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Identification of Kaolinite and Metahalloysite in Tropical

By YASUO KITAGAWA

Department of Soils and Fertilizers, National Institute of Agricultural Sciences

Lateritic soils develop under tropical condi­ and chlorite in sedimentary rocks by the combi­ tions of high and high precipi­ nation of several experimental techniques. tation that is often seasonal. The primary The authors> attempted to work on the are quickly broken down, and the differentiation of kaolinite from metahalloysite extensive precipitation causes the quick re­ both of which have 7 A basal spacing, by moval in solution of any alkalies and alkaline applying electron microscopy, X-ray diffrac­ earths. Aluminum and iron tend to be en­ tion method, infrared absorption spectroscopy, riched in horizon, and the influence of and thermal analysis. Kaolinite and metahal­ material rock frequently disappears. The loysite samples as the from geological organic matter is very rapidly decomposed so deposit were the fraction less than 211. of that it does not accumulate. It is well known Georgian Kaolin and Hongkong Kaolin, re­ that dominant of lateritic soils spectively. Soil minerals were obtained from is kaolin minerals, and other accessory the clay fraction of the soils listed in Table 1. minerals are and minerals. Which species of kaolin minerals occurs in Electron microscopy such soils is interesting and important in studying the properties and the genesis of Electron micrograph of kaolinite and meta­ tropical soils, consequently. obtained from geological deposit is We are often confronted with some diffi­ shown in Plates 1 and 2, respectively, and that culties in identifying clay minerals in soils, of the minerals occurring in soils is repre­ especially, differentiation of (1) sented in Plates 3 and 4. These electron from , (2) kaolin minerals micrographs were taken by direct magnifi­ from chlorite, and (3) kaolinite from meta­ cation of 10,000 at 75 kV after the specimen halloysite. Walker•> differentiated vermiculite was suspended in distiled water and placed from montmorillonite. Wada et aJ. 2 >·3> presented on a mesh covered with thin collodion film. the differentiation of kaolin minerals from The shape of kaolinite and metahalloysite chlorite by intersalation with potassium ace­ particle is hexagonal plate and tubular, re­ tate. Oinuma et aJ.•> identified kaolin minerals spectively (Plates 1 and 2), which is well

Table 1. Soil samp les

Locality Soil type Texture Parent Land and horizon material utilization

Kaolinite Ammy, Southern Diluvial Soil, SiL River deposit Paddy field Ap (0~30 cm) ~ Metahalloysite Kedung halang, Reddish-brown Latosol, HC Old fan deposit Paddy field Bogor, West Java Big (27~46 cm) 59

Plate l. Electron micrograph"'• of kaolinite from Plate 3. Electron micrograph of kaolinite from geological deposit soil

~C!nlllm·~ "<· Plate 2. Electron micrograph of metahalloysite Plate 4. Electron micrograph of metahalloysite from geological deposit. from soil known. On the other hand, the particles of like particles coexisted with metahalloysite soil minerals also show same shape although particles in Plate 4 is halloysite. their size are generally smaller than the form­ Electron microscopy is surely very effective ers (Plates 3 and 4). A little amount of onion- to differentiate kaolinite from metahalloysite 60 J ARQ Vol. 10, No. 2, 1976 in soils, but much skill is needed to prepare specimen and to take electron micrograph I\ Original N2H4-KOAC N2 H4- Nt-k.Cl properly.

X-ray diffraction method I ·t· _J_ ~ 14.2~ 14.5 10.3 1.2 X-ray diffraction pattern of kaolinite and 7.2 7.2 l metahalloysite by powder method is shown in Fig. 1. These were obtained with Cu-Ka H _J _L 7.4 14.2L 7. 1 10.5 7.4 l I II 7.2 A ·3.59'A 7.4 A 3.62A Fig. 2. Changes of 7 A basal spacing of kaolinite and metahalloysite in soils by treatment 002/001 002/001 with hydrazine-potassium acetate and Deposit =0:J. :0.5 -ammonium chloride. I, kaolinite ; II, metahalloysite 001 002" 001 002

7.2 'A 3.59'A 7.4 'A 3.621' pletely in metahalloysite with .hydrazine­ ammonium chloride system. Wada et a1.3>.a> 002/001 002/001 Soil :0.9 = 0.5 already reported that kaolinite in deposit tends to resist against intersalation. This method 001 002 001 002 is only effective to identify metahalloysite, consequently. Fig. 1. Position and intensity of basal spacing of kaolin minerals obtained from geo­ logical deposits and soils. I, kaolinite; Infrared absorption spectroscopy II, metahalloysite The infrared absorption band associated radiation at 40 kV, 20 mA, slit system of with 0 -H stretching vibration of structural 1·(DS, SS)-0.3mm(RS), and a scanning hydroxyl group in kaolin minerals appears speed of 2· (28) / min. Basal spacing of in the range of wave number from 3,700 to kaolinite was 7.2 A for 001-reflection and 3,600 cm· 1, and splits to three or four band 3.59 A for 002-reflection, irrespective of de­ in kaolinite and two in metahalloysite, irre­ posit or soil mineral. The intensity ratio, spective of deposit or soil origin as shown I (002) /I (001 ) was 0.8 or 0.9 in kaolinite. in Fig. 3. Accordingly, kaolinite and meta­ On · .the other hand, the basal spacing of halloysite can be differentiated by observing metahalloysite was 7.4 and 3.62 A, and in­ this infrared absorption band. Coexist­ tensity ratio was 0.5 in both origin mineral. ence of some amount of gibbsite and Kaolinite and metahalloysite could be differ­ 2 :1-type minerals did not interfere the differ­ entiated by measuring the position and relative entiation of kaolinite and metahalloysite by intensity pf basal spacings. this method. Only one band associated with The change of ba'~al spacing of kaolin 0 -H stretching vibration of structural hy­ minerals in soils by hydrazine intercalation­ droxyl group in other clay minerals such as intersalation is shown in Fig. 2. The Teflection montmorillonite, ve1·miculite, and chlorite at 7 A of soil kaolinite was hardly changed, is situated near 3,620 cm·', and the band of while that of metahalloysite was shifted to gibbsite that is frequently detected in Jateritic 14 A, by the treatment with hydrazine­ soils splits to five bands at 3,630, 3,530, 3,450, potassium acetate. The basal spacing was 3,400 and 3,380 cm-•. In gibbsite, the band shifted to 10 A partially in kaolinite and com- at 3,630 cm-• was not so strong, and on ly two 61

Deposit Soil Thermal analysis I II I[ It was difficult to differentiate kaolinite and metahalloysite by means of differential thermal analysis and thermogravimetry although these techniques are very effective to differentiate kaoline minerals from other clay minerals. kaolin minerals from other clay minerals. 3670 3650 550°C and a sharp exotherm near 900°C in 3620 differential thermal analysis. The weight loss 3620 3690 of kaolin minerals in the temperature region 3690 from 400 to 600°C is about 14 per cent, and Fig. 3. Infrared absorption band associated with far larger than other clay minerals. 0 - H stretching vibration of structural hydroxyl group in kaolin minerals obtained from geological deposits and Conclusion soils. I, kaolinite; II, metahalloysite. The combination of X-ray diffraction method, infrared absorption spectroscopy, Deposit Soil electron microscopy and hydrazine intercala­ II II tion-intersalation is most effective to identify kaolinite and metahalloysite occurring in the clay fraction of soils. If it is difficult to employ all techniques mentioned above together, kaolinite and metahalloysite might be identi­ 1080 fied by combining two techniques which are 0 w 1030 easily available. 1030 1005 1025 1005 1025 This method for the differentiation of kaolinite and metahalloysite is surely effective Fig. 4. Infrared absorption band associated with to be applied in the case of lateritic soils of Si- 0 stretching vibration of kaolin minerals in geological deposits and soils. which dominant is kaolin miner­ I, kaolinite; II, metahalJoysite als, but is hardly applicable to soils with large amount of 2 :I-type minerals and others bands at 3,530 and 3,450 cm· 1 were strong. The coexisting. bands shown by G in Fig. 3 are associated with gibbsite. References The absorption band near 1,000 cm·1 is associated with 0 -H stretching vibration of 1) Walker, G. F.: Differentiation of vermiculite kaolin minerals, and splits to three bands in and smectites in clays. Clay Miner. Bull., 3, 154-163 (1957) . kaolinite and two in metahalloysite, irrespec­ 2) Wada, K.: Lattice expansion of kaolin tive of deposit or soil minerals (Fig. 4), which minerals by treatment with potassium ace­ also would be applied to the differentiation tate. A1ne1·. Mineral., 46, 78-91 (1961). of kaolinite and metahalloysite. 3) Wada, K. & Yamada, H.: Hydrazine inter­ The infrared absorption spectrum was calation-intersalation for differentiation of measured by tablet method with potassium kaolin minerals from chlorites. Amer. Min,­ ernl., 53, 334-339 ( 1968) . bromide. The tablet was prepared by pressing 4) Oinuma, K., Kodama, H. & Kobayashi, K.: a mixture of 1 or 0.5 mg of specimen with chlorite. Nenclo Kagaku (J. Clay Sci. Soc. 2 200 mg of potassium bromide at 400 kg/cm • J av

5) Kitagawa, Y.: Identification of kaolinite 6) Wada, K.: Use of salt complex in differen­ and metahalloysite occurring in soils. Nenclo tiation of halloysite from kaolinite. Nendo l(agakit (J. Clay Sci. Soc. Japan), 14, 90-97 l(agaku no Shinpo ( Abs. Adv. Cl