The present investigation explored the use of Citrus reticulata waste biomass (CWB) for the removal of Pb(II) and Co(II) from the aqueous solutions. The Pb(II) and Co(II) biosorption was found to be dependent on pH of the solution, biosorbent dose, biosorbent particle size, temperature, shaking speed, contact time and initial concentration of metal ions. A metal uptake capacity of 41.16 and 52.64 mg/g was observed at pH 5 and 7 for Pb(II) and Co(II), respectively. The biosorption data followed the Freundlich model for both metals. The overall biosorption process was best described by pseudo-second order kinetics. The effect of several pretreatments on the biosorption efficiency of CWB was also investigated. The results demonstrated that pretreatments influenced the biosorption capacity of the biomass for the both metals significantly. Maximum biosorption capacity of 83.77 and 95.55 mg/g was observed for Pb(II) and Co(II) with sodium hydroxide treated and simply heated biomass, respectively. FTIR spectrum indicated the presence of -OH, -NH, -COOH groups in the biomass. The surface structure of CWB was analyzed by JEOL JMT 300 scanning electron microscope (SEM), and the existence of metal ions on the surface of biosorbent was determined by energy dispersive X-ray (EDX) spectroscopy.

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