Effect of Inorganic Ions on Oleate Adsorption at a Nigerian Hematite–Water Interface

Using “pure” natural hematite selected from a high silica Nigerian hematitic ore, oleate adsorption densities at the hematite–water interface were determined in the presence of various inorganic ions (anions and cations) of different charges and at varying concentrations. Adsorption density was determined using electrical conductivity measurements. The specific surface area of the hematite particles was determined using the method of adsorption of paranitrophenol in aqueous solution. Inorganic ions in solution depressed oleate adsorption at the aqueous hematite surface. The charge of the ion proved to be the dominant factor determining the depression of oleate adsorption. Ionic strength also was an influence, up to a limiting value at which monolayer oleate coverage of the hematite surface occurred. The inorganic ions in solution are considered to function through nonspecific adsorption in the diffuse region of the electric double layer.     

Kinetics of Oleate Adsorption at a Nigerian Hematite-Water Interface

The rate of adsorption of oleate soap onto a Nigerian hematite in an aqueous medium was determined from 29 to 60°C using the differential analysis method. The activation energy and frequency factor were determined at 57.1 kJ mol⁻¹ K⁻¹ and 4.0 × 10³ liter mol⁻¹ min⁻¹, respectively, indicating that the chemical processes are the slow, rate-determining step and that the reaction proceeds relatively fast. The adsorption isotherm was the Langmuir type: chemisorption was considered the dominant mode of adsorption. The desorption isotherm indicated a minor contribution of physical adsorption to the overall adsorption process.