Study On Adsorption Of Granular Red Mud Adsorbent For Heavy Metal Ions

As the development of the society and the industry, the hazard that the pollution of heavy metal ions bring to the humanity and environment is becoming more and more serious.This study puts forward a new adsorbent- granular red mud adsorbent (GRM) and evaluates the potential use of it to remove heavy metal ions from aqueous solutions as a low-cost adsorbent. The properties of the novel adsorbent were presented and the adsorbent were then used in batch experiments.Batch experiments were conducted to evaluate the change of adsorption capability under different conditions, such as pH, dimension, dosage initialization concentration, reaction time. The properties of the removal of copper(Ⅱ), lead(Ⅱ), cadmium (Ⅱ)and arsenide(V) by GRM were measured and it proved that GEM was a effective adsorbent for heavy metal ions.The high removal occurred at high pH value for copper (Ⅱ), lead (Ⅱ), cadmium (Ⅱ), but the opposite for arsenide. The optimized condition for the adsorption of these four heavy metal ions was 3 mm of dimension, 4g/L of dosage. The reaction time for adsorption equilibrium was 3 hours for copper (Ⅱ), 5 hours for lead (Ⅱ), 8 hours for cadmium and 12 hours for arsenide(V).Batch experiments were conducted to evaluate the adsorption equilibrium and adsorption kinetics under different pH value and temperature. Equilibrium isotherms at different temperatures have been determined and analyzed by Langmuir model and Freundlich model. We could conclude that 1n was intervenient 0.1 and 0.5. It suggested that GRM was propitious to adsorption.The thermodynamic parameters for GRM adsorption systems were measured at 20℃, 30℃, 40℃. The negative of free energy△G0 showed that the adsorption on GRM was a spontaneous and feasible process. The positive value of enthalpy△H0 confirmed the endothermic nature of cadmium adsorption and the positive entropy△S0 suggested the increased randomness at the solid–solution interface during the adsorption of cadmium on GRM, which all indicated that the adsorption performance of GRM was influenced by the change of temperature to a great extent.Pseudo-second-order kinetics parameters were obtained and external mass transfer coefficients, effective particle diffusion coefficients were determined for aqueous-GRM adsorption system. We could conclude the equilibrium adsorption of copper(Ⅱ), lead(Ⅱ), cadmium (Ⅱ)and arsenide(V) were 30.27 mg/g, 48.86 mg/g, 36.062 mg/g, 4.414mg/g from pseudo-second-order kinetics parameters. The adsorption processes were slow reaction.The adsorption of copper(Ⅱ), lead(Ⅱ), cadmium (Ⅱ)and arsenide(V) by GRM were exterior-complexation. The order of the adsorption capacity for these four heavy metal ions was lead(Ⅱ)>copper(Ⅱ) >cadmium(Ⅱ)> arsenide(V).