The adsorption behavior of sulfur dispersing agents, including lignosulfonate, Quebracho, o-phenylenediamine (OPD), and humic acid on elemental sulfur and nickel sulfide concentrate was investigated. The charge changes on elemental sulfur surface were characterized by the measurement of the electrokinetic sonic amplitude (ESA) signal. The adsorption behavior of OPD was investigated by measuring the interfacial tension between liquid sulfur and nickel sulfate solution at 140 degrees C. The adsorption of lignosulfonate on the molten sulfur surface was calculated by the Gibbs Equation. The adsorption of lignosulfonate, Quebracho, and humic acid on the nickel concentrate was studied at ambient temperature. The adsorption mechanism of sulfur dispersing agents on both elemental sulfur and nickel concentrate were discussed. The stability of OPD in the nickel concentrate slurry was discussed. (C) 2008 Elsevier Ltd. All rights reserved.