Adsorption performance and mechanism of iron-loaded biochar to methyl orange in the presence of Cr6+ from dye wastewater.

Biochar prepared from sludge and liriodendron leaves (SLAC) was modified by Fe3+ (SLAC-Fe), and they were used to remove methyl orange (MO) from single system and aqueous solution with Cr6+. The physical and chemical properties of biochar were characterized by BET, SEM, TEM, EDS, FTIR and XPS. The influences of initial MO concentration, adsorbent dose, pH, contact time and temperature on the adsorption of MO by biochar were investigated. The results indicated that SLAC-Fe had a higher removal efficiency for MO than SLAC. In the binary system, the maximum adsorption capacities of MO were 0.26 and 0.22 mmol/g with Cr6+ concentrations of 0.2 and 0.8 mmol/L, respectively. The adsorption kinetic model of pseudo-second-order fitted well with the experimental data of MO in single system. The equilibrium experimental data of MO in single and binary component systems were fitted well to Freundlich isotherm models. It was based on chemical and multilayer adsorption. It could be concluded that there was a competitive adsorption between Cr6+ and MO. The reason was that the HCrO4- and Cr2O72- competed with SO3- for the effective adsorption sites on the surface of SLAC-Fe, resulting in a reduction in the adsorption capacity of MO.