Clarifying Action of Fuller’s Earth -
M. E. FOGLE AND H. L. OLIN State University of Iowa, Iowa City, Iowa
F
ULLEK’Y earth is one uf a group of d ~ s t a n c e rwliieh , J’iisvrous VIEWSox Arrlos O F I’1ULLEN’S EARTH includes vegetable and animal rlinrooals and t.lie diatomites, widely nscd t,o remove colloidal mat.ter froni Some ‘twenty-five years ago in a11 extensive report Porter inineral and vegetable oils and otlier indost,rial sds. As R (12) wrote: “The color adsorbing power of fuller’s earth is a c l ~ s stheir action is g e n e r a l l y most interesting subject which does not *Wear to have been uttrihted to surface adsorptiirn; Fullrr’s earth is used for thr jhci;ulutiori qf but, vvliilo t h i s e x p l a n a t i o n ~ o n i e lypical sols in an eflorl to./irid u suti.$uctory may b e s a t i s f a c t o r y f o r c l i a r s ,ritl, relatively sirlrple rxplanation for its clarifying aclioii. The irradror I,j,ysieal e h e r n i c a l s t r u c t u r e , it fails yuu(;y ofthe theory rfsimple udsorptiori i,spri,wd. irection, if 7 ’ h ~exislerice of (I small umoziiit of mlciuni iri cmpositioi to a c c o u n t a d e q u a t e l y for fuller’s earlh in Ihr,form r(f a zeolite is poslulufc~d, earth. l o generally a c c e p t e d substiarid ubout g.2 prr cent of zcolitic ealciurri i.q tutc theory has, however, bem tentbin sild would d o u b t l e s s adopted. ,found. A Iheory busrd on the possible :eoklir +iC, il,teresting aIld v a ~ u a h ~ e This industrially impurtant urlion i$ Itre r r p l ~ r ~ ~ i calcium ble f a i l s , howe7:er. rc. s to investigittion.” s u h s t a n c e iz a widely distrihto espluiit fully the rpszilts obtained. ..I theory p s r d and Mullory (8) atactio,u i s triilote the bleaching power of ukd clay of great ~ i o r o s i t y . irlco[r;rly both udsurplioe and It contains u s u a l l y f r o m 80 fuller’s t:arth to a combination developed and found lo agree closely w i t h ezprrito 90 p e r c e n t of a l u r n i n u n i l,recllal,ical and electrical silicates---some in the ~iydratec~ form such as srnectite (AI10riSiO2-12II,O)---2 to 9 per cent of calcium conii~ounds,a small amount of c o m b i n e d magnes i u m , a n d t r a c e s of o t h e r minerals, Alt]lough tile properties uf some of the fuller’s earths are reported to belittle affected by h e a t i n g a t high temperatures, most investigators have found that loss of vater of hydration deereases it.s blesciling effectiveness.
mental data. I1 seems plausible lhut /he clurllyirig rfrct i$ J~ller’s .yols is dzw p a r t lo adsorljtiori eolloida~m&r on tiE surface of the uizd in. part to coagulalion. resulting frani a buse exchange betweri IhP Z O l i l e arid I h C SO1 w h ~ r e b y dizwlent calcium is liheraled f r o m the mineral arid ioiiized ujhile nionovalrnt pepti:iiig ions are remoz.edfroni (he sol sysien,, The rat;o of rrLagnitudes of these two efects i s found lo oary widely with the ~ f f f ~18~&;rim i 1 :eolite in the difrreizt earths. 1069
groperties and further describe it a s the result of a d s o r p t i o n and n ~ e c l i a n i c a lfiltrat.ion aceumpanied bysoinechemicaldisi n t e g r a t i o n due to selective ndsorl,tioll, hydrous aluminum silicate being suggested as the a c t i r e constituent. Benedict ( I ) advances t h e t h e o r y that fnller’s earth first promotes the oxidatirm of the colloidal matter alrd tlren adsorbs the Ic1,tzeinigg (7) honrever shows tlmt any oxidizing action pos-
INDUSTRIAL AND ENGINEE RING CHEMISTRY
lOi0
sessed by materials with large specific surface, including fuller’s earth, is a question of adsorbed oxygen entirely. Therefore, an oxidizing action would not account for the difference in behavior between fuller’s earth and other adsorbents such as charcoals. Many other explanations have been advanced. The one most generally adopted is perhaps that of Parsons (11) who, in a survey made 20 years ago, concluded that it was entirely physical in nature and that it was due to adsorption. Since the present study was made, Kobayashi and Yamamoto (6) report that fuller’s earth, among other substances, follows the adsorption formula of Freundlich in decolorizing petro-
/O
08 06
FIGURE1. EXTRACTION OF CALCIUM FROM FULLER’S EARTH
leum distillates. Just as recently, however, Haseman (4) makes a directly opposing statement. Summing up the suggested theories, Haseman states: “Some writers have maintained that bleaching with fuller’s earth is a chemical process; others that it is a physical process; and still others that the two are combined. Some have maintained that fuller’s earth contains an unknown substance which combines with the coloring matter rendering it insoluble; others that bleaching is associated with the colloidal silica contained in the earth; and still others that it polymerizes the color compounds. It has been suggested by some that the color is removed by a process of dialysis, while many writers maintain that it is due to selective adsorption. Most have agreed that bleaching is in some way associated with its porosity.” I n opposition to these theories, Haseman affirms that he has shown that porosity and adsorption have nothing to do directly with the action of fuller’s earth, and concludes somewhat vaguely that “fuller’s earth and activated clays bleach oils by virtue of their disilicic acid content that precipitates the colors by liberating electronic energy, and some materials, such as carbon, etc., filter out mechanically.” He also states, “Even though fuller’s earth has generally been considered to be hydrous aluminum silicate, it is not-the active part is disilicic acid.” SCOPEOF PRESEKT STUDY The present study of the flocculation of some typical sols was undertaken in an effort to throw some light on this general problem; in particular to investigate the possible existence of a zeolite in fuller’s earth, and once its presence was detected to determine its relation, if any, to the action of the mineral. Some weight was lent this idea by a statement by Whitney (9) who suggested, in discussing the colloid chemistry of soils, that zeolite-like compounds might account for certain reactions that were not explainable on the basis of surface phenomena, He says: “It is now coming to be generally believed that the inorganic colloidal material of the soil is essentially the same as the artificial (zeolite) gels of silica, iron, and alumina which have been prepared.” Significant also was the observation of Mutti and Reginelli (10) who found while studying the reduction of the sodium content of sugar juices with a calcium zeolite that it also removed much of the color.
Vol. 25, No. 10
Postulating, therefore, the presence of calcium zeolite in fuller’s earth and of monovalent peptizing ions in the sol, the familiar base exchange may be expected to take place whereby divalent calcium ions will replace monovalent ions in the sol. It follows directly from the classic Freundlich observations that, with the substitution of a divalent ion for one bearing only a single charge, the flocculating effect upon the colloidal particle is increased about seventy fold, and that coagulation should be accelerated in proportion. DETECTION OF ZEOLITESIN FULLER’B EARTH The physics and chemistry of zeolytic action have been given much study, and the main characteristics of the reaction a t least are known. Ungerer’s results (14) show that the removal of calcium from permutite (one of the commerical synthetic zeolites) is dependent upon the concentration of the potassium chloride solution used. For the exchange between calcium and sodium in a zeolite, Frankforter and Jensen (3) found practical equilibrium conditions to exist after one half-hour of contact. Ramann and Spengel (IS)in their study of the displacement of calcium with potassium conclude that the exchange follows the law of mass action, that it is of a chemical nature, and that no signs of physical adsorption were detected. To test the validity of the postulate that fuller’s earth may contain zeolites, seven 15-gram samples of earth, previously crushed t o -200 mesh and dried a t 110’ C. for 15 hours, mere treated with exactly 50 cc. of potassium chloride solution in concentrations ranging from 0.0 to 3.0 normal. After uniform agitation for 5 hours they were carefully decanted Kith distilled water, filtered, and washed free of chlorides. The solid residue was dried and recrushed, then heated as before to expel adsorbed moisture, and stored in tightly stoppered containers.
o
0.2
0 . 4
qa
0.8
1.0
FIGURE 2. FLOCCULATION OF TYPICAL SOLS WITH PARTIALLY EXTRACTED FULLER’S EARTH
The decanted liquor and filtrates from the washings were retained for the determination of calcium, magnesium, and aluminum. I n brief, merely a trace of magnesium was detected. I n view of the possibility that potassium ions may have liberated aluminum ions from hydrous aluminum silicates in the fuller’s earth to produce a three-hundred-fold coagulating effect, a most painstaking search was made for aluminum in the filtrates. However, application of the sensitive Hammett and Sottery method as developed by Yoe and Hill (16), which employs the ammonium salt of aurin tricarboxylic acid or Aluminon, failed to show its presence. Calcium was determined by the standard volumetric method with potassium permanganate solution.
October, 1933
INDUSTRIAL AND ENGINEERING CHEMISTRY
Assuming that the extracted calcium is of zeolitic origin as postulated, the familiar base exchange reaction should take place on treating the earth with potassium chloride solution:
+ 2K+==
Ca
+ Ca++
2K
(1)
This equation represents a third-order reversible reaction so that we may write as the rate of calcium ion formation: =
dCca++
de
Since an equivalent of K is produced for every equivalent of Ca++ ionized, c3c,
K = (CKI'I
-
++
CCa+')'
(a
(4)
- CCa")
total replaceable calcium in the earth
Results of the calcium determinations and values of the equilibrium constant K. are shown in Table I. The values of K , were calculated under (1) on the assumption that all calcium removed was of zeolitic origin; those under ( 2 ) on the postulate that the 0.53-mg. equivalents removed with pure 15-aterrepresent nonzeolitic, water-soluble calcium in the sample. I n either case the constancy of the value of K , gives strong confirmation to the theory that the calcium is present in zeolitic form and that it is liberated by base exchange. TABLEI. EXTRACTION OF CALCIUM FROM FULLER'S EARTH (Sample weight, 15 grams) EQUIV.
EQCIV. OF OF C a + + KCl I N REMOVEDK e , E Q U I LCON.
NORMALITY OF KC1
Ca 50-cc. S A M P L ESOLN. R E M O V E D SOLN. 1 2 3 4 5 6 7
0 0.2 0.6 1.0 1.5 2.0 3.0
02
?B
30
(3)
=
by adding a concentrated solution of ferric chloride to boiling water in such a ratio as to make a 0.5 per cent ferric hydroxide (or hydrated ferric oxide) suspension and dialyzing to remove the strong acid liberated.
54
klCc,CZK+ - klCCa++Czi
