Preparation,Modification And Application Of Polymeric Ferric Sulfate In Water Treatment

In recent years,with the rapid development of economy,the discharge of industrial wastewater and domestic sewage is increasing day by day.At present,flocculation sedimentation is still the most widely used method with low cost in water treatment technology,and flocculant is the main factor affecting flocculation performance.Polymeric ferric sulfate（PFS）has good flocculation effect and is widely used in water purification treatment.However,it has some problems such as low molecular weight and poor adsorption bridging ability,which makes the research and development of PFS transform to composite flocculant.Therefore,the research and development of efficient,safe and low-cost new flocculant has important theoretical significance and practical application value.Therefore,the direct oxidation method and programmed temperature rise method were used to prepare PFS,and the influence of various factors on the product quality and flocculation effect of PFS was investigated.The results showed that the optimum preparation conditions were as follows:n(Fe²⁺)/n（H⁺）was 1:0.33,n(Fe²⁺)/n（H₂O₂）was 1:0.25,oxidation temperature was 20℃,polymerization temperature was 50℃,polymerization time was 2 h.Under this condition,the total phosphorus removal rate of the product was 74.72%,the total iron content was 11.89%,the ferrous content was 0.016%,and the basicity was 11.81%.The product quality met the first-class standard of"Water treatment agent Polyferric sulfate".On this basis,polysilicic acid（PS）was introduced and inorganic modification of PFS was carried out by copolymerization to prepare polyferric silicate sulfate（PFSS）.The effects of various factors on the flocculation performance of PFSS were investigated by single factor method and orthogonal experiment.The results showed that under the conditions of Si O₂content of 2.0%,n（Fe）/n（Si）ratio of 2:1,polymerization temperature of 50℃and polymerization time of 2 h,PFSS had the best flocculation effect.The total phosphorus removal rate was 86.17%,and the remaining total phosphorus concentration was 4.87 mg/L.The PFSS prepared by this process was compounded with the self-made oligo-chitosan（COS）to prepare COS-PFSS.The influence of various factors on the flocculation performance of COS-PFSS was investigated by single factor method and orthogonal experiment.The results showed that the optimal preparation conditions of COS-PFSS were as follows:V（COS）/V（PFSS）was 1:7,p H was 1.5,reaction temperature was 60℃,reaction time was 1.5 h.At this time,COS-PFSS had the best flocculation effect,the removal rate of total phosphorus was up to 94.59%,and the concentration of remaining total phosphorus was 1.90 mg/L.The XRD,FTIR and SEM images showed that the three flocculants were amorphous materials with amorphous structure.After PS was introduced,a new Fe-O-Si bond was formed between Si,Fe and-OH,forming PFSS.After the introduction of COS,the active group of COS reacted with metal ions to formed a new Fe-OH-Fe bond and generated COS-PFSS flocculant.PFS,PFSS and COS-PFSS were applied to the treatment of phosphating wastewater to optimize the flocculation conditions.The optimal flocculation conditions of the three flocculants were as follows:dosage of flocculant was 80 mg/L,p H was 9.0,dosage of PAM was 1 mg/L,stirring time was 10 min and precipitation time was 25 min.Three kinds of flocculants were applied to treat heavy metal wastewater and domestic sewage,the removal effects of Ni²⁺,COD and turbidity were satisfactory,and the flocculation effect of COS-PFSS was the best.The residual iron content of the domestic sewage after flocculation was detected.The residual iron content in domestic sewage treated by the three flocculants were low,and the residual iron content of COS-PFSS was the lowest,indicating that it was a new type of efficient and safe composite flocculant.Finally,the cost of COS-PFSS preparation in the laboratory was calculated,and the cost was 10.73 yuan/kg.In this study,PFS was prepared and modified to prepare a compound flocculant,which was applied to a variety of wastewater treatment,providing theoretical basis and reference for the development of new flocculant.