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Title: Mechanistic understanding and performance of biosorption of metal ions by grapefruit peel using FTIR spectroscopy, kinetics and adsorption isotherms modeling, alkali and alkaline metal displacement and EDX analysis

item Cameron, Randall - Randy

Submitted to: Journal of Chemical Technology & Biotechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/6/2009
Publication Date: 5/13/2009
Citation: Iqbal, M., Schiewer, S., Cameron, R. 2009. Mechanistic elucidation and evaluation of biosorption of metal ions by grapefruit peel using FTIR spectroscopy, kinetics and isotherms modeling, cations displacement and EDX analysis. Journal of Chemical Technology & Biotechnology. 84:1516-1526.

Interpretive Summary: Enhanced industrial activity during recent decades has led to the discharge of unprecedented volumes of heavy metals. Nickel and Zinc are among the most common heavy metals encountered in raw wastewater streams from industries such as mining, battery production, paint formulation and electroplating. Due to their toxicity it is mandatory that these heavy metals are removed from effluents before discharge into the environment. Various treatment procedures, such as chemical precipitation and coagulation, ion exchange, osmosis and reverse osmosis, membrane processes, and electrolytic technologies are available for the removal of heavy metal contaminants in effluents and industrial wastewaters. Techno-economic considerations, however, limit their wide scale application. Citrus peel contains several water soluble and insoluble monomers and polymers rich in carboxyl and hydroxyl functional groups, and that strongly bind metal cations in aqueous solution. Due to its high pectin and cellulose content citrus peel offers the potential for use as adsorbent for the removal of toxic metals, dyes, and other organic materials from industrial effluents. In this study we show that citrus peel is an effective biosorbent and is capable of regeneration and reuse.

Technical Abstract: The performance and mechanism of the sorptive removal of Ni2+ and Zn2+ from aqueous solution using grapefruit peel (GFP) as a new sorbent was investigated. The sorption process was fast, equilibrium was established in 60 min. The equilibrium process was described well by the Langmuir isotherm model, with maximum GFP sorption capacity of 1.33 and 1.51 meq g-1 for Ni2+ and Zn2+, respectively. Release of cations (Ca2+, Mg2+, Na+, K+) and protons H+ from GFP during uptake of Ni2+ and Zn2+ and EDX analysis of GFP before and after metal sorption revealed that the main mechanism of sorption was ion exchange. FTIR spectrophotometry showed that carboxyl and hydroxyl functional groups were involved in the sorption process. Blocking these groups revealed the carboxylic group was responsible for 78.75% and 73.31% of Ni2+ and Zn2+ removal, respectively whereas 22.63% and 28.54% was due to the hydroxyl group. The GFP could be regenerated using 0.1M HCl, with more than 98% metal recovery and reused for five cycles without any significant loss in initial sorption capacity. The study suggests that GFP could lead to the development of a viable and cost-effective adsorbent for the removal of heavy metals from aqueous solution.