Production of electrolytic iron from red mud in alkaline media.

In this study, the feasibility of producing electrolytic iron from red muds in a strongly alkaline medium at 110 °C was studied. The red mud samples from a French industry were characterized by various techniques (ICP-AES, SEM, XRD) to determine their chemical and mineralogical compositions. The main phase in the red mud investigated was hematite (α-Fe2O3). Iron electrodeposition tests from red mud suspended in a 12.5 mol/L NaOH electrolyte were conducted at constant current in a stirred electrochemical cell. The solid:liquid ratio and amounts of impurities contained in red mud were varied to optimize the faradaic yield and the production rate of electrolytic iron. Whereas hematite can be reduced to iron with a current efficiency over 80% for a current density (cd) up to 1000 A/m2, the current efficiency with red muds was highest for a cd below 50 A/m2 and then decreased regularly to 20% at 1000 A/m2. In all cases, the deposit produced contained more than 97% metal iron. The moderate performance of the process investigated with red mud was attributed to a troublesome adsorption of red mud particles on the cathode, making the reduction far less efficient than that with hematite.

Uranium removal from mining water using Cu substituted hydroxyapatite.

In this study, synthetic copper substituted hydroxyapatite (Cu-Hap), CuxCa10-x(PO4)6(OH)2 were prepared by co-precipitation method and were used as reactive materials in batch experiments to immobilize uranyl. The limit of incorporation of Cu into a single-phased Cu-Hap reached xCu ≤1.59. The synthetic Cu-Hap samples obtained with various Cu contents were contacted with synthetic uranyl doped solutions and with real mining waters showing various pH and chemical compositions. A fast and strong decrease of the uranium concentration was observed, followed by the establishment of an equilibrium after 1-4 days of contact with the solutions. Examination of the solid phase after uranium uptake was performed using a combination of techniques. Depending on the composition of the solution and the copper content of the Cu-Hap, various mechanisms of uranium removal were observed. Based on the experimental results and geochemical simulations, it appeared that the main interest for using Cu-Hap is to enlarge the domain of water compositions for which the precipitation of meta-torbernite, (H3O)0.4Cu0.8(UO2)2(PO4)2·7.6 H2O is the predominant mechanism associated to the uranium removal, especially for pH > 6.7 where carbonate uranium species are predominant.