Simultaneous adsorption of phosphate and zinc by lanthanum modified zeolite

Lanthanum modified zeolite (LMZ) has been proven to be an effective inactivation agent for lake internal phosphorus load control. However, its performance in the co-sequestration of P and heavy metal is still unclear. Thus, simultaneous adsorption of phosphate and zinc by LMZ was investigated in this study, and its co-inactivation performance in sediment was also verified. Separate adsorption capacities of LMZ for phosphate and zinc were 2.31 and 0.367 mmol/g, respectively. In co-adsorption scenario, removal rate of zinc (0.15 mmol/L) increased from 73.53 to 84.60% when co-existing phosphate increased from 0.097 to 0.48 mmol/L (pH 6.5), while zinc had an inapparent impact on phosphate adsorption. Furthermore, an increase of background NaCl concentration in the system inhibited zinc removal by 25%, indicating that part of zinc was physically adsorbed by the zeolite fraction of LMZ. XPS and Raman spectra suggested that phosphate in the simultaneous adsorption system was innerspherically adsorbed by lanthanum oxide component of LMZ, while zinc was adsorbed by forming both outer-sphere complex and inner-sphere complex. Part of zinc could chelate with the adsorbed phosphate, forming phosphate bridged ternary complex and enhancing zinc removal. Finally, a lab-scale inactivation experiment showed that simultaneous stabilization of P and zinc in sediment could be achieved by dosing 5% weight percentage LMZ, making it a promising inactivation agent in the future. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

Lanthanum modified zeolite (LMZ) has shown to be an effective agent for controlling internal phosphorus load in lakes, and its performance in co-sequestration of phosphorus and zinc was investigated in this study. The results indicated that the removal rate of zinc increased with higher concentrations of co-existing phosphate, while the presence of zinc had minimal impact on phosphate adsorption. Increasing the background NaCl concentration inhibited zinc removal, suggesting that part of zinc was physically adsorbed by the zeolite fraction of LMZ.