Redox reactions of platinum elements. XI. Kinetics of reaction between rhodium(IV) and nitrous acid

In previous work, the authors have studied the features of Rh(IV) reduction with hydrogen peroxide, FeF(II), and U(IV). These studies are of practical interest for recovering radiogenic rhodium from wastes of nuclear-fuel cycle. Along with stable Rh(III), tetravalent state of rhodium may be promising for isolating and purifying Rh. Initial steps of reduction of Rh(IV) with nitrite ions in HClO{sub 4} solution follow the equation {minus}d[Rh(IV)]/dt = k[Rh(IV)][HNO{sub 2}]/[H{sup +}], where k is equal to 730 {plus_minus} 160 min {sup {minus}1} at ionic strength {mu} = 2 at 15 and 25{degrees}C respectively. The activation energy is E = 83.0{plus_minus}0.1 kJ mol{sup {minus}1}. The reduction of Rh(IV) is inhibited by formation of Rh(IV) nitrite complex. At 15{degrees}C the rate constant of this reaction is k{sub 2} = 100 {plus_minus} 30 1 mol{sup {minus}1} min{sup {minus}1}. The reaction mechanism is discussed.