PREPARATION OF BIOCHAR BY LOW TEMPERATURE PYROLYSIS OF LANTHANUM MODIFIED SHRIMP SHELLS FOR EFFICIENT PHOSPHORUS ADSORPTION

In order to improve the phosphorus removal effect of biochar and resource utilization of food waste, we obtained lanthanum-modified biochar (CSLa) by using waste shrimp shells as raw material and attaching LaCl₃ to the surface of shrimp shells in the form of La(OH)₃ precipitation with NaOH by pyrolysis. The modified and unmodified biochar samples were characterized and analyzed by XRF, SEM, BET, FTIR and XRD. The adsorption kinetic and adsorption isotherm models were used to fit the phosphorus absorption characteristics of the biochar. The effects of modifier dosage, initial pH and coexisting interfering ions on phosphorus adsorption by biochar were investigated. The results showed that lanthanum modified shrimp shell biochar (CSLa) had abundant oxygen-containing functional groups on its surface. CSLa consisted mainly of La₂O₃, and its pore size distribution was dominated by mesoporous pores. The phosphorus adsorption process was better fitted with Langmuir isotherm, indicating the adsorption of phosphorus on CSLa was monolayer adsorption. The adsorption of phosphorus on CSLa was better described by quasi-secondary kinetics, indicating the phosphorus adsorption process by CSLa was chemisorption. The maximum theoretical adsorption capacity of CSLa was found to be 160.51 mg/g, achieved after 12h of adsorption. The adsorption and removal rates of phosphorus by CSLa were higher than those by CS400 at low or high phosphorus concentrations, which was more practical in real aquaculture tailwater. The adsorption rate of phosphorus on CSLa was mainly controlled by chemical adsorption and intraparticle diffusion. The mechanism analysis indicated that surface precipitation, electrostatic attraction, ligand exchange and internal complexation were the main mechanisms of phosphorus adsorption by CSLa. CSLa demonstrated better phosphorus removal performance under weakly acidic conditions, while the adsorption capacity was relatively high under alkaline environmental conditions. The interfering ions Cl^–, \rmNO^-_3 , \rmNO^-_2 and \rmSO^2-_4 had no effect on CSLa phosphorus adsorption, while \rmHCO^-_3 and \rmCO^2-_3 had some inhibitory effect on CS400 phosphorus adsorption. In this study, lanthanum-modified biochar was prepared at a low temperature of 400℃ as the pyrolysis temperature, which not only enhanced the adsorption and removal rate of phosphorus by biochar, but also consumed less thermal energy, which was more beneficial to practical applications.