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Coconut waste is also used as an adsorbent for chromium removal. Its sorption properties are due to the presence of coordinating functional groups such as hydroxyl and carboxyl (Tan et al. 1993). Coconut coir pith and coconut shell are coconut wastes suitable for heavy metal removal. Coir pith is a light fluffy biomaterial and is generated during the separation process of fibre from coconut husk (Namasivayam & Sureshkumar 2008). Notably, 7.5 million tons per year of coconut is produced in India (Chadha 2003). Raw coir pith consists of 35% cellulose, 1.8% fats, 25.2% lignin and resin, 7.5% pentosans, 8.7% ash content, 11.9% moisture content and 10.6% other substances (Dan 1992). Namasivayam & Sureshkumar (2008) modified coir pith using the surfactant hexadecyltrimethylammonium bromide for chromium removal. The maximum removal obtained with this material was reported as being higher than 90% at an optimum pH of 2 and the maximum adsorption capacity was 76.3 mg/g. This was higher than the maximum adsorption capacity obtained using raw coir pith which was only 1.24 mg/g (Sumathi et al. 2005). This demonstrates that the adsorption capacity obtained after modification was much higher. Similarly, Shen et al. (2012) removed chromium using coconut coir and derived char and reported a maximum removal of 70%. Table 8 summarises the reported use of modified coconut waste as an adsorbent for chromium removal.

Table 8

Chromium removal using modified coconut waste as an adsorbent

AdsorbentMetal concentration (mg/L)Optimum pHBest model fitContact time (min)Adsorbent dose (g/L)Adsorbent capacity (mg/g)Removal per cent (%)References
Modified coir pith using the surfactant hexadecyltrimethylammonium bromide 20–100 Langmuir, Freundlich and Dubinin–Raduskevich 30–90 50 76.3, 1.24 >90% Namasivayam & Sureshkumar (2008)  
Coconut coir and derived char 10–500 – 7,200 1.0 70.4 70% Shen et al. (2012)  
AdsorbentMetal concentration (mg/L)Optimum pHBest model fitContact time (min)Adsorbent dose (g/L)Adsorbent capacity (mg/g)Removal per cent (%)References
Modified coir pith using the surfactant hexadecyltrimethylammonium bromide 20–100 Langmuir, Freundlich and Dubinin–Raduskevich 30–90 50 76.3, 1.24 >90% Namasivayam & Sureshkumar (2008)  
Coconut coir and derived char 10–500 – 7,200 1.0 70.4 70% Shen et al. (2012)  

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