Factors Affecting Stability of Aqueous Potassium Ferrate(VI) Solutions

Abstract

ECEST interest in the use of ferrate compounds as strong ' oxidizing agents prompted an investigation of some factors influencing the stability of potassium ferrate solutions. In a study of the st,ahility of ferrate ions in aqueous solutions, Schreyer and Ockerman (2j found that the more dilute solutions of ferrate are more stable. They found also that some added salts, after increasing the initial deconiposition rate of ferrate solutions, apparently staliiljze the remainder; and that ferrate ions are more stable in buffer solutions of p H 8 than those of pH 7. These authors believe that the major factor influencing stability is the alkalinity of the solution. From qualitative experiments Schreyer ( 1 ) reported that solutions of potassium ferrate were partially decomposed photochemically over a period of 9.5 hours.Since it seemed desirable to establish the factors influencing the stability of ferrate compounds in connection with other xork, a quantitative study of t,he effects of light, temperature, alkalinity, and concentration, on the decomposition of aqueous solutions of potassium ferrate was made under carefully controlled conditions. PROCEDUREThe potassium ferrate was prepared by the method reported by Thompson, Ockerman, and Schreyer (4). To determine the effect of light on the decomposition rate of solutions of potassium ferrate under varying conditions, each of the experiments described below was performed using identical solutions in three flasks placed in a thermostat. One flask was exposed to the daylight in the laboratory, one was placed in the path of a beam of light from a 150-m-att G.E. spotlight, and one was painted black to exclude light. The latter was fitted with a rubber stopper containing a release valve to permit the escape of oxygen.As it was impossible to maintain a constant temperature with the splotlight shining directly on the bath, a 3000-ml. beaker of water was inserted between the bath and the spotlight to absorb most of the heat radiation. In this manner the temperature was successfully maintained constant to within +O.l O C.The solutions were analyzed by pipetting 10-ml. portions and determining the ferrate concentration by the chromite method ( 3 ) . Analyses were performed at varying intervals over a 2-hour period after the potassium ferrate solutions were prepared.Preliminary experiments indicated that several factors such as stirring, vibrations, and exposure of dry samples to the atmosphere influenced the decomposition. To minimize these factors the solutions were not stirred, and every effort was made to maintain constant conditions except for the one condition varied in 1 Present address, University of Cincinnati, Cincinnati, Ohio. rvlc each series of experiments. obtained.In this way reproducible rcwults were RESULTSEffect of Temperature. To study the effect of temperature on stability, quantitative determinations 15-ere made on aqueous solutions of potassium ferrate at' temperatures of 25' and 0.5' C. The results in Figure 1 shox that at 25" C. the concentration of potass...

Prevention of Ichthyophthirius multifiliis infestation in goldfish (Carassius auratus) by potassium ferrate(VI) treatment

“…The decomposition rate of potassium ferrate(VI) highly depends on the pH of the aquatic environment. Generally, with reducing pH values, the stability of potassium ferrate(VI) reduces (Wanger et al, 1952). For example, 49% of potassium (7) 19.20 0 AE 0 0 (0)…”

“…Temperature should be considered in the applications, because temperature in the field also influences the decomposition rate of ferrate(VI) solution (Wanger et al, 1952;Johnson and Sharma, 1999). For a given 2-h test period, potassium ferrate(VI) solution (initial concentration: 0.01 M) was reduced by 10% at 25 8C and almost unchanged at 0.5 8C (Wanger et al, 1952).…”

Ferrate(VI) in the Treatment of Wastewaters: A New Generation Green Chemical

“…The ferrate solution prepared with buffer solution at pH 8 was more stable than that prepared at pH 7 [31]; 49% of the original potassium ferrate remained after 8 h when the pH was 7, and 71.4% of that remained after 10 h when the pH was 8. Temperature dependence data showed that ferrate(VI) solutions are relatively stable at low temperature conditions (0.5 0 C) [32]. The 0.01 M solution of Fe(VI) was reduced by 10% at a constant temperature of 25 0 C and almost unchanged at 0.5 0 C for a period of 2 h.…”

Mechanism and Kinetics of Cyanide Decomposition by Ferrate

“…This oxidant is considerably stable in strongly alkaline solution around pH 10, whereas it decomposes spontaneously at a very rapid rate in acidic or neutral solution. 18,19 In an aqueous solution three types of ferrate coexist in equilibrium: non-protonated ( …”