Search Results (24)

One of the promising raw materials for the synthesis of geopolymers is perlite, which is a natural low-calcium aluminosilicate. This research studied the physical, mechanical and microstructural characteristics of perlite-based geopolymers modified with different mineral additives that were prepared using different methods of introducing the alkali components and curing conditions. The experimental results of the consolidated perlite-based geopolymer pastes showed that curing conditions and the method of introducing the alkali component into the geopolymer matrix had a minimal effect on the average density while demonstrating a significant boost in compressive strength. So, after thermal treatment, the compressive strength increased by 0.63 to 11.4 times for the mixes when fresh alkali solution was used and by 0.72 to 12.8 times for the mixes with the 24 h conditioned alkali solution. Maximum-strength spikes from 1.1 MPa to 13.2 MPa and from 0.7 MPa to 9.7 MPa were observed for the mixes with kaolin when prepared with fresh and conditioned alkali solutions, respectively. It was also observed that thermal treatment facilitates the compaction of the matrix structure by 18% and 1% for the non-modified mix and the mix modified with Portland cement. Perlite-based geopolymers modified with Portland cement and citrogypsum demonstrated a significant reduction in the initial and final setting times with both methods of introducing the alkali solution. On the surface of mixes modified with citrogypsum, regardless of the curing conditions and method of introducing the alkali component, an efflorescence substance was observed. The microstructural analysis of the consolidated geopolymer perlite-based pastes containing citrogypsum demonstrated a loose structure and the presence of efflorescence, which can be associated with a retardation in interaction processes between alkali cations and the aluminosilicate component. EDS analysis demonstrated that the presence of such elements as oxygen, sodium and sulfur may indicate the efflorescence of unreacted sodium hydroxide (NaOH), citrogypsum (CaSO₄) and the products of their interaction in the form of crystalline hydrates of sodium sulfate (Na₂SO₄). Full article

Alunogen, Al₂(SO₄)₃·17H₂O, occurs as an efflorescent in acid mine drainage, low-temperature fumarolic or pseudofumarolic (such as with coal fires) terrestrial environments. It is considered to be one of the main Al-sulphates of Martian soils, demanding comprehensive crystal-chemical data of natural terrestrial samples. Structural studies of natural alunogen were carried out in the 1970s without localization of H atoms and have not been previously performed for samples from geothermal fields, despite the fact that these environments are considered to be proxies of the Martian conditions. The studied alunogen sample comes from Verkhne–Koshelevsky geothermal field (Koshelev volcano, Kamchatka, Russia). Its chemical formula is somewhat dehydrated, Al₂(SO₄)₃·15.8H₂O. The crystal structure was solved and refined to R₁ = 0.068 based on 5112 unique observed reflections with I > 2σ(I). Alunogen crystalizes in the P-1 space group, a = 7.4194(3), b = 26.9763(9), c = 6.0549(2) Å, α = 90.043(3), β = 97.703(3), γ = 91.673(3) °, V = 1200.41(7) ų, Z = 2. The crystal structure consists of isolated SO₄ tetrahedra, Al(H₂O)₆ octahedra and H₂O molecules connected by hydrogen bonds. The structure refinement includes Al, S and O positions that are similar to previous structure determinations and thirty-four H positions localized for the natural sample first. The study also shows the absence of isomorphic substitutions in the composition of alunogen despite the iron-enriched environment of mineral crystallization. The variability of the alunogen crystal structure is reflected in the number of the “zeolite” H₂O molecules and their splitting. The structural complexity of alunogen and its modifications ranges from 333–346 bits/cell for models with non-localized H atoms to 783–828 bits/cell for models with localized H atoms. The higher values correspond to the higher hydration state of alunogen. Full article

Potassium (K) is an essential element, which is often supplied to horticultural crops via foliar spraying. Some studies have investigated the effect of different foliar-applied K compounds; however, most studies have focussed on crop quality and yield parameters, or were performed with isolated leaf cuticles. The aim of this study was to evaluate the rates of the foliar ion penetration and leaf surface deposition of 130 mM K sprays of compounds with markedly different point of deliquescence (POD) and efflorescence (POE) values, the rates having been previously estimated in climate chamber trials. Shoots of field-grown, commercial olive trees were sprayed with K-nitrate (KNO₃), K-sulphate (K₂SO₄), K-chloride (KCl), K-phosphate (K₃PO₄), K-carbonate (K₂CO₃) and K-bicarbonate (KHCO₃), and leaf samples were collected after 3 and 24 h. Cation and anion concentrations were determined in the leaf tissues, and in a preliminary leaf water wash for estimating surface-deposited ion concentrations. No significant leaf tissue K increments were recorded between the K sprays. Olive tissue anion concentrations showed different patterns, and a chloride (Cl⁻) increase was detected 3 h after the foliar KCl supply. On the other hand, the foliar K applications led to leaf nitrate changes regardless of the K source supplied. High amounts of K and accompanying ions were recovered in the washing liquid of the foliar K-supplied leaves. Some foliar K treatments increased the leaf surface concentration of sulphate and chloride, suggesting a potential effect on leaf cell anion extrusion. Hence, despite no evidence of foliar K uptake, an effect of leaf anion concentrations was observed, indicating that foliar nutrient sprays may influence leaf and leaf surface anion balance. Full article

Salt efflorescences from metal sulphides and their waste are important drivers of pollution both in and around mining areas. However, little is known about these supergene minerals, particularly in the mining areas of the Mediterranean. This study aims to characterise saline efflorescences and their leachates from a Mediterranean mining area located in Southeast Spain. The physicochemical characteristics were determined using stereomicroscopy and compositional analysis, with the following techniques: XRD, WDXRF and TG-MS. Additionally, to assess the risk and potential mobility of their analytes, the samples were subjected to the leaching test DIN 38414-S4. The results showed that the salt efflorescences presented a wide range of crystalline habits and colours. Sulphates were by far the largest mineral group, followed by silicates, oxides and sulphides. Their geochemistry was dominated by elements such as S or Fe, although other potentially toxic elements such as Cd, As, Zn, Pb, Ni and Cu were also present. Due to their high metal(loid) concentrations, the salt crusts studied may act as sources of environmental contaminants, demonstrating that their leachates pose a considerable risk to soil and drinking water quality. An analysis of the correlations and provenances of the components of the salt efflorescences revealed the possible presence of some rare supergene minerals of great interest, such as cuprocopiapite and Pb-As-jarosite. Full article

In the present study, the salinization trends of different soil types from a small hydrographic basin situated in NE Romania (Roșior basin) are investigated. The climatic conditions are favorable for long dry summers and intensive evaporation. The soils are developed on immature evolved clay sediments, as revealed by geochemical analysis. The salinity varies among soil types, attaining maximum values for Solonetz with total dissolved salts (TDS) between 1165.75 to 1881.25 mg/L. The aqueous solutions are represented by natural water and soil solution. The hydrogeochemical facies of the natural waters change from HCO₃⁻—Mg²⁺ in the upper basin to SO₄²⁻—Na⁺ in the middle or lower basin. The soil solution is moderately or strongly salinized and shows anionic variations from HCO₃⁻ to SO₄²⁻ in the studied profiles, whereas Na⁺ is always the main cation. The concentrations of Na⁺ and SO₄²⁻ evolve simultaneously. Raman spectroscopic exploration of the white efflorescences, which occur on topsoil, reveals the presence of thenardite as the dominant phase. The composition of soil solution results from both the ionic exchange and evaporation processes. The nature of soil solution mineralization and summer temperatures are two main factors that interact and promote the thenardite precipitation. The soil salinization induces negative effects on crop nutrition, impacting further the crop yields. The results of this study can be extrapolated to larger areas formed on Sarmatian sedimentary deposits affected by salinization processes. Full article

The new mineral chenowethite, Mg(H₂O)₆[(UO₂)₂(SO₄)₂(OH)₂]·5H₂O, was found in efflorescence crusts on tunnel walls at the Blue Lizard, Green Lizard and Markey uranium mines in Red Canyon, San Juan County, Utah, USA. The crystals are long, thin blades up to about 0.5 mm long, occurring in irregular sprays and subparallel groups. Chenowethite is pale green yellow. It has white streak, vitreous to silky luster, brittle tenacity, splintery and stepped fracture and two cleavages: {010} perfect and {001} good. It has a hardness (Mohs) of about 2 and is nonfluorescent in both long- and short-wave ultraviolet illumination. The density is 3.05(2) g/cm³. Optically, crystals are biaxial (−) with α = 1.530(2), β = 1.553(2) and γ = 1.565(2) (white light). The 2V is 72(2)° and dispersion is r > v (slight). The optical orientation is X = b, Y = a, Z = c and the mineral exhibits weak pleochroism in shades of pale green yellow: X < Y < Z. The Raman spectrum is consistent with the presence of UO₂²⁺, SO₄²⁻ and OH^–/H₂O. The empirical formula from electron microprobe analysis and arranged in accordance with the structure is (Mg_0.71Fe²⁺_0.09Co_0.05Ni_0.04)_∑0.89(H₂O)₆[(UO₂)₂(SO₄)₂(OH)₂]·[(H₂O)_4.78(NH₄)_0.22]_∑5.00. Chenowethite is orthorhombic, space group Cmcm; the unit-cell parameters are a = 6.951(2), b = 19.053(6), c = 16.372(5) Å, V = 2168.19(7) ų and Z = 4. The crystal structure of chenowethite (R₁ = 0.0396 for 912 I > 2σI reflections) contains [(UO₂)₂(SO₄)₂(OH)₂]²⁻ sheets that are topologically equivalent to those in deliensite, feynmanite, greenlizardite, johannite, meitnerite and plášilite. Full article

Mineral building materials suffer from weathering processes such as salt efflorescence, freeze–thaw cycling, and microbial colonization. All of these processes are linked to water (liquid and vapor) in the pore space. The degree of damage following these processes is heavily influenced by pore space properties such as porosity, pore size distribution, and pore connectivity. X-ray computed micro-tomography (µCT) has proven to be a valuable tool to non-destructively investigate the pore space of stone samples in 3D. However, a trade-off between the resolution and field-of-view often impedes reliable conclusions on the material’s properties. X-ray dark-field imaging (DFI) is based on the scattering of X-rays by sub-voxel-sized features, and as such, provides information on the sample complementary to that obtained using conventional µCT. In this manuscript, we apply X-ray dark-field tomography for the first time on four mineral building materials (quartzite, fired clay brick, fired clay roof tile, and carbonated mineral building material), and investigate which information the dark-field signal entails on the sub-resolution space of the sample. Dark-field tomography at multiple length scale sensitivities was performed at the TOMCAT beamline of the Swiss Light Source (Villigen, Switzerland) using a Talbot grating interferometer. The complementary information of the dark-field modality is most clear in the fired clay brick and roof tile; quartz grains that are almost indistinguishable in the conventional µCT scan are clearly visible in the dark-field owing to their low dark-field signal (homogenous sub-voxel structure), whereas the microporous bulk mass has a high dark-field signal. Large (resolved) pores on the other hand, which are clearly visible in the absorption dataset, are almost invisible in the dark-field modality because they are overprinted with dark-field signal originating from the bulk mass. The experiments also showed how the dark-field signal from a feature depends on the length scale sensitivity, which is set by moving the sample with respect to the grating interferometer. Full article

Environmental conditions present in mines generally are very favourable to decay; high temperature, high humidity, variable oxygen content, numerous metal-wood connections and the presence of a high content of inorganic compounds typical of mines have a significant impact on the biotic and abiotic degradation factors. The state of conservation of wooden artefacts from the Złoty Stok (Poland) gold mine was investigated using a multi-analytical approach. The aim was to select the conservation treatments that would stop decay and improve the conditions and dimensional stability of the wood. FT-IR and Py-GC/MS were used to assess the state of preservation of lignocellulosic material. ED-XRF and SEM-EDS were used to determine—and XRD to identify crystalline phases—salts and minerals in the wood structure or efflorescence on the surface. Highly degraded lignocellulosic material that had undergone depolymerisation and oxidation was found to be severely contaminated by iron-based mineral substances, mainly pyrite, and in some cases greigite and magnetite. The presence of inorganic salts made it difficult to choose the best consolidating material to reduce the level of decay and improve the dimensional stability of the wood. Full article

In this study, sulphate efflorescent minerals covering the surface of the Donnoe and Dachnoe fields of the Mutnovsky volcano are described. The minerals were precipitated on the argillic facies as the result of water–rock interaction and fumarole emission. A chemical composition of Ca, Ba, (NH₄)⁺, Na-Fe³⁺, (NH₄)⁺-Al, (NH₄)⁺-Fe³⁺, Na-Al, K-Al, and K-Fe³⁺ sulphates was reported. Elements such as Sr, Mg, Co, Ni, Ti and P were found as isomorphic impurities. Ammonia species were concentrated around fumaroles. The mineral assemblage described herein is unique in relation to other geological settings and reflects the process of low-temperature mineral formation associated with volcanism. The thermal water contains cations such as H, Na, K, NH₄, Ca, Mg, Fe²⁺, Fe³⁺, and Al in different proportions with pH ranging from 2.4 to 6.5 and the dominance of acidic waters. The gas condensate bears such cations as (NH₄)⁺, Ca, and Mg and has a pH of ~5. Thus, the rest of the main cations are derived from the leaching of the host rocks. Among the identified phases, the alunite-supergroup minerals are more prone to isomorphism. The Ti, Co, and Ni impurities mark the unique geochemistry of thermal water at the Mutnovsky volcano. We postulate that the chemical composition of alunite-supergroup minerals reflects the types of hydrothermal occurrences and contains important information on the geochemistry of the hydrothermal process. Full article

Medium and highly sulfidic tailings are high-volume wastes that can lead to severe environmental damage if not properly managed. Due to the high content of sulfide minerals, these tailings can undergo weathering if put in contact with oxygen and water, generating acid mine drainage (AMD). The moderate-to-high sulfide content is also an important technical limitation for their implementation in the production of construction materials. This paper reviews the use of sulfidic tailings as raw material in construction products, with a focus on cement, concrete, and ceramics. When used as aggregates in concrete, this can lead to concrete degradation by internal sulfate attack. In building ceramics, their implementation without prior treatment is undesirable due to the formation of black reduction core, efflorescence, SO_x emissions, and their associated costs. Moreover, their intrinsic low reactivity represents a barrier for their use as supplementary cementitious materials (SCMs) and as precursors for alkali-activated materials (AAMs). Nevertheless, the production of calcium sulfoaluminate (CSA) cement can be a suitable path for the valorization of medium and highly sulfidic tailings. Otherwise difficult to upcycle, sulfidic tailings could be used in the clinker raw meal as an alternative raw material. Not only the SO₃ and SiO₂-rich bulk material is incorporated into reactive clinker phases, but also some minor constituents in the tailings may contribute to the production of such low-CO₂ cements at lower temperatures. Nevertheless, this valorization route remains poorly explored and demands further research. Full article

This paper provides new insights into the geochemical cycling of rare earth elements (REEs) in acid sulfate soils developed on salt marsh sediments of the Huelva estuary (Spain) as a result of sulfide mineral oxidation in abandoned ore stockpiles. The study was aimed at determining the REE abundance, fractionation pattern and mineralogical control of the dispersal and retention of REEs in the soil system. Forty-one samples were collected at 13 core sampling sites along two transects extending across the degraded marshland, and they were subjected to XRD, ESEM-EDS and ICP-MS analyses. Measurements revealed that the soil receiving acid discharges has relatively high concentrations of ΣREEs (174.77 ± 19.77 mg kg⁻¹) compared to local baseline concentrations. Shale-normalized REE patterns are generally flat, but a slight middle REE (MREE) enrichment is consistently apparent in all soil samples, involving relatively low La_N/Gd_N ratios (0.83 ± 0.08) and Gd_N/Lu_N ratios up to 1.42. The convex-upward REE pattern supports the possibility that iron oxy-hydroxide minerals play an important role in MREE retention through adsorption and co-precipitation mechanisms. Efflorescent sulfate salts left on the topsoil by the evaporation of acid waters show a strong depletion of light REEs (La_N/Gd_N = 0.16 ± 0.10) and act as a temporary reservoir of labile MREEs and heavy REEs during dry periods. Full article

The sheltered environment of the Algares +30 level adit (underground mine gallery) contributes to the preservation of secondary water-soluble minerals formed on the tunnel walls. The massive sulphide and related stockwork zone are hosted by the Mine Tuff volcanic unit and are exposed in the walls of the gallery, showing intense oxidation and hydrothermal alteration. Minerals from the halotrichite group were identified on the efflorescent salts, typically white fine-acicular crystals but also on aggregates with dark orange/brownish colour. Mineral characterization was performed using several methods and analytical techniques (XRD, XRF-WDS, SEM-EDS, DTA-TG), and the chemical formulas were calculated maintaining the ratio A:B ≅ 1:2 in accordance with the general formula of the halotrichite group, AB₂(SO₄)₄·22H₂O. This methodology allowed the assignment of the orange colour to the presence of trivalent iron on iron-rich pickeringite in partial substitution of aluminium. Full article

Efflorescence is aesthetically undesirable to all cementitious materials products and mainly results from the carbonation of hydrates and salt precipitation. Alternative binders without portlandite formation theoretically have much lower efflorescence risk, but in practice, the efflorescence of ettringite-rich systems is still serious. This study reports the impacts of mineral additives on the efflorescence of ettringite-rich systems and the corresponding microstructural evolution. The effects of silica fume, limestone powder, and diatomite on efflorescence and the capillary pore structure of mortars were investigated from a multi-scale analysis. The composition and microstructure of efflorescent phases were revealed by optical microscope (O.M.), in-situ Raman spectroscopy, and Scanning Electron Microscopy (SEM). Results indicate that the addition of mineral additives can efficiently inhibit the efflorescence of reference, especially with silica fume. Similar to the ettringite-rich system, the efflorescence substances of all modifies are composed of ettringite and CaCO₃, indicating that the addition of mineral admixture does not lead to chemical reactions, lower capillary absorption coefficient of mineral additives modified specimen, the denser pore structure and the lower efflorescence degree. Full article

This research focuses on the analysis of the influence of two secondary salt weathering processes on the durability of rocks exposed to marine environments: chemical dissolution of rock forming minerals and differential thermal expansion between halite and the hosting rock. These processes are scarcely treated in research compared to salt crystallisation. The methodology followed in this paper includes both in situ rock weathering monitoring and laboratory simulations. Four different calcite-bearing rocks (a marble, a microcrystalline limestone and two different calcarenites) were exposed during a year to a marine semiarid environment. Exposed samples show grain detachment, crystal edge corrosion, halite efflorescences and microfissuring. Crystal edge corrosion was also observed after the laboratory simulation during a brine immersion test. Calcite chemical dissolution causes a negligible porosity increase in all the studied rocks, but a significant modification of their pore size distribution. Laboratory simulations also demonstrate the deterioration of salt-saturated rocks during thermal cycles in climatic cabinet. Sharp differences between the linear thermal expansion of both a pure halite crystal and the different studied rocks justify the registered weight loss during the thermal cycles. The feedback between the chemical dissolution and differential thermal expansion, and the salt crystallisation of halite, contribute actively to the rock decay in marine environments. Full article

Weathering and transport of potentially acid generating material (PAGM) at abandoned mines can degrade downstream environments and contaminate water resources. Monitoring the thousands of abandoned mine lands (AMLs) for exposed PAGM using field surveys is time intensive. Here, we explore the use of Remotely Piloted Aerial Systems (RPASs) as a complementary remote sensing platform to map the spatial and temporal changes of PAGM across a mine waste rock pile on an AML. We focus on testing the ability of established supervised and unsupervised classification algorithms to map PAGM on imagery with very high spatial resolution, but low spectral sampling. At the Perry Canyon, NV, USA AML, we carried out six flights over a 29-month period, using a RPAS equipped with a 5-band multispectral sensor measuring in the visible to near infrared (400–1000 nm). We built six different 3 cm resolution orthorectified reflectance maps, and our tests using supervised and unsupervised classifications revealed benefits to each approach. Supervised classification schemes allowed accurate mapping of classes that lacked published spectral libraries, such as acid mine drainage (AMD) and efflorescent mineral salts (EMS). The unsupervised method produced similar maps of PAGM, as compared to supervised schemes, but with little user input. Our classified multi-temporal maps, validated with multiple field and lab-based methods, revealed persistent and slowly growing ‘hotspots’ of jarosite on the mine waste rock pile, whereas EMS exhibit more rapid fluctuations in extent. The mapping methods we detail for a RPAS carrying a broadband multispectral sensor can be applied extensively to AMLs. Our methods show promise to increase the spatial and temporal coverage of accurate maps critical for environmental monitoring and reclamation efforts over AMLs. Full article