Preparation of macroporous bead adsorbents based on poly(vinyl alcohol)/chitosan and their adsorption properties for heavy metals from aqueous solution
Highlights
► Novel PVA/chitosan (CS) composite beads were successfully prepared by IPN and cross-linking. ► PVA and CS exhibited a synergistic effect on heavy metals removal from wastewaters. ► PVA/CS beads with macroporous structure showed good mass transfer performance. ► The novel beads were easily separated and reused, which reduced the operation cost. ► The resulting bead was a low-cost, efficient, eco-friendly and reusable adsorbent.
Introduction
Water pollution by heavy metals is a worldwide environmental problem and results in serious threats to ecosystem and human health. Heavy metals can be distinguished from other toxic pollutants, since they are not biodegradable and can be accumulated in living tissues, causing various diseases and disorders even at very low concentrations. These toxic heavy metals, especially Pb2+ and Cd2+, can be accumulated in bone, brain, kidney and muscles and may cause brain, bone, liver and kidney damage, and dysfunction of the central nervous system in human beings due to their cumulative effects [1], [2], [3]. Although Cu2+ and Zn2+ are known to be the essential trace elements to humans, but higher Cu2+ and Zn2+ intake can also cause adverse effects [4], [5]. The maximum acceptable concentration of Pb2+, Cd2+ and Cu2+ recommended by the World Health Organization (WHO) for drinking water is less than 0.01, 0.003 and 2 mg/L [6], respectively, while that of Zn2+ for drinking-water at levels above 3 mg/L may not be acceptable to consumers. Therefore, removal of these toxic heavy metal ions before discharging them into the receiving systems is essential from the standpoint of environment protection and public health.
Adsorption is one of the most effective and economical methods for the removal of heavy metals from aqueous solutions. In recent years, many types of adsorbents including activated carbon [3], chitosan [4], fly ash [5], zeolite [7], perlite [8], kaolinite clay [9], activated alumina [10], grape stalk waste [11], rice husk [12], tea waste [13], various resins [14], [15] and microorganisms [16], [17] have been used to remove various heavy metal ions from aqueous solutions. However, most of these materials are either prepared in certain conditions, e.g., high temperature, controlled pressure and additional chemicals which increase operation costs or of low efficiency, poor mechanical strength and difficult separation from reaction system. Therefore, there is a need to develop low cost, easily available, effective and reusable adsorbents for the removal of heavy metal ions from the aqueous environment.
Poly(vinyl alcohol) (PVA) is a water-soluble material containing large amounts of hydroxyl groups. PVA has been widely applied because it has many advantages such as low cost, non-toxicity, biocompatibility, high durability and chemical stability [18], [19]. In our previous study, a new, economical and eco-friendly way to prepare macroporous PVA beads has been developed in our lab to immobilize microorganism for wastewater treatment [20]. The macroporous PVA-based beads also showed a good removal for heavy metals from aqueous solution [21]. However, it will be very significant if nitrogen with much better coordination property is introduced into PVA materials. In this work, a novel spherical composite of PVA and chitosan (CS) with macroreticular structure, i.e. PVA/CS bead adsorbents, was prepared by the interpenetrating polymer network (IPN) and crosslinking process. It is expected that the hydroxyl and amino groups present in the PVA/CS bead adsorbents would exhibit a synergistic effect on removal of heavy metals from wastewaters. The common metallic pollutants, Cu2+, Pb2+, Cd2+ and Zn2+, were selected as adsorbates. Effects of pH, initial metal concentration, contact time, temperature, ionic strength and competing ions were studied in details for process design and optimization. The Langmuir and Freundlich isotherms were used to evaluate the equilibrium data. The adsorption kinetics were also studied based on the pseudo-first and pseudo-second-order kinetic models. Thermodynamic parameters were also computed. Finally, desorption efficiency and reusability of the adsorbents were investigated based on five consecutive adsorption–desorption cycles.
Section snippets
Materials
Poly(vinyl alcohol) (PVA) with a degree of polymerization of 1750 and an alcoholysis degree higher than 99% was purchased from Lanzhou Vinylon Factory (Gansu, China). Chitosan (CS) with a degree of deacetylation of 90% (80 mesh) was purchased from Yuhuan Ocean Biology Company (Zhejiang, China). All other chemicals were of analytical reagent grade. Distilled water was used to prepare all the solutions.
Preparation of macroreticular PVA/CS bead adsorbents
The macroreticular PVA/CS bead adsorbents were prepared as follows: PVA, sodium alginate (1.3 g)
Characterization of PVA/CS bead adsorbents
In the absence of sodium alginate, the formed beads had a strong tendency to agglomerate and were very difficult to break. In order to form spherical beads, a mixed solution of PVA and sodium alginate and a mixed solution of boric acid and CaCl2 were used in this study. The introduction of sodium alginate could improve the surface properties of the beads by eliminating the agglomeration problem. Water regain factor for I, II, III, IV, V, VI and VII was 85.08, 77.64, 75.42, 77.72, 81.55, 75.29,
Conclusion
Poly(vinyl alcohol)/chitosan (PVA/CS) composite beads were synthesized, characterized and were used for the adsorption of Cu2+, Pb2+, Zn2+ and Cd2+ from aqueous solution. PVA/CS bead adsorbents not only possessed good chemical stability, but also exhibited excellent adsorption ability for Cu2+, Pb2+, Cd2+ and Zn2+. Some factors affecting the adsorption such as pH, initial metal concentration, contact time, temperature and ionic strength were studied. The equilibrium data of Cu2+, Pb2+ and Cd2+
Acknowledgements
The authors gratefully acknowledge financial supports from the National Major Specific Program of Science and Technology on Controlling and Administering of Water's Pollution (2009ZX07212-001-04), the Sustentation Program of Science and Technology of China (2006BRD01B03).
References (43)
- et al.
A simple method to prepare poly(amic acid)-modified biomass for enhancement of lead and cadmium adsorption
Biochem. Eng. J.
(2007) - et al.
Single- and multi-component adsorption of cadmium and zinc using activated carbon derived from bagasse—an agricultural waste
Water Res.
(2002) - et al.
Comparative and competitive adsorption of copper, lead, and nickel using chitosan immobilized on bentonite
Carbohydr. Polym.
(2011) - et al.
Removal of lead and zinc ions from water by low cost adsorbents
J. Hazard. Mater.
(2009) - et al.
Sorption hysteresis of Cd(II) and Pb(II) on natural zeolite and bentonite
J. Hazard. Mater.
(2010) - et al.
Kinetic and thermodynamic studies of the adsorption of lead(II) ions onto phosphate-modified kaolinite clay
J. Hazard. Mater.
(2007) - et al.
Adsorption of Cd(II) and Pb(II) from aqueous solutions on activated alumina
J. Colloid Interface Sci.
(2009) - et al.
Removal of lead(II) and cadmium(II) from aqueous solutions using grape stalk waste
J. Hazard. Mater.
(2006) - et al.
Removal of Cu and Pb by tartaric acid modified rice husk from aqueous solutions
Chemosphere
(2003) - et al.
Tea waste as a low cost adsorbent for the removal of Cu and Pb from wastewater
Chem. Eng. J.
(2007)