Sdudying On Preparation Of Potassium Ferrate And Its Pre-oxidation And Enhanced Coagulation

Traditional oxidants,such as ozone,permanganate,hypochlorite,etc,is easy to produce toxic secondary pollutants in the course of use,so there are some limitations.The FeO42-of potassium ferrate has a much strong oxidability,in the meantime,potassium ferrate will not produce secondary pollutants that is harmful for environment,and the low-cost iron which is reduced to produce also has the effect of coagulation,so potassium ferrate is an efficient,clean,versatile water treatment agent,in recent years,more and more researchers begin to research it.In this paper,potassium ferrate was acquired by the process of traditional potassium hypochlorite oxidation,and the factors that may affect the yield or purity of potassium ferrate was analyzed.The paper also confirmed the quality of potassium ferrate by the way of IR,and compared three quantitative methods for the determination of potassium ferrate:oxidation reduction titration,indrect spectrophotometry and direct spectrophotometry,established the primary way to assay potassium ferrate.Then this paper researched the stability of potassium ferrate in different conditions,such as pH,temperature,concentration,Fe3+ and SiO32-.In the application part of potassium ferrate,the effects of preoxidation and coagulation of potassium ferrate were investigated in the conditions of different turbidity,chroma,UV254 and TOC,finally,the removal effect of ferrate preoxidation on Mn²⁺ was explored finally.The results showed that the purity of potassium ferrate prepared at the reaction temperature for 15? or vacuum drying time for 36h was about 98%,on the other hand,when the iron salt was too large,the excess Fe3+ would catalyze the decomposition of FeO42-and decreased its yield.Compared with the redox titration and the indirect spectrophotometry,the error of direct spectrophotometry was only 0.44%and 2.37%respectively,the veracity of assay would be affected by unnecessary Fe?OH?3 or Fe???.It was found by studying the decomposition of potassium ferrate in different conditions that the stability of potassium ferrate will be decreased with the increasing of its own concentration and temperature,and the stability of potassium ferrate is best when pH reached to 10 nearly.In addition,Fe3+ promoted the decomposition of potassium ferrate,and the addition of low concentration?10-30mg/L?SiO32-ion to potassium ferrate solution helped to improve its stability.The removal rates of turbidity,chroma,UV254 and TOC were only 81.67%,38.32%,72.15%and 13.48%respectively with PAC alone,after pre-oxidation and enhangced coagulation with potassium ferrate,potassium permanganate and potassium ferrate composite reagent,the removal rate of turbidity was 94.2%,90%and 95.8%respectively,the removal rate of tchroma was 49.22%,42.99%and 52.02%respectively,the removal rates of UV254 was 84.81%,77.2%and 97.34%respectively,and the removal rate of TOC was 21.12%,20.92%and 24.11%.There was no removal effect on Mn²⁺ when adding PAC alone,but the removal effect of Mn²⁺increased with the addition of potassium ferrate,the remaining manganese droped obviously when the dosing was 0.6-0.8mg/L,and the best oxidation time was 5min,with the improving of pH,the removal rate of potassium ferrate for Mn²⁺ gradually increased,2mg/L potassium ferrate has been able to remove more than 50%Mn²⁺ when the pH is 12 nearly.