Adsorption characteristics and removal mechanism of quinoline in wastewater by walnut shell-based biochar

Quinoline is a representative refractory ammonia nitrogen contaminant in coking wastewater, which presents a hazard to the environment and humanity. Thus, effective settlement of quinoline is eagerly required. Nevertheless, existing adsorbents are expensive and inefficient in quinoline adsorption. It is significant to explore a low-cost and efficient adsorbent. Herein an environmental-friendly activated biochar derived from agricultural waste walnut shell was synthesized. Activated biochar displays large surface area, rich pores and high surface activity. The adsorption behavior of activated biochar was tested under static and dynamic adsorption systems. Activated biochar represents excellent adsorption performance and industrial application potential. Under the conditions of 298 K, 650 rpm and pH = 7, the activated biochar's saturated adsorption capacity and equilibrium time for quinoline are 342.56 mg g −1 and 20 min, respectively. After five adsorption-desorption cycles, the adsorption capacity retained 93.43 % of the incipient value, indicating that activated biochar exhibits excellent regeneration performance. Moreover, activated biochar could maintain good adsorption performance in real wastewater. More importantly, using walnut shell as the raw material could save costs and realize resource utilization. The negative Δ G θ and positive Δ H θ values demonstrate that the adsorption process is spontaneous and endothermic, which follows the pseudo-first-order kinetics and fits well with the Langmuir–Freundlich model. This work has a good guiding significance in the domain of sewage purification.