Adsorption Characteristics Of Phosphorus And Hexavalent Chromium By Protonated Chitosan And Its Magnetic Composites

With the increase of population and the development of industrial society,water pollution has become more and more serious.The excessive levels of heavy metals such as hexavalent chromium in water and the eutrophication of water caused by phosphorus have made China gradually become a water quality-deficit country.At present,the research on water treatment technology is in the ascendant,and the adsorption method with simple advantages,high efficiency,and low cost has been greatly developed.Chitosan is a natural polymer organic material commonly found in the natural environment.It has the characteristics of adsorption,metal ion chelation,and flocculation.It is a water treatment agent with great research and application value.The adsorption performance of chitosan alone is limited and it must be modified in various ways.Taking into account the application of magnetic separation technology,a protonated chitosan was firstly prepared for this project,and then the protonated chitosan and the magnetic ferroferric oxide were composited using a reversed-phase suspension cross-linking method.Different protonated chitosan and protonated chitosan magnetic composites with different ratios were used to investigate the adsorption characteristics for phosphorus and hexavalent chromium in the simulated sewage.First,the structural properties of the material were characterized by X-ray diffraction?XRD?,scanning electron microscopy?SEM?,and Fourier transform infrared spectroscopy?FTIR?.For protonated chitosan,the XRD pattern indicates that the chitosan crystal morphology remains after protonation of chitosan,and the protonation peak of the sample with the highest protonation degree is observed by FTIR.For composites,the XRD,SEM,and FTIR characterization results show the structural characteristics of cross-linking of chitosan with triiron tetraoxide.The magnetic properties of the composites were also measured using a vibrating sample magnetometer?VSM?.The results show that the higher the Fe₃O₄ content in the composites,the stronger the magnetic properties.Secondly,for the adsorption characteristics of protonated chitosan on simulated wastewater containing phosphorus and chromium,the effects of the protonation degree of chitosan,adsorption time,pH value of simulated wastewater solution and initial concentration on the adsorption characteristics of protonated chitosan were investigated.The results showed that the higher the degree of protonation of chitosan,the greater the adsorption capacity of phosphorus and hexavalent chromium.The protonated chitosan treated by sulfuric acid with a pH value of 1.5,which presents the highest protonation degree,has the best adsorption effect.And the protonated chitosan shows better adsorption effect on hexavalent chromium than on phosphorus adsorption.The maximum adsorption capacity for phosphorus is 34 mg/g,and the maximum adsorption capacity for hexavalent chromium is 54 mg/g.For the chitosan with high protonation,the pH value of the original adsorbed water is 3.Isothermal adsorption simulation and adsorption kinetics analysis show that the adsorption of protonated chitosan is mainly monolayer chemisorption.Thirdly,for the adsorption characteristics of protonated chitosan magnetic composites for simulating phosphorus-containing wastewater,combined with orthogonal experiments,the effects of adsorption time,initial concentration,pH value of the solution,adsorbent type,and dosage on adsorption were examined.The research results show that the adsorption properties of the composites are better than those of protonated chitosan because of the synergistic adsorption of triiron tetraoxide and protonated chitosan.In addition,for the composite materials,the degree of protonation of chitosan does not dominate the adsorption.The isothermal adsorption model and adsorption kinetics analysis show that the adsorption mechanism of phosphorus on the composite adsorbent is more complex,including single-layer chemical adsorption and multi-layer adsorption.Orthogonal experimental results show that the pH value has the most obvious effect on the adsorption effect of the composite material,and the optimal pH value for the phosphorus adsorption is 6.The effect of the adsorbent and the dosage is secondary,and the best adsorbent and dosage was F2 and 2 g/L,respectively.The initial concentration and adsorption time had the lowest impact.Finally,for the adsorption characteristics of protonated chitosan/ferroferric oxide composites for simulated chromium-contaminated wastewater,combined with orthogonal experiments,the adsorption time,initial concentration,pH value,type of adsorbent,and dosage were examined for adsorption.The research results show that the composite adsorbents have good adsorption properties for hexavalent chromium.The removal rate reaches above 90%,and the best removal rate amounts to 98%.The adsorption mechanism analysis shows that the Freundlich isothermal adsorption model has a higher degree of fitness.The Lagergren quasi-second order kinetic equation can well describe the adsorption process of hexavalent chromium.The adsorption mainly belongs to the multi-layer chemical adsorption.Orthogonal experimental results show that pH value has the most obvious effect on the adsorption effect of chitosan magnetic composites,and the optimal pH value for hexavalent chromium adsorption is 4.5.The effect of adsorbent and dosage is secondary,and the best adsorbents and dosages were F2 and 2 g/L,respectively.The initial concentration and time had the lowest impact.