1. Introduction
Brazil stands out among Latin American countries for the greatest inequality in income distribution [
1,
2]. This is reflected in the quality of life linked to the characteristics of the environment in which people live, especially housing [
3,
4]. The lack of investment in housing credits in Brazil has generated a housing deficit, which for 2011 was 5,409,210 units [
5]. In 2015, estimates were proposed by the João Pinheiro Foundation (2015), based on data from the Pesquisa Nacional por Amostragem de Domicílios (National Household Sample Survey) (PNAD), this number rose to 6,355,743 units.
Building requires a labor force, which, when receiving earnings proportional to the services rendered, would then be able to acquire goods such as their own homes. This housing, if properly designed and implemented, would provide better living conditions for its occupants and society in general [
6]. Such housing has variable construction costs depending on the proposed project, location of implementation, and materials used, which are usually conventional materials characterized as impactful and unsustainable [
7]. One of the most commonly used materials in civil construction is concrete [
8], which is usually produced by mixing Portland cement (binder), aggregates (sand and gravel), water, and additives. According to the granulometry, aggregates can be identified as fine (sand) and coarse (gravel) [
9]. Both are mostly classified as natural materials, that is, taken directly from nature. Limestone, granite, and quartz are mentioned among aggregates with mineralogical classifications [
10].
To use such materials, it is necessary to intervene in the environments that contain them, and after the removal of the mineral mass from a certain area, this becomes characterized as a degraded area. Mining damage could be mitigated through the adoption of impact reduction measures [
11], including the application of recovery plans for degraded areas. Another possible action aiming to reduce such impacts would be the search for minerals, classified as mining waste (tailings or sterile) that could be used as aggregates [
12]. Thus, materials that are initially classified as waste, with characteristics harmful to the environment due to disposal and storage, would be treated as a material that can be used in relevant activities, leading to a sustainable measure.
These waste materials generally have a low commercial value [
13], as they are not the main object of the mining project. Moreover, such materials are an inconvenience to the main activity, as large areas must be made available for temporary or permanent storage. Waste products need to be controlled to maintain the environment and prevent contact with workers, thereby preventing accidents and the spread of diseases [
14]. Specifically, exposure to small particles can cause environmental problems and/or harm human health [
15].
Thus, building housing at the lowest possible cost using mineral waste materials is a sustainable activity [
16]. To achieve this objective, a preliminary study of the technical, economic, and environmental feasibility of the waste to be used is necessary [
17]. The use of a product classified as waste will promote environmental benefits and better living conditions for its users, highlighting the possibility of reducing construction costs.
Brazil is one of the largest producers and exporters of minerals in the world [
18]. Among other minerals, quartz stands out, with Brazil holding 95% of world reserves [
19], with the largest explorations in the states of Pará and Minas Gerais, where, in Serra do Espinhaço Meridional (SdEM) there are many outcrops of this mineral [
20]. Studies on the reuse of waste generated by quartz mining companies can serve as an example to reduce the negative impacts generated by its exploration.
On average, industries connected to mineral extraction and processing represented 2.33% of the value of Brazilian GDP between the years 2000 and 2017 [
21]. One of the guidelines that should be strengthened in the Brazilian mining sector is the reuse of mining waste [
22]. For example, in Gouveia-MG, there is a quartz mining venture with an annual production of approximately 420,000 tons/year, where the quantity of waste material that is commercialized is practically nil. To improve sustainability in this industry, it is important to promote the use of generated waste.
The general aim of this study is to relate the use of quartz mining residues in the SdEM to the promotion of occupational health and housing health. The contribution to occupational health relates to the mineral exploration environment. Housing health is implemented by proving the technical and economic feasibility of using mining waste as civil construction materials.
Based on the specific study of a mining venture located in the SdEM, this article demonstrates the benefits existing in the potential reuse of quartz mining waste. The study was divided into three (3) phases (1) profile of the mining venture and the mining waste generated; (2) analysis of the economic feasibility of the reuse of the waste; and (3) analysis of the technical feasibility.
2. Materials and Methods
The study was carried out in 3 phases (
Figure 1). Initially, the characteristics and location of the SdEM were described, and the mining venture was characterized, with an emphasis on the potential negative impacts on occupational health due to the piling of waste. Subsequently, an assessment of the economic feasibility of using the waste as an input in concrete production was carried out. This reuse can mitigate the project’s negative impacts, reducing the waste disposal area and enabling the improvement of housing health by reducing construction costs. Finally, the technical feasibility of using the residue for concrete production was evaluated. The following equipment was used: (a) 12.1 MP cyber-shot digital camera, manufacturer-Sony; (b) digital hydraulic press for 100 T, manufacturer-SOLOCAP; (c) GPS 60CSX, manufacturer-GARMIN; (d) energy dispersive X-ray fluorescence spectrometer, model-EDX-720/800HS, manufacturer-Shimadzu.
2.1. Phase 1-Characterization of Quartz Mining in SdEM
A search was carried out on the State Secretariat for the Environment and Sustainable Development website. The technical report for the environmental feasibility analysis of the project was evaluated. The project was located in the municipality of Gouveia (State of Minas Gerais (MG)), under the responsibility of the Superintendência Regional de Meio Ambiente Jequitinhonha (Jequitinhonha Regional Environment Board) [
23]. In addition, a search for similar studies in the literature was conducted using the following keywords: “healthy and sustainable housing”; “occupational health in mining”; “concrete and quartz”; and “concrete and phyllite.” This survey of preliminary information provided a basis for discussions on the negative impacts of the mining project and the positive impacts of the proposed material reuse.
To better characterize the mining venture, a survey of field data was carried out regarding mineral exploration and processing, in addition to the characteristics of the surrounding area, enabling conformity verification of the collected information. All visits to the mineral exploration, which included a walk around the area of direct intervention to characterize both the internal area and the surroundings, were recorded using a notebook and digital camera for the collection of georeferenced images of the environment and the collected materials.
Initially, the data generated in the field were imported to the TrackMaker® application to proceed with the treatment of pathways to generate information on the perimeter and area and later transferred to Google Earth®, where satellite imagery information was obtained on various dates, enabling comparison of the environmental characteristics on the dates made available by the program. The notes from the field surveys referred to exploration, processing, the destination of the main mineral product and tailings, as well as the value of the latter transferred to third parties and nearby cities for trade purposes. In addition to the verification in documentary records, a walk was carried out around the area of direct intervention of the project to characterize both the internal part and the surroundings.
2.2. Phase 2-Assessment of the Economic Feasibility of Using the Waste as an Aggregate for Concrete Production
To confirm the lower cost of concrete production through the use of waste, the sales values of the material classified as waste were compared with the aggregate values of limestone gravel. The same company under study has a quartz mine in the municipality of Gouveia and a limestone mine in the municipality of Curvelo, both in Minas Gerais, southeast Brazil.
The following costs were analyzed: diesel fuel type, mineral transport truck model, fuel consumption per kilometer, and type of concrete dosage used in single-family homes. As the concrete production would take place in the city of Diamantina, this was the location used to define the distances for transporting materials. The origins of the materials were as follows: (a) waste: location of the mining venture (municipality of Gouveia) (b) limestone: the cities of Curvelo, Sete Lagoas, and Montes Claros. The distances covered were obtained using Google Earth® software (Versão 9.152.0.1). The value of the material at the point of mineral exploration and the value of the fuel used in transportation were used. With the data obtained, it was possible to calculate the following values:
- (a)
Cost of transportation and material used as coarse aggregate for the production of concrete in the city of Diamantina-MG. The four (4) alternatives evaluated were: waste from the project located in Gouveia and the use of limestone purchased at three (3) different locations: Curvelo, Sete Lagoas, and Montes Claros.
- (b)
Calculation in percentage cost reduction that 1 m3 of concrete from the use of waste would have. For this calculation, concrete with a compressive strength of 20 MPa was considered.
2.3. Phase 3-Evaluation of the Technical Feasibility of Using the Waste as an Aggregate for Concrete Production
The following steps were carried out: (a) characterization of the materials involved (fine and coarse aggregates, cement, water, and silica fume additive); (b) definition of the composition of mixtures, from dosage by the ABCP Method, for the production of 2 types of concrete; (c) production of waste and crushed concrete; (d) production of twelve (12) specimens from the 2 types of concrete produced; (e) curing by submerging the specimens in water; (f) execution of the axial rupture test using a hydraulic press to characterize the resistance to simple axial compression stress; (g) compilation and analysis of results, enabling comparison; and (e) Visual inspection of the specimen breakage.
The compositions of the produced concrete had the following denominations: BQSA—concrete with quartz gravel with a percentage of 5% silica fume in relation to the Portland cement mass; and BC—concrete with limestone gravel as a coarse aggregate. The specifications of the materials used were:
- (a)
Portland cement CP IV 32 RS, with low hydration heat, from the manufacturer CAUÊ.
- (b)
According to the specifications of NBR 7211 [
24], the fine aggregates were sand of natural origin or resulting from the crushing of stable rocks, or a mixture of both, whose grains pass through a 4.8 mm mesh sieve and are retained in a 0.075 mm mesh sieve.
- (c)
The coarse aggregates were gravel of limestone origin from a mining venture in the municipality of Curvelo, and quartz mining residue, from a mining venture located in the municipality of Gouveia. The first material was acquired from the construction materials retailer and the second directly from the mining area, where it was collected from the tailings piles.
- (d)
Silica fume from the steel industry in the city of Pirapora was also included. This residue comes from the production of metallic iron and silicon alloys and is sold at low cost to concrete manufacturers in the region (around R$5.00 per ton). This silica originated from the quartz extracted to supply the steel industries, which at its source produces mineral residues that are being proposed as aggregates for incorporation in concrete. Thus, the proposal includes the use of residues from the origin of the mineral material and residue from the silicon metal alloy industry, enhancing the sustainability factor.
- (e)
The mass mix for concrete cast with limestone, with the objective of meeting the fck of 20 MPa, was 1:1.71:2.61:0.54, referring, respectively, to the proportion of cement for sand, gravel, and water. The mass mix defined for the concretes to be produced from the residue was presented as 1:1.81:2.40:0.54, also with the objective of meeting the fck at 20 MPa. The traces were calculated thus that the amount of cement per m
3 of concrete was the same for both types of concrete (
Table 1). According to the class specification as per NBR 8953 [
25], the concrete used in this study is of C20 type (20 MPa) from Group 1.
The tests were conducted at the following laboratories: that of the Programa de Mestrado Profissional em Saúde Sociedade e Ambiente (Professional Master’s Program in Health, Society and Environment) at UFVJM, JK Campus (physical analysis, concrete production, and specimens); that of the Integrado de Pesquisa Multiusuário dos Vales do Jequitinhonha e Mucuri (Jequitinhonha and Mucuri Valleys Multiuser Research Institute) at UFVJM-LIPEMVALE (chemical composition analysis of aggregates); that of the Curso de Edificações e Engenharia Civil (Buildings and Civil Engineering Course) at IFNMG, Pirapora Campus (physical analysis of aggregates); and that of the Concreteira Pirapora private company, in the city of Pirapora (simple axial compression rupture test—press). A press with a load capacity of 100 t (tons) was adopted. This hydraulic press was equipped with an electronic device that displays information on the maximum load (breaking load) applied, with an accuracy of 100th of a ton.
4. Conclusions
A mining venture that generates residues that could be introduced to the production of concrete was identified. This residue can be used as a coarse aggregate in concrete and has a 47.2% lower cost compared to conventionally aggregates.
When material is classified as mineral waste from quartz exploration, if kept in the area of the mining project, it tends to generate negative impacts. Among these, the impact related to occupational health was emphasized since the residue contains silica (SiO2), which can cause the pathology known as silicosis when in direct contact with the human respiratory tract.
Thus, it was found that the proposed adoption of such waste to produce aggregates for civil construction meets the demand for the construction of low-cost housing. Furthermore, it reduces negative impacts, including the minimization of dust dispersion in open environments. This minimization is due to the mass reduction of the risk component, thereby generating positive impacts through the appropriate final destination of the waste.
In addition to environmental and occupational health benefits, the use of quartz mining waste for the production of concrete reduces the cost per m3 of concrete by 7.57%. Thus, there is the economic feasibility of using this aggregate for concrete production.
The concrete produced from coarse aggregates from the quartz mining tailings under study have characteristics similar to those of concrete produced with limestone gravel. It meets the simple axial compressive strength specifications of NBR 8953 [
25] and NBR 6118 [
46] for the strength class of concrete, defined for this study as C20 (minimum load capacity of 20 Mpa).
The main parameters of the concrete were described in the technical feasibility analysis. The compressive strength test of the produced concrete and the Los Angeles abrasion test performed on the waste is considered the main parameters to demonstrate whether the use of the waste is technically viable or not. However, it should be emphasized that in future studies, more specific complementary parameters could be evaluated, such as flexural and tensile strengths, microscopic analysis of the produced concrete, analysis of the alkali-silica reactions, and other aggregated analysis (Micro Deval, Flakiness index, surface cleanliness). Another important aspect is that if it were necessary to use concrete with compressive strength above 30 MPa, further research should be carried out.
The reuse of quartz ore waste is an example of how this type of waste could be reused in other mining projects similar to the one shown in the present study, which is very common in SdEM. The results fit into the exercise of interdisciplinary professional practices that transform procedures, being presented across disciplinary boundaries of occupational and housing health, the environment, the economy, and construction materials, with the development of tools for anticipating health problems. This research corroborates the objectives of the National Health Research Agenda [
50], which includes the theme of quality of health at work in activities that promote environmental change. It is also part of health promotion through the development of materials that enable the production of housing at low cost.