Submitted to: Bioresource Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/26/2017
Publication Date: 3/1/2017
Citation: Han, L., Sun, H., Ro, K.S., Sun, K., Libra, J., Xing, B. 2017. Removal of antimony (III) and cadmium (II) from aqueous solution using animal manure-derived hydrochars and pyrochars. Bioresource Technology. 234:77-85.

Interpretive Summary: In this study, carbonaceous solid products from pyrolysis (pyrochar) and hydrothermal carbonization (hydrochar) of swine solids and poultry litter were compared for their potential to be used as environmental sorbents for the removal of Antimony (Sb) and Cadmium (Cd) from aqueous solution. The removal capacities of all the sorbents via adsorption were observed to increase with increasing the pH of the solution. Both pyrochars and hydrochars removed more Cd than Sb. Although the hydrochar had lower removal capacity for Cd and Sb than the pyrochar in this study, its removal capacity for Cd and Sb was still higher than most plant-based pyrochars reported in the literature. This study showed that animal manure based pyrochars and hydrochars showed the potential to be used as part of a water treatment process trains in removing Cd and Sb from water.

Technical Abstract: Very few studies have been done to explore the impact of hydrothermal carbonization and conventional dry pyrolysis in the sorption capacities of biochars towards heavy metals. In this study, hydrochars and pyrochars prepared from swine solids and poultry litter were characterized and were used as adsorbents for the removal of Antimony (Sb) and Cadmium (Cd) from aqueous solution. The adsorption capacities of all the sorbents were observed to increase with increasing pH (3.0-6.0). Fourier transform infrared spectroscopy (FTIR) analysis revealed that adsorption of Sb and Cd induced the variation of vibrational band of carbon-oxygen single bond (C-O) and carbon-oxygen double bond (C=O) of hydrochars and pyrochars. Additionally, the weaker hydroxyl (-OH) peak was found after Sb adsorption. These data, along with the less negative zeta potential of hydrochars and pyrochars after loading Sb and Cd, suggested the formation of surface complexes between Cd and C-O and C=O groups within biochars and between Sb and C-O, C=O and OH groups, respectively. For all the biochars, the maximum adsorption capacities (Qmax) for Cd were higher than those for Sb, likely due to the different metal ion species present in aqueous solution over the investigated pH range. The Qmax for both Sb and Cd regularly followed the order of 250 Cellsius (oC) pyrochar > 450 oC pyrochar > 600 oC pyrochar > hydrochar. The less negative surface charge and lower content of surface polar functional groups on hydrochars, respectively, led to the weaker electrostatic adsorption and surface complexation, explaining its lower adsorption capacity. However, by tabulating the data of sorption capacities of other biochars for Cd and Sb in the literature, hydrochars in this study were noted to have higher sorption capacities for Cd than most of plant-based pyrochars.