Rearrangement of Oxide Scale on Ni-11Fe-10Cu-6Al Pre-Oxidized at 950 °C during Anodic Polarization in Molten Carbonate

The effect of anodic polarization in molten Na2CO3-K2CO3 at 750 °C was investigated on the structure of oxide scale formed by pre-oxidation of Ni-11Fe-10Cu-6Al alloy at 950 °C in air. The pre-formed oxide scale evolves and rearranges under anodic polarization related to melt corrosion and non-uniformly distributed electric field. Both of pre-oxidized and as-rearranged electrodes can serve as inert anodes with oxygen evolution. Anodic polarization exhibits a negative rearrangement-destructivity effect for the pre-formed oxide scale with corrosion protection of the rearranged oxide scale decreasing. The structure rearrangement of pre-formed oxide scale is also discussed during anodic polarization in the melt.

On the question of using solid electrodes in the electrolysis of cryolite-alumina melts. Part 1.

This article is aimed at identifying issues associated with the use of solid cathodes in the electrolysis of cryolitealumina melts in order to determine conditions for their practical application. The contemporary technology of using solid anodes and cathodes is reviewed from its inception to the present time. The problems of stable electrolysis are discussed, such as effects of the electrode surface on the technological process. It is shown that all attempts undertaken over the recent 100 years to use solid electrodes, both reactive and inert, have been challenged with the emergence of electrolysis instability, formation of precipitates of varying intensity on the electrodes and impossibility of maintaining a prolonged process at current densities of above 0.4–0.5 A/cm2. Information is provided on the attempts to use purified electrolyte components with different ratios, metal-like and ceramic electrodes with a high purity and a smooth surface in order to approach real industrial conditions. However, to the best of our current knowledge, these experiments have not found commercial application. The authors believe that the most probable reason for the decreased current efficiency and passivation of solid electrodes consists in the chemical inhomogeneity and micro-defects of the bulk and surface structure of polycrystalline cathodes and anodes. It was the physical inhomogeneity of carbon electrodes that directed the development of the nascent electrolytic production of aluminium towards the use of electrolytic cells with a horizontal arrangement of electrodes and liquid aluminium as a cathode. This reason is assumed to limit the progress of electrolytic aluminium production based on the use of inert anodes and wettable cathodes in the designs of new generation electrolytic cells implying vertically arranged drained cathodes. The theoretical and experimental examination of this assumption will be presented in the following parts of the article.

Improvement of Anode of Prebaked Cell in Aluminum Electrolysis

Compared with the previous self-cultivation anode electrolyzer, the current prebaked anode electrolyzer has advanced technical and economic indexes, high degree of mechanization and automation, and relatively little environmental pollution, which has achieved great development. However, the continuity of aluminum electrolysis production and the limited economic height of anode constitute two contradictory opposites. In order to solve this contradiction, the processes of replacing anode periodically, cleaning the residual electrode and electrolyte, pressing off the residual electrode and phosphorus-iron ring, crushing and grinding the residual electrode have been produced, which has increased the investment and labor cost per ton of aluminum. Moreover, when the anode is replaced, the operator can say that the working environment is harsh and dangerous directly in front of the high-temperature electrolyte, and a large amount of fluorine-containing flue gas is discharged out of order and pollutes the environment due to the opening of the slot cover plate and the placement of the high-temperature residual electrode during the anode replacement. At the same time, pole change has great interference on electrolytic production. At present, inert anodes can't be put into industrial production, and the continuous preparation anodes in Germany have high power consumption, so it is of great practical significance to perfect or improve the existing anode structure. This paper discusses how to solve this problem.

Advanced technologies for processing liquid waste of galurgical productions

The accumulation of highly mineralized waters and brines in the mining-industrial regions of Ukraine carry a threat of salt pollution of underground and surface water sources. Low-waste processing of these waters is prevented by iron compounds, hydrogen sulfide and sulfur-containing organic compounds. The process of accumulation of iron compounds in brines and groundwater in the presence of hydrogen sulfide has been studied. Comparative calculations of the thermodynamic potentials of the corresponding reactions have been carried out. The calculation results are confirmed by experiments on model solutions and brine of the Dombrovsky quarry. To remove iron compounds from brines and other highly mineralized waters, it is proposed to use electrolysis with inert anodes. It was found that 99.9% of iron compounds pass into the precipitate of iron hydroxide (III). At the same time, the overwhelming amount of heavy metals also passes into the sediment.

Recent progress of inert anodes for carbon-free aluminium electrolysis: a review and outlook

This review introduces the latest research progress of inert anodes for aluminium electrolysis and compares the comprehensive performances of different kinds of materials, including metals, ceramics and cermets.

Effects on primary energy use, greenhouse gas emissions and related costs from improving energy end-use efficiency in the electrolysis in primary aluminium production

Primary aluminium production is energy- and GHG-intensive in which electrolysis is by far the most energy- and GHG-intensive process. This paper’s aim is to study the effects on (1) primary energy use, (2) GHG emissions and (3) energy and CO2 costs when energy end-use efficiency measures are implemented in the electrolysis. Significant savings in final and primary energy use, GHG emissions and energy and CO2 costs can be achieved by implementing the studied measures. Vertical electrode cells and the combination of inert anodes and wettable cathodes are among the measures with the highest savings in all three areas (primary energy use, GHG emissions and energy and CO2 costs). Direct carbothermic reduction is one of the measures with the highest savings in primary energy use and energy and CO2 costs. For GHG emissions, direct carbothermic reduction is the more beneficial choice in regions with a high proportion of coal power, while inert anodes are the more beneficial choice in regions with a high proportion of low-carbon electricity. Although a company potentially can save more money by implementing the direct carbothermic reduction, the company should consider implementing the vertical electrode cells together with other energy-saving technologies since this would yield the largest GHG emission savings while providing similar cost savings as the direct carbothermic reduction. It may be necessary to impose a price on GHG emissions in order to make inert anodes cost-effective on their own, although further evaluations are needed in this regard. There is a potential to achieve carbon-neutrality in the reduction of aluminium oxide to pure aluminium.