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Chitosan is a derivative of the N-deacetylation of chitin which is a naturally occurring polysaccharide obtained from crustaceans. Chitosan is an efficient adsorbent for the removal of heavy metals (Ren et al. 2008). Chitosan is cheap, hydrophilic and biodegradable and it also offers ease of derivatisation. It contains amino and hydroxyl groups that may form chelates with heavy metals (Huo et al. 2009; Hu et al. 2011). Chitosan has the advantage of being cheap yet effective, but has the disadvantages of being mechanically weak, soluble under acidic conditions and may leach carbohydrate when used in raw form (Ren et al. 2008; Huo et al. 2009). Various efforts have been made to stabilise chitosan using cross-linking agents, but this results in a decrease in adsorption capacity (Wang et al. 2011). Thus, Chen et al. (2012) have developed ‘ion imprint technology’ for achieving higher adsorption capacity and stability. This involves the development of a novel adsorbent that is a thiourea-modified magnetic ion imprinted chitosan/TiO2 composite for the removal of cadmium. The maximum adsorption capacity obtained for this material was reported to be 256.41 mg/g at an optimum pH of 7. Chitosan has also been modified by a coating process involving ceramic alumina. Coating helps increase accessibility of binding sites and improves mechanical stability. Maximum adsorption capacity obtained was reported to be 108.7 mg/g at an optimum pH of 6 and the maximum removal reported was 93.76% (Wan et al. 2004). Similarly, Hydari et al. (2012) modified chitosan by coating with activated carbon and reported an adsorption capacity of 52.63 mg/g adsorption capacity at an optimum pH of 6 with 100% removal. Table 13 presents cadmium removal data for chitosan as an adsorbent from wastewater.

Table 13

Cadmium removal using chitosan as an adsorbent

AdsorbentMetal concentration (mg/L)Optimum pHBest model fitContact time (min)Adsorbent dose (g/L)Adsorption capacity (mg/g)Removal (%)References
α-Ketoglutaricacid-modified magnetic chitosan 100–500 Langmuir 90 0.04 201.2 93% Yang et al. (2014b)  
Electrospun nanofibre membrane of PEO/chitosan 50–1,000 Freundlich, Langmuir and Dubinin–Radushkevich 120 – 248.1 72% Aliabadi et al. (2013)  
Nano-hydroxyapatite/chitosan composite 100–500 5.6 Freundlich and Langmuir 90 5.0 92, 122 92% Salah et al. (2014)  
Polyaniline grafted cross-linked chitosan beads 40–220 Langmuir 120 4.5 145 99.6% Igberase & Osifo (2015)  
O-carboxymethyl functionalisation of chitosan 675 10 – 1,440 – – 95% Borsagli et al. (2015)  
Multi-walled carbon nanotubes modified with chitosan – 6–7 – – – – >90% Salam et al. (2011)  
AdsorbentMetal concentration (mg/L)Optimum pHBest model fitContact time (min)Adsorbent dose (g/L)Adsorption capacity (mg/g)Removal (%)References
α-Ketoglutaricacid-modified magnetic chitosan 100–500 Langmuir 90 0.04 201.2 93% Yang et al. (2014b)  
Electrospun nanofibre membrane of PEO/chitosan 50–1,000 Freundlich, Langmuir and Dubinin–Radushkevich 120 – 248.1 72% Aliabadi et al. (2013)  
Nano-hydroxyapatite/chitosan composite 100–500 5.6 Freundlich and Langmuir 90 5.0 92, 122 92% Salah et al. (2014)  
Polyaniline grafted cross-linked chitosan beads 40–220 Langmuir 120 4.5 145 99.6% Igberase & Osifo (2015)  
O-carboxymethyl functionalisation of chitosan 675 10 – 1,440 – – 95% Borsagli et al. (2015)  
Multi-walled carbon nanotubes modified with chitosan – 6–7 – – – – >90% Salam et al. (2011)  

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