Preparation of La/Mg modified sheep dung activated carbon and its adsorption characteristics for phosphorus in wastewater

Abstract

The resource utilization of sheep dung from farming waste was evaluated in adsorption of total phosphorus (TP). Four types of modified sheep dung activated carbon (SDAC) were prepared: SDAC without metal (SDAC-N), SDAC with lanthanum (SDAC-La), SDAC with magnesium (SDAC-Mg), and SDAC with La and Mg (SDAC-La-Mg). The various SDACs prepared were tested in the adsorption TP from wastewater. The main components of the SDAC-La-Mg surface were MgO and La2O3. The SDAC-La-Mg surface was rich in functional groups such as CC and CO and acquired a negative charge. At 25 °C and pH of 4, the TP adsorption capacity of SDAC-La-Mg was 1.94 mg/g. Among the four SDAC adsorbents, SDAC-La-Mg exhibited the highest adsorption capacity. TP adsorption by SDAC-La-Mg followed the secondary kinetic and Langmuir isothermal adsorption models, primarily through chemisorption mechanisms such as ion exchange, chemical precipitation, and covalent bonding. SDAC-La-Mg was regenerated, and the TP removal rate remained at 65% after three regeneration cycles. Mg and La ions combine with carboxylate ions to form ligand compounds, enabling TP adsorption by displacing the -OH group on the surface of SDAC-La-Mg to form an inner complex. Thus, SDAC-La-Mg can be used as an effective adsorbent for TP in wastewater treatment.

Keywords

• Sheep dung activated carbon
• Phosphorus
• Adsorption