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Coffee residue has been reported as an efficient adsorbent for the removal of cadmium from wastewater. For example, Boonamnuayvitaya et al. (2004) used coffee residues for cadmium removal and also blended them with clay to prepare an adsorbent with a negative charge which promotes cadmium complexation and removal. The prepared adsorbent contains hydroxyl, carbonyl and amine groups and has a pyrolysis temperature of 500 °C (this temperature gives maximum adsorption capacity) and a particle size diameter of 4 mm. A weight ratio of coffee residue to clay of 80:20 was found to be the most suitable blend. Oliveira et al. (2008) employed coffee husks that comprise the dry outer skin, pulp and parchment as these are likely to represent the major residue obtained from the handling and processing of coffee. For this material, the maximum adsorption capacity was reported to be 6.9 mg/g at an optimum pH of 4 with a removal of 65–85%. Kaikake et al. (2007) soaked and degreased coffee beans (DCB) in water and methanol to produce an adsorbent. The prepared DCB material behaved as a cation exchanger with 90% removal at an optimum pH 8. Azouaou et al. (2010) used waste material from cafeterias as an adsorbent for cadmium removal and reported an adsorption capacity of 15.65 mg/g with more than 80% removal at an optimum pH of 7. Table 15 presents cadmium removal data for coffee residue as an adsorbent.

Table 15

Cadmium removal using coffee residue 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
Coffee residues blended with clay 25–250 1.6–2.5 Langmuir 30 10 17.5–17.9 88–92% Boonamnuayvitaya et al. (2004)  
Coffee husks 50–100 Langmuir 4,320 6.7 6.9 65–85% Oliveira et al. (2008)  
Coffee beans 6–202 Langmuir 1,440 10 3.80 90% Kaikake et al. (2007)  
Coffee grounds from cafeterias 10–700 Langmuir 120 15.65 >80% Azouaou et al. (2010)  
AdsorbentMetal concentration (mg/L)Optimum pHBest model fitContact time (min)Adsorbent dose (g/L)Adsorbent capacity (mg/g)Removal per cent (%)References
Coffee residues blended with clay 25–250 1.6–2.5 Langmuir 30 10 17.5–17.9 88–92% Boonamnuayvitaya et al. (2004)  
Coffee husks 50–100 Langmuir 4,320 6.7 6.9 65–85% Oliveira et al. (2008)  
Coffee beans 6–202 Langmuir 1,440 10 3.80 90% Kaikake et al. (2007)  
Coffee grounds from cafeterias 10–700 Langmuir 120 15.65 >80% Azouaou et al. (2010)  

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