Effect of copper-nickel matte ingot cooling time on its floatation separation selectivity indicators

A criterion used to evaluate the efficiency of converter matte foam separation into nickel and copper concentrates is a selectivity index based on the total recoveries of metals into target concentrates that in turn defines their cumulative impurities (secondary metals) content. In addition to various factors (meeting density and reagent flow charts, comminution parameters, etc.), the time of preceding cooling of ingots is also known to have a substantial effect on the process of converter matte separation at commercial scale. Laboratory studies on selective separation were made to evaluate the influence of converter matte crystallization conditions at constant comminution and floatation parameters. Commercial converter matte ingots produced at different cooling rates were ground and floated in the closed circuit under laboratory conditions according to the existing floatation flowsheet. The lab studies allowed to exclude the multifactor nature of the system and to examine the commercial converter separation process only from the viewpoint of converter matte melt cooling rate since the other factors were kept constant during the laboratory tests. The temperature field in the body of the converter matte ingot was measured during its cooling in the conditions of the current production – this is reflected in the chemical and phase composition of various ingot sections. The temperature of the ingot, due to its massiveness, varies considerably throughout the material volume. A small change in the ingot surface temperature can be accompanied by significant changes in the temperature in its body. The measurement results showed that the temperature gradient from the center to the periphery of the ingot exceeds400 °C. In this regard, reducing the time of converter matte cooling can lead to significant violations of the cooling mode in the central zones of the ingot. In accordance with the optical mineralogical analysis of samples, the longer was the ingot cooling time, the higher was its decrystallization implying the formation of coarse-particle structures of copper and nickel sulfides with sharp interface boundaries. The chemical analysis revealed that the highest possible selectivity index of converter matte copper and nickel separation with resulting copper and nickel sulfide concentrates, respectively, is reached after 72 h of cooling for converter matte ingots from the smelting shop of the Nadezhdinsky Metallurgical Plant.

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