Recycle of Fenton sludge through one-step synthesis of aminated magnetic hydrochar for Pb2+ removal from wastewater

Highlights: • A novel disposal method of Fenton sludge reuse was proposed. • AHFS was prepared through one-step hydrothermal carbonization. • The Pb²⁺ adsorption capacity of AHFS could be up to 359.83 mg g⁻¹. • The adsorption capacity of AHFS increased by 39.23% over that of HFS. • Possible adsorption mechanisms and their contribution proportion were investigated. In order to achieve proper disposal of Fenton sludge, a new recycle method for preparing adsorbents based on one-step hydrothermal carbonization synthesis of aminated hydrochar from Fenton sludge (AHFS) was developed. It was found that AHFS prepared at 340 °C for 60 min showed Pb²⁺ adsorption capacity as high as 359.83 mg g⁻¹. Adsorption kinetics and thermodynamics results indicated that chemical interaction, intra-particle diffusion and monolayer homogeneous surface of AHFS dominated in adsorption process. The contribution proportion of different mechanisms, including cation-exchange (43.15%), acidic groups complexation (28.17%) and amino groups complexation (24.06%) to overall Pb²⁺ adsorption, demonstrated that complexation of surface functional groups played the dominated role in the adsorption process. Especially, the addition of amino was conducive to the increased adsorption capacity of hydrochar. In addition, according to the regeneration test, the magnetic AHFS exhibited a satisfactory reproducibility and recyclability. These findings illustrated that the synthesis of aminated magnetic hydrochar not only provided an innovative and efficient heavy metal adsorbent to remove Pb²⁺ from wastewater, but also explored a new method for the resource utilization of Fenton sludge.