Long-term performance: strength and metal encapsulation in alkali-activated iron ore tailings.

Understanding the strength behavior and leaching characteristics of mining tailings stabilized with alkali-activated cements in the short, medium, and long term is crucial for the feasibility of material applications. In this context, this study assessed the stabilization/solidification of iron ore tailings (IOT) using alkali-activated binder (AAB) composed of sugarcane bagasse ash and eggshell lime at curing times of 7, 28, 60, 90, 180, and 365 days. Additionally, leaching tests were conducted, along with the examination of possible changes in the chemical and mineralogical composition resulting from exposure to acidic environments. Tests included unconfined compression strength (UCS), leaching, X-ray diffraction, and Fourier-transform infrared spectroscopy for the IOT-AAB mixtures. The highest increase in UCS was observed between 7 and 60 days, reaching 6.47 MPa, with minimal variation thereafter. The AAB-bonded IOT exhibited no metal toxicity over time. Elements Ba, Mn, Pb, and Zn present in IOT and ash were encapsulated in the cemented matrix, with complete encapsulation of all metals observed from 90 days of curing time. The mineralogy of the stabilized/solidified tailings showed no changes resulting from leaching tests. Characteristic bands associated with the presence of N-A-S-H gel were identified in both pre-leaching and post-leaching samples for all curing times analyzed. Exposure to acidic environments altered bands related to carbonate bonds formed in the IOT-AAB mixture.

Paint booth waste as an alternative aggregate for the production of interlocking concrete blocks.

Inadequate disposal of hazardous waste results risks to the environment and human health. Although the use of hazardous waste in new processes and/or products has received limited attention in the literature, there is still significant potential to be investigated. Reducing the usage of natural resources and waste management are important for sustainable practices during concrete production. This study investigated the mechanical and leaching behavior of paint booth waste (PBW) as a partial substitute (10, 20, 30 and 40%) of coarse aggregate in concrete mixtures for the manufacture of interlocking blocks. A sample of PBW used in this research differs from those in the literature due to its granulometry characterized by aggregates of different sizes. Concrete consistency, compressive strength, water absorption, X-ray diffraction, scanning electron microscopy, and leaching tests were carried out. The PBW did not influence the consistency in the fresh state of the concrete. The blocks with smaller substitutions (10 and 20%) presented denser structures and with greater strengths, surpassing 35 MPa after 28 days. Higher levels of PBW resulted in more porous concrete blocks with greater water absorption. The concrete-PBW mixtures showed no metal toxicity, i.e., the incorporation of this waste in the construction material avoided metal leaching. Concrete blocks with up to 20% PBW demonstrated satisfactory mechanical and environmental performance.

Use of sludge from the vehicle industry and its encapsulation of toxic metals in ceramic products.

Despite the various existing studies with wastes from wastewater treatment plants for the production of bricks, there is still a lack of further studies on the technological characterization and application only of hazardous industrial wastes from the treatment of wastewater from the metal-processing automotive industry in the stabilization/solidification with ceramic materials. Therefore, the objective of this work was to evaluate the use of waste from the treatment of wastewater from the metal processing automotive industry for the production of red ceramics by evaluating the mechanical behavior and the potential for encapsulation of contaminants. The waste was originally classified as Class I-Hazardous due to the presence of Se. A clay with a clayey-silty character was used to produce ceramic test specimens by pressing and calcining at 950 °C. In the production of these test specimens, the clay was replaced with 0%, 5%, and 10% waste, and the mechanical properties of linear shrinkage, apparent porosity, water absorption, and three-point flexural strength of the test specimens, as well as the mineralogical, chemical, and microstructural composition such as the leaching of contaminants and potential encapsulation of all test specimens were evaluated. The results showed that after incorporation into the red ceramic, the wastes led to a reduction in flexural strength associated with greater water absorption and porosity, the higher the incorporated percentage. Changes in mineralogy and chemical composition were observed but did not affect microstructure and mechanical properties. The samples did not show metal leaching above national and international standards for toxicity and limits for groundwater and human consumption. It can be concluded that the use of up to 5% of the waste as a replacement for clay meets the requirements for good mechanical performance and encapsulation of the metals originally present in the waste.

Metal encapsulation of waste foundry sand stabilized with alkali-activated binder: Batch and column leaching tests.

Waste stabilization processes are important to add value and reduce environmental risks related to metal contamination of soils and groundwater. This study evaluated the metal encapsulation of: (i) waste foundry sand (WFS) stabilized with an alkali-activated binder (AAB), compared to (ii) WFS-Portland cement (PC) mixture. The AAB was composed by sugar cane bagasse ash (SCBA), hydrated eggshell lime, and sodium hydroxide solution. The metal leaching behavior from WFS-AAB and WFS-PC was investigated through batch and column tests according to NBR 10005 and ASTM D4874 methods, respectively. All WFS-AAB and WFS-PC mixtures showed no metal toxicity. WFS-AAB matrices encapsulated the heavy metals Cd, Cr, and Pb from WFS and SCBA. Leaching results from NBR 10005 method were more favorable than ASTM D4874 for water quality limits (CONAMA 460, Dutch List, and EPA). Binder type, metals leaching patterns, and leaching test procedures were key factors in understanding the environmental performance of cemented WFS.

Mechanical and microstructural properties of iron mining tailings stabilized with alkali-activated binder produced from agro-industrial wastes.

This study evaluated the stabilization of iron ore tailings (IOTs) with an alkali-activated binder (AAB) produced from sugar cane bagasse ash, hydrated eggshell lime, and sodium hydroxide solution. Unconfined compressive strength, split tensile strength, initial shear stiffness, mineralogy, chemical composition, and microstructure of IOTs-AAB were evaluated. Strength values up to 6.59 MPa were achieved after 28 days-curing at 40 °C. Reducing porosity and increasing the binder content improved the overall mechanical behavior. N-A-S-H like gels were identified in IOTs-AAB mixtures. Finally, longer curing times led to more compact structures.

Rice husk ash-carbide lime as an alternative binder for waste foundry sand stabilization.

Rice husk ash (RHA) is an excellent pozzolana and associated with hydrated lime (HL), it becomes an alternative binder to Portland cement in soil stabilization. In the context of waste valorization, waste foundry sand (WFS) and carbide lime (CL) have been investigated in civil construction and environmental geotechnical applications. However, stabilizing WFS with alternative binders to Portland cement represents a large field of research to be explored. This study evaluated the stabilization of WFS with a binder based on RHA and CL, compared to the use of RHA-HL. An experimental design was carried out to evaluate the influence of different dry-specific weights (12.00, 12.75, and 13.50 kN/m3), RHA contents (10%, 20%, and 30%), and curing times (28, 60, and 90 days) under unconfined compressive strength (UCS). UCS results were submitted to statistical analysis and correlated to the porosity/binder content index (η/Biv). Healing capacity, mineralogy, microstructure, and leaching of metals from mixtures of interest were evaluated. The results showed that higher specific weights and higher percentages of RHA promoted better strength. The η/Biv0.28 index proved to be an adequate parameter to assess the UCS of WFS-RHA mixtures with different limes (CL and HL), lower porosity, and higher binder content leading to higher strengths. The mixture's mineralogy and microscopy showed the formation of cementing gels, corroborating the strength gains. WFS stabilized with both binders (RHA-CL and RHA-HL) presented satisfactory environmental performance, allowing the immobilization of metals in the waste compositions.

Mining tailings and alkali activation: a comprehensive bibliometric review.

Significant amounts of mining tailings are generated and disposed of every year in dams, leading to potentially serious environmental and safety problems. To identify alternatives for the disposal of these wastes, research works involving their potential application as precursors in the development of alkaline-activated materials have been published in recent years. In this context, the objective of this paper is to present an overview of the main contributions already made on the subject, identified through a bibliometric review and content analysis in the Scopus and Web of Science databases. There was an exponential growth of interest in the subject in the period 2019-2021, when more than 50% of the papers were published. The most used tailings and sub-areas of research were also identified.

Experimental investigation of binder based on rice husk ash and eggshell lime on soil stabilization under acidic attack.

This study evaluates the use of rice husk ash (RHA)-eggshell lime (ESL) and RHA-commercial lime (CL) as alternative binders for clayey soil stabilization, as well as the performance of soil-binder mixtures under acidic attack. A central composite design was carried out to analyze the reactivity by batch tests with a sulfuric acid solution. Physical and mechanical behavior was evaluated by compaction test and unconfined compressive strength (UCS). Reactivity tests demonstrated better neutralization of contaminant acidity for mixtures with ESL. The highest compressive strength, reactivity and partial encapsulation of toxic elements are associated with application of 30% RHA and 6% ESL in the soil. A C-S-H gel is observed in poorly crystalline phases through the XRD pattern. The application of RHA-ESL in soils exposed to acidic attack has environmental feasibility. Analysis of RHA grinding processes combined with the mixture strength over time, and its application tests in impermeable barriers, in landfills, are recommended.

Leaching assessment of cemented bauxite tailings through wetting and drying cycles of durability test.

Disposal of mine tailings can cause negative environmental effects by releasing contaminants to surface and underground water. Alkali activation is a promising technique for immobilizing metals in stabilization/solidification of these wastes. This study evaluates the leaching behavior of cemented bauxite tailings (BT) submitted to weathering conditions. The alkali-activated binder was composed of sugar cane bagasse ash, carbide lime, and sodium hydroxide solution. Comparisons of the durability and leaching behavior of BT stabilized with alkali-activated binder and high initial strength Portland cement were performed. The durability results for alkali-activated were similar to the Portland cement, showing an average difference of 16%. Portland cement showed favorable results in the encapsulation of heavy metals like Cd and Hg, while the alkali-activated cement on Al, Cr, and Se. For Ba, Fe, Mn, and Zn immobilization, both types of cement presented an equal performance. The durability and leaching behavior of stabilized bauxite tailings is governed by the cement content and porosity of the blends, as well as their pH.

Mobility and environmental monitoring of pesticides in the atmosphere - a review.

Knowledge of the partition mechanisms in the agrochemical environment is fundamental for understanding their behavior within an ecosystem and mitigating possible adverse effects of these products. In this review, the objective was to present the main transport mechanisms, physical-chemical properties, and atmospheric monitoring methodologies of the most diverse types of agrochemicals used in agriculture that can reach the atmosphere and affect different compartments. It has been verified that volatilization is one of more considerable significance of the various forms of transport since a significant part of the applied pesticides can volatilize in a few days. As for monitoring these compounds in the atmosphere, both passive and active sampling have their advantages and disadvantages. Passive samplers allow sampling in large quantities and at remote locations, in addition to making continuous measurements, while active samplers have the advantage of being able to detect low concentrations and continuously. Since a significant portion of the applied pesticides is directed to the atmosphere, monitoring makes it possible to understand some properties of the pesticides present in the air. This monitoring can be done from different existing methodologies based on adopted criteria and existing technical standards. Graphical representation of mobility and environmental monitoring of atmospheric pollutants from pesticides.

Effects of acidic attack on chemical, mineralogical, and morphological properties of geomaterials.

Exposure of geomaterials to acidic leachates may compromise their structure and functionality due to changes in physicochemical, mineralogical, and hydraulic behavior. The literature identifies the need to evaluate changes in a pure state and in conditions of extreme acidity. This study aimed to evaluate changes in the chemical, mineralogical, and morphological properties of Osorio fine uniform sand (OFS), basalt residual soil (BRS), kaolin (KAO), and bentonite (BEN) exposed to sulfuric acid in concentrations of 0.00 mol/L (distilled water), 0.01 mol/L, and 1.00 mol/L. The tested samples were characterized using X-ray fluorescence spectrometry, X-ray diffraction, thermogravimetry, differential scanning calorimetry, and scanning electron microscopy. The acid attack on geomaterials by contact with the solution 1.00 mol/L has resulted in the solubilization of some constituent minerals, as well as the formation of sulfate minerals, changes in the water dehydration peak in the pores, and mass loss. The morphology of the sand and bentonite particles did not change with exposure to sulfuric acid. The acidic attack resulted in changes in the morphology of the particles for BRS and KAO. The results of this study are important for determining operational parameters of waste containment systems and contaminated areas, as well as for applying geomaterials as founding materials.

Removal of chromium from wastewater by swine hair residues applied as a putative biofilter.

Swine production chain generates residues with potential application in environmental processes. This study aimed at the use of swine hair as a potential biofilter for hexavalent chromium (Cr(VI)) removal from wastewater of tannery industry. The hair was pretreated using H2O2 in alkaline medium, and statistical analysis was carried out to evaluate the hair degradation, as well the Cr(VI) removal by the potential pretreated biofilter. The results showed 99% of Cr(VI) removal in 105 min of treatment in large pH range (1-10). Treated and untreated effluents were submitted to cytotoxicity study using vegetable and animal cells, demonstrating a significant reduction on toxicity to both cells. Therefore, swine hair demonstrated to be a promising residue for heavy metal removal on the perspective of an environmentally friendly technique.