Preparation And Performance Of Modified Chitosan By Xanthogenation

Heavy metal wastewater has a wide range of sources and is highly toxic.At present,among all the treatment methods of this kind of wastewater,the method of removing heavy metals by polymer chelating flocculant is novel and efficient,which has many advantages such as economy,simple operation,easy settlement and separation,and no secondary pollution.At the same time,it can effectively reduce the turbidity in the actual wastewater.As a flocculant,chitosan?CTS?is widely used because of its abundant resources,low price and low risk of secondary pollution.In this paper,in order to further enhance and improve performance of CTS,on the basis of the existing product xanthogenated schiff base chitosan?XCTS?,new type of heavy metal dignified flocculants,called O-xanthogenated chitosan?AXCTS?and O-xanthogenated-N-Benzyl chitosan?RXCTS?,are prepared by two kinds of reagents?HCl and NaBH₄?transformed the imine of XCTS into primary amine and secondary amine,using chitosan as raw material.In this paper,the optimum preparation conditions of AXCTS and RXCTS were determined by single factor method and orthogonal test method,and determined the properties of two products.Cu²⁺and Cd²⁺were selected to study the chelating efficiency of the product,including the hydraulic conditions of flocculation experiment,the initial concentration of heavy metal ions,the initial pH value,turbidity,and the influence of organic coordination agents such as disodium ethydiamine tetraacetic acid,sodium citrate and sodium pyrophosphate.By means of infrared analysis,energy spectrum and scanning electron microscopy,structure,chemical composition and surface morphology of the four chelating flocs AXCTS-Cu?AXCTS-Cd?RXCTS-Cu and RXCTS-Cd after flocculation were characterized,and the stability of the flocs and the recovery performance of heavy metals were measured.The main experimental conclusions are as follows:?1?The main factors for the preparation of AXCTS were reaction system pH,reaction time and temperature;and the RXCTS were reactant ratio,reaction time and temperature.The removal rate of Cu²⁺in water samples was taken as the research object.Through single-factor experiment and orthogonal experiment,the optimal preparation condition of AXCTS was determined as the reaction system pH value was 10.0,the reaction time was 1h,and the reaction temperature was 30?;and the RXCTS was determined n?CTS?:n?NaBH₄?=1:1.5,the reaction time was 0.5h,and the reaction temperature was 30?.?2?The isoelectric points(pH_iep)of AXCTS and RXCTS in the tap water are 2.18 and3.02,2.73 and 3.24 in the distilled water system,respectively.They are easy to store in the refrigerator at 4?.Through elemental analysis,infrared analysis and energy spectrum analysis on AXCTS and RXCTS,it was found that xanthan acid group was successfully grafted on the molecular chain of AXCTS and RXCTS.Meanwhile,the–N<in XCTS was acidic by HCl to–NH₂ in AXCTS,and was reduced to–NH–in RXCTS by NaBH₄.The solid particle morphology of AXCTS and RXCTS was observed by scanning electron microscopy.The surface area of the two particles was large,which was conducive to the adsorption of heavy metal ions.?3?The treatment of water samples containing Cu²⁺or Cd²⁺by AXCTS and RXCTS was carried out under the optimal hydraulic conditions.The specific performance was that the best hydraulic conditions for AXCTS to remove Cu²⁺was the time for rapid stirring was 1.5min at speed of 140r/min,and the time for slow stirring was 20min with 40 r/min,for Cd²⁺was2.0min at speed of 180 r/min,and the time for slow stirring was 20min with 40r/min.The best hydraulic conditions for RXCTS to remove Cu²⁺was the time for rapid stirring was 2.0min at speed of 140r/min,and the time for slow stirring was 20min with 40 r/min,for Cd²⁺was2.0min at speed of 160r/min,and the time for slow stirring was 15min with 40 r/min.When the concentration of Cu²⁺was 25mg/L,the pH value of water sample was adjusted to 6.0,and the dosage of AXCTS was 120mg/L,the Cu²⁺removal rate can reach 97.70%,which was significantly improved compared with 92.42%of Cu²⁺removal rate of XCTS.If RXCTS is added to the same water sample,the removal rate of Cu²⁺can reach 98.82%while the dosage is only 60mg/L.Organic coordination agent had a certain effect on the Cu²⁺and Cd²⁺removal of AXCTS and RXCTS.EDTA had a completely inhibited effect.SC and TSPP have the same effect.The addition of kaolin to the water sample promoted the AXCTS and RXCTS to Cu²⁺and Cd²⁺?under certain dosage?,and both of them also had good removal ability to turbidity.?4?IR and EDS showed the–OCSS^-?–NH₂ and–NH–in AXCTS and RXCTS reacted with heavy metal ions.Scanning electron microscope analysis showed that the the flocs particles from AXCTS and RXCTS were larger and more compact than XCTS after chelating with heavy metal.The stability of the four kinds of flocs is good,in the range of pH value from 2 to 12,the highest leaching rates of AXCTS-Cu?AXCTS-Cd?RXCTS-Cu and RXCTS-Cd were 77.93%,58.46%,75.36%were 59.91%.When Cu²⁺and Cd²⁺are separated by AXCTS,heavy metal ions in the flocs after chelation can be recovered by HNO₃.When Cu²⁺was removed by RXCTS,Cu could be recovered from the chelated flocs by H₂SO₄,while when Cd was recovered by HCl.The highest recovery were 86.10%and 92.05%.?5?AXCTS and RXCTS had a good treatment effect on the actual copper containing wastewater in the smelter,with the highest removal rate up to 95.09%and 97.89%,respectively.After treatment,the sewage can be discharged to the standard,and the turbidity in the wastewater can also be significantly reduced,indicating that the application of AXCTS and RXCTS in heavy metal wastewater treatment has a good prospect.