Synthesis of an easily recyclable and safe adsorbent from sludge pyrochar for ciprofloxacin adsorption

Utilization of sludge pyrochar (SP) is the terminal step to loop the entire harmless disposal process of sewage sludge with pyrolysis. A new, easily recyclable, and safe adsorbent with well-immobilized heavy metals (HMs) was prepared from SP for ciprofloxacin (CIP) adsorption. The operational conditions for the adsorbent preparation were systematically optimized based on recycling rate and adsorption performance. Additionally, the adsorption conditions, adsorption kinetics, isotherms, and regeneration of adsorbents were further investigated in the present study. The results showed that easily recyclable and safe adsorbents were successfully prepared at 1100 °C under N₂ atmospheric conditions (SPA-N-1100) with a maximum CIP adsorption capacity of 10.42 mg/g. SPA-N-1100 exhibited good CIP adsorption performance at an adsorption temperature of 45 °C and pH between 8.0 and 9.0. The adsorbents were regenerated by thermal desorption at 450 °C with a thorough decomposition of CIP. The adsorption mechanism was mainly dominated by its special porous microspheres-accumulation structure and surface species (e.g., FeP and graphite). Moreover, HMs in the adsorbents were well immobilized in SPA-N-1100 by the generation of new metal mineral phases and encapsulation of melting minerals, which had an ultralow potential for ecological risk during application.