This study examined the dissolution kinetics of granular zero-valent Mg (ZVMg) at pH 7 in water that was open to the atmosphere and buffered with 50mM Na-MOPS. The oxidative dissolution of ZVMg was rapid; the initial amount of ZVMg (10-50mg/L) dissolved completely within 200min. The rate and extent of ZVMg dissolution was not affected by atmospheric oxygen. Although the oxidation of ZVMg is thermodynamically more feasible by dissolved oxygen or proton ions (H+), the primary oxidants are water molecules. The initial rate of ZVMg dissolution obeys first order kinetics with respect to ZVMg concentration with an observed rate constant, kMg,7=1.05±0.06×10-2min-1. Model calculations using the rate constant perfectly predict the extent of ZVMg dissolution for an extended time period at lower [Mg0]0 but underestimate at 50mg/L [Mg0]0. The offset is likely attributed to the rapid dissolution of ZVMg particles, which could cause a substantial increase in the specific surface area. As to the reactivity of Mg-water system, we suggest that the hydrated electron (eaq-), the most powerful reducing agent, would probably be the major reactive entity under neutral and alkaline conditions. In addition, we discuss briefly the factors affecting the rate and extent of the Mg-water reaction such as background electrolytes, ZVMg impurities, surface passivation, solution pH and temperature based on literature review.
Bibliographical noteFunding Information:
This research was supported by a Korean Research Foundation Grant funded by the Korean Government ( KRF-2010-0012629 ). G.L. deeply appreciates the fruitful comments and suggestions by Janet G. Hering, Stephan Hug, and three anonymous reviewers which helped to greatly improve the manuscript. G.L. also acknowledges the support from Pacific Northwest National Laboratory through the Alternate Sponsored Fellowship and from EAWAG for his sabbatical stays, during which this manuscript was mostly prepared.
All Science Journal Classification (ASJC) codes
- Geochemistry and Petrology