Rate equations for modeling carbon dioxide sequestration in basalt

Dissolution rate equations are developed from published data for glassy and crystalline basalt to predict the silica release flux (J(Si)) as a function of hydrogen ion activity (2 < pH < 12) and temperature (0 degrees < T < 100 degrees C). For glassy basalt the silica flux is J(Si)= (5.0 x 10(2))e((-39700/R)1/T) a(H+)(1.01) + (5.26 x 10(-5))e((-38400/R)1/T) a(H+)(-0.258) and for crystalline basalt the silica flux is J(Si)= (7.40)e((-40100/R)1/T) a(H+)(0.680) + (8.67 x 10(-7))e((-32900/R)1/T) a(H+)(-0.286) These rate equations are implemented in TOUGHREACT to simulate a CO2 saturated solution reacting with glassy and crystalline basalt in batch and semibatch reactors. The crystalline basalt models are compared with a more complex basalt representation comprising a composite mixture of olivine, plagioclase and pyroxene dissolution rates. Results show that numerical models based on the newly developed rate equations make reasonable predictions. Batch reactor models initially contained a solution spiked with CO2. These models showed relatively rapid CO2 consumption followed by cessation of the reaction with the glassy and crystalline basalt after the CO2 was exhausted and a terminal pH near eight. The composite basalt model was less successful because the plagioclase continued to react after the CO2 was exhausted causing the pH to rise to an unreasonably high value near 12. Semibatch reactor models containing a solution continuously supplied with CO2 showed relatively rapid CO2 consumption until all basalt was consumed. Complete semibatch reaction produced a sodium and bicarbonate rich solution with a pH near eight for all three basalt compositions. (C) 2017 Elsevier Ltd. All rights reserved.