Fractal analysis of sulphidic mineral

In this paper, the application of fractal theory in the characterization of fragmented surfaces, as well as the mass-size distributions are discussed. The investigated mineral-chalcopyrite of Slovak provenience is characterised after particle size reduction processes-crushing and grinding. The problem how the different size reduction methods influence the surface irregularities of obtained particles is solved. Mandelbrot (1983), introducing the fractal geometry, offered a new way of characterization of surface irregularities by the fractal dimension. The determination of the surface fractal dimension DS consists in measuring the specific surface by the BET method in several fractions into which the comminuted chalcopyrite is sieved. This investigation shows that the specific surface of individual fractions were higher for the crushed sample than for the short-term (3 min) ground sample. The surface fractal dimension can give an information about the adsorption sites accessible to molecules of nitrogen and according to this, the value of the fractal dimension is higher for crushed sample.The effect of comminution processes on the mass distribution of particles crushed and ground in air as well as in polar liquids is also discussed. The estimation of fractal dimensions of particles mass distribution is done on the assumption that the particle size distribution is described by the power-law (1). The value of fractal dimension for the mass distribution in the crushed sample is lower than in the sample ground in air, because it is influenced by the energy required for comminution.The sample of chalcopyrite was ground (10min) in ethanol and i-butanol [which according to Ikazaki (1991)] are characterized by the parameter µ /V, where µ is its dipole moment and V is the molecular volume. The values of µ /V for the used polar liquids are of the same order. That is why the expressive differences in particle size distributions as well as in the values of fractal dimensions of fine particles distribution were not observed

Mechanochemical pretreatment and thiosulphate leaching of silver from complex sulphide concentrate

The refractory character of complex ores and concentrates is at present one of the main problems of their metallurgical processing. The research activity in this sphere is aimed at the methods of improving the process of metal extraction from the sulphidic minerals representing the major components of these ores and concentrates.One of the sulphidics components of complex ores is tetrahedrite. It represents a compound of complicated structure containing several metals among which copper, antimony and arsenic prevail. Some deposits are aspecially rich in silver. The Peruvian complex sulphidic concentrate of provenience Casapalca is each from these rich deposits.In this study the physico-chemical transformations and leachability of silver from Peruvian sulphide concentrate mechanochemically activated by ultrafine alkaline milling in the attritor were investigated. The experiments with alkaline leaching of using samples have shown that this hydrometallurgical process represents an effective method to prepare of treated concentrate with physico-chemical means for further leaching process. Ammonium thiosulphate were used as agent for obtain of silver to leaching solution.The leaching of as-received concentrate with the alkaline thiosulphate solution afforded only 6 % Ag into leach. The use of milling in attritor as an innovation method of pretreatment brought about 57% of structure degradation of tetrahedrite as silver-bearing mineral in concentrate as well as to the increase in specific surface area from the original value 0.26 m2g-1 to the maximum value of 16 m2g-1. This pretreatment has been performed in an attritor using the method of experiment design. The physico-chemical changes had influence on the two step process of thiosulphate leaching of silver.The optimum results obtained by mechanochemical pretreatment and subsequent leaching of the concentrate with ammonium thiosulphate were achieved by using milling time 30 min and weight of sample 30 g. Maximum 99 % recovery of Ag was reached already after 3 min of leaching

Fractal characterization of the coal surface

The aim of this paper is to point up to the characterization of the brown coal using the fractal theory. On the base of BET measurements on the adsorption surface, the surface fractal dimension of crushed and milled coal samples have been determined. These values of the fractal dimension are used in the estimation of the processes by the energy input

The utilization of mechanochemistry in the extractive metallurgy and at the nanocrystalline materials preparation

The possibility of the application of mechanochemistry in the extractive metallurgy and the nanocrystalline materials preparation is studied. The aim of the experiments is the chloride leaching of a complex sulphidic CuPbZn concentrate (Hodrua-Hámre), the modification of properties of CaCO3 (Yauli, Peru) for zinc sorption from model solutions and the mechanochemical reduction of copper sulphide by elemental iron.The chloride leaching of mechanically activated complex sulphidic CuPbZn concentrate is a selective process. While the recoveries of copper, lead and zinc are 65-85 %, the recoveries of silver and gold are less than 7 % and 2 %, respectively.The positive influence of CaCO3 mechanical activation for zinc sorption from ZnSO4 solution was observed. While only 58 % of zinc sorption was determined after 30 minutes for a non-activated sample, 98 % of zinc sorption was determined after 3 minutes sorption for the sample mechanically activated for 15 minutes.By the mechanochemical reduction of copper sulphide with iron, nanocrystalline copper and iron sulphide are formed. This reaction is an example of the new solid state technology, where chemical processes in the gaseous and liquid states are excluded.The results can serve as a contribution to the optimization of copper, lead and zinc extraction from complex sulphidic concentrates, the increase of non-ferrous metals sorption efficiency on mineral sorbents as well as to the nanocrystalline copper preparation.The application of mechanical activation has grown in the laboratory research. The Institute of Geotechnics of SAS has also achieved significant theoretical results in study of mechanical activation of sulphides and their reactivity in the different solid-phase reactions with the effect on industrial applications. The Institute has developed the technology of mechanochemical leaching (process MELT) which was successfully tested in a pilot plant unit

Environmental aspect of chemical pretreatment of slovak brown coal with nitric acid

With the aim to produce a low-sulphur coal by the nitric acid pretreatment, a research was undertaken on the influence of the different process parameters, such as temperature, time, acid concentration, particle size and physical pretreatment on the sulphur decrease, nitrification of the product and the variation in the ash composition for Slovak brown coal