The effect of chemical treatment on ITDI coconut shell based activated carbon for arsenic adsorption

Arsenic is a naturally occurring element and is abundant in the environment. It is perilous to humans and aquatic life and is known for its acute and long-term toxicity. Arsenic may be introduced in the environment through various human activities in the urban, industrial and mining areas. In addressing the problem of arsenic pollution in water, adsorption has been one of the accepted technologies. Coconut which is abundant in the Philippines was used as base material in the manufacture of the activated carbon used as adsorbent. The activated carbon was treated using three different ratios of nitric acid to sulphuric acid (1:0 1:1 3:1) in order to study its effect on the arsenic adsorption capacity of the ITDI-AC. The untreated and treated ITDI-AC have high porosity and low surface iron content (0.33%) as shown in the SEM/EDX analyses. Ferrous-ferric oxide (magnetite) was found present in the XRD characterization while carboxylic acid, phenol groups, alkynes, and alkanes are the functional groups determined through FTIR. Following the pH drift tests, the treated carbons were found acidic (pHPZC 1.88, 2.18, 2.11) while the untreated ITDI-AC is almost neutral (7.17). Batch adsorption was carried out by varying the initial arsenic concentration (1.25, 2.50, 3.75, 5.00, 6.25, 7.50, 8.75, and 10.00 mg/L) while the temperature, shaking speed, and pH were held constant at 25oC, 150 rpm, and 7.8, respectively. Isotherm results showed that the arsenic adsorption process can be well fitted in both Langmuir and Freundlich adsorption model. The maximum adsorption capacity was 0.0269mg/g and was observed in the nitric acid-treated carbon (ACNA). However, the highest percent arsenic removal average was observed in the untreated ITDI-AC. Arsenic removal in an up-flow fixed bed column was investigated using the best treated ITDI-AC which is ACNA. The effect of varying initial arsenic concentration and pH was investigated at constant flow rate of 5ml/min and 10cm bed height. Highest per cent arsenic adsorption of 68% was observed at pH 8 and 0.3mg/L initial arsenic concentration after one hour of contact