Adsorption performance of tetracycline by the biomass ash derived from the pyrolysis of FeCl3-activated municipal sludge without gas protection

The municipal sludge activated by FeCl3 solution was pyrolyzed at 500 °C without gas protection, and the pyrolysis products, named as biomass ash, could effectively adsorb tetracycline (TC) from aqueous solution. Different FeCl3 concentrations could directly affect the physicochemical properties of the biomass ash, so that the biomass ash as adsorbent showed different adsorption efficiency toward TC. The activation of FeCl3 increased the oxygen-containing functional groups and surface polarities of the biomass ash. When the concentration of FeCl3 solution was 0.5 mol/L, the biomass ash behaved the maximum specific surface area (37.74 m2/g) and the best adsorption efficiency. The pseudo-second-order kinetics model and the Freundlich multi-molecule model could fully explain the TC adsorption process by the biomass ash pyrolyzed from municipal sludge activated by FeCl3. Moreover, the adsorption mechanism was mainly attributed to the chemical adsorption.