Sulfation roasting, a common activation technique, is a potential method for cleaner production of nickel from complex low-grade ores. In this study, nickel oxide–sulfide mixed ore concentrate was roasted with the addition of ammonium sulfate under a static air atmosphere, and the roasted products were leached by water, in order to evaluate the extraction of metals. The ammonium sulfate activation roasting was investigated thoroughly and systematically by thermogravimetry–differential scanning calorimetry, X-ray diffraction, and scanning electron microscopy. Particularly, the interface sulfation behavior and path were studied by the density functional theory (DFT) method. The results showed that a large amount of nonferrous metal sulfate (70% Ni, 89% Co, and 90% Cu) was generated, while iron was almost entirely transformed into iron oxide under appropriate roasting conditions of adding ammonium sulfate at a mass ratio of 200%, heating to 650 °C at 10 °C/min, and holding for 120 min. It was found that activation of ammonium sulfate can take two different paths: one in which ammonium sulfate directly reacts with raw ores below 500 °C and the other in which the SO2 decomposed from sulfates (ammonium sulfate, intermediate ammonium ferric sulfate, and ferric sulfate) reacts with the intermediate metal sulfides (NiS and Cu2S). The interface sulfation mechanism of NiS and Cu2S was investigated deeply by DFT method, which showed that there are two paths of sulfation for NiS or Cu2S, and both of them are thermodynamically favored. Thus, a thorough and systematic investigation of ammonium sulfate activation roasting of nickel oxide–sulfide mixed ore is provided; this might be a potential basis for future industrial applications of ammonium sulfate activation roasting techniques in complex mineral metallurgy.

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Sulfation Roasting of Nickel Oxide–Sulfide Mixed Ore Concentrate in the Presence of Ammonium Sulfate: Experimental and DFT Studies

The moisture-retaining properties of rocks in the rock mass are considered at ascending capillary leaching. The dependences of the moisture capacity of disperse material of flotation tailings at ascending motion of solutions are found. The dependence of specific moisture capacity and specific moisture-yielding ability of finely dispersed material at water, pH-neutral, and capillary filtration on the grain size and level of feeding water solutions to the rock mass is revealed. Based on a laboratory experiment, the specific parameters of capillary ascending filtration for the tailing dump are calculated with regard to moisture-capacity properties of the rock mass.

Moisture-Retaining Properties of Rocks in Ascending Capillary Leaching

In shale vanadium ore, vanadium is mainly formed as a low-V(III) homogeneous phase to partially replace Si and exists in the lattice structure of aluminosilicate minerals such as biotite. During the acid leaching of shale vanadium ore, an activator is needed to effectively extract vanadium. Using biotite as a tetrahedral structure doped with Aluminum-Silicon tetrahedron structure, the interaction between leaching-agent ions (H+), activator ions (F−), and vanadium-containing biotite surface was discussed by DFT quantum chemical calculations. The dissolution behavior of activator fluoride ions on the surface of vanadium-bearing biotite during sulfuric acid leaching was revealed. According to the simulated leaching results, the oxygen on the biotite surface first absorbed hydrogen ions to undergo complete hydroxylation, and then combined with hydrogen ions to form water molecules. However, in the presence of activator (NaF), fluoride ions were adsorbed on the surface cations, which catalyzed the formation of water molecules and promoted the dissolution of surface cations. SEM–EDS analysis showed that the surface of vanadium-bearing minerals became very irregular, and the number of voids and cracks greatly increased. At the same time, XPS showed that the addition of activator fluoride ions destroyed the Al-O tetrahedron structure. Many Al and V atoms dissolved in the solution, which improved the leaching rate of vanadium.

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Effect of Fluoride Ions on the Surface Dissolution of Vanadium-Bearing Biotite

The process of leaching oxidized nickel ore in sulphuric acid with the additives of sodium sulfite and fluoride is investigated. Tochilnogorsky deposit ore (Sverdlovsk Region) is used to prove theoretically and experimentally efficient application of fluoride in dissociation of nickel minerals (nontronite and garnierite) in oxidized nickel ore. It is shown that at NaF consumption of 10 kg/t, it is possible to enhance maximum extraction of nickel to solution from 82.3–86.9 to 96.0–98.7% at the residual sulphuric acid concentration of 10–20 g/l in the working bath. It is found that the sodium fluoride additives lower the process activation energy from 22.8 to 12.9 kJ/mole. This means that the reaction of sulphuric-acid leaching proceeds in diffusion–kinetic mode and that sodium fluoride is applicable as the leaching accelerator.

A. M. Klyushnikov

Papers

Sulphuric-Acid Leaching of Ural Oxidized Nickel Ore with Sodium Sulfite and Fluoride Additives