Conversion of chrysotile asbestos to smectite

In the United States, chrysotile asbestos is legally declared a carcinogenic health hazard, which requires the removal of all forms of asbestos in all public places. Upon removal, the chrysotile is disposed in landfills; thus moving the hazard to another relatively secure location. In this study, we are investigating the possibility of altering chrysotile to a non-hazardous mineral, such as smectite, which potentially may be economically viable. Chrysotile from Thetford Mines in Quebec, Canada was treated first with mild organic acids, such as formic and oxalic acids, at concentrations 0.5 to 2.0N at 200‹C in Teflon-lined 12.0 ml Parr bombs. Examination of the reaction products with X-ray diffraction and Analytical Electron Microscopy indicated a poorly crystalline iron-bearing kerolite-type 2:1 layer silicate with a thin foily morphology was found to form during the acid pretreatment along with significant amounts of amorphous silica. The magnetite impurity in the initial chrysotile asbestos served as the source of iron in the above reactions. Kerolite seems to form from the following reaction: Mg6Si4O10(OH)8(S)+6.02H+(aq)+0.54Fe2+ (aq) ¨ (chrysotile) (Mg2.46Fe2+0.54)Si4O10(OH)2∙nH2O(S)+3.55Mg2+(aq) (kerolite) Subsequently, kerolite was reacted with 0.2N NaOH for 48 to 96 hours at 200‹C. A highly crystalline smectite was found to form with the same foily morphology as the kerolite precursor. X-ray spectral analyses of the kerolite precursor and smectite suggest the following reaction to take place: (Mg2.46Fe2+0.54)Si4O10(OH)2∙nH2O(S)+3.55Mg2+(aq) + 0.54NaOH(aq) + 0.01Fe3+ (aq)¨ Na0.54(Mg2.99Fe2+0.01)(Si3.46 Fe3+0.54)O10(OH)2(s)+0.54Si 4+(aq) (saponite) The reaction products, kerolite and smectite, definitely possess a non-hazardous morphology and has promising economic potential.