Developing a sorptive material of cadmium from pyrolysis of hen manure

A large amount of manure is generated from concentrated animal feeding operations (CAFOs), leading to serious environmental issues and hazardous risks from pathogens, such as methicillin-resistant Staphylococcus aureus. Therefore, developing an effective method for manure disposal is essential. Thus, in this study, we suggest the use of CO₂ in pyrolysis of hen manure (HM) as an effective method to convert the carbon in HM into syngas (especially carbon monoxide (CO)). HM was used and tested as the model compound. From the results of thermo-gravimetric analysis, the decarboxylation of CaCO₃ in HM in the presence of N₂ was realized at temperatures ranging from 638 to 754 °C. The Boudouard reaction was observed at ≥ 664 °C in the presence of CO₂. Despite the lack of occurrence of the Boudouard reaction, more CO formation was observed in the presence of CO₂ at ≥ 460 °C. This was deemed as a homogeneous reaction induced by CO₂. Considering the high Ca content of HM, HM biochar in N₂ and CO₂ were used as adsorbent for removal of Cadmium (Cd), which is toxic heavy metal. The adsorption capacities of HM_N₂ and HM_CO₂ were 302.4 and 95.7 mg g^-1, respectively. The superior performance of HM_N₂ is mainly attributed to the presence of Ca(OH)₂, which provides favorable (alkaline) conditions for precipitation and ion exchange. Our results indicate the environmental benefits from using CO₂. Specifically, CO₂ (representative greenhouse gas) converted into fuel. Given this, pyrolysis of HM in the presence of CO₂ was achieved at ≤ 640 °C, and the atmospheric condition should be switched from CO₂ to N₂ at ≥ 640 °C to ensure the decarboxylation of CaCO₃.