Abstract
The biosorption ability of Lemna gibba for removing Ni2+ and Zn2+ ions in aqueous batch systems, both individually and simultaneously, was examined. The influences of solution pH and initial single and binary metal concentrations on equilibrium Ni2+ and Zn2+ biosorption was explored. The optimal solution pH for Ni2+ and Zn2+ biosorption was 6.0, for both the single and binary metal systems. Ni2+ and Zn2+ biosorption capacities increased with increasing initial metal concentrations. The presence of Zn2+ ions more adversely affected the biosorption of Ni2+ ions in the binary metal systems than vice versa. The single and binary biosorption isotherms of Ni2+ and Zn2+ revealed that L. gibba’s affinity for Zn2+ ions was higher than that for Ni2+ ions. The Redlich–Peterson and Freundlich isotherm models fit well to the experimental equilibrium data of Ni2+ ions, whereas Redlich–Peterson and Langmuir models better described the equilibrium data of Zn2+ ions in single metal systems. The modified Sips isotherm model best fit the competitive biosorption data of Ni2+-Zn2+ on L. gibba. FTIR analyses suggest the involvement of hemicellulose and cellulose in the biosorption of Ni2+ and Zn2+. The presence of Ni2+ and Zn2+ on the L.gibba surface was validated by SEM-EDX.
Highlights
Soil, surface water, and groundwater pollution by divalent nickel (Ni2+ ) and zinc (Zn2+ ) ions can occur by natural processes, but is predominantly due to anthropogenic activities [1], especially theNi2+ - and Zn2+ -contaminated discharges from industrial and commercial processes, including mining; mineral processing; electroplating; production of paints, batteries, coins, and electronic commodities; and many other applications [2,3].Ni2+ and Zn2+ are essential minerals for some living beings [4]
Similar experiments covering the same range of solution pH values were performed to explore the influence of metal solution pH levels on the simultaneous biosorption of Ni2+ and Zn2+ ions onto L. gibba, using an equimolar initial concentration of 2 mM of both heavy metals
Results of energy dispersive X-ray spectrometry (EDX) analysis showed the presence of carbon, oxygen, nitrogen, sodium, magnesium, silicon, sulfur, chlorine, and potassium, and the absence of nickel and/or zinc on the L. gibba surface before interacting with heavy metals (Figure 7a)
Summary
Ni2+ - and Zn2+ -contaminated discharges from industrial and commercial processes, including mining; mineral processing; electroplating; production of paints, batteries, coins, and electronic commodities; and many other applications [2,3]. Ni2+ and Zn2+ are essential minerals for some living beings [4]. At high concentrations, they are of serious environmental, public health, human well-being, and economic concern due to their toxic effects on cell physiology and metabolism, which can decrease the viability of living organisms or even cause their death [5]. Human exposure to high Ni2+ and Zn2+ levels has been associated with serious acute and chronic health effects. Ni2+ impairs the natural balance of essential minerals and is a carcinogenic and Processes 2020, 8, 1089; doi:10.3390/pr8091089 www.mdpi.com/journal/processes
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