| In recent years,industrial and agricultural production and human activities are the main causes of excessive phosphorus in water.Eutrophication is a typical ecological problem caused by phosphorus enrichment in water.In addition,the shortage of phosphate rock resources and low utilization rate of phosphate fertilizer are the main barriers to limit phosphorus recovery.The harm caused by the above two is not only not conducive to the balance of aquatic ecosystems,but also limits the sustainable development of global ecology and economy in the long term.It has attracted wide attention of scientific researchers and all sectors of society.Therefore,in order to alleviate the negative impact of phosphorus enrichment in water,zeolite-biochar composites were prepared by combining the advantages of zeolite and biochar in phosphate adsorption.The physicochemical properties of the adsorption materials were characterized by scanning electron microscopy（SEM）,transmission electron microscopy（TEM）,Fourier transform infrared spectroscopy（FT-IR）,BET specific surface area（SSA）and ZETA potential.The adsorption characteristics of phosphate on zeolite-biochar composites under different environmental conditions were studied by adsorption experiments.The adsorption mechanism of phosphate on zeolite-biochar composites was revealed based on the adsorption kinetics and adsorption isothermal model.Finally,a pot experiment was conducted to study the effects of phosphorus-loaded composite materials on the growth of maize and the change of soil physical and chemical properties after mixing the phosphorus-loaded composite materials with soil,so as to explore the feasibility of resource utilization of phosphorus-loaded composite materials as a theoretical basis for the practical application of zeolite-biochar composite materials.The main conclusions of this study are as follows:（1）The physicochemical properties of zeolite,biochar and zeolite-biochar composites are different.Due to the influence of biomass carbonization on zeolite during pyrolysis,the p H value of zeolite-biochar composite was higher than that of zeolite,and the H/C value was lower than that of biochar.It indicated that the stability of zeolite-biochar composites was enhanced.The results of SEM showed that biochar attached to the surface of zeolite particles,making the specific surface area of zeolite-biochar composite closer to that of biochar.According to the FT-IR results,zeolite-biochar composite has more surface functional groups,which is more conducive to the removal of phosphate.（2）Based on the simulated 50mg?L-1phosphate solution in this study,the composite prepared with zeolite-biochar mass ratio of 7:3（PZC 7:3）had the best adsorption effect.Compared with zeolite,zeolite-biochar composites significantly enhanced phosphate adsorption（phosphorus removal rate was 90%of biochar）.The best preparation conditions were selected based on different dosage,p H and temperature.The results showed that 40g?L-1(0.8g?20m L-1)was the best dosage.When the p H value of the initial solution was 7.0～11.0,the zeolite-biochar composite（PZC 7:3）had little change(the adsorption capacity was 1.01～1.06mg?L-1),indicating that it had strong acid-base universality and wide application range.The temperature screening experiment showed that 25℃was the best adsorption temperature,and the adsorption capacities of the three materials were the largest at this temperature.The kinetic experiment results based on the above conditions showed that the adsorption of phosphate by the three materials was mainly chemical adsorption and particle diffusion.The results of isothermal adsorption experiment and Langmuir fitting showed that the maximum adsorption capacities of zeolite,biochar and zeolite-biochar composites were 0.69mg?g-1,3.60mg?g-1and 2.41mg?g-1,respectively.The results of R2showed that Freundlich model was more suitable for describing the adsorption process of phosphate on biochar and PZC 7:3,and Langmuir model was more suitable for describing the adsorption process of phosphate on zeolite.（3）In order to further explore the adsorption mechanism,FT-IR and TEM-EDS methods were used in this study to characterize the three materials after adsorption.The results show that the adsorption mechanism of zeolite and biochar is relatively simple,mainly physical adsorption and ligand exchange,respectively.The adsorption of phosphate by zeolite-biochar composite is a complex coupling process,mainly involving ligand exchange,electrostatic attraction and ion exchange.This is likely to be attributed to the formation of a amorphous film-like calcium magnesium phosphate compound during the adsorption of phosphate by the composite.The product adheres to the surface of zeolite,making it difficult for phosphate to be desorbed,thereby significantly enhancing the stability of the composite.The desorption experiment showed that the desorption rate of zeolite-biochar composite was the lowest,followed by biochar,and zeolite was the highest.This indicates that the composite material has higher phosphate adsorption and recovery ability,and has higher stability.（4）A pot experiment was carried out to verify the effects of three materials on the growth of corn,an economic crop widely planted in the world.The results showed that 3%was the optimal feeding ratio,which was more conducive to promoting the growth of maize,as follows:3%BP>3%PZCP 7:3>3%ZP（BP:phosphorus-loaded biochar;PZCP 7:3:phosphorus loaded zeolite-biochar composite;ZP:phosphate-carrying zeolite）.This is completely consistent with the results of adsorption experiments,indicating that the addition of composite materials is conducive to crop production.This is due to the fact that the composites not only release more phosphorus by their own biochar components,but also absorb more phosphorus from the soil to supply plant growth,thus providing more nutrients for plant growth.At the same time,the zeolite component in the zeolite-biochar composite material strengthened the stability of the material,enhanced the retention ability of phosphorus after adsorption,and made it difficult to re-release phosphorus in the soil after adsorption.This further promoted crop growth.Finally,through the soil physical and chemical analysis experiment,this study confirmed that the composite materials could improve the growth environment of crops by slowing down soil acidity,promoting nutrients and increasing organic matter components,so as to improve crop yield.In summary,zeolite-biochar composite is an efficient and environmentally friendly new adsorbent,which can be considered to be widely promoted in the treatment of environmental pollution such as eutrophication.This new composite material is not only beneficial to alleviate a series of ecological crisis caused by excessive phosphorus in water,but also provides reliable scientific and technological support for the benign cycle of global biogeochemistry and the sustainable development of social economy. |
