOOOOOOOQQno...000.00.000.0000000000000 L 11;"? ‘.mTT‘7‘"‘ CINE?) ___~1JAQ“.LKJ.LLL / .LJJ»OOOOCOOOOOOOOOOOOOO0.0...OOIOOOOOOOOOOOOOOOIOOOO VI VII I T TC'm ‘ u; .2- C's} 1-3 } mixes L...) ,J BEBE-CT CT." -LCIDS CT? SOL’WILITY. . .. . . . . . . . . . BI‘V'BCT I- ’LKLYIT'TG I“I’7C>TTI"TTS OP' TIICRIU.‘ T. . . . . . “EFFECT OI" CBKITI'...H......... .... . ..... ... VARYITTC} A_;IDITY IFT TE PRES-SECS 015 (‘31: U". EFFECT F‘ T?" ZIITTTFCSYII’TI I'LATIO. . . . . . . . . . . . TZICIIITIT7 IIT "CITAZI'I‘B SKID. . . . . . . . . . . . . . . . . . TIZOI‘ZITT' :BCCYIEEIYOO......IOOOO0000.00.00.00. INTRODUCTION The use of hypophosphate for the quantitative estimation of thorium was first proposed by Kauffman (11) in 1899. He found that thorium formed a white amorphous precipitate when sodium.hypophosphate or hypo- phosphoric acid was added to a thorium solution. The precipitated thor- ium hypophosphate was insoluble in water, acids and alkalis. This procedure was carried out in strongly acid solution and was important in the separation of thorium from the rare earths and for its quantitative gravimetric estimation. It is assumed that the precipitate was ignited to the pyrophosphate or converted to the oxalate and then ignited to the oxide as the final weighing form. Rosenheim (24) was also successful in using hypophosphate for the determination of thorium. He dissolved the precipitated thorium hypo- phosphate in sulfuric acid, changed to the chloride, converted to the oxalate and ignited to the oxide. The method is described in detail by Yeyer and Hauser (15). Koss (12) found that thorium could be separated from the cerium earths in 6% hydrochloric acid solution by hypophosphate precipitation. Hecht (9) also used hypophosphate to separate thorium from the rare earths. The Rosenheim method as modified by Birth (30) was used to decompose the hypophosphate and the final weighing form'was the oxide. Since the precipitation of thorium.was quantitative in strongly acid solution and a reasonable separation from the rare earths was ..1... possible, it was believed that a rapid volumetric method for one de- termination of thorium utilizing hypophosphate as the preci itating agent, would be feasible. The oxidation of hypophosphate with dichron- ate in strongly acid solution was investigated by Chulski (7). He found that the oxidation of hypophosphate by excess potassium dichromate in 12? milfuric acid was quantitative. The initial investigation on the volumetric determination of thorium.by oxidation of thorium hypophOSphate was begun.by Paine (20). Thorium hypophosphate was precipitated from a 10$ hydrochloric acid solution with a 10¢ excess of disodium dihydrogen hypophosphate reagent. Paine found that the precipitate contained a thorium.to phosphorus ratio of 1 to 2.271 instead of a ratio of l to 2. The amount of excess hypo- phosphate must be calculated on.this basis. The precipitate was washed free of chloride and hypophOSphate with 250 ml. of 1% sulfuric acid. The choice of a proper acid concentration of the wash solution was in- vestigated and Paine found that the precipitate was soluble in Si sul- furic acid causing low results. The thorium hypophosphate was oxidized with an excess of standard dichromate in 12’T sulfuric acid. An excess of standard ferrous sulfate was added and the excess back titrated with standard dichromate using diphenylamine sodium sulfonate as a redox indicator. It was found that a thick asbestos suspension facilitated the filtration of the gelatinous precipitate. The asbestos blank was determined and this value was sub- tracted from the final volume of standard dichromate used. -2- An empirical factor was found to be necessary and it was suggested that the apparent equivalent weight of thorium.oxide, 118.4, be used instead of the normal equivalent weight, 152.1. The purpose of this investigation is to continue the study begun by Paine, to extend the method by studying the effect of interfering ions, and ultimately to apply the method to the determination of thorium in monazite sands. -3- HISTORICAL The chief source of thorium at the present time is monazite sand, a phosphate of cerium earths with varving amounts of thorium as an accessory constituent. The deposits in Brazil and Travancore are the fl 2. principle source of supply. Thorium also occurs as a rare silicate, ThSiO4, thorite and thoranite, a mineral containing rare earths asso- ciated with uranium (10). Thorium was principally used in the prepara- tion of incandescent gas mantles but recently has been used in.the manufacture of photocells, X—ray targets, glow tubes, alloys for jet engines, and as a catalyst in the preparation of aldehydes and ketones (14). ‘ Thorium normally exists in a single valency state of plus four, however, under special conditions unstable lower valency states have been prepared (1). Because of its similarities in ionic charge and ionic size, thorium.resemb1es the elements of Group IV-A, and cerium IV. The fact that thorium is less basic than the trivalent rare earths makes possible the separation of thorium from.the rare earths by con- trolled hydrolysis methods. F3 he literature prior to 1948 has been extensively reviewed by Hoeller, Schweitzer and Starr (18), therefore, the historical will be limited to a literature survey since that time. Since the thorium ion is colorless, colorimetric methods are rela- tively few. The methods depend on the formation of colored derivatives -4, or of compounds from.which a color may be developed. An indirect colorimetric method has been proposed by Rider and hellon (21) in.which thorium oxalate is precipitated with an excess of oxalic acid at a pH of 0.7-3.2. The excess oxalate is reacted with potassium.permanganate. The unreduced permanganate gives the colored system. This method pre- supposes a separation of thorium from the rare earths. Ions which react with oxalate or reducing agents which destroy the permanganate color interfere. Vurthy and Iaghavarao (19) have used sodium alizarin sulphonate (alizarin red-S) to determine thorium colorimetrically. This method has been applied to monazite sand only after the removal of zir- conium, titanium and cerium. The use of l-(o-arsenophenylazo)-2- Yaphthol-3,6 disulfonic acid has been suggested by Thomason, Perry and Byerly (25) as a rapid colorimetric method. The interferences are so numerous that the method is not practical. Iodine liberation, when thorium iodate is treated with hypophosphorous acid in.the presence of sulfuric acid, has been used by Williams (29) as a basis for a colori- metric method. Gravimetric procedures for the determination of thorium.have re- ceived the greatest amount of attention. As a rule gravimetric methods are involved and require a great number of operations. An example of this is the hexamine method of Ismail and Iarwood as published by the Tew'Brunswick Laboratory (22). There are seventy-three separate opera- tions in the analysis which ends with an oxalate precipitation followed by ignition to the oxide as the final weighing form. This is typical of most gravimetric procedures. Volumetric methods for the determination of thorium have received little attention. Zanks and Diehl (2) have determined thorium by an oxidimetric method based on the precipitation of thorium as the normal molybdate followed by reduction and titration of the molybdenum equiva- lent to the thorium. An electrometric method is described in which the thorium is titrated with ammonium paramolybdate in 7X acetic acid solu- tion using a 0.13 calomel-molybdenum wire electrode_system. Hoeller and Fritz (16) have described the use of iodate for the volumetric deter- mination of thorium. Thorium iodate is precipitated from.a strong nitric acid solution and the thorium estimated by iodometric determination of the iodate content of the precipitate. This is a refinement of the method of Chernikhov and Uspenskaya (6) and has the disadvantages of loss due to hydrolysis and difficulty in removing the adsorbed iodate. Toeller and Schweitzer (17) have published a radiometric method in which the thorium is precipitated with an excess of standard pyrophosphate containing a known activity of radioactive phosphorus (P32). The amount of excess pyrophosphate is determined by its radioactivity. Ytterium earths cause high results and a preliminary separation is recommended. The use of thorium periodate has been suggested by Tenkataramanick and Raghavarao (26) as a volumetric method. Thorium periodate is precipi- tated from a hot neutral solution'with potassium periodate. The gela- tinous precipitate is dried and dissolved in hydrochloric acid. A slight excess of potassium iodide is added and the liberated iodine titrated with standard thiosulphate. A recent method employing high frequency titrimetry has been in- vestigated by Blaedel and *almstadt (3). Cxalic acid is used in an indirect titration of thorium. Small amounts of titanium and zirconium may be tolerated but the method can not be used in the presence of rare earths and ions which complex or precipitate oxalate. -7- 1—Y'l' :3“) - 'TV‘).'\T'T‘ Q L Maud. J-kI— L—JLOJ. A A. Reagents tandard Disodium Dihydrogen.7ypophosphate Solution Disodium dihydrogen hypophosphate was prepared by the oxidation of red phosphorus with sodium chlorite solution according to the di- rections of Leininger and Chulski (13). Exactly 7.8535 grams of the air dried reagent was dissolved in water and diluted to one liter to give a 0.05U solution with respect to the oxidation of hypophosphate to phosphate. Because the compound was difficult to dry to the exact state of hydration, HaZHZP206°6HZO, the solution was standardized with standard potassium dichromate. Standard Potassium Dichromate Solution Baker's primary standard grade potassium.dichromate was ground to o o o 0 F?“ a fine powder and dried 1n an oven at 140 C. for four hours. Lfle crystals were cooled in a desiccator for thirty minutes and the correct amount was weighed out to give a 0.15H standard redox solution. Standard Ferrous Sulfate Solution A 0.15N ferrous sulfate solution was prepared by dissolving approxi- mately the correct amount of ferrous ammonium.sulfate in six liters of IV sulfuric acid solution. The solution was standardized daily against the standard dichromate. Diphenylamine Sodium Sulfonate Indicator Exactly 0.52 grams of barium diphenylamine sulfonate was dissolved in 100 ml. of water and 0.5 grams of sodium.sulfate was added. The solution was filtered by decantation from the precipitated barium.sul- fate. An indicator blank of 0.05 ml. was subtracted from the amount of dichromate used (25 ). Asbestos Suspension Approximately 50 grams of Baker's acid washed asbestos were weighed into a Euechner funnel and washed with concentrated hydrochloric acid and concentrated nitric acid. The asbestos was washed free of acid with water and transferred to a one liter beaxer. It was allowed to digest overnight on the steam bath in a dichromate-sulfuric acid solution. The asbestos was then filtered and washed a number of times with large quantities of distilled water. It was finally diluted to a thick sus- pension.with two liters of distilled water. Fifty ml. of this suspen- sion were digested for three hours on a steam bath with exactly 25 ml. of standard dichromate in 12K sulfuric acid. The solution was cooled and diluted to 250 ml. Eighteen ml. of 85% orthophosphoric acid were added. A measured excess of standard ferrous sulfate was added and the xcess back titrated with standard dichromate using diphenylamine sodium sulfonate as the redox indicator. The amount of dichromate used con- stitutes the asbestos blank. The asbestos blank was not a constant one but varied considerably for each preparation. The asbestos absorbs dichromate into its pores and this is only partially removed during the washing with distilled water. The same lot of asbestos was used throughout this study and the blanks ranged from 0.16 ml. to 0.33 ml. Standard Thorium Yitrate Solution A standard thorium nitrate solution prepared by Paine (20) was used throughout this study. An approximately 0.053’thorium.nitrate solu- tion was prepared from Baker's thorium.nitrate crystals and distilled water. The thorium content was determined by the gravimetric potassium iodate method as described by Bonardi (4) and checked by precipitation of thorium oxalate. The oxalate was ignited to the oxide and weighed. The solution was found to contain 0.3046 grams of thorium oxide in 24.92 ml. (calibrated pipet). -10- B. Factors Influencing the Apparent Tilliequivalent“fleight l. Acidity of Vedium and Wash Solution It has been shown that an empirical factor is necessary in this method (20). The apparent equivalent weight of thorium.oxide must be used in place of the normal equivalent weight. The formula, ThPZOG’ would require an equivalent weight for the thorium dioxide of 132.0. The apparent equivalent weight is obtained by dividing the grams of thorium.di xide present by the number of equivalents of dichromate used. in the oxidation of hypophosphate to phosphate. The change in oxidation number is one for each phosphorus aton. The general procedure followed was to precipitate thorium.hypophos- phate from an acid solution. The precipitate was filtered through a Gooch crucible and washed with a dilute acid solution. The precipitated hypophosphate was transferred to the original container and oxidized with an excess of standard dichromate. A measured amount of standard ferrous sulfate was added and the excess back titrated'with standard di- chromate using diphenylamine sodium.sulfonate as the redox indicator. The initial problem was to study the effect of the wash solution on the solubility of the precipitated thorium hypophosphate. Precipita- tion was carried out in a 10% hydrochloric acid solution as suggested by Fecht (9). The following were mixed in.a 250 m1. centrifuge bottle: 25 ml. of standard thorium.nitrate solution 18 ml. of concentrated hydrochloric acid 5 ml. of 3% hydrogen peroxide 50 ml. 0: distilled water 50 ml. of asbestos suspension -11.. The solution is heated in a boiling water bath and a Iii excess of standard disodium dihydrogen hypophosohate, based on the ratio of ther- ium to phosphorus of 1:2.3 (20), is added. The hypophosphate is added slowly from.a burst and the hot solution is stirred constantly during the addition. ”he precipitate is allowed to digest several minutes. The solution is then centrifuged for thirty minutes and filtered through a Gooch crucible fitted with an asbestos mat. The precipitate is washed with 250 ml. of a 1% sulfuric acid solution which effectively removes the chloride and the excess hypophosphate. The precipitate and the asbestos mat is transferred with a nickel spatula to the original bottle and the crucible is rinsed thoroughly with 50 ml. of hot water. exactly 25 ml. of 0.153 potassium dichroxnte and enough concentrated sulfuric acid to make the solution 123 (55 ml.) are added. The solution is heated in a boiling water bath for two hours with constant stirring. Adjustable electric stirrers were used. After the precipitate has been completely xidized, the contents are cooled and transferred to a 500 4 . Erlenmeyer flask. The solution is diluted to 250 ml. and 18 ml. of 85fi orthophos- phoric acid are added. A measured excess of standard ferrous sulfate, exactly 25 ml., is added and the excess is back titrated with 0.15? di- chromate. The asbestos blank and the indicator blank are subtracted from the volume of potassium dichromate used. The esults are recorded in Table I. Willard and Gordon (27) have shown. that 70:? perchloric acid has several advantages over sulfuric acid in the decomposition of monazite sand. It was, therefore, decided to determine the effect of precipitating \ -13- ETFECT OF ACIDS CW SCLTBILITY fit. Th02 Present Acidity by flash Solution Apparent Teq. g. Volume we. 0.5048 10% KCl 250 ml. 1% IIClO4 0.1045 (125) 0.1051 0.1045 0.1047 Av.0.1048 ’7.) . 4 -1 1 0.5048 1e: :01 150 ml. 1? 3 so ‘, 2 4 <12-) <3