THE INTERACTION OF NONSTOICHIOMETRIC MANG ANESE OXIDES WITH WATER SOLUTIONS - SOLUBILITY AND REDOX EQUILIBRIA

The solubility of amorphous delta-MnOx (analogues of natural vernadite ) was experimentally studied at 20 degrees C in the broad pH range. Th e solubility depends strongly on the oxidation degree x at pH less tha n or equal to 5 and does not depend on x at pH greater than or equal t o 7-8 for x = 1,41-1,99, being about (1-2).10(-6) mole/l. The EPR meas urements show the possibility of tri- and tetravalent manganese existe nce in the solution. Eh-pH measurements in solutions with different Mn Ox phases permit to determine the reaction controlling Eh: delta-MnO2 + H+ + (e) over bar = beta-MnOOH with E = 930 +/- 10 mV This phenomeno n is proved also for natural Fe-Mn nodules.