Precipitation of Nickel and Cobalt Sulfides in a Crystalline State By Hydrogen Sulfide in the Presence of Pyridine' E. -4.OSTROU&IOV, Institute of Economic Ilineralogy, ~ I O S C O W U., S. S. R.
I
i\: THE separation of nickel and cobalt from calcium, magnesium, and alkalies, nickel is generally precipitated by ammonium sulfide ( 3 ) . This method, holvever, has a number of drawbacks, which are the source of errors and make slower the course of the analysis: (1) Sickel and cobalt sulfides are precipitated in an amorphous state, and because of a strongly developed surface have a great adsorbing capacity; (2) the filtration proceeds slowly; (3) nickel and cobalt sulfides (particularly the former) easily form colloidal solutions, m-hich pass through the filter; and (4) when carbonate is contained in ammonium sulfide, alkaline earth metals may precipitate with the sulfides. One of the most convenient methods is electrolysis with a mercury cathode. But in the case of the salts, when the amount of nickel and cobalt is large, the deposition of the metal continues for rather a long time, sometimes is not complete, and, in addition, i t is necessary to purify large amounts of mercury. The most desirable method was to precipitate nickel and cobalt in a crystalline form in order to minimize adsorption, to obtain the separation in one precipitation without resort to reprecipitation; and to accelerate the process of filtration. Haring and Leatherman and Haring and Westfall (1, 2 ) give directions concerning the precipitation of nickel and cobalt sulfides in the dense modification in a solution of definite pH, ammonium acetate being used as a buffer. However, these authors note that the sulfide precipitates obtained were readily oxidized when exposed to air, while they found i t impossible to wash the cobalt sulfide precipitate, because of rapid oxidation. The present author proposes a new method of precipitating nickel and cobalt sulfides, based on the fact that from the pyridine-containing solution hydrogen sulfide precipitates nickel and cobalt sulfides as a lustrous crystalline precipitate, which settles quickly, and filters very easily. Owing to its crystalline structure the precipitate has a niinimum adsorption capacity and is practically not oxidized a t all during filtration. Moreover, pyridine does not form any carbonates, and the possibility of the alkaline earth being coprecipitated as carbonates with the sulfides is eliminated. The process of sulfide precipitation in the crystalline form is unquestionably influenced by the p H of the solution, established by the addition of definite amounts of pyridine, but the pyridine itself also exercises a certain specific influence, resulting in the formation of coarsely crystalline precipitates, very slowly oxidizable during filtering.
out in the presence of ammonium salts have shown that the latter exercise no influence upon t'he precipitation of the sulfides. If feebly acid solutions of nickel and cobalt are neutralized by a 20 per cent pyridine solution against methyl red as an indicator and then heated to boiling, an excess of pyridine is added, and hydrogen sulfide is passed in, the sulfides are precipitated in larger crystals than when a neutral solution is used. h study of this phenomenon has shown that the presence in the solution of a pyridine salt favors the format'ion of larger crystals of sulfides, especially in the case of cobalt sulfide. A lowering of the p H of the solution in which the precipitation of sulfides is carried on seems to favor the formation of crystals. The influence of the pyridine salt may be accounted for by its buffer action in lowering the p H of the solution, to which free pyridine is added. However, the neutralization of the acid solution by pyridine is difficult, owing to the coloration of the cobalt and nickel solutions. Therefore the author added to the neutral or very feebly acid solution analyzed a solution of pyridine salt obtained by neutralizing a definite amount of acid by pure pyridine to an orange color against methyl red. After having established the completeness of the precipitation of nickel and cobalt under various conditions of temperature and amount of reagents added, and having obtained good results, the author began experiments on the separation of nickel and cobalt from calcium, magnesium, and alkalies. For these experiments, definit'e volumes of metal salt solutions were used, the titers of which had been previously determined gravimetrically. To the neutral or feebly acid solution in an Erlenmeyer flask a solution of the pyridine salt of hydrochloric acid was added (obtained separately by neutralizing 0.5 ml. of hydrochloric acid sp. gr. 1.12, diluted with 25 ml. of water, with pure pyridine, using methyl red as an indicator). After this, the solution was diluted with water to about 150 ml. and heated to boiling. Then about 5 ml. of a 20 per cent pyridine solution were added, and hydrogen sulfide was passed in for about 15 minutes with frequent shaking. The nickel and cobalt were quantitatively precipitated as crystalline sulfides. The precipitate sometimes adheres to the malls of the flask, and after standing exposed to air it is rat,her difficult to remove this film from the wall of the vessel. Therefore before starting the filtration, a piece of ash-free filter paper was placed in the flask and was used to remove the sulfide precipitate adhering to the walls, with the aid of a glass rod. The precipitate ivas then filtered off and washed with hydrogen sulfide water. Kickel sulfide was placed, together with the filter paper, in a flask and dissolved while being heated in nitric acid, the solution was diluted with water and filtered off, and the nickel was then precipitated by dimethylglyoxime &s usual. The cobalt sulfide precipitate, together with the filter paper, was carefully ashed in a weighed porcelain crucible, gently heated, and converted to sulfate by evaporating with sulfuric acid. The sulfate was first heated on an electric plate; then the crucible with the cobalt sulfate was placed in another larger porcelain crucible on an asbestos ring, carefully ignited for about 40 minutes with a dull red heating of the bottom of the external crucible, and finally weighed as cobalt sulfate. I n the filtrates from sulfides, after acidulating them with hydrochloric acid and boiling to remove the hydrogen sulfide, calcium, magnesium, and alkalies were determined. Calcium and magnesium were determined in the usual way: calcium, by pre-
Experimental For his experiments the author used solutions of nickel and cobalt chlorides, the titer of which had been previously established gravimetrically. If to a neutral solution of a nickel or cobalt salt, heated to boiling, a pyridine solution is added, and hydrogen sulfide is then passed in, nickel and cobalt are quantitatively precipitated as sulfides in a crystalline state. Kickel sulfide is obtained in larger crystals than cobalt sulfide. Tests carried 1
Translated into English by -1.S. Braslinina.
693
Experiments 1
2 3 4 5 6
0.0331
.... . . .
0.053; 0.053T
10 11
....
12
0 0531 0 0531
0.053i 0 .0 5 3 i
.... ...
9
Talen----------? COO CaO Ginm Gram
Gram 0 0537 0 0537
8
7
TABLE I. SEPARATION OF NICKEL ASD COBALT
---Xi0
.
.
....
-
0 0 0 0 0
0504
0304 0504 0504
0504 0.0804
0.0531 0 0531
0.0531
.... ... . .
hIgO
Gram
....
.... ....
0.0308 0.Oj08 0.0508
.... ....
0.0~08 0.0608 0,0508
-------
5 6
NiO Gram 0 . 0537 0.0537 0.0537 0,0537 0.0537 0.0537
9 10 11
.... ... . . ...
1 2
3 4
7 8
12
NiO Gram
0 031; 0 0.537 0 0336 0 O53T o 0.530 0 0.3G
Found-COO Gram
.
. .. . . 0,0505
0.0503
0.0506
. . . . .
0.0504 0 0503 0,0505
n ,0530 ....
.... ....
0.0533 0.0330 0.0529
....
MgO Gram
0.0~08 0.0508
0.0508
.... .... . . .
....
....
Taken-COO NazO Gram Gram .... 0.0527 0.0527 .... 0.0527 .... ..
0 :0504 0,0504 0.0504 0.0604 0 0504 0,0504
.... .... ....
0,0527 0.0527 0,0527
.... . . ...
IizO Gram
.... ....
.... 0.0512 0,0512 0.0512
....
.... 0:0;12 0.0512 0.0812
---
COO
CaO
\IpO
Gram
Gram +O 0001
C r i l ft1
-0 0 -0 0 -0 -0
0001
0000 0001 0000
+0 000‘ - 0 0001 .. . .
0001 0001 T O 0001
0001
-0 +0 0 -0
0,0507 0 0508 0.0509
:
Practical Directions This method may be very conveniently applied to filtrates obtained in the separation, with the aid of pyridine, of the subgroup of iron from bivalent metals of the third analytical group, and alkaline earths, magnesium, and alkalies (4, 5, 6). To precipitate cobalt and nickel, the filtrate is heated, a solution of Dvridine salts is added, and the filtrate is treated with hydrogensulfide. If the solution is acid, and no determination of alkalies is required, it is neutralized with a solution of sodium carbonate until a turbidity is developed which is cleared by a few drops of dilute hydrochloric acid, and a pyridine salt solution is added (see above). The solution is nom heated to boiling and 5 to 10 ml. of 20 per cent aqueous pyridine solution are added according to the approximate proportion of 5 to 6 ml. to 0.1 gram of nickel or cobalt (a moderate excess of pyridine is not objectionable) and, with B volume of about 150 to 200 ml , hydrogen sulfide is passed in to precipitate the nickel or cobalt. If alkalies should be determined in the filtrate, the excess of acid is removed by evaporating on a water bath. If the concentration of cobalt or nickel salts is low, the solution may be neutralized with ammonium in the presence of a methyl red indicator until
40
h?KJ:!
-0
0002
0 . oliiio 0 0000
0.0000
. . . .
-0 0001
0002
0000
--O
on01
0001
0 0000 +0.0001
+o. 0001
- --
The results of the experiments on the separation of nickel and cobalt from calcium and magnesium are given in Table I, and on the separation of potassium and sodium, in Table 11. As shown by the experiments cited in the tables, the results obtained are satisfactory. The flasks in which the precipitation of sulfides is carried on should be well washed with a chromic-sulfuric acid mixture immediately before hhe precipitation. This considerably decreases the adhesion of sulfides to the malls of the vessel.
7
S1O
Gram
SEPARATION O F P O T A S s I U X ASD SODIUM Found Si0 COO XagO IGO Xi0 Gram Gram Gram Gram Gram 0.0537 .... 0.0526 .... 0.0000 0 . 053s .... 0.0529 .... +o ,0001 0.0536 .... 0,0528 .... -0.0001 0.0536 .... .... 0 0513 -0.0001 0.0538 . . . .... 0.0514 +0.0001 0.0537 .... 0.0513 0.0000 0 0506 0,0529 .... ...... 0.0528 0.0503 .... ...... 0,0504 0.0529 .... . . . . . 0.0503 0.0514 . . . . 0,0504 ...... 0.0511 0,0504 ...... 0.0514
cipitating with ammonium oxalate; magnesium, by the phosphate method after adding ammonium chloride. Pyridine which is in solution not only does not interfere with the precipitation but seems even t o favor the format’ionof more coarsely crystalline precipitates b0t.h of calcium oxalate and of magnesium ammonium phosphate. To determine the alkalies, the filtrates from sulfides were evaporated in Pyrex beakers t o remove hydrogen sulfide and then on a water bath in platinum dishes, until a constant volume had been reached. After careful evaporation to dryness on an electric plate the residues were gently ignited but not to red heat, The residues were leached with hot mater, and the solutions were filtered off from the carbon into a weighed platinum dish, evaporated on a water bath with 2 to 3 drops of sulfuric acid, and then gently ignited until the excess of sulfuric acid was expelled.
a
Error
I
CaO
Gram 0.0332 0.033
~~~
TABLE 11. Erpcriments
-
~~~
coo
Error------
Gram
KZO
Sa?O
Gram
Gram
-0 0001 1 0 0002 +0.0001
...... . . . .
+o -0
0002 0001
0 -0 0 0
0000
0001
0000 0000
-0
0001
.....
+0 0002 +0 0001
...... .....
+0 0002 +o -0 0002 0001
+0.0002 +0.0001 +0.0002
.....
a yellow coloration develops, and then acidulated with dilute hydrochloric acid until a pink coloration of the indicator appears.
The separation proceeds very smoothly and rapidly, and the precipitate is readily filtered and washed. If in the solution other metals are present, such as zinc, iron, lead, copper, bismuth, and cadmium, they are also precipitated as sulfides.
Conclusions The new method Forked out by the author for the separation of nickel and cobalt from calcium, magnesium, and alkalies is based on the precipitation of nickel and cobalt sulfides in a crystalline state from solutions containing pyridine. The ammonium salt,s do not exercise any influence. The presence in the solut’ion of pyridine salt favors the formation of larger crystals. The separation is very clean since the sulfides in the crystalline form possess a minimum adsorption capacity, and the precipitate settles well and is very rapidly filtered. The crystalline sulfides are oxidized only very dow1y and do not produce colloidal solutions; therefore the precipitate does not pass through the filter. The method may be used in the analysis of various materials; in particular, the author has used it for the determination of alkalies in nickel and cobalt salts. The use of the method simplifies and accelerates the analysis, without creating any difficulties and without requiring any special apparatus.
Acknowledgment The author wishes to express his sincere thanks to V. I. Lisitzyn for the interest shown in the present investigation and for his valuable suggestions.
Literature Cited (1) H a r i n g , bI. XI., a n d L e a t h e r m a n , M., J. Am. Chem. Soc., 52, 5133-41 (1930). ( 2 ) H a r i n g , XI. AI., a n d Westfall, B., I b i d . , 52, 5141-5 (1930). (3) Murray, B. L., “ S t a n d a r d s a n d Tests for R e a g e n t a n d c. P . C h e m i c a l s , ” 2 n d ed., p. 206, K e w York, D. Van N o s t r a n d Co., 1927. (4) Ostroumov, E. A,, Ann. ckim. anal. chim. appl., 19, S o . 4 , 1 4 5 52 (1937); 20, SO. 1, 9-12 (1938). ( 5 , Ostroumov, E. h.,2. anal. Chem., 106, 170-6, 243 (1936). (13)O s t r o u m o v , E. A , , Zawdskaya Lab., 4, No. 11 (1935); 6, No. 1 (1937). RECEIVED March 19, 1938.
