Valorisation of residue organic substances by electrochemical applications

The main goal of the experimental activity was the electrolytic manganese dioxide (EMD) recovery, at high degree of purity, from leaching solutions containing Mn, by electrowinning process, also considering the effect of the presence of the organic substances, such as carbohydrates and impurities. Electrochemical kinetics studies have been conducted at laboratory scale utilising synthetic solutions, of characteristics similar to the real process solutions, containing Mn, Mn + Fe+3, Mn + lactose, Mn + lactose + Fe+3 respectively. Synthetic process solutions have been prepared taking into account the characteristics of an italian manganiferous ore and supposing the use of sulphuric acid and carbohydrates (waste biomasses) as leaching agents: lactose was added to simulate the presence of waste biomasses. The results show that, also in presence of iron and lactose in solutions, it is possible to achieve a quantitative EMD recovery after electrowinning process (about 99%). Diffractometric analyses (RXD) demonstrate the high degree of purity of the EMD deposited on the cylindrical platinum mesh anode (> 93 %). The faradic efficiency (?) decreases from 91% (pure solution containing only Mn) to 78% in presence of Mn and Fe3+ and to 69% when Mn, Fe3+ and lactose are presents. Consequently, energetic consumption increases from 1.4 kWh/kg (pure solution containing only Mn) to 2.2 kWh/kg, in the case of contemporaneous presence of Mn, Fe3+ and lactose in leaching solution. The further work will consists in the scale up of the process in continue system, utilising molasses from agro-industrial activities to perform the leaching tests.