Dissolution behaviour of biosoluble HT stone wool fibres

The dissolution behaviour of two types of fibres, the biosoluble HT and the traditional MMVF21 stone wool fibres, in synthetic simulated lung fluid (Gamble's solution) at pH 4.5 was investigated in order to clarify the mechanisms, and the effect of the various constituents in the liquid. The Gamble's solution contains various organic acids and salts. The study showed that organic acids which are able to form complexes with aluminium (e.g. citric and tartaric acid) caused both fibres to dissolve at a high rate at pH 4.5. Organic acids without the ability to form complexes with aluminium (e.g. acetic, maleic, lactic and pyruvatic acid) have no (or minor) impact on the dissolution rate at pH 4.5. The presence of sodium chloride lowers the dissolution rate, especially that of MMVF21. The silica that remains when the silica network has been depleted of aluminium ions (due to citric and tartaric acid) behaves differently in the two fibres. In HT fibres the silica dissolves at a high rate, probably as a diluted sol. Thus the HT fibre has a high dissolution rate in Gamble's solution at pH 4.5. For the MMVF21 fibre, condensation of the silica network as a gel results in a lower dissolution rate. It is assumed that the different Al/(Al+Si) ratios for HT and MMVF21 fibres explain why the fibres behave differently.