Rapid+Chemical+Analysis+of+Clays

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Clay3 and Clay Minerals, Vol . 31, No. 6 , 440 -446 , 1983.

C O M P A R I S O N O F R A P I D M E T H O D S F O R C H E M I C A LA N A L Y S I S O F M I L L I G R A M S A M P L E S

O F U L T R A F I N E C L A Y S

S. L. R E T T I G , l J. W. M A R I N E N K O , 2 H. N. K H O U R Y , 3 A N D B. F. J O N E S 1' U.S. Geological Survey, National Center, MS 432, Reston, Virginia 220922 U.S. Geological Survey, National Center, MS 973, Reston, Virginia 22092

3 Department of Geology and Mineralogy, University of Jordan, Amman, Jordan

Abstract--Two rapid methods for the decomposition and chemical analysis of clays were adapted for usewith 20-40-mg size samples, typical amounts of ultrafine products (


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Vol. 31, No. 6, 1983 Chemical analysis methods for clays 441< 2.0-~m portion was subjected to high-speed centrif-ugation to obtain suspensions of


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442 Rettig, Marinenko, Khoury, and Jones Clays and Clay Mineralsthe addition of 1:1 ammonium hydroxide at a pH of6.6-6.7. The solut ion was filtered through filter paper,the precipitate was washed with hot 2% ammoniumchloride, and the filtrate was reserved for the deter-mination of calcium and magnesium. The R203 pre-cipitate was dissolve d off the filter paper with di luteHCI, and the precipitation and filtration process re-peated. The precipitate was then ignited at 1100~ toconstant weight. After weighing, the precipitate wastransferre d to a Vycor crucible, fused with 1 g of po-tassium pyrosulfate, leached with dilute sulfuric acid,and d iluted to 100 ml in a volumetr ic flask. A n aliquo tof this solution was used to determine total ironspectrophometrically with o-phenanth roline.

The solution containing calcium and magnesium wasmade basic with NH4OH, and heated to boiling. Cal-cium was precipitated by the addition of ammoniumoxalate. After digestion on a steam bath, the precipitatewas filtered onto filter paper an d red issolved with HC1.The process was then repeated, and the second precip-itate was ignited to oxide.

The combined filtrates from the calcium determi-natio n were treated with 20% di am mon iu m hydrogenphosphate and made basic with ammo ni um hydroxideto precipitate magnesium. After standing overnight,the pre cipitate was filtered on filter paper, redissolved,and the precipitation process repeated. The precipitatewas then ignited to constant weight at 1000~176

To determine Na and K, a separate sample was putinto solution by heating with HF and HC104 and di-luted to 100 ml in a volumetric flask. An aliquot ofthis solution was used for a sodi um det ermina tion aftersufficient KCl was added to make the con centratio n ofpotassium equal to 0.2%. Anoth er aliquot was similarlytreated with NaC1 and then used to determine potas-sium. Both determin ations were made by atomic ab-sorption spectrophotometry.

C o m p a r a t i v e m e t h o d o l o g yTo evaluate the results of the three methods it was

necessary to use a co mmon basis for comparison. Thus,the sum of the major constituents, i.e., SiO2, A1203,Fe203, CaO, MgO, Na20, and K20 for each analysiswas multiplied by the appropriate factor to make thesum equal 100%. In the classical rock analysis, FeOwas recalculated as Fe203 and added to the de ter mine dFe203 to give a total iron value. Tables 1 and 2 showthe chemica l analyses of the eight clays from the Amar -gosa Desert, Nevada, and the two from Lake Abert,Oregon.

In the lithium borate fusion and HF-dissolutionmethods, aluminum was determined colorimetricallyby reaction with ferron (8-hydroxy, 7-io do-5-qui nolinesulfonic acid) as described by Skougstad et al . (1979).They reported that the presence of fluoride was re-sponsible for low alu min um values. In the lith ium bo-

rate fusion method, a lum inu m values were unaffectedbecause fluorine was complexed as fluoborates. In theHF-dissol ution method, however, the alumi num de-termination was seriously affected even though boricacid was added after the dissolution. Probably somefree fuoride ions remained uncomplexed. To ensurethe removal of any excess fluoride ion, an aliquot ofthe sample solution was evaporated to dryness in aplat inum dish with 1 ml of concentrated H2SO4 andredissolved by gentle warming with dilute HC1. Thissolution was used for the alu min um determination ,and the results agree well with the classical rock anal-ysis values, as can be seen in Tables 1 and 2. Thefluoboric acid matrix, however, led to low results forcalcium, sodium, and potassium when compared tothe lith ium borate fusion and the classical rock method.Lee and Gfiven (1975) reported similar problems ofchemical interferences in the HF-d issolut ion method.They overcame the probl em by preparing the standardsolutions of calcium, magnesium, and iron with siliconand alum inu m concentrations matching those of thesample. We attempted to solve the problem by ex-tending the use of the fluoride-free solution to includeevery consti tuen t except silica. To ans wer the questio nof whether sample in homogene ity might be responsiblefor the differences, a few samples were divided intotwo equal portions after the HF-dis solutio n and onlyone was evaporated with H2SO4. Iron, calcium, mag-nesium, sodium, and potassium were then determinedon each portion. Results in Table 3 show that Ca, Na,and K are consistently lower in the por tion untreate dwith H2SO, and therefore the discrepancy was notcaused by sample inhomogeneity. Iron values areslightly higher in the untre ated port ion, an d there is nodiscernible trend for magnesium. The low results forcalcium in the fluoboric acid matrix can be readilyaccounted for by the precipitation of insoluble calciumfluoride, but the lower results for sodium and potas-sium are harder to explain. If the fluoborate matri x hasa depressant effect, why does not the lithium boratematrix have a similar effect? In the HF-dissolutionmethod, some free fluoride ions may remain eve n afteran excess of boric acid has been added. Furthermore,the total amou nt of HF and boric acid added is greaterthan the am oun t of lithium borates used in the fusionmethod so that the HF-diss olution matrix is more con-centrated by a factor of 10.

The results o f a study o f reagent blan ks are expressedin Table 4 as percentages of an ass umed sa mple weightof 30 mg. It can be seen that blank values are lowestfor the lithium borate fusion and highest for the HFdissolution followed by evaporation. Surprisingly, itappears that most of the reagent contami nati on in theHF dissolution is due not to the rather large quantityof boric acid which had to be used to complex the HF,but to the sulfuric and hydrochloric acids used to vol-atize the HF and boric acid. Reagent grade acids were


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Vol. 31, No. 6, 1983 Chemi cal analysis met hod s for clays 443

Table 1. Chemical analyses of 20--40-mg samples of clays from the Amarg osa Desert, Nevada, by three analytical methods.Sample number SiO2 A1203 FezO3 CaO MgO Na20 K20

12-14Classical rock anal.Li borate fusionP7Classical rock anal.Li borate fusionHEC-1Classical rock anal.Li borate fusionKinney bentonite #1Classical rock anal.Li borate fusionKinney bentonite #2Classical rock anal.Li borate fusion

HF diss. z

HF diss. + H2SO 4 evap.

63.7 4.33 1.21 n.d. 28.0 0.77 1.9463.2 3.72 1.79 n.d. 28.7 0.89 1.6863.8 1.57 0.51 n.d. 28.4 4.54 1.1662.9 1.30 0.69 n.d. 28.7 5.27 1.1464.0 3.08 1.16 n.d. 26.7 4.54 0.5162.8 2.73 1.20 n.d. 26.8 5.43 0.9660.5 3.01 1.21 n.d. 28.7 5.40 1.0967.9 23.0 0.75 n.d. 6.80 1.21 0.3167.9 21.9 1.64 n.d. 6.82 1.50 0.3267.29 21.01 1.29 1.68 7.22 1.29 0.2668.82 21.06 1.70 0.95 6.85 1.38 0.2067.06 21.99 1.67 0.97 6.72 1.40 0.2069.67 18.99 1.99 0.48 7.48 1.23 0.1570.45 18.15 1.84 0.56 7.61 1.24 0.1770.47 18.58 1.82 0.49 7.25 1.28 0.1568.92 19.61 1.83 0.26 8.08 1.16 0r. 1568.59 20.02 1.72 0.28 8.09 1.18 0.1365.08 22.54 1.70 1.58 7.44 1.43 0.2366.47 21.65 1.59 1.58 7.10 1.36 0.21

KeroliteClassical rock anal. 63.32 0.86 0.37 0.37 33.88 0.74 0.49Li borat e fusion 64.61 0.52 0.32 1.94 32.15 0.23 0.27HF diss. + H2SO4 evap. 67.07 0.25 0.41 0.41 30.69 0.83 0.3365.48 0.17 0.41 0.37 32.62 0.66 0.32SEP-2Classical rock anal.Li borate fusion 67.5 1.49 0.62 n.d, 29.1 0.85 0.4266.5 0.95 0.64 n.d, 30.6 0.74 0.57

66.5 1.33 0.52 n.d, 30.4 0.77 0.42SepioliteClassical rock anal. 66,70 1.12 0.37 0.37 30.43 0.37 0.62Li borate fusion 67,83 0.69 0.48 0.05 29.98 0.53 0.47HF diss. + H2SO4 evap. 67,75 0.64 0.71 0.05 30.09 0.49 0.30All values in anhy drou s wt. %; n.d. = not determ ined.2 Alu min um dete rmined in fluoride-free aliquot.

Table 2. Chemical analyses of 20-40 -mg samples of clays from Lake Abert, Oregon by three analytical methods.sample number SiO2 A1203 F%O3 CaO MgO Na20 KzO

AB21jbLi borat e fusion 57.70 13.09 12.64 0.12 10.38 2.64 3.43HF dis s? 59.15 12.39 13.33 0.01 10.87 2.19 2.05HF diss. + H2SO4 evap. 61.32 10.50 12.50 0.16 10.02 2.47 3.02HF diss. + HzSO4 evap. 60.83 11.59 12.48 0.17 9.41 2.55 2.98

AR33


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444 Rettig, Marinenko, Khoury, and Jones C l a y s a n d C l a y M i n e r a l sTable 3. Comparison of methods employing HF dissolutionand HF dissolution followed by evaporation with H2SO4.

Sample number Fe203 CaO MgO Na20 K20A B 2 1 jbHFdi ss. 12.78 0.07 10.49 2.20 2.26HFd iss .+H 2SO, evap. 12.50 0.16 10.02 2.47 3.02

HFdiss. 12.56 0.05 10. 40 2.16 2.11HFdiss.+ H2SO4ev ap. 12.48 0.17 9. 41 2.55 2.98A H 3 3 < 0 . 2 u mHFdiss. 8.55 0.14 3.43 2.99 0.63HF diss. + H/SO4 evap. 8.25 0.30 4.37 3.50 1.06

HFd iss. 8.41 0.08 3.77 3.06 0.62HFdiss.+ H2SO4ev ap. 8. 23 0.2 1 4.18 3.30 0.79A R 3 3 0 . 2 -2 . 0 # mHFdi ss. 6.70 0.40 2.47 1.06 0.76HFdi ss. +H2S O, evap. 6.53 0. 91 3. 15 1.33 1.19

HFdi ss. 6.70 0.34 2.56 1.01 0.74HFdiss.+H 2SO4eva p. 6.48 0.8 1 2.89 1.19 1.08All values in anhydrous wt. %.

used in this study; higher-purity acids would be pref-erable.

DISCUSSION OF RESULTSStandard deviation s from the classical analysis were

calculated from the data in Tables 1 and 2 for thosesamples whic h were analyzed by all three meth ods, i.e.,Kinney bentonite #2, kerolite, sepiolite, and sampleAR33 0.2-2.0 urn. The standard deviations for SiO2,AlzO3, Fe203, and MgO were calculated from all 18analyses, but for Na20 and KzO, the results of HFdissolution alone were considered erroneous, and theirstandard deviations were calculated from only 12 anal-yses. Th e standa rd devi atio ns are SiO2 = 1.83%,A1203 = 1.49%, Fe/O 3 = 0.23 %, Mg O = 0.9 6%,Na20 = 0.18%, and KzO = 0.09%.

The data in Tables 1 and 2 show several rather large

variations in CaO between the different methods. Forthe Kinney bentonite #2 and the sepiolite, the valuesfor the classical rock analysis are muc h greater, and forthe kerolite sample, the lithium borate fusion value ismuch larger than the others. Some o f this variationmay be due to the presence of calcite. The samples inthis study were not treated to remove carbonates, andthe Amargos a Flat clays are associated with authigeniccalcite and d olomit e (Eberl e t a l . , 1982). It is also pos-sible that in samples with very low calcium content,the classical rock analysis is less accurate than atomicabsorption method s for calcium, especially when mag-nesium is abundant. Maxwell (1968) noted that thegreatest possibility for error in the calcium determi-nation lies in the co-precip itation of magnesium.

The presence of dolom ite may also be responsiblefor some o f the va riation in SiO2:Mg ratios in the mi xed-layer kerolite/smectites. Serpentine has also been sus-pected (Eberl e t a L , 1982), and its higher magnesiumcontent would increase the magnesium levels of sam-ples relative to silica.

The data in Tables 1 and 2 also show that the sampleswith high alumi num content, such as Kinney bentoniteand the Lake Abert clays, have similar inverse ratiosbetween silica and aluminum. As silica increases, alu-minu m decreases so that combi ned percentages remainrelatively constant. The shift is only between valuesfor silica and al uminum , and other constituents are notnoticeably affected. Kinney bentonite m ay cont ain micaimpurity (Khoury e t a l . , 1982), and the Lake Abertsediments contain fine-grained volcanic plagioclase(Deike and Jones, 1980). The potassium and sodiumcontent, respectively, in these miner als is small relativ eto silica and alumina so that it would be difficult todetect small amounts in the analyses which had es-caped detection by X-ray powder diffraction.

Thus, it appears that some o f the discrepancies inTables 1 and 2 are caused by sample hetero geneit y

Table 4. Reagent blanks for Li borate fusion and HF-dissolut ion methods.Metthod of dissolution SiO2 AI203 Fe203 CaO MgO Na20 K2O

Li borate fusion 0.00 0.09 0.03 0.14 0.00 0.04 0.020.00 0.09 0.01 0.11 0.00 0.03 0.000.00 0.08 0.01 0.06 0.00 0.04 0.000.080.050.05HF dissolution

HF dissolution + H2SOa evap. 0.000.000.060.06

0.00 0.00 0.00 0.04 0.000.00 0.110.00 0.060.30 0.06 0.17 0.03 0.07 0.000.30 0.06 0.15 0.05 0.11 0.08

0.13 0.08 0.15 0.040.13 0.03 0.07 0.02

All values in wt. %.


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V o l . 3 1 , N o . 6 , 1 9 8 3 C h e m i c a l a n a l y s i s m e t h o d s f o r c l a y s 4 4 5

e x a c e r b a t e d b y t h e u s e o f v e r y s m a l l s a m p l e s . N e v e r -t h e le s s , b o t h t h e l i t h i u m b o r a t e f u s i o n a n d t h e H F -d i s s o l u ti o n m e t h o d s p r o v i d e a r a p id a n d c o n v e n i e n tm e a n s o f a n a l y z in g s m a l l a m o u n t s o f cl ay s. T h e a n a l -y s e s h a v e p r o v e d s u f f ic i en t ly re p r o d u c i b l e t o m i n i m i z ee r r o r i n t h e c a l c u la t i o n o f cl a y m i n e r a l f o r m u l a e . R e p -r e s e n t a t i v e m a x i m u m v a r i a ti o n s , in a t o m s p e r u n i tf o r m u l a o f t h e s m e c t i t e t y p e b a s e d o n 2 2 n e g a t i v ec h a r g e s a r e a s f o l lo w s : 0 . 0 9 f o r S i, 0 . 0 3 f o r A 1, 0 . 0 1 5f o r F e , 0 . 0 7 f o r M g , 0 . 0 3 f o r N a , a n d 0 . 0 1 f o r K .

I t s h o u l d b e k e p t i n m i n d t h a t s o m e e r r o r h a s b e e ni n t r o d u c e d t h r o u g h d e t e r m i n a t i o n o f o n l y t h e m a j o rc o n s t i t u e n t s w h i c h h a v e b e e n a s s u m e d t o co n s t i t u te1 0 0 % o f th e s a m p l e . I f o t h e r e le m e n t s , s u c h a s t i t a n i u mo r m a n g a n e s e , a r e p r e s e n t in s i g n if i c a n t a m o u n t s , t h e yc a n e a s i ly b e a p p r a i s e d . T h e p r e s e n c e o f s i g n i fi c a n tq u a n t i t i e s o f a n i o n s o t h e r t h a n o x y g e n o r h y d r o x y lp r e s e n t s a g r e a t e r p r o b l e m , h o w e v e r , a n d t h e t e c h -n i q u e s f o r s u c h a n a l y s e s i n v e r y s m a l l s a m p l e s w e r en o t i n v e s t i g a t e d i n t h i s s t u d y .

A C K N O W L E D G M E N T SW e t h a n k F . B r o w n , F . J . F l a n a g a n , a n d H . M a y f o r

t h e i r re v i e w o f t h e m a n u s c r i p t . W e a l s o p a r t i c u l a r l yw i s h t o t h a n k D . D . E b e r l a n d F . A . M u m p t o n f o r t h e i rv a l u a b l e s u g g e s ti o n s , a n d B e t t y L . H u d n e r f o r p a t i e n th e l p d u r i n g t h e p r e p a r a t i o n o f th e m a n u s c r i p t .

R E F E R E N C E SB e r n a s , B . ( 1 9 6 8 ) A n e w m e t h o d fo r d e c o m p o s i t i o n a n dc o m p r e h e n s i v e a n a l y s i s o f s i l i c a t e s b y a t o m i c - a b s o r p t i o ns p e c t r o m e t r y : Anal. Chem. 4 0 , 1 6 8 2 - 1 6 8 6 .D e i k e , R . G . a n d J o n e s , B . F . ( 1 9 8 0 ) P r o v e n a n c e , d is t r i -b u t i o n , a n d a l t e r a t i o n o f v o l c a n i c s e d i m e n t s i n a s a l i n ea l k a l i n e l a k e : i n Hypersaline Brines and Evaporitic Envi-

ronments, A . N i s s e n b a u m , ed . , E l s e v ie r , A m s t e r d a m , 1 6 7 -193.E b e r l , D . D ., J o n e s , B. F . , a n d K h o u r y , H . N . ( 1 9 8 2 ) M i x e d -l a y e r k e r o l i t e / s t e v e n s i t e f r o m t h e A m a r g o s a D e s e r t , N e -v a d a : Clays & Clay Minerals 3 0 , 3 2 1 - 3 2 6 .H i l l e h r a n d , W . F . , L u n d e l l , G . E . F . , B r i g h t , H . A . , a n d H o f f -m a n , J . I . ( 1 9 5 3 ) Applied Inorganic Analysis: W i l e y , N e wY o r k , 3 9 3 - 9 5 7 .I n g a m e l l s , C . O . ( 1 9 6 4 ) R a p i d c h e m i c a l a n a l y s i s o f s i li c a ter o c k s : Talanta 1 1 , 6 6 5 - 6 6 6 .J o n e s , B . F . a n d W e i r , A . H . ( 1 9 8 3 ) C l a y m i n e r a l s i n a s a l i n e ,a l k a l i n e l a k e : Clays & Clay Minerals 3 1 , 1 6 1 - 1 7 2 .K h o u r y , H . N . ( 1 9 7 9) M i n e r a l o g y a n d c h e m i s t r y o f s o m eu n u s u a l c l a y d e p o s i t s i n t h e A m a r g o s a D e s e r t , s o u t h e r nN e v a d a : P h . D . t h e s i s , U n i v . I l l i n o is , U r b a n a , I l l in o i s , 1 71PP .K h o u r y , H . N . a n d E b er l , D . D . ( 1 9 7 9 ) B u b b l e - w a l l s h a r d sa l t e re d t o m o n t m o r i l l o n i t e : Clays & Clay Minerals 2 7 , 2 1 9 -2 9 2 .

K h o u r y , H . N . a n d E b e r l , D . D . ( 1 9 8 1 ) M o n t m o r i l l o n i t ef r o m t h e A m a r g o s a D e s e r t, s o u t h e r n N e v a d a , U . S . A . : N .Jahrb. Mineral Abh. 1 4 1 , 1 3 4 - 1 4 1 .L a n g m y h r , F . J . a n d P a u s , P . C . ( 1 9 6 8 ) T h e a n a l y s i s o fi n o r g a n i c s il i c eo u s m a t e r i a l s b y a t o m i c a b s o r p t i o n s p e c t r o -p h o t o m e t r y a n d t h e h y d r o f lu o r i c a c id d e c o m p o s i t i o n t e c h -n i q u e : Anal Chim. Acta 43, 3 9 7 - 4 0 8 .L e e , R . W . a n d G t i v e n , R . ( 1 9 7 5 ) C h e m i c a l i n t e r f e r e n c e s i na t o m i c a b s o r p t i o n s p e c t r o m e t r i c a n a l y s i s o f s i li c a te s i n t h ef l u o b o r i c - b o r i c a c id s m a t r i x : Chem. Geol. 1 6 , 5 3 - 5 8 .L u n d e l l , G . E . F . a n d H o f f m a n , J . I . ( 1 9 3 8 ) Outlines ofMethods of Chemical Analysis: W i l e y , N e w Y o r k , p . 1 8 3 .M a x w e l l , J . A . ( 1 9 6 8 ) Rock and Mineral Analysis: W i l e y ,I n t e r s c i e n c e , N e w Y o r k , 5 8 4 p p .S h a p i r o , L . ( 1 9 7 5 ) R a p i d a n a l y s is o f s i l i c a t e , c a r b o n a t e , a n dp h o s p h a t e r o c k s - - r e v i s e d e d i t i o n : U.S. Geol. Surv. Bull.1 4 0 1 , 7 6 p p .S k o u g s t a d , M . W . , F i s h m a n , M . J . , F r i e d m a n , L . C . , E r d -

m a n n , D . E ., a n d D u n c a n , S . S . ( 1 9 7 9 ) M e t h o d s f o r d e -t e r m i n a t i o n o f i n o r g a n i c s u b s t a n c e s i n w a t e r a n d f l u v i a ls e d i m e n t s : U.S. Geol. Surv. Techn. Water Resour. Invest.,B o o k 5 , C h . A 1 , 6 2 6 p p .(Received 17 May 1982; accepted 27 January 1983)

Pe3mMe---~Ba 6blCTphle MeTO jla jUIa pa3no>KeHnn n XnMl4qecKoro ana.nn 3a r~nH 6bIAn aj lanTnpoBaHbinprl Hcnoyib3OBaHllr l o6 pa3 tlo8 pa3MepoM 20 -40 Mr, Wrll lMqHbIX KoJmqecTB yJlbTpaMe.rlKl 'lX npo~yKToB(JlnaMeTpOM


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446 Rettig, Marinenko, Khoury, and Jones Clays and Clay MineralsResiimee--Zwei schnelle Methoden ftir die AuPoereitung und chemische Analyse yon Tonen wurden aufProbernmengen yon 20-40 mg zugeschnitten, da dies der typischen Probenmenge yon extrem kleinenProdukten (< 0,5 ~m Durchmesser) entspricht, die bei der Trennung von Ton mineralen mittels modernerMethoden entstehen. Die Ergebnisse dieser schnellen Methoden wurden mit denen klassischer Gesteins-analysen verglichen. Die zwei Method en bestehen aus der Herstellung einer Lithium-Metaborat schmelzeund d er Aufl6sung in HF in ei nem geschlossenen Beh~ilter. Die letzte Meth ode wurde dah inge hendabgewandelt, dal3 sie eine anschliel3ende Verdampfung mit konzentrierter H2SO 4 und Wiederaufl~sungin HCI beinhalt ete, wodurch die Beeinflussung durch das F-Ion bei d er Best immung yon AI, Fe, Ca, Mg,Na, un d K verringert wurde. Die Ergebnisse diese r zwei Metho den sti mmen recht gut fiberein mi~ denErgebnissen yon klassischen Methoden zur Minimisierung der Fehler bei der Berechnung yon Struktur-formeln yon Tonmineralen. ReprSsentative Maximalabweichungen betragen in Atome n pro Formelein-heit eines Sme ktittyps, ba sieren d auf 22 negativen Ladungen, 0,09 ftir Si; 0,03 for A1; 0,15 ftir Fe; 0,07ftir Mg; 0,03 ft~r Na; und 0,01 ftir K. [U.W.]R~sumr--Deux mrtho des rapides pour la drcomposit ion et l'analyse chimique d'argiles ont 6t6 adoptrespour ~tre employres avec des 6chantillons de taille 20-40 rag, quantitrs typiques de produits ultra-fins(

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