Dissolution behavior of feldspar in oxalic acid at 40–100 °C: Implications for Al enrichment during chemical weathering

The dissolution behavior of feldspar is fundamental to understand geological processes such as surface mass cycling, chemical weathering, mineral deposition and global climate change. In this study, we select oxalic acid – one of the most popular organic acids in nature as a buffer solution to simulate the chemical weathering process of feldspar under natural environments. A total of 34 fluid–feldspar reaction experiments are performed to investigate the effects of temperature, pH, and specific surface area (SSA) on the dissolution mechanism of feldspar. Based on PHREEQC modelling of saturation index of secondary minerals, we obtain the overall dissolution rate of feldspar, which is predominantly influenced by pH and temperature, with SSA exerting a secondary effect. The dissolution rates of Na, K, Ca and Si show a positive correlation with temperature and SSA, whereas that of Al exhibits a negative correlation with SSA and a weak correlation with temperature. Based on chemical reaction kinetics, the reaction order of feldspar dissolution in oxalic acid is estimated to be approximately 0.47, suggesting that the dissolution rate of feldspar is primarily controlled by a desorption process. Our new experimental results reveal that the anomalous Al dissolution behavior, which are likely due to the formation of aluminum complexes on the feldspar surface, have potentially significant for understanding the Al enrichment mechanism during the chemical weathering of the continental crust.