Kinetics of Monomolecular Adsorption of Reagent Systems

The article considers the kinetics of the process of monomolecular isothermal adsorption of drilling reagents: of the raw material base (sulfite lignosulfonate (LST) and neutral-sulfite lignosulfonate (N‑LST)); and of a form based on neutral lignosulfonate modified by polyvalent cations (ferrochromolignosulfonate (FCLC)) and by polyvalent cations and phosphonic groups of ethidronic acid (Ferrochromolignosulfonate (FCLC-2M)). The study is based on the 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 are determined. According to the main Langmuir equation, the dependences of the number of adatoms in the saturated layer of each regent are obtained. The 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 are 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 is revealed that the rate of adsorption of sulfite lignosulfonate LST is almost 125 times, and the rate of adsorption of the modified form based on neutral lignosulfonate by polyvalent cations and phosphonic groups of ethidronic acid (ferrochromolignosulfonate FCLC-2M), more than 20 times higher than the rate of adsorption of N-LST at the maximum “working concentration.” The analytical dependences of the adsorption/desorption rates on the adsorption/desorption coefficients are graphically constructed. The corresponding coefficients are numerically obtained. It is noteworthy that the adsorption coefficient exceeds the desorption coefficient at equal speeds. It is revealed that the adsorption on a solid surface (clay) of the studied lignosulfonate systems in the “liquid–solid” system is physical.