Modification of Schwarz von Bergkampf's Method. for Determining AI uminum HENRI SHEHYN Aluminium Laboratories, Ltd., Arvida, Quebec, Canada
as the sulfide, it was concluded that the excess hydrogen sulfide remained in solution was protecting the cupferron from oxidation, and this was confirmed experimentally. It was found that the addition of 25 nil. of saturated hydrogen sulfide or sulfurous anhydride water before making the solution ammoniacal eliminated the trouble completely. In view of the inconvenience in preparing and handling hydrogen sulfide or sulfurous acid solutions, other reducing agents were triednamely, h>-droxylamine hydrochloride and hydrazine hydrate.
Schwarz von UerglLanipf's niethod for determining aluminum in the presence of titanium and iron has been modified to eliminate difficulties with high-iron ferroaluminurn alloys w-hen 8-quinolinol is used to precipitate aluminum.
I
S T H E classicnl methods for the determination of aluminum
in the presence of titanium and iron, it was customary to precipitate the three elements together with ammonium hydroxide and to obtain the sum of the oxides; after determination of iron and titanium, alumilium was obtained b y difference. 111 1!)31, Schware von Bergkampf ( 1 ) proposed a method in nliich iron was precipitated as the sulfide in the presence of tartrate. nEter which titanium was precipitated with cupferron without eliminating the excess hydrogen sulfide from the filtrate; he then precipitated alumi~iumxvith 8-qninolinol(oxine) in ammoniacal medium without eliminating hydrogen sulfide arid excess cupferron.
l'ahle I.
Table 111. Determination of Iluniina in High-Iron Bauxites Sample S o .
Sone
.\nalyst
R
5 0 . fi 48 9
88 123
57 5
These two reagents achieved the intended purpose, but tlie hydrazine hydrate (or a hydrazine salt) proved to be the most efficient by far. When aluminum oxinate precipitat,es were digested in the presence of cupferron and hydroxylamine hydrochloride for 0.5 hour, brownish streaks began to appear; similar precipitates digested in the presence of 1 ml. of 65% aqueous hydrazine hydrate (or the equivalent amount of hydrazine sulfate) were still free from cupferron decomposition products after 4 hours.
A I , 31%. Present Founti 10.24 10a9J 10.24 10 24 10.1.5 10.24 10.22 10 24 10.24 10 '4 10 23 10.24 10 ? I ) 10.24 I 0 20 ~
Sone 50 nil. of saturated HsR soiution 50 ml. of s a t u r a t e d H2S solution 25 ml. of s a t u r a t e d SO? solution 25 ml. of s a t u r a t e d 502 solution 1 nil. of (i5(? aqucoiis hydrazine hydrate 1 nil. of ii.i'-, aqueoris hydrazine 115-drate
Analy9t A
44
Determination of Aluminum in Spthetic Samples Reducing Agent .lil,ied
.il.rO~ _ _ _ ~Found, 7,
PROCEDURE
After removing the iron Tvith a niercury cathode and precipitating titanium with cupferron from an acid solution according to the usual procedure, add to the cupferron-containing filtrate 5 ml. of tartaric acid (100 grams per liter) and 1 ml. of 65% aqueous hydrazine hydrate (or its equivalent in hydrazine sulfate or hydrochloride). A lvhite precipitate of hydrazine sulfate may form but this willdisappear xhen the solution is made ammoninc:tl and heated. Add rapidly sufficient ammonium hydroxide t o provide a 5-ml. excess per 100 ml. of solution, heat to 70' C., and precipitate aluminum Kith a slight excess of 5% oxine solution in acetic acid. Digest for 30 minutes, filter aluminum oxinate, and complete the determination iri the known manner.
Precipitate so contaniinated wit11 t a r r y drcoiiiposition product.; of cup-
ferron tliat titration \\-a? iinIioa,ihle.
This excelleiit method has been used successfull>- for many years on niaterials containing moderate amounts of iron, but Then high-iron ferroaluminuni :illoys containing titanium had to be analyzed, the removal of iron as the sulfide was replaced by electrolysis on a m o c i q - cathode. This change did not affect the cupferron precipitation of titanium in any way, but i t caused dificult,ies in the precipitation of aluminum with 8-quinolinol;
RESULTS
Table 11. Alunlinum Determinations on IronTitaniuni-,iluminuni .illoys Sample
Reducing Agent Used Present 1 Kone 4.53 la 2.5 ml. of s a t u r a t e d SO? solution lb 50 ml. of s a t u r a t e d HzS solution IC 50 ml. of s a t u r a t e d HzS solution '2 1 ml. of 65Ya hydrazine hydrate 5.91 ?* 25 ml. of s a t u r a t e d SO2 solution Precipitate contaminated, titration impossible NO.
'1
AI,
0;
Found 4 5i 4 , s
4.50
5.87 S.83
when the solutions were made ammoniacal and warmed up the cupferron began to decompose, and the aluminum ovinate was contaminated with tarry decomposition products which made the subsequent titration difficult if not altogether impossible. As this trouble had never been experienced when iron was removed
Table I 9 h O w S results obtained on :L pure aluminum sulfate solution of known aluminum content. Ten-milliliter aliquots were treated with tartaric acid, 1.5 ml. of 36AVsulfuric acid, and water to make a 200-ml. total volume. The solutions were cooled to 50" C. and 5 ml. of cold 6% cupferron solution were added, followed by 50 ml. of 1Y hydrochloric acid. Such a mixture approximated closely the composition of the filtrate from a c u p ferron precipitation. Aluminum was next precipitated both in the presence and in the absence of the reducing agents shown in the table. Typical results on irori-titanium-aluminum alloys are shorn-n in Table 11. Table 111 shows results obtained on three high-iron bauxite samples by two analysts working i n different laboratories. LITERATURE CITED
( 1 ) Schwarz von Bergkampf, E., 2.anal. Chern., 83, 345 (1931). R E C E I V EfDo r review November 1 . 1954.
1341
.kccepted March 9. 1955
