Utilization of eucalyptus bark waste for recovery of copper and lead

Abstract

This dissertation comprised two main parts which are the characterization of activated carbon obtained from eucalyptus bark by phosphoric acid activation and the application of activated carbon along with solvent extraction in the recovery of copper from binary mixture between copper and lead. In the characterization part, the optimum temperature for the activation by phosphoric acid was 500°C at the weight by volume ratio of raw material and phosphoric acid (impregnation ratio) of 1:1 and activation time of 1.5 h. This condition gave the highest iodine number at 1,226 mg g-1, methylene number at 425.5 mg g-1 and also highest BET surface area of 1,457 m2 g-1. The activated carbon product was tested for its adsorption capacities for Cu(II) and Pb(II). Experiments demonstrated that both Cu(II) and Pb(II) were best adsorbed at pH 5 where the adsorption reached equilibrium within 45 minutes for the whole range of initial heavy metal concentrations investigated here (0.1-10 mM). The adsorption kinetics followed the pseudo second-order model where equilibrium adsorption capacities and adsorption rate constants increased with initial heavy metal concentrations. The adsorption isotherm followed Langmuir better than Freundlich models within the temperature range of 25-60 ℃ The highest maximum adsorption capacities (qm) occurred at 60 ℃ where qm for Cu(II) and Pb(II) were 0.85 and 0.89 mmol g-1, respectively. The enthalpies of adsorption of Cu(II) and Pb(II) were 43.26 and 58.77 kJ mol-1, respectively. The positive enthalpy of adsorption indicated endothermic nature of adsorption. The desorption/extraction of metals from the activated carbon was investigated using a few common extraction agents, i.e. citric, phosphoric and sulfuric acids. The results illustrated that the extraction process was completed in 60 min where citric acid at 1N was the best desorbing agent with almost 100% extraction of the bound metals. Sulfuric acid (1N), on the other hand, was suitable for the recovery of Cu(II) and Pb(II) from binary system as sulfuric acid could only extract Cu(II) from the activated carbon while leaving Pb(II) on the carbon surface. This therefore allowed effective separation of Cu(II) and Pb(II) from the adsorption column. In fixed bed experiments, the sorption capacity increased with increasing bed depth of the column or decreasing wastewater flow rate. The BDST and Thomas models could well predict the performance of the adsorption column for both metals.