Phosphate Recovery From Aqueous Solutions Using Nano-CaO2/BC Composite And Its Resourceable Utilization

In this study,a porous biochar was used as a carrier,and CaO₂ nanoparticles were loaded on the surface and pores of the biochar by surface precipitation to prepare a functional material?nano-CaO₂/BC composite?for efficient phosphate removal.Meanwhile,the influence of the main preparation conditions on phosphate removal of the composite was investigated.The physicochemical properties of the composite were fully characterized and analyzed.A series of batch experiments were conducted to test the phosphate removal performance of the composite under different influencing factors,investigating the adsorption condition.Meanwhile,the adsorption mechanism was investigated by the analysis of adsorption model and characterization,which provided theoretical basis and technical support for the composite in practical applications.Based on the biological effects of the used composite on tomato seedlings,the feasibility of waste disposal and resource utilization were explored.?1?During the preparation of nano-CaO₂/BC composite,the synthesized composite can be more efficient for phosphate removal with the 600°C of pyrolysis temperature of biochar,80 mesh of biochar particle size,0.8:1 of Ca Cl₂ to biochar mass ratio,12.6 m L of H₂O₂ and 15 m L of NH₃·H₂O.SEM,TEM,BET,XRD and FTIR were used to characterize the physicochemical properties of biochar and nano-CaO₂/BC composite.The results showed that biochar contained micropores,mesopores and slit pores,which provided a large number of adsorption sites for the loading of CaO₂.Meanwhile,CaO₂ on the surface of biochar increased the active substance for the phosphate removal,so that the phosphate can be efficiently adsorbed by nano-CaO₂/BC composite.?2?The nano-CaO₂/BC composite was used to adsorb phosphate in aqueous water.By investigating the dosage of the composite,the initial p H of the phosphate solution,the coexisting ions,and the initial phosphate concentration,the phosphate removal performance of composite under different influencing factors was analyzed.The results showed that:The phosphate removal efficiency and removal rate can achieve a higher level with the 2 g L^–1 of the dosage;When the initial p H of the phosphate solution was in the range of 3-11,the phosphate removal rate was faster under high p H conditions and slower under low p H conditions.Howerver,the final phosphate removal efficiency was not significantly different.It showed that the composite can neutralize the acidic wastewater,contributing to the smooth conducting of phosphate removal under the acidic conditions;The presence of coexisting ion HCO₃^–could reduce the phosphate removal efficiency of nano-CaO₂/BC by about 6.2%,while coexisting ions SO₄^2–,NO₃^–and Cl^–had no negative effect on phosphate removal.Therefore,the composite had certain anti-interference ability;When the initial phosphate concentrations were in the range of 5-200 mg L^–1,the phosphate removal efficiency of the composite can reach more than 99%.However,due to the limited adsorption capacity of the composite,when the concentrations of phosphate exceeded 200 mg L^–1,it was necessary to increase the dosage of the composite to achieve the desired removal efficiency.Besides,the buffering capacity of the phosphate solution can reduce the change of p H values.Therefore,the buffering capacity of the solution can affect the phosphate removal to a certain extent.For the recyclability of the material,nano-CaO₂/BC could remove phosphate steadily with at least four cycles,suggesting that this composite has a great potential for practical application.?3?The pseudo-second-order kinetic model,Langmuir-Freundlich and Redlich-Peterson isothermal adsorption models,as well as XRD and FTIR characterization analysis results demonstrated that the predominant adsorption mechanism was the chemisorption onto the heterogeneous surface by producing multiple layers of amorphous calcium phosphate?ACP?and Ca HPO₄·2H₂O?DCPD?precipitations.The rate-limiting step was chemisorption between phosphate ions and adsorbent binding sites.The maximum adsorption capacity was 213.22±13.57 mg g^-1?298K?.?4?The pot experiment showed that:According to the color,stem height,and leaf size of the seedlings,the growth of seedlings in the used nano-CaO₂/BC group was found to be the best.This is due to that,in used nano-CaO₂/BC group,the biochar and the phosphorus played a role in improving soil and providing nutrients for plants,respectively.The bioassay results demonstrated that the used nano-CaO₂/BC could be recycled back to soil to improve soil quality and promote plant growth.