METALLIC PHASE FORMING IN BARBOTAGE OF MULTICOMPONENT OXIDE MELT BY REDUCTION GAS REPORT 3. FERRONICKEL AND OXIDE MELT SEPARATION

Using the equations of physico-chemical hydrodynamics and the data obtained earlier on the surface and interfacial properties of metallic and oxide melts, conditions for the formation of the metallic phase during bubbling of the oxidized nickel ore melt by carbon monoxide are described. Critical dimensions of the gas bubble (Rb ) cr and the metal droplet (rd)cr are determined, moving in the oxide melt without crushing in the temperature range from 1550 to 1750 °C. It was found that the value of (Rb)cr varies with temperature and increases from 6.35·10–2  m (1550 °C) to 6.58·10–2  m (1750  °C), (rd ) cr depends on composition of the droplet and temperature and varies from 2.1·10–3  m to 2.9·10–3  m. The size of metal droplets formed on a single bubble is determined upon reduction of nickel and iron from the oxide melt. As the content of nickel and iron oxides decreases in the melt with an increase in the total CO flow rate, nickel content in ferronickel drops decreases from 89 to 18  %, and their diameters decrease from 1.4·10–3  m to 8.0·10–4  m. In this case, mass of the drop decreases from 9.4·10–5 to 1.6·10–5  kg. The conditions for emergence of the “gas bubble – a drop of metal” system from their dimensions are revealed. In all intervals of temperature and nickel content, the “bubble CO  – a  drop of metal” system begins to rise in the oxide melt at a ratio rk  / Rn of less than 0.68  –  0.78. To assess the stability of the “bubble CO  – drop of metal” system at the above bubble and droplet sizes, calculations of the parameters determining their joint motion were carried out. It is shown that the separation of a drop of metal from a bubble is not possible under the conditions of the process in pyrometallurgical aggregates. The process of metal phase formation as a result of barbotage reduction of nickel and iron by carbon monoxide is described, which consists in the following. The interaction of the oxide melt with the gas is accompanied by formation of metal droplets, which are fixed to the bubbles moving to the surface of the oxide melt. Initially, a metal with content of 80  –  90  % Ni is formed, and as the proportion of nickel in the oxide melt decreases, its content in the metal drops is reduced to 20  %. On the surface of the oxide melt, the metal droplets merge, when they reach a size of more than 5·10–3  m, they “break through” the surface and descend to the bottom. In the case of a collision of a drop with the “bubble-drop” systems approaching them, they can how to merge with them, and flow around them. At the confluence, small drops will be assimilated and raised to the surface. The force of separation of the droplet from the bubble is substantially greater than the gravity of the droplets, so the bubble-drop system of the metal is stable for all considered ratios of their sizes. 

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