An experimental study of slag foaming

[摘要] ENGLISH ABSTRACT:Slag foaming occurs in several pyrometallurgical processes. These processes includesteelmaking in basic oxygen steelmaking furnaces and electric arc furnaces (EAF) as wellas various non-ferrous operations like sulphide smelting/converting and base metal slagcleaning. Although slag foaming in steelmaking processes has been extensively researched,little attention has been given to slag foaming in non-ferrous operations. Slag foamingphenomena are complex because often the system consists of three or more phases.The objectives of this study is to review the published work on slag foaming, to obtainthrough physical modelling an understanding of the principles governing foaming and toinvestigate slag foaming phenomena through pyrometallurgical experiments.To obtain these objectives, experiments were carried out with aqueous mixtures at differentcolumn sizes, different pore sizes for gas injection and varying liquid depths, and also forhigh temperature metallurgical slags with varying composition and at differenttemperatures. Through gas injection, foaming conditions were simulated and theequilibrium foam height was measured for different gas velocities.The following conclusions were drawn:1. For physical modelling of slag foaming in 3-phase systems the average foam indexincreases with increasing amounts of solids present in the system. The effect ofadditional solids in the system is independent of the system geometry.2. The following conclusions were reached by determining coefficients for anempirical dimensional model fitted to aqueous mixtures: Higher liquid density leadsto lower foam index values. The influence of the liquid viscosity is dependent onthe system investigated and may have a positive or negative result on foaming. The empirical model should only be applied to the property range and geometric set-upfor which it was derived, as coefficients may vary greatly for different systems.3. Influence of solid precipitates on slag foaming can be summarised by noting thatsmall amounts of magnetite stabilise slag foaming, while precipitates ofwollastonite and anorthite decreased foaming. The influence of solid precipitates isthought to be related to the density, morphology and degree of surface activity ofthe solid precipitates.4. The foam index decreases with increasing basicity due to the lowering of the slagviscosity. This continues until the precipitation of solids starts and the foam indexonce again increases.5. For increasing FeO concentration the foam index will decrease due to lowerviscosity, but higher surface tension depression may lead to increased foam indexvalues at high FeO concentrations.6. Higher foam index values were obtained for slags with lower densities. The_1empirical relationship observed is L IX: P 3 .7. Higher foam index values were obtained for slags with higher viscosity. Theempirical relationship observed is L IX: f1 .8. Higher foam index values were obtained for slags with lower surface tensions. Theempirical relationship observed is L IX: U-I.9. Models derived for the foaming of basic steelmaking slags does not satisfactorilydescribe the foaming behaviour of acidic slags.10. The physical properties of the slag influence the foam stabilisation mechanism.

[发布机构] Stellenbosch University