Lignosulfonates as Surfactants to Stabilize Elemental Sulfur Dispersions

During sulfite delignification of wood, sulfo derivatives of lignin-lignosulfonates (LS)-are formed as a byproduct. Due to their amphiphilic nature, LS are used as plasticizers, dispersants, and stabilizers. The functions and performance characteristics of this surface-active polyelectrolyte are determined by its behavior in aqueous solution, at surfaces and interfaces, which, in turn, is determined by its chemical composition. This study investigated the effect of LS with various molecular weight compositions (M_w 9-50 kDa) on the behavior and aggregation stability of aqueous dispersions of elemental sulfur (S⁰) under conditions simulating hydrothermal leaching of sulfide ores. Using conductometry, potentiometry, tensiometry, and viscometry, a detailed study of the physicochemical properties of aqueous LS solutions (C_LS 0.02-1.28 g/dm³) obtained from a few sources (Krasnokamsk, Solikamsk, and Norwegian Pulp and Paper Mills) was conducted. The composition, molecular weight, and concentration of LS were found to significantly affect their specific electrical conductivity, pH, intrinsic viscosity, and surface activity. LS introduction during the formation of sulfur sols is shown to promote their stabilization through electrostatic and steric mechanisms. Optimum dispersion stability (293 K, pH 4.5-5.5) was observed at moderate LS concentrations (0.02-0.32 g/dm³), when a stable adsorption layer forms on the surface of sulfur particles. High-molecular-weight LS samples provided more effective spatial stabilization of sulfur particles. It has been established that increasing temperature (293-333 K) and changing pH (1-7) significantly affect the aggregative stability of systems; specifically, the sol stability decreases with increasing temperature, and the stabilizing effect of different LS types reverses upon changing pH. The obtained results highlight the potential of using naturally occurring polymeric dispersants to control the aggregation stability of sulfur-containing heterophase systems and can be applied to the design of stable colloidal systems in chemical engineering and hydrometallurgy.