Dissolução da crisotila brasileira na presença de dodecilsulfato de sodio e dipalmitoilfosfatidilcolina

AUTOR(ES)
DATA DE PUBLICAÇÃO

2006

RESUMO

The use of chrysotile has decreased markedly because of health risks in the lungs associated with its inhalation. Inhaled particles become coated by extracellular lung fluid, which is mainly dipalmitoylphosphatidylcholine (DPPC). It is known that Brazilian chrysotile is rapidly removed from the lungs, but quantitative studies about DPPC or any other surfactant on chrysotile dissolution process were not investigated. In this work, chemical behavior of chrysotile and its dissolution process in the presence of DPPC were investigated using physiological conditions. Additionally, the influence of the sodium dodecylsulphate (SDS) on the chrysotile dissolution process was studied. Adsorption isotherms for DPPC on sonicated chrysotile were obtained in water and in a buffer solution with pH and ionic strength comparable to lungs medium, at different temperatures 25, 37 and 55 ºC. Adsorbed DPPC onto sonicated chrysotile from water reaches a plateau at approximately 15 mg g, which is half the value observed for physiological conditions. Adsorption isotherms of SDS on sonicated chrysotile were obtained with and without ionic strength control at different temperatures 25 and 40°C. For both temperatures, a maximum of about 14 mg g was observed for the isotherm obtained for the system without ionic strength control. This value is two times lower than the value observed for the systems with ionic strength control. Chrysotile dissolution process was investigated through quantification of magnesium and silicon released in the medium by chrysotile. In the presence of water/DPPC at 37 °C, the magnesium concentration released in the medium by chrysotile was lower than the control, which was about 6.5 x 10 mol L. Silicon concentration, at 37 °C, was not altered by the presence of DPPC. Its concentration was around 3.0 x 10 mol L. In physiological conditions at 37 ºC, magnesium concentration is similar to the control, which is about 2.0 x 10 mol L, meaning that the dissolution process is not affected by the presence of DPPC. The silicon released was also not influenced by the presence of DPPC. The silicon concentration released by chrysotile is similar at all medium tested. The critical micelle concentration (CMC) of SDS influences on the magnesium released by chrysotile. The dissolution mechanisms of brucite and tridymite layers are different. Under physiological conditions, the proposed mechanism of brucite dissolution was based on its interaction with H ions. The mechanism of tridymite dissolution was based on the hydrolysis process. For SDS at water/SDS/chrysotile medium, the mechanism of brucite dissolution was based on the salt formation between magnesium and surfactant.

ASSUNTO(S)

crisotila dissolução surfatante adsorção surfactant adsorption chrysotile dissolution

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