K. Tkáčová

Structural and temperature sensitivity of leaching of chalcopyrite with iron(III) sulphate

Abstract In this study, the leaching of chalcopyrite with acid solution of iron (III) sulphate was investigated. It has been found that the rate of leaching may be favourably influenced by mechanical activation of CuFeS 2 . The linear relationship between the initial rate constant of leaching k o and the ratio S / X describes the joint influence on reaction rate of the increase in surface S and of the decrease in content of the crystalline phase X due to mechanical activation and represents the evidence of structural sensitivity of the reaction. The investigation of temperature dependence of reaction (1) for mechanically activated chalcopyrite in the temperature region 333–368 K discloses a change in mechanism of the reaction at 363 K. It can be assumed that the mechanical activation influences the self-diffusion of the ions of copper and iron. Its acceleration by mechanical activation results in the fact that the chemical reaction gradually assumes the function of the rate determining stage. However, the increasing thickness of elemental sulphur on the surface of the non-consumed CuFeS 2 enhances the retarding effect of this solid product.

Mechanically induced cation redistribution in ZnFe2O4 and its thermal stability

The changes in zinc ferrite caused by high-energy ball-milling are investigated. Formation of spin arrangement in the ball-milled ZnFe2O4 is caused by the onset of the exchange interaction of the Fe3+ (A)O2−Fe3+[B] type, taking place due to the mechanically induced inversion as well as by the onset of the interaction of the Fe3+[B]O2−Fe3+[B] type with deformed bond angle. Structural metastability of the milled ZnFe2O4 is manifested by the gradual recrystallization terminating at 900 K by a total recovery of the structure.

Selective leaching of zinc from mechanically activated complex CuPbZn concentrate

Abstract The leaching of some mechanically activated complex CuZn and CuPbZn sulphidic concentrates with hydrogen peroxide solutions was investigated. The results have shown that the use of this model leaching agent effects the passage of copper and zinc into the leach solution, while lead and iron remain in the insoluble residue. In the process of mechanical activation the differences in chemical stability of sphalerite and chalcopyrite become so evident that it is, in principle, possible to carry out the selective extraction of zinc. The selective recovery of zinc increases with increasing reaction surface and reaches its maximum in the region of selective amorphization of sphalerite due to grinding.

Energy transfer and conversion during comminution and mechanical activation

Abstract A structural and phenomenological-energetic investigation on fine grinding were carried out. The decisive role of amorphisation in the mechanical activation of particulate solids has been proved. Amongst the factors controlling the amorphisation, the rate of stress and the efficiency of energy transfer in the mill are the most important.

Reactivity of mechanically activated chalcopyrite

Abstract Mechanical activation by grinding is a complex process involving alteration of structure, chemical composition and properties of solid substances. In this article the characteristic features of mechanically induced changes in minerals with close packed anion sublattice are illustrated on the example of planetary and vibration ground chalcopyrite. Summarizing the results of a longlasting research involving data obtained by Mossbauer spectroscopy, ESR, XPS, XRD and measuring of magnetic susceptibility, the changes in surface composition are characterised and a critical structure favourable loosening for a magnetic order-disorder transformation is specified. The chemical consequences of the structural metastability have been demonstrated by promoting of industrially important processes, namely non-oxidative and oxidative decomposition as well as direct leaching of mechanically activated chalcopyrite.

Thermal characterization of changes in structure and properties of chalcopyrite after mechanical activation

Abstract Changes in specific surface area, surface layer composition, structural disorder, magnetic susceptibility and the rate of non-oxidative decomposition of chalcopyrite brought about by vibration grinding in air and methanol were investigated. Significant differences in structure and reactivity between systems ground in different environments enabled confirmation of the threshold phenomenon of mechanical activation, and led to the conclusion that plastic strain resulting in destruction of the long-range order in the structure may be considered as the source of changes in magnetic properties and excess reactivity.

Contamination of quartz by iron in energy-intensive grinding in air and liquids of various polarity

Abstract The influence of mill power and grinding environment on the contamination of quartz by iron during vibration grinding was studied. It was found that the Fe content of ground powders increased with an increase in specific grinding energy that was independent of the conditions of energy supply, that is whether it was supplied by varying the mill power or the grinding time. The specific contamination expressed as the ratio of Fe content to newly created surface area depended upon the physical properties of the grinding environment. The influence of grinding conditions on the state of the iron in the products of grinder wear was investigated by Mossbauer spectroscopy and by measuring the magnetic susceptibility of the ground powders. It was shown that the iron produced from grinder wear is present in tow main forms: as a magnetically ordered form identical with the basic material of the grinder and in a form of finely dispersed iron/iron compound showing superparamagnetic behaviour. Based on the results obtained, the formation of a silica-supported iron or iron oxide catalyst was presumed. By this assumption, the catalytic decomposition of water and methanol that takes place during quartz at grinding by iron containing grinders can be explained.

Change in structure and enthalpy of carbonates and quartz accompanying grinding in air and aqueous environments

Abstract The influence of aqueous environment as well as the grinding work consumption on energy storage in magnesite, calcite and quartz in the course of vibrational grinding was investigated. The determination of the enthalpy content by the method of heats of dissolution and the study of structural transformations by X-ray diffraction have shown that the excess enthalpy as well as the X-ray-amorphous phase content in the ground material increases with increase in grinding work although it remains unaffected by grinding environment. Use of an aqueous environment results only in enlarged specific surface area of the ground products. Comparison of the theoretical assumptions with the experimental results suggests that at high crack propagation velocities in the process of energy-intensive grinding, the surface-active environment plays the most significant role by preventing agglomeration.

Mechanochemical oxidation of silicon and selectivity of oxide superficial layer dissolution in aqueous solutions of HF and KOH

Mechanochemical oxidation of silicon and selectivity of oxide layer dissolution in diluted solutions of HF and KOH were investigated. Energy-intensive grinding of Si is accompanied by changes in state and composition of superficial layers and by significant decrease in crystallinity. The effect of the polarity of liquid grinding environment on the amorphisation is not significant. The permittivity of liquid influences oxidation of silicon and surface concentration of damage centers. The porous oxide shell covering the ground particles controls the adsorption behaviour of Si and consequently its dissolution in diluted solutions of HF and KOH. Stimulating or inhibiting effect of mechanically induced pre-oxidation depends upon the mechanism of dissolution. While selective dissolution of oxide in HF is facilitated by the pre-oxidation, the direct dissolution of silicon in alkaline solvents is inhibited by oxide surface layer.

Influence of mechanical activation on the Mossbauer spectra of the sulfides

Abstract Mossbauer spectroscopy, X-ray photoelectron spectroscopy, infrared spectroscopy, electron paramagnetic resonance and X-ray diffraction were used to identify changes of surface, structure and spectroscopic properties of sulfide minerals produced by mechanical activation. In the present study we report the results of chalcopyrite (CuFeS 2 ), pyrite (FeS 2 ), cinnabar (HgS), bornite (Cu 5 FeS 4 ) and zinc sulfide (ZnS). The influence of energy input to the mill and the nature of grinding environment have been investigated upon the Fe contamination of the materials.