Study on physicochemical properties of magnetic modified biochar derived from pyrolysis of pomelo peel and apricot kernel shell

Abstract: Magnetic modified biochar was prepared using pomelo peel and apricot kernel shell as the feedstock. The effects of temperature on the physicochemical properties of the magnetic modified biochar materials were investigated. Magnetic biochar was obtained through the process of initially loading iron chemicals on the raw biomass by combining with the impregnation and co-precipitation and then carbonization under different temperatures. In the magnetic biochar, iron was distributed heterogeneously, more in the outer layer than in the inner layer. The iron existed mainly in the form of Fe3O4, and a small amount in the form of complex metal oxides with aluminum, magnesium. The contents of ash and volatile matter in the magnetic biochar was increased compared to the native biochar obtained at the same temperature; while the fixed carbon contents and heating values were significantly reduced. The augment/reduction effects of magnetic modification were intensified with increasing temperature. The specific surface area and total pore volume of magnetic biochar were both increased. The specific surface area of biochar derived from pomelo peel increased from 4.163 3-5.782 7 to 4.793 7- 24.887 8 m2/g with the magnetic modification. For the apricot kernel shell, the specific surface area was elevated from 3.540 4-27.192 8 to 22.291 4-41.953 1 m2/g. The total pore volume was improved from 0.025 7-0.031 4 to 0.027 8- 0.062 2 cm3/g for the biochar derived from pomelo peel and from 0.025 3-0.065 7 to 0.0888-0.0792 cm3/g for the biochar derived from apricot kernet shell. The average pore size was overall decreased by the modification, with the mesopores still dominant. The magnetic modification treatment improved the pH values of these two feedstocks (4.82/4.78 vs. 6.26/5.38) as well as with the pH values of biochar derived from pomelo peel being pyrolyzed at temperature of 400-600 ℃, while the pH values of the magnetic biochar derived from apricot shell were generally lowered compared to the native biochar. The pH values were boosted from 9.59-10.09 to 10.24-10.75 for pomelo peel biochar pyrolyzed at temperatures of 400-600 ℃ by the magnetic modification. The values were reduced from 7.39-9.05 to 6.26-8.86 for the apricot kernel shell biochar pyrolyzed at temperature of 300-500 ℃. The contents of oxygen-containing functional group in the magnetic apricot kernel biochar were increased, which was indicated by the enhancement of characteristic peak of carbonyl and phenolic hydroxyl stretching vibration and explained why the pH values reduced with the increment of ash content. These results revealed that the effects of magnetic modification on the pyrolysis of pomelo peel and apricot kernel shell were very different.