Ore Processing Research Articles

Process mineralogy characteristics of a very fine disseminated refractory gold deposit

The grade, recovery rate, or leaching rate of gold concentrate obtained by the flotation process or cyanide leaching process of gold ore is low, which is typical refractory gold ore. In order to fully understand the properties of the gold ore and optimize the gold recovery process and indicators, the process mineralogy of the ore was systematically studied by means of chemical multi-element analysis, optical microscope, scanning electron microscope (SEM), X-ray energy spectrometer, automatic mineral parameter analysis system (BPMA), and other test methods. The results show that the average grade of valuable element gold in the ore is 2.98g/t, and the contents of harmful elements mercury and carbon are 0.50% and 0.32% respectively; The main gold ore is natural gold, with a small amount of silver gold and tellurium gold; The main metal minerals are pyrite, pyrrhotite, magnetite, hematite, etc; The main gangue minerals include quartz, feldspar, kaolinite, mica, calcite, etc. Under the condition that the grinding fineness is -0.074mm, accounting for 90%, the distribution rates of single gold and bare gold in the ore are 3.15% and 57.66% respectively, and the distribution rates of gold with pyrite and quartz crystals are 5.77%, and the total distribution rates of the three are 66.58%, that is, the maximum theoretical flotation recovery rate of gold under the grinding fineness, but the particle size and fineness of gold minerals are both 5 μ Below m, the particle size of some gold ores is less than 0.5 μ m. It exists in the form of fine particles, micro gold, or ultra-micro gold, and it is difficult to recover gold by the flotation process, so it is recommended to adopt the whole slime cyanidation leaching process.

Эффективная переработка полезных ископаемых определяется правильностью стратегии выбора техники и технологии при производстве работ. В современных условиях, когда необходимо наращивание производственной мощности действующих горно-обогатительных комбинатов, повышение производительности производства не может рассматриваться в отрыве от возможностей конкретного технологического оборудования. При решении вопросов повышения эффективности горно-обогатительного оборудования требуется особо уделять внимание оптимизации его взаимодействия в единой технологической схеме. Общеизвестно, что на горно-перерабатывающих

The efficiency of mineral processing is determined by the correct selection strategy for equipment and technology in the production process. In the present-day context, when it becomes necessary to increase the production capacity of existing mining and processing plants, enhancing the production capacity cannot be considered in isolation from the potential performance of the specific process equipment. When addressing the challenges associated with improving the efficiency of mining and processing equipment, special attention needs to be paid to streamlining its interaction within a unified process flowchart. It is generally known, that the bin storages at mining and processing facilities are intended to receive rock mass and secure batching and uniform supply of loose and lumpy materials from the bin to the downstream technological equipment. The bin storage parameters have to be defined with account of the properties of the materials to be used. The aim of this study is to develop an optimal design of the bin-and-feeder system that would ensure the material path close to the brachistochrone curve. Based on the presented analytical dependences, the main characteristics of releasing the mineral raw material from the bin-and-feeder systems have been established for the conditions of mining and processing plants. The received data can be used in further research to provide a mathematical model of material flow, as well as in the finding an optimal design of the bin. A complex approach that included a system scientific analysis and generalization of previously published studies was used in addressing the tasks set. An approach is suggested to develop a promising design of the bin-and-feeder system to deliver the mineral raw materials based on using the guides that would ensure the material flow as close to the brachistochrone curve as possible. This approach can be implemented in the bin-and-feeder systems for ore processing plants in order to reduce the energy consumption for the transportation and feeding of the mineral raw materials.

Опыт освоения магнитно-гравитационной сепарации на предприятиях России и стран СНГ для повышения качества железорудного сырья

The paper analyzes the tasks of producing high-quality iron ore concentrates suitable for nonblast-furnace metallurgy and the challenges of processing magnetite ores with the current technological level of dressing equipment and technologies. One of the best methods to improve the quality and the grade of iron ore raw materials is the use of magnetic gravity separation in the technological process, which allows selective separation of the liberated magnetite particles from their aggregates in processing of undersize products of fine vibrating screening. This trend is implemented in the innovative magnetite ore processing technology that uses the principle of the staged output of finished concentrate. The technology makes it possible to produce a high-quality concentrate after the first grinding stage. The magnetic gravity separation has undergone industrial validation, has proven its efficiency in practice, and has become widespread at mining and processing plants not only in Russia, but also in the CIS countries. Over 180 MGS-2.0 magnetic gravity separators produced by Russian manufacturers have already been or are being implemented at various Russian and CIS companies. Industrial separators are equipped with modern automation systems providing high technological separation performance, have no rotating parts and are simple in design. The authors continue R&D works on creation of automated control systems for the magnetic gravity separation process based on designing digital models adapted for introduction into the plant’s automated process control systems.

Processing of ore from the Nud II deposit by the method of low-temperature roasting with ammonium sulfate

The Murmansk region has a significant amount of sulfide copper-nickel raw materials. Deposits of the Nud massif associated with Monchepluton are promising for processing. The Nud II deposit cut-off grade ore with an initial Ni content of 0.45 % and Cu of 0.39 % has been chosen as the research object. During the research, the ore was mixed with ammonium sulfate, grinded, and the mixture was roasted in a muffle furnace with static air atmosphere. The roasted mixture was leached in heated distilled water with constant stirring. The maximum metals recovery was achieved when crushing to a fraction of –40 µm, the ratio of ore : ammonium sulfate is equal to 1 : 7, roasting temperature 400 °C, roasting duration 300 min. In the mixture roasted at these parameters, reflexes of copper and nickel sulfates were recorded by the x-ray phase analysis (XRD) method. At the stage of water leaching, the maximum recovery was: Ni – 79.1 %, Cu – 75.8 %.

Recovery of non-ferrous metals from sulfide ores by bioleaching on the example of the Allarechensk technogenic deposit

The possibility of processing sulfide copper-nickel raw materials by heap bioleaching due to the environmental attractiveness of this approach is becoming an increasingly relevant topic for mining and processing. On the example of the Allarechensk technogenic deposit ore, the effectiveness of the bioleaching method for the copper and nickel recovery has been considered. The content of metals in the original ore sample: nickel – 2.42 % and copper – 0.75 %. The ore grinded to the size of –5+3 mm has been irrigated with a solution containing a strain of Acidithiobacillus ferrivorans. The S : L ratio is 4 : 1, the flow rate is equal to 0.1 mL/min. In pregnant solutions, the pH and redox potential values have been controlled, and the concentrations of ferrous and ferric iron, copper, and nickel ions have also been measured. The experiment duration is 11 months, 8.9 % nickel and 6.1 % copper have been recovered. Copper has been extracted from pregnant solutions by cementation on iron, the maximum recovery is 97.3 %. Thus, it has been shown that the proposed scheme for the recovery of metals is promising for the processing of sulfide raw materials, in particular, low-grade ores and enrichment waste.

Ресурсосберегающая технология утилизации хвостов обогащения руд цветных металлов

Introduction. The article presents the results of research on the problem of waste disposal of ore processing by changing the properties of metal-containing raw materials. The research methods are based on experiments using the method of electrochemical activation of metal extraction processes. Results. The purpose of the study is formulated as modernization of the technology of extraction of metals from ores by leaching in relation to non-ferrous metals. It has been determined that the tailings of the enrichment of metal ores contain valuable metals that are not fully extracted by traditional methods of enrichment, which form compounds dangerous to the environment. It is determined that the leaching efficiency increases due to a decrease in the activated reaction area of the working solution with minerals containing the extracted metal. A mathematical description of the leaching kinetics is given depending on the surface area of the particles and the applied energy. Models for evaluating technology options and determining savings from the use of the phenomenon of mechanical activation are proposed. Discussion of the results. It is shown that a promising direction of metal extraction is combined chemical enrichment and mechanical activation with high energy in a disintegrator. It is determined that the activation of minerals in the disintegrator increases the recovery of metals by more than one and a half times, and the combination of grinding and leaching processes increases it even more. Conclusion: during the disposal of ore dressing waste, the mechanochemical activation of binders increases the extraction of metals, reducing risks to the environment.

Проблемы и перспективы внедрения многостадийной выемки руды при отработке запасов калийных месторождений

Introduction. Most of the potash deposits in the world are mined using room-and-pillar mining method with natural support, which is accompanied by high mineral losses, as well as a high mine accidents due to the destruction of supporting elements, waterproof strata continuity and breakthroughs of oversalt water and brines into the mined-out void. Methods. Generalisation, systematisation and analysis of theoretical and experimental research on increasing the extraction ratio of potash ore to establish the methods degree for increasing extraction of potash reserves, to identify unexplored and problematic issues, to determine directions and approaches. Results. Theoretical justification of the possibility and expediency of several-stage stoping for potash mining implementing the principle of re-extraction of reserves from pillars with the provision of necessary protection measures of aquifer in the form of backfill. Conclusion. The article presents the results of an analysis of the specifics of underground mining of potash deposits. The concept of several-stage stoping for potash mining is formulated. Generalized variants of several-stage stoping are presented. The main problems of several-stage stoping implementation at potash deposits are described: the problem of gap-filling in rooms; prediction of altered physical and mechanical properties of seams and host rocks; the influence of multiple excavation on water-resistant properties of waterproof strata in several-stage stoping; the role of time in geomechanical processes; rational composition and recipe of backfill preparation; organization of stowing and clean-up operations at the site; technical and economic expediency of several-stage stoping. Possible lines of approach are suggested. Resume. The use of several-stage stoping for potash mining will increase the extraction ratio, improve the reliability of the waterproof strata during mining by replacing potash seams with a continuous fill mass, utilize waste from potash ore processing, and extend the service life of potash mines. A competent scientific and methodological foundation on the implementation of such technology at potash deposits needs to be built for a deep evaluation of the mining and geomechanical processes in the operation areas and the technical and economic performance of several-stage stoping. Suggestions for practical applications and future research line. The variants of several-stage stoping presented in the article can be used to develop methods of potash mining considering specific mining and geological conditions. Application of the described and similar variants of several-stage stoping in practice will significantly increase the extraction ratio while maintaining a minimal impact on the seam. Future research line will focus on the underground deposit development plan and the geomechanical justification of the parameters of the several-stage stoping.

A research of the effect of an underwater electric explosion on the selectivity of destruction of quartz raw materials

The work is devoted to the study of the effect of an electric explosion on the selectivity of the destruction of quartz raw materials. The object of the study is quartz ore of the Nadyrbay deposit of the Republic of Kazakhstan. An electrohydroimpulse plant for crushing and grinding quartz raw materials has been developed and assembled. Using the electrohydroimpulse method, the granulometric composition of quartz can be adjusted. This makes it possible to adjust the magnitude of the voltage in the discharge channel and time. In this technology, quartz ore processing was carried out with an increase in the discharge voltage of the storage from 14 kV to 25 kV, the length of the interelectrode distance from 8 to 12, the capacitance of the capacitor 0.5 µF, 0.75 µF and the processing time of 5 min. Using the electrohydroimpulse method, quartz ore particles with an initial fraction of 5 mm, 10 mm and 1 mm were crushed to 0.8. The results of the grinding of quartz raw materials with the influence of an underwater electric explosion in a liquid medium allowed us to determine the degree of grinding of the material. The obtained results can be used in the course of studying the characteristics of crushing and grinding of ores. In the food industry, quartz sand within 0.25–0.5 millimeters can be used as a filler to create filters for water purification, as well as products from oil, industrial effluents, etc. Particles ranging in size from 0.5 to 1 millimeter can be used for rough processing of metal, stone and glass. The structural and quantitative analysis of powdered quartzite samples was made using a scanning electron microscope and the stoichiometry of the elements was calculated

Substantiation of the Technology of Refining Gold Reserves at the Zholymbet Deposit

A set of technical solutions for the opening, preparation and clean-up of the reserves of the Zholymbet gold deposit at the stage of completion in order to maintain the production capacity of the underground mine is outlined. The Zholymbet deposit is located in the south-east of the Seleta-Stepnyak Megasynclinorium in the southern part of the Aksu-Zholymbet structural-metallogenic zone. The deposit of the Zholymbetskoye deposit includes 3 sections (Central, Southern, Northern) and a number of manifestations of the gold-quartz formation. The sites lie in the endo- and exocontact parts of Steppe-type intrusions (Central and Southern) and on the rise of the roof of the Sorokkuduk massif (Northern). The gold mining factory is intended for processing ore from the central section of the Zholymbet deposit («Quarry No. 6», «shh. Center»). The production capacity is 500,000 tons of ore per year. The gold content in commercial ore is 3.07 g/t. The peculiarity of this stage is the need to involve ore bodies bordering on previously worked blocks into operation, as well as taking into account the diversity of mining and geological and mining technical conditions caused by a large number of disconnected ore bodies with insignificant reserves. These technical solutions provide timely access to all reserves of the deposit, safety of mining operations, efficient transportation of ore and ventilation of treatment faces. The adopted technical and technological solutions ensure the effective development of all reserves of the field

Uranium tailings in the Istiqlol city: history, problems, solutions

The article provides an overview of the problems associated with the uranium tailings in Istiqlol city. Many uranium heritage sites in Central Asia, including the uranium tailings in Istiqlol, hadn’t been mothballed before the collapse of the USSR. The burial complex consists of a quarry, dumps of the “Poor Ores Factory”, an unpreserved open mine, destroyed industrial buildings and four tailings which contain 12 million tons of the uranium production waste. In the area of the tailings, the ambient dose rate of gamma radiation is 0.5–0.6 μSv/h, and at some points it reaches 3.0–4.0 μSv/h. The average annual radon emission from the surface is estimated at 3.9×1011 Bq/year. The contaminated areas also include the Sarym-Sakhly Sai stream, mine, industrial and quarry waters, which are characterized by an increased content of 234U, 238U and 226Ra. The facilities aren’t physically fenced, allowing free access for the public and livestock. Natural disasters such as mudflows, landslides, and earthquakes can lead to an ecological disaster. Attention is paid to the ways of solving problems such as monitoring radionuclides in water, soil, and air; working with the local population to inform and involve them in rehabilitation work; donors search. The Program for the Implementation of the National Concept for the Rehabilitation of Tailings of Uranium Ore Processing Wastes for 2016–2024 was developed and approved by the Government of the Republic of Tajikistan to minimize the radiation impact on the population and the environment. Implementation of the Program requires significant financial investments and trained personals in the field of radiation safety. Only through the joint efforts of the state, population and international organizations is it possible to fully carry out rehabilitation works. Only by joint the state, public, and international organizations efforts, it is possible to solve these problems. Also, one of the main reasons why the population had received unnecessary overexposure was its ignorance of the danger of using water, soil and building materials contaminated with radionuclides. Therefore, the culture of radiation safety should be studied starting from middle school, where students will be taught about ionizing radiation and possible ways of exposure. Then, both cases of intake of radionuclides into the body, which could have been avoided, and radiophobia among the population living near the extraction and processing of uranium ore, will be much lower. Some social and economic aspects are also touched upon.

Improving the technology of copper-zinc ore beneficiation of a Uralian-type pyrite deposit

Introduction and research objective. Copper-zinc ore of pyrite deposits of the Uralian type are refractory. Difficulties in beneficiation are due to their material composition: fine coarseness and emulsion impregnation of ore minerals in each other, a large amount of flotation-active pyrite, a high content of finely dispersed and submicroscopic gold in sulfides, etc. In the course of pyrite ore processing at dressing mills, 83–91% of copper and 10–45% of gold are extracted into copper concentrates, and 46–78% of zinc and 5–15% of gold are extracted into zinc concentrates. Increasing the process performance of pyrite deposit ore processing is a promising and urgent task. Methods of research included copper-zinc pyrite ore material composition study through quantitative chemical analysis, chemical phase analysis for the forms of copper, zinc, gold and silver compounds, and mineralogical analysis. Technological studies were carried out by flotation and gravity methods using a centrifugal concentrator and a concentration table. Conclusions. In the course of pyrite deposit copper-zinc ore beneficiation at the dressing mill, the effect of circulating concentration of gold in the coarse copper concentrate regrinding cycle was established. The results of studies on the centrifugal concentration of gold in a centrifugal concentrator with further secondary cleaning of its heavy fraction on a concentration table show the possibility of obtaining a gravity product with a mass fraction of gold up to 200 g/t under its operational extraction up to 29%. It was noted that the integrated flotation-gravity technology for copper-zinc ore beneficiation will increase the through extraction of gold into marketable mineral products by more than 1.5%. The use of a combination of butyl potassium xanthate and FRIM-2920 reagent-collector in the copper-zinc pyrite ore flotation technology contributes to increased extraction of copper and gold into copper concentrate by 0.87% and 3.22%, respectively, and zinc into zinc concentrate by 0,4%. Increasing the pulp temperature in the zinc flotation cycle to 40–45 °C and returning the control zinc flotation concentrate and tailings from the first cleaning flotation of zinc to the II main zinc flotation allows increasing the mass fraction of zinc in the zinc concentrate from 48.5 to 51.1% under a simultaneous increase in the extraction of zinc into zinc concentrate from 62.6 to 65.6%.

Features of Copper Mobility During the Transition from Clinkers to an Aqueous Solution at the Belovsky Zinc Plant (Kemerovo Region)

Experimental data were presented on the mobility of copper during the transition from old wastes of pyrometallurgical processing of polymetallic ores (Belovsk zinc plant, Kemerovo region) into solution. Based on the data of percolation experiments, the article proposes the extraction method of copper with minimal environmental risks.

Artisanal gold mining in Kakamega and Vihiga counties, Kenya: potential human exposure and health risk

Artisanal and small-scale gold mining (ASGM) represents 20% of gold supply and 90% of gold mining workforce globally, which operates in highly informal setups. Pollutants from mined ores and chemicals introduced during gold processing pose occupational and inadvertent health risks to the extent that has not been well elucidated in Africa. Trace and major elements were analysed using inductively coupled plasma mass spectrometry in soil, sediment and water samples from 19 ASGM villages in Kakamega and Vihiga counties. Associated health risks for residents and ASGM workers were assessed. This paper focuses on As, Cd, Cr, Hg, Ni and Pb for which 96% of soil samples from mining and ore processing sites had As concentrations up to 7937 times higher than the US EPA 12 mg kg−1 standard for residential soils. Soil Cr, Hg and Ni concentrations in 98%, 49% and 68% of the samples exceeded respective USEPA and CCME standards, with 1–72% bioaccessibility. Twenty-five percentage of community drinking water sources were higher than the WHO 10 µg L−1 drinking water guideline. Pollution indices indicated significant enrichment and pollution of soils, sediment and water in decreasing order of As > Cr > Hg > Ni > Pb > Cd. The study revealed increased risks of non-cancer health effects (98.6) and cancer in adults (4.93 × 10−2) and children (1.75 × 10−1). The findings will help environment managers and public health authorities better understand the potential health risks in ASGM and support evidence-based interventions in ASGM processes, industrial hygiene and formulation of public health policy to protect residents and ASGM workers’ health in Kenya.

OBTAINING OF ALKALINE FROM ALUMINATE SOLUTION BY ELECTRODIALYSIS METHOD

In the study, electrodialysis of alunite mud and aluminum hydroxide washing solutions, obtained during the processing of alunite ore, has been carried out in the study. Acid and alkali extraction from the electrodialysis process, as well as the conditions for solidification of the obtained alkali and acid, has been researched. PC Cell 64004 electrodialysis device and bipolar, anion, cation exchange membranes and the processes occurring in the membranes has been used in the experiments. Studies show that during the electrodialysis of sodium sulfate solution, if it is possible to obtain a 3–4% sodium hydroxide solution in the initial experiments, the concentration of the alkali can be increased to 5% in the alkali thickening experiments. The flow rate of 1 ml/sec, current strength – 3–4 A, voltage – 4–5 V have been adopted as the optimal conditions of the experiments. During the study of the factors effect on the concentration of the products, it has been determined that the flow rate is the main factor affecting the process. So reducing the flow rate leads to an increase in the concentration of alkali and acid. The longer the sodium sulfate solution remains in the electrolysis chambers, the higher the concentration of the obtains alkali. At the same time, although increasing the current intensity and voltage allows to achieve an increase in the thickness of the products, the rise of these parameters is not considered favorable, since the increase in the current strength has a negative effect on the quality of the membranes

Production of metallic magnesium based on polymineral ores of the Kaliningrad-Gdansk salt basin

Purpose of the work. Rational subsurface use implies the most complete and comprehensive development of mineral reserves. In this regard, the aim of the study is to determine the possibility of obtaining metallic magnesium from the ores of the Kaliningrad-Gdansk salt basin, along with planned potassium sulfate and magnesium sulfate production. Methods. In the course of the study, ore samples were selected, the existing technologies of polymineral (kainite, carnallite and kizerite) ore processing are analyzed, a technological process for obtaining metallic magnesium from the available ore raw materials and by-products of the main production was developed, tests were organized to obtain metallic magnesium by electrolytic means based on the Nivenskoye deposit ore, the quality of the obtained material was evaluated, the possibilities of creating production in Kaliningrad region based on the available raw materials were analyzed. Results. As a result of the development of raw material processing technology and laboratory tests, the possibility of obtaining metallic magnesium from polymineral (carnallite) ores of the Kaliningrad-Gdansk salt basin has been established. At the same time, it was revealed that the production of magnesium by the electrolytic method is complicated by the presence of a high concentration of sulfate ions in the initial processed raw materials, which requires the inclusion of the desulfatization stage in the technological process. Conclusions. Natural carnallite ores of the Kaliningrad-Gdansk salt basin, as well as the obtained by-products arising during the main technological process (production of potassium sulfate), can be used for the production of high-quality metallic magnesium according to GOST 804–93 quality level. The results of the study make it possible to develop the natural resources of the polymineral ores of the Kaliningrad-Gdansk salt basin in the most comprehensive way, obtaining a wide range of products, including metallic magnesium.

Extractive Metallurgy and Chemistry

In recent years, the proper management and recycling of metallurgical waste have become increasingly important due to their significant environmental impact and the potential for the recovery of valuable metals in order to save natural resources [...]

The relationships between the kinetic grinding parameters with interstitial fillings and the liberation degree of a chromite ore

In this study, the relationships between the liberation degree and the kinetic breakage parameters of a chromite ore obtained from the Burdur (Türkiye) were examined under the laboratory conditions. Firstly, liberation degrees for chromite particles were determined by the particle counting method in a metal microscope for 4 different size groups. Secondly, the breakage parameter of chromite ore which was dry ground with a ball mill was obtained using standard test methods. Additionally, the model parameters were also determined for the fractional interstitial fillings (U) of the chromite sample. Thirdly, the kinetic grinding parameters were compared with the liberation degree of the chromite sample. As a result of the tests, a very good correlation was obtained with R2=0.998, and regression analysis in the grinding processing of the chromite ore was used to verify the validity of the relationship parameter of Si that was produced. To these, it was found that interstitial fillings (U=0.6, 0.8, 1.0, and 1.2) have an effect on the grinding.

An investigation into the dry processing of low specific gravity ores using a laboratory Knelson concentrator

ABSTRACT The Knelson concentrator (KC) was originally invented and developed for treating gold ores, and due to its high efficiency, low cost and minor environmental impact, it has become an active research area for processing low specific gravity (SG) deposits. The laboratory scale KC has shown its potential for processing high-density ores on a dry basis. This work investigated the feasibility and the optimum operating conditions when processing a dry low SG feed with a modified KC. A synthetic mixture of magnetite (SG 5.2) and quartz (SG 2.65) with a grade of 1% magnetite and three synthetic mixtures of magnetite and quartz with a grade of 5% magnetite in different sizes were used to mimic a low-density ratio ore. Central composite design (CCD) and response surface method (RSM) were used to design the experiments and optimise each process. The effects of each individual factors and their interactions on concentrate grade and magnetite recovery were evaluated for each feed. Optimum operating conditions were obtained at a bowl speed, solids feed rate and air fluidising pressure of 20G, 100 g/min and 12 psi, for 1% grade feed; 14, 300 g/min and 13 psi, for 5% coarse feed; 18 G, 300 g/min and 13 psi, for 5% intermediate feed; and 10 G, 100 g/min and 14 psi for 5% full-size feed.

Remediation of Cr(VI)-contaminated soil mixed with chromite ore processing residue by ferrous sulfate and enzyme residue

In this study, Cr(VI)-contaminated soil mixed with COPR by using ferrous sulfate (FeSO4), enzyme residue (ER), and their combination under aerobic or anaerobic condition were investigated. The concentration of Cr(VI) decreased from 1498.05 to 104.63 mg kg−1 after the simultaneous addition of FeSO4 (30 %, w/w as FeSO4·7H2O) and ER (30 %, w/w) at 45 d under the anaerobic condition with a reduction efficiency of 93.02 %, which is higher than that by single FeSO4 (72.39 %) or ER (75.47 %) under the anaerobic condition. XRD, XPS, FTIR, and fluorescence spectroscopy were conducted to characterize soil and ER composition. Metagenomic analysis was performed to reveal the reduction mechanisms of FeSO4 and ER. The anaerobic condition with lower Eh was beneficial for Cr(VI) reduction than aerobic condition, and Eh was the main driver for the evolution of Cr(VI) reduction-related microorganisms. Moreover, the addition of ER enriched the organic matter and microbials in the soil. During the decomposition of organic matter under the anaerobic condition, organic acids were generated, leading to a decrease in pH and promoting the release of Cr(VI) from minerals. They also served as electron donors in Cr(VI) reduction. Additionally, the addition of excess FeSO4 stimulated the growth of iron-reducing bacteria and sulfate-reducing bacteria, facilitating to Cr(VI) reduction. Metagenomic analysis showed that Acinetobacter, related to the nemA and nfsA genes, was the dominant Cr(VI) reduction genus. Thus, the combination of FeSO4 and ER is a promising method for the remediation of Cr(VI)-contaminated soils mixed with COPR.

URANIUM MINING AND MILLING SITES AS SOURCES OF TECHNOLOGICALLY-ENHANCED NATURALLY OCCURRING RADIOACTIVE MATERIALS

Data on the uranium deposits database for the identification of radioactive material and sources of natural radiation within the Ukrainian Crystalline Shield are provided. The territories of uranium ore mining and processing are considered from the point of technologically enhanced naturally occurring radioactive materials view according to the proposed classification of uranium legacy sites. Measures to refer the uranium mining and processing sites to the “legacy” category of Ukraine are presented.