Heavy Metal Release and Environmental Risk Assessment During Olivine Dissolution: Implications for Coastal Enhanced Silicate Weathering

Wenlu Zou, Wenhao Wang

School of Marine Sciences, Sun Yat-sen University & Southern Marine Science and Engineering Guangdong Laboratory, Zhuhai 519000, China

Coastal Enhanced Silicate Weathering (ESW), as a marine negative emission technology, has great potential in achieving the global carbon neutrality goal. Nevertheless, the release and environmental fate of associated metals (Ni, Cr, etc.) during olivine weathering are key factors restricting its large-scale engineering application. Taking the typical estuarine environment as the research background, this work explores the effects of mineral particle size and organic ligands on the release of characteristic elements in the process of olivine weathering through laboratory-controlled experiments. The results show that reducing particle size can significantly increase the apparent release rate of metals, and organic ligands (including low-molecular-weight organic acids and humic substances) can further accelerate mineral dissolution via complexation. Experimental monitoring demonstrates that homogeneously released Fe, Ni and Cr present obviously inconsistent evolution characteristics in the aqueous phase, which are jointly controlled by secondary precipitation, interfacial adsorption and complexation stability. Combined with the measured background data of the Pearl River Estuary, two extreme scenarios where metals fully enter the water body or completely deposit in sediments were set up in this study, and the boundary of environmental capacity was calculated in accordance with the current marine environmental quality standards. On the basis of kinetic characteristics and environmental capacity assessment, it is suggested that ESW projects should be preferentially located in open sea areas with strong hydrodynamic conditions, and physical and chemical management measures such as particle size regulation and mineral pre-washing should be adopted to reduce environmental risks. Overall, this study provides experimental basis and risk assessment reference for the implementation of ESW technology in coastal zones.