Nucleation and crystallization of otavite, witherite, calcite, strontianite, hydrozincite, and hydrocerussite by CO2 membrane diffusion technique |
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| Authors: | Maurizio Bucca Martin Dietzel Jianwu Tang Albrecht Leis Stephan Jürgen Khler |
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| Institution: | aInstitute of Applied Geosciences, Graz University of Technology, Rechbauerstrasse 12, A-8010 Graz, Austria;bDepartment of Earth and Environmental Sciences, Tulane University, 6823 St. Charles Avenue, New Orleans, LA 70118, USA;cInstitute of Water Resources Management, Joanneum Research, Elisabethstrasse 16 II, A-8010 Graz, Austria |
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| Abstract: | Otavite, witherite, calcite, strontianite, hydrozincite and hydrocerussite nucleation was induced by CO2 diffusion through a polyethylene membrane into a metal bearing solution. Nucleation and ongoing precipitation was followed at 25 ± 1 °C by the chemical evolution of the solution and the consumption of sodium hydroxide (pH-stat conditions). X-ray diffraction patterns as well as FT-infrared and Raman spectra confirmed the formation of well crystallized solids, except for less crystalline hydrozincite. In several experiments simonkolleite and laurionite precipitated concurrently with hydrozincite and hydrocerussite. The carbonate end-member minerals, smithsonite and cerussite, however were not formed. Carbonate minerals crystallized as spherical aggregates of thin layered otavite, spherical orientated witherite needles, rhombohedral calcite, pseudo-hexagonal strontianite laths, fibrous lumps of hydrozincite and planar hexagonal hydrocerussite crystals. Crystal and aggregate sizes range between 1 and 100 μm. Nucleation occurred at well defined reaction times and distinct critical supersaturation indices (SIcrit). The time for nucleation at constant pH decreased as the initial metal concentration increased for a given solid. The SIcrit values decreased in the order of hydrocerussite (3.2), otavite (2.5), strontianite (1.6), witherite (0.9) and calcite (0.7). |
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| Keywords: | Heavy metals Carbonates Nucleation Hydroxides CO2 diffusion |
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