<p>The need for clean water is the most basic human right. Water scarcity will be one important environmental problem of all countries in the future. Phosphorus in the water environment, come from some untreated industrial, agricultural and domestic wastewater, pose a significant threat to human health and and other biota due to their toxicity. In this study, the modified corn straw biochar (LBC) /sodium alginate (SA) composites (LBS) adsorbents were prepared to remove phosphate from water. The results showed that the best pyrolysis temperature of preparing LBS was 550&#xa0;°C. When pH was 2 and mass ratio of 550LBC (at 550&#xa0;°C)/SA was 0.3&#xa0;g/0.3&#xa0;g, the adsorption capacity&#xa0;and removal efficiency of phosphate by 550LBS were 61.4&#xa0;mg/g and 92%, respectively. The adsorption of phosphate by 550LBS was consistent with Langmuir model and pseudo 1st order model (R² &gt; 0.95), and reached adsorption equilibrium at 20&#xa0;min, indicating that 550LBS was monolayer adsorption, physical adsorption was the main adsorption and chemical adsorption was the secondary adsorption. The adsorption of 550LBS was the protonation between surface hydroxyl group and H⁺, the phosphate adsorption of 550LBS was dominated by ligand exchange and electrostatic attraction. Compared with the maximum adsorption capacity of 550LBS, used 550LBS could be reused, the adsorption efficiency of adsorbents after three tests was still above 41%. This showed that reusability and renewability of 550LBS were good, and promotes its application in water purification processes.</p> Graphical Abstract <p></p>