Variability of Monomolecular Adsorption of Lignosulfonate Systems

Abstract— Specific features of lignosulfonate systems FCLC and FCLC-2M, as well as of the raw materials for the preparation of these modified forms, the lignosulfonates derived from wood pulping by the sulfite (LST) and neutral-sulfite (N-LST) methods, were studied. Based on the calculated data from the Gibbs equation and the Langmuir equation, the limiting monomolecular adsorption was determined, and broad variability of its numerical values was revealed; the calculated adsorption characteristics were correlated with the previously examined physicochemical properties of the systems studied. The physical meaning of the coefficient K in the Langmuir equation was investigated, and its correlation with the phenomenon of affinity of lignosulfonate systems to the adsorbent (rock) was established. The numerical values of the Gibbs energy were correlated with the physical properties of the lignosulfonate systems, which confirmed the need for additional modification of the inactive neutral lignosulfonate matrix by the phosphonate groups of 1-hydroxyethylidene-1,1-diphosphonic acid (HEDP) into an effective reagent FCLC-2M. The applicability of the Szyszkowski equation to the problem of evaluating the effect of the concentration of the lignosulfonate reagents on the magnitude of reduction of the surface tension of aqueous solutions was demonstrated, reasonable assumptions about the factors responsible for negative adsorption observed in the case of the FCLC-2M system were made, and the need for introducing the concept of the working zone of concentrations, as well as that of “effective concentration,” which has not been previously applied to lignosulfonates and their modified forms, was substantiated. Based on the change in the surface tension of aqueous solutions, through analysis of the mathematical form of the Szyszkowski equation, the physical meaning of the coefficients a and b was identified and correlated with the numerical values of the limiting adsorption (coefficient a), the adsorption layer capacity А_∞, and the ability to restore equilibrium (coefficient b) for all the systems studied.