Thermodynamic modeling of nickel and iron reduction from multicomponent silicate melt in bubling process. Report 1. Reducing agent – a mixture of CO – CO2

The thermodynamic modeling method, which is based on calculation of the equilibrium in «oxide melt-metal-gas» system, is intended to describe the bubbling reduction of metals from a multicomponent oxide melt by reducing gas. Originality of the technique is that the equilibrium was determined for each unit dose of gas introduced into the working body, with contents of the metals oxides being reduced in each subsequent design cycle equal to equilibrium in the previous one. This approach allows modeling processes and qualitatively assessment of the completeness of reactions in pyrometallurgical aggregates using blowing the melt with reducing gas. The initial oxide system NiO  (1.8  %)  – FeO  (17.4)  – CaO  (13.5)  – MgO  (1.9)  – SiO2  (58.0)  – Al₂O₃  (7.4  %) by content of the components close corresponded to the composition of oxidized nickel ore. The ratio of CO₂ /CO in the gas mixture varied between 0 and 0.33. Depending on the amount and composition of the gas introduced into the working body, content of nickel and iron oxides in the melt (1823  K) was evaluated, the amount and composition of the formed metal (ferronickel) was determined, as well as the parameters (ratio of slag and metal, reduction degree of metals) that are important in the process implementation in industrial conditions. Increase in the consumption of pure carbon monoxide monotonously reduces the content of nickel oxide in the melt, while the content of iron oxide at the beginning increases, and then decreases. With the introduction of CO in the amount of about 100  m³ per ton of the melt, the content of nickel oxide in it is reduced to 0.05  %, and of iron oxide  – to 17  %. The resulting ferronickel contains 70  %  Ni, the ratio of slag and metal is 41  units. A further increase in CO consumption leads to preferential iron reduction. Increase in the CO₂ /CO ratio worsens the recovery of metals from the melt: the degree of reduction of nickel and iron decreases, Ni content in the alloy increases and the ratio of slag and metal increases. At CO₂ /CO equal to 0.33 corresponding to 25  % CO₂ in the gas mixture the reduction process stops. On the basis of the data obtained, it is proposed to process oxidized nickel ore in two stages, the first of which is melt bubbling by gas (preferably, pure CO) to the degree of nickel reduction of 80  –  85  % and to separate ferronickel with 70  %  Ni. Further reduction of metals from the oxide melt (second stage) can be carried out by known carbothermic methods.

technique, thermodynamic modeling, kinetics, reducing gas, bubbling processing, multicomponent oxide melts

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