Alkaline leaching of coal by the mechanochemical treatment

The possibility of application of a new process GACL (Grinding and Aqueous Caustic Leaching) for the reduction of mineral components in the brown coal Nováky was tested. The simultaneous grinding and chemical leaching enable us to extract 41 % total sulphur, 95 % arsenic and to reduce the ash content to 43 %. The process proceeds at the atmospheric pressure, temperature 90oC and in diluted NaOH solutions (5 %)

Technology GRAVIMELT and possibilities of their application in preparation of Slovak brown coal

The results of alkaline treatment tests on Slovak brown coal (from Nováky, Handlová and Cíge¾ localities) using the MCL procedure (Gravimelt) are presented in this paper. On the basis of conclusions of an optimal variant of the technology, the samples were pre-treated and submitted to a subsequent test at the NAOH/coal ratio = 1.0. The recovery of chemically treated coal, effectiveness of desulphurization and ash removal were assessed. This treatment procedure is less suitable for Slovak brown coal

Usage of a statistical method of designing factorial experiments in the mechanical activation of a complex CuPbZn sulphide concentrate

Mechanical activation belongs to innovative procedures which intensify technological processes by creating new surfaces and making a defective structure of solid phase. Mechanical impact on the solid phase is a suitable procedure to ensure the mobility of its structure elements and to accumulate the mechanical energy that is later used in the processes of leaching.The aim of this study was to realize the mechanical activation of a complex CuPbZn sulphide concentrate (Slovak deposit) in an attritor by using of statistical methods for the design of factorial experiments and to determine the conditions for preparing the optimum mechanically activated sample of studied concentrate.The following parameters of the attritor were studied as variables:the weight of sample/steel balls (degree of mill filling), the number of revolutions of the milling shaft and the time of mechanical activation. Interpretation of the chosen variables inducing the mechanical activation of the complex CuPbZn concentrate was also carried out by using statistical methods of factorial design experiments. The presented linear model (23 factorial experiment) does not support directly the optimum search, therefore this model was extended to the nonlinear model by the utilization of second order ortogonal polynom. This nonlinear model does not describe adequately the process of new surface formation by the mechanical activation of the studied concentrate. It would be necessary to extend the presented nonlinear model to the nonlinear model of the third order or choose another model. In regard to the economy with the aspect of minimal energy input consumption, the sample with the value of 524 kWht-1 and with the maximum value of specific surface area 8.59 m2g-1 (as a response of the factorial experiment) was chosen as the optimum mechanically activated sample of the studied concentrate. The optimum mechanically activated sample of the complex CuPbZn sulphide concentrate was prepared under the following conditions: the weight of sample/steel balls (degree of mill filling) 125 g/2000 g; the number of revolutions of the milling shaft - 900 min-1 and the time of mechanical activation - 64 min.Indeed, it is necessary to emphasize that the application of mechanical activation has exceeded the framework of the laboratory research. The Institute of Geotechnics of SAS has achieved significant theoretical and technological results in the study of mechanical activation of sulphides and their reactivity in the different solid state reactions. Nowadays the mechanical activation is frequently applied in Australia, New Zealand and South Africa for the pretreatment of sulphide concentrates with a gold content

CAPTO method application to the quality assessment of Slovak brown coal

This paper describes the principle and application of CAPTO (Controlled - atmosphere programmed - temperature oxidation) method for the sulphur content valuation in coal. The principle of CAPTO consists in mixing the coal with an inert material (WO3) and oxidation of the sample by a linear increase of temperature to 1000oC. The evolved gases (CO2, H2O, SO2 and NO2) are analyzed by infrared sensors. The method enables the determination of different sulphur forms (sulphidic, elemental, sulphate, organic aromatic and organic non-aromatic), hydrogen, carbon and humidity. The results on Americal coal Illionois No. 6 and Slovakian brown coal Nováky serve as an illustration of the CAPTO method possibility

Mössbauer spectroscopy of sulphidic minerals

Principles of the Mössbauer effect and the possibilities of its utilization for the study of sulphidic minerals are discussed. There is possibility to apply the Mössbauer spectroscopy in mineralogy for the identification of sulphides (fingerprint technique, geobarometer) and for the study of their bulk changes as a consequence of mechanical activation

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

Particle properties and their modification in mechanically activated realgar As4S4

In this work mechanical activation of realgar As4S4 was studied. The addition of sodium chloride NaCl as a solid diluent into the milling process substantially improved solid state properties of the obtained fines. However, the polymorphous transformation of �-As4S4 to �-As4S4 is reduced. Key words: Realgar, Mechanical activation, Sodium chlorid

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