The removal of Pb2+ ion by MnFe2O4/waste tea leaves biochar and mechanism of adsorption

In order to transform waste tea leaves into a useful/valuable material for removal of Pb 2+ ions from wastewater, MnFe 2 O 4 /biochar was synthesized. The tea waste was pyrolyzed at 500 °C to obtain the biochar. Effects of the composition of tea leaves on the physicochemical properties of biochar were evaluated. Biochar and MnFe 2 O 4 /biochar were mainly organic matter. Regarding inorganic components, aside from Fe and Mn there were considerable albeit small amounts of the mineral elements K and Ca in the MnFe 2 O 4 /biochar. The MnFe 2 O 4 /biochar is porous with a specific surface area of 24.38 m 2 g −1 , and the surface is loaded with MnFe 2 O 4 and amorphous MnO 2 particles. Also carboxylic acid, hydroxyl, and carbonyl functional groups were formed on the MnFe 2 O 4 /biochar surfaces. The surface area and pore volume characteristics of the MnFe 2 O 4 /biochar were also increased compared with the baseline biochar, and the prepared MnFe 2 O 4 /biochar had mesostructure. The modification of biochar into MnFe 2 O 4 /biochar improved adsorption of Pb 2+ ions with the removal increased to ∼98%. The Freundlich isotherm and the pseudo-second order kinetic models matched well Pb 2+ adsorption onto the MnFe 2 O 4 /biochar.