Adsorption Equilibrium and Adsorption Kinetics of Rare Earth Elements in Coal Rocks

Abstract The adsorption pattern and mechanism of rare earth elements on coal reservoirs are still unclear, leading to difficulties in the application of rare earth elements in monitoring the fracturing effect of coal reservoirs. Through indoor adsorption experiments, the adsorption equilibrium and adsorption kinetics of rare earth elements Nd, Y and La on coal rocks were studied to simulate the adsorption of rare earth elements tracers on coal reservoirs and to explore the adsorption pattern of rare earth elements on coal rocks under different initial concentrations of rare earth elements, different adsorption times and different rare earth element types. The experimental results showed that the Langmuir isotherm equation fitted best, and the adsorption of rare earth elements on coal samples belonged to unimolecular layer adsorption, and the maximum adsorption of rare earth elements Nd, Y and La on coal samples at 25°C were 41.052 mg/kg, 34.301 mg/kg and 95.465 mg/kg, respectively. The proposed secondary kinetic equation can better describe the adsorption process of rare earth elements on coal rocks, indicating that chemisorption is the controlling step of the adsorption rate, with the coal samples showing the fastest adsorption rate for La elements and the slowest adsorption rate for Nd elements. The results of this study provide a reference for the application of rare earth elements in the evaluation of fracturing effects in coal reservoirs.