F L O C C U L A T I O N OF S E L E C T E D CLAYS BY V A R I O U S E L E C T R O L Y T E S

by

HUEY-RONG H s I 1 AND DONALD F. CLIFTON

College of Mines, University of Idaho, Moscow, Idaho 2

A B S T R A C T

The flocculation behavior of clay specimens from altered basalt, altered granodiorite, and a transported (?) deposit in Latah County, Idaho, was investigated in order to determine if floeculation behavior would be an aid in characterizing clay samples in a way that could be related to the origin and history of the clays. The clay minerals are of the kaolinite group.

As flocculants, various chlorides differ one hundred-fold and sodium salts twenty-fold in the concentrations necessary to flocculate a clay to a fixed sett!ing rate. The concentrations of individual chlorides necessary to flocculate different clays vary three-fold and the con- centrations of individual sodium salts vary ten-fold. In all cases the higher the valence of the cation the lower is the concentration required for flocculation; the relative effectiveness, however, varies with the clay. The relative effectiveness of the anions as flocculants varies greatly with the clay and no definite order of effectiveness is apparent.

I-[alloysite requires less electrolyte for flocculation and has a larger settling volume than kaolinite. Well crystallized kaolinite has a smaller settling volume than poorly crystal- lized kaolinite.

Wide differences of flocculation behavior may provide a valuable, rapid method of clas- sifying the clays of a district.

I N T R O D U C T I O N

A s t u d y of t h e f loccu la t ion b e h a v i o r of v a r i o u s c lay s a m p l e s is be ing m a d e as p a r t of a b r o a d i n v e s t i g a t i o n of t h e c lay depos i t s in a n d a r o u n d L a t a h

Coun ty , I d a h o . T h e s t u d y was u n d e r t a k e n p r i m a r i l y t o d e t e r m i n e ff f loccu-

l a t ion b e h a v i o r w o u l d be an a id in c h a r a c t e r i z i n g c l a y samples in a w a y

t h a t cou ld be r e l a t e d to t h e o r ig in a n d h i s t o r y of t h e clays, and poss ib ly t o

add to t h e gene ra l u n d e r s t a n d i n g of f loccu la t ion p h e n o m e n a .

1 Present address: Thompson Products Division of Thompson-Ramo-Wooldridge, Inc., Cleveland, Ohio.

2 Work done under Special Research Project. 60 of the University of Idaho in co- operation with the Idaho Bureau of Mines and Geology.

269

270 NINTh[ NATIONAL CONFERENCE oN CLAYS AND CLAY MINERALS

EXPERIMENTAL PROCEDURE

Clay Samples

For the first part of the work three clay samples known to differ in origin or history were chosen.

Sample A was obtained about half a mile north of Helmer, Idaho. The clay had washed from a steep bank and settled from suspension in a t iny pond at the foot of the bank. The sample was almost pure clay and showed fine stratification evidently produced by successive rain storms. The clay bank is stratified and does not show relic structures of importance so is thought to be a transported deposit (Hubbard, 1957). The apparent source of the clay is altered granodiorite from the nearby Thatuna batholith and altered Permian volcanic rocks from Potato Hill (Mount Deary).

Sample B is highly altered Columbia River basalt.

Sample C is highly altered granodiorite. Samples B and C came from the same location in the Benson deposit (Hubbard, 1957) northeast of Troy. Locally the granodiorite is overlain by about 6 ft of basalt. The highly altered zone is more than 20 ft thick. The samples were taken about 18 in. apart just above and below the basalt-granodiorite contact.

X-ray diffraction and electron microscope examination of the clay from these specimens showed the transported (~.) clay, A, to be a mixture of metahalloysite and poorly crystallized kaolinite; the basaltic cIay, B, to be metahalloysite ; and the granitic clay, C, to be well crystallized kaolinite. Plate 1 is the electron micrographs of these specimens.

Flocculants

The flocculating reagents were chosen to represent a range of valences, ion size, and calcium salt solubility which are known to affect their efficiency (Searle and Grimshaw, 1959, pp. 438444). The final choice, however, was arbitrary. The chlorides used to study the effect of the cations were NaC1, CaCI~, FeCl~, A1Cla, and SnC14. The sodium salts used to study the anion effect were NaC1, NaF, NaOH, Na~SO,, Na~COa and Na~HPO 4.

Experimental Procedure

The clay suspensions were prepared by dispersing sufficient sample in distilled water with a malted-milk mixer to give about 4 percent solids. The suspensions were allowed to settle for 20 min (enough essentially to remove the > 10/t fraction), then diluted to give suspensions containing 1 and 2 percent solids.

PLATE 1.--Electron micrographs. (A) transported (?) clay, sample A. (B) basalt: clay, sample B. (C) granitic clay, sample C.

FLOCCULATION OF SELECTED CLAYS BY VARIOUS ELECTROLYTES 271

The clay was flocculated by adding sufficient reagent solution of appro- priate strength to give about 30 ml of clay suspension containing just under 1 percent solids.

Settling time was taken as the time for a sharp boundary to appear between the settled" floc and the liquid. Settling volumes were measured at this time. Preliminary tests in which the white-light transmission of the liquid was measured showed that there was essentially no change in trans- mission after the end of settling as determined by the development of the sharp interface. This, plus reasonable reproducibility, indicates good relia- bility for the method of determining settling times.

All work was done at room temperature because tests at 13 ~ 25 ~ and 54 ~ showed no significant dependence of the fiocculation rate on tempera- ture. A dependence of flocculation behavior on solids concentration was observed but eliminated as a variable by working with suspensions of uniform strength. Because the size distribution of the clay particles is characteristic of the sample the entire < l0 # fraction was used in each case, although more details of the floeculation process might have been gained by using closely sized material.

The p H of the flocculated suspensions in all cases changes by less than half a unit through the concentration ranges investigated. The pH at which rapid flocculation first occurred with any one reagent varied as much as one unit from sample to sample. The pH data are summarized i n Table 1.

Clay A Clay B Clay C

TABLE 1.--pH OF FLOCCULATED SUSPENSIONS

NaC1 CaC12 A1C13 SnC14 Original Suspension

6.6 6.6 5.8 4.6 6.4 7.4 7.2 5.6 5.1 7.6 7.1 7.0 5.2 4.1 7.2

R E S U L T S A N D D I S C U S S I O N

The settling t ime versus electrolyte concentration curves for the three clay samples and six cation chlorides are shown in Fig. 1 and the settling volume curves in Fig. 2. The effectiveness of a reagent is clearly a function of the valence of the cation. Although the curves shift slightly from one clay sample to another the dependence on the clay is fairly small. The ratios of concentrations of the reagents at which the settling t ime curves level off are given in Table 2. The similarity between the ratios for clays B and C and the difference between these and the ratio for clay A suggest that factors in the environment other than the parent rock are the most effec- tive in determining cation flocculation behavior. I t should also be noted

272 NINTH NATION~ CONF]~]~ENOE ON CLAYS AND ~-~-,AY MINERALS

that these ratios are very different from those reported by other workers (Michaels, 1958, p. 29; Brindley, 1958, p. 19). The anomalous effectiveness of ferrous iron relative to calcium, and the unusual settling time settling

I i~,~ ' , . ~ \ ', \ SAM LE A

t l ~ \ l ; ~ I, \ {\,

I ~1 ~, / i t',. _t~~ ~ , ,,

i~ ',,t x ',,/ \ \ \

.. _\7",., ', ;':,, \)' ,-

I ~ = ~ - 4 7 lO 20 -"

ELECTROLYTE CONCENTRATION (MILLIMOLES / LITER)

FIGURE 1.--SettUng times with cationic floeculants.

/ \ / / k /

SAMPLE A 46 - / \ / S,~PLE B

-30 43 - /FeCI z ~ . . ~ / SAMPLE C . . . . . . . . . . .

/ ..'--;;> .....

�9 ZO j ) ~ / / / / / J / / / /

o, _ J V , " - : ~

/ ~ " . J . ~ ... . . . . . . . . ~ ...... z / ~ 7 7 3 . . . - " .>ooo~., ._-< .. . . .

.-'" ~ . .~L_ . ~ ___ I N o e l ( t / .... / / ] ,..J-~ ; . . . - - , _::,j---,: ~

J ELECTROLYTE CONCENTRATION (MILLIMOLES/ LITER)

FIOV~av, 2.-Settling volumes with cationic flocculants.

volume behavior of clay B flocculated with ferrous chloride both invite further investigation. The high-concentration minimum in the settling t ime curve for clay B at a concentration ratio value close to tha t of CaC12 suggests it is a remnant of the effect of valence on the flocculation efficiency of the

FLOCCULATION OF SELECTED CLAYS BY VARIOUS ELECTI~OLYTES 273

ion; the position of the low-concentration minimum and the breaks in the curves for clays A and C must be explained on the basis of other factors.

The results of the anion flocculation experiments are shown in the settling time curves in Figs. 3 and 4, and some settling volumes in Fig. 5. The variation in behavior from one clay to another is much greater with the

TABLE 2. - -CATIONIC FLOCCUIANT CONCEI~'TI~TION RATIOS

N a + : Ca ~+ : F e 2+ : A1 S+ : F e s+ : S n 4 + : :

C l a y A 1 .0 : 0 .125 : 0 . 044 : 0 .017 : 0 .021 : 0 .007

C l a y B 1.0 : 0 . 086 : 0 . 029 : 0 . 020 : 0 .021 : 0 .013

C l a y C 1.0 : 0 . 100 : 0 .037 : 0 . 025 : 0 . 020 : 0 .012

-,o \'.. , \ '. " - . L ~- ; ~ - , ' , \ . . . .

~ o~. 07 : ,2 4, ; ,,o =, ELECTROLYTE CONCENTRATION (MILLIMOLES/ LITER)

F z G u ~ E 3. - - S e t t l l n g t i m e s w i t h m o n o v a l e n t a n i o n i c f l o c c u l a n t s

various anions than with the cations. This greater variation is not un- expected since the anions are not only adsorbed on. the clay surface to a limited extent but also interact with the cations and influence their adsorp- tion and the resulting flocculation of the clay (Grim, 1953, p. 146). On an empirical basis floceulation with the sodium salts of various anions seems to have considerable promise as a tool in clay investigations.

Measurement of settling volumes also seems to hold some promise as a research method. The curves in Fig. 2 show appreciable variation in settling volume from clay to clay. For example, clay B has a larger settling volume than clay C when flocculated with FeC12 or SnCl~, but a smaller settling volume when flocculated with the other chlorides. Fig. 5 shows that clay B has a greater settling volume than clay C when flocculated with NaF, N a 0 H , or Na2S04, although C has the greater volume when floccu- lated with NaCl.

274 NINTH NATIONAL COI~RENOE ON CLAYS AND CLAY MINERALS

In the application of flocculation studies to a geologic problem, tests have been made using anion flocculation in the s tudy of two sets of clay samples. The first set consisted of four samples taken from a vertical sec- tion of a transported (?) deposit at depths of 37, 45, 52 and 59 ft. The apparent source of the clay is altered granodiorite. Structures in the clay suggesting relic feldspar cleavage fragments and pebbles, and considerable alteration of the basalt underlying the clay, seem to indicate considerable postdepositional alteration. The other set consisted of two samples of chalky, white clay identical in appearance, texture, diffraction patterns, and apparent source rock taken from locations 20 miles apart . Table 3

t- ~, , \ ~ - ~ \ . . . . . . . I / ~ l \ ~ ! ~ ~ \ SAMPLE C . . . . . . . |

\\; \ \ "\ ' ,;l \ \ ',

: \ ' , , , ~. \ \ \ / . .

,o ',,....-~-~",'t~.~:,, ""~ ",, / \, ....... % . ~ . . . . _..y,,_ . . . . \ . . . . . . . . x=:z_~.-.-~-. ::- - - \ \

ELECTROLYTE CONCENTRATION { M I L M M O L E S / L I T E R )

FIGURE 4.--Set t l ing t imes with divalent anionic flocculants.

=. 3 .o

t

SAMPLE A SAMPLE B SAMPLE C . . . . . . . . .

- 2O /

/ N%so. , ...f// ~ ,\

? ,,o ~, ~ ,oo fro EI~ECTROLYTE CONCENTRATION {M ILL IMOLES/ L I T E R )

FIGURE 5.--Set t l ing volumes with anionic flocculants.

FLOCCULATION OF SELECTED CLAYS BY VARIOUS ELECTROLYTES 275

gives the resul ts of these tes ts in t e rms of reagent concent ra t ions a t which the se t t l ing t ime curves leveled off. Because the 45-ft sample in the first set would no t disperse in dis t i l led wa te r i t is not inc luded in the table .

These resul ts cannot be in t e rp re t ed wi th ce r t a in ty bu t t hey suggest for the first set of samples e i ther t h a t there was considerable difference in the different layers of clay or rock in the or iginal deposi t , or t h a t the post- deposi t ional a l t e ra t ion was not sufficient to produce uni formi ty . The results with set 2 show large differences in behav ior where s imi la r i ty was expected.

TABLE 3.--REAGENT CONCENTRATION IN MILLII~IOLES PER LITER FOR RAPID FLOCCULATION

Sample 37 ft 52 ft 59 ft

CW 1 CW 2

NaF

23 23

460 230 23

NaC1 ~ FeC1 a

46 460 I 230

_ ~ 145 > 230

37 320

> 400 250 100

0.14 0.14 0.40 0.14 0.10

C O N C L U S I O N S

The exper iments show t h a t the response of different c lay samples to flocculation b y several e lect rolytes , especia l ly wi th different anions, varies g rea t ly bu t there are indica t ions t h a t to some ex ten t the var ia t ions are sys temat ic . The tes t is ve ry sensi t ive bu t th is sens i t iv i ty m a y make i t impossible comple te ly to i n t e rp re t the expe r imen ta l resul ts unt i l the theo ry of f locculat ion is more ful ly deve loped so t h a t the effects of the var ia- bles can be c lear ly eva lua ted . As an empir ica l me thod of compar ing c lay samples, f locculat ion b y e lec t ro ly tes holds considerable promise.

Severa l phenomena were observed in the course of the exper iments t h a t do not seem to be expla ined b y the presen t theories of f locculation. F u r t h e r work is needed on these points .

R E F E R E N C E S

Brindley, G. W. (1958) Ion exchange in clay minerals: in Ceramic Fabrication Processes (edited by Kingery, W. D.): John Wiley & Sons, Inc., New York, pp. 7-23.

Grim, R. E. (1953) Clay Mineralogy: McGraw-Hill Book Co. Inc., New York, 384 pp. Hubbard, C. R. (1957) Mineral resources of Latah County: Idaho Bur. Mines and Geology,

County Rept. 2, 29 pp. Michaels, A.S. (1958) Rheological properties of aqueous clay suspensions: in Ceramic

Fabrication Processes (edited by Kingery, W. D.): John Wiley & Sons, Inc., New York, pp. 23-31.

Searle, A. B. and GrimshavG R. W. (1959) The Chemistry and Physics o/Clays: Interscience, New York, 942 pp.