We systematically explore the role of magnesite distribution patterns in dictating its dissolution rates under an array of flow velocity and permeability contrast conditions using flow-through column experiments and reactive transport modeling. Columns were packed with magnesite distributed within quartz matrix in different spatial patterns: the Mixed column has uniformly distributed magnesite while the zonation columns contain magnesite in different number of zones parallel to the main flow. Dissolution rates are highest under conditions that maximize the water flowing through the magnesite zone. This occurs under fast flow and high-permeability or uniformly distributed magnesite zones. Under high flow and low permeability magnesite conditions, dissolution only occurs at the magnesite-quartz interface, leading to rates an order of magnitude lower in the One-zone columns than those in the Mixed columns. Spatial patterns do not make a difference under low flow when the system approaches equilibrium (v < 0.36 m/d) or under high permeability magnesite conditions. The bulk column-scale rate depends on A e through , where A e is the surface area that effectively dissolves with IAP/K eq < 0.1. The rate constant of 10-9.60 is very close to 10-10.0 mol/m 2 /s under well-mixed conditions, suggesting the potential resolution of laboratory-field rate discrepancy when A e , instead of the total BET surface area A T , is used. The A e values are 1 to 3 orders of magnitude lower than A T. The effectively-dissolving magnesite-quartz interface area ranges between 60~100% of A e , pointing the importance of "reactive interfaces" in heterogeneous porous media. This work quantifies the significance of magnesite spatial distribution patterns and has important implications in understanding biogeochemical processes and ecosystem functioning in the Critical Zone, as well as energy extraction from the deep subsurface.
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