Determination of diffusion coefficients and effective charge numbers of lignosulphonate. Influence of ionic strength and the valency of the counter-ion

Abstract

The diffusion coefficients and the effective charge numbers of ligno-sulphonate as a function of ionic strength and the valency of the counter-ion have been measured. The ionic strengths studied were 0.01, 0.1 and 1.0 mol dm^–3 and the salts used were NaCl, BaCl₂ and MgCl₂. The measurements were based on a convective diffusion process across a porous membrane. The diffusion coefficients increased with increasing salt concentration and also when a monovalent counter-ion was replaced by a divalent counter-ion, except in 1 mol dm^–3 MgCl₂ solutions, where the diffusion coefficients decreased remarkably. It was also shown that lignosulphonate molecules are spherical in every solution studied. The effective charge numbers of lignosulphonate decreased with increasing salt concentration in all cases, and in 1 mol dm^–3 BaCl₂ solution they were even positive.