Study On Phosphorus Adsorption By Biochar Of Chaetomorpha Valida And Its Resource Reuse

In order to utilize the green tide algae-Chaetomorpha valida,the possibility of preparing biochar from the algae for the removal of phosphate from water was explored,under three temperatures of 450°C,650°C,and 850°C.At the optimum temperature,three kinds of modified biochar were prepared by incorporating metal（Fe,Mg,and Al）chlorides into the original biochar by co-precipitation method.Fe³⁺and Fe²⁺were introduced into biochar by co-precipitation method in the form of hydroxides to increase the content of Fe₃O₄ on the surface of the modified biochar,which was magnetized and combined with Al,La,Mg,and Mn respectively to prepare biochar at300～700℃.SEM-EDS,FTIR,BET and Zeta potential were characterized for biochar.Colorimetric method was used to evaluate the adsorption capacity of biochar for phosphate.The adsorption properties of biochar were studied by fitting kinetic and isothermal adsorption equations.The influence of different factors on the phosphate adsorption capacity and the mechanism of biochar adsorption on phosphate were explored.The potential of biochar as a slow-release fertilizer after phosphorus absorption was evaluated by pot experiment.The results showed that:（1）The modification of Chaetomorpha valida biochar with ferrous chloride and other metal chlorides could significantly improve the adsorption capacity of phosphate by biochar.The micropore structure of BC-650-Fe surface and a variety of functional groups such as Fe-O were the main reasons for the high adsorption capacity of phosphate.Biochar adsorbed phosphate in a uniform single molecular layer chemical adsorption mode.The optimum p H environment of BC-650-Fe for phosphate adsorption is neutral and weakly acidic,and the adsorption capacity decreases significantly under alkaline conditions.With the increase of the dosage of BC-650-Fe,its removal rate was negatively correlated with the adsorption amount.When the dosage of BC-650-Fe was more than 8 g·L^-1,the removal rate of phosphate in water could exceed 90%,and when the dosage was 10 g·L^-1,the maximum removal rate was 93.16%.These results indicated that the Chaetomorpha valida biochar had a good ability to absorb phosphate in water,which could provide a new way for the resource utilization of Chaetomorpha valida.In terms of phosphate adsorption performance,the adsorption capacity of Chaetomorpha valida biochar could meet the demand of general water treatment.（2）Among the different magnetic biochar,MBC400La had the highest phosphate adsorption capacity,which was 91.03±0.56 mg·g^-1.The combination of Fe and La metal has a synergistic effect on the phosphate adsorption capacity of biochar.The pyrolysis temperature has no significant effect on the phosphate adsorption capacity of MBCLa.The magnetic field intensity of MBC400La increases with the increase of p H of the modified solution,but decreases with the increase of La load.Compared with one-step precipitation method,fractional precipitation method has no significant effect on phosphate adsorption.The optimum conditions for preparing magnetic biochar were p H 8 and La dosage 0.1 mol·L^-1.The p H,ash content,yield and conductivity of MBC400La were 7,40.32±0.45%,42.56±0.19%and 546.26 us·cm^-1,respectively.SEM-EDS showed that Fe and La were found on the surface of MBC400La-P.The BET surface area of MBC400La is 36.9452m²·g^-1,and the infrared spectrum shows that La-OH and Fe-O are stretching vibration on the surface.P-O is observed on MBC400LA-P.The p H _PZC of MBC400La was 6.14,and the p H _PZC value decreased to 5.36 after phosphorus absorption.The adsorption of phosphate by MBC400La is controlled by chemisorption process,which is carried out by homogeneous adsorption of monolayer.During the adsorption process,solution p H,dosage of MBC400La and high concentration of anion SO₄^2-all have significant effects on the phosphate adsorption process of MBC400La.The adsorption mechanism includes surface precipitation,electrostatic adsorption,coordination and surface complexation.（3）The total adsorption capacity and dynamic adsorption capacity of MBC400La were affected by bed height,initial phosphate concentration and flow velocity.When the bed height was5 cm,the initial phosphate concentration was 10 mg·L-1,and the flow rate was 5 m L·min-1,the total adsorption capacity was the highest,and the unit adsorption capacity was higher at the bed height of 2.5 cm.The Thomas model can predict the phosphorus removal and adsorption behavior of MBC400La more accurately.（4）Soil fertility and lettuce yield could be improved by applying MBC400La-P in saline-alkali soil.MB400La-P had positive effects on soil fertility and lettuce growth.The soil phosphorus absorption and biomass of lettuce increased after MB400La-P combined application.The higher the amount applied,the higher the lettuce yield.The addition of MB400La-P can provide phosphorus and organic carbon to the soil and maintain soil fertility,and reduce the p H and EC values of saline-alkali soil.At the same time,the phosphorus adsorbed from the water can be used by lettuce,thus promoting the germination and growth of lettuce.In this study,a variety of biochar was prepared by metal modification using Chaetomorpha valida as raw material carrier,among which MBC400La realized efficient recovery of phosphate in water.The adsorption behavior of MBC400La in fixed bed column was predicted by Thomas model.The MBC400La-P was applied to the soil to achieve the effect of increasing fertilizer and yield.Therefore,MBC400La not only realizes the resource utilization of Chaetomorpha valida,but also recycles phosphorus in water,which has a good application prospect.