Open-access Mobility assessment of potentially toxic elements contained in flotation and cyanidation tailings dam from gold mine located in Brazil

Abstract

In Brazil, the recurring environmental impacts due to insufficient inspection and inadequate management of potentially toxic mining tailings have raised significant concerns. The study concentrates on examining the mobility of elements in flotation (ft) and cyanidation (ct) tailings from gold mining operations, following successive extractions. The influence of extractants on the release of elements from both ft and ct samples, including As, Cd, Cu, Cr, Pb, Se, and Zn, was examined and compared to the ABNT NBR 10004:2004 standard. The samples were obtained from a gold mining company in Brazil. Sequential extraction tests for ft and ct samples were conducted to simulate weathering effects, using solutions of 0.1 mol L-1 citric acid, 0.1 mol L-1 acetic acid, 0.1 mol L-1 oxalic acid, 0.1 mol L-1 ammonium acetate, and distilled water at pH 5.5. The results revealed that the established limits for Pb and Cd under the ABNT NBR 10004:2004 standard were exceeded in a 1:1 tailing-to-extractor ratio. In ct samples, both elements surpassed the standard limits for all extractors, except for Cd when using water. In ft samples, Pb exceeded the limits with all acids, while Cd exceeded the limits only in the presence of acetic acid and ammonium acetate.

Key words gold mining dam; environmental risk; successive extractions; sulfide minerals; mobility of elements

INTRODUCTION

Anthropogenic processes, particularly mining activities for iron, lead, gold, and nickel, have led to increased concentrations of potentially toxic elements (PTEs) in Brazil. These elements, associated with sulfide minerals like arsenopyrite, pyrite, sphalerite, and galena, can pose significant environmental risks when released from mining tailings. The tailings from gold extraction processes, such as flotation and cyanidation, are typically deposited in dams, which can lead to serious environmental issues if not managed properly. The beneficiation steps in these processes enhance the mobility of PTEs, increasing the risk to local ecosystems (Kusin et al. 2019, Helser et al. 2022, Cesar et al. 2022).

According to the World Gold Council (Metals Focus), Brazil was the 8th largest gold producer in 2020, with approximately 107 tons of commercial gold. Dias et al. (2022) noted that of the 105 primary and secondary gold mining tailings dams in Brazil, about 46% pose environmental risks. The potential damage from these dams is significant; in the event of a rupture, both environmental reserves and cities could be affected, depending on their location. Seven dams are classified as having a high risk of structural and operational failure, with three located in the state of Minas Gerais (Dias et al. 2022).

Incorrect disposal of tailings can result in floods, spills, and environmental disasters if containment fails, spreading contaminants to soil and water systems (Marshal 2018, Buch et al. 2020). Over time, weathering can leach these elements into the environment, raising their concentrations to harmful levels for organisms (Fashola et al. 2016, Barcelos et al. 2020). The oxidation state of these elements influences their mobility, bioavailability, and toxicity, affecting environmental conditions (Barcelos et al. 2020, Xie & Zy 2020, Cesar et al. 2022).

Given the environmental and health risks posed by PTEs, it is crucial to understand the composition of tailings and the variation of physical and chemical parameters. The Brazilian standard ABNT 10004:2004 (2004a) sets maximum limits for the concentration of elements in leachates, classifying waste as toxic when these limits are exceeded. In scenarios of dam failure, tailings mix with soil, potentially increasing the mobility of metals due to environmental factors such as soil type, organic matter content, vegetation, and water quality.

The mobility of PTEs can be assessed using sequential or single extraction protocols. Sequential extraction methods simulate different chemical environments to determine how elements are bound to the matrix, using methodologies like the Tessier and BCR methods (Marin et al. 1997, Tessier et al. 1979, Barcelos et al. 2020).

The Tessier method evaluates the distribution of metals in different fractions of soils and sediments across five stages, representing the various forms of metal binding in the samples. In contrast, the BCR method assesses the mobility of metals in soil, sediment, and soil waste samples using four distinct fractions (Soylak & Turkoglu 1999, Soylak et al. 2016). Although the reagents used in these methods are differ in concentration. The objective of these reagents is to extract specific metals from the samples: fraction 1 targets exchangeable metals, fraction 2 targets acid-soluble metals, fraction 3 targets reducible metals, and fraction 4 targets oxidizable metals. Fraction 5, corresponding to the Tessier method, aims to extract metals that were not extracted in the previous fractions, thus not utilizing a specific reagent (Marin et al. 1997, Tessier et al. 1979, Barcelos et al. 2020).

Simple extraction methods, using a single step with various extractors, provide information on the mobility of elements under simulated environmental conditions (Pérez-Sirvent et al. 2018). Several extractors with diverse physicochemical characteristics can be employed to obtain the fractions extracted in the simple extraction protocol, including solutions of CaCl2, Ca(NO3)2, NaNO3, NH4NO3, NH4OAc, MgCl2, HOAc, EDTA, NH4OAC and diluted acids as HCl, HNO3, and mixture as EDTA + NH4OAc + HOAc and also water as an extractor (Meers et al. 2007, Tasić et al. 2016).

In recent studies, the environmental impacts of mining tailings are being evaluated to assess contaminated scenarios and promote mitigation actions. Bioavailability is considered crucial in estimating the potential risk of contaminants (Barcelos et al. 2020, Buch et al. 2020, Mngadi et al. 2020).

This research investigates the release of elements weakly associated with gold mining tailings using acidic, basic, and neutral extractors in a simple extraction protocol. This protocol simulates environmental disaster conditions, evaluating the mobility of PTEs and estimating ecological and human health risks. The study also includes chemical characterization by ICP OES and mineralogical characterization by scanning electron microscopy (SEM) to understand the association of elements in the tailing’s matrices.

MATERIALS AND METHODS

Sample

This research was carried out with representative samples obtained from the tailings dam of the flotation (ft) and cyanidation (ct) processes of the gold ore industry, located in the Midwest region of Brazil. The information of the tailings sample supplier could not provide in greater detail due to ethical issues. These samples were used in their natural state, without any previous treatment other than homogenization.

The solid sample of flotation tailing was previously homogenized in longitudinal piles until obtaining a representative aliquot of 1 kg. This aliquot was dried in an oven at 50 °C, disaggregated manually with a smooth ceramic roller until particles below 2 mm were obtained, and then homogenized in a conical and prismatic pile before being quartered, as described in Silva et al. (2017). The cyanidation tailing pulp was homogenized following the procedures outlined by Silva et al. (2017) and Barcelos et al. (2020). For the resuspension of the cyanidation tailing, water was added to this pulp in a 1:30 ratio (water to tailing pulp), and homogenization was performed with a mechanical stirrer operating at 30 rpm for one hour. After homogenization, an aliquot of 6 L was collected and placed in stainless steel trays before being dried in an oven at 50 °C. The sample was then manually disaggregated with a smooth plastic roller until particles below 2 mm were obtained, homogenized in a conical and prismatic pile, and divided into 1 kg aliquots.

Sample characterization

The mineral components of the samples were identified by X-ray diffraction (XRD), and their contents were converted into oxides by X-ray fluorescence (XRF), following the procedures outlined in Silva et al. (2017). In summary, X-ray diffraction (XRD) analysis was conducted using a Bruker-AXS D5005 instrument with Co Kα radiation (35 kV/40 mA), a goniometer velocity of 0.02° (2θ) per step with 1 s per step, and data collected from 5 to 80° (2θ). For X-ray fluorescence (XRF) analysis, samples were pressed using an automatic squeezer VANEOX (20 mm mold, P 20 ton, and t 30 s), with boric acid (H3BO3) used as a binder in a 1:0.2 proportion (0.6 g of boric acid and 3 g of dried sample at 100 °C). The contents were verified and expressed as percentages of their oxide forms through semi-quantitative analysis (Standardless Method mode) using an X-ray fluorescence spectrometer (Panalytical WDS) in AXIOS MAX mode.

Sample characterization was performed through Scanning Electron Microscopy coupled with Energy Dispersive X-ray Spectroscopy (SEM/EDS), which enabled visualization of the morphology and determination of the surface elemental chemical composition of the tailings. Scanning Electron Microscopy (SEM) was conducted using a tabletop microscope, brand HITACHI TM303 Plus. For this, the samples were fixed on a conductive adhesive surface in a Sputter coater BAL-TEC, model SCD 005, to increase conductivity for analysis by SEM. An energy dispersive spectrometer (EDS) was coupled to the electron microscope for qualitative determination of the chemical elements present in the sample.

Reagents

Solutions used in the successive extraction were prepared with analytical grade reagents and distilled water at pH 5.5. The reagents solutions were 0.1 mol L-1 citric acid (C6H8O7), 0.1 mol L-1 oxalic acid (C2H2O4), 0.1 mol L-1 acetic acid (C2H4O2), 0.1 mol L-1 ammonium acetate (NH4CH₃CO₂) solution at pH 7 and water at pH 5.5. These are supplied by VETEC-SIGMA-ALDRICH (São Paulo, SP, Brazil).

Apparatus and operating conditions

The elements were determined in an Inductively Coupled Plasma with Optical Emission Spectrometer (ICP OES) from Jobin Yvon, Ultima 2 model, with radial view plasma (Longjumeau, France) using operation parameters indicated by the supplier (Table I).

Table I
Operation parameters of ICP OES.
Successive extractions

The samples of both tailings (ct and ft) underwent successive extractions, a methodology widely used in studies aiming to evaluate the mobility of contaminants. Utilizing successive extractions in a single step allows for comparison of the different physicochemical conditions of each extractor used, which directly influences the analysis results of the various fractions obtained. This approach aims to enhance the verification of the selectivity of the extractors with respect to the extracted elements (Barcelos et al. 2020, Caraballo et al. 2018). This methodology can be likened to the initial step in the MARIN (BCR - Community Bureau of Reference) protocol and the first and second steps of the Tessier (TESSIER) protocol (exchangeable fraction and fraction soluble in weak acid), as described by the authors in their original work (Marin et al. 1997, Tessier et al. 1979).

The extraction analytical procedure, as described by Teixeira et al. (2015), is outlined in Table II. This involved transferring 5 g of the sample to a 250 mL Erlenmeyer flask containing 50 mL of extractive solutions. The extractive solutions were 0.1 mol L-1 citric acid (C6H8O7), 0.1 mol L-1 oxalic acid (C2H2O4), 0.1 mol L-1 acetic acid (C2H4O2), 0.1 mol L-1 ammonium acetate (NH4CH₃CO₂) solution at pH 7 and water at pH 5.5 to simulated. The concentration choice aimed to simulate low concentrations of these acids in the soil. The tests were conducted in triplicate to ensure method performance through repeatability. An orbital shaker model NT 155 from Novatecnica, operating at 200 rpm at room temperature (25 °C), was used. After each extraction period, the samples were allowed to settle for 2 hours. Subsequently, approximately 50 mL of the supernatant were collected and filtered through a 0.45 μm Millipore membrane. Eight successive extractions of ft and ct samples were conducted, totaling 571 hours of extraction time.

Table II
The analytical procedure of successive extractions of ft and ct samples.

Leached extracts were analyzed by inductively coupled plasma optical emission spectroscopy, according to Table I. The concentrations obtained by ICP OES were accumulated due to the extraction time.

RESULTS AND DISCUSSION

Successive extraction tests are crucial in assessing the concentration of elements available in tailings, as they can help predict long-term mobility and environmental contamination risks. The results are presented in Section 3.1, focusing on the mineral characterization of the tailings, and Section 3.2, detailing the successive extraction of elements present in the tailings.

Sample characterization: ft and ct samples

The XRD analysis revealed that the ft samples consisted of the following minerals: muscovite (KAl₂O₁₀(OH,F)2), quartz (SiO2), dolomite (CaMg(CO3)2), chamosite ((Fe2+,Mg,Fe3+)5Al(Si3Al)O10(OH,O)8) and pyrite (FeS2). Conversely, the ct samples, in addition to these minerals, also contained calcite (CaCO3), albite (NaAlSi3O8), microcline (KAlSi3O8), sphalerite (ZnS), and galena (PbS). Therefore, sulfide minerals (pyrite, sphalerite, and galena) are present in the residues, alongside minerals resulting from hydrothermal modifications such as aluminosilicates (Bidari et al. 2020, Han et al. 2020). Among the PTEs, the ct sample contains Pb and Zn, which are found in galena and sphalerite minerals, respectively. The presence of pyrite associated with gold suggests the presence of arsenopyrite, which, upon processing, undergoes oxidation and is not detected by XRD (Chryssoulis & Mcmullen 2016).

Regarding XRF, Silva et al. (2017) observed a significant content of sulfur (15.4% m/m) in the sample from cyanidation. They also verified higher contents of lead oxides (1.6% m/m) and cadmium oxides (1.8% m/m) in ft samples. This fact may be related to sulfide minerals associated with the gold present in the flotation concentrate that is sent to the second processing stage, cyanidation (Chryssoulis & Mcmullen 2016).

Microscopy images of flotation and cyanidation tailings are shown in Figures 1 and 2, respectively. Figure 1a was mapped and each colored dot represents an atom or a cluster of atoms of the analyzed sample. Wide distribution of Si and Al (Figures 1c and 1d) referring to particles with larger granules associated with quartz and a cluster of thinner particles associated with aluminosilicates predominant in ft were observed. These minerals generally constitute the gangue minerals found in gold deposits (Han et al. 2020).

Figure 1
ft photomicrographs, In (a) quartz particles and in (b), fine clay mineral particles. Mapping through EDS of elements, in (c) Si, in (d) Al, in (e) As, in (f) Ca, in (g) Mg and in (h) Fe.
Figure 2
ct photomicrographs. In (a) general vision of the sample, in (b), larger granules characteristic of quartz. Mapping through EDS of elements, in (c) Fe, in (d) Pb, in (e) S.

It is important to highlight that As (Figure 1e) is associated to Al, Ca, Mg and Fe atoms (Figures 1d, 1f, 1g and 1h), as minerals such as clays, iron and aluminum oxyhydroxides and magnesium oxides can adsorb As on their crystalline structure (O’Day 2006). This indicates a possible adsorption on the clay minerals dolomite and chamosite present in flotation tailings.

The micrograph in Figure 2a shows that ct samples has finer particles than ft samples. This fact is associated to the regrinding of the mineral concentrate after flotation, before following the hydrometallurgical process (Bragin 2018). However, in Figure 2b, larger granules associated with quartz are still observed as in Figure 1b. According to the mapping in Figures 2d and c and Pb and Fe are associated with sulfur in ct (Figure 2f), related to minerals galena and pyrite (Han et al. 2020).

Successive extractions of ct and ft samples

The extractive reagent solutions employed in this study comprised: 0.1 mol L-1 citric acid (C6H8O7), 0.1 mol L-1 oxalic acid (C2H2O4) at pH < 3, 0.1 mol L-1 acetic acid (C2H4O2), 0.1 mol L-1 ammonium acetate (NH4CH₃CO₂) solution at pH 7, and water at pH 5.5. The latter was utilized to assess the natural mobility of potentially toxic elements (PTE) (ABNT 10004:2004a, García-Lorenzo et al. 2014). Ammonium acetate extraction aimed to investigate the cation exchange capacity of organic matter in soil (Moniz 2009, Verdade 1956). Conversely, the extraction in an acidic medium simulated tailing availability in soils with high acidity, considering exposure to air, water, and chemicals (García-Lorenzo et al. 2014, Tum et al. 2022). According to García-Arreola et al. (2018), in hydrometallurgical extraction processes such as leaching, PTE exhibit a higher tendency to be solubilized in an acidic medium. Therefore, considering the extraction strength of the leaching agents employed, oxalic acid, citric acid, and acetic acid possess different acid ionization constants, specifically concerning the first deprotonation, with values of 5.6x10-2, 7.45x10-4, and 1.75x10-5, respectively (Skoog 2006).

Extraction results after 571 hours are presented in Table III, juxtaposed with the limits stipulated by the prevailing ABNT NBR 10004:2004 (2004a) standard. The table illustrates that all elements examined in this study were extracted with varying results based on the extractive solution utilized.

Table III
Results from leaching tests of ft and ct samples in comparison with maximum limits established by ABNT standard in force.

The ABNT NBR 10005:2004 (2004b) standard stipulates the criteria for obtaining leached extracts from solid tailings, utilizing analytical grade glacial acetic acid (HOAc) with a pH of 2.88 ± 0.05 as the extractive agent if the sample’s pH exceeds 5 following the stirring of 5 g of sample with 96.5 ml of deionized water for 5 minutes on a magnetic stirrer, followed by the addition of 3.5 ml of 1 mol L-1 HCl with heating at 50°C for 10 minutes. The standard’s protocol involves mixing the extracted sample with the extracting solution at a 1:20 ratio, maintaining constant agitation for 18 hours at temperatures up to 25°C, after which the solution is filtered and subjected to analysis. In order to assess the transferability of metallic substances from the tailings under study via dissolution in the extractive medium, acids with a higher degree of ionization than acetic acid, as defined by ABNT 10005:2004 (2004b), were employed.

According to the ABNT NBR 10004:2004 (2004a) standard, for ft samples, the levels of Pb exceeded the allowed limit for all acid extractive agents, and those of Cd exceeded in acetic acid, oxalic acid, and ammonium acetate solutions. Regarding ct samples, Cd levels exceeded the allowed limits in all extractors, except for water. Pb levels exceeded the allowed levels in all extractors, and As levels exceeded for citric and oxalic acid. Additionally, a higher As content was observed in the extract from ct samples with the use of oxalic acid, followed by citric acid, and higher Cd content in the extract from ft and ct samples using oxalic acid.

ABNT NBR 10004:2004 (2004a), despite having low limits for potentially toxic metals in effluents, is stricter than some international standards such as the US EPA, which establishes maximum allowed limits for Pb and As of 5 mg L-1 in the liquor leached from solid residues (US EPA 2015, US Geological Survey 2020). The levels allowed by China Water Risk for Cd (0.1 mg L-1) and As (0.5 mg L-1) are stricter than those of the aforementioned standards (China Water Risk 1996).

In the literature, there are studies on the extraction of potentially toxic elements (PTE) from tailings dams, which involve the use of acetic acid to extract samples mixed with soil. The discussions that follow were informed by a modified BCR protocol (Caraballo et al. 2018), where acetic acid serves as the extractive agent, and some parallels can be drawn with the findings of this study.

Mngadi et al. (2020) evaluated the metal contents in a soil sample following tailings handling from a gold mine in Gauteng, South Africa. They conducted leaching with 0.1 mol L-1 acetic acid for 60 minutes. The results revealed that only Bi was extracted at levels considered environmentally toxic. The permissible limits in that context are 7, 10, and 6 mg kg-1 for Pb, Zn, and Cu, respectively.

Wang et al. (2019) investigated the leaching of toxic metals in tailings from abandoned mines in Southern China, employing, among other methods, the modified BCR technique. They evaluated the leaching of tailings with acetic acid at pH 2.64 for 18 hours. The results indicated that the analyzed elements (As, Cd, Cu, Cr, Pb, Se, and Zn) exhibited mobility and bioavailability, emphasizing their relevance in assessing ecological risk.

Hence, we propose a reevaluation of the standard for classifying mining tailings from dams, incorporating studies on metal release using various extractors. These findings should be disseminated to the academic community and the public to foster a deeper understanding of contamination sources and prompt implementation of suitable remediation measures.

All elements were extracted using a successive extraction protocol, yielding varying results depending on the extractor employed. Figures 3a, b, c, d, and e display the extraction outcomes for acid extractors pertaining to the ft sample, while Figures 4a, b, c, d, e, and f illustrate the results for ct samples.

In both the ft and ct tailings, Pb, Zn, and Cu exhibited the highest solubility capacity among the metals (Figures 3 and 4). Notably, ct samples displayed higher metal extraction results compared to ft samples (Figure 4), attributed to cyanidation being the subsequent processing step after flotation, indicating greater chemical mobility of metals in ct than in ft (Burat et al. 2020). Possible equilibrium reactions involving potentially toxic metals and the acid extractor are illustrated in Equations (1) oxalic acid and (2) citric acid (Cruz-Rodríguez et al. 2022) and (3) acetic acid (Vogel 1981) where “Mn+” represents the metals Pb, Zn, and Cu.

Figure 3
Successive extraction results for the ft samples. Acid extractors: (a) acetic acid (all elements), (b) oxalic acid (Zn and Pb), (c) oxalic acid (Se, Cr, Cu, Cd and As), (d) citric acid (Zn and Pb) and (e) citric acid (Se, Cr, Cu, Cd and As).
Figure 4
Successive extraction results for the ct samples. Acid extractors: (a) acetic acid (Zn, Pb and Cu), (b) acetic acid (Se, Cr, Cd and As), (c) oxalic acid (Zn, Pb and Cu), (d) oxalic acid ( Se, Cr, Cd and As), (e) citric acid (Zn, Pb and Cu) and (f) citric acid (Se, Cr, Cd and As).
n [ C 2 H O 4 ] + M n + M [ C 2 H O 4 ] n
n [ C 2 O 4 2 ] + M n + M 2 [ C 2 O 4 ] n (1)
n [ C 6 H 7 O 7 ] + M n + M [ C 6 H 7 O 7 ] n
n [ C 6 H 6 O 7 2 ] + M n + M 2 [ C 6 H 6 O 7 ] n
n [ C 6 H 5 O 7 3 ] + M n + M 3 [ C 6 H 5 O 7 ] n (2)
n [ C 2 H 3 O 2 ] + M n + M [ ( C 2 H 3 O 2 ) n ] n m (3)

Carboxylic acids can form ionically bound soluble complexes with metals. The formation of these chelates occurs through an equilibrium reaction that depends on both ionization constants and stability constants, which can vary with the pH of the medium. At very low pH, the acid will be protonated, inhibiting complex formation, while at very high pH, the precipitation reaction may be favored (Cruz-Rodríguez et al. 2022).

Pb showed the highest extraction yield through citric and acetic acid solutions in both tailings. Meanwhile, for oxalic acid, Zn exhibited the highest extraction levels in ft (Figure 3b) and Cu in ct (Figure 4c). Zn displayed notable extraction levels in all acid extractors for both tailings.

In ft samples, Cr and As displayed elevated extraction levels in citric acid (Figure 3e), while in ct samples, Cr exhibited similar extraction levels in oxalic acid (Figure 4d) and citric acid (Figure 4f), with low levels observed for As in all acid extractors. In ct samples, acetic acid demonstrated the highest extraction capacity for Cd and Se (Figure 4b). Conversely, in ft samples, Cd showed higher extraction levels in oxalic acid and Se in acetic acid.

Some studies have reported the extraction of potentially toxic elements using acetic acid from dam samples mixed with soil. In this context, discussions were based on the modified BCR protocol (Caraballo et al. 2018), employing acetic acid as the extraction agent, allowing for comparisons with the research findings, such as the study by Mngadi et al. (2020) mentioned earlier.

Considering the ionization degree of acids, it was expected that oxalic acid would exhibit higher extractability. However, it’s noteworthy that organic acids with more carboxylic groups have a stronger extraction capacity (Suanon et al. 2016, Onireti et al. 2017), as they are prone to stabilization through the formation of 5 or 6-membered rings with metallic centers. According to Cheng et al. (2019), citric acid demonstrates the highest leaching capacity for potentially toxic metals from Fe mining tailings compared to oxalic acid. Thus, citric acid can dissolve more metal ions present in these tailings.

According to Cheng et al. (2019), mining tailings can leach, migrate, and infiltrate into the soil before being adsorbed by possible soil matrix components, underscoring the importance of tailing characterization. The authors investigated the leaching of toxic metals in tailings from abandoned mines in southern China, among various methodologies, employing the modified BCR. In this method, the first stage evaluated tailing leaching with acetic acid at pH 2.64 for 18 hours, revealing mobility and bioavailability of elements (As, Cd, Cu, Cr, Pb, Se, and Zn), pertinent for ecological risk assessment.

Figures 5a and b depict leaching results for ft samples using water and ammonium acetate extractors, respectively, while Figures 6a and b present results for ct samples, also using water and ammonium acetate extractors, respectively.

As indicated by the results depicted in Figures 5a and b and 6a and b, the accumulated amounts of extracted Pb and Zn are notably higher in ct samples for both ammonium acetate solution and water, followed by Cu in the ammonium acetate solution. These elements exhibit a cumulative progressive increase over time. However, in ft samples, the highest solubilization capacity can be observed in water for Pb and in both, water, and ammonium acetate, for Zn and Se. Additionally, Cd and Cr in ft samples were extracted in greater amounts in the ammonium acetate solution.

According to the study by Abegunde et al. (2020), in a soil sample contaminated with gold mining tailings from a region of South Africa, the amounts of metals with higher mobility—Pb and Zn in water—were 1.40 and 86.43 mg kg-1, respectively. Using an ammonium acetate solution, concentrations of Pb were 2.33 mg kg-1 and Zn 3.58 mg kg-1 were observed. In this research the maximum extracted amount of Pb (12.50 mg L-1) in ct, under the action of ammonium acetate, exceeds the maximum limit allowed for Pb (1.00 mg L-1) stipulated by the ABNT standard NBR 10004:2004 (2004a) by 12 times (Table III).

Results for non-acidic extractors revealed lower quantitative values of element extraction for both ft and ct samples compared to acid leaching. Zhang et al. (2018) evaluated the effect of Cd and Cu extracted from polluted river sediment using water. The results indicated low leaching of Cu in water (between pH 6 and 7), which was more pronounced under acidic pH. For Cd, leaching was observed in neutral media, albeit more favored in acidic conditions.

Based on Figures 3, 4, 5, and 6, it’s apparent that the solubilization of metals occurs in two stages: initially, there’s a higher concentration of elements in the extracting solution in a short period, followed by a slower rate of solubilized elements per hour. According to Pires & Mattiazzo (2007) and Sposito (1981), the processes of metal solubilization from solids first involve elements on the solid surface, primarily governed by electrostatic connections and susceptible to ionic exchanges with the solution, followed by reactions at specific sites via sorption/desorption reactions.

Figure 5
Successive extraction results for the ft samples with (a) distilled water and (b) ammonium acetate.
Figure 6
Successive extraction results for the ct samples with (a) distilled water and (b) ammonium acetate.

CONCLUSIONS

Scanning Electron Microscopy results, for both tailings, confirmed an expressive amount of Pb and Zn in the leaching processes, proving a significant presence of minerals such as galena (PbS) and sphalerite (ZnS), besides, the occurrence of clay minerals such as chamosite and dolomite, which may adsorb potentially toxic metals, as evidenced by XRD and XRF of the tailings conducted by Silva et al. (2017).

In this context, the study utilized various extractive reagent solutions, including citric acid, oxalic acid, acetic acid, ammonium acetate, and water, to assess the mobility of potentially toxic elements (PTE) and investigate cation exchange capacity in soil. The choice of extraction agents aimed to simulate conditions relevant to mining tailings in high-acidity soils and hydrometallurgical processes, considering their respective acid ionization constants. Results after 571 hours of extraction revealed varying levels of PTE extraction depending on the solution used, with some exceeding permissible limits set by standards such as ABNT NBR 10004:2004 (2004a).

Notably, the study found that Pb, Zn, and Cu exhibited the highest solubility among the metals tested, with cyanidation processes in certain tailings contributing to increased metal mobility. Equilibrium reactions with extractive agents demonstrated the formation of metal complexes, indicating the potential for leaching and migration of these metals. Furthermore, the study highlighted the importance of considering different extraction methodologies, such as the modified BCR protocol, in assessing ecological risks associated with mining tailings.

According to ABNT NBR 10004:2004 (2004a) standard and CONAMA 420 resolution (2009), the elements Pb, Cd, Zn, and Cu extrapolated the maximum concentrations allowed in ct, Pb standing out as a highly dangerous metal in gold mining tailings as its release from ct in citric acid corresponded to 20.439 mg kg-1. Regarding the successive extraction protocol, the highest release of PTE recorded occurred in ct under the action of 0.1 mol.L-1 of acid extractors (C6H8O7, C2H2O4 e C2H4O2), configuring a high solubilization in successive extraction in the first hours of extraction. This trend was observed in all other extractors used.

Results from non-acidic extractors indicated lower levels of metal extraction compared to acidic leaching, with the solubilization process occurring in two stages. Understanding the mechanisms of metal solubilization from solids is crucial for assessing environmental contamination and implementing appropriate remediation measures. The study emphasizes the need for reevaluation of current standards for classifying mining tailings and suggests disseminating findings to facilitate informed decision-making in addressing contamination sources.

Hazardousness assessment determines that if the level of only one element is above the limit allowed by the Brazilian standard (NBR) 10004, the sample is considered dangerous. In our research, in all extractors, including water, the levels of Pb in ct exceeded the maximum limits established by the Brazilian standard. It could be interesting to reassess the methodology proposed by ABNT NBR 10005:2004 (2004b) standard, to cover different acid extractors and integrate different types of potentially toxic elements present in polluting mining tailings.

ACKNOWLEDGMENTS

The authors would like to thank the Universidade Federal do Rio de Janeiro (UFRJ), Centro de Tecnologia Mineral (CETEM), and Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq, PQ1C grant nº 304018/2020-1) for technical and finance support.

REFERENCES

  • ABEGUNDE OA, OKUJENI C & PETRIK L. 2020. The use of factor analysis and acid base accounting to probe the speciation of toxic metals in gold mine waste. Environ Earth Sci 79: 152.
  • ABNT NBR. 2004a. Resolution no10004/2004 (in Portuguese). https://analiticaqmcresiduos.paginas.ufsc.br/files/2014/07/Nbr-10004-2004-Classificacao-De-Residuos-Solidos.pdf (accessed 18 May 2022)
    » https://analiticaqmcresiduos.paginas.ufsc.br/files/2014/07/Nbr-10004-2004-Classificacao-De-Residuos-Solidos.pdf (accessed 18 May 2022)
  • ABNT NBR. 2004b. Resolution no10005/2004 (in Portuguese). https://wp.ufpel.edu.br/residuos/files/2014/04/ABNT-NBR-10005-Lixiviacao-de-Residuos.pdf (accessed 18 May 2022)
    » https://wp.ufpel.edu.br/residuos/files/2014/04/ABNT-NBR-10005-Lixiviacao-de-Residuos.pdf (accessed 18 May 2022)
  • BARCELOS DA, PONTES FVM, DA SILVA FANG, CASTRO DC, DOS ANJOS NOA & CASTILHOS ZC. 2020. Gold mining tailing: Environmental availability of metals and human health risk assessment. J Hazard Mater 397: 122721. https://doi.org/10.1016/j.jhazmat.2020.122721.
    » https://doi.org/10.1016/j.jhazmat.2020.122721
  • BIDARI E, AAZAMI M & AGHAZADEH V. 2020. Process Mineralogical Study of the Arsenical Zone from a Carlin-type Gold Deposit. Min Metall Explor 37(4): 1307-1315. https://doi.org/10.1007/s42461-020-00221-w.
    » https://doi.org/10.1007/s42461-020-00221-w
  • BRAGIN VI, BURDAKOVA EA, KONDRAT’EVA AA, PLOTNIKOVA AA & BAKSHEEVA II. 2018. Dressability of Old Gold-Bearing Tailings by Flotation. J Min Sci 54(4): 663-670. https://doi.org/10.1134/s106273911804447.
    » https://doi.org/10.1134/s106273911804447
  • BUCH AC, NIEMEYER JC, MARQUES ED & SILVA-FILHO EV. 2020. Ecological risk assessment of trace metals in soils affected by mine tailings. J Hazard Mater 403: 123852. https://doi.org/j.jhazmat.2020.123852.
    » https://doi.org/j.jhazmat.2020.123852
  • BURAT F, DEMIRAĞ A & ŞAFAK MC. 2020. Recovery of noble metals from floor sweeping jewelry waste by flotation-cyanide leaching. J Mater Cycles Waste Manag 22: 907-915. https://doi.org/10.1007/s10163-020-00982-y.
    » https://doi.org/10.1007/s10163-020-00982-y
  • CARABALLO MA, SERNA A, MACÍAS F, PÉREZ-LÓPEZ R, RUIZ-CÁNOVAS C, RICHTER P & BECERRA-HERRERA M. 2018. Uncertainty in the measurement of toxic metals mobility in mining/mineral wastes by standardized BCR®SEP. J Hazard Mater 360: 587-593. https://doi.org/10.1016/j.jhazmat.2018.08.046.
    » https://doi.org/10.1016/j.jhazmat.2018.08.046
  • CESAR R ET AL. 2022. Deposition of gold mining tailings in tropical soils: metal pollution and toxicity to earthworms. J Soils Sed 22: 547-558. https://doi.org/10.1007/s11368-021-03105-8.
    » https://doi.org/10.1007/s11368-021-03105-8
  • CHENG H, HU Y, SUN Z & WANG P. 2019. Leaching of heavy metals from abandoned mine tailings brought by precipitation and the associated environmental impact. Sci Total Environ 695(10): 133893. https://doi.org/10.1016/j.scitotenv.2019.133893.
    » https://doi.org/10.1016/j.scitotenv.2019.133893
  • CHINA WATER RISK. 1996. China Water Risk: based on the National Standard of the People’s Republic of China Integrated Wastewater Discharge Standard GB 8978 – 1996 and the US Environmental Protection Agency drinking water contaminants list. Maximum Allowable Discharge Concentrations for Heavy Metals in China. https://www.chinawaterrisk.org/wp-content/uploads/2011/05/Maximum-Allowable-Discharge-Concentrations-for-Heavy-Metals-in-China.pdf (accessed 18 May 2022)
    » https://www.chinawaterrisk.org/wp-content/uploads/2011/05/Maximum-Allowable-Discharge-Concentrations-for-Heavy-Metals-in-China.pdf (accessed 18 May 2022)
  • CHRYSSOULIS SL & MCMULLEN J. 2016. Mineralogical Investigation of Gold Ores. Gold Ore Processing: 57-93. https://doi.org/10.1016/b978-0-444-63658-4.00005-0
    » https://doi.org/10.1016/b978-0-444-63658-4.00005-0
  • CONAMA. 2009. Resolution CONAMA no420/2009 (in Portuguese). http://www.mma.gov.br/port/conama/legiabre.cfm?codlegi=620
    » http://www.mma.gov.br/port/conama/legiabre.cfm?codlegi=620
  • CRUZ-RODRÍGUEZ IA, ROJAS-AVELIZAPA NG & RIVAS-CASTILLO AM. 2022. Microbially-Produced Organic Acids as Leaching Agents for Metal Recovery Processes. Adv Microbiol 61(4): 179-190. https://doi.org/10.2478/am-2022-019.
    » https://doi.org/10.2478/am-2022-019
  • DIAS DF, SANTOS LSG, SILVA FANG, DOMINGOS LMB, CASTILHOS ZC & AMADO RS. 2022. MINERAÇÃO DE OURO NO BRASIL: INVESTIGAÇÃO SOBRE BARRAGENS DE REJEITOS. Anais do XXIX Encontro Nacional de Tratamento de Minérios e Metalurgia Extrativa XXIX: 146638. ISBN: 978-65-89463-34-4.
  • FASHOLA M, NGOLE-JEME V & BABALOLA O. 2016. Heavy Metal Pollution from Gold Mines: Environmental Effects and Bacterial Strategies for Resistance. Int J Environ Res Public Health 13(11): 1047. https://doi.org/10.3390/ijerph13111047.
    » https://doi.org/10.3390/ijerph13111047
  • GARCÍA-ARREOLA ME, FLORES-VÊLEZ LM, LOREDO-TOVÍAS M, AQUILLÓN-ROBLES A, LÓPEZ-DONCEL RA, CANO-RODRÍGUEZ I, SORIANO-PÉREZ SH. 2018. Assessment of the acid draignage neutralization capacity and the toxic metals lixiviation of tailing from Guanajuato mining distric, Mexico. Environ Earth Sci 77: 1-15. https://doi.org/10.1007/s12665-018-7521-4.
    » https://doi.org/10.1007/s12665-018-7521-4
  • GARCÍA-LORENZO ML, PÉREZ-SIRVENT C, MOLINA-RUIZ J & MARTÍNEZ-SÁNCHEZ MJ. 2014. Mobility indices for the assessment of metal contamination in soils affected by old mining activities. J Geochem Explor 147: 117-129. https://doi.org/10.1016/j.gexplo.2014.06.012.
    » https://doi.org/10.1016/j.gexplo.2014.06.012
  • HAN Z, ZHANG B, WU H, LIU H, QIAO Y, ZHANG S & LI R. 2020. Microscopic characterisation of metallic nanoparticles in ore rocks, fault gouge and geogas from the Shanggong gold deposit, China. J Geochem Explor 217: 10656. https://doi.org/10.1016/j.gexplo.2020.106562.
    » https://doi.org/10.1016/j.gexplo.2020.106562
  • HELSER J, VASSILIEVA E & CAPPUYNS V. 2022. Environmental and human health risk assessment of sulfidic mine waste: Bioaccessibility, leaching and mineralogy. J Hazard Mater 424: 127313. https://doi.org/10.1016/j.jhazmat.2021.127313.
    » https://doi.org/10.1016/j.jhazmat.2021.127313
  • KUSIN FM, AWANG NHC, HASAN SNMS, RAHIM HAA, AZMIN N, JUSOP S & KIM KW. 2019. Geo-ecological evaluation of mineral, major and trace elemental composition in waste rocks, soils and sediments of a gold mining area and potential associated risks. CATENA 183: 104229. https://doi.org/j.catena.2019.104229.
    » https://doi.org/j.catena.2019.104229
  • MARIN B, VALLADON M, POLVE M & MONACO A. 1997. Reproducibility testing of a sequential extraction scheme for the determination of trace metal speciation in a marine reference sediment by inductively coupled plasma-mass spectrometry. Anal Chim Acta 342(2-3): 91-112. https://doi.org/10.1016/S0003-2670(96)00580-6.
    » https://doi.org/10.1016/S0003-2670(96)00580-6
  • MARSHAL J. 2018. Tailings dam spills at Mount Polley and Mariana: CHRONICLES OF DISASTERS FORETOLD. CCPA: Canadian Centre for Policy Alternatives. Social Science and Humanities Research Council of Canada (SSHRC). https://www.policyalternatives.ca/sites/default/files/uploads/publications/BC%20Office/2018/08/CCPA-BC_TailingsDamSpills.pdf (accessed 18 May 2022)
    » https://www.policyalternatives.ca/sites/default/files/uploads/publications/BC%20Office/2018/08/CCPA-BC_TailingsDamSpills.pdf (accessed 18 May 2022)
  • MEERS E, DU LAING G, UNAMUNO V, RUTTENS A, VANGRONSVELD J, TACK FM & VERLOO MG. 2007. Comparison of cadmium extractability from soils by commonly used single extraction protocols. Geoderma 141(3-4): 247-259. https://doi.org/10.1016/j.geoderma.2007.06.002.
    » https://doi.org/10.1016/j.geoderma.2007.06.002
  • MNGADI S, SIHLAHLA M, LEKOADU S, MOJA S & NOMNGONGO PN. 2020. Evaluation of mobility, fractionation, and potential environmental risk of trace metals present in soils from Struibult gold mine dumps. J African Earth Sci 172: 104008. https://doi.org/10.1016/j.jafrearsci.2020.104008.
    » https://doi.org/10.1016/j.jafrearsci.2020.104008
  • MONIZ AC, JORGE JA & VALADARES JMAS. 2009. Methods of Chemical, Mineralogical and Physical Analysis of Soils at the Instituto Agronômico de Campinas. Campinas, Instituto Agronômico, 77 p. Boletim Técnico 106, Edição revista e atualizada (in Portuguese). http://www.iac.sp.gov.br/produtoseservicos/analisedosolo/docs/Boletim_Tecnico_106_rev_atual_2009.pdf (accessed 18 May 2022)
    » http://www.iac.sp.gov.br/produtoseservicos/analisedosolo/docs/Boletim_Tecnico_106_rev_atual_2009.pdf (accessed 18 May 2022)
  • O’DAY PA. 2006. Chemistry and Mineralogy of Arsenic. Elements 2(2): 77-83. https://doi.org/10.2113/gselements.2.2.77.
    » https://doi.org/10.2113/gselements.2.2.77
  • ONIRETI OO, LIN C & QIN J. 2017. Combined effects of low-molecular-weight organic acids on mobilization of arsenic and lead from multi-contaminated soils. Chemosphere 170: 161-168. https://doi.org/10.1016/j.chemosphere.2016.12.024.
    » https://doi.org/10.1016/j.chemosphere.2016.12.024
  • PIRES AMM & MATTIAZZO ME. 2007. Cinética de solubilização de metais pesados por ácidos orgânicos em solos tratados com lodo de esgoto. Rev Bras de Ciênc Solo 31(1): 143-151.
  • PÉREZ-SIRVENT C, GARCÍA-LORENZO ML, HERNÁNDEZ-PÉREZ C & MARTÍNEZ-SÁNCHEZ MJ. 2018. Assessment of potentially toxic element contamination in soils from Portman Bay (SE, Spain). J Soils Sediments 18: 2248-2258. https://doi.org/10.1007/s11368-017-1756-7.
    » https://doi.org/10.1007/s11368-017-1756-7
  • SILVA VP, PASSOS FA, DOMINGOS LM, FARIA RB, CASTILHOS ZC & SILVA FA. 2017. Technological characterization of waste from gold mining dam. Characterization of Minerals, Metals, and Materials 2017: 269-278. Springer International Publishing.
  • SKOOG DA, WEST DM, HOLLER FJ & CROUCH SR. 2006. Fundamentals of Analytical Chemistry, 8th ed., Editora Thomson, p. 211-251.
  • SOYLAK M & TURKOGLU O. 1999. Trace metal accumulation caused by traffic in an agricultural soil near a motorway in Kayseri, Turkey. J Trace Microprobe Tech 17: 209-217.
  • SOYLAK M, SANGUR A & OZCAN H. 2016. Trace metal accumulation caused by traffic in an agricultural soil near a motorway in Kayseri, Turkey. Environ Earth Sci 75: 334. https://doi.org/10.1007/s12665-016-5268-3.
    » https://doi.org/10.1007/s12665-016-5268-3
  • SPOSITO G. 1981. Trace metals in contaminated waters. Environ Sci Technol 15: 396-403.
  • SUANON F, SUN Q, DIMON B, MAMA D & YU CP. 2016. Heavy metal removal from sludge with organic chelators: comparative study of N,N-bis (carboxymethyl) glutamic acid and citric acid. J Environ Manage 166: 341-347. https://doi.org/10.1016/j.jenvman.2015.10.035.
    » https://doi.org/10.1016/j.jenvman.2015.10.035
  • TASIĆ A, IGNJATOVIĆ IS, IGNJATOVIĆ L, ILIĆ M & ANTIĆ M. 2016. Comparison of sequential and single extraction in order to estimate environmental impact of metals from fly ash. J Serb Chem Soc 81(9): 1081-1096. https://doi.org/10.2298/JSC160307038T.
    » https://doi.org/10.2298/JSC160307038T
  • TESSIER APGC, CAMPBELL PG, CBISSO NM & BISSON MJAC. 1979. Sequential extraction procedure for the speciation of particulate trace metals. Anal Chem 51(7): 844-851. https://doi.org/10.1021/ac50043a017.
    » https://doi.org/10.1021/ac50043a017
  • TUM S, TODA K, MATSUI T, KIKUCHI R, KONG S, MEAS P, EAR U, OHTOMO Y, OTAKE T & SATO T. 2022. Seasonal effects of natural attenuation on drainage contamination from artisanal gold mining, Cambodia: Implication for passive treatment. Sci Total Environ 806: 150398. https://doi.org/10.1016/j.scitotenv.2021.150398.
    » https://doi.org/10.1016/j.scitotenv.2021.150398
  • US GEOLOGICAL SURVEY. 2020. Mineral Commodity Summaries, p. 70. January 2020. https://pubs.usgs.gov/periodicals/mcs2020/mcs2020.pdf (accessed 2 September 2022)
    » https://pubs.usgs.gov/periodicals/mcs2020/mcs2020.pdf (accessed 2 September 2022)
  • US EPA - ENVIRONMENTAL PROTECTION AGENCY. 2015. Heavy Metal Waste Regulation: Which Substances Make Up the RCRA 8 Metals?. Hazardous Waste Experts. https://www.hazardouswasteexperts.com/heavy-metal-waste-regulation-which-substances-make-up-the-rcra-8-metals/ (accessed 18 May 2022)
    » https://www.hazardouswasteexperts.com/heavy-metal-waste-regulation-which-substances-make-up-the-rcra-8-metals/ (accessed 18 May 2022)
  • VERDADE F. 1956. Observations on methods of determining the exchange capacity of soils. Bragantia 15: 393-401. https://doi.org/10.1590/S0006-87051956000100029.
    » https://doi.org/10.1590/S0006-87051956000100029
  • VOGEL AI. 1981. Química Analítica Qualitativa, 5th ed., Mestre Jou, p. 75-89.
  • WANG P, SUN Z, HU Y & CHENG H. 2019. Leaching of heavy metals from abandoned mine tailings brought by precipitation and the associated environmental impact. Sci Total Environ 695: 133893. https://doi.org/10.1016/j.scitotenv.2019.133893.
    » https://doi.org/10.1016/j.scitotenv.2019.133893
  • XIE L & ZY DV. 2020. Distinguishing reclamation, revegetation and phytoremediation, and the importance of geochemical processes in the reclamation of sulfidic mine tailings: A review. Chemosphere 252: 126446. https://doi.org/10.1016/j.chemosphere.2020.126446.
    » https://doi.org/10.1016/j.chemosphere.2020.126446
  • ZHANG Z, ZHANG Y, ZHANG H, LIU C, SUN C, ZHANG W & MARHABA T. 2018. pH Effect on Heavy Metal Release from a Polluted Sediment. J Chem 18: 2090-9063. https://doi.org/10.1155/2018/7597640.
    » https://doi.org/10.1155/2018/7597640

Publication Dates

  • Publication in this collection
    15 Nov 2024
  • Date of issue
    2024

History

  • Received
    28 Feb 2024
  • Accepted
    12 Aug 2024
location_on
Academia Brasileira de Ciências Rua Anfilófio de Carvalho, 29, 3º andar, 20030-060 Rio de Janeiro RJ Brasil, Tel: +55 21 3907-8100 - Rio de Janeiro - RJ - Brazil
E-mail: aabc@abc.org.br
rss_feed Acompanhe os números deste periódico no seu leitor de RSS
Acessibilidade / Reportar erro