STUDIES ON HYDROTHERMAL REACTION OF ALKALI SOLUTIONS TO KAOLIN, III

Abstract

Continuing the previous studies (This Journal, 1936, 44, 531; 1937, 45, 605), the present authors reported here the results of further studies on the various reactions of alkali to kaolin in wet and dry methods. The following is the brief abstract from the original Japanese communication, as following:
(1) Three kaolin samples were used; (1) Zettlitz kaolin, (2) German kaolin and (3) Hongkong kaolin. They were compared on their chemical compositions by the ordinary total analysis and also by the rational analysis.
(2) These kaolin samples were treated by (a) water, (b) 5% NH₄OH, (c) 5% NaOH or (d) 5% KOH solution for two hours by heating on water bath. The products were compared by their chemical analysis and proved that water and 5% NH₄OH did not react but 5% NaOH and 5% KOH reacted clearly on kaolin.
(3) Concentrated ammonia cal water (28%) was used to heat with kaolin for 1-3 hours under high pressures of 20-70 atmospheres, but it was not observed any clear effect or reaction by ammonia.
(4) Nextly, kaolin samples were heated with 10% or 20% solution of NaOH or KOH on water bath for 5-10 hours, and the products were proved to be nearly (0.4-0.6.)R₂O⋅Al₂O₃⋅(1.9-2.1)SiO₂⋅nH₂O from (1) Zettlitz kaolin and (0.8-0.9)R₂O⋅Al₂O₃⋅(2.7-2.9)SiO₂⋅nH₂O from (2) German kaolin. So that, the reaction was not complete, but it is clear that alkali kaolin hydrate xR₂O⋅Al₂O₃⋅ySiO₂⋅zH₂O can be easily obtained by alkali solution of propper concentration even under ordinary pressure, which fact was already observed and reported by one of the present author in foregoing reports.
(5) These products were tested on the point of dehydration by heating from 110°C to 700°C or 800°C. The curve of weight decrease-heating temperature was clearly different between the products (a) and (b) treated by water and 5% NH₄OH and those (c) and (d) treated by 10% NaOH and 10% KOH solutions. The latter samples of alkali hydrokaolin or alkali kaolin hydrate as abtained in the former section (4) lost some part of their combined water even by warming at 25-110°C and then completely, heating at 200°-300°C but the former samples (a) or (b) obtained by treating with water or NH₄OH solution lost difficultly their combined water by heating at 400-500°C.
(6) These calcined product and alkali kaolin were tested their solubility by the soluble analysis with dilute (10%) HCl solution and then dilute (5%) NaOH solution, and the dissolved part was proved to be R₂O⋅Al₂O₃⋅2SiO₂⋅nH₂O or artificial nepheline type compound.
(7) The mixed powder of kaolin and sodium carbonate was heated at 950°C, the sintered mass was powdered and then extracted by warm water on water bath for excluding completely the excess and free alkali (Na₂O). The final product was proved to be Na₂O⋅Al₂O₃⋅2SiO₂⋅H₂O, which is completely equal to that obtained by heating kaolin and alkali solution as above mentioned in the section (4).
(8) The authors are now further studying on these products for various points and objects, which results will be reported hereafter.