Preparation And Performance Of O-xanthogenated Chitosan Used As Heavy Metal Chelating-flocculant

Because heavy metals are toxic and cannot be biodegraded in the environment,they can cause serious harm to the environment and human health directly or indirectly.Heavy metal wastewater mainly comes from industries such as mining,non-ferrous metals,electroplating,electrolysis,paint,and pigment production.The types,contents,and existing forms vary with the production conditions.How to effectively remove heavy metal ions from wastewater and recover and utilize them has become the current hot spots.At present,the main treatment methods include chemical precipitation,electrolytic,adsorption and biological treatment.However,these technologies have the disadvantages of high cost and difficulty in recovery of heavy metals.The flocculation method has many advantages such as easy operation and simple treatment process,so it has a good development prospect.Based on this,in this paper,new type of heavy metal dignified flocculants,called O-xanthogenated chitosan（XCTS,HXCTS）,are prepared by using chitosan as raw material.Sulfonium regiment disulfide generation is introduced in carboxyl chitosan molecular structure by xanthate acidification.In this paper,Chitosan（CTS）,benzaldehyde（C₇H₆O）carbon disulfide（CS₂）and sodium hydroxide（NaOH）are used as raw materials.The optimal conditions for the preparation of XCTS and HXCTS are determined by single factor method and orthogonal test method.Infrared analysis,elemental analysis,energy spectrum and scanning electron microscopy analysis are used to characterize the XCTS and HXCTS,and the solution properties and storage stability are studied.To study the effect of various factors such as the initial concentration of heavy metal ions in water sample,initial pH value and the hydraulic conditions of flocculation experiment on removal of copper,chromium and cadmium by XCTS,and the effects of the presence of ethylenediamine tetraacetic acid disodium,sodium citrate,sodium pyrophosphate and kaolin suspension on the performance of XCTS for removing heavy metal ions were studied.The structure of chelating flocs is characterized,its stability and recovery of heavy metals are discussed.The experimental results are as follows:（1）The main factors influencing the synthesis of XCTS and HXCTS by single factor experiment are as follows:the sequence of reactants dosing,the molecular weight and degree of deacetylation of chitosan,the dosage of benzaldehyde,the dosage of CS₂,the concentration of NaOH,the pre-reaction temperature,the pre-reaction time,the main reaction temperature,the main reaction time,etc.（2）The dosage of CS₂,the concentration of NaOH,the pre-reaction temperature,the pre-reaction time,the main reaction temperature and the main reaction time are selected as the six orthogonal factors,and the removal rate of Cu²⁺and Cd²⁺in the water sample is taken as the inspection index.Comprehensive analysis shows that the optimal preparation conditions for XCTS are as follow:the dosage of CS₂ is 1.5mL,the concentration of NaOH is 10.0%,the pre-reaction temperature is 35℃,the pre-reaction time is 10 min,the main-reaction temperature is 50℃and the main-reaction time is 210 min.（3）XCTS is an amphoteric chelating flocculant,and it is isoelectric point(pH_iep)is 2.6 in the distilled water system.If it is in the tap water system,the isoelectric point is 2.0.（4）XCTS has good performance on removal of heavy metal ions in wastewater containing Cu²⁺or Cr³⁺under acidic conditions.When the initial pH value of the water sample is 6.0,the highest removal rate of Cu²⁺is 92.42%.When the initial pH of the water sample is 4.0,the highest removal rate of Cr³⁺is 98.77%.The dosage of XCTS increases with the increase of initial concentrations of Cu²⁺and Cr³⁺in water samples.The effects of coexisting ethylenediaminetetraacetic acid（EDTA）,sodium citrate（TSPP）,sodium pyrophosphate（SC）and turbidity on the removal of heavy metal ions by XCTS are different.EDTA inhibites the removal of Cu²⁺by XCTS significantly SC and TSPP,sometimes play positive role,sometimes play negative role on the removal of Cu²⁺.Co-existing EDTA,SC and TSPP all have an inhibitory effect on Cr³⁺removal by XCTS.XCTS has the dual function of removing turbidity and trapping heavy metal ions.The resulting flocs have a rapid sedimentation rate and good effluent quality.（5）The stability of the chelating flocs XCTS-Cu and XCTS-Cr are superior,and the recovery performance of Cu²⁺and Cr³⁺is good and it is not easy to cause secondary pollution.（6）Selecting O-xanthogenated chitosan as chelating flocculant to treat waste water containing heavy metals by flocculation method has many advantages.For example,O-xanthogenated chitosan can effectively remove heavy metal ions in wastewater and do not need to add other flocculants,and it has the advantages of low raw material price,simple synthesis method,and good removal effect of Cu²⁺and Cr³⁺when the dosage is less.The heavy metal chelating flocculants O-xanthogenated chitosan prepared in this paper has the advantages of simple synthesis method and low preparation cost,etc.;it can effectively remove heavy metal ions(such as Cu²⁺,Cr³⁺)in wastewater and do not need to add other flocculant.Therefore,XCTS has a good application prospect in the treatment of heavy metal wastewater.