No abstract

Divalent iron and zinc cations can be removed from water by electrocoagulation (EC) with aluminium electrodes in a discontinuous system: the effect of hydrocarbonate HCO3-ion often present in liquid waste and in groundwater on the EC process has been investigated. For the two ions, the presence of hydrocarbonate strongly limits the pH variations by its buffering properties and reduces the rates of Al dissolution by corrosion. Removal of the two cations was then shown to require longer treatment times and larger amounts of dissolved aluminium. Whereas the local pH gradients near the electrode surface with HCO3free water was previously shown to allow local formation of stable Zn and Fe hydroxides, which actively contribute to their elimination, the presence of hydrocarbonate nearly suppresses this positive phenomenon, resulting in far less efficient EC treatment. Whereas removal of zinc cations from carbonated water can be considered as their simple adsorption on the Al flocs, Fe 2+ ions are oxidized to Fe(OH)3 by air oxidation after their adsorption. Use of an overall adsorption model allowed quantitative comparison of the EC treatments, with very different adsorption parameters for the two metal studied.

Metals such as cobalt are particularly strategic since they are present in many high-added-value products. Besides, at the rate of current consumption, specifically of cobalt, the manufacturers are facing risks of shortage for their supply. So, research on these metals' recovery from industrial or urban waste is highly important for the future. Current work focuses on cobalt recovery from Li-ion batteries by precipitation. Literature was evaluated on the various anions allowing to precipitate Co(II), in particular hydroxide, carbonate, and sulfide ions, and the focus was set on the hydroxide way. Simulations were performed using speciation software to highlight the various parameters influencing the precipitation process and the formed species. From simulation results, experiments were carried out in a synthetic solution containing only Co(II).