The removal of Pb(II) ions from synthetic wastewater using Delonix regia pods and leaves as low-cost biosorbents was investigated. The elemental, morphological and phase characterization of Delonix regia pods and leaves were examined before and after biosorption. The adsorption process at various pH values, contact times, initial concentration of Pb(II) ions and adsorbent doses was studied with the aim of investigating the consequences of these parameters on the process of biosorption. The Langmuir adsorption isotherm provided the best fit for the experimental data of the pods while the Freundlich isotherm gave a better fit for the leaves of Delonix regia. The optimum adsorption capacity of 30.27 mg/g for the pods and 27.60 mg/g for the leaves was achieved when 0.5 g of the adsorbent was mixed with 20 mL of 1,000 mg/L Pb(II) ions solution for 30 min at 21 ± 2 °C and a stirring speed of 18 rpm. The data obtained from the time-dependent experiment of the biosorbents followed the pseudo-second-order kinetic model. This study showed that Delonix regia pods and leaves could be developed further as a low-cost sorbent that could be harnessed for removing Pb from industrial wastewater and thus limit water pollution from point sources.

Abstract. In this study, the adsorption of Ni(II) and Cu(II) ions from aqueous solutions by powdered Delonix regia pods and leaves was investigated using batch adsorption techniques. The effects of operating conditions such as pH, contact time, adsorbent dosage, metal ion concentration and the presence of sodium ions interfering with the sorption process were investigated. The results obtained showed that equilibrium sorption was attained within 30 min of interaction, and an increase in the initial concentration of the adsorbate, pH and adsorbent dosage led to an increase in the amount of Ni(II) and Cu(II) ions adsorbed. The adsorption process followed the pseudo-second-order kinetic model for all metal ions' sorption. The equilibrium data fitted well with both the Langmuir and Freundlich isotherms; the monolayer adsorption capacity (Q0 mg g−1) of the Delonix regia pods and leaves was 5.88 and 5.77 mg g−1 for Ni(II) ions respectively and 9.12 and 9.01 mg g−1 for Cu(II) ions respectively. The efficiency of the powdered pods and leaves of Delonix regia with respect to the removal of Ni(II) and Cu(II) ions was greater than 80 %, except for the sorption of Ni(II) ions onto the leaves. The desorption study revealed that the percentage of metal ions recovered from the pods was higher than that recovered from the leaves at various nitric acid concentrations. This study proves that Delonix regia biomass, an agricultural waste product (“agro-waste”), could be used to remove Ni(II) and Cu(II) ions from aqueous solution.

Abstract. In this study, the adsorption of Ni(II) and Cu(II) ions from aqueous solutions by powdered pods and leaves of Delonix regia was investigated by batch adsorption techniques. The effects of operating conditions such as pH, contact time, metal ions concentration and the presence of sodium ions interfering on the sorption process were investigated. The results obtained showed that the equilibrium sorption was attained within 30 min of interaction and the adsorption process followed the pseudo-second-order kinetic model for all the metal sorption with the exception of Cu(II) sorption on the leaves. The equilibrium data fitted well with both the Langmiur and Freundlich Isotherms; the desorption study revealed that the percentage of metal ions recovered from the pods were higher than the leaves at various concentration of nitric acid. This study has proven that Delonix regia biomass, an agro-waste could be used for removing Ni(II) and Cu(II) ions from wastewater.