LITHIUM ADSORPTION BY KAOLIN MINERALS
Nov., 1955
1151
LITHIUM ABSORPTION BY KAOLIN MINERALS BY R. GREENE-KELLY Contribution from Rothamsted Experimental Station, Harpenden, Herts, England Receaved M a y 16, 1966
Lithium ions introduced into the cation exchange positions on kaolin minerals are found to be non-exchangeable after the minerals are dried by heating to 200".
Introduction Recent investigations1V2on the effect of drying of montmorillonite minerals as a prelude to adsorption studies have shown that under certain conditions interlamellar sorption is inhibited at room temperature. Minerals that are dioctahedral, possess a large proportion of the silicate sheet charge due to octahedral substitution, and are saturated with cations of small size (e.g., Li+) are particularly susceptible t o irreversible changes during drying. The inhibition of interlamellar sorption is always accompanied by a decrease in the cationexchange capacity due t o the fixation of the interlamellar cations. It was naturally of interest to see whether other clay minerals showed the effect of ion fixation on drying and if so how far this affected their adsorption of water. Preliminary unpublished work on illites indicated that these minerals did not fix lithium ions. The kaolin group of minerals were found, however, to show lithium fixation and this result appeared of particular interest in view of the work of Keenan, Mooney and Wood3 who found that lithium kaolinite (Peerless No. 2) showed the lowest water adsorption a t any relative vapor pressure of water compared with kaolinites saturated with ions of hydrogen, sodium, potassium, rubidium, cesium, calcium, strontium and barium. This paper presents the results of ion-exchange work on three kaolinites and a halloysite and discusses the fixation effects in relation to the adsorption of water. TABLE I Am:
Mineral
Origin
Impurities
monia retention, m a / 100 g .
Kaolinite Merck Colloidal None 1.9 Kaolin Kaolinite English Clays Tracemica 1.6 RL0/314 Cornwall Kaolinite Peerless No. 2 Trace mica 3.5 (Vanderbilt Co.) HalloyEureka, Utah Trace gibb- 10 site site
mined by other authors using nitrogen on kaolinites of the same origin.3~4 These preliminary results are given in Table I. The minerals were washed four times with normal solutions of the chlorides of the cations to be introduced and then washed free of chloride ions with alcohol or water. The samples were then dried a t various temperatures and when this was completed the cations introduced were washed off with normal ammonium acetate ( p H 7) over a period of several days. The resultant solutions were analyzed by the Lundegardh flame spectrographic method. By this procedure it was found possible to introduce the desired cation into a proportion of the cation-exchange positions. If the washing of the excess chloride was carried out with water substantially lower amounts were introduced owing apparFor example Merck ently to hydrolysis of the "clay-salt." kaolinite was found to bind 0.3 meq./100 g. of lithium when the mineral was washed with water, whilst with alcohol washing, 1.6 meq./100 g. of lithium was introduced. This difficulty of preparing homogeneously saturated kaolinites has been a major factor in the development of special methods of determining the net change of kaolinite where the excess salt is not removed by washing with water or alcohol but is displaced by another electrolyte.6 Clearly such methods could not be used in this work. Keenan, et al.,3 prepared their samples by electrodialysis followed by titration with the appropriate hydroxide to neutrality. This procedure has been criticised on the grounds that the resultant titration curve represents at least in part the precipitation of aluminum oxides released during electrodialysis .E Finally the ammonium acetate treated kaolin minerals were washed free of excess ammonium ions with alcohol and the minerals analyzed for retained ammonia by steam distillation of samples with sodium hydroxide, the evolved ammonia being collected in boric acid.
Results Tables I1 and 111summarize the experimental results for different cations and different minerals. It will be noticed that the excess salt was removed by washing with water in the first series and by alTABLE I1
Surface area, m".g.g.
10
MERCKKAOLINITE Cation introduced"
Li +
..
Na +
17
..
Mgz+
Experimental Methods
Drying temp., OC.
Cations recovered meq./100
Unheated 300 Unheated 100 200 300 Unheated 100 200
The selected minerals were examined by X-ray diffraction for impurities and their "exchange capacities" and surface areas determined by ammonia retention and carbon dioxide adsorption at its sublimation point, respectively. The latter values were obtained by use of the B.E.T. equation and proved to be in excellent agreement with those detera
300 Ca2+ Unheated 100 200 300 Excess salt washed off with water.
i.
0.3 .02 .6
"4'
retained meq./100'g.
1.8 1.5 1.8
.7 .8
...
.6 1.8 1.6 1.4 0.9 1.1 1.0 1.0 0.5
1.4 2.1
...
... ...
1.1 2.3
... ... 1.8
(1) U. Hofmmn and R. Klemeno, Zeit. anorg. Chem., 262, 95 (1950). (4) H. R. Samson, P1i.D. Thesis, London, p. 115, 1953. (2) R. Greene-Kelly, Clay Min. Bulletin, 2, 52 (1953). ( 5 ) R. I
