When they are in put in contact with carbonate minerals dangerous environmental pollutants such as Pb2+ and Cd2+ are taken up by the solid phase assemblage and can be removed from aqueous solutions.*
As carbonates can be found almost everywhere and are easily exploitable this makes them interesting materials for environmental remediation.*
However, magnesite ( MGS ) is well-known for the slow dissolution and growth kinetics at room temperature conditions in the so-called dolomite problem.*
In their article “Pb2+ Uptake by Magnesite: The Competition between Thermodynamic Driving Force and Reaction Kinetics” Fulvio Di Lorenzo, Tobias Arnold and Sergey V. Churakov use in situ atomic force microscopy (AFM) to investigate the growth of {10.4} magnesite surfaces in the absence and in the presence of Pb2+ as well as the effect of solution ageing.*
In their study the authors attempt to answer the question if and under which circumstances magnesium carbonate could be used in removing Pb from wastewater.*
The experimental results presented in above mentioned article have the object to discuss and evaluate the theoretical possibilities and the practical limitations that must be taken into account for the development of environmental remediation technologies based on magnesite.*
The experiments conducted in this study by Fulvio Di Lorenzo et al. demonstrate that, although the thermodynamic conditions are encouraging, the transformation reaction between magnesite and cerrusite makes it improbably that it will play a crucial role in the development of remediation processes for PbII pollution.*
The authors of the study conclude that, although the thermodynamic conditions are encouraging, an environmental remediation process based on MGS as the substrate for a solvent-mediated transformation reaction is unlikely to play a crucial part in industrial applications due to the slow kinetics of MGS dissolution. However, the sluggish kinetics of MGS precipitation is favourable for Pb entrapment by the precipitation of carbonate from Mg2+ and Pb2+-bearing solutions, leading to a strong PbII enrichment in the solid phase even in far-from-equilibirum conditions.*
The in situ flow-through Atomic Force Microscopy was performed using Arrow-UHFAuD AFM probes in tapping mode.
In situ observation of {10.4} surfaces of MGS in contact with acidic solution, pH 4 (HNO3). The images were acquired in tapping mode. The first row corresponds to height channels, while the second row reports the respective amplitude channels. (A) The dissolution at 25 °C is sluggish and it is not possible to detect any dissolution feature. (B) In the same conditions but at higher temperature (60 °C), dissolution features are observed on the {10.4} surfaces of MGS, despite the retrograde solubility. Yellow and blue lines of constant size are used to highlight the evolution of etch pits and step edges, respectively. This evidence demonstrates that the existence of kinetic barriers controls the dissolution of MGS at room temperature conditions.
*Fulvio Di Lorenzo, Tobias Arnold, and Sergey V. Churakov
Pb2+ Uptake by Magnesite: The Competition between Thermodynamic Driving Force and Reaction Kinetics
Minerals 2021, 11(4), 415
DOI: https://doi.org/10.3390/min11040415
Please follow this external link to read the full article: https://www.mdpi.com/2075-163X/11/4/415
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