Kinetics of Monomolecular Adsorption of Reagent Systems

Abstract

The article considers the kinetics of the process of monomolecular isothermal adsorption of drilling reagents: raw material base - sulfite lignosulfonate (LST); - neutral-sulfite lignosulfonate (N-LST); modified form based on neutral lignosulfonate: - polyvalent cations – ferrochromolignosulfonate (FCLC) and polyvalent cations and phosphonic groups of ethidronic acid – Ferrochromolignosulfonate (FCLC-2M). The study is based on kinetic concepts of the adsorption process, which determine the rates of adsorption and desorption in equilibrium conditions. Their main adsorption characteristics are calculated. The values of the average residence time of the adatoms (adsorbed atom) of the studied reagents at the liquid–solid boundary were determined. According to the main Langmuir equation, the dependences of the number of adatoms in the saturated layer of each regent were obtained. Empirical dependences and values of adsorption rates for the "working" concentration zone (5.1·10-5-76·10-5 mol/L) of these reagents at a constant temperature of 298 K were obtained. It is revealed that the adsorption equilibrium constant in the Langmuir equation Kl carries information about the rate of the adsorption process and knowing its value and its relationship with the filling density of the saturated layer at a certain concentration, it is possible to obtain the value of the rate of adsorption of the reagent. As a result, it was revealed that the rate of adsorption of sulfite lignosulfonate LST is almost 125 times, and the rate of adsorption of a modified form based on neutral lignosulfonate by polyvalent cations and phosphonic groups of ethidronic acid – ferrochromolignosulfonate FCLC-2M, is more than 20 times higher than the rate of adsorption of N-LST at the maximum "working concentration". Analytical dependences of adsorption/desorption rates on adsorption/desorption coefficients are graphically constructed. The corresponding coefficients were numerically obtained. It is noteworthy that the adsorption coefficient exceeds the desorption coefficient at equal rates. It is revealed that the adsorption on a solid surface (clay) of the studied lignosulfonate systems in the "liquid – solid" system is physical.