A multi-methodical characterization of a sauconite (Zn-bearing trioctahedral smectite) specimen from the Skorpion ore deposit (Namibia) was obtained by combining X-ray powder diffraction (XRPD), Cation Exchange Capacity (CEC) analysis, Differential Thermal Analysis (DTA), Thermogravimetry (TG), Fourier Transform Infrared spectroscopy (FTIR) and Transmission Electron Microscopy (TEM-HRTEM-AEM). The X-ray diffraction powder pattern exhibits the typical features of turbostratic stacking disorder with symmetrical basal 00l reflections and long-tailed hk- bands, confirmed also by TEM observations. Besides sauconite, the sample also contains minor amounts of kaolinite, dioctahedral smectite and quartz. CEC analysis provides a total of Ca (∼69%), Mg (∼26%), Na (∼4%) and K (0.7%) exchangeable cations. Therefore, Zn is located exclusively within the octahedral site of sauconite. TG analysis provides a total mass loss of about 17% in the studied sample. Three endothermic peaks can be observed in the DTA curve, associated to dehydration and dehydroxylation of the material. An exothermic peak at 820°C is also present as a consequence of dissociation and recrystallization phenomena. The infrared spectrum shows the typical Zn3OH stretching signature at 3648 cm-1, whereas, in the OH/H2O stretching region two bands at 3585 and 3440 cm-1 can be associated to stretching vibrations of the inner hydration sphere of the interlayer cations and to absorbed H2O stretching vibration, respectively. Diagnostic bands of kaolinite impurity at ~3698 and 3620 cm-1 are also found, whereas 2:1 dioctahedral layer silicates may contribute to the 3585 and 3620 cm-1 bands. Finally, using the one layer supercell approach implemented in the BGMN software, a satisfactory XRPD profile fitting model for the Skorpion sauconite was obtained. The findings have implications not only for economic geology/recovery of critical metals but, more generally, in the field of the environmental sciences.
New insights into the crystal chemistry of sauconite (Zn-smectite) from the Skorpion zinc deposit (Namibia) via a multi-methodological approach
Schingaro E.
Writing – Review & Editing
;Ventruti G.Investigation
;Vinci D.Investigation
;Lacalamita M.Investigation
;
2021-01-01
Abstract
A multi-methodical characterization of a sauconite (Zn-bearing trioctahedral smectite) specimen from the Skorpion ore deposit (Namibia) was obtained by combining X-ray powder diffraction (XRPD), Cation Exchange Capacity (CEC) analysis, Differential Thermal Analysis (DTA), Thermogravimetry (TG), Fourier Transform Infrared spectroscopy (FTIR) and Transmission Electron Microscopy (TEM-HRTEM-AEM). The X-ray diffraction powder pattern exhibits the typical features of turbostratic stacking disorder with symmetrical basal 00l reflections and long-tailed hk- bands, confirmed also by TEM observations. Besides sauconite, the sample also contains minor amounts of kaolinite, dioctahedral smectite and quartz. CEC analysis provides a total of Ca (∼69%), Mg (∼26%), Na (∼4%) and K (0.7%) exchangeable cations. Therefore, Zn is located exclusively within the octahedral site of sauconite. TG analysis provides a total mass loss of about 17% in the studied sample. Three endothermic peaks can be observed in the DTA curve, associated to dehydration and dehydroxylation of the material. An exothermic peak at 820°C is also present as a consequence of dissociation and recrystallization phenomena. The infrared spectrum shows the typical Zn3OH stretching signature at 3648 cm-1, whereas, in the OH/H2O stretching region two bands at 3585 and 3440 cm-1 can be associated to stretching vibrations of the inner hydration sphere of the interlayer cations and to absorbed H2O stretching vibration, respectively. Diagnostic bands of kaolinite impurity at ~3698 and 3620 cm-1 are also found, whereas 2:1 dioctahedral layer silicates may contribute to the 3585 and 3620 cm-1 bands. Finally, using the one layer supercell approach implemented in the BGMN software, a satisfactory XRPD profile fitting model for the Skorpion sauconite was obtained. The findings have implications not only for economic geology/recovery of critical metals but, more generally, in the field of the environmental sciences.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
