ADSORPTION BY METALLIC HYDROXIDES. PART 111. ADSORPTION BY PRECIPITATED ALUMINIUM HYDROXIDE B Y KSHITISH CHANDRA SEN
In previous papers, I have studied exhaustively the behaviour of hydrous ferric oxide as an adsorbent. In the following pages, the experimental results with hydrous aluminium oxide are given. Adsorption of Arsenious Acid The adsorption of arsenious acid by hydrated alumina has been studied by Lockemann and Paucke', who have shown that arsenic, in the form of arsenite or arsenate is completely removed from a dilute solution by aluminium hydroxide a t the temperature of the water bath (80-90°), but not at room temperature. When the aluminium hydroxide was precipitated at higher temperature in presence of arsenite, more adsorption was noticed than when it was precipitated in the cold, the apparent explanation being due to the difference in the nature of the precipitate formed a t the two temperatures. Lockemann and Paucke were however interested in the complete separation of arsenic, and they did not carry out their experiments in details. Further, in their experiments, considerable quantities of other electrolytes were present, and hence it was thought desirable to obtain some quantitative data with freshly prepardd and well washed hydrated alumina. While the manuscript of this paper was being prepared Yoe2published an article in which some experiments on the adsorption of arsenious acid by precipitated alumina have been made. As my experiments are however more exhaustive and differ in some respects, the full results are therefore given.
TABLE I Adsorption of arsenious acid. A1203 = 0 . 2 6 7 0 gr. VOl. = IO0 cc. Time = 20 hours; KCl = 0.05 mole per litre
(1) (2)
(3 1
(4) (5) (6)
Cone. of AsgOs in terms of iodine N/18.65
Adsorption in terms of iodine
185.75 cc 185.75cc 148.6 cc 148.6 cc 111.45 cc 111.45 cc
23.25 CC
'Lockemann and Paucke: Iiolloid-Z., 8 , 273 (1911). * J. Am. Chem. SOC., 46, 2390 (1924).
2 3 . 2 5 CC
cc cc 18.45cc 18.45 cc
21.1
21.1
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ADSORPTIO?: BY METALLIC HYDROXIDES
The experimental method employed is the same as in the case of ferric hydroside. The alumina was precipitated in the cold from a two-normal solution of aluminium chloride by a slight excess of ammonia. The sample was partly washed by decantation, and then completely by dialysis. The same sample has been used in all the experiments given below. In order to eliminate the effect of ageing, the sample has been used after 2 5 days after preparation. The oxide was always kept under water. The data in Table I were obtained to study the reproducibility of the results. These results show that in duplicate measurements, the same values of adsorption mere obtained. h t this place, the effect of KC1 on the final equilibrium was investigated, but it was found that KC1 does not show any effect on the amount of adsorption of acids by hydrated alumina. E,(fect of lime. The data in Table I1 show the effect of time on the adsorption equilibrium.
TABLE I1 Conc. of . h O I in grms.
Amount sdsorbed after zo hours
0.39424
o ojj98
0.29568
0.04891
Amount adsorbed after 48 hours
0.05598 0.04894
From these results, it is evident that the equilibrium has been reached within 20 hours. Yoe (loc. cit.) however found that there is a further change in the amount of adsorption after 7 2 hours, but he considers that this change is due to some other cause. In Table I11 the results obtained with varying concentration of the arsenious acid with a fixed amount of alumina are shown. T.4BLE
Original conc. of As20ain grams 0.49280
111
Conc. of the solution after adsorption
Adsorption in grms per gram adsorbent
0.43I IO
0.2311
0,39424
0,33826
0.2096
0.29j68 0.19j12 0.09856
0.24674
0.1833
0.15j20
0.1570
0.06899
0.1108
Effect of temperature on the adsorptzve power of alumina.
The effect of heating the sample of alumina on its adsorptive power was investigated by taking I O cc of the alumina suspension in the experimental flask, and keeping the flask in boiling water for I j minutes. The flask was then cooled t o the l a h a t o r y teinperature, and the amount of adsorption of the arsenious acid ~vaqinvestigated in the usual way. In Table IV the results are shown.
688
KSHITISH CHANDRA SEN
TABLE IV Original, conc. of AslOa in grms
Amount of adsorption alumina-not heated
Amount of adsorption with heated alumina
0.05598 0,04894 0.04192 0.02957
0.39424 0.29568 0.1q712 0.09856
0.04669 0 , 0 3 9 67 0 . 0 3 I30 0.02162
It will be thus observed that the amount of adsorption decreases appreciably when the alumina is heated before the experiment is made. The effect of heating is doubtless to change the physical nature of the precipitate. Effect of volume-when the concentration of the arsenious acid in terms of normality is constant. The actual amount of solute is thus different, Table V.
TABLE V Concentration of A s 2 0 3 = 0.19712 grni. per roo cc. Wt. of A1203 = 0.2670 grams. Volume of solution
Amount adsorbed in grms
60 cc
7 0 cc 80 cc 90 cc
0.0387 7 0.03956 0.04059 0.04130
cc
0 . 0 4 19 2
IO0
Effect of aolume. When the amount of solute is the same in every case. The concentration in terms of normality is thus different in each case, and the sample of alumina was an old one, Table VI.
TABLE VI Concentration of LkSzo3 = 0.2278 gr. Jvt. of 1i1203 = 0.2670 grams. Volume of solution in cc IO0
Amount adsorbed in grms
0 . 0 2 6j 3
90
0 . 0 2 740
80 70 60
0.02808
0,02943 0.03024
From Tables V-VI it will be observed that the volume of the solution has a great effect on the actual amount of adsorption by a given weight of the adsorbent. When the normality of the acid is the same, t,he amount of adsorption increases with the increase in the volume of the solution, and if the amount of the solute is constant, the less the volume of the solution the greater is the amount of adsorption. These results are therefore quite similar to those obtained with ferric hydroxide and given in Tables XIV t o XVIII in part I of this series of papers.
689
ADSORPTION BY METALLIC HYDROXIDES
Eflect of some non-electrolytes like sugar and alcohol which usually decrease the surface tension of water was also investigated. The results obtained however showed that with moderate addition of either cane sugar or alcohol, there was no change in the amount of adsorption. I n Table VI1 the e$ect of varying the quantity of the adsorbent on the amount of adsorption of arsenious acid is shown.
TABLE VI1 Conc. of AslOl = 0.19712 gr. Amount of adsorbent in grms
Conc. of sdution after adsfxption
0.2136 0.2670 0.3738 0.4806 0.6408 0.7476
0.16317
Amount adsorbed per gram adsorbent 0 . 1590 0.1570 0.1441 0.1396 0 .I 296 0.1235
0.15520
0.14326 0.13001 0.11409 0.10480
Reversibility of Equilibrium. I n order to test whether the adsorption of arsenious acid by hydrated alumina is reversible or not, two sets of experiments were tried. I n one set, 0.2670 gram of Alto3 was treated with so cc of N j 2 j . 1 1As203 solution and kept for 20 hours. Then j o cc more of water was added, the mixture shaken and allowed to settle for another 20 hours. At the end of this period, the supernatant liquid was analysed. In an exactly similar experiment, the alumina was treated with IOO cc of N/50.22 AssOI solution. The final concentration of the supernatant solution in both the cases was found to be N170.41. In another set, proceeding in the same way, 50 cc of a solution of A S 2 0 3 Nj12.55 WRS added, and after 20 hours another 50 cc of water. I n another flask, IOO cc of N / z 5.1 As203 solution was added a t the same time. After analysis, the concentration of the supernatant liquid in both the cases u-as found to be 5 / 3 1 . ? . It was thus clear that the adsorption equilibrium in this case was perfectly reversible. T'p to this time, the adsorption of arsenious acid by hydrated alumina has been investigated. It became here a matter of interest to study the adsorption of sodium arsenite by hydrated alumina and to compare the relative adaorbability of the two substances. In Table VIII, the results obtained with sodium arsenite are shown. TABLE VI11 Wt. of A1203 = 0.2670 gr. Original conc. of Na arsenite in terms of I* S / 1 8 . 6 5
148.6 I 1 1 45 74.3 53.7 37.15
cc cc cc cc cc
Amount adsorbed in terms of I* S/18.65 21.1
cc
1 8 . 4 5 cc 1 8 . 8 cc 1 3 . 7 cc 11.15
cc
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KSHITISH CHAKDRA SEN
The adsorption values have been given in terms of iodine because it was found that mainly the arsenite ion was adsorbed. In Table IX a comparative study was made of the amounts of adsorption of As203and sodium arsenite when the original concentrations in terms of iodine are the same.
TABLEIX Original conc. in terms of iodine S/18.65
Adsorption of AS2Os
Adsorption of Sodium arsenite
2 1 . 1 cc 2 1 . 1 CC cc cc 18.45 cc 1 8 . 4 5 cc 1 5 . 8 cc cc 15.8 cc 11.15 cc cc 11.15 CC These experimental result,s therefore show that with both these substances, it is the arsenite ion which is actually adsorbed and from equivalent solutions, the amount of adsorption in terms of iodine is the same. The i'esult is therefore different from that obtained with ferric hydroxide. Having thus studied the adsorption of arsenious acid under various change of conditions, the adsorption of other mineral and organic acids by the same sample of hydrated alumina was investigated, Tables X-XV. The concentration of the acids has been varied as was done in the case of experiments with hydrous ferric oxide. Several acids like hydrochloric, acetic, propionic, butyric, etc., could not be used owing to their great peptising power, and hence the choice of acids used in this investigation is somewhat limited. Rt. of A1203 used = 0.2670 Volume = I O O cc Time = 2 0 hours, KCl = 0.05 mole per litre.
148.6 111.45 74.3 37.15
TABLE X Adsorption of Oxalic Acid Original conc. milliequivalents I . 1320 0.9517 0.761 j 0,5711
0,3808
Conc. of solution after Adsorption
0.6336 0,4752 0.3168 0.1386 0.0396
Adsorption per gram adsorbent I
,866
1 , 784
1.665 1.620 I . 2770
TABLE XI Adsorption of Sulphuric Acid OFiginal conc. milliequivalents I .1320
0.9902 0.792 I 0.5940 0.3960 j
Conc. of solution after adsorption
Adsorption per grm adsorbent
7930 7060 1.6310 I . 4840 I . 1870 1
'
I .
ADSORPTION BY METALLIC HYDROXIDES
TABLE XI1 Adsorption of Racemic Acid ,9040 1.8180 I . 6760 I . 4980
0.6237 0.4950 0.3366 0 .I882 0.0396
I . 1320 0.9802 0.7841
0.5882
0,3921
I
I ,3200
TABLEXI11 Adsorption of Malic Acid I . 1320 0.9219 0.7902 0.6582 0.5267
I.
0.6735 0.4753 0.3566 0.2472 0 ,I j84
7180
I . 6730 I . 6240
1.5390 1.3790
TABLEXIS' Adsorption of Citric Acid OTiginal conc. milliequivalents
Conc. of solution after adsorption
I . 1320 0.9109 0.6831 0.4554
0.5048 0.3268 0 .I584 0,0594
0.2277
0.0099
Adsorption per grm adsorbent
2.3490 2 . I880 I . 9650 I I4840 0.8158
TABLE XS' Comparative adsorption of some acids when the initial concentration is the same Conc. of acid = 1.1320 milliequivalent per IOO cc. Wt. of A1203 used = 0.2670 gr. Acid
Citric Racemic Oxalic Sulphuric
Adsorption per grm adsorbent.
Acid
2,3490 I . 9040 I . 8660 1.7930
Malic Hippuric Succinic Benzoic
Adsorption per grm adsorbent I . 7180
1.2740 I.
2740
0.7543
So far, the results obtained in the adsorption of acids by alumina has been given. It has however been shown that sodium arsenite is also highly adsorbed by alumina and the amount of adsorption expressed in terms of iodine is the same for both the arsenite and pure arsenious acid. I n this connection the adsorption of some other salts and alkali has been investigated. I n the case of salts like sodium phosphate, sodium citrate, etc., usually the negative ion is preferentially adsorbed when the solutions of these salts are shaken with freshly precipitated alumina. This change is noticeable by adding to
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KSHITISH CHANDRA SEN
the solution some phenolphthalein when the pink colour is obtained. Quantitative results were however difficult to obtain owing to the smallness of the value of adsorption. The amount of adsorption of alkali by alumina is however quite appreciable, and has been investigated in the usual way. In Table XVI, the results are shown. The amount of alumina is the same as used in the experiments with acids, and other conditions also remain the same.
TABLE XVI Adsorption of Caustic Soda Criginal, cone. milliequivalents I , 1320 0.9909 0,7921 0.5940 0.3960
Conc. of solution after adsorption
0,7999 0.8608 0.4960
Adsorption per gram adsorbent
1.244 I . 161 I . 109
From these results it is obvious that the adsorption of alkali by alumina is fairly great, and in some cases comes to about 2 5 per cent of the total amount. Alumina, therefore, adsorbs not only acids, but also bases to a considerable extent. Chemical Laboratory Allahabad University
