ADSORPTIOK BY LIETALLIC HYDROXIDES. 11. ADSORPTIOS O F ACIDS, ALKALI AKD SALTS BY PRECIPITATED FERRIC HYDROXIDE BY KSHITIRH CHANDRA SEN
Though a certain amount of experimental work exists in the literature on the adsorpt,ion of acids and acid ions by colloidal ferric hydroxide in course of its precipitation, no comparative study of the adsorption of acids by precipitated ferric hydroxide seems t o have been made. Freundlich’ cites the experiments of Wohler, Pluddeman and Wohler? to the effect, that ferric oxide adsorbs benzoic acid about ten times as strongly as acetic acid, but besides one or two such references, no systematic attempt has been made. Even the direct estimation of adsorption of ions by colloidal ferric hydroxide has been made by only a few investigators, the reason being that hitherto the order of adsorption of ions has been assumed t o be the same as t h a t obtained from the order of the precipitating power of the ions on the colloidal solutions. The usual difficulty of working with precipitat’ed substances however is that the amount of adsorption is generally small and hence the measurements are liable to be in error. As with hydrated ferric, aluminium, and chromium oxides, no such difficulty has been experienced, the adsorption values being quite large, this procedure has been adopted. Two advantages are thereby gained over the colloidal solutions; ( I ) the amount of the adsorbent may be varied at will in the same volume of the solution and ( 2 ) the objection that during coagulation the colloid may adsorb some v ,ter does not, come in, Further the precipitated substances can be obtained chemically almost pure, and hence the adsorption values will not ’ne ritiat,ed y the presence of ot,her ionic impurities. Owing to these reasons, it was thought advisable to use a freshly precipitated and well washed hydrated ferric oxide as the adsorbent. The method of experiment was the same as described in the case of arsenious acid. T h t sample of the ferric hydroxide was prepared about twenty-five days before the experiment, and on experimenting showed no ageing effect. The excess of acid in the supernatant liquid was estimated volumetrically by means of carbonate-free alkali using phenolphthalein as the indicator and test experiments showed that the method was quite accurate. To get comparative results, equivalent concentrations of acids were used in almost all cases; only in the cases of formic and acetic acid, a slightly higher concentration was used. The acids were used in rather dilute solutions, so that a high value of adsorption may be obtained and in certain cases dilute solution was necessary to include some of the less soluble acids. The results obtained are shown in Table I. 1 2
Freundlich: “Kapillarchemie”, 155 (19091. Z. physik. Chem., 62,664 (1~08).
KSHITISH CHANDRB SEN
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TABLE I Adsorption of acids by hydrated ferric o d e .Imount of oxide = 0.4882 gr. Vol. = I O O cc; KCl = 0.0; mole per litre Time = 2 0 hours Original strength of the acids = 0 . 4 6 1 j milli-equivalents per 103 cc. The strength of formic and acetic acids was 0.4627milli-equivalents per 103 cc, TO.
Acid
Formic Acetic 3. Monochlor-acetic 1. Trichlor-acetic ). Propionic 6. Butyric Valeric 1. 8. Caproic 9. Benzoic IO. m-Oxy-benzoic 11. o-Amido-benzoic 1 2 . m-Amido-benzoic 13. p-Amido-benzoic 14. Hippuric Succinic 15. 16. Dibrom-succinic '7. m-Toluic 18. o-Toluic 19. Malic 20. Oxalic Racemic 21. Aleso-tartaric (inactive) 22. 2 3 . 1-Tartaric 24. Lactic 2 j. Malonic 26. Citric Hydrochlorlc 27. 28. Sulphuiic I .
2.
Amount of adsorption milli-equivalents 0.4147
0.3978 0.4326
Dissociation constant X IO? 0.021
o.oor8 0.155
0,4350
0.3846 0.3846 0.3870 0.3842 0,4373 0.4349 0,4325 0.4253 0.4300 0.4422
0.0013 0.OOIj
0.0016 0.0014 0.0060 0.008j
04 o.oor6
0.00I
0.0012 0.022
0.4422
0 . op68
0.4277
0'4349
5.0 o.ooj1
0,4300
0.012
0.4470
1.20
0,4470
10.0
0,4422
0.097
0.3470
0.4422
0.09;
0.4277
0.014
0.4373
0 .I
0,4470
0.082
0.4422
j8
(7)
0.4422
Relatively strong acids like hydrobromic, nitric, etc: could not be examined and the result with hydrochloric acid is also somewhat doubtful owing to the ease with which these acids peptise ferric hydroxide. The supernatant liquid was turbid even in presence of .o; mole KCl. It will be evident from these results that a t the dilution studied, the amount of adsorpt,ion is quite high and the percentage of adsorption lies between 80 t,o 9 j per cent. Obviously in such high adsorptions, the effect of concentration of t h e original solution
ADSORPTION BY JlETALLlC HYDROXIDES
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is masked in some cases and, owing to this reason, some of the adsorption values haye been found t o be equal. .I second series of determination v a s therefore iiiade with varying concentrations of the acids using the same adsorbent. Tables 11-SIII.
TABLE I1 Adsorption of acetic acid wt. of Fe?03 = 0.4882 gr. Conc. of original acid in milli-equivalents
Cnnc. after adsorption 0 . j90 0.640
I .3880 I . 2144 1 . 0410
.idsorption per gram adsorbent I .2 2 5 LIji
0.480 0,330
1 . I49
0.8674 0.6940
0.200
1.012
I , I02
TABLE 111 .Idsorption of propionic acid wt. of Fe203= 0.4882 gr. Conc. of original acid rnilli-equivalents
Adsorption per gram adsorbent
1,9450
Conc. of solution after adsorption 1.3110
I .
5560 I . 1670
0.9600 0.6100
1.2210
0.9j2j
0,4303
1.1110
0.2800
I .0 2 0 0
0.
j;80
I .
2990
I .I 4 1 0
TABLE IT .Idsorption of butyric acid v t . of Fe?Os = 0.4882gr. Conc. of acid milli-equivalents
Conc. of solution after adsorption
I ,3640
I . I j60
I ,0230
0.7900 0.6400 0.4800
0.8522
0.3400
0.6820
0.2100
I . 0690 0,9668
1.1934
Adsorption per gram adsorbent I .I 3 3 0 I . I120
'r.IBLE 1. .Idsorption of hippuric acid n't. of Fe?Oa = 0 . 2 5 j g gr.
1320
0.7452
I , \;I20
0.90j;
0.5378
I . 4380
0.7921
I ,4020
0.6792
0,4339 o 3302
0,4528
0.I
I .
jr;
I . 3640 I
1730
KSHITISH CHASDR.I >EX
TABLE VI Adsorption of oxalic acid wt. of Fe20a= 0 . 2 j ; g gr. 1790
0.590i
2.06jo
0.9434
0.4340
I
0.
io?.& 0 . j896
0.24jI
I . 8070
0.169;
I .
0.4i1;
0.Oi.j.i
I . j480
I ,
.grjro 6410
TABLE VI1 ;idsorption of eulphuric ncicl wt. of 12eL03= 0 . 2 ; 5 ( 1 gr. Conc. of solution after adsorption 0.6081 0.5381
Conc. of acid milli-equivalen t I . 1320
adsorption per gram adsorbent
1.6960
0.823j
0.4IiO
0.6861
0.2922
.6j10 5970 I . .i360
0.5491
0.16yg
I
0.960;
I
I .
.48,;0
2.0650 1
,
()?,jO
I .
so30
I .
6500
I
..;3 j o
\vt. of I,’e20s = 0 . ~ 5 5 9gr. Conc. of acid
C‘onc. of solution
adiorption per
I . 1320
after adsorption 0.6414
0.8716
O.Jog6
I .8 2 2 0
0.633; 0 .j 4 4 S
0.23.78
I
0.1.+2,;
I . ,7720
0.43.;s
0.0663
1
milli-equivalents
gram adsorbent 1 .()Ij o
,6330 4450
ADSORPTIOS BY METALLIC HYDROXIDES
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TABLE XI Adsorption of succinic acid wt. of F e z 0 3 = o . z j j g gr. 0 7075
1320
529
I . 6590
0.8680
o 4822
I .5 1 2 0
0.6509
o 2830 0 I888 o 1132
I . 3820
0.5425
0,4339
1 ,4370 I.
2530
TABLE SI1 .idsorption of benzoic acid wt. of Fe20s = 0 . 2 5 j 9 gr. 1320
7735
I . 4020
0.9143
0 5700
I . 3460
0.7358 0.5.518
0
4057 o 2641
I . I240
o 1038
I
I.
0
0
36i9
I . 2900
,0320
TABLE SI11 Comparative adsorption of some acids when the initial concentration is the same. Conc. = 1.1320 milli-equivalent per I O O cc wt. of Fe201used = 0.2;;9 gr. .hid
Citric lialic Oxalic (conc. I . I ;go) Racemic
Adsorption per gram 2..:810
2.0560 2
,06j o
I .
91 j o
.hid
Sulphuric Succinic Hippuric Benzoic
.Idsorption per gram I . 6960
I . 6590
I.5120 I ,4020
.4t/norption of salts and cilkali. I n the foregoing p a p s , the adaorption of acids liy hydrated ferric oxide 1:ns mainly tieen given. It has however been shoIvn in the previous paper that both sodium arsenite and caustic soda are actsorbed by ferric hydroxide, a n d in the easa of sodium arsenite niainll- the arsenite ion was adsorbed. In this connection the adsorption of many other salts such as potassium sulphate, sodium citrate, sodium phosphate, potassium permanganate, potassium dichromate, etc, by precipitated hydroxide was determined, but, owing t o the very m a l l amounts of adsorption. quantitative resuks could not he obtained. It was however found that with salts like citrate, phosphate, etc, appreciable adsorption of the negative ions takes place on shaking a solution of these salts with ferric hydroxide, a corresponding amount of alkali being set free. which can be test.ed by means of phenolphthalein. The adsorption therefore seems to he preferential. h a it is known that alkali is also adsorbed Iiy ferric hydroxide, a comparative study of the adsorpt,ion of acid and alkali seemed desirable. Hence some adsorption experiments have also been made with the ferric hydroxide S o . 3 and caustic soda of almost the same concentration as has been used in the case of sulphuric acid. The results are given in Table XIV.
KSHITISH CHANDRA S E N
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TABLE XIV Amount of Fe203 = 0 . 2 j j 9 gr. Ofiginal conc. of SaOH milli-equivalents per I O O cc 0,9434 O.ij48
3.5659 0.3ii3 0.2830
Cone. of t h e s o h . after adsorption 0.7401 0.5801
Adsorption per grm. adsorbent 0,7949
0.6828
0.4098
0.6098
0.2399
0 . j368
0 . I joo
0.5199
I t may be assumed that at t,he dilution studied, both the sulphuric acid and caustic soda are practically completely ionised. Hence if these results are compared to that given in Table T I I j it mill be noticed that H' ion is much more adsorbed by ferric hydroxide than OH' ions. There is no doubt that this is connected with the chemical nature of the adsorbent, which is a basic substance. A similar inst,ance is known in the case of manganese dioxide.' This substance is acidic in nature and it adsorbs both the acidic and basic portions of several substances such as copper sulphate. The adsorption of the basic portion is however much greater than that of the acidic one, and when the adsorption of acids and bases are studied, it is seen that H'ion is much less adsorbed than OH' ions. Chemical Laboratory, Allahabad T;?izr,cr.szty, Allahabad, Feb. 8, 19P6. Dhar, Sen and Ghosh: J. Phys. Chem., 28, 469 (1924)
