Study On The Characteristics Of Uranium (Ⅵ) Stability By Calcium Doped Biochar Recovering Phosphorus From Aqueous Solution

In this paper,the high carbon content flour with a single chemical component and the different mass Ca（OH）₂ micro-powder are used as biomass and loading agent,respectively,and the porous biochar composite（Ca-BC）with interior-doped calcium is prepared by the pyrolysis and carbonization at 800°C in a tubular resistance furnace under the protection of N₂ The phosphate in aqueous solution is adsorbed.The optimal proportion of calcium doped biochar is determined by the adsorption capacity.Besides,the phosphate fixed matter with excellent adsorption performance is filtered and recovered,and the products are used continuously as the adsorbent to adsorb uranyl ions in aqueous solution.The adsorption of phosphate,and the adsorption of phosphate fixed products on uranyl ions are studied in the different environmental conditions.The physical-chemical properties of materials,and the final adsorption mechanism is obtained by the characterization of XRD,FTIR and SEM before and after adsorption.In the adsorption experiment of calcium-doped biochar for phosphate,the calcium-doped biochar with different proportion is prepared,and the proportion of calcium hydroxide to flour are 1:1,1:2,1:4,and 2:1.Besides,the biochar with pure flour or calcium hydrogen micro-powder are prepared for comparison.The results of isotherm adsorption show the maximum adsorption capacity of Ca-BC is 314.4 mg/g when the initial concentration of phosphate is 300 mg/L,which suggests the Langmuir model can well fitted the experimental data.The results of kinetic experiments show that the adsorption reach equilibrium at about 3 h,and the adsorption capacity increase with the rate of calcium on biochar.And the pseudo second order model is consistent with the adsorption process.The results of materials characterization before and after adsorption indicate that the calcium on biochar can promote the binding of adsorbents to phosphate,and the phosphate is presented in the form of hydroxyapatite（HAP）after adsorption.During the adsorption experiment of uranyl ions,the phosphate stationary products（BC-HAP）are prepared by selecting Ca-BC（1:1）which has excellent adsorption effect and is convenient for filtration and recovery.To explore further the effect of phosphate stationary products on the adsorption of uranyl ions,three adsorption materials with different phosphate of BC-HAP1,BC-HAP2,BC-HAP3 are prepared.Meanwhile,the nano-hydroxyapatite（HAP）is used as a comparison.The experiments of different reaction conditions show the reaction is more favorable at the pH of 3.The isotherm adsorption exhibit the BC-HAP1 and BC-HAP2 achieve the adsorption equilibrium at the uranyl ions concentration of 60 mg/L and 70 mg/L,and the maximum adsorption capacity are 477.98 mg/g and 658.45 mg/g,respectively.The results indicates the Langmuir model can better describe the adsorption of uranyl ions by BC-HAP.The kinetic experiments show the adsorption reach equilibrium at the time of 30 min,and the pseudo second order kinetic model can better clarify the adsorption process.The characterization of materials before and after adsorption suggest the phosphate stationary products is helpful to the binding of uranyl ions and phosphate,and the adsorbed phosphate are presented in the form of H-autunite and Ca-autunite.In this study,the adsorption mechanism of phosphate by the calcium-doped biochar,and uranyl ions by phosphate stationary products are further explored.The biochar has the advantages of high adsorption capacity,high adsorption rate and easy to separate in the solid-liquid phase,which can provide corresponding theoretical basis for the removal of phosphate and uranyl ions pollutants.