ALUMINOSILICATE PHASES DURING INITIAL CLAY FORMATION - H+-AL-3+-OXALIC ACID SILICIC ACID-NA+ SYSTEM

The solid phases and the precipitation boundary characterizing the system H+‐Al3+‐oxalic acid‐silicic acid‐Na+ are discussed. Model experiments have been used to throw more light on two environmental problems: the formation of sparingly soluble aluminium silicates in oceans and alkaline lakes, which could be determining aluminium and silicate concentrations in pore waters of sediments, and the validity of inorganic and organic mechanisms of podzolization and their significance for soil science. pH and Tyndallometric measurements were performed at constant ionic strength of 0.6 M NaCl at 25°C. Three phases Al(OH)4, H4SiO4 (phase Via), Al2, (OH)6.H4SiO4 (phase VIb) and NaAl(OH)4.(H4SiO4), (phase VIII) determine the precipitation boundary. Phase NaAl(OH)4.H4SiO4 (phase VII precipitates at 0.4pH units above NaAl(OH)4.(H4SiO4)2. Using a set of previously determined binary and ternary complexes, and phases of the subsystems, the following formation constants were deduced: (Formula Presented.) Phases VIa and VIb are described as end‐members of the allophane series with Si: Al ratios of 1:1 and 1.2. Phase VIb was identified with protoimogolite allophane. These two phases are good model clays for podzolic soils and are extremely soluble at pH < 4. Sodium phases could be hydrous feldspathoids. These phases are possible in sediments of seawater or saline lakes. It is suggested that organic and inorganic mechanisms of podzolization operate sequentially and that neither of them alone can completely describe the process. Copyright © 1990, Wiley Blackwell. All rights reserved