ats5482 Posted September 22, 2022 Share Posted September 22, 2022 Hi, I'm trying to reproduce Fig. 3 from Ibarra et al. (2019; attached). However, I'm getting a component bicarbonate concentration that is too high. In the text, they describe how they model the weathering of soil containing the primary mineral Plagioclase Feldspar (An20Al80), which forms secondary minerals such as Halloysite and Kaolinite. The system is in equilibrium with atmospheric CO2 at a fixed fugacity and the initial fluid composition is dilute rainwater. For simplicity, I am using 100% Albite as the primary mineral, and Kaolinite as the secondary mineral with GWB's default thermo database (i.e., I am trying to approximate the orange line from panel B). My React script is as follows: 4 kg free H2O T = 25 swap Quartz for SiO2(aq) swap CO2(g) for HCO3- P CO2(g) = 0.0002 bar fix fugacity CO2(g) # rainwater SiO2(aq) = 9e-7 molal Al+++ = 2e-7 molal Ca++ = 9e-5 molal K+ = 1.6e-5 molal Mg++ = 6.8e-5 molal Na+ = 4.2e-4 molal Cl- = 1e-7 molal NO3- = 5.1e-7 molal SO4-- = 4.6e-4 molal balance H+ react 10 g Albite react 30 g Quartz suppress all unsuppress Kaolinite unsuppress Quartz This script gives an HCO3- concentration of ~8,000 umol/L (attached), but it should be ~1,200 umol/L (for pCO2 of 200 ppm and T of 25 C). How can I decrease the concentration of bicarbonate? I am also confused about why Quartz and Kaolinite seemingly become saturated instantaneously (attached). Note: the amount of water, Qtz, and Al are to give a water/rock ratio of 100 Thanks! -- Adam Quote Link to comment Share on other sites More sharing options...
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