Tailings Material Research Articles

Characteristics of Deposited mine tailing on the Senunu Canyon, Indonesia

The characteristics, distribution, and accumulation of detrital sediment on the surface sediment in the Senunu Sea are used as a preliminary study to identify the detrital and sedimentation processes’ origin. This study aims to present the characters and composition of detrital sediment on Senunu seabed. It illustrates the influence of land sediment sources on sediment compositions settled on the bottom of the surrounding seas. Specific review on the sediment character in this region was done to identify surface sediment layers carrying tailings materials from ore mining on land and differentiate them from natural sediment. 53 sediment core from the Senunu bottom were collected and analyzed for their detrital characteristics using a binocular microscope. In general, sediment composition in Senunu seabed was terrigenous sediment with dominant material quartz, andesite, and tuffaceous breccia. Based on the detrital analysis, sediment lithology of natural seabed sediment and sediment containing tailing material is distinguished by color, layer contact, grain packing, grain shape, biota association, and specific mineral content quartz, mica, and magnetite. Surface sediment containing tailing material had more quartz mineral, had more similar grain size and crystal shape, fresher mineral condition, clearer color, and looser grain relation than seabed sediment that did not contain tailings material.. Based on the different characters and distribution patterns, sediment carrying tailings in the Senunu seabed. Based on the other characters and distribution patterns, sediments carrying tailings in the Senunu seabed on average were 2-167 centimeter thick at the surface with accumulated tailing 1-50% of total sediment at the sea bottom. Furthermore, the distribution of these tailing deposits is influenced mainly by morphodynamic, hydrodynamic conditions and the process of redeposition.

Effect of Land Reclamation on Soil Properties, Mineralogy and Trace-Element Distribution and Availability: The Example of Technosols Developed on the Tailing Disposal Site of an Abandoned Zn and Pb Mine

Land reclamation is a common practice leading to the restoration of areas affected by industrial activity. Soil studies in reclaimed areas are very useful to determine the effectiveness of reclamation works. The goal of the study was to investigate soil properties, mineral composition, total concentrations of Zn, Pb, Cd and As and chemical forms of these elements in order to assess the success of land reclamation of the abandoned mine tailing disposal site of the “Trzebionka” Zn-Pb mine in Trzebinia, southern Poland. The disposal site was reclaimed by covering tailings with a layer of inert material with a thickness up to 25 cm. The topsoil of the studied soil profiles was comprised of sandy loamy/loamy materials and the subsoil was comprised of sandy tailing materials. The soils were characterized by a neutral or slightly alkaline reaction due to the high content of carbonates. The dominant mineral in the subsoil was dolomite. The studied soils were considerably contaminated with Zn, Pb, Cd and As. A high load of mobile Zn, Pb and Cd was typical of the subsoil material. The reclamation layer does not provide sufficient isolation of toxic tailings from the environment and there is still a high risk of element uptake by plants.

Effect of fine particle content on mechanical properties of tailings under high confining pressure

The influence of dam height and fine grain content on the stability of the tailings dam is not a simple function. According to the layering rules of ultra-fine tailings in deep and large tailings ponds, four kinds of fine-grained (particle size less than 0.074 mm) tailings materials were prepared. Simulation of the physical and mechanical properties of ultra-fine tailings during the accumulation of high tailings dam was conducted. The optimal tailings mix ratio was determined through multi-physical index experiments and multi-evaluation index analysis. Multi-stage confining pressure triaxial shear failure test was conducted using TSZ-6A strain-controlled triaxial apparatus to recur the change law of mechanical properties of tailings based on large amounts of experimental data. Through high-precision laser particle size analysis and analysis of pore water pressure at full pressure, intrinsic influence factors and mechanism of physical and mechanical properties from the perspective particle fracture and pore water were analyzed. Finally, using elementary error theory, the method for evaluating Mohr strength parameter of tailings materials was modified, and the factor that caused confining pressure to change the structure of the material was taken into account.

Influence of particle size scale on mechanical properties of tailings under high pressure

Particle size has an effect on the mechanical properties of tailings materials. The mechanics and crushing characteristics of tailings at high pressure are a research focus for high tailings dams. Tailings with different particle sizes were tested under laboratory high-pressure triaxial compression. The effect of particle size on the compression characteristics of tailings was studied, along with the strength and deformation of tailings with different particle sizes. Based on particle size distribution, the crushing characteristics of the tailings were quantitatively analysed. A mathematical model for crushing index and tailings strength was established. Under high pressure, shearing contraction failure occurred in the tailings samples. The stress–strain relation of the tailings showed strain softening at low confining pressure and continuous hardening at high confining pressure. The confining pressure at which the stress–strain relation changed from strain softening to strain hardening increased with increased particle size. Due to the higher degree of particle crushing for coarse tailings during the shearing under high pressure, the volume deformation of the coarse samples decreases continuously further. It shows increase in the amount of particle breakage as the confining pressure, but the increase rate decreased with the confining pressure increased. The Box Lucas loading accumulation model was used to describe the change in particle breakage with confining pressure. The peak strength of tailings increased exponentially with the improved relative crushing rate.

Study on the physical and mechanical properties of bauxite residue by laboratory and field in-situ tests

The determination of physical and mechanical properties of bauxite residue plays an important role on the stability assessment of tailing disposal dams. This paper studies the composition, physical properties, shear strength, and bearing capacity of bauxite residue by laboratory and field in-situ tests. The bauxite residue near the discharge point are mainly coarse particles, and the size of particle far away from the reservoir shows a decreasing trend. Through X-ray diffraction, the composition of bauxite residue is analyzed: the tailing material are mainly composed of seven main crystalline materials containing aluminum, iron, titanium, and silicon. The variation of water content with depth is measured by field tests; the water content distribution shows obvious stratification characteristic and sudden change occurs between layers. The shear vane tests show that the shear strength at a depth of more than 5 m is much larger than the material in the shallow layer close to the surface. Through dynamic penetration tests, the stratum can be categorized according to the distance from the discharge point. The bearing capacity of the soil layer close to the edge area is higher than that in the center of tailings pond. The bauxite residue shows anisotropic behavior and the mechanical property varies along horizontal and vertical directions.

Study on the oxidation and acidification characteristics of the sulfur-containing tailings material

For studying the mechanical properties of sulfur-containing tailings material in the acidification environment, the tailings material was soaked in H2O2 solution with different concentrations to simulate the oxidation and acidification of the tailings with different accumulation history. The change laws and mechanisms of its mechanical properties after oxidation and acidification were discussed, and through the PFC (particle flow code) mesoscopic discrete element analysis method, the connection between mesoscopic particles and its macroscopic properties was established. The experimental results show that the chemical immersion tests on tailings materials with a certain ratio of hydrogen peroxide to concentrated sulfuric acid can well simulate the joint action of oxidation and acidification, so as to simulate the tailings with different accumulation history. Under the action of oxidation and acidification, the physical and mechanical properties of tailings material are mainly affected by the particle size and contact characteristics. The angle of internal friction decreases, influenced by the reduction of particle size, while the change of cohesive force is greatly correlated with both of the two factors. The shear modulus under different porosity and friction coefficients is basically the same, but the increase of porosity or the decrease of mesoscopic particle friction coefficient will greatly weaken its shear capacity, that is, its mesoscopic particle compactness and contact characteristics have an important impact on the macroscopic mechanical properties of tailings.

A study on the mechanical behaviour of three different fine-grained mine tailings

Mine tailings stored in the tailings storage facility (TSF) are normally loose and failure-prone for several reasons, such as liquefaction, erosion, overtopping, piping, and high excess pore water pressure (PWP). The investigation of the mechanical behavior of tailings material is essential for engineering design and safety evaluation of the TSF during mining operations, closure, and rehabilitation. As such, laboratory compaction, consolidation, and direct shear strength experiments are carried out on three different fine-grained mine tailings, named coal tailings (CT), red mud (RM), and gold tailings (GT). Compared to CT and RM, GT showed higher dry density at the optimum moisture content (OMC) and lower compressibility. The permeability of GT is similar to RM but much higher than that of CT. CT and GT showed the highest cohesion and angle of internal friction, respectively, among the tested materials. The direct shear test, among all the methods used, provided the highest dry density and lowest void ratio. The final state parameters obtained in compaction, consolidation, and direct shear tests are critically compared, which is the novelty of this study. This research explored useful information on the geotechnical properties of different tailings that can help mining operators and researchers effectively design and manage the tailings in the TSF.

Geochemical changes of Mn in contaminated agricultural soils nearby historical mine tailings: Insights from XAS, XRD and, SEP

Manganese is ubiquitous in nature and essential for some metabolic reactions, but also it is present in the environment as a product of anthropogenic activities. Despite evidence linking high concentrations of Mn to several diseases, it is not commonly considered during environmental risk assessment of soils. Changes in chemical forms, oxidation state, and speciation of Mn in impacted agricultural soils by historical mine tailings in central Sonora in northwestern Mexico were studied using X-ray Absorption Near Edge Spectroscopy (XANES), X-ray Diffraction (XRD), and Sequential Extraction Procedures (SEP) techniques. Mn concentrations ranged from 1093 to 2919 mg·kg−1 in these soils, which exceeded the local geochemical background by up to six-fold. According to SEP, the tendency found in agricultural soils was reducible (42–66%) > soluble and exchangeable (16–42%) > residual (5–22%) > oxidizable (4–24%). In contrast, the tendency in sulfide-rich tailings samples was soluble and exchangeable (47–49%) > residual (35–41%) > oxidizable (5–11%) > reducible (5–7%), and in oxide-rich materials was residual (21–79%) > soluble and exchangeable (1–30%) > reducible (1–45%) > oxidizable (2–15%). The considerable percentage of the soluble forms indicated the potential of mobilization and availability to exposed organisms. No Mn-bearing mineral phases were identified with XRD, which suggested that manganese was mostly found in low-crystalline forms. XANES measurements indicated that the oxidation state of Mn in agricultural soil samples varied from Mn2+ through Mn4+. Conversely, the main oxidation state in mine tailings samples was Mn2+. Substantial changes were detected in Mn XANES spectra in the whole sample and residues left from SEP in agricultural soils, which confirmed the presence of all chemical forms (e.g., soluble and exchangeable, reducible, oxidizable, residual). A well-defined structure spectrum was obtained in soils once low crystallinity species and/or organic compounds were removed, which was similar to that acquired for mine tailings, suggesting mobility from tailings deposit to agricultural soils. Substantial contribution of compounds with mineral structures like birnessite (((Na, Ca, K)0.6(Mn4+, Mn3+)2O4·1.5H2O) and minor contributions of hausmannite (Mn3O4), spessartine (Mn3Al2(SiO4)3) and szmikite (MnSO4) were identified by Linear Combination Fitting (LCF) in soils, whereas the significant contribution of structures like hausmannite and spessartine, and minor contributions of rhodochrosite were found in tailings material. An LCF analysis in residues from SEP also suggests that the chemical species involved in the Mn mobilization were scachite and szmikite. In general, the results obtained indicate that leaching processes favored the presence of chemical species of Mn with a considerable potential of mobility and toxicity in agricultural soils interacting with historical mine tailings in central Sonora.

Investigation of the solubility of dust particles in soil solution at different temperatures (on the example of the tailings of the loparite ores' concentration)

A number of large mining enterprises are located on the territory of the Murmansk region. Dusting overburden dumps and tailings storage sites leads to a complex of long-term consequences for the environment. The output of the silty fraction (-0.071 mm) of "stale" tailings of loparite ore dressing (the first field of the tailing dump) is about 22 %. The investigated material is represented by nepheline, microcline, aegirine; loparite, analcime are diagnosed in impurity quantities; the average content of cerium, lanthanum, neodymium - rare earth elements of the light group - 0.18, 0.03 and 0.015 %, respectively. In laboratory conditions, a simulation of the ingress of a fine fraction of loparite ore dressing tailings into the soil has been carried out; the interaction of tailings material with distilled water and water extract from conditionally background soil at different temperatures has been studied. In the course of the study, it has been found that the introduction of dissolved organic matter intensifies the processes of destruction and partial dissolution of the aluminosilicate matrix of rock-forming minerals; an intensive transition of rare earth elements and heavy metals into soluble forms has been recorded. The research results indicate the ecological danger of the finely dispersed material of "stale" tailings of loparite ore dressing due to the ingress of dust particles into the soil and their interaction with soil waters.

Use of iron mine tailing as fillers to polyethylene

The iron mine tailings accumulation in dams is an environmental and economic problem. The composite based on high-density polyethylene/iron mine tailing production for the application of wood plastic and some items of domestic plastic industry can be a good alternative to reduce the rejects in the environment. This work presents the influence of the processing methodology in the mechanical, thermal and morphological properties of composites based on the high-density polyethylene/iron mine tailing. Four methodology processing by continuous and/or batch mixing were available. The iron mine tailing particles in the polymer matrix promoted an increase in mechanical strength and thermal stability. Besides, the particles acted as flame retardant. The iron mine tailing materials produced using batch mixing showed more significant modifications in the properties due to the better dispersion of the filler as shown by scanning electron microscopy.

Geo-electrical characterization of physical and mechanical properties of zinc tailing

In the present study, an attempt is made to characterize the tailing material using the electrical resistivity method through a series of laboratory experiments. Tailing materials are a by-product of the metal extraction industry, which are usually disposed off in the form of slurry to the disposal area surrounded by tailing impoundment. Nowadays, a large amount of water is removed through the filtration process, and dry stacking of tailing is followed. Effect of various basic (physical) geotechnical properties on the electrical resistivity of compacted tailing material is investigated using fabricated soil resistivity box based on four-electrode method (ASTM G57–20). To establish the correlation between electrical resistivity and permeability, measurements were made using modified rigid wall falling head permeameter at different densities. Triaxial shear tests, i.e., consolidated undrained (CU) test and consolidated drained (CD) tests were conducted on zinc tailings specimens to study the evolution of electrical resistivity with stress-strain and effective shear strength parameters (c’ and ϕ’) using customized triaxial cell. The present study can be useful for the estimation of in-situ soil properties using electrical resistivity measurement, which will help to understand the engineering properties of the compacted tailings and thus prevent failure of tailing dams.

Incorporation of sulphidic mining waste material in ceramic roof tiles and blocks

The demand for building and construction materials increases as the world population keeps growing, thus increasing the need of shelter, as a basic human need. This increasing demand for building and construction materials not only leads to higher demand for primary raw materials, such as clay or sand, but also to higher emissions of carbon dioxide that contribute to the greenhouse effect, leading us to the biggest and ongoing threat to life on earth: global warming. The potential use of secondary raw material sources, such as mining waste, in building and construction products not only minimises the ecological footprint of this sector but also minimises the pressure on the primary raw material sector, hence fostering the transition towards a more resource efficient and sustainable world. The goal of this study is to evaluate the potential use of uncleaned sulphidic mining tailing material from two inactive Pb-Zn (Plombières, Belgium) and Cu-Zn-Pb (Freiberg, Germany) mines, and uncleaned sulphidic mining waste rock material from an active Cu-Zn mine (Neves-Corvo, Portugal), in ceramic roof tiles and blocks taking into account production parameters (shaping, drying, and firing processes), product quality (technical, aesthetical, and chemical properties) and environmental compliance of secondary raw materials for use as building products. After a detailed physical, mineralogical, chemical, and thermal characterisation of the materials, blends for ceramic roof tiles and blocks were made by partly or totally replacing some primary raw materials (mainly clay and sand) by 4 different mining waste materials. Roof tile and block blends containing 5 wt% and 10 wt% mining waste materials, respectively, were produced on a lab scale. The required technical, aesthetical, and chemical properties for each ceramic product were evaluated. Freiberg tailing and Neves Corvo waste rock materials presented considerable amounts of sulphur and metal(loid)s. Moreover, technical, aesthetical, and chemical properties of the blends using these mining waste materials were not satisfying and the Neves Corvo waste rock materials have the disadvantage of needing a mechanical treatment (grinding and sieving) before integrating them into the ceramic blends. Therefore, the Freiberg tailing and both of the Neves Corvo waste rock materials are less suitable to replace primary raw materials in ceramic roof tile and block blends, even in smaller amounts (5 wt% and 10 wt%, respectively). In contrast, the Plombières fine tailing material was characterised by a low sulphur and metal(loid) content, as well as satisfying environmental performance. The roof tile and block blends, in which the Plombières tailing material was integrated, showed satisfying technical, aesthetical, and chemical properties. Consequently, the Plombières tailing material can be considered as the best fit to partly or totally replace primary raw materials in both ceramic roof tile and block blends.

Contamination, sources and environmental risk assessment of heavy metals in water, sediment and soil around an abandoned Pb mine site in North East Morocco

Metal Mining Contamination is a widespread problem in the world. However, the assessment of abandoned mine metal contamination, especially in Morocco, has not been studied sufficiently. In this study, a total of 83 samples of water, sediments, and soils were collected to investigate the concentrations of heavy metals (HMs) around an abandoned mining area, named: Zeida in North East Morocco. Furthermore, geochemical mapping of these elements has been also conducted. The contamination and environmental risk introduced by the accumulation of HMs has been assessed using numerous ecological indexes, such as: geo-accumulation (Igeo), Potential Ecological Risk Index and Modified Contamination Degree (MCd) to name just a few. Add to that the assessment of water quality using water quality assessment indexes. The results showed that all major elements and HMs of the river and its tributaries were within the Guidelines for Drinking-Water Quality (GDWQ), except for levels of HCO3−, and K+. The hydrochemical facies was dominated by calcium magnesium bicarbonate (CaMg–HCO3), and the concentrations changed in the range (µg/l): Zn: 14.78–152.00, Cr: 2.56–13.23, Cu: 0.96–12.35, Pb: 0.03–11.26, As: 0.98–3.24, Ni: 0.11–1.34 and Cd: 0.01–0.31, respectively. The spatial distribution of HM concentration and numerous ecological indexes in soil and sediment samples revealed that the highest values were located in and near the tailings, and declined downstream, which classified these sites as very highly contaminated and severely hazardous. Vertically, the soil concentration of HMs accumulated increasingly in relation to depth, and that in fact highlighted their potential mobility. HM concentrations (mg/kg) in sediments were in the range of: Pb: 43.79–9889.30, As: 104.57–289.00, Cr: 25.84–125.00, Zn: 40.78–121.75, Cu: 8.85–36.11, Ni: 1.99–21.00 and Cd: 0.10–0.46, respectively. While the average concentration in the three depths of soil (mg/kg) were in the range of: Pb: 27.00–11,400.00, Zn: 36.00–231.33, As: 42.33–172.00, Cr: 21.67–105.33, Cu: 18.33–143.33, Ni: 13.67–40.33 and Cd: 0.04–1.33, respectively. Multivariate statistical analysis indicated that HMs were related to the dispersion of tailings materials, with the exception of Ni and Cr which were related to lithological source.

On the effect of void ratio and particle breakage on saturated hydraulic conductivity of tailing materials

Particle size of tailings in different areas of dams varies due to sedimentation and separation. Saturated hydraulic conductivity of high-stacked talings materials are seriously affected by void ratio and particle breakage. Conjoined consolidation permeability tests were carried out using a self-developed high-stress permeability and consolidation apparatus. The hydraulic conductivity decreases nonlinearly with the increase of consolidation pressure. The seepage pattern of coarse-particle tailings is channel flow, and the seepage pattern of fine-particle tailings is scattered flow. The change rate of hydraulic conductivity of tailings with different particle sizes under high consolidation pressure tends to be identical. A hydraulic conductivity hysteresis is found in coarse-particle tailings. The hydraulic conductivity hysteresis is more obvious when the water head is lower. A new hydraulic conductivity-void ratio equation was derived by introducing the concept of effective void ratio and breakage index. The equation integrated the hydraulic conductivity equation with different particle sizes over a wide range of consolidation pressures.

Pengembangan Media Pembelajaran Boneka Tangan Mata Pelajaran Bahasa Indonesia Materi Menyimak Dongeng Pada Siswa Kelas II Sekolah Dasar

AbstractThe lack of teaching effectiveness in teaching learning activity made students felt bored easily and noisy in the classroom. To resolve that problem needed teaching media used in learning process, one of them was puppet that developed as learning media completed with the stage to show the location of the story. This medium was used for understanding fairy tale material to intermediate grade 2. This writing used the development of Addie model (analysis, design, development, implementation, and evaluation). According to this unable condition to do a research, so this research ended in validity step as a measurement of worthiness using puppet medium for understanding fairy tale material. The worthiness of the validity media result was 94%, whereas validity material result in the first validator was 88,3% and the second was 86,6%. According to that validity result, we could conclude that teaching media using puppet could be used for understanding fairy tail material for intermediate grade 2. Keywords: media development of hand puppets, Indonesian language learning, listening to fairy tales.

Geochemical and Mineralogical Characterisation of Historic Zn–Pb Mine Waste, Plombières, East Belgium

Mine wastes and tailings derived from historical processing may contain significant contents of valuable metals due to processing being less efficient in the past. The Plombières tailings pond in eastern Belgium was selected as a case study to determine mineralogical and geochemical characteristics of the different mine waste materials found at the site. Four types of material were classified: soil, metallurgical waste, brown tailings and yellow tailings. The distribution of the mine wastes was investigated with drill holes, pit-holes and geophysical methods. Samples of the materials were assessed with grain size analysis, and mineralogical and geochemical techniques. The mine wastes dominantly consist of SiO2, Al2O3 and Fe2O3. The cover material, comprising soil and metallurgical waste is highly heterogeneous in terms of mineralogy, geochemistry and grain size. The metallurgical waste has a high concentration of metals (Zn: 0.1 to 24 wt.% and Pb: 0.1 to 10.1 wt.%). In the tailings materials, Pb and Zn vary from 10 ppm to 8.5 wt.% and from 51 ppm to 4 wt.%, respectively. The mining wastes comprises mainly quartz, amorphous phases and phyllosilicates, with minor contents of Fe-oxide and Pb- and Zn-bearing minerals. Based on the mineralogical and geochemical properties, the different potential applications of the four waste material types were determined. Additionally, the theoretical economic potential of Pb and Zn in the mine wastes was estimated.

Bioleaching for detoxification of waste flotation tailings: Relationship between EPS substances and bioleaching behavior

The production of large volumes of waste flotation tailings results in environmental pollution and presents a major ecological and environmental risk. This study investigates bioleaching of waste flotation tailings using Acidithiobacillus ferrooxidans. The experiments were performed with 5.00% solid concentration, pH 2.0 with 100 mL medium for 25 d in the lab. The pH, OPR, metal concentration, dissolved organic matter (DOM) in leachate and extracellular polymeric substances (EPS) were recorded. Bioleaching tailing materials were finally characterized. Results showed that microorganisms, acclimating with mine tailings, effectively accelerated the bioleaching process, achieving maximum Zn and Fe extraction efficiencies of 95.45% and 83.98%, respectively, after 25 days. Compared with raw mine tailings, bioleaching could reduce 96.36% and 95.84% leachable Zn and Pb, and Pb presented a low risk (4.13%), while Zn, Cu, and Cr posed no risk (0.34%, 0.64%, and 0%). Toxicity and environmental risk analysis revealed bioleaching process significantly reduced the environmental risk associated with mine tailings. EPS analysis indicated that the loosely-bound EPS (LB-EPS) and tightly-bound EPS (TB-EPS) fractions contained different organic substances, which played different roles in the bioleaching process. Pearson correlation analysis revealed that EPS was highly correlated with bioleaching behavior (p < 0.05), and EPS was the main factor affecting the bioleaching process, promoting bioleaching in the LB-EPS and TB-EPS fractions.

Effects of Relative Density in Progressive Sliding of Tailings deposits: Insights from Flume Tests

We present a series of flume tests to observe the process of tailings slope failure when subjected to a concentrated water flow. Progressive flow slides were observed in a range of tailing deposits with varying relative densities, in which hydraulic conductivity reduced with increasing relative density. Slope densification by compaction of very loose or loose tailings deposits can lead to a lower permeability, generating excess pore pressure, and subsequently reducing slope stability. This is evident from the great number of acoustic emission signals before sudden failure, and from a sharp increase in the surface displacement and internal displacement observed after excess pore pressure generation. The variation of fluid-pressure distribution results in successive sliding, onset at the toe and progressing from the toe to the rear of the slope. Excess pore pressure generation is found to occur after, rather than prior to sliding, and it only occurs along the slip surface. An optimal relative density of 0.35 was identified, in which the slope failure changes from a sudden collapse to a progressive failure. However, the optimal relative density may vary with the height of the slope. This research extends existing knowledge about behavior of tailings materials, while the observed discrepancy between the failure mechanisms of slopes made of loose and dense deposits could provide insights for preventing failures of tailings dams.

Mobility of Mn and other trace elements in Mn-rich mine tailings and adjacent creek at Kanye, southeast Botswana

Mine tailings rich in Mn and an adjacent creek at Kanye, southeast Botswana, have been investigated by total decomposition of solids, X-ray diffraction, EMPA techniques, sequential extraction, and water leaching to understand binding and mobility of Mn and other trace elements. The investigation revealed weathering of tailings close to the surface of the tailings and higher concentrations of Fe compared to Mn. There also are high concentrations of Ba and Pb in the tailings solids. The principal minerals of Mn and Fe are cryptomelane, K(Mn4+, Mn2+)8O16, and hematite, Fe2O3, respectively. Most Mn is bound to less crystalline phases dissolved in the reducible step of sequential extraction, suggesting high potential for release of Mn and related trace elements. The situation is very different for Fe, which is found mostly in the residual (Aqua Regia) insoluble fraction. This is in a good agreement with high concentrations of mobilized Mn and with low concentrations of mobilized iron in the water leaching test. The order of water-leached trace elements is Ba>Zn > As>V > Cu > Co > Pb where trace elements bound in Mn-oxyhydroxides are preferentially mobilized. In particular, As and V may represent a potential risk for the environment during rainy periods when mine tailings are probably flooded, and tailings material is transported by water in an ephemeral creek. Currently, sediments in the creek are contaminated at least to the boundaries of the Kanye settlement and they can be a source of groundwater contamination during the rainy period. Another possible source of contamination is wind transport and settling of dust particles from mine tailings with resulting ingestion when local farming products are consumed.

Combining zinc desorption with EXAFS speciation analysis to understand Zn mobility in mining and smelting affected soils in Minas Gerais, Brazil

Zinc contents exceeding regulatory levels have been documented in several areas in Brazil and elsewhere, especially in sites surrounding mining and smelting sites. Studies involving Zn release and speciation are keys to assess the mobility and bioavailability and thus the potential ecological risk of this element. This study evaluated Zn desorption and speciation from soils affected by mining (soils from a mine area, classified as Technosols) and smelting (mine tailing) activities in Brazil with high total Zn contents, ranging from 1.8 to 8.2%, using a stirred-flow approach and synchrotron-based X-ray absorption spectroscopy (XAS), in order to better assess Zn availability and mobility in these environments. The exchangeable fraction, extracted by 0.1 M CaCl2 solution, represented only a small (<0.5%) portion of the total Zn from soils of the mining site, while accounting for ~80% from tailings of the smelting site. In the mine area, X-ray absorption fine structure (XAFS) showed that Zn was associated with hemimorphite, Zn-ferrihydrite, Zn-phyllosilicates (Zn-kerolite), and Zn-layered double hydroxides (Zn-LDH); this is the first time these Zn precipitate/sorbed forms have been detected in Brazilian mining soils, which have been exposed to tropical conditions. The formation of these insoluble phases of Zn could explain the low Zn desorption from these soils, taking into consideration that Zn-ferrihydrite, Zn-kerolite, and Zn-LDH can lead to a significant decrease of the exchangeable/mobile fraction of Zn in soils. The higher amount of Zn desorbed (⁓80%) from the tailing material located in the smelting site could be attributed to the predominance of weakly bound forms of Zn (~70%). These findings were also seen by analyzing the Fourier Transform (FT) and Wavelet Transform (WT). This study has shown that combining EXAFS analyses with desorption extraction is relevant to better understand Zn mobility and how it is related to Zn speciation.