The kinetics of pyrophosphate leaching of partially reduced manganese dioxides

✍ Scribed by M.A. Malati; M.W. Rophael; I.I. Bhayat

• Publisher: Elsevier Science
• Year: 1981
• Tongue: English
• Weight: 420 KB
• Volume: 26
• Category: Article
• ISSN: 0013-4686
• DOI: 10.1016/0013-4686(81)85009-8

✦ Synopsis

y-MnO, (R2) and BMnO,(R4) were reduced with hydra&e hydrate. The kinetics of leaching the recluced'products with pycophosphate was followed by measuring the absorbance of the Mn(lI1) complex formed. The results of fast reduction indicated that diffusioncontrolled leaching was preceded by faster leaching. The results of slow reduction were in agreement with the relation:

wherefis the fraction of Mn(III) leached at time t, D is the diffusion coefficient, A is the surface area of a sample and V its volume. The use of BET surface area led to very low values of D. The results of leaching different size fractions suggested that it is preferable to use the geometrical surface for A. The corresponding value for D in R2 was found to be 0.67 and 0.54 x 10~" cm2 s-l for two size fractions. For samples reduced to a greater extent, D was 3.6 and 2.2 x lo-I2 cm ' s -I for the same size fraction of R2 and R4 respectively. The kinetics of leaching was practically unaffected by the speed of shaking or by the pyrophosphate concentration.