Detection and Characterization of Polymeric Al-Si Species in acidic forested soils

The present study is aimed to the detection and characterization of polymeric HAS in solutions collected in acidic forest soils (pH greater 4.5) located in France and in Austria. The presence and stability of monomeric HAS (one mole of Si per mole of HAS) is almost well-known for experimental studies(e.g. Farmer and Lumsdon, 1994; Pokrovski et al., 1996; Salvi et al., 1998). However, the occurence and behavior of polymeric HAS remains to be studied. Dietzel (2000) showed that upon dissolution of silicate minerals monosilicic as well as polysilicic acids are liberated into the solution. Such polysilicic acids are thermodynamically unstable but may survive up to several months in acid solutions. These polymeric Si species very likely react with Al to polymeric HAS of a enhanced metastabilities. Occurence of monomeric and polymeric HAS may significantly reduce the availability of Al3+ (toxic) and Si(OH)4 for weathering and neoformation of silicates in natural systems