Physical, Chemical and Mineralogical Characterization of Emerald Mining Tailings in Nova Era, Minas Gerais

Abstract

This study characterized emerald mining tailings from the city of Nova Era, Minas Gerais, Brazil. Analyses included granulometry, density, and moisture content, along with leaching tests, XRF analysis, and chemical composition assessment using an EDS detector coupled with SEM. Additionally, stereomicroscope and SEM imaging were performed, as well as XRD analyses. The granulometric analysis revealed that 46.49% of the particles were smaller than 0.85 mm. XRF analysis identified Mg, K, and Ca in the sample. Leaching tests indicated levels below 1 ppm for potentially toxic metals As, Cd, and Pb. XRD analyses identified the following mineral phases: phlogopite, quartz, actinolite, kaolinite, and vermiculite. These findings indicate that the tailings could serve as a potential soil remineralizer; however, further agronomic testing is required to confirm their suitability for agricultural use.

Keywords:
mineral characterization; tailings; reuse; soil remineralizer

1. Introduction

In the late 1980s, in Capoeirana, local miners and those from various Brazilian states began extracting gemstones from the beryl mineral family (Be₃Al₂(SiO₃)₆). These included transparent crystals, blue aquamarine, and, most notably, emeralds, which are highly valued for their quality and crystal size¹. Epstein² documented the onset of mining activities in Capoeirana. The site is located in the municipality of Nova Era, 8.5 km northeast of the city, in the state of Minas Gerais.

Emerald mining, like other extractive activities, produces significant solid waste and tailings, which can be repurposed for various applications. These tailings, though no longer economically valuable after emerald extraction, contain mineral and chemical components suitable for reuse in various sectors. For instance, the mica found in the tailings, rich in potassium, can be used in agriculture to partially replace traditional fertilizers while improving soil properties³.

The reuse of tailings in the mining industry not only contributes to more sustainable solid waste management but also aligns with ESG (Environmental, Social, and Governance) principles. This approach enhances environmental responsibility, social equity, and corporate governance, that are some factors increasingly prioritized by investors, customers, and society at large⁴. By adopting an ESG-focused strategy, mining companies can mitigate their negative impacts while maximizing benefits for the environment, governance structures, and the well-being of surrounding populations. Achieving sustainability in this sector, however, requires the collective involvement of governments, businesses, civil society organizations, and local communities.

Thus, this study focuses on the characterization of emerald tailings, aiming to analyze their physical, chemical, and mineralogical properties. These tailings, generated during the extraction and processing of emeralds, hold significant potential for resource recovery. The characterization process is essential for understanding the composition of the tailings, identifying valuable components that can be repurposed, and developing effective strategies for environmentally sustainable treatment and disposal.

The physical characterization of the emerald tailings included analyses of density, moisture content, and granulometry. Chemical characterization tests included leaching assays, X-ray fluorescence (XRF), and chemical analysis using scanning electron microscopy (SEM) with an EDS detector. The mineralogical characterization aimed to identify the minerals present and understand their distribution, conducted through X-ray diffraction (XRD) analysis and imaging using a stereomicroscope and backscattered electron imaging in SEM. The primary mineralogy associated with emerald tailings in the region typically includes quartz, feldspar, muscovite, biotite, and other secondary minerals⁵.

This information is essential for evaluating environmental safety and determining optimal tailings management strategies, including the development of recycling techniques, the proposal of secondary applications, and the implementation of appropriate disposal methods.

2. Materials and Methods

The study material was randomly collected from various tailings stockpiles located at the Capoeirana Mine in Nova Era, Minas Gerais. The area lies between parallels 19° 40’ and 19° 43’ South and meridians 43° 04’ and 43° 08’ West, as shown in Figure 1.

Figure 1
Location map of the mining area in Capoeirana, Nova Era-MG.

The tailings originate from the mining and processing operations of beryl (emerald variety) in the region. The sample was then sent to the Technological Center of UEMG-João Monlevade (CTec) for further analysis.

The collected material was weighed, totaling 5 kg, and then evenly spread on trays for drying in an oven at 110 °C for 24 hours. After this period, the sample was weighed again, totaling 4.91 kg. Using Equation 1, the moisture content of the emerald tailings was calculated.

$\text{h}=\frac{\text{Ph}-\text{Ps}}{\text{Ph}}\text{x}100$ (1)

Where:

h is the moisture percentage.

Ph is the weight of wet material.

Ps is the weight of oven-dried material.

The homogenization process involved placing the sample at the center of a tarp and mixing it for five minutes by lifting the tarp's diagonal edges until a uniform sample was obtained. Following this procedure, sample splitting was performed using the coning and quartering method with the aid of a cross, dividing the sample into four equal portions. The two diagonally opposite portions were then combined, forming two samples. Subsequently, a riffle/Jones splitter was employed as a secondary method, further reducing the sample into aliquots of approximately 600 g.

The sample density was calculated using the pycnometer method, following the procedure described by Sampaio and Silva⁶. This method required a 25 ml pycnometer and a 5 decimal analytical balance to ensure accuracy.

The procedure consisted of the following steps:

• The empty pycnometer was cleaned, oven-dried at 110°C, and weighed.

• The pycnometer was filled with water until overflow, dried externally, and reweighed.

• The pycnometer was again cleaned and oven-dried at 110°C.

• Approximately 15 g of emerald tailings sample was added to the clean, dry pycnometer and weighed.

• The pycnometer containing the sample was then filled with water until overflow, dried externally, and reweighed.

The density of the material was calculated using Equation 2.

$\text{ds}=\frac{\left(\text{A}2\right)-\left(\text{A}1\right)}{\left(\text{A}4+\text{A}2\right)-\left(\text{A}1+\text{A}3\right)}$ (2)

Where:

ds density of solids;

• A1 mass of the empty pycnometer;

• A2 mass of pycnometer+sample;

• A3 mass of pycnometer+sample+water;

• A4 mass of pycnometer+water.

For the particle size analysis, dry sieving was performed using a vibrating sieve. Eight sieves from the Tyler series were used for particle classification, with openings of 4.00 mm (5#); 0.85 mm (20#); 0.425 mm (35#); 0.25 mm (60#); 0.15 mm (100#); 0.104 mm (140#); 0.074 mm (200#); and 0.037 mm (400#), following the procedures of Luz et al⁷.

The leaching test was conducted at the Soloquímica Laboratory (Brasília-DF), using the procedures described in the Normative Instruction No. 24, of 2007, from the Ministry of Agriculture, Livestock and Supply (MAPA)⁸. The X-ray fluorescence analysis was conducted at ASIC Services Laboratory (Santos-SP) after preparing the sample to produce a pressed pellet for reading by the equipment.

Point chemical analyses were performed at the Scanning Electron Microscopy Laboratory of CTec UEMG-João Monlevade, using the Oxford Instruments X-MaxN EDS detector coupled with the VEGA 3-TESCAN scanning electron microscope, with a 20 kV tension and beam intensity of 14. A small portion of the sample was mounted on a stub using double-sided carbon tape. The sample was then coated with gold and palladium, and a few points were selected for analysis. The semiquantitative analyses with SEM-EDS provide complementary information to the data obtained from leaching and X-ray fluorescence analyses, since they only yield point composition results in selected areas of the sample. The other methods, in turn, provide a more representative composition of the sample as a whole.

For mineralogical analysis and detailed observation of the sample's morphology, the SEM was used in the Backscattered Electrons (BSE) mode, with magnification from 50 to 300x. The binocular microscope was primarily used for visual observation of the mineral compounds in the samples from the fractions retained on the sieves, after sieving, at enlarged details. The X-ray diffraction analyses were conducted at the NANOBUSINESS Laboratory (Rio de Janeiro-RJ), using a Bruker D2 PHASER X-ray diffractometer with a resolution of <0.02, SSD 160-2 detector, and copper tube (1.5406 Å).

3. Results and Discussion

The moisture content of the tailings is relatively low, as 5 kg of sample was weighed for drying in the oven, and after the procedure, the sample weighed 4.91 kg. Using Equation 1, the calculated moisture value was 1.8%, resulting from the washing process for the manual sorting of the mined material.

The expected density was between 2 and 3 g/cm³, based on the main mineralogy found in the tailings (minerals with specific gravity between 2 and 3 g/cm³). As calculated using Equation 2, the sample has an average density of 2.559 g/cm³, as shown in Table 1.

Table 1
Values obtained to calculate the sample density. A1 = mass of the empty pycnometer; A2 = mass of the pycnometer+samp le; A3 = mass of the pycnometer+sample+water; A4 = mass of the pycnometer+water.

Analysis	A1 (g)	A2 (g)	A3 (g)	A4 (g)	Density (g/cm3)
1	15.62894	30.38695	50.38654	41.28517	2.60897
2	15.93013	30.43115	49.97901	41.24871	2.51286
3	15.90667	31.09300	50.60040	41.35719	2.55528
Average	-	-	-	-	2.559

• Source: Authors' personal archive, 2024.

The sieving process provided information about the particle size distribution of the emerald tailings discussed in this study, through the predominant size ranges, as shown in the results obtained in Table 2.

Table 2
Granulometric distribution of emerald tailings.

Granulometric Range Feeding
Mesh (#)	Opening (mm)	Mass x (g)	Mass y (g)	Average mass (g)	% Retained	% Accumulated Retained	% Passing
5	4.00	90.82	96.27	93.545	15.627	15.627	84.37
20	0.85	228.21	226.34	226.775	37.884	53.511	46.49
35	0.425	95.73	94.92	95.325	15.925	69.436	30.56
60	0.25	99.56	98.57	99.065	16.549	85.985	14.02
100	0.15	0.33	0.19	0.26	0.043	86.028	13.97
140	0.104	59.15	58.22	58.685	9.804	95.832	4.17
200	0.074	10.87	10.47	10.67	1.782	97.614	2.39
400	0.037	9.91	10.27	10.09	1.686	99.3	0.7
<400	0.037	4.16	4.21	4.185	0.7	100	-

• Source: Authors' personal archive, 2024.

Based on the results obtained, the particle size curve was plotted to represent the passing percentage as a function of the opening of each sieve. According to Table 2 and Figure 2, it can be verified that 46.49% of the particles are smaller than 0.85 mm, considered fine and ultrafine particles.

Figure 2
Granulometric curve of emerald tailings.

The results of the leaching test are presented in Table 3. According to Normative Instruction No. 5, of March 10, 2016, from MAPA⁹, the maximum allowable concentrations of potentially toxic metals As, Cd, and Pb for the use of rock powder as a soil remineralizer are 15, 10, and 200 ppm, respectively. The leaching test revealed low levels of these metals, all below 1 ppm, as 1 ppm is equivalent to 1 mg/kg. For comparison, Bloise et al.¹⁰,¹¹ have assessed potentially toxic elements content in asbestos minerals, finding much more high levels.

Table 3
Leaching test results.

Compound	Symbol	Content [g/Kg]
Calcium	Ca	4.6
Magnesium	Mg	19.7
Compound	Symbol	Content [mg/Kg]
Copper	Cu	0.1
Iron	Fe	4460.4
Manganese	Mn	255.7
Zinc	Zn	103.1
Arsenic	As	< 1.0
Cadmus	Cd	< 1.0
Lead	Pb	< 1.0
Chrome	Cr	14.7
Nickel	Ni	< 1.0
Aluminum	Al	18753.1
Barium	Ba	5.7
Cobalt	Co	< 1.0
Titanium	Ti	< 1.0

• Source: Authors' personal archive, 2024.

The results of the X-ray fluorescence analysis (Table 4) revealed the presence of important chemical elements for plant development, especially Mg, K, and Ca, indicating potential for using the tailings as soil remineralizers. The analyzed sample was mainly composed of SiO₂ (46.182%), MgO (20.664%), Al₂O₃ (11.966%), Fe₂O₃ (10.449%), K₂O (6.241%), and CaO (2.88%). The other oxides analyzed had a concentration below 0.5%. The Normative Instruction No. 5 of MAPA⁹ establishes the specifications and minimum guarantees for remineralizers. The sum of bases, for example, must be greater than 9%, defined as the sum of the contents of CaO+MgO+K₂O, or the sum of CaO+K₂O, or the sum of MgO+K₂O. The potassium oxide (K₂O) content must be equal to or greater than 1% w/w. The analyzed sample shows both values above the minimum established, 29.785% and 6.241%, respectively.

Table 4
Result of X-ray fluorescence analysis.

Compound	%	Compound	%
Ag2 O	0.12	Nb2O5	0.002
Al2 O3	11.966	NiO	0.032
As2O3	0.686 ppm	PbO	4.573 ppm
BaO	0.02	PdO	1.658 ppm
CaO	2.88	Rb2O	0.091
CeO2	0.003	RuO2	0.152 ppm
Cl	0.047	Sb2O3	0.004
Cr2O3	0.302	SiO2	46.182
Er2O3	0.012	SnO2	0.015
Eu2O3	0.053	SO3	0.022
Fe2O3	10.449	SrO	9.26 ppm
Ga2O3	0.003	Tb4O7	0.149
Gd2O3	0.038	TeO2	0.009
GeO2	5.291 ppm	ThO2	0.001
K2O	6.241	TiO2	0.359
MgO	20,664	Ti2O3	7.49 ppm
MnO	0.157	U	7.52 ppm
MoO3	7.103 ppm	V2O5	0.018
Na2O	0.058	WO3	0.031

• Source: Authors' personal archive, 2024.

Although expressed in the form of oxides, these elements are found in the structure of silicate minerals and are not readily available for plant uptake. However, some minerals as K-silicates, for example biotite/phlogopite, may have a high agronomic potential as slow-release K fertilizers and should be tested¹². Other studies have addressed the possibility of applying emerald tailings in agriculture, presenting the composition of the studied rocks³,¹³-¹⁶. Despite the benefits of using rock powder in agriculture, the low solubility of the nutrients that make up the rocks is currently one of the main obstacles to its effective use in the field¹⁷.

SEM-EDS point analyses in four different spots of the sample also detected the presence of Mg, K and Ca (Figure 3). According to Duarte et al.¹⁸, EDS detects the energy of X-rays emitted by the interaction of electrons with the chemical elements present in the sample, thus enabling the identification and quantification of the elements, as illustrated in Figure 3.

Figure 3
SEM-EDS spectra obtained in the analysis of the tailings sample.

The X-ray diffraction analysis identified the following mineral phases: phlogopite, quartz, actinolite, kaolinite and vermiculite. Figure 4 shows the experimental diffractogram for the analyzed sample. The data on position [°2Th.], d-spacing [Å], and relative intensity [%] are presented in Table 5. References of assigned phases are:

Figure 4
A. Experimental X-ray diffractogram of the sample. B. Comparison between the experimental diffractogram of the sample and the diffraction pattern of the phlogopite mineral phase (ICDD: 0850-0001); the orange lines represent the diffraction pattern of the phlogopite mineral phase. C. Comparison between the experimental diffractogram of the sample and the diffraction pattern of the quartz mineral phase (ICDD: 0828-0001); the orange lines represent the diffraction pattern of the quartz mineral phase. D. Comparison between the experimental diffractogram of the sample and the diffraction pattern of the actinolite mineral phase (ICDD: 0851-0001); the orange lines represent the diffraction pattern of the actinolite mineral phase. E. Comparison between the experimental diffractogram of the sample and the diffraction pattern of the kaolinite mineral phase (ICDD: 0852-0001); the orange lines represent the diffraction pattern of the kaolinite mineral phase. F. Comparison between the experimental diffractogram of the sample and the diffraction pattern of the vermiculite mineral phase (ICDD: 0853-0001); the orange lines represent the diffraction pattern of the vermiculite mineral phase.

Table 5
Position [°2Th.], d-spacing [Å], and Relative intensity [%] for the diffraction pattern of the analyzed sample.

No.	Pos. [°2Th.]	d-spacing [Å]	Rel. Int. [%]
1	6.069(9)	14.55000	0.19
2	8.8569(2)	9.97610	100.00
3	9.50(4)	9.30157	0.53
4	9.798(1)	9.02040	3.41
5	10.554(8)	8.37566	0.60
6	12.27(2)	7.20927	0.20
7	17.668(2)	5.01600	1.27
8	26.5949(3)	3.34903	52.47
9	28.279(5)	3.15325	0.39
10	28.44(3)	3.13531	0.31
11	30.6(1)	2.91881	0.12
12	35.684(1)	2.51407	4.41
13	44.9483(8)	2.01508	7.84
14	45.151(1)	2.00651	6.06
15	54.743(5)	1.67544	0.65
16	64.956(1)	1.43452	1.52

• Source: Authors' personal archive, 2024.

• Phlogopite (reference code: 0850-0001)¹⁹;

• Quartz (reference code: 0828-0001)²⁰;

• Actinolite (reference code: 0851-0001)²¹;

• Kaolinite (reference code: 0852-0001)²²;

• Vermiculite (reference code: 0853-0001)²³;

These results are consistent with the data presented by Lima et al.¹⁵, who identified through X-ray diffraction analysis the minerals phlogopite – KMg₃AlSi₃O₁₀(OH)₂, quartz – SiO₂, actinolite – Ca₂(Mg,Fe)₅Si₈O₂₂(OH)₂ and talc – Mg₃Si₄O₁₀(OH)₂ as the most abundant in the material from the processing of an emerald mine located in Itabira-MG, close to the Capoeirana mine in Nova Era. In the study carried out by Aguiar³, the main minerals observed were micas, amphiboles and pyroxenes, analyzing similar material to evaluate the use of emerald mining residue as an alternative input for agricultural soil.

The images obtained by SEM in BSE mode (Figure 5A) provide information about the texture, morphology and distribution of the different components of the sample; on the left, lamellar minerals predominate, while in the image on the right, more elongated minerals with prismatic habit appear. According to Klein and Dutrow²⁴, phlogopite is generally found in plates, while actinolite crystals are generally prismatic, which is in agreement with maps of elements shown in Figure 5B, where calcium predominates in prismatic minerals (actinolite), whereas potassium is more present in platy minerals (phlogopite).

Figure 5
A. Images of the tailings sample in SEM, BSE mode. Act: actinolite; Phl: phlogopite. B. Map of elements by SEM-EDS.

Images with a binocular magnifying glass were obtained for each of the granulometric fractions separated during sieving (Figure 6), and it was possible to observe the predominance of phlogopite in most of them. In the material retained between the 0.85 mm and 0.104 mm sieves, the presence of emerald fragments was observed, indicating a possibility of reprocessing the material. Some of these fragments were selected and are shown in Figure 7.

Figure 6
Images of the tailings obtained with a binocular magnifying glass in the different granulometric fractions obtained by sieving of the sample. Phl: phlogopite; Emr: emerald. A. 4 mm; B. 0.85 mm; C. 0.425 mm; D. 0.25 mm; E. 0.15 mm; F. 0.104 mm; G. 0.074 mm; H. 0.037 mm; I. below 0.037 mm.

Figure 7
Emerald fragments selected from the tailings.

4. Conclusion

The analyses conducted in this study aiming the physical, chemical and mineralogical characterization of the mining tailings from the extraction and processing of emerald in the Capoeirana Mine, Nova Era-MG, allowed to acquire essential information on the material. The analyses by SEM-EDS and FRX showed the presence of elements such as Mg, K and Ca, indicating a potential for use of the material in the agricultural sector.

Leaching tests revealed low levels, below 1 ppm, of potentially toxic metals As, Cd and Pb. XRD analyses identified the following mineral phases: phlogopite, quartz, actinolite, kaolinite and vermiculite. Therefore, the results obtained indicate great potential for using the mining tailings as a soil remineralizer, based on specifications defined by MAPA. However, further agronomic testing is required to evaluate the applicability of the material in the agricultural sector.

Furthermore, in the images obtained through a binocular magnifying glass, the presence of emerald crystals was verified in some of the fractions resulting from the sieving test, indicating the possibility of reprocessing the material to obtain these crystals, which could be used in mineral crafts, since their dimensions are not viable for cutting.

The assessment of the feasibility of reusing the studied tailings in various applications is essential and aligns with the concepts of circular economy. It investigates new possibilities for the use of the material, which is often inadequately disposed of, without control or planning, potentially posing social and environmental risks. The reuse of tailings in agriculture, for example, would help reduce the volume of material to be stored while also generating benefits for farmers as an alternative to chemical fertilizers, lowering costs and decreasing external dependence.

5. Acknowledgments

To FAPEMIG for the financial support through Call 09/2022, and to UEMG João Monlevade for providing the infrastructure and materials for the development of the project. The first author also thanks the Research Productivity Grant Program (PQ/UEMG) for granting a research productivity grant.

• Data Availability
  The entire dataset supporting the results of this study was published in the article itself.

6. References

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Edited by

• Associate Editor: Eliana Muccillo.
  Editor-in-Chief: Luiz Antonio Pessan.

Data availability

The entire dataset supporting the results of this study was published in the article itself.

Publication Dates

• Publication in this collection
  19 Jan 2026
• Date of issue
  2025

History

• Received
  09 Jan 2025
• Reviewed
  04 Sept 2025
• Accepted
  25 Oct 2025