The application of anthraquinone redox catalysts for accelerating the aeration step in the becher process

Laboratory test-work using two Australian reduced ilmenites (RI) confirmed that a class of redox catalysts based on anthraquinone derivatives is effective in accelerating the rate of removal of metallic iron from RI in the aeration step of the Becher process. Two water-soluble anthraquinone derivatives, 9,10-anthraquinone-2,6-disulfonic acid, disodium salt (catalyst AQ-2,6) and 9,10-anthraquinone-2-sulfonic acid, monosodium salt (catalyst AQ-2), were found to be particularly efficient. When 0.2% w/v of either catalyst was added to 2% w/v NH4Cl, the rate of metallic iron removal was accelerated by two to three times. Alternatively, adding 0.2% w/v of either catalyst allowed the initial concentration of NH4Cl to be reduced fourfold. Furthermore, addition of as little as 0.1% w/v of either catalyst guaranteed that the dissolved iron precipitated from the bulk solution as magnetite (Fe3O4), the iron oxide phase preferred in commercial practice. Q-2,6 and AQ-2 disappear rapidly from solution during aeration and several mechanisms are proposed that could account for this. Remarkably, however, the efficacy of both catalysts persists after concentrations in solution fall to very low levels (<0.05% w/v). proposed that the reversible electrochemistry of these compounds is responsible for their catalytic activity during aeration. The redox couples of these reagents provide an additional electron transport mechanism between the dissolved oxygen and the metallic iron wherein the oxidised forms oxidise the metallic iron, and the reduced forms are oxidised by the dissolved oxygen.