CO2 Absorption and Magnesium Carbonate Precipitation in MgCl2–NH3–NH4Cl Solutions: Implications for Carbon Capture and Storage

Chen Zhu,Xiaofeng Ding,Hui Teng,Siyu An,Gen Li,Han Wang,Liang Zhao

doi:10.3390/min7090172

Chen Zhu, Xiaofeng Ding + Show 5 more

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https://doi.org/10.3390/min7090172

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Journal: Minerals	Publication Date: Sep 19, 2017
Citations: 16	License type: CC BY 4.0

Affiliation: Nanjing University, University of Southern California

Abstract

CO2 absorption and carbonate precipitation are the two core processes controlling the reaction rate and path of CO2 mineral sequestration. Whereas previous studies have focused on testing reactive crystallization and precipitation kinetics, much less attention has been paid to absorption, the key process determining the removal efficiency of CO2. In this study, adopting a novel wetted wall column reactor, we systematically explore the rates and mechanisms of carbon transformation from CO2 gas to carbonates in MgCl2–NH3–NH4Cl solutions. We find that reactive diffusion in liquid film of the wetted wall column is the rate-limiting step of CO2 absorption when proceeding chiefly through interactions between CO2(aq) and NH3(aq). We further quantified the reaction kinetic constant of the CO2–NH3 reaction. Our results indicate that higher initial concentration of NH4Cl ( ≥ 2 mol · L − 1 ) leads to the precipitation of roguinite [ ( NH 4 ) 2 Mg ( CO 3 ) 2 · 4 H 2 O ], while nesquehonite appears to be the dominant Mg-carbonate without NH4Cl addition. We also noticed dypingite formation via phase transformation in hot water. This study provides new insight into the reaction kinetics of CO2 mineral carbonation that indicates the potential of this technique for future application to industrial-scale CO2 sequestration.

Highlights

This study provides new insight into the reaction kinetics of CO2 mineral carbonation that indicates the potential of this technique for future application to industrial-scale CO2 sequestration
We report our results from the experiments of CO2 absorption under various initial Mg concentrations and pH values, and of Mg-carbonate precipitation under different ammonium concentrations
This study systematically investigated the reaction kinetics of CO2 absorption and Mg-carbonate precipitation in MgCl2 –NH3 –NH4 Cl solutions using a novel pH-controlled wetted-wall column device

Summary

Introduction

Mineral carbon sequestration mainly uses naturally abundant material resources like Mg-silicates [2,3] to react with atmospheric CO2 to form carbonate minerals. Compared to other options (e.g., storing CO2 in geological reservoirs like bedrock), mineral carbon sequestration has two major advantages: nearly unlimited raw material supplement, and relatively longer-term storage (>1 Myr, over geological timescales) [4]. At the Earth’s surface conditions, the rate of the silicate-CO2 reaction, or carbonation, is quite low (~10−10 to 10−17 mol·m−2 ·s−1 ) [5]. To accelerate the reaction rate, several strategies have been tested, including increasing the ambient temperature and CO2 pressure, enhancing the reactive surface areas of silicates [6,7,8], and removing the passivating

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