Determination of Zirconium by Precipitation from Homogeneous Solution HOBART H. WILLARD AND R. B. HAHN', University of Michigan, A n n Arbor, Mich.
Zirconium can be precipitated quantitatively from solutions 3.6 N in hydrochloric or sulfuric acid by adding 15 to 20 ml. of trim.ethy1 phosphate and heating for 12 to 15 hours. The precipitate obtained is a mixture of zirconyl methyl phosphate, ZrO[H(CHs)(PO,>]p.2H20,and zirconyl phosphate, ZrO(HPPOI)~.Upon ignition at 900" to 950" C. this precipitate is completely converted to zirconium pyrophosphate, which is weighed. The method can be used to determine zirconium in samples containing from 2 to 60 mg. of zirconium oxide. Antimony, bismuth, cerous, and stannic ions interfere. Large amounts of ferric, titanium, thorium, and uranyl ions give high results. When acid solutions containing zirconyl ions are treated with an excess of meta-
0
Preliminary experiments showed that dense, crystalline precipitates resulted when 3.6 N sulfuric acid solutions containing zirconyl ions were heated with triethyl phosphate, trimethyl phosphate, and tetraethyl pyrophosphate. After the corresponding precipitate was filtered off and the filtrate made alkaline with ammonium hydroxide, no precipitate of zirconium hydroxide resulted; the zirconium was quantitatively precipitated by the hydrolysis of the organic phosphates. Quantitative precipitation could be achieved with triethyl phosphate only upon heating for 18 to 24 hours a t the boiling point, whereas trimethyl phosphate and tetraethyl pyrophosphate gave quantitative precipitation upon heating for 12 to 15 hours. As triethyl phosphate had no advantages over the other reagents, no further studies were made with it. Further investigation of tetraethvl pyrophosphate showed that this reagent also formed a precipitate when heated with ferric ions. As iron is usually associated with zirconium in its ores and alloys, no further inve3tigations were made with this reagent and full attention was given to trimethyl phosphate. Trimethyl Phosphate a s Reagent. As the precipitate obtained by the hydrolysis of triethyl phosphate \vas shown to have the formula ZrOH(C2Hj)(P04)2.2H20( 6 ) , the precipitate obtained with triethyl phosphate was expected to be ZrO [H(CHI)(POJ]2.2H20. The precipitate, homerver, was found to be variable in composition and x-ray diffraction studies showed that it also conCained varying amounts of zirconyl phoaphate. Hence, accurate results could not be obtained by TT cighing the precipitate directly. Upon ignition a t 950" C. for 2 hours the precipitate was converted completely to zirconium pyrophosphate, ZrP20e. X-ray diffraction pictures showed that this ignited precipitate was of the same composition as that obtained by ignition of pure zirconyl phosphate. To study the effect of different acids of various concentrations, the following procedure was used:
XE of the most widely used methods for the deteimination of
zirconium consists of precipitating the zirconium as zirconyl phosphate, ZrO(H2P04)2, from a warm 3.6 ,V sulfuric acid Yolution by addition of a large excess of ammonium phosphate. lfter filtering and washing with a 5'3$ solution of ammonium nitrate, the precipitate is ignited to the pyrophosphate, ZrP20,, and weighed (2-4. The method can be used accurately only for the determination of small amounts of zirconium (up to 20 mg. of zirconium oxide). The precipitate of zirconyl phosphate is bulky and gelatinous, and therefore difficult to filter and wash. Upon ignition the precipitate decrepitates and losses may occur. Many normally gelatinous precipitates can be improved by sloivly forming the precipitating ion in homogeneous solution by hydrolysis. N'illard and Freund (6) used triethyl phosphate to fractionate zirconium and hafnium by precipitation as the phosphates. They found that acid solutions containing zirconyl ions gave a dense crystalline precipitate of zirconyl ethyl phosphate, ZrO [H(C,H,) (POa)I22H20, when heated with triethyl phosphate. This method gave a more efficient fractionation than the usual nicthods in which the orthophosphate ion \vas added directly to the solution (6). S o attempts were made by the authors, however, to use this reagent for the separation and quantitative determination of zirconium in the presence of other elements. PRECIPITATION AND DETER\IINATION OF ZIRCOYIUM BY HYDROLYSIS OF ORGANIC PHOSPHATES
In this investigation of the quantitative precipitation of zirconium by hydrolysis of organic phosphates, three reagents were studied: triethyl phosphate, trimethyl phosphate, and tetraethyl pyrophosphate. All these substances are completely miscible with water and dilute mineral acids. Khen added to a solution containing zirconyl ions, no precipitates resulted unless the solutions were heated for a time. Experimental. Standard solutions were prepared by dissolving chemically pure zirconium sulfate and zirconium nitrate in 1 N sulfuric acid, taking 25-m1. portions with a pipet, and determining the zirconium content by precipitation with cupferron following the procedure given by Hillebrand and Lundell ( 1 ) . The same pipet was used to measure the samples used for the experimental work. I
phosphoric acid, a soluble metaphosphate complex is formed. A precipitate of zirconyl phosphate is slowly deposited at room temperature. The precipitate thus obtained is more dense than the precipitate formed by direct addition of a soluble orthophosphate, althoughnot so dense as that obtained by- precipitation with trimethyl phosphate. This precipitate does not decrepitate upon ignition and is completely converted to zirconium pyrophosphate by heating at 900" to 950" C. RIetaphosphoric acid can be used to determine zirconium in samples containing from 0.2 to 200 mg. of zirconium oxide. Best results were obtained by adding a large excess of metaphosphoric acid to solutions 3.6 N in sulfuric acid. Bismuth, stannic, and perchlorate ions interfered.
Procedure. The volume of the solution as adjusted to 150 t o 200 ml. and the acidity adjusted to the desired concentration. Fifteen to 20 ml. of trimethyl phosphate were then added and the sample was heated just under its boiling point for a t least 12 hours. Longer periods of heating are not harmful. Water was added occasionally to replace that lost by evaporation. After heating for a sufficient length of time, the solutions were allowed t o cool, then filtered through No. 40 Whatman filter paper and washed with 250 to 300 ml. of cold 5% ammonium nitrate solution. The beaker was wiped out with a small piece of filter paper
Preaent address, Wayne University, Detroit, Mich.
293
294
ANALYTICAL CHEMISTRY
to remove any zirconyl phosphate which still adhered to the sides of the beaker The precipitate was ignited over a Meker burner until the filter paper had completely charred, then in a muffle a t 900" to 950' C. to constant weight. The theoretical factor, Zr02/ZrP20, = 0.4657, was used to compute the weight of zirconium oxide (Table I). All results given in this paper are averages of two closely agreeing determinations.
.
These data show that trimethyl phosphate can be used to precipitate zirconium quantitatively from 3.6 A' solutions of hydrochloric, nitric, or sulfuric acid. If the solutions are filtered hot or if the acid concentrations are more than 3.6 IT, the results ill be low, owing to the increased solubility of the precipitate. Sulfuric and hydrochloric acid solutions of the above concentration must be heated for a t least 12 hours to ensure complete precipitation, and more dilute solutions must be heated much longer. Sitric acid solutions must be heated for at least 24 hours. Perchloric acid gives low results probably due to the coprecipitation of some perchlorate. Trimethyl phosphate was used to precipitate various amounts of zirconium from 3.6 hJhydrochloric and sulfuric acid solutions to determine the useful range of the method (Table 11). The procedure followed as the same as in the previous experiment. Tables I and I1 show that trimethyl phosphate can be used as a reagent to determine zirconium in samples containing from 2 to 60 mg. of zirconium oxide. Larger amounts give loir results, probably caused by partial hydrolysis of the precipitate.
Table I.
Determination of Zirconium in Pure Solution
Acid K e i g h t of and Hours ZrPzO7, Xormality Heated Gram 3.6 N &SO4 8 0.1251 12 0.1209 3.6 2%' HzSO4 12 0.1290 7.0 N HzSO4 24 3.6 N "01 0.1296 0.1212 12 3.6 N HCl 12 0.1288 7.0 N HC1 12 0.1234 3.6 2%' KC104 0.1262 12 3.6 N HzSOd Zr detected in filtrate. b Filtered hot.
ZrOz Calcd., Gram 0,0581 0,0862 0,0599 0,0602 0.0663 0.0598 0.0573
ZrOz Taken, Gram 0.0602 0.0562 0.0602
0.0586
0.0602
0.0602 0,0562 0.0602 0.0602
Error, Gram -0.0021a 0.0000 -0.0003 0,0000 +o. 0001 0.0004 -0.0029 -0.0016b
-
Table 11. Determination of Range of Method
Acid
Total Vol. of Soln., 311. 50 50 100 100 100 100 100 100
150 150 175 175 200 200
(CH3)sPo4 Weight of Added, ZrPnO;, RI1. Gram 0 0.0048 5 0.0047 0.0098 10 0.0097 10 0.0240 10 0,0238 10 0.0480 10 0.0478 10 0.2400 30 0.2395 30 0.3578 35 35 0.3574 0.4800 45 0.4770 45
ZrOz Calcd., Gram 0,0022 0,0022 0.0046 0.0045 0.0112 0.0111 0.0223 0,0222 0.1115 0.1113 0.1663 0.1661 0.2230 0.2217
ZrOr Taken, Gram 0.0022 0 0022 0 0045 0.0045 0 0112 0 0112 0 0225 0 0225 0 1124 0.1124 0 1686 0.1686
0.2248 0.2248
Error Grad 0 0000 0.0000 +0 0001 0 0000 0 0000 -0 0001 -0 0002 -0 0003 0.0009 -0 0011 -0 0023 -0.0025 -0 0018 -0.0031
-
,
Table IV.
Acid and Normality 1.8 N HzSO4 3.6 N HzSO4 7.2 A' HzSOh 3.6 1%' HC1 3.6 N "Os 3.6 N HClO4 3.6 JV HzSO4 a Filtered hot.
..
.. ..
ZrOz Calcd., Gram 0.0555 0.0564 0.0555 0.0428 0.0604 0,0592 0.0426
ZrOz Taken, Gram 0.0562 0.0562 0.0562 0.0433
Error, Gram -0.0007 4-0.0002 0.0007 -0.0005
0.0602
+O.OOOZ
0.0602 0.0433
-0.0010 0,0007"
-
DETERMINATION OF ZIRCONIU3ZI BY HYDROLYSIS OF METAPHOSPHORIC ACID
In studying the reaction of metaphosphoric acid nlith the zircony1 ion, it was found that a soluble metaphosphate complex x a s formed R-ith the zirconyl ion in acid solutions. When these solutions were allowed to stand a t room temperature, a granular precipitate of zirconyl phosphate was thrown down. X-ray diffraction pictures of this precipitate shoived it to be identical with the precipitate obtained by adding a soluble orthophosphate to acid solutions of the zirconyl ion. Although the precipitate obtained with metaphosphoric acid R as not so dense and crystalline as those obtained by the hydrolysis of organic phosphates, it was much better than that obtained by direct precipitation with the orthophosphate ion. Further experiments showed that the zirconium was quantitatively precipitated if a large excess of metaphosphoric acid was added. Experimental. To determine the conditions necessary for quantitative precipitation of zirconium, precipitations were made in the presence of different acids of various concentrations. The following procedure was used in the absence of other metals: Five grams of reagent quality metaphosphoric acid dissolved in 25 ml. of water were added to 150 to 175 ml. of an acid solution containing a known quantity of zirconyl ions. This solution TT as allowed to stand 12 hours a t room temperature. During this time a precipitate of zirconyl phosphate was slowly formed. The solution was then heated to boiling and maintained just under its boiling temperature for 1 hour to ensure complete hydrolysis of the metaphosphoric acid. After cooling, the solution was filtered and the precipitate washed with cold 57, ammonium nitrate solution and finally ignited a t 900" to 950' C. in a muffle. The factor ZrO*/ZrPnOi= 0.4657was used to compute the weight of zirconium oxide from the weight of pyrophosphate _ _ - . (Table IV).
Separ ations in 3.6 hr HC1 ZrOz ZrOz calcd., taken, Error, gram gram gram 0.0624 0.0602 $0.0022 0.0623 0.0602 +0.0021 0.0604 0.0562 +O ,0042 0.0660 0.0602 +0.0058 0.0609 0.0602 +0.0007 0.059s 0.0562 +0.0036 0.0567 0.0562 +0.0005 0.0562 0.0562 0.0000 0.0722 0.0562 4-0.0160 0.0567 0.0562 +0.0006 0.0563 0.0562 4-0.0001
.. ... ..
Weight of ZrPzOr, Gram 0.1194 0.1213 0.1194 0.0921 0,1299 0.1274 0.0916
Separations. To determine the influence of other ions, precipitations were made both in 3.6 A- sulfuric acid and in 3.6 S hydrochloric acid using the procedure described. Successful determinations were made in the presence of aluminum, arsenate, borate, cadmium, calcium, chromic, cobalt, cupric, magnesium, manganese, mercuric, nickel, potassium, sodium, tartrate, vanadyl, and zinc ions. When more than 0.025 gram of ferric or 0.010 gram of thorium ions were present, high results were obtained. The presence of uranium also caused slightly high results. Antimony, bismuth, cerous, and stannic ions interfered. The extent of these interferences is given in Table 111.
Table 111. Interferences Separations in 3.6 N HzSOc Added ZrOz ZrOz Substance, calcd.. taken. Error, Gram gram gram gram 0.26 S b + + + a 0.0622 0,0602 +o .0020 0.25 B i + + + 5 0.0674 0.0602 4-0.0072 0.20 C e + + + 0.0587 0.0562 +0.0025 0.25 S n + + + + " 0.0725 0.0602 +0.0123 0.25 UO*++ 0.0610 0.0602 +0.0008 0.25 F e + + + 0.0602 0,0562 +0.0040 0.05 F e + + + 0.0569 0.0562 +0.0007 0.025 F e + + + 0.0563 0,0562 +0.0001 0.050 T h + + + + 0.0706 0.0562 +-0.0144 0.010 T h + + + + 0.0568 0.0862 4-0.0008 0.005 T h + + + + 0.0563 0.0562 +0.0001 0.100 TiOpb 0.0577 0.0562 4-0.0015 0.025 TiOzb 0.0572 0.0562 +0.0010 0.010 TiOgb 0.0563 0.0562 +0.0001 a 10 g. of tartaric acid added t o HrS04 solution. b 5 ml. of 30% HzOz added every 2 hours.
Determination of Zirconium in Pure Solutions
....
.... ....
Quantitative results were obtained in the 3.6 X nitric and sulfuric acid solutions. Percliloric acid gave low results, as it did in precipitation by the hydrolysis of organic phosphates. The determinations made in the hydrochloric acid were slightly low. The precipitates from the sulfuric acid were the moqt dense; therefore, this acid was used in the following experiments t o determine the range of the method. Varying amounts of zirconyl sulfate were added to 3.6 N sulfuric acid solutions and the zirconium was determined by the procedure described above (Table V). Tables IV and V shorr that metaphosphoric acid can be used as a reagent to determine 0.2 to 200 mg. of zirconium oxide. For amounts less than 10 mg. - of zirconium oxide, the method had no particular ad-
V O L U M E 2 1 , N O . 2, F E B R U A R Y 1 9 4 9
295
Table 1.. Determination of Range of 33ethod Total
Vol. of Sohition 311.
_
~
HPO< .4(ldml, Orarii
ZrP20-, Gram 0 . no04 n.0018 0 0041 0.0182 n ,0372
n 2190 0.2392 n .329n n.mi
-_ -
ZrO? Calcd., Gram
o n
ZrO? Taken, Gram
eon?
Error, Gram 0 0000
-0.nno~
on08 o.ooi9 0.0083 0.0174 0.1017
-0.0002 -0.0001 -won01 in.0001
n nono
0.1204 0 1.529 0.2036
f 0 0004 +o ,0004
Table YI. Interferences ZrO?
Zr02
.\dded
Substnnr e, Gram 0.10 C e + - + 0.10 T t i - + - 0.025 TIi-’-o.oin V - T + ~
n.noi - r t L + + 0.10 Ti02 0.10 Ti02 0.0.50 Ti&
+ 3IH?02 ml 30vc H?O? 0.020 Ti02 + FIKl? 0.010 TiO? H?02 A
1.
0.10
0.2.5 0.10 0.0.50 0.025 0.010
Calcd.. Gram 0,0640 0,0.558
0.0fi.51 0.0310 0,030s 0 0985 0.0.517 0.0i13 o.niii
0.0.509
r o ?- -
0.0.514
Fij-+-
0.0541
Fe+’+
0,0.596 0.0.598
Fr Fi.
-- f + +
0.0600 0 ,ocon
0.20 B i ^ t HzCaHaOe 0.1329 0.20 S O - + - H ~ C ~ H ~ O ~0.1399 0.0600 0.26 TiOi f 5 ml. H?O? 0.10 T h T + + + 0.0523 0.050 Th;: 0,0600 0.0fio0 1.0 Fe
+
’
Taken, Gram 0.0.508 0.0.508 0 OR03 0.0.508 0,0508 0.0.m 0.O.iOY 0.0.508
n 0.508 0 0.508 n . onn8
0.0i08 0.0602
o ofin:!
0.0R02 0.0’502
n, m a
0.03fi2 0.0502 0 .on09 0.ofi02 0.0fi02
Error.
Gram
Ao.nix
Ao.onin
-LO.OO~~
+n.nnoa 0 onno
A n . 0473
cn
0009 C 0 000.5 +o on03 ~0.0001 +0 0006 +O ,0033 - 0 ,0006 -n. 0001- 0 . onoa
- 0.0002
+o
,0767
t n ,0837 - 0 . 0002 t o ,0015 - 0.0002 - n .oooz
wiped out with a small piece of filter paper to remove any zirconyl phosphate which adhered to the walls of the beaker. The filter paper and the precipitate were slowly charred, then ignited t o constant weight at 900” to 950” C. in a muffle. The precipitate of zirconium pyrophosphate should be pure white. The theoretical factor ZrO?/ZrP,O, = 0.1657 was used to compute the weight of zirconium oxide. If antimony was present, 10 grams of tartaric acid were added to the sulfuric acid solution to prevent hydrolysis of the antimony ion. Zirconium can be determined in the presence of antimony and bismut,h if the precipitation is made from 3.0 S hydrochloric acid solution instead of sulfuric acid. I n this case the precipitate must be XTashed first with 200 ml. of 5vo hydrochloric acid solution which a1w contains 2pc of ammonium phosphate, then n-ith 100 ml. of 5 7 ammonium nitrate solution. If more than 25 mg. of iron are present, most of it should be removed by extraction with ether. The zirconium determination is then carried out as directed above. The method will give good separations from as much ai: 0.250 gram of titanium oside or 0.050 gram of thorium if a double precipitation is made. The first precipitation should be carried out in the usual manner, and the precipitate filtered and wa.;hed with ammonium nitrate. The filter paper and the precipitate are then put back into the original beaker, and 20 ml. of concentrated nitric acid, then 20 nil. of concentrated sulfuric acid are added. The beaker should be covered n-ith a watch glass and heated gently until all the filter paper is destroyed. The watch glass is then elevated and the solution evaporated t o fumes of sulfur trioxide. The zirconyl phosphate dissolves in the concentrated sulfuric acid. This solution is cooled and diluted to 200 ml. with water, and 5 ml. of 30c.S. hydrogen peroxide, then 5 grams of metaphosphoric acid dissolved in 25 ml. of water are added. The precipitation, filtration, etc., are carried out as previously directed. ANALYSIS O F A ZIRKITE ORE
vantage over direct precipitation TT ith ammonium phosphate. I n either case the precipitate is small and can be easily filtered and washed. The method is not recommended for amounts more than 200 mg. of zirconium oxide. With larger amounts the bulk of the precipitate n-ould make its manipulation difficult. To investigate the separation from other metals, precipitations JTere made from 200 ml. of 3.6 S sulfuric acid using the procedure described. Successful separations xere made from aluminum, arsenate, borate, cadmium, chromic, cerous, cobalt, cupric, magnesium, manganous, mercuric, nickel, potassium, sodium, tartrate, vanadyl. yttrium, and zinc ions. The presence of more than 0.025 gram of ferric ions, 0.010 gram of thorium, or 0.020 gram of titanium oxide interfered. Bismuth, stannic, and perchlorate ions int,erfered. The estent of the interferences is shown in Table VI. Successful determinations 11-ere made in the presence of 0.25 gram of titanium dioxide and 0.050 gram of thorium by using a double precipitation. Large amounts of iron can be removed by ether extraction and the zirconium then determined in the reniaining solution. Determination can also be made in the presenre of antimony if tartaric acid is added to prevent hydro11
Procedure. Ore samples were put in solution by fusion ‘n-ith borax and treatment n-ith acids ( 5 ) . Alloy samples were dissolved in hydroc!iloric, nitric, or sulfuric a c d . The solutiori was evaporatd with sulfuric acid t o remove the excess of the other acid.;. If barium, lead, or large amounts of calcium were present, thev w c r ~removed by precipitation with sulfuric acid. The total volume of the solution was adjusted t o 150 to 200 ml. and made 3.6 S in sulfuric acid (10C, b,v volume of concent,rated sulfuric acid‘l. This solution n-a? cooled and 5 grams of metaphosphoric acid diqsolred in 25 ml. of n.ater n-erc added to it. If titanium waq present, 5 ml. of 3 0 7 , hydrogen peroside were also added. This solution was allowed to stand a t room temperature for about 12 hours, a t the end of which time a granular precipitate of zirconyl phosphate had settled out. The solution was then heated just under its boiling point and held a t this temperature for 1 hour. If iron m s present, the heating was continued for an extra hour to ensure complete solution of any precipitated ferric metaphosphate. The sample was allowed to cool to room temperature, then filtered through Whatman Yo. 1 0 filter paper, and wa3hed with about 300 to 500 ml. of 5% ammonium nitrate solution also at room temperature. The beaker was
The method was checked by determining the zirconium in a zirkite ore, shown by a qualitative analysis to be composed largely of zirconium oside. Silica, ferric oxide, titanium oxide. and a trace of vanadium were also present. Thorium, aluminum, and the rare earths were not present in detectable amounts. For quantiative analysis, the ore was put into solution by fusion with borax. After removal of t,he ea, the zirconium as determined by the standard cupferron method ( 6 ) . The zirconium was also determined n-ith metaphosphoric acid using the procedure given.
Table \ 11. Analysis of Zirkite Ore Cupferron Sample, Zr02, Sample 1 2 3 Av.
AIg.
0,2000 0.2000 0.4000
7%
74.51 74.20 74.38 74.36
Metaphosphoric Acid Sample, ZrO?, LIg.
“c
0.1000 0.1000 0.2000
74.3.5 74,33 74.23 74.38
The determinations made with the metaphosphoric acid are in close agreement JTith those of the standard cupferron method. The metaphosphoric acid method is more rapid and requires fev-er separations and manipulations. It is, therefore, recommended for the determination of zirconium in ores that contain small amounts of iron, titanium, and thorium. LITERATURE CITED
Hillebrand, 11’. F.. and Lundell, G. E. F., “Applied Inorganic Analysis,” New York, John TViley & Sons, 1929. (2) Lundell, G . E. F., and Knon-les, H. B., I n d . Eng. Chem., 12, 562
(1)
(1920). (3) Lundell, G.
E.F., and Knowles, H. B., J . Am. Chem. Soc., 41, 1801 (1919). (4) Ibid., 42, 1439 (1920). (5) U. S. Bur. Mines, Bull. 212 (1923). EXG.CHEM.,ANAL.ED.,18, (6) Willard, H. H., and Freund, H., IXD. 195 (1945). RLCEIVED M a y 3, 1948. From a dissertation submitted by R. B. Hahn in partial fulfillment of t h e requirements for the degree of doctor of philosophy in t h e University of Michigan, February 1948.
