Enhanced adsorption of phosphorus in soil by lanthanum-modified biochar: improving phosphorus retention and storage capacity

Use of soil adsorbent is an effective method for the promotion of phosphorus adsorption capacity of soil, though most of the soil adsorbents have weak phosphorus retention ability. Herein, we compared the traditional gypsum (GP) and zeolite (ZP) adsorbents to explore the phosphorus retention ability of lanthanum modified walnut shell biochar (La-BC) in soil. The results showed that with the increase of exogenous phosphorus concentration, the adsorption amount of phosphorus by adsorbents in soil increased at first and then tended to be stable. The maximum adsorption capacity of soil to phosphorus is gypsum, lanthanum-modified biochar > zeolite, and the addition of lanthanum-modified biochar can improve the adsorption capacity of soil to phosphorus, enhance the binding strength of soil and phosphorus, improve the ability of soil to store phosphorus, reducing phosphorus adsorption saturation, and is beneficial to control the leaching of soil phosphorus. FTIR and XRD analysis showed that the adsorption of phosphorus by each adsorbent in soil was mainly chemical precipitation. The response surface analysis showed that the adsorption performance of La-BC+S was the best when the concentration of exogenous phosphorus was 50.0 mg/L, pH was 6.47, and the reaction time was 436.98 min. This study provides a reference for soil adsorbents to hold phosphorus and reduce the risk of phosphorus leaching to avoid groundwater pollution.