Study On The Preparation Of Peanut Shell Activated Carbon And Its Performances For Removal Of Chromium Ions

Peanut shell is one of the rich renewable biomass resources and an agriculture residual. Chromium, in the forms of Cr(VI) and Cr(III), is recognized as a pollutant. Transforming peanut shell to activated carbon (AC) adsorbent and using the absorbent to remove Cr(VI) and Cr(III) from effluents will kill two birds with one stone: not only may peanut shell be utilized and be value-added, but also chromium pollutants are deleted cost-effectively.Both physical and chemical methods were used to prepare activated carbon from peanut shell. The effects of various parameters, such as activator species, the amount of activators, temperature and activation time on the performance of the activated carbon were investigated. The results show that the activated carbon prepared by ZnCl2 activation has the maximum iodine adsorption capacity. The optimal conditions are liquid-solid ratio 2, ZnCl2 concentration 35%, pyrolysis temperature 550℃, and duration of 150min. Iodine adsorption capacity of the best sample was 1039.6mg/g.The use of the activated carbon made from peanut shell in the removal of Cr(III) from aqueous solutions was studied. The influences of the solution pH, activated carbon dosage, temperature, contact time, Cr(III) concentration were investigated. The results show that the pH is the key factor and Cr(III) removal percentage increases with the pH rising. 99.08 percent of Cr(III) was removed at pH 5, temperature 35℃, 3.0 g AC /L and 60mg Cr(III) /L respectively. The isotherm experiments show that the adsorption fitted well with the Langmuir model. The maximum Cr(III) adsorption capacity of the activated carbon at 25, 35 and 45℃was 56.43, 72.69, 90.59mg/g respectively. The adsorption rate of Cr(III) follows the pseudo-second-order kinetics and the rate equation was deducted.The adsorption of Cr(VI) on the peanut shell AC was also studied using the similar procedures to the Cr(III) adsorption. Still, pH is the key factor to the adsorption of Cr(VI). Inversely, however, the adsorption capacity of Cr(VI) on the peanut shell AC increases with the pH dropping. At pH 2, temperature 30℃and initial Cr(VI) of 100mg/L, 2.0g AC /L from H3PO4 pretreatment and 2.0g AC /L from ZnCl2 pretreatment can remove 97.45 and 97.63 percent of Cr(VI) respectively. FTIR analysis show that C=O and C-O from the activated carbon are involved in the Cr(VI) adsorption. Isotherm experiments showed that the process can be simulated by Langmuir model quite well.Desorption experiments show that adsorbed Cr(VI) and Cr(III) can not be released completely from the AC, which indicates that they bond strongly to the surface of the activated carbons.