The Effect of Organic Compounds on Si Concentration in Soil Solution - the Comparision of Poly(N-vinylpyrrolidone) and N-methyl-2-pyrrolidone -

The dissolution of amorphous silica in aqueous solution in the presence of organic compounds was investigated as a preliminary experiment to elucidate the effect of organic compound on the Si concentration in soil solution. The organic compounds used in this study were Poly-N-vinylpyrrolidone (PNVP) and N-methyl-2-pyrrolidone (NMP) with carbonyl group that is a common functional groups of natural organic compounds. The dissolution rate and solubility of amorphous silica in each solution containing the organic compounds were investigated and compared with those of pure water under same condition. In PNVP solution, the dissolution of amorphous silica was retarded by covering PNVP adsorbed on silica surface. This fact may be due to stabilization by simultaneous and many hydrogen bonds between silanol groups on silica and carbonyl groups in PNVP. In contrast, in NMP solution, the solubility of amorphous silica increased compared with that in pure water, suggesting the formation of NMP-silicic acid complex. The DFT calculation showed that the stability energy of NMP silicic acid complex was lager than that of silicic acid-water complex {Si(OH)(4) NMP > Si(OH)(4) + H(2)O} in gas phase, suggesting that NMP-silicic acid complex may be stabilized in aqueous solution.