Die elektroherwinning van Fe en H2SO4 uit ’n FeSO4-logingsoplossing met behulp van anioonruilmembrane

Abstract

The purpose of this study was to develop an economical, safe and environmentally friendly electrochemical process for the conversion and recovery of Fe and H2SO4 from a FeSO4 leaching solution. For this purpose, two basic processes were investigated: electrorefining (ER) and electrowinning (EW). Firstly, EW implies that Fe is recovered directly from the leaching solution, leaving pure H2SO4 (leaching agent). Secondly, during ER anodes containing the Fe are cast eliminating the need for leaching during the recovery of the Fe. During the studying of the respective recycling techniques, the effect of two electrolytes was investigated during ER. However, for EW both the influence of the design that differed i.t.o. the overall shape (cylindrical or square) as well as the influence of membranes was investigated. Accordingly, the following series of experiments were performed: ER with Na2SO4 and H2SO4 electrolyte, EW with a cylindrical (CEW) design without or with a non-porous anion exchange membrane (ARM) and EW with a square design (SEW) i) without a membrane, ii) with a porous Terylene membrane (TM) and iii) with a non-porous ARM. For the latter design, i.e. SEW with a non-porous ARM, the effect of the Fe concentration as well as the type of membrane was investigated thereby determining it’s influence on the effectiveness and specific energy consumption (SEC) of the process. It was found that H2SO4 was a more suitable electrolyte when ER was used as a recovery process, but when comparing ER with EW results, it was found that H2SO4 recovery was only obtained during EW and not during ER. It was further found that the laminar flow based SEW process had a significant lower specific energy consumption than the CEW. The membrane studies (porous vs. non-porous) showed that the ARM-SEW process - where a Fumasep® FAB-PK-130 anionic exchange membrane (ARM) (Fumatech, Germany) was used as a non-porous membrane - was the most suitable recovery process. This process had an efficiency of 99.16 %, which is higher than the efficiency achieved with the commercial Pyror process (85 %). The ARM-SEW process also achieved a 3.55 kWh/kg SEC which is 0.7 kWh / kg lower than wat is achieved with the Pyror process. During the change of the Fe concentration influence on the ARM-SEW process, it was found that a Fe concentration of 40 g/ℓ, as is used for the Pyror process, was optimal. Furthermore, it was shown that, the increase in side reactions under 10 g/ℓ was such that both the effectiveness and SEC of the processes were significantly impaired. On the other hand, it was found that the resistance of the solution above 80 g/ℓ became so high that it also significantly impaired both the effectiveness and the SEC of the process. For the optimization of the type of ARM that can be used for the ARM-SEW process, the commercial Fumasep® FAB-130-PK membrane was compared to nine novel membranes (produced by Dr Kerres’s group at the University of Stuttgart). According to the results, the newly developed ARM 2252A could match the effectiveness of the commercial Fumasep® FAB-130-PK and even reduce the SEC of the process by 0.20 kWh/kg. However, it was found that all newly developed ARM’s deformed during the process. Since it was practically independent from the composition of the membrane, it appears that it is not only the composition’s contribution that is instrumental to the stability of the membranes, but also the absence (in the case of novel membranes) or presence of an internal support label matrix (Fumasep® FAB-130-HP). In summary the study has shown that the ARM-SEW process yielded the lowest SEC and highest efficiency. Being a closed device, the experimental setup isolated both reactions and chemicals and made the safe handling of the reagents and products possible. It was then also shown that only O2 was formed as a waste product during the ARM-SEW process. It can be confirmed that ARM-SEW process developed in this study is an economical, safe and environmentally friendly electrochemical process that can recover both Fe and H2SO4 from a FeSO4 leaching solution.