Mineral Processing and Extractive Metallurgy: Transactions of the Institutions of Mining and Metallurgy

This paper investigated the bioleaching of different copper sulphide minerals. The bioleaching experiments show that the order of the copper bioleaching rates of four copper sulphide minerals, regardess of whether the optimum conditions or the initial ferrous iron concentration of 0 g L^− 1, was identical: djurleite> bornite> covellite> chalcopyrite. Properties of mineral, such as rest potential, lattice energy, conductivity type and solubility product constant, are the intrinsic factors influencing the bioleaching of minerals. Among these parameters, rest potential and lattice energy can explain the difference of the bioleaching of four copper sulphide minerals. Conductivity type can interpret the low copper leaching efficiency of chalcopyrite and covellite. However, it cannot explicate the high copper leach rate of djurleite and bornite. The decrease of the lag phase of Acidithiobacillus ferrooxidans with an increase of solubility product constant of minerals is observed in the bioleaching system of four copper sulphide minerals. However, solubility product constant is not the crucial parameters dominating the bioleaching efficiency of copper sulfide minerals.

The impact of microbubbles on flotation efficiency has been studied for ultrafine ( < 12 μm) chalcopyrite recovery from chalcopyrite/quartz artificial mixtures using laboratory pneumomechanical and column flotation cells. The findings show that significant enhancement in the efficiency of ultrafine minerals beneficiation is ensured by using the method known as combined microflotation based on simultaneous use of both coarse air bubbles (conventionally produced in flotation cells) and microbubbles generated by a standalone generator in the form of air in water microdispersion. Introduction of microbubbles at the dosage of 8–16 L per 1 kg of chalcopyrite before its treatment in a pneumomechanical flotation cell increased the flotation rate by several times. In the case of column flotation, introduction of microbubbles at the dosage of around 50 L per 1 kg of chalcopyrite following pulp treatment in a static mixer for 60 s before feeding it into the column cell increased the copper recovery by more than 50%. Increasing the treatment time of the pulp in the static mixer to 80 s led to gains in copper recovery by more than 60%, even in the absence of cell aeration by coarse air bubbles (turbulent microflotation regime).

In this study, the effects of various process parameters on the adhesive strength of copper electrodeposits on stainless steel cathodes produced in a laboratory scale electrowinning cell were investigated. The experimental results showed that the chloride ion concentration and the current density had a significant effect on the adhesive strength. Electrolyte temperature and cupric ion concentration also influenced the adhesive strength to some extent, whereas cobaltous ion concentration and Guar dosage showed no noticeable effect. Microstructure analysis of the copper electrodeposits indicated that the process parameters which affected the grain size of the deposit at the substrate/deposit interface influenced the adhesive strength, i.e., fine grains exhibited higher adhesive strength than coarse grains.

In order to provide a better theoretical foundation for utilisation of Xinjiang siderite resources in China, its thermal decomposition behaviour was studied in neutral and oxidising atmospheres by employing thermodynamics analysis, chemical titration, thermogravimetric, and X-ray diffraction means. Isothermal experiments were conducted to investigate the thermal decomposition kinetics of siderite lump in a weakly oxidising atmosphere at 500–850°C. The results reveal that siderite has self-magnetisation characteristics under controlled conditions, and the phase evolution process and final products of decomposition depend temperature and atmosphere. The phase transformation process in weak oxidising atmosphere follows the steps as: FeCO₃ → Fe₃O₄ → γ-Fe₂O₃ at 550°C, and FeCO₃ → FeO + Fe₃O₄ → Fe₃O₄ → γ-Fe₂O₃ → α-Fe₂O₃ at 800°C. In inert atmosphere, the decomposition pathway is FeCO₃ → Fe₃O₄ below 733°C and FeCO₃ → FeO + Fe₃O₄ above 733°C. The molar ratio of FeO/Fe₃O₄ increases with temperature. The decomposition kinetics of siderite lump in oxygen-deficient atmosphere is consistent with chemical reaction control in the temperature range 500–700°C and nucleation and growth mechanism in the 750–850°C. The corresponding activation energies are 53·73 and 38·15 KJ mol⁻¹, respectively.

The reduction of yttrium fluoride (YF₃) by calcium in a molybdenum crucible was investigated. A visual observation technique was used to monitor the reduction process. It was observed that the reaction initiated immediately after the melting of calcium. Based on the results, a two-step reduction sequence was attempted. First, the charge was heated to 950°C to minimise the calcium loss by vaporisation and to ensure completion of reaction. The products were then fast heated to 1600°C for slag/metal separation. Molybdenum content of yttrium was found to be in a range of 3.5–4.75 wt-%, which is much lower than the equilibrium content predicted by Mo–Y phase diagram. The yttrium/molybdenum interface was studied using an electron probe microanalyser, which confirmed that the overall equilibrium was not reached, indicating the possibility of lowering the molybdenum contamination further by process optimisation.

Bed permeability, rate of reductant and productivity of blast furnace (BF) performance mainly depends on both iron bearing material but also carbonaceous material. Most of the BFs have the sinter being a major burden; hence, in JSW Steel Ltd, four sinter plants are operating to fulfill the four BF's requirement. For efficient BF operations, sinter plants are key units whose proper performance is vital to produce desired sinter strength. The tumbler index of the sinter is an important property of the sinter, and sinter strength depends on the raw material composition and machine parameters. For smooth sinter plants operation, changes to the operating conditions should be few and precise. To achieve this, a much better understanding of the mechanisms relating control inputs to a sinter production rate and quality needs to be established. In the present work, a neural network based model has been developed and trained relating sinter strength with a set of nine process variables, namely, basicity, Al₂O₃/SiO₂, MgO, MnO, FeO, moisture, coke breeze, burnthrough temperature and machine speed, to predict the tumbler index ( − 6.3 mm) of the sinter. The variables to which strength of the sinter was most sensitive were Al₂O₃/SiO₂, basicty, machine speed, and MgO, MnO and FeO. Tumbler index of the sinter was influenced by sinter porosity, which was itself determined by the firing temperature and green sinter mix carbon content. The predicted results were in good agreement with the actual data with < 3.5% error.

The Altonorte Smelter implemented a daily scheduling algorithm in 2013, which has now been generalised for all conventional copper smelters. It applies a combinatorial search, in which the possible converter feeding sequences are evaluated using a greedy heuristic; the daily schedule is then constructed using the heuristically optimal sequence. Depending on the mode of operation, the objective may be to maximise copper production, maximise profits or control concentrate stockpiles. This combinatorial greedy approach has been incorporated within discrete event simulations, which mimic hundreds of days of operation, hence analysing alternate modes of operation. Automated scheduling is fundamental to the scientific management of copper smelters, as scheduling parameters characterise the operational modes.

Ferrovanadium is essential for the production of many alloy steels. It is made by the aluminothermic reduction of vanadium oxides, together with scrap steel and burnt lime as a flux at very high temperatures. In this work, the theory of aluminothermic reduction is discussed, and then a computational thermodynamics model is described and its input parameters are discussed and justified. The model predicted very satisfactorily the composition of both the ferrovanadium and waste slag from a heat at the Windimurra smelter in Western Australia. Moreover, the modelling revealed that published data on the activity coefficient of VO_1.5 in slag were likely to be seriously in error. It was shown that increasing the recovery of vanadium to the ferroalloy was accompanied by a rapid increase in its aluminium content, which is limited by commercial specifications. The limit on the silicon content of ferrovanadium can only be met by limiting the input of SiO₂ to the furnace. The model provides a useful basis for assessing process improvements.