Electrochemical recovery of MnO2 from solutions containing waste biomasses

The present study started to develop a production process of manganiferous products of industrial interest, such as MnO2, by using an innovative chemical leaching, at low environmental impact, in presence of waste biomasses coming from agro-industrial activities. 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, manganese concentration and impurities. The experimental activity was conducted at laboratory scale, utilising an italian manganiferous ore. Sulphuric acid was the leaching agent, while lactose was added as carbohydrate, to simulate the presence of waste biomasses. The subsequent electrowinning tests were conducted by a cylindrical glass laboratory cell, with the main objective to determine the process parameters. Electrochemical kinetics studies have been conducted utilising synthetic solutions, of characteristics similar to the real process solutions, containing Mn, Mn + Fe+3, Mn + lactose, Mn + lactose + Fe+3. Finally, the results have been compared. The purity of the EMD, deposited on the cylindrical platinum mesh anode, was detected by diffractometric analysis (RXD) . The results shows that, also in presence of iron and lactose in solutions, it is possibile to achieve high EMD recovery after electrowinning process (98-99%). Diffractometric analyses (RXD) demonstrate the high degree of purity of the EMD deposits (> 92 %). The faradic efficiency (?) decreases from about 90% (pure solution containing only Mn) to about 80% in presence of Mn and Fe3+ and to about 70% when Mn, Fe3+ and lactose were presents. Consequently, energetic consumption increases from about 1.5 kWh/kg (pure solution containing only Mn) to about 2 kWh/kg, in the case of contemporaneous presence of Mn, Fe3+ and lactose in leaching solution. The current density was about 15 mA/cm2. The further work consists in the scale up of the process in continue system, whit the main objective to simulate the industrial process and to obtain increasing of the manganese recovery and decreasing of the energetic consumption. Moreover, molasses from agro-industrial activities will be utilised to perform the leaching tests.