CO2 dual roles in food scraps-derived biochar activation to enhance lead adsorption capacity

Driven by China's waste classification system, the recycling of food scraps is a work of great importance. The carbonate (CO32-) and phosphate (PO43-) in food scraps indicate that its derived biochar can be a good candidate for Pb immobilization. In the current study, Pb2+ adsorption sites (CO32- and PO43-) of biochar were adjusted by carrier gas atmosphere and activation temperature. Results indicate that CO2 has dual roles in activation of food scraps-derived biochar. CO2 can not only inhibit the decomposition of CO32- but also increase the content of PO43- via consuming aromatic carbon combined with phosphorus at high temperature (>600 degrees C). Thus, the biochar prepared at 700 degrees C and CO2 atmosphere has more adsorption sites, resulting in an outstanding Pb adsorption capacity (up to 555.6 mg/g) via coprecipitation mechanisms. As-prepared biochar sample also can be prepared to a hydrogel with a remarkable mechanic strength. But biochar hydrogel decreases Pb adsorption capacity to 104.2 mg/g due to the pore blocking effect. Life cycle assessment illustrates that the scene of food scraps activated by CO2 has lower Global Warming Potential (GWP) and Primary Energy Demand (PED). Therefore, current research provides a high-efficiency method for treatment of food scraps.

Automated summary

The study focuses on using CO2 to activate food scraps for the preparation of biochar, which can enhance Pb immobilization. The adjustment of Pb2+ adsorption sites in the biochar leads to an outstanding Pb adsorption capacity, and the biochar can also be made into a hydrogel with remarkable mechanical strength. However, the Pb adsorption capacity of the biochar hydrogel is reduced due to pore blocking effects. Life cycle assessment shows that CO2-activated food scraps have lower environmental impacts and energy consumption.