Search Results (54)

Mining activity in Peru generates environmental liabilities with the potential to release toxic metals into the environment. This study conducted a comprehensive physical, chemical, mineralogical, and toxicological characterization of ten active and inactive tailings samples from the Arequipa region in southern Peru. Particle size distribution analysis, inductively coupled plasma atomic emission spectroscopy (ICP-AES), scanning electron microscopy with energy-dispersive spectroscopy (SEM-EDS), and the Toxicity Characteristic Leaching Procedure (TCLP) followed by ICP-MS were employed. The results revealed variable particle size distributions, with the sample of Secocha exhibiting the finest granulometry. Chemically, 8 out of 10 samples exhibited concentrations of at least two metals surpassing the Peruvian Environmental Quality Standards (EQS) for soils with values reaching >6000 mg/kg of arsenic (Paraiso), 193.1 mg/kg of mercury (Mollehuaca), and 2309 mg/kg of zinc (Paraiso). Mineralogical analysis revealed the presence of sulfides such as arsenopyrite, cinnabar, galena, and sphalerite, along with uraninite in the Otapara sample. In the TCLP tests, 5 out of 10 samples released at least two metals exceeding the environmental standards on water quality, with concentrations up to 0.401 mg/L for mercury (Paraiso), 0.590 mg/L for lead (Paraiso), and 9.286 mg/L for zinc (Kiowa Cobre). These results demonstrate elevated levels of Potentially Toxic Elements (PTEs) in both solid and dissolved states, reflecting a critical geochemical risk in the evaluated areas. Full article

Flotation tailings (FT), as a product of the exploitation and processing of copper ore, represent a significant environmental and health risk due to the high content of heavy metals and sulfide compounds. Contemporary concepts of sustainable development and circular economy increasingly emphasize the need for rational use of resources and minimization of all types of waste, including mining waste. In this context, the reuse of flotation tailings in the construction industry represents a significant step towards closing the material flow in the mining and construction sectors. In order to reduce the negative impact of FT on the environment, the possibility of its application as a substitute for a portion of cement in the production of concrete was investigated. The main challenge is to reduce the negative impact of sulfides, originating from sulfide compounds, in order to achieve the desired concrete quality. Limestone aggregates of different size fractions (0/4, 4/8, 8/16 mm) were used for sulfide neutralization. Pyrite concentrate was used as a sulfide source, which together with FT provides the mixtures FT-7, FT-14, FT-25, and FT-40, with sulfur contents of 7.56, 13.84, 25.02, and 39.82%, respectively. FT mixtures were used as a substitute for Portland cement (PC) in the preparation of concrete. Test methods included XRD (X-ray diffraction), XRF (X-ray fluorescence), SEM (scanning electron microscopy), LP (leaching procedure), TCLP (toxicity characterization leaching procedure), assessment of acid eluate generation potential (AP—acid potential, NP—neutralization potential, and NNP—net neutralization potential), NEN (determination of heavy metals in cured concrete eluate), and UCS (uniaxial compressive strength of cured concrete). The results showed that the chemical characteristics of FT, as well as the chemical and mechanical properties of hardened concrete, allow the efficient use of these tailings in concrete mixes, which significantly utilizes FT, reduces the generation of mining waste, and contributes to the reduction of the negative impact on the environment and achieving sustainable development in mining. Full article

Sludge is a semi-solid waste generated during the process of wastewater treatment. Due to the addition of polymerized ferric chloride in the flocculation process, the sludge produced by the sewage treatment plant in Liaocheng Jiaming Industrial Park contains a high content of iron oxide. In this paper, chemical analysis and particle size analysis of local sludge and sludge ash were conducted. In order to assess the potential of substituting cement as cementitious material with different dosages of sludge or sludge ash with high iron oxide content, setting time, compressive strength, microscopic analysis using microscopic testing (XRD, TG/DTG, SEM) and a toxicity characteristic leaching procedure (TCLP) were analyzed. These procedures determined the physical properties, compressive strength, hydration products, microstructure, and heavy metal contaminants of cement slurries replaced by local sludge or sludge ash with different dosages of high iron oxide content. The results show that less than 5% of local sludge or sludge ash can be incorporated into cement slurry as an alternative cementitious material for solid waste disposal. Full article

The substantial volumes of tailings produced during ore beneficiation present significant challenges for sustainable management due to potential public health hazards, particularly from metal leaching. The risk associated with tailings varies greatly depending on their mineralogical composition and climatic conditions. If tailings are classified as a non-hazardous by-product, they may serve as secondary raw materials, offering a sustainable alternative to the reliance on non-renewable primary resources. In this study, the recycling feasibility of tailings from an active copper mine was assessed through mineralogical characterization, environmental tests (e.g., static, kinetic, and leaching tests), and geochemical modeling. This multi-faceted approach aimed to predict the geochemical behavior and reactivity of tailings under varying conditions. Results from the static tests indicated that the tailings were non-acid generating. Weathering cell tests revealed circumneutral pH conditions (6.5–7.8), low sulfide oxidation rates, and low instantaneous metal concentrations (<1 mg/L), except for copper (0.6–3.5 mg/L) and iron (0.4–1.4 mg/L). These conditions are attributed to the low abundance of sulfide minerals, such as pyrite, chalcopyrite, bornite, covellite (<0.1 wt.%), and chalcocite (0.2 wt.%), which are effectively encapsulated within gangue minerals. Additionally, the presence of neutralizing minerals, specifically dolomite (27.4 wt.%) and calcite (2.4 wt.%), further stabilizes pH and promotes metal sequestration in secondary mineral forms. The Toxicity Characteristic Leaching Procedure (TCLP) test confirmed low leachability, classifying the tailings as non-hazardous. Full article

This study investigates the use of geopolymer technology as an alternative for the management of mine tailings, which is a serious environmental problem in mining areas, including the Arequipa region of Peru. In this study, the mixture of stabilized mine tailings with different percentages of binders (i.e., metakaolin and pumice) and their impact on the mechanical, microstructural, and toxicological properties of the synthesized geopolymers were analyzed. The ratios of mine tailings to binder material varied between 100/0 and 0/100. The activation was carried out with an alkaline solution of sodium hydroxide (10 M) and sodium silicate (modulus 2.5). Specimens were fabricated as 50 mm cubes, and the seven mix designs were evaluated in triplicate. The evaluations included compressive strength at 7, 14, 28, and 56 days of curing, chemical analysis by Fourier Transform Infrared Spectroscopy (FT-IR), microstructural characterization by X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM/EDS), thermal behavior by thermogravimetry and differential thermal analysis (TGA/DTA) between 40 °C and 1000 °C, and toxicological tests by the Toxicity Characteristic Leaching Procedure (TCLP, EPA 1311) to determine the efficiency of immobilization of toxic metals. The results demonstrate significant improvements in compressive strength for the F50 specimens compared to A0, with increases of approximately 300%, 270%, and 461% observed at 7, 28, and 56 days of curing, respectively, with microstructural stability with an average pore size of 7.21 μm, and efficiency in the immobilization of heavy metals in geopolymers with 30% or 40% binder (60%–70% mine tailings). The leachate concentrations of As, Cd, Pb, and Hg were below the established thresholds, indicating that the stabilized mine tailings can be classified as “non-hazardous materials”. Geopolymers with 30% to 50% binder showed strength development with microstructural stability and efficiency in the immobilization of heavy metals, complying with current regulations. Therefore, these geopolymers are suitable for various applications and in different environmental conditions. Full article

Phosphate mining generates substantial quantities of waste rock during the extraction of sedimentary ores, leading to significant environmental concerns as these wastes accumulate around mining sites. The industry is under increasing pressure to adopt more sustainable practices, necessitating considerable financial investments in remediation and technological advancements. Addressing these challenges requires a holistic strategy that balances social responsibility, environmental preservation, and economic viability. This study proposes an innovative, cost-effective, and environmentally friendly method to manufacture compressed stabilized earth bricks by combining the valorization of phosphate waste rock (PWR) and phosphate washing sludge (PWS). These bricks offer numerous advantages, including low embodied energy, robust mechanical performance, and excellent insulation and thermal properties. Initially, a Toxicity Characteristic Leaching Procedure (TCLP) test and radiometric surface contamination measurement, carried out on raw materials (PWR and PWS), showed that the results were below the permissible limits. Then, the chemical, mineralogical, and geotechnical properties of the raw materials were characterized. Subsequently, various mixtures were formulated in the laboratory using PWR and PWS, with and without cement as a stabilizer. Optimal formulations were identified and scaled up for pilot production of solid bricks with dimensions of 250 × 125 × 75 mm³. The resulting bricks exhibited thermal conductivity and water absorption coefficients that satisfied standard requirements. This method not only addresses the environmental issues associated with phosphate mining waste but also provides a sustainable solution for building materials production. Full article

Powdered layered double hydroxide (CaFe-LDH) was synthesized via hydrothermal co-precipitation, demonstrating successful preparation upon characterization. Subsequently, experiments were conducted to assess its efficacy in immobilizing divalent cadmium (Cd(II)). The findings substantiated the effectiveness of CaFe-LDH in immobilizing Cd(II) within soil. Various influencing factors, including LDH dosage, pH, and soil heavy metal concentration, were systematically investigated, revealing CaFe-LDH’s superiority in Cd(II) immobilization. Notably, the leaching concentration of Cd(II) was notably reduced from 142.30 mg/L to 32.99 mg/L, with a maximum adsorption capacity of 31.10 mg/L, underscoring the significant role of CaFe-LDH in Cd(II) removal. Furthermore, the stability of CaFe-LDH was confirmed via toxicity characteristic leaching procedure (TCLP) experiments and plant potting tests. In-depth analysis of the immobilization mechanism through X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared spectroscopy (FTIR), energy-dispersive X-ray spectroscopy (EDS), and scanning electron microscopy (SEM) elucidated isomorphous substitution and surface adsorption as the primary mechanisms responsible for Cd(II) immobilization in contaminated soils. Additionally, isomorphic substitution and adsorption onto oxygen-containing functional groups were observed. This comprehensive study underscores the promising potential of CaFe-LDH in immobilizing Cd(II) in contaminated soil. With its commendable immobilization properties and recyclability, CaFe-LDH emerges as a promising solution for remediating heavy-metal-contaminated soils. Full article

Stabilizing materials were prepared by different ratios of attapulgite/humic acid composites, and the optimum proportion for the remediation of Cd-polluted soils was found. The results suggested that the bioavailability of Cd in soil was decreased by the application of material prepared with humic acid and attapulgite in a ratio of 1:5. CaCl₂-Cd, diethylenetriaminepentaacetic acid (DTPA-Cd) and the toxicity characteristic leaching procedure (TCLP-Cd) were reduced by 34.03%, 26.62% and 43.66%, and the ecological risk was depressed accordingly. The addition of stabilizing materials could transform the acid-soluble and reducible speciation to residue speciation, with a ratio of 1:5, significantly increasing the residue proportion of Cd in soil. The content of the residue state was increased by 63.13%, and the content of the acid-soluble state was significantly decreased by 34.10% compared with the control. The bioavailability, acid-soluble and reducible speciation of Cd had a highly negative correlation with the growth of corn, and the accumulation of Cd in corn had a significantly negative correlation with the residue speciation. Attapulgite/humic acid composites can reduce the bioavailability and increase the ratio of residue Cd in soil effectively, and they have the potential to remediate the pollution of heavy metals in soil. Full article

As an industrial waste, basic oxygen furnace (BOF) slag is an ideal substitute for natural rubble and sand. However, its potential instability of volume restricts the application of the BOF slag in engineering. This study aims at investigating the volume stability and mechanical properties of BOF slag and its application as an aggregate in cement-stabilized macadam. As part of this research, the physicochemical properties, especially the volume stability, of two types of BOF slags and andesite were first studied. Then, mechanical properties, volume stability, and an environment analysis are used to evaluate the application of pyrolytic BOF slag in cement-stabilized macadam. The experimental results show that different types of BOF slags have similar thermal expansion coefficients, which are higher than andesite. The free CaO content of pyrolytic BOF slag is much lower than that of ordinary BOF slag and the volume expansion of pyrolytic BOF slag is less than 0.5%. The unconfined compressive strength (UCS) of cement-stabilized macadam using pyrolytic BOF slag is about 30% higher than that of andesite. Although the water loss rate is higher than a natural aggregate, dry shrinkage of pyrolytic BOF slag cement-stabilized macadam is about 30–50% less than that of a natural aggregate. Meanwhile, its shrinking speed is also slower than that of a natural aggregate. The micro-expansion properties of pyrolytic BOF slag could effectively partially offset the shrinkage characteristics of cement-stabilized macadam. Finally, the Toxicity Characteristic Leaching Procedure (TCLP) test results indicated that the metal leaching concentration meets the Chinese environmental standards. This study provides a direction for the large-scale and effective sustainable application of pyrolytic BOF slag. Full article

Municipal solid waste incineration fly ash (MSWI FA) consists predominantly of compounds comprising elements such as calcium, aluminum, silicon, sodium, and others. Additionally, it encompasses a complex mixture of heavy metals, chlorides, sulfates, organic pollutants, and other constituents. The effective and economically viable treatment of MSWI FA poses a formidable challenge for resource cycling at the current stage. In this research report, we adopt a novel low-temperature sintering method called the “Cold Sintering Process” (CSP) as a means to immobilize heavy metals within the fly ash. By utilizing a Taguchi orthogonal array method, we will adjust five control factors in the CSP, including sintering temperature, uniaxial pressure, sintering time, initial water addition, and sodium carbonate dosage. The leaching of cadmium from the fly ash, as measured by the Toxicity Characteristic Leaching Procedure (TCLP), will serve as the quality indicator of products. Through the application of CSP, MSWI FA was transformed into structurally stable ceramic blocks, and the heavy metals within the blocks were effectively immobilized. The results of the experiments showed that MSWI FA under the conditions of a temperature of 300 °C, uniaxial pressure of 312 MPa, sintering time in 60 min, 25 wt% water addition, and 9 wt% Na₂CO₃ addition could effectively reduce the leaching of cadmium by 77.71%, lead by 21.14%, zinc by 42.37%, and chromium by 99.99%, as compared to the original MSWI FA TCLP results. The X-ray Diffraction (XRD) results indicate that during the CSP, fly ash forms phases such as calcium silicate, rankinite, hydrogrossular, anorthite, and marilite. These phase transformations are considered beneficial for preventing the leaching of internal heavy metals. Scanning Electron Microscopy-Energy Dispersive X-ray Spectroscopy (SEM-EDS) results reveal that CSP is advantageous for compacting the overall structure, and EDS results further demonstrate that some of the Pb and Zn are carried out from the interior of the blocks, with uneven distribution on the surface of fly ash particles. The aforementioned experimental results serve as preliminary indications of CSP’s capability to stabilize detrimental components within high-purity fly ash. Future research endeavors may entail the refinement of material proportions, modification of experimental parameters, and other methodologies, thus facilitating potential scalability to industrial applications. Such developments align with the overarching goal of resource utilization. Full article

This article deals with the study of hazardous chromium leaching, stabilized/solidified by cement CEM II after 28 days of curing, in an acidic environment. The mortars subjected to this study were investigated by X-ray diffraction (XRD) characterization to evaluate the influence of chromium waste on their mineralogical structure. In the study range (0.6–1.2%), increasing the mass percentage of Cr₂O₃ in the mortars indicates that chromium accelerates the hydration process and setting of the mortar and increases the mechanical strength of the mortars compared to the control sample. It was observed that the release of chromium during the Toxicity Characteristic Leaching Procedure (TCLP) test and the efficiency of the stabilization/solidification process depended on the initial Cr concentration and the leaching time. The use of XRD allowed the identification of new crystallized phases in the cement matrices, namely, CaCrO₄·2H₂O and chromium–ettringite Ca₆Cr₂(SO₄)₃(OH)₁₂·26H₂O, which confirms the immobilization of chromium and the efficiency of the stabilization/solidification process. In this research, the release mechanism was found to be primarily a surface phenomenon by modeling the experimental data (dissolution or precipitation). Full article

Many biomass wastes or their modified forms have been investigated as heavy metal adsorbents. However, less emphasis has been placed on post-adsorbent management or possible further utilization. In this study, biochar (BC) derived from modified bamboo adsorbent after the adsorption of Cu from an aqueous solution was used for the in situ remediation of lake sediment contaminated with Cd and Cu. The results indicated that the Cu concentration was extremely low (≤0.015 mg/L), while Cd was not detected in the overlying water or the interstitial water after the 90-day BC treatment. The pH value (7.5–8.1) slightly increased, and the toxicity characteristic leaching procedure (TCLP) leachability of the Cu and Cd in the sediment decreased overall. Cu and Cd were preferentially transformed into more stable species. The findings highlighted the potential possibility of BC derived from post-adsorbent being used for sediment remediation. However, the BC addition produced significant effects on the sediment microbial activity and community structure. In general, with an increase in BC, the urease activity increased, while the alkaline phosphatase and invertase activity decreased, which could be attributed to the BC itself. In addition, significant changes in both bacterial and fungal genera were observed. Hence, a cautious approach should be taken in the practical application of BC. Full article

The safe disposal of hazardous waste from zinc hydrometallurgy, such as jarosite residue, is crucial for the sustainable development of the industry. The chemical, structural and morphological properties of jarosite residue from zinc smelting were studied by a combination of various characterizations, and environmental stability was evaluated using the toxicity characteristic leaching procedure (TCLP), Chinese standard leaching tests (CSLT) and long-term leaching experiments (LTLE). Phase composition analysis revealed that zinc ferrite and sodium jarosite were the main phases present in the jarosite residue. TCLP and CSLT analyses indicated that the Zn and Pb contents exceeded their respective toxicity identification standards by more than 30 times and 8 times, respectively, exceeding the threshold values of the standard. The LTLE results demonstrated that Pb concentrations continued to exceed the standard limits, even after long contact times. This study has paramount significance in the prediction of jarosite residue stability and the evaluation of its potential for secondary environmental pollution. Full article

Lead is the main toxic factor in jarosite residue. It is important to study the release behavior of lead from simulated lead-bearing jarosite (SLBJ) for predicting the stability of jarosite residue and its secondary pollution to the environment. To identify the technical issues and limitations associated with its safe disposal, a comprehensive analysis of the chemical, structural, and morphological characteristics of SLBJ was conducted using various detection techniques including XRF, XRD, SEM-EDS, FTIR, XPS, etc. The environmental stability of SLBJ was assessed through the toxicity characteristic leaching procedure (TCLP), Chinese standard leaching tests (CSLT), and a long-term leaching experiment (LTLE). Phase composition analysis revealed that the primary components of SLBJ are sodium jarosite and lead sulfate. TCLP and CSLT results indicated that lead content surpassed the toxicity identification standard limit by more than 47 times. Furthermore, LTLE indicated that the lead concentration surpassed the standard limit about 15 times after prolonged contact time. This study is of great significance for predicting the stability of jarosite residue and its secondary pollution to the environment. Full article

The solidification of chromium-contaminated soil using polyurethane (PU) was systematically investigated. The unconfined compression test was conducted to investigate the effects of the curing time, PU dosage and the content of chromium ions on the unconfined compressive strength (UCS) of chromium-contaminated soil. The effect of the PU dosage on the pore structure was investigated using nuclear magnetic resonance (NMR) and scanning electron microscopy (SEM), and the mechanism of strength change was revealed by combining the strength law with the pore structure development law. In addition, the ability of the PU to solidify the chromium-contaminated soil was studied by the toxicity characteristic leaching procedure (TCLP). According to the above test results, the UCS and the ability of the PU to solidify the chromium ions increased with the increase in curing time. The NMR tests showed that with the increase in PU dosage, the porosity decreased and the soil became more compact, hence increasing the strength. When the chromium ion content was 2000 mg/kg and the PU dosage was 8%, the strength of the sample was 0.37 MPa after curing for 24 h, which met the requirement of 0.35 MPa set by the U.S. Environmental Protection Agency. Consequently, PU is a solidification agent with high-early strength. Full article