and reached a temperature of approximately 950' C. The program of the dissolution of the crystal chips could be observed visually through the clear melt and it required normally not more than 3 hours. According to the reaction: Ti02 NazCOa = NaTiO, COz, the dissolution IS accompanied by a fine bubbling which ceases after the reaction is completed. The COZ pressure was held within 5 to 10 mm. For small deficiencies it is advisable to reduce the reaction temperature to 920' C. and to keep the COZ pressure below 0.6 mm. Thus, the oxygen dissociation pressure of COzis well matched to the oxygen equilibrium pressure of TiOz. After cooling and removing crucible A from the Vycor tube, the solid cone of frozen melt containing the titanate product could be easily taken out and was broken into a few large lumps, which were transferred into a Pyrex tube F , code Corning 6580. A surplus of diluted HzS04 FeZ(SO& was added to dissolve the salt cone and then the Pyrex tube was immediately closed with a stopcock fitted to the tube by a ground joint, (size 29/42). The dissolution process was sufficiently slow (2 hours), because of the relatively large lumps, that the evolved COz could be pumped off in a controlled manner, without losing any liquid. Although the applied liquids had been freed from oxygen by bubbling with nitrogen, the additional COz evolution helped to rinse out any traces of oxygen completely as shown by blank tests with known amounts of metallic Fe. After complete dissolution of the salt cone, the Fe+2 ion product was titrated with 0.0207N KMn04.
+
+
+
RESULTS
Table I compiles a number of representative data. Reliability and Ultimate Sensitiv-
ity. As already shown for oxides with oxygen surplus, the strict exclusion of parasitic oxygen is mandatory. For the vacuum melting phase this was accomplished by adjusting the COZ pressure between 5 and 10 mm. Separate experiments with oxygen deficient Ti02 crystals had shown t h a t under this condition neither oxidation nor reduction occurs. The fact that the same results were obtained with and without pumping during the dissolution process in the melt, as shown for bluish transparent Japanese I1 crystals, seemed to indicate that under these conditions the COzpressure is still less critical. The problem of parasitic oxygen was more critical during the wet phase of the dissolution. Since it was difficult to introduce welldefined oxygen deficiencies into Ti02 crystals, blank tests were made only for this phase of the process. Small portions of pure iron wire (0.002 inch in diameter) equivalent in reduction value to the observed oxygen deficiency were dissolved under the same conditions as the titanate containing melt cones and the produced Fe +2 concentration was titrated. The observed deviation was within k0.8 microatom of iron resulting in the same precision of measurement of oxygen deficiency.
With crystal samples of more than 100 mg., the deficiency value is accurate within *5%, for larger sample weights even better. The accuracy is finely limited by the blank; if larger crystal specimens are available for analysis, the sensitivity limit could easily be boosted by another order of magnitude. ACKNOWLEDGMENT
The authors thank Keystone Carbon Co. for the support of this work, and Eiso Yamaka of Nippon Telephone & Telegraph Public Corp. for supplying rutile crystals. LITERATURE CITED
(1) Breckenridge, R. G., Hosler, W. R.,
Phys. Rev. 91, 793 (1953).
(2)fCronemeyer, D. C., Ibid., 87, 876 (1952). (3) Fntsch, O., Ann. Phys. 22, 375 (1935). (4) Sachse, H. B., ANAL. CHEM.32, 529 (1960). (5) Slack, G. A., Newman, R., Phys. Rev. Letfen 1,59 (1958). (6) Verwey, E. J., Phil. Tech. Rd. 9, 47 (1947). (7) Ibid., 10, 232 (1949). (8) Yamaka, E., Sawamoto, K., Phys. Rev. 112, No. 6, 1861 (1959). (9) Zerfoss, A., Stokes, R. G., Moore, C. H.,Jr., J. Chem. Phys. 16, 1166 (1948).
RECEIVED for review March 24, 1961. Accepted June 29, 1961.
Rapid Chemical Determination of Aluminum, Calcium, and Magnesium in Raw Materials, Sinters, and Slags L. L. LEWIS, M. J. NARDOZZI, and L. M. MELNICK Applied Research laboratory, United States Steel Corp., Monroeville, Pa.
b A chemical method has been developed for the determination of aluminum, calcium, and magnesium in raw materials, sinters, and slags. The method provides for a rapid group separation of these elements from mixtures, and for their subsequent direct determination. The separation is made by anion exchange chromatography with 1 OM hydrochloric acid as eluent. After the separation, the three metals are selectively titrated with (ethylenedinitri1o)tetraacetic acid. The method has the advantage of speed, yet retains the accuracy of the conventional methods used for determining these elements.
C
for the determination of aluminum, calcium, and magnesium in various materials are particularly time consuming and tedious because these elements have no selective and specific chemical reactions. Consequently, all procedures have required the isolation of these elements from mixtures. A procedure for a rapid group separation of these three elements and their subsequent rapid and direct determination would be useful. Numerous multistep procedures have been based on precipitation, extraction, and electrodeposition for the separation of aluminum, calcium, and magnesium from mixtures containing iron, HEMICAL PROCEDURES
manganese, and titanium. A onestep separation of aluminum, calcium, and magnesium as a group is possible, as indicated by the data of Kraus and Nelson (8), on the adsorption of metallic ions on anion exchange resins in 10M hydrochloric acid. The separation would be rapid because aluminum, calcium, and magnesium (in contrast with iron, manganese, and titanium) are not adsarbed on the resin and would thus be collected immediately. The separation scheme would also be useful for determining aluminum, calcium, and magnesium in nonferrous ores and alloys because copper, cobalt, zinc, tungsten, molybdenum, zirconium, and tin, in addition to iron, manVOL 33, NO. 10, SEPTEMBER 1961
* 1351
ganese, and titanium, are adsorbed on the resin under these conditions (8). Of those elements that are not adsorbed, only the metals barium, strontium, vanadium, nickel, and the rare earths would interfere in the determination of aluminum, calcium, and magnesium by titration with (ethylenedinitri1o)tetraacetic acid (EDTA). Fortunately, these potentidly interfering elements are usually present a t insignificant concentration levels. Of the nonmetals that are not adsorbed, phosphate is a potential interference. The EDTA titration of various metals has been reported in the literature, and the interference of phosphate in these titrations has been recognized (3, IO). However, no reports have dealt with the selective titration of mixtures of these three metals either in the presence or absence of phosphate. This work describes a n analytical method for the removal of aluminum, calcium, and magnesium from other metals by ion exchange, and for their titrimetric determination with EDTA. MATERIALS AND EXPERIMENTAL W O R K
Solutions of the elements aluminum, calcium, and magnesium were prepared from the following primary standard substances: aluminum metal (99.99%) from the Johnson, Matthey, & Co., Ltd.; calcium carbonate (No, 4071) from the Rlallinckrodt Chemical Co.; and magnwium metal (99.99%) from The Dow Chemical Co. Ion Exchange Separation. Phosphorus, probably present as nonionized phosphoric acid, is not adsorbed on an anion resin in 10M acid. When separations in lithium chloride-hydrochloric acid (8) n-ere attempted, manganese was strongly adsorbed but phosphate was not adsorbed. Means were sought t o cause the adsorption of phosphate by performing the ion exchange separation in a solution of hydrochloric acid and a n organic substance. Increases in the adsorptivitics of metal ions on an anion resin in mised solvents have been reported ( 7 ) . Phosphate was strongly adsorbed on a resin column in 1OJ4 acid with a n eluent of 75 volume % ’ isopropyl ether25 volume % concentrated hydrochloric acid. However, the recovery of aluminum, calcium, and magnesium was only about 95Yo for each element. (The solubilities of the metal chlorides may have been exceeded in this eluent, with resulting precipitation on the column.) Thus, because phosphate could not be removed with iron, titanium, and manganese, the analysis scheme was developed to provide for the separation of everything but phosphate from aluminum, calcium, and magnesium, and for their determination in the presence of phosphate. 1352
ANALYTICAL CHEMISTRY
of 1-(2-pyridylazo)-2-naphthol in 50 ml. of methanol. Eriochrome Black T Indicator. Triturate 0.2 gram of the indicator with 50 grams of potassium chloride. Carbonate-Tetraborate Fusion Mixture. Thoroughly mix anhydrous sodium carbonate and sodium tetraborate decahydrate in a weight ratio of 5 to 1. Hydroxylamine Hydrochloride. 2,2’,2”-Nitrilotriethanol. Analytical Procedure. MATERIALS. Sample Solution. The treatment required for sample dissolution will Ion Exchange Resin. Remove the depend on the nature of the sample. fines from Dowex l-XlO, 200- t o 400Samples which contain no acid-inmesh anion exchange resin (J. T. soluble aluminum, calcium, or magBaker Chemical Co.) by mixing the nesium and which are low in silica can resin as a n aqueous slurry and debe dissolved in acid and added directly canting the fines. Remove traces of t o the ion exchange column. A preiron and aluminum remaining from liminary treatment with hydrofluoric the resin synthesis by washing alterand perchloric acids can be used to nately with concentrated hydrochloric remove silica from some samples quickly acid and water until the washings are and to render all constituents acidcolorless. soluble. (The excess hydrofluoric acid Column Preparation. Obtain a is removed by evaporating the mix%ure column approsimately 2.5 cm. in diamuntil perchloric acid fumes are evolved. eter and 23 cm. long and tapered a t one To ensure the complete removal of end. For convenience, provide a means fluoride, about 0.2 gram of boric acid for flow control, although for separations and a few milliliters of perchloric acid with 200- to 400-mesh resin this control are added and the misture again is not necessary. Place a tuft of glass evaporated to fumes. Some boric acid wool in the bottom of the column, add a may remain, but boric acid does not slurry of cleaned resin, allow it to settle, interfere in the titrations.) Certain and add more resin until the packed samples, however, will require a more bed is 18 cm. high. Into the column vigorous treatment, the procedure for insert a 1-holed rubber stopper fitted which is as follows: with a funnel. Pretreat the column Moisten 0.3 gram of sample in a 150with 100 ml. of concentrated hydroml. beaker with distilled watcr and add chloric acid and then 100 ml. of dis20 ml. of concentrated hydrochloric tilled water. If the eluate is still acid and 10 ml. of concentrated percolorless, pass 100 ml. of concentrated chloric acid. Heat moderately until hydrochloric acid through the column the sample has dissolved. Police the to prepare it for sample addition. beaker if any siliceous material adheres. REAGENTS.Standard Calcium SoluContinue heating until most of the tion, 0.01M. Accurately weigh and perchloric acid has been volatilized or dissolve 2 grams of dried primary until the salts begin to precipitate. standard grade calcium carbonate in a Cool and dilute to about 50 ml. with minimum of dilute hydrochloric acid, distilled water. Filter through a White and dilute to 2 liters with distilled water. Ribbon (No. 589) paper, and collect the EDTA Solution, 0.01M. Dissolve filtrate in a 250-ml. beaker. Retain 7.4 grams of disodium dibydrogen the filtrate. Wash the residue and (cthylcnedinitri1o)tetraacetic acid dipaper five times with distilled water. hydrate in 2 liters of distilled water, Boil the filtrate to near dryness and and store in a polyethylene bottle. add 1 or 2 ml. of concentrated hydroStandardize this solution with the chloric acid. Transfer this portion of standard calcium solution. To a the sample to an ion eschange column mensured volume of the calcium solution with a medicine dropper. Begin collect.add 10 ml. of pH 12.5 buffer and about ing the column effluent. Wash the 0.2 gram of Cal-Red indicator; then beaker several times with small amounts titrate with EDTA to a color change of of concentrated hydrochloric acid and red to clear blue. Place a filament add these washings to the column. lamp behind the titration beaker to Use a minimum of acid (less than 10 fwilitate observation of the end point ml.) to wash the beaker. in this and the other titrations. Transfer the filter paper containing Copper Solution, 0.01~V. Dissolve the residue to a platinum crucible and approyimately 3.4 grams of cupric add 6 or 7 drops of concentrated sulfuric chloride dihydrate in distilled water. and acid. Cautiously heat the crucible dilute to 2 h e r s . on a hot p k t e until the fumes from the Buffer, p H 12.5. Dissolve 280 grams sulfuric acid have been driven off and of potassium hydroside in 1 liter of disthe paper is charred. Burn off the tilled water, a
