Olivine dissolution and carbonation under conditions relevant for in situ carbon storage

详细信息    查看全文

• 作者：Natalie C. Johnson^a ; ^{nataliej@stanford.edu" class="auth_mail} ; Burt Thomas^b ; Kate Maher^c ; Robert J. Rosenbauer^b ; Dennis Bird^c ; Gordon E. Brown Jr.^a ; ^c ; ^d
• 关键词：Carbon sequestration ; Mineral carbonation ; Olivine dissolution
• 刊名：Chemical Geology
• 出版年：12 May, 2014
• 年：2014
• 卷：373
• 期：Complete
• 页码：93-105
• 全文大小：1225 K

文摘

In order to evaluate the chemistry and kinetics of mineral carbonation reactions under conditions relevant to subsurface injection and storage of CO_2, olivine alteration was studied at 60 掳C and 100 bar CO₂ pressure, including olivine dissolution and the formation of carbonate minerals. Batch experiments were performed with olivine (Fo92), water, CO₂, and NaCl inside gold cells contained within rocking autoclaves. Two reproducible experiments yielded an initial (1 h) dissolution rate of 9.50 卤 0.10 脳 10^鈭?#xA0;11 and a long-term (10-70 days) rate of 1.69 卤 0.23 脳 10^鈭?#xA0;12 mol cm^鈭?#xA0;2 s^鈭?#xA0;1. The long-term rate is consistent with previously published rate laws at 4.5 < pH < 5.5. The dissolution rates presented here are constant with increasing pH in the same range, suggesting a pH-independent dissolution mechanism at elevated CO₂(aq) and SiO₂(aq) at 60 掳C. A Si-rich surface layer forms on olivine grains within 2 days of reaction and appears to slow dissolution by passivating the surface. The olivine dissolution rate decreases by 2 orders of magnitude over 4 days as the system approaches amorphous silica saturation but remains constant thereafter based on a linear increase in Mg concentrations. Secondary phases consist of amorphous silica and magnesite, with up to 7 mol% olivine converted to Mg-carbonate over 94 days of reaction. Magnesite precipitation rates could not be precisely quantified due to experimental limitations. However, our minimum estimate of 1.40 脳 10^鈭?#xA0;13 mol cm^鈭?#xA0;2 s^鈭?#xA0;1 suggests that the precipitation rate is several orders of magnitude greater than predicted by previous studies. Finally, the presence of 0.5 M NaCl resulted in a decrease in olivine dissolution rate at reaction times of less than 4 days, but a significant enhancement of the reaction rate at reaction times greater than 4 days relative to electrolyte-free experiments. Our results suggest that geochemical models developed to predict the behavior of subsurface CO₂ storage systems in mafic and ultramafic rocks should incorporate the effects of dissolved species, including SiO₂ and NaCl.