Co-pyrolysis characteristics of lignite and biomass and efficient adsorption of magnetic activated carbon prepared by co-pyrolysis char activation and modification for coking wastewater

Activated carbon plays an important role in the field of wastewater treatment due to its excellent adsorption, but improving the recovery and utilization efficiency of activated carbon is a major challenge for its application. In this study, lignite (LC) and poplar leaves (PL) were used as raw materials to prepare magnetic activated carbon (MAC) by co-pyrolysis and char activation modification. The adsorption performance of the product was studied. The results showed that with different blending ratios of LC and PL, a large amount of alkali metal oxides contained in PL had different promoting effects on the pyrolysis of LC. When the mass ratio of LC to PL in the mixture was 3:2, the experimental value of hydrocarbons in the obtained tar reached 53.00%, which was 7.20% higher than the calculated value. The optimal preparation conditions of MAC were determined. Under the conditions of activation temperature of 700 °C, activation time of 2 h, ZnCl 2 mass fraction of 30%, impregnation liquid–solid ratio of 3:1 and impregnation time of 16 h, the activated carbon exhibits a relatively desirable performance. The obtained products were characterized by VSM, XRD, FT-IR, N 2 adsorption and SEM. As a result, the obtained MAC exhibits a better porous structure and higher specific surface area, and Fe 3 O 4 was observed on the surface of the MAC. The adsorption performance of coking wastewater by MAC was studied. We demonstrate that the prepared MAC could effectively adsorb organic matter in wastewater. After MAC was used to adsorb the coking wastewater for 3 h, the COD concentration in the wastewater decreased from 280 to 60 mg/L, and the MAC could be effectively recovered by magnets after adsorption.