Response Surface Methodology for the Optimization of Zn-Contaminated Soil Remediation by Soil Washing with Water-Soluble Chitosan.

Soil washing is an important method for the remediation of contaminated soil. This research presents the optimization of soil washing conditions in the remediation of Zn-contaminated soils with water-soluble chitosan (WSCS). Response surface methodology (RSM) was used to optimized the washing conditions after single factor experiments. The central composite design (CCD) with three factors and five levels was applied to the optimization of the removal efficiency of Zn from soils, and WSCS concentration, pH value, and washing time were evaluated variables in the washing process. Results indicated that the pH value (p < 0.0001) was the most significant factor which mainly affected the distribution and content of metal species in aqueous solution, ion exchange and adsorption/desorption behavior of metals, solubility of chelating agent, as well as readsorption of metal complexes. The optimal conditions for the Zn removal from soils were WSCS concentration of 1.5%, pH of 3.3, and washing time of 72 min. The removal efficiency could reach 65.4% under the optimized conditions, which was close to the predicted value of 68.3% by the response surface method. Therefore, it could be found that the response surface methodology was an effective method to determine the optimal conditions for the removal of metals from contaminated soils by soil washing.

Remediation of zinc-contaminated soils by using the two-step washing with citric acid and water-soluble chitosan.

Remediation of heavy metal contaminated soil with appropriate washing agents is crucial to the decline in the harmfulness of contaminated soil by heavy metals to the environment and human health. In this study, citric acid (CA) and water-soluble chitosan (WSCS) as natural and degradable washing agents were used to remove Zn in the soil by two-step washing method. Results indicated that the two-step washing with CA and WSCS were found to be suitable for the removal of Zn from the contaminated soils, which significantly decreased the total concentration of Zn in the soil. After the remediation process with two-step soil washing, the contents of Zn in different chemical species decreased, especially for the carbonate-bound fraction. Therefore, the two-step soil washing with CA and WSCS was advisable for the remediation of Zn-contaminated soils. The washing mechanism could include the acid dissolution, ion exchange and complexation reaction between zinc ions and functional groups such as hydroxyl, carboxyl, amine and amide groups. This study provided the theoretical support for the exploitation and application of suitable washing agents used for the remediation of contaminated soils by heavy metals.

Preparation of cotton-based fibrous adsorbents for the removal of heavy metal ions.

Cotton fiber functionalized with tetraethylenepentamine and chitosan (CTPC) was prepared and used as absorbents for the removal of Cu(II), Pb(II) and Cr(III) ions from aqueous solution. The functionalized materials (CTPC) were characterized by SEM/EDX, FTIR, BET and XRD to confirm the characterization and structural changes of fibers before and after the modifying process. The adsorption performance of CTPC was investigated with different pH, contact time and initial concentration of three kinds of metal ions. Results showed that the maximum adsorption capacity was 81.97 mg g-1 for Cu(II), 123.46 mg g-1 for Pb(II) and 72.99 mg g-1 for Cr(III) based on the Langmuir isotherm model at optimal pH (5.0). Adsorption kinetics of CTPC fibers for Cu(II), Pb(II), and Cr(III) ions followed the pseudo-second-order model. The adsorption-desorption experiments demonstrated that CTPC showed better stability, and CTPC would be an effective and practical material for the treatment and recycling of heavy metal ions in the wastewater.

Novel recyclable adsorbent for the removal of copper(II) and lead(II) from aqueous solution.

Adsorbents synthesized with biopolymer have been widely used in the removal of toxic metal ions. Novel high-efficiency, recyclable, and low-cost adsorbents have received more and more attention. Chitosan and cellulose are the most abundant biopolymers in nature. Composite modified adsorbent (CSTEC) was synthesized as novel fibrous materials for the adsorption of Cu2+ and Pb2+ ions from water in this study. The functional fiber was characterized to investigate the surface appearance, functional groups, crystallinity, and thermal stability. The kinetics study revealed that adsorption processes of Cu2+ and Pb2+ ions on the CSTEC followed the second-order kinetics model. CSTEC showed better performance (Cu2+, 95.24; Pb2+, 144.93mgg-1) than most of other adsorbents. The co-existing ions (K+, Na+, Mg2+) had no significant influence on the removal of target ions by the CSTEC. The excellent reusability indicated that CSTEC had the promising application in the treatment of toxic metal pollution.

Fast removal of copper ions from aqueous solution using an eco-friendly fibrous adsorbent.

Functional PET fiber (PET-AA-CS) was prepared by oxygen-plasma pretreatment and grafting of acrylic acid (AA) and low-molecular-weight chitosan (LMCS) on the polyethylene glycol terephthalate (PET) substrate. This adsorbent was targeted for quick removal of metal ion in river pollutions with an easy recycling of the fiber after emergency processing. The fabricated PET-AA-CS was characterized by the scanning electron microscope (SEM), contact angle, fourier transform infrared (FTIR) spectra and X-ray photoelectron spectroscopy (XPS) to look into its morphology, surface functional groups, and adsorption mechanism of copper ions from the aqueous solution. The overall adsorption process of copper ions on the PET-AA-CS was pH-dependent with an optimal pH value of 5.0, at which a maximum capacity of 68.97 mg g(-1) was obtained. The result of fitting also shows that adsorption process follows the Langmuir isotherm and pseudo-second-order model. Moreover, the material shows good stability during 5 cycles of adsorption and desorption, and also shows no significant effect of co-existing ions including Ca(2+), Mg(2+), K(+), Cl(-), and et al. In general, PET-AA-CS developed in this study shows significant benefit of eco-friend and cost-efficiency for fast removal of copper ions in potential river metal pollutions comparing with traditional adsorbents.