Adsorption of cadmium ions onto the yellow river sediment

Adsorption of cadmium ions onto Yellow River sediment was studied in a batch reactor. Equilibrium adsorption of cadmium ions onto Yellow River sediment can be well described by the Langmuir adsorption isotherm. In view of common experimental conditions in the batch reactor, a set of equations for describing variations of both the dissolved heavy metal pollutant concentration and the particulate heavy metal pollutant concentrations (the adsorption content of heavy metal pollutant on unit weight of sediment) with time was formulated with the use of an adsorptive reaction kinetic equation of heavy metal pollutant, mass balance equation and corresponding initial conditions. Furthermore, formulae for calculating the equilibrium dissolved heavy metal concentration and the equilibrium particulate heavy metal concentration (the equilibrium adsorption content of heavy metal pollutant on unit weight of sediment) in the batch reactor were obtained. These can be used as tools for further study. It was found that the saturation adsorption content, b, constant of adsorption-desorption rate, k, and coefficient of adsorption rate, k(1) (and coefficient of desorption rate k(2)), in the adsorptive reaction kinetic equation of the Langmuir type are independent of the suspended sediment concentration. Adsorption contents of heavy metal pollutants on unit weight of sediment (the suspended particulate heavy metal concentration) decreases with increasing suspended sediment concentration and can be well explained by the law of mass conservation. Adsorption capacity, which is defined as adsorption content of heavy metal pollutant by unit volume of (muddy) water, increases with an increase in either the suspended sediment concentration or initial dissolved heavy metal concentration.