Slag Dumps Research Articles

Assessing the mobility of Zn, Pb and Ni during the weathering of Nkana smelter copper slag, Zambia

Mine slag dumps could be point-sources of possible pollutants to the surrounding water and soils. The purpose of this study was to investigate the leaching behavior of zinc, lead and nickel from Nkana copper slag dump of Kitwe in Zambia. To assess the toxicity and hazardous nature of the slag, Bath Leaching EN 12,457–2:2002, Toxicity Characteristic Leaching Procedure (TCLP) and Synthetic Precipitation Leaching Procedure (SPLP) were employed. The results from these techniques revealed that the copper slag was inert in the open or natural environment. Sequential extraction analysis was conducted to analyze the fractionation of the zinc, lead and nickel using a seven-step procedure. The sequential extraction analysis showed that the 3 metals were predominantly present in the residual fraction. The risk assessment code (RAC) showed that zinc and lead's mobility could pose an environmental risk categorized as low risk, with RAC values of 1.31 % and 1.50 %, respectively. Nickel's mobility fell within the no-risk category with a RAC of 0.32 %. Additionally, the effect of pH, particle size and contact time on the release of the 3 metals were investigated. The results showed that the highest concentrations of zinc and nickel were observed for longer period of exposure (>33 days), in acidic environments (pH 2.2 and pH 3.0), for particle size distribution (<75 μm). However, lead leaching was not affected by the variation of pH or particle size distribution but mostly by duration of exposure. X-ray diffraction (XRD) analysis revealed that diopside (CaMgSi2O6) and quartz (SiO2) constitute the primary phases within the sample. It is recommended to limit the exposure of slag material to acidic environments and minimize the fragmentation of the slag into finer particles as these conditions would promote increased release of zinc, lead and nickel to the surrounding environment.

Technology of extraction of fuel mass from ash and slag waste in Ukraine

Purpose. Development of a technological scheme for the processing of ash and slag waste from coal-fired thermal power plants. The methods. The ash and slag dumps of thermal power plants are made up of the main components - slag, ash and unburned coal particles, drawing up an appropriate scheme for the extraction of coal particles allows the development of an effective scheme for the processing of ash and slag outputs of thermal power plants. The slag is separated from the fly ash by classification on a screen. Next, the method of extracting fuel mass from fly ash is used - the flotation method, based on the selective fixation of coal particles on the surface of air bubbles in the flotation chamber, with subsequent extraction of coal particles into a foam product. The mineral part of the ash cleaned from the fuel mass is ready for use in the road construction industry. Findings. A technological scheme for the processing of ash and slag waste of coal-fired thermal power plants has been developed, which makes it possible to obtain slag, high-quality coal concentrate, and the mineral part of ash. The originality. For the first time, a mathematical model was developed for forecasting indicators of enrichment of ash and slag waste of coal-fired thermal power plants by the flotation method. To predict beneficiation indicators, it is necessary to use three disclosure values: the initial ash content of the coal fraction (Aпd), the number of coal grains (PРЗ), the number of rock grains (PНЗ), provided that the separation characteristics of the beneficiation equipment are experimentally determined in advance. On the basis of the developed mathematical model of forecasting indicators of ash slag waste enrichment, an appropriate flotation scheme for effective extraction of fuel mass was drawn up, which made it possible to develop a technological scheme for processing ash slag waste of coal-fired thermal power plants. Practical implementation. The developed technological scheme for the processing of ash and slag waste makes it possible to obtain slag with a yield of 3.11% suitable for filling industrial roads, coal concentrate with a yield of 25.75% with an ash content of 21.80% can be used as a secondary fuel for thermal power plants or as a raw material for production solid fuel briquettes, as well as the mineral part of ash with a yield of 71.14% with an ash content of 98.10%, which can be used in the road construction industry.

Environmental characterization of ferrochromium production waste (refined slag) and its carbonization product

This paper presents the results of research on the method of utilization of self-disintegrating slags of refined ferrochrome production by autoclave carbonization in carbon dioxide environment. The work has a complex character, including earlier laboratory studies of the slag carbonization process under different conditions, as well as studies of chemical and mineralogical composition of initial waste slags taken from the slag dump and samples of bricks subjected to carbonization. The composition of slags and obtained products was investigated by XRD, DTA, DTG and XRF analyses, which showed that the main phases of the studied samples are dicalcium silicate, montichelite, periclase, magnesiochromite, calcite. Thermal analytical studies showed that magnesium carbonate is present only in the samples of artificially carbonized material. Also, the process of carbonate formation in the thickness of bricks during forced carbonization was investigated. As a result, it was obtained that with increasing CO2 pressure, the amount of bound carbon in the products increases proportionally in all layers. It was determined that the amount of CO2 absorbed during carbonization can reach 20 % of the mass of the initial slag. Stale slag can be used simultaneously as a carbon dioxide absorber and as a building product.

Assessing viability of processing ash and slag dumps for energy-efficient ash beneficiation at Magadan CPP

Complex processing of ash and slag waste is a supported directions for the development of environmental friendliness and performance in power engineering. The rational use of this waste in large-scale production processes has now been realized in the construction field. The development of up-to-date beneficiation technologies raises the possibility of extracting various useful components from ash and slag wastes. This study aims to investigate the potential for using energy-efficient ash beneficiation to produce a heavy metal-containing fraction and separate the magnetic fraction. To assess the feasibility of ash beneficiation and its rational use, the technical documentation of ash and slag dumps of PJSC “Magadanenergo” was studied, and semi-quantitative analyses of samples collected from these dumps were carried out. The data on the content of useful components and quantities of ash and slag enabled us to develop complex beneficiation flow sheets, assess their process efficiency, and evaluate their potential financial viability. The estimated volume of metals to be recovered includes 785 tons of Ti (me-1), 183 tons of Sr (me-2), and 4,867 tons of Fe (me-3). The performance indicators of the beneficiation and aggregated values of economic indicators for this project implementation on an industrial scale were calculated. The economic feasibility of the ash processing project showed good values for two out of three models over a ten-year planning horizon. Implementing the project also effectively improves the environmental situation by potentially processing up to 10% of the total volume of ash dumps, fulfilling one-fifth of the Energy Strategy of the Russian Federation’s requirements until 2035. While investigations of ash from the Magadan Cogeneration Power Plant (MCPP) are not new, they were not previously carried out within the framework of studying integrated processing of ash to obtain various useful components.

Study on the pore structure and capillary water migration characteristics of microbially improved strongly weathered phyllite

Phyllite is in a loose accumulation state after weathering, and there is a lack of suitable slag dump sites. The engineering properties of strongly weathered phyllite with poor strength and water stability can be improved by microbiological modification so that it is suitable for roadbed filling. This paper uses microorganisms to improve the strongly weathered phyllite filler, which does not conform to the hydrophysical properties of highway roadbed filler and studies the effects of different gelling fluids on the improvement. The spontaneous imbibition experiment is carried out on the modified sample to analyze the change rule of pore structure with time. The capillary water migration of the three sample groups is studied by using the nuclear magnetic resonance technique and finite element software. The results show that the carbonates produced by different gelling liquids have different particle encapsulation properties. After the calcium acetate improvement, the crystal content of calcium carbonate reached 20.5%. The pore ratio and equivalent average pore size of the three groups of samples increased with increasing spontaneous imbibition time. The fractal dimension of capillary pores is inversely proportional to the proportion of capillary pores. The capillary water absorption coefficient of the modified sample is 0.01. Both laboratory tests and numerical simulation results show that the improvement effect of calcium acetate is superior to that of the other two gelling liquids. The research results provide a reference for predicting the distribution of groundwater movement in strongly weathered phyllite modified by microorganisms as roadbed fillers.

STUDY OF THE PROPERTIES OF OILED FINE-DISPERSED OIL FROM THE VILALS OF THE METALLURGICAL PLANT

The task of obtaining of iron-containing secondary raw materials from finely dispersed oily slag accumulated in the dumps of metallurgical plants of Ukraine is important and urgent. This slag contains from 60 % to 75 % of iron oxides. Every year, up to 2.5 million tons of it is dumped into the dumps of PJSC “Kryvorizhstal” alone. To determine the favorable conditions for degreasing and cleaning of dump slag, studies of its structure, composition, physicochemical and technological properties were conducted. It is shown that, in addition to iron oxides, oil and water, there is a significant amount of more than 30 % of the amount of organic matter. The relative amount of components is different. A liquid reagent for the separation of organics from the starting material is defined. When the slag cleaned of organic matter is heated to 500 °C, a gradual decrease in the mass of the sample occurs, until it stops with exposure, with the preservation of all original iron oxides, FeO, Fe3O4 and Fe2O3, in the final product, in the absence of oil. When the slag is further heated to 950 °C, up to 97.5 % of hematite, Fe2O3, was obtained as the final product. In addition to hematite, oxides of other metals and more than 1.3 % of quartz are present in the final product in small quantities, up to 1.2 %. Bibl. 12, Fig. 8, Tab. 1.

Herbaceous plants as heavy metals accumulators in conditions of ash and slag dumps

Storage of ash and slag waste causes a number of environmental problems, including the transformation of natural geochemical cycles and the change of the natural radioactive background due to the increased concentration of heavy metals and radioactive isotopes in coal combustion products. Plants can provide an effective approach for the analysis and monitoring of heavy metals contamination. Additionally, vegetation plays a significant role in the restoration and remediation of heavy metal-contaminated soils. The application of plants in phytoremediation is a green and sustainable solution for decontaminating polluted sites. Moreover, the key role in the restoration of contaminated sites belongs to native species. Within the presented research, the abilities of native dominant species to accumulate and tolerate heavy metals in conditions of ash and slag dumps were investigated on a limited number of samples. Primary analysis of the bioaccumulation of heavy metals through the bioaccumulation coefficient showed that zinc has the highest accumulation capacity in the studied species. The ability to bioaccumulate the analyzed heavy metals decreases in the following order: Zn &gt; Fe &gt; Cu &gt; Mn &gt; Cd &gt; Ni &gt; Pb. Indexing the biogeochemical activity of the tested species showed higher levels of biochemical activity for Anthemis arvensis L. than for Achillea millefolium L., however, these data need to be confirmed by statistical analysis. Determination of the translocation index of elements reflected the high mobility of zinc and cadmium with a high rate of transferring to above-ground biomass, but the potential for accumulation requires scaling up the experiment with the involvement of a larger number of samples and performing statistical data processing. Due to their ability to accumulate heavy metals in roots, plant species could be used for phytostabilization. Establishing methods of biomonitoring and the development of green reclamation technologies with native species application need further research with both selected species and other local species. The presented research showed primary results of bioindication and references for phytoremediation of heavy metal contamination of the ash and slag dumps, which is relevant for other similar environmental conditions.

Mulching as a restoration method of revegetation at ash and slag dumps of Burshtyn TPP

The study of the effect of mulching to establish vegetation cover at industrial sites is promising and relevant in terms of environmental restoration and reduction of environmental risks in the area of influence of industrial facilities. The study aims to investigate and evaluate the effectiveness of mulching and sowing seed mixtures as a method of establishing vegetation cover at ash and slag dumps of thermal power plants. To conduct the study, the soil cover of ash and slag dumps was assessed, and experimental plots were laid out for mulching and sowing seed mixtures. The study revealed that ash and slag dumps ecotopes are characterised by a high concentration of pollutants, namely heavy metals, which makes it difficult for vegetation to grow there. In the course of studying the ecological features of the ecotopes and phytodiversity of the territory, a list of species of native flora for seed mixtures was proposed. Mulching was done on the experimental plots and seed mixtures were sown. Mulching has proven to be an effective method for accelerating the processes of natural regeneration of vegetation in areas affected by anthropogenic impact. The results of the study can be used in practice by ecologists, environmental organisations, and a wide range of specialists to develop and implement measures to restore the ecological balance of degraded and technologically transformed ecosystems

Role of Additives: Modified Hemihydrate Phosphogypsum Morphology and Enhanced Filtration Performance of Wet-Process Phosphoric Acid.

The morphology of hemihydrate phosphogypsum crystals is of vital importance in the hemihydrate-dihydrate (HH-DH) wet-process phosphoric acid production for high filtration strength. The morphology of hemihydrate phosphogypsum is commonly needlelike due to the strong acidic crystallization environment, which is unfavorable to the following filtration process. In this study, the crystal habit of hemihydrate phosphogypsum with a large aspect ratio was skillfully modified by additives to achieve a higher filtration strength. d-Glucitol (DG) reduces the theoretical aspect ratio of hemihydrate phosphogypsum crystals from 2.076 to 1.583 by interacting with the (002) face of CaSO4·0.5H2O preferentially, and poly(vinyl alcohol) (PVA) facilitates the aggregation of small grains to gather into a clusterlike structure. The modified morphologies of hemihydrate phosphogypsum have a lower bulk density and a larger porosity of the formed filter cake, which increases the filtration strength up to 45.9% when DG is added. Our work provides an in-depth explanation of the evolution mechanism of hemihydrate phosphogypsum morphology with the additives and its influence on the filtration performance. The improved filtration strength would reduce the water content of hemihydrate phosphogypsum and relieve the storage pressure of the phosphogypsum slag dump, which is meaningful to the clean production and process emission reduction of the phosphorus chemical industry.

Taxonomic revision of the Erigeronacris group (Asteraceae) in Murmansk Region, Russia, reveals a complex pattern of native and alien taxa.

Based on the evidence of morphology and a comprehensive revision of herbarium collections and field records, the taxonomy of the Erigeronacris group in Murmansk Region, European Russia, is completely revised. Its accepted diversity is increased from 2 to 8 taxa, including putative hybrids. The only native species, E.politus, is distributed in mountainous regions, along sea coasts and in the Kutsa River basin. Five species are alien: E.rigidus (previously confused with E.acris s.str.), E.acris s.str. (first recorded in the narrow taxonomic definition), E.brachycephalus (previously unrecorded), E.droebachiensis and E.uralensis (previously reported in error). Two major waves of the introduction of alien taxa are discovered, with different occurrences and species compositions. Regional and local dispersal by pomors (historical Russian settlers) occurred during their colonisation and traditional activities since the 12th century (archaeophytes or early neophytes); such alien taxa (E.rigidus, E.brachycephalus, and partly E.acris) are particularly common within the territory traditionally settled by Russian colonists but also found elsewhere along historical trade routes. Other alien species of the E.acris group (E.droebachiensis, E.uralensis, and partly E.acris and E.brachycephalus) colonised industrial areas in the 1960s-1990s as seed contaminants introduced during revegetation of slag dumps, stockyards, dams and channels. Putative hybrids between E.politus (native), E.rigidus and E.acris (aliens) are found in the places of co-occurrence. Updated nomenclature, synonymy and descriptions are provided for all accepted taxa.

Simulation of ash dump embankment stability

Ash and slag materials are removed from boiler rooms of CHP “Combined Heat and Power Plant” (Teploelektrotsentral’) by hydraulic transport and disposed in ash dumps. These are specially organized areas encircled by protective dams depending on the relief either along the entire perimeter or only in certain low-lying areas. The dams of hydraulic structures must provide stability to the whole structure against the following factors: shear; stability of slopes against sliding; filtration resistance of a dam body soils; reliable slope protection against possible failure due to atmospheric precipitation; as well as against wave action of water (within a settling pond); sufficient excess of dam crest over water level of a pond, etc. The study focuse on the design of ash and slag dump embankment (for storage of the ash and slag removed from the boiler rooms of Karaganda CHP by hydraulic transport). Ash dump design requires a broad range of problems to be solved. These include determination of location, design features and type of embankment, area of the basin and volume of the stored waste, strength of the embankment structures, etc. In order to assess the condition of the ash dump design, the stability of the facility embankment slopes for different combinations of loads, the conditions of possible watering of the dams, the presence of “geomembrane”, and pore pressure need to be analysed. A software program based on the finite element method allows simulation of ground (soil) conditions based on the strength and strain characteristics of the dam body filling soils and the base soils. Safety factors of the outer (downstream) slopes of hydraulic structures is determined taking into account the category and design of a structure, type of base (foundation), criticality of the design process stage, and other factors on the basis of conditions that ensure the prevention of the onset of limit states. The most critical and characteristic cross-sections across the perimeter of the ash dump embankment were selected for the computations, based on the analysis of the designed hydraulic structure base lithological composition. According to the computations performed, the outer slopes of the embankment at the paths of wells No. 373-19, No. 381-19, characteristic of almost the entire length of the embankment, are stable for different combinations of loads.

Coupling electrokinetic remediation with flushing using green tea synthesized nano zero-valent iron/nickel to remediate Cr (VI).

This study focuses on a flushing-electrokinetic remediation technology of hexavalent chromium from the chromium slag dump site. A suspension of nanoscale zero-valent iron/nickel fabricated from green tea (GT-nZVI/Ni), was employed as an eluent to degrade Cr (VI) and enhance the remediation effectiveness of a single EK. The removal efficiency of Cr (VI) was compared under different voltages, electrode spacings and pH values of the anolyte. The results demonstrated that the combined flushing and EK achieved a removal rate of Cr (VI) in the soil throughout all the experiments ranging from 83.08 to 96.97% after 120h. The optimal result was obtained when the voltage was 28V, the pH value of anolyte was 3 and the electrode spacing was 15cm. The removal of Cr (VI) reached 91.49% and the energy consumption was 0.32606kW·h·g-1. The underlying mechanisms responsible for the removal of Cr (VI) by GT-nZVI/Ni flushing-EK primarily involved electromigration, reduction and adsorption co-precipitation processes. The fractionation analysis of Cr (VI) concentration in the soil after remediation showed that the presence of GT-nZVI/Ni facilitated the conversion of Cr (VI) into oxidizable and residual states with low mobility and toxicity. The results of toxicity characteristic leaching procedure (TCLP) indicated that the leaching concentration of Cr (VI) was below 1mg·L-1, complying with the standards set by the Environmental Protection Agency. Additionally, the phytotoxicity testing revealed that the germination index (GI) of the remediated soil reached 54.75%, indicating no potential harm to plants.

Accumulation of heavy metals in leaves of tree species on the ash and slag dumps of the Burshtyn Thermal Power Plant

Thermal power plant (TPP) facilities are considered as one of the major reasons for environmental pollution. Ash and slag dumps as a special construction for storage of combustion wastes of TPPs are recognized as sources of heavy metals (HMs) contamination for surrounding ecosystems. The present study is the first report of analyzing HMs contamination of the ash and slag dumps of the Burshtyn TPP.&#x0D; The aim of the study is to estimate the content of HMs in the technogenic substrates of ash and slag dumps and investigate soil-plant interactions through analyzing potential of HMs accumulation in the leaves of native dominant woody species.&#x0D; Materials and methods of research. Soil sampling was carried out in the period of July 2021 at previously determined points. The most common woody species (Populus tremula L., Betula pendula Roth., Salix caprea L.) were selected for testing of HMs accumulation abilities. Samples of plants and soil were subjected to an atomic absorption spectrometer for being analyzed for heavy metals: Cd, Zn, Ni, Cu, Pb, Mn and Fe.&#x0D; Results of research and discussion. The results showed that the substrates of ash and slag dumps of the Burshtyn TPP were mainly contaminated by lead, copper and cadmium. All tested species concentrated high amounts of magnesium, iron, zinc and low concentration of cadmium. Bioaccumulation factor reflected the highest abilities of accumulation of zinc in all tested species and low level of bioaccumulation of cadmium. The highest index of biochemical activity showed Betula pendula. Salix caprea were found as a promising species for remediation due to intensive accumulation of such elements like cadmium, lead, copper, zinc and nickel.&#x0D; Conclusions and prospects for further research. We consider plant organisms particularly useful for analyzing HMs accumulation as they can provide a cost-effective and long-term approach for bioindication and monitoring HMs pollution. Moreover, vegetation covers could be used for remediation of HMs contaminated sites

Source apportionment and migration characteristics of heavy metal(loid)s in soil and groundwater of contaminated site

The rapid industrial growth has generated heavy metal(loid)s contamination in the soil, which poses a serious threat to the ecology and human health. In this study, 580 samples were collected in Henan Province, China, for source apportionment, migration characterization and health risk evaluation using self-organizing map, positive matrix factorization and multivariate risk assessment methods. The results showed that samples were classified into four groups and pollution sources included chromium slag dump, soil parent rock and abandoned factory. The contents of Cr, Pb, As and Hg were low in Group 1. Group 2 was characterized by total Cr, Cr(Ⅵ) and pH. The enrichment of total Cr and Cr(Ⅵ) in soil was mainly attributed to chromium slag dump, accounting for more than 84.0%. Group 3 was dominated by Hg and Pb. Hg and Pb were primarily attributed to abandoned factory, accounting for 84.7% and 70.0%, respectively. Group 4 was characterized by As. The occurrence of As was not limited to one individual region. The contribution of soil parent rock reached 83.0%. Furthermore, the vertical migration of As, Hg, Pb and Cr(Ⅵ) in soil was mainly influenced by medium permeability, pH and organic matter content. The trends of As, Pb, and Hg with depth were basically consistent with the trends of organic matter with depth, and were negatively correlated with the change in pH with depth. The trends of Cr(Ⅵ) with depth were basically consistent with the changes in pH with the depth. The content of Cr(Ⅵ) in the deep soil did not exceed the detection limits and Cr(Ⅵ) contamination occurred in the deep aquifer, suggesting that Cr(Ⅵ) in the deep groundwater originated from the leakage of shallow groundwater. The assessment indicated that the non-carcinogenic and carcinogenic risks for children and adults could not be neglected. Moreover, children were more susceptible than adults.

Gamma Spectrometry Analysis of Natural and Man-Made Radioactivity and Assessment of Radiological Risk in Soils Around Steel Industry

"In this paper low background high-resolution gamma spectrometry was used for the determination of the activity concentrations of the natural and man-made radionuclides in topsoil samples collected in the vicinity of a large steel plant in Galati, Romania. Their values (mean ± standard deviation) for 238U, 226Ra, 232Th, 235U, 210Pb, 40K and 137Cs were: 38.1 ± 6.2; 35.9 ± 5.4; 35.5 ± 3.0; 1.8 ± 0.4; 47.3 ± 8.6; 504.5 ± 38.9 and 7.2 ± 4.7 Bq·kg–1, respectively. 60Co and 241Am had activities below the detection limit: 0.6–1.3 and 2.2–4.7 Bq·kg–1, respectively. The results indicate inputs of natural radionuclides in the sites close to the slag dump, raw materials transportation facility, ore and coal processing factories, blast furnaces, and iron scrap deposit. The evaluation of the associated radiological impact was performed based on selected hazard parameters: absorbed gamma dose rate, total external gamma dose rate, radium equivalent activity index, external hazard index, representative level index, annual effective dose, excess lifetime cancer risk, and annual gonadal dose."

Bioleaching of chalcopyrite using native Acidithiobacillus ferrooxidans isolated in a mining area in Kitwe Zambia

This study aimed to assess the influence of the physical-chemical factors (particle size, shake flask speed, starting pH, and pulp density) in bioleaching of Zambian chalcopyrite using a novel native isolated Acidithiobacillus ferrooxidans strain DJN1 2021 from samples collected within mining area at Copper Nkana slag dump also known as the Black Mountain in Kitwe, Copperbelt Province in Zambia. The bacterium isolation was done using the modified 9 K selective media and was identified as A. ferrooxidans by using conventional procedures and 16S rRNA gene sequencing. The resulting sequences were analyzed by trimming and generating consensus sequences using Bio-edit software. Blasting results produced a significant alignment of 99.6% similarity with the corresponding sequences of A. ferrooxidans in GenBank. The phylogenetic analysis entails that the isolated strain was identified as A. ferrooxidans and named A. ferrooxidans strain DJN1 2021 with accession number MZ713091. Bioleaching of chalcopyrite (CuFeS2) by A. ferrooxidans (DJN1 2021) was conducted in shake flasks (100 ml) with a 9 K medium. The experiments were tested to optimize the initial pH, particle size, pulp density, and shake flask speed in the recovery of copper from its ore. The results revealed that all of the factors significantly influence the bioleaching process. When the initial pH was 1.8, copper was extracted at the rate of 30.6% within 30 bioleaching days. This was the maximum dissolution observed. The effect of revolution speed in the three different shake flask speeds (i.e. 50 rpm, 90 rpm, and 150 rpm) showed a significant difference in the rate of copper dissolution. A marked difference was observed between shake flask speeds of 50 rpm and 90 rpm with dissolutions of 29.4% and 30.0% respectively. In experiments to look into the effect of particle size, two size fractions were subjected to bioleaching on a shake flask, i.e. (<45 and 45-<63) µm. Results showed that the (45-<63) µm size fraction gave the highest copper extraction of 29.2%. A pulp density of 6% produced the highest extraction of 32.6%. These findings reveal that this novel native A. ferrooxidans strain DJN1 2021 has the potential to bioleaching of copper from chalcopyrite upon optimization in a bioreactor.

Effects of microorganisms on the migration and transformation of typical heavy metal (loid)s in mercury-thallium mining waste slag during the combined application of fish manure and natural minerals

Mercury-thallium mining waste slag has the characteristics of extremely acidic, low fertility and highly toxic polymetallic composite pollution, making it difficult to be treated. We use nitrogen- and phosphorus-rich natural organic matter (fish manure) and calcium- and phosphorus-rich natural minerals (carbonate and phosphate tailings) individually or in combination to amend the slag, analyze their effects on the migration and transformation of potentially toxic elements (Tl and As) in the waste slag. We set up sterile and non-sterile treatments specifically to further investigate the direct or indirect effect of microorganisms attached to added organic matter on Tl and As. The results showed that addition of fish manure and natural minerals to the non-sterile treatments promoted the release of As and Tl, resulting in an increase in As and Tl concentrations in the tailing lixiviums from 0.57 to 2.38–6.37 μg/L and from 69.92 to 107.51–157.21 μg/L, respectively. Sterile treatments promoted the release of As (from 0.28 to 49.88–104.18 μg/L) and inhibited the release of Tl (from 94.53 to 27.60–34.50 μg/L). Use of fish manure and natural minerals alone or in combination significantly reduced the biotoxicity of the mining waste slag, in which the combination was more efficient. XRD analysis showed that microorganisms in the medium promoted the dissolution of jarosite and other minerals, which indicated that the release and migration of As and Tl in Hg–Tl mining waste slag were closely related to microbial activities. Furthermore, metagenomic sequencing revealed that microorganisms such as Prevotella, Bacteroides, Geobacter, and Azospira, which were abundant in the non-sterile treatments, had remarkable resistance to a variety of highly toxic heavy metals and could affect the dissolution of minerals and the release and migration of heavy metals through redox reactions. Our results may aid in the rapid soilless ecological restoration of related large multi-metal waste slag dumps.

Radioactivity of metallurgical enterprises waste

Abstract. Problem. The problem of obtaining environmentally friendly materials is especially relevant when using the wastes that concentrate natural radionuclides (NRN) dangerous for public health. The concentrators of radionuclides include dump and granular blast-furnace slags. Goal. The purpose of the work is to determine the radionuclide composition of the fractions of dump and granular blast-furnace slags from Ukrainian enterprises, their compliance with the radiation safety standards of Ukraine and international radiological indicators, and to identify the factors that determine the level of natural radioactivity of the slags. Methodology. The specific activity of natural slag radionuclides was determined by the gamma spectrometric method on a SEG-001 scintillation gamma spectrometer. The mineral composition of the crystalline component of the slag was determined using X-ray phase analysis performed on a Siemens D500 powder diffractometer. The elemental composition of blast furnace slag was determined by the method of electron-probe microanalysis on a JSM-6390 LV scanning electron microscope with an INCA micro-X-ray analysis system. The particle charge and electrokinetic potential were determined during macroelectrophoresis of suspensions. Results. The blast-furnace slag contains natural radionuclides: 226Ra, 232Th and 40K. The content of radionuclides varies by waste fractions. According to the contribution to the total activity value, NRN can be arranged in a row: 40К &gt; 226Ra &gt; 232Th. The most radiation-clear is the fraction &gt; 20 mm of the “Zaporizhstal” dump slag, the radioactivity of the fractions 1.25‒2.5 mm for DMC, 5‒10 and 0.63‒1.25 for MMC and the “ArcelorMittal” granulated slag is increased. All investigated slags belong to the first class of radiation hazard (Сef 370 Bq/kg) and can be used in construction without restrictions. Originality. All investigated slags correspond to international radiological indicators: Raeq 370 Bq/kg, radiation hazard indices are Iγ, Iex, Iin and Iα 1, which indicates that there is no danger of increased gamma radiation and emanation of radon and the daughter products of its decay into the room air. The concentration of radon indoors does not exceed 200 Bq/m3. For the average sample and slag fractions &lt;2.5 mm of “ArcelorMittal”, the activity utilization index which determines the safety of practical waste use is overestimated; the absorbed dose rate in the open air and the annual effective equivalent dose are higher than the world average values, they are, respectively, 58 nGy/h and 0.07 mSv, but at the same time below the value recommended by the IAEA for the population of 1 mSv/year. The excess lifetime carcinogenic risk for dispersed fractions of “ArcelorMittal” slag is higher than the world average: 0.29·10–3, but below the 0.05 limit set by the International Commission on Radiation Protection. A direct correlation between the acidity of the slag fractions and the increase in radiological parameters was determined. Practical value. An attempt has been made to relate the radioactivity of blast-furnace slag with the NRN sorption on the negatively charged surface of slag particles, which is more reliable for amorphous sorption-active granular slag.

Construction of a geoecological map of dust particles transfer from the surface of the Shymkent lead (plumbum) factory dump

The study of horizontal migration of heavy metals is relevant for Shymkent city. In 1934, lead processing began, and sludge waste was stored on the territory of the lead factory. Ameliorative or other structures capable of reducing dust emissions have not been built around the lead dump, allowing lead dust to freely spread over long distances from the SPZ (sanitary protection zone). In this article, the horizontal migration of lead dust was studied based on climatic and calculated data by building a physical model; in addition, a geoecological map was built. This work has practical significance for further ecological and geochemical assessment of soils for the content of heavy metal concentrations, since it visually characterizes the spread of lead dust along the wind rose. To build a geoecological map of the transfer of impurities, we are faced with the task of determining the rate of settling of hovering particles and their distributions depending on the masses of particles and wind speed. To determine the rate of deposition of lead particles in the atmosphere, we need to study the shape of lead, background meteorological situation, particle diameter, solid particle density, medium density and dynamic viscosity of the medium. The removal of dust particles from the surfaces of ash and slag dumps of industrial facilities into the atmosphere under the influence of wind erosion, followed by their deposition on the soil, is one of the most common ways of polluting the territories of industrial facilities. As a result of the calculations, the surface concentration of dust particles was derived and a geoecological map was compiled. Keywords: geoecological map, lead dumps, assessment of dust emissions, horizontal migration of heavy metals, physical model of transport and scattering.

Research of iron extraction from primary steelmaking slag

The article examines the issue of involving primary steel making slag in the processing with the extraction of iron and the production of slag, which can be used in the manufacture of construction products. Currently, primary steel slag is not used for the production of construction products due to the large amount of iron, and its use is limited to road construction and in most cases, primary slag is sent to landfills. In the Pavlodar region of the Republic of Kazakhstan, during steel production at electric steel making enterprises, the resulting electric furnace slag and dust are stored in slag dumps. They are practically not used, despite their high content of iron oxides and metallic iron particles (up to 40% by weight in some types of slag). The work experimentally determined the chemical and mineralogical composition of primary electric furnace slag with a total iron content of more than 20%. The slag contains the following minerals: wüstite (FeO), magnetite (Fe3O4), gehlenite (Ca2Al(Al,Si)2O7), merwinite (Ca3Mg(SiO4)2). In the course of experimental studies on the recycling of primary electric furnace smelting slags by reduction induction melting of slag-lime-coke pellets, the possibility of extracting iron in the form of iron-carbon alloys and using the slags for the production of concrete was established.