Preparation Of Potassium Ferrate And Its Potential Application To Water Treatment

In recent years, ferrate (iron in +6 oxidaton state) has gained increasing attention as a novel water treatment chemical for oxidation/disfection and coagulaton processes due to its strong oxidizing properties and its yields of ferric ion, however, owing to its high cost, low purity and low yield. Up to now application of potassium ferrate in full scale was unrealized.The wet method, a most popular method for ferrate preparation, required large amount of alkali without reuse, resulting in high cost and pollution. This study aimed at reducing the preparation cost by purifying the waste alkali for reuse. Stablity of ferrate and its application to textile wastewater were also studied. The major works were as follows:(1) Simple analytical methods were chosen for potassium ferrate both in solid state (arsenite-bromate method) and in solutions (spectroscopy method).(2) The method for purifying of waste alkali was studied, and the purified alkali was reused for preparation of hypochlorite and potassium ferrate. With the use of waste potash lye, the cost is reduced more than 45% compared with the traditional wet method, and the purity was higher than 90%, and the yield ranged from 50% to 70%.(3) Several factors such as pH, concentration of ferrate and the co-exist ions affectting the stability of ferrate were also studied in this study. Results showed that addition of sodium silicate was consedered to be more stable for potassium ferrate in solutions.(4) Considering the characteristics of strong oxidizing and coagulation of potassium ferrate, a pretreatment technics using potassium ferrate was designed. Results indicated that for 0.01mM textile wastewater, dye decolorization was higher than 80% in condition that the molar ratio of ferrate and dye was than 5:1, and pH value was 9.2.