Redox Behavior of Am(IV) and Methods of Its Preparation in Alkaline Media

摘要

A scheme was suggested for Am(OH)_(4) isolation by treatment of Am(OH)_(3) suspension in 0.1-1.0 M NaOH with ozone (3.5-5 vol percent)-oxygen mixture (4-5 1 h~(-1) flow rate) at 20 deg C for 40 min, followed by ultrasonic treatment of the resulting Am(VI) (44 kHz, 1 W cm~(-3)) for 45 min. The separated precipitate of Am(III) hydroxy peroxide was treated with 1-2 ml of 7-10 M NaOH to form Am(OH)_(4). Mixing suspensions of equivalent amounts of Am(III) and Am(V) hydroxides in NaOH also gives Am(IV) hydroxide in a >98percent yield. The reproportionation Am(III) + Am(V) velence 2Am(IV) in 1 M NaOH starts on heating above 70 deg C, whereas at NaOH concentration higher than 7 M it is completed even at room temperature. The reaction of Am(III) with Am(VI) in alkaline solutions, Am(VI) + 2Am(III) -> 3Am(IV), occurs during mixing the reactants. The equilibrium reaction of Am(OH)_(3) with [Fe(CN)_(6)]~(3-) in alkaline solutions was studied. It was shown that increasing the alkali concentration to 2 M NaOH promotes formation of Am(OH)_(4). At further increase in the alkali concentration, Am(V) is formed.