Kinetics, equilibrium and mechanism of Cu²⁺, Ni²⁺ and Zn²⁺ ions biosorption using wheat straw

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• 作者：Milan Gorgievski ; Dragana Bo?i? ; Velizar Stankovi? ; Nada ?trbac ; Sne?ana ?erbula
• 关键词：Heavy metals ; Wheat straw ; Biosorption ; Adsorption mechanism ; Adsorption kinetics
• 刊名：Ecological Engineering
• 出版年：2013
• 出版时间：September, 2013
• 年：2013
• 卷：58
• 期：Complete
• 页码：113-122
• 全文大小：1113 K

文摘

The adsorption of Cu²⁺, Zn²⁺ and Ni²⁺ ions from synthetic solutions was performed by using wheat straw. Physical and chemical characterization of wheat straw was done. The content of alkali and alkaline-earth metals, before and after rinsing of wheat straw with water, and after loading with Cu²⁺, Zn²⁺ and Ni²⁺ ions, was given. Chemical oxygen demand (COD) of rinsed water was determined prior to the adsorption experiments. The consumption of oxygen was 18 mg dm^?3. Besides the COD, the total cation exchange capacity (CEC) of alkali and alkaline-earth metals, exchanged in the reaction with NH₄Cl, was also determined. The determined CEC of the wheat straw was 1.86 mmol Me^z+ g^?1. FTIR analysis of wheat straw, before and after adsorption of copper ions, revealed that hydroxyl functional groups were mainly responsible for the adsorption of Cu²⁺ ions. The point of zero charge (pHzpc) of wheat straw was experimentally found, being at pH = 6.7.

The kinetics of adsorption is described by a pseudo-second order reaction kinetic model, allowing the determination of kinetic parameters for each of the considered metal ions. The ion exchange mechanism was confirmed assuming that the alkali-earth metals (mostly calcium), from wheat straw, are substituted by the considered heavy metal ions and protons. For a single metal ion system, the adsorption equilibrium data can be modeled by the Langmuir adsorption isotherm for all considered ions. The maximum adsorption capacity of 5 mg g^?1 was achieved for copper ions, while the adsorption capacity for nickel and zinc ions was 2.5 mg g^?1 and 3.25 mg g^?1, respectively. The obtained results show that wheat straw can be successfully used as an adsorbent for the adsorption of Cu²⁺, Zn²⁺ and Ni²⁺ ions from weakly acidic effluents.