Inge Bellemans

Origin and sedimentation of Cu-droplets sticking to spinel solids in pyrometallurgical slags

Cu-droplet losses in slags are an important problem in Cu-industry, limiting the metal recovery. An important cause responsible for the entrainment of copper droplet losses in slags is their sticking behaviour to spinel solids. In the present study, the interaction between spinel solids and Cu-droplets is investigated in an industrially relevant slag system (PbO–CaO–SiO2–Cu2O–Al2O3–FeO–ZnO) using two complementary experimental set-ups. Firstly the influence of the sedimentation time is studied and secondly the presence of entrained (sticking) droplets is studied as a function of height in the slag layer. Based on the experimental results, a mechanism that explains the sticking Cu-droplets is proposed. Finally, a model describing the sedimentation of sticking and non-sticking droplets is formulated based on the experimental data.

Wetting behaviour of Cu based alloys on spinel substrates in pyrometallurgical context

Metal droplet losses in slags are an important issue in copper industry. One significant aspect that promotes the entrainment of metal droplets in the slag is their attachment to spinel solids. In the present study, the wetting behaviour of copper alloys on spinel substrates has been investigated in the presence and absence of a slag phase. At first, the attachment was investigated using a synthetic slag containing spinel particles. Microstructural analysis of quenched slag reveals the presence of microdroplets sticking onto a surface of the spinel particles. Second, the metal–spinel interaction was investigated using the sessile drop technique. Wetting angle measurements were performed between Cu–Ag alloys and MgAl2O4 substrates. A non-wetting behaviour between the alloys and substrates was observed. The results suggest that the oxygen partial pressure and the amount of Ag in the alloy both influence the wetting behaviour.

Sessile drop evaluation of high temperature copper/spinel and slag/spinel interactions

Abstract Metal droplets sticking to spinel solids, present in metallurgical slag systems, play an important role in hindering the sedimentation of copper in slags. To understand this phenomenon, the interaction between spinel particles with Cu on one hand and with slag, on the other hand, was evaluated. A dedicated approach was applied, using an industrially relevant synthetic slag system PbO–FeO–SiO 2 –CaO–Al 2 O 3 –Cu 2 O–ZnO, pure copper and MgAl 2 O 4 substrates to represent the industrial slag, the entrained copper droplets and the spinel solids, respectively. Both the copper–MgAl 2 O 4 and the slag–MgAl 2 O 4 interaction were studied using sessile drop measurements, combined with an extensive microstructural analysis. Additionally, the effect of time on the slag–MgAl 2 O 4 interaction was studied using immersion experiments. Copper displayed a non-wetting behaviour on MgAl 2 O 4 , whereas slag displayed a reactive wetting and an interaction layer of (Mg, Fe, Zn)(Al, Fe) 2 O 4 spinel was formed at the interface, which was also observed in the immersion experiments. Moreover, the diffusion of MgO and Al 2 O 3 from the spinel substrate into the slag droplets was noted.

Study of the Effect of Spinel Composition on Metallic Copper Losses in Slags

In both primary and secondary copper production, copper losses in slags are a decisive factor confining the process efficiency. An important cause for mechanical entrainment of metal droplets in slags is their attachment to solid spinel particles present in the slag phase, hindering sedimentation. To further optimize the production process, it is important to gain insights in the fundamental mechanisms governing this attachment. In the present study, the influence of the spinel composition on the attachment of copper droplets is investigated. First, the attachment is studied in an industrially relevant synthetic PbO–CaO–SiO2–Cu2O–Al2O3–FeO–ZnO slag system. Second, the wetting of copper on two spinel substrates (ZnFe2O4 and MgAl2O4) has been studied in the absence of a slag system, by sessile-drop experiments. Based on the results of both types of experiments, a clear influence of the spinel composition on the sticking behavior of copper droplets is noted. These observations might be transferred to industrial processes to adapt processing parameters to diminish copper losses in industrial slags.

Investigation of Reactive Origin for Attachment of Cu Droplets to Solid Particles

AbstractBoth primary and secondary copper productions encounter a limitation in the process efficiency due to droplet losses in slags. One of the causes for the mechanical entrainment of these droplets is their interaction with solid spinel particles, hindering the sedimentation of the copper droplets. Previous experiments with synthetic slags provided insights into this interaction and yielded two possible mechanisms: separately formed droplets and particles become attached to one another due to fierce agitation of the slag and metal phases; or the spinel particles and metal droplets form as the result of a chemical reaction together with a new droplet or alongside a droplet that was already present in the system. This experimental study aims to investigate the hypothesis of the formation of copper droplets sticking to spinel particles due to a chemical reaction further. A slag that is initially free from Cu droplets was prepared. After creating controlled conditions to induce the chemical reaction, the formation of sticking droplets was observed. The results from this experiment therefore confirm the previously proposed reactive mechanism.

Metal droplet entrainment by solid particles in slags : an experimental approach

This study investigates the origin of the attachment of metal droplets to solid spinel particles in liquid slags. Previous research hinted a reactive origin: the spinel particles form by a chemical reaction together with a new droplet or alongside a droplet that was already present in the system. In this study, a smelting experiment was used to investigate this hypothesis. For such a study of the mechanism, a simple chemical system was used to avoid complex reactions. However, performing smelting experiments in simple slag systems requires an adaptation of the previously developed experimental methodology, resulting in a new ‘partial melting’ methodology. During the experiment, the atmosphere of the system was first set as oxidative, to dissolve the metallic copper in the slag and then a reductive atmosphere was used to actuate the reaction. Moreover, Ag was added to the metallic phase to act as a tracer element. The results show that the amount and size of copper droplets increase over the duration of the experiment. The fact that silver is present in the attached copper droplets in a smaller concentration than in the master alloy in this study indicates that the origin of the attachment is not purely dispersive, and either a purely reactive or a dispersion–reaction combination is possible, which confirms the hypothesis.

Investigation of Origin of Attached Cu-Ag Droplets to Solid Particles During High-Temperature Slag/Copper/Spinel Interactions

This study investigates the origin of mechanically entrained metal droplets in liquid slag due to their interaction with solid spinel particles. Two possible mechanisms were proposed previously: separately formed droplets and spinel particles get attached to each other due to agitation of the slag and metal phases; or the spinel particles form by a chemical reaction together with a new droplet or alongside a droplet that was already present in the system. In this study, an inert tracer element was added to the metallic phase in adapted sessile drop experiments. For this purpose, Cu-Ag alloys, with various Ag-contents, were produced. The results showed that the small entrained metal droplets within the slag droplet contained Ag, but in very low amounts with respect to the amount of Ag in the Cu-Ag alloy. This indicates that the entrained metal droplets are formed due to a sequential combination of the two origins: first, very small metal droplets are dispersed in the slag drop, due to the emulsification process. Then, these metal droplets are nucleation sites for the Cu-spinel reactive formation.

Phase-Field Modelling in Extractive Metallurgy

ABSTRACT The phase-field method has already proven its usefulness to simulate microstructural evolution for several applications, e.g., during solidification, solid-state phase transformations, fracture, etc. This wide variety of applications follows from its diffuse-interface approach. Moreover, it is straightforward to take different driving forces into account. The purpose of this paper is to give an introduction to the phase-field modelling technique with particular attention for models describing phenomena important in extractive metallurgy. The concept of diffuse interfaces, the phase-field variables, the thermodynamic driving force for microstructure evolution and the phase-field equations are discussed. Some of the possibilities to solve the equations describing microstructural evolution are also described, followed by possibilities to make the phase-field models quantitative and the phase-field modelling of the microstructural phenomena important in extractive metallurgy, i.e., multiphase field models. Finally, this paper illustrates how the phase-field method can be applied to simulate several processes taking place in extractive metallurgy and how the models can contribute to the further development or improvement of these processes.

Metal losses in pyrometallurgical operations - A review

Nowadays, a higher demand on a lot of metals exists, but the quantity and purity of the ores decreases. The amount of scrap, on the other hand, increases and thus, recycling becomes more important. Besides recycling, it is also necessary to improve and optimize existing processes in extractive and recycling metallurgy. One of the main difficulties of the overall-plant recovery are metal losses in slags, in both primary and secondary metal production. In general, an increased understanding of the fundamental mechanisms governing these losses could help further improve production efficiencies. This review aims to summarize and evaluate the current scientific knowledge concerning metal losses and pinpoints the knowledge gaps. First, the industrial importance and impact of metal losses in slags will be illustrated by several examples from both ferrous and non-ferrous industries. Throughout the remainder of this review, the main focus will be put on the particular issues in copper industry. In a second section, the different types of metal losses in slags will be discussed. Generally, metal losses in slags can be subdivided into two types: chemical losses and physical losses. The fundamental insights concerning the responsible mechanisms will be discussed for each type. Subsequently, an overview of the most frequently used techniques for research investigations of the losses will be given. In a fourth section, a more detailed overview will be given on the post-processing treatment of metal-containing slags, i.e. performing slag cleaning operations. The most frequently applied methods will be discussed.