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The experimental studies into stimulation of chemical and electrochemical leaching of gold from rebellious concentrates by ultrasound are presented. From the assessed efficiency of saturation of chloride solutions with electrochemically activated chlorine and the analysis of change in the surface morphology and in the composition of elements, phases and particle sizes in concentrates, the leaching stimulation mechanism is determined and the efficient ultrasonic treatment parameters are found for a mineral suspension to ensure higher gold recovery by 39% in 5 h.

Using a combination of energy – dispersive X-ray spectroscopy, X-ray diffraction, X-ray fluorescence, Infrared and X-ray photoelectron spectroscopies, the effect of acids (sulfuric, hydrochloric, a...

The values of pH, temperature and initial concentrations of valuable components have influence on recovery efficiency of zirconium and rare earth elements (REE) from pregnant solutions of nitric-acid leaching of eudialyte concentrate by the chemical deposition method. Zirconium and rare earths exhibit selective recoverability of 99.95% and 87.50%, respectively. The loss of REE is 8.0% with zirconium product and 4.5% with pregnant solution. Micromorphology, structural chemistry and chemical composition of products are analyzed using the scanning electron microscopy, IR spectroscopy and X-ray fluorescence analysis.

The parameters for efficient nitric acid leaching were experimentally determined, which ensured the recoveries of Zr and REEs from eudialyte concentrate up to 87.0%–91.7% and 76.0%–81.1%, respectively. The possibility was shown of intensifying the leaching process through preliminary energy treatments to ensure the intensive breakdown of mineral complexes and grains; as a result, the recovery of Zr and REEs increased by more than 10%. A process was developed for the selective recovery of up to 91.5% of zirconium and up to 71.2% of REEs in the form of carbonate compounds from the pregnant solution of nitric acid leaching by chemical precipitation as well as up to 81.1% REEs and up to 91.7% zirconium on hypercrosslinked polystyrene sorbents.

The influence of nitric, sulfuric and chlorohydric acids on the morphology, composition of elements, structural and chemical transformation of mineral surface and leaching of eudialyte concentrate is studied using a set of the modern analytical techniques. Specific features are revealed in the nature and degree of eudialyte decomposition under the influence of different acids. These features affect the intensity of removal of basic cations of Al, Na, Ca, Mg, K, Ti, Mn, Fe, Sr and Zr from the mineral surface. The behavior and regular patterns in the formation of silica gel and secondary phases during dissolution of eudialyte concentrates are examined. Sulfuric acid, which ensures the highest extraction of Zr and rare earth metals in pregnant solution, contributes to maximum formation of silica gel and considerable quantity of gypsum and insoluble sulfates, which results in high loss of Zr and rare earth metals. The use of nitric and chlorohydric acids reduces the loss of Zr and rare earth metals by 2-5 times.

Using the methods of X-ray phase analysis, analytical scanning electron microscopy and inductively coupled plasma mass spectrometry, the influence of preliminary energy effects on transformations of eudialyte concentrate base minerals during nitric acid leaching, their micromorphology and phase composition of the surface is studied. It is found that preliminary mechanical activation of the concentrate provides a 34–45% increase in the recovery of zirconium and the sum of rare-earth metal oxides into pregnant solution. Electrochemical processing of mineral suspension during nitric acid leaching and, to a greater extent, ultrasound effects contribute to an additional increase in the recovery of these elements into pregnant solution by 12–23% due to the cleaning of mineral grain surface from amorphous phases and formation of structural inhomogeneities.

The mechanism of change in the structural, chemical, physicochemical, and technological properties of Lavozero-deposit eudialyte, caused by the effect of high-voltage nanosecond pulses and combined (sequential) electropulse and acid treatment of mineral samples, is studied by means of X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy, electrophoretic light scattering (zeta-potential), confocal laser scanning microscopy, microhardness testing, etc. The results show it is possible in principle to use pulsed energy and combined physical and physicochemical effects to improve the effectiveness of disintegration and softening, and to alter the hydrophobicity, sorption activity, and technological properties of eudialyte-group rock-forming minerals.

The mechanism of weakening and directional change in structural and chemical properties of eudialyte under nonthermal exposure to nanosecond high-voltage electromagnetic pulses and nitric-acid leaching is studied. The methods of X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy, scanning electron microscopy and microhardness measurement are used. The rational mode of high-energy pulsed treatment is determined. After such mode treatment, the acid leaching of eudialyte concentrate results in recovery of zirconium and total rare earth elements higher by 1.7 and 1.4 times as against reference standards.

The investigation of influence exerted by ultrasound processing on recovery of zirconium and rare earth elements in pregnant solution of acid leaching of eudialyte concentrate is described. The methods of X-ray photoelectron spectroscopy and analytical scanning electron microscopy are used to study structural, chemical and morphological characteristics as well as elemental composition of minerals in eudialyte concentrate before and after acid leaching.

The article gives test data on the influence exerted by energy impacts (ultrasonic, electrochemical and thermal) on the recovery of zirconium and rare earth elements from eudialyte concentrate to leach solution in acid leaching. An original installation is developed for the implementation of leaching. Based on the research findings on the kinetics of acid leaching of eudialyte concentrate and on the change in the concentrate micro-structure and phase composition, the mechanism for the influence of integrated energy effects on the efficiency of recovery of zirconium and rare earths into leach solution is substantiated.

The results of experimental studies and scientific substantiation of an effect of directional change in the chemical and phase composition of the surface and increase in the contrast of physicochemical and electrical properties of tantalite, columbite, and zircon in the course of treatment with anolyte (pH < 5) and a hydrochloric acid solution (HCl, pH 3–3.5) are reported. The mechanism of structural and chemical transformations of the mineral surface in the process of leaching with acid solutions are studied. This mechanism includes the activation of oxidation of iron atoms in the surface layer of tantalite and columbite with the transition from Fe(II) to Fe(III), destruction of the zircon surface with the formation of oxygen–vacancy defects of the SiO 3 2- - and SiO 2 0 -types, and intense dissolution of iron- and silicate-bearing films from the surface of rare-metal minerals.

The article gives a report on integrated experimental research into targeted change of chemical and phase composition of surface and increase in contrast of physicochemical, electrical and electrochemical properties of tantalite, columbite and zircon under treatment by acid product of water electrolysis—anolyte (pH < 5) and by muriatic solution (HCl, pH 3–3.5). The X-ray photoelectron spectroscopy, high resolution spectroscopy and chemical and electrophysical techniques reveal the mechanism of structural–chemical surface transformation of tantalite, columbite, zircon and feldspar under leaching in acid solutions; this surface transformation mechanism consists in activation of dissolving of iron- and silicate-containing surface films and high-rate oxidation of iron atoms in surface layer of tantalite and columbite, with transition of Fe(II) to Fe(III) and surface destruction of zircon, with formation of oxygenvacant defects of SiO32− and SiO20 type under influence of anolyte.

The article reports tests on studying mechanism of interaction between modified chlorine solutions and gold-bearing sulfides. The change in texture, structural properties and elemental composition of sulfides after electrochemical treatment is analyzed. The authors indicate basic negative factors reducing dissolution velocity of sulfides.

The authors describe experimental research findings on chemical-electrochemical leaching of gold from rebellious minerals. A laboratory-scale plant has been designed for studying the leaching kinetics. Rational parameters of chemical-electrochemical leaching are specified (duration of the process, electrode current density, NaCl concentration). The researchers analyze the changed microstructure and phase composition of arsenopyrite surface after the leaching and substantiate the leaching improving practices.

Electrochemically treated acid wastedump water is assumed a promising intensifier for heap leaching of Cu-Zn ores. The electrochemical water preparation allows reagent-free adjustment of acidbase and redox properties and ion composition of water product, as well as the saturation of the water with fine-dispersion electrolysis gases. In this context, it is necessary to analyze the influence of the electrochemically treated wastedump water on pyrite, chalcopyrite and sphalerite.

The article theoretically and experimentally validates the effective applicability of the electrochemically treated acid wastedump water as a leaching agent for low-grade copper-zinc ores instead of sulphuric acid solutions. The authors have found the way to intensify the Cu-Zn ore leaching by adding 20 mg/l of NaCl in the electrochemically treated wastedump water, which allows the active chlorine concentration of 1.5 g/l and accelerates dissolution of copper and zinc to product solution by a factor of 2.8–6.