Distribution of Pb, Zn and Cd in stream and alluvial sediments in the area with past Zn smelting operations

The sources of Zn, Pb and Cd in alluvial and stream sediments have been studied in the area of historical Zn smelting tradition. 30 samples of stream sediments and samples from 4 alluvial sediment profiles were collected. Fractions 0.125–0.063 and < 0.063 mm were analysed by the means of ICP-MS prior 4-acid digestion. The highest levels of Zn, Cd and Pb were detected in the alluvial sediments in the closest vicinity to the abandoned slag and ore roasting residue waste dumps, reaching 96 and 4520 mg/kg, 522 and 26,800 mg/kg and 3.7 and 31 mg/kg for Pb, Zn and Cd in stream and alluvial sediments, respectively. The Voglajna River then transports contamination particles into the Savinja River, which afterwards flows into the Sava River. Consequently, the anomaly can even be detected in the Sava River, more than 30 km downstream. Higher levels of Pb, Zn and Cd have been found in fraction < 0.063 mm compared to 0.125–0.063 mm fraction. Impacts of historically contaminated soil erosion and in particular the wash-out of Zn-smelting waste from the improperly managed waste dump were recognised as the dominant sources of Zn, Cd and Pb in the stream and alluvial sediments.

Process Development for Solid Fuel Use at Siderite Ore Roasting in Shaft Furnace

Lean coal burning kinetics was studied and the main burning rate dependence on oxygen content in gas phase and heating rate was obtained. Preliminary dressed lump siderite ore from Bakal deposit with the fraction of 18-25 mm and average iron content of 35% was roasted in a pilot unit in neutral (low reducing) atmosphere, obtained by coal grate firing. It was established that such roasting allowed iron oxidation level reduction, as compared to roasting in oxidizing atmosphere and iron content increase in the roasted product. The evaluation results allowed development of a roasting process for siderite ore in neutral (low reducing) atmosphere and designing of a shaft furnace operating on solid fuel. Such roasting process is of a certain interest, as far as saving the insufficient fuel types, and predominantly natural gas, is concerned.

Phase composition and thermal properties of the Sakharinskoe deposit oxidized nickel ore

X-ray diffraction, optical microscopy and X-ray microanalysis were used to determine the composition and distribution of elements in the main mineral constituents of oxidized nickel ore at the Sakhalin deposit (goethite, hematite, serpentine, talc and chlorite). The main fraction of nickel is concentrated in iron oxides, where its content reaches 2,4 %, while in magnesium silicates it does not exceed 0,4 %. The sequence and temperature intervals of transformations were established when heating ore in inert and reducing media by means of thermal analysis methods combined with mass-spectrometric analysis of gases and subsequent X-ray phase analysis of products. The temperature regimes of ore roasting for the reduction of nickel and iron from their minerals were justified. The temperature regimes of sample heating are assumed to be close to the conditions implemented in industrial units (electric furnaces) where the rate of charge heating varies within 5—15 degrees/min, up to the melting point (1450 °С) of ferronickel and slag. It is proposed to use information on material composition, thermal properties and metal forms in ore to select regimes and technologies for their pyro-or hydrometallurgical processing. Nickel and iron recovery from oxides in CO environment occurs above 800 °С, while serpentines remain stable up to 1200 °С. The use of coke as a reducing agent allows reducing iron and nickel from serpentines at temperatures above 1250 °С. The obtained data were used to substantiate the operating conditions of roaster and electric furnaces during ferronickel smelting from oxidized ores. When roasting, resulting ferronickel particles will contain 2—4 % Ni. Completing recovery processes in the electric furnace will ensure metal recovery from magnesium silicates, which will slightly increase the nickel content in ferro-nickel.

Kinetics of Siderite Ore Roasting in the Shaft Furnace

Kinetics of the siderite ore roasting in the air, helium and hydrogen flows has been studied in a gasometrical unit with continuous mass variation logging. We have derived the expression for determination of an apparent degree of calcination and identified its dependence on the size of the prill, the heat treatment duration, and gas-phase composition. Using a generalized chemical kinetics equation, we have obtained a formula for calculation of the decomposition period for siderite ore samples. It has been found that calcination rate increases with the temperature rise, irrespective of the sample size and atmospheric composition. Calcination process has been studied at low temperatures. We have demonstrated that it is feasible to describe the process of siderite ore thermal dissociation by a first-order kinetics equation. We have obtained the expression to calculate the duration of this process depending on different parameters. Using a generalized chemical kinetics equation, we have obtained a formula for checking the expressions that describe the experimental data. We have studied kinetics of the reduction of roasted ore samples at various temperatures using different sizes of the samples. The obtained results have been applied for optimization of the design values and operating conditions of the siderite ore roasting in shaft furnaces. These will also be used for designing a shaft furnace consisting of a calcination zone, reduction zone (metallization zone) and metallized product cooling zone, which will increase iron content in the end-product to 65-70%.

Study of the process of siderite ore thermal treatment in a shaft furnace

Results of a study of kinetics of siderite ore roasting process in flows of air, helium and hydrogen presented. The study was carried out at mass measuring device with continuous registration of mass changing. An expression received for determining of apparent decarburization degree and its dependence determined on a piece dimension, thermal treatment duration and gas phase content. Using a generalized chemical kinetics equation, a formula received for determining of decomposition time of siderite ore specimens. Increase of decarburization pace at temperature rise determined for specimens of all dimensions independent on the atmosphere content and mechanism of decarburization process at low temperatures considered. A possibility shown to describe the process of thermal dissociation of siderite ore by a kinetic equation of first order and an expression obtained for determining of this process duration depending on different parameters. By application of generalized chemical kinetics equation a formula obtained, which was used to check the expression, describing the test data. Kinetic of roasted ore specimens reduction studied at different temperatures and specimens dimensions.The results obtained in this work were used for optimization of structural and mode parameters of siderite ore roasting process in shaft furnaces. They will be applicable at designing of a shaft furnace, comprising decarburization zone, reduction zone (metallization zone) and cooling zone of the metalized product, that will enable to increase the iron content in the final product till 65–70%.

Study of Decarbonization Processes During Siderite Ore Roasting

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