Chemical and structural characterization of UICC amosite fibres from Penge mine (South Africa)

Crystal structure of UICC amosite fibres

Abstract

In the present work we report the full structural and spectroscopic characterization of an UICC amosite (fibrous grunerite) standard sample from Penge mine (South Africa). The chemical composition was obtained by SEM-EDS and cation site partition was retrieved by complementing chemical, Mössbauer and X-ray powder diffraction data. Cell parameters, fractional coordinates, and site scattering for M(1), M(2), M(3), M(4) were refined using the Rietveld method. The retrieved crystal chemical formula ^A[Na_0.02]_Σ0.02 ^B(Fe²⁺_1.54Mn_0.29Na_0.10Ca_0.07)_Σ2.00 ^C(Fe²⁺_2.92Mg_1.93Fe³⁺_0.15)_Σ5.00 ^T(Si_7.93Al_0.07)_Σ8.00 O_22.00 ^W(OH_2.00)_Σ2.00 is in reasonable agreement with reference data.

Rietveld refinement results evidenced that Fe²⁺ is allocated in the octahedral layer following the site preferences M(1) » M(3) > M(2), whereas Mg preferentially is ordered at M(2). Refined cell parameters are: a = 9.55264(17) Å, b = 18.3069(3) Å, c = 5.33487(8) Å, β = 101.840(3)°, V = 913.11(3) ų. Quantitative Phase Analysis indicates about 10 wt.% of accessory phases including quartz, ankerite and minor stilpnomelane and biotite/annite. Obtained results are the basis for further studies aimed at investigating possible correlation between physico-chemical features of the fibres and their chemical reactivity and toxicity.