Search Results (18)

Regulating the dissolution and interfacial behavior of minerals via external force fields is considered a promising strategy for enhancing the flotation of soluble minerals. This study explored the potential of ultrasound-assisted pulp conditioning in improving ultrafine smithsonite flotation. Specifically, we systematically evaluated the effects of ultrasonic pretreatment (UP) on the physicochemical properties of smithsonite suspensions (focusing on surface erosion behavior) and assessed subsequent flotation performance using flotation tests and modern analytical techniques. It has been found that UP can significantly modify smithsonite suspension characteristics, including particle morphology, ionic composition, electrokinetic properties, and pulp pH. Flotation results demonstrate that UP yields higher recovery compared to traditional stirring (TS) conditioning, especially at medium-to-high sodium oleate (NaOL) concentrations. Comparative analysis reveals that ultrasonic-assisted dissolution and ion-selective migration are the main factors driving improved flotation performance. Unlike TS, UP promotes greater zinc ion release, facilitates the dissolution–hydrolysis–precipitation equilibrium, generates more and finer nanoparticles in the bulk phase, and induces the deposition of hydrozincite on smithsonite surfaces. These changes increase active zinc sites for more stable NaOL adsorption, thereby enhancing the flotation of ultrafine smithsonite particles. Full article

Weathering products of sphalerite-bearing ores play an important role in controlling the fate of Zn in the environment. In this framework, the relative stability of Zn carbonates is of special relevance for the common case of ore weathering by carbonated groundwater in the presence of calcium carbonates. We investigated the experimental (co)nucleation and growth of Zn and Ca carbonates at 25 °C in finite double diffusion silica hydrogel media with the purpose of deciphering the system’s reactive pathway and unraveling the major governing factors behind the obtained mineral assemblages. The crystallized solids were carefully extracted two months post-nucleation and studied with micro-Raman spectroscopy, micro X-ray diffraction (XRD), scanning electron microscopy, and electron microprobe (EMP) methods. The obtained results indicate that the grown Zn-bearing phases corresponded to smithsonite and/or Zn hydroxyl carbonate, while CaCO₃ polymorphs aragonite and calcite were also crystallized. Moreover, the observed mineral textural relationships reflected the interplay between supersaturation with respect to CaCO₃/pCO₂ and the grown Zn-bearing carbonate. Experiments conducted in more supersaturated conditions with respect to CaCO₃ polymorphs (higher pCO₂) favored the precipitation of smithsonite, while the opposite was true for the obtained Zn hydroxyl carbonate phase. The gathered Raman, XRD, and EMP data indicate that the latter phase corresponded to a non-stoichiometric, poorly crystalline solid. Full article

Mining wastes are often both a potential source of Strategic and Critical Raw Materials (SRMs and CRMs) and a threat to the environment. This study investigated the potential of mining wastes from the Montevecchio district of Sardinia, Italy, as a source of SRMs and CRMs. The tailings from Sanna mine processing plant were characterized by X-ray diffraction, Scanning Electron Microscopy, and Plasma Mass Spectometry, showing contents of 1.2 wt% of lead, 2.6 wt% of zinc, and about 600 mg/kg of Rare Earth Elements (REEs). White patinas formed in the riverbed, composed by Zn-bearing minerals (hydrozincite and zincite), also contain about 2900 mg/kg of REEs. Characterization of white patinas along the Rio Roia Cani evidenced that their precipitation from water also involves an uptake of Rare Earth Elements, enhancing their contents by an order of magnitude compared with tailings. The process of REEs concentration in Zn-bearing minerals of white patinas is a candidate as a tool for the economic recovery of these elements. These findings suggest that mining wastes from the Montevecchio district could be considered a potential resource for extracting SRMs and CRMs. Full article

We report on high-pressure angle-dispersive synchrotron X-ray diffraction data of a natural Zn_3.78(2)Cu_1.22(2)(CO₃)₂(OH)₆ aurichalcite mineral up to 7.6 GPa and ab initio total energy calculations of the aurichalcite structure with three different Zn-Cu stoichiometries (Zn:Cu ratios = 10:0, 8:2 and 6:4). A monoclinic-to-triclinic displacive second-order phase transition was found experimentally at 3 GPa. The experimental bulk modulus of the initial P2₁/m aurichalcite is B₀ = 66(2) GPa, with a first-pressure derivative of B₀′ = 9(2). A comparison with other basic copper and zinc carbonates shows that this B₀ value is considerably larger than those of malachite and azurite. This relative incompressibility occurs despite the fact that aurichalcite features a layered structure due to the number of directed hydrogen bonds between carbonate groups and the cation-centered oxygen polyhedra forming complex sheets. The existence of different bond types and polyhedral compressibilities entails a certain anisotropic compression, with axial compressibilities κ_a0 = 3.79(5)·10⁻³ GPa⁻¹, κ_b0 = 5.44(9)·10⁻³ GPa⁻¹ and κ_c0 = 4.61(9)·10⁻³ GPa⁻¹. Additional density-functional theory calculations on the C2/m hydrozincite-type structure with different Zn:Cu compositional ratios shows that the aurichalcite structure is energetically more stable than the hydrozincite one for compositions of Zn:Cu = 10:0, 8:2 and 6:4 at room pressure. The pure Zn aurichalcite phase, however, was predicted to transform into hydrozincite at 18 GPa, which suggests that the experimentally observed hydrozincite structure is a metastable phase. Full article

Zinc oxide is one of the well-known photocatalysts, the potential applications of which are of great importance in photoactivated gas sensing, water and air purification, photocatalytic synthesis, among others. However, the photocatalytic performance of ZnO strongly depends on its morphology, composition of impurities, defect structure, and other parameters. In this paper, we present a route for the synthesis of highly active nanocrystalline ZnO using commercial ZnO micropowder and ammonium bicarbonate as starting precursors in aqueous solutions under mild conditions. As an intermediate product, hydrozincite is formed with a unique morphology of nanoplates with a thickness of about 14–15 nm, the thermal decomposition of which leads to the formation of uniform ZnO nanocrystals with an average size of 10–16 nm. The synthesized highly active ZnO powder has a mesoporous structure with a BET surface area of 79.5 ± 4.0 ${\mathrm{m}}^2/\mathrm{g}$, an average pore size of 20 ± 2 nm, and a cumulative pore volume of 0.507 ± 0.051 ${\mathrm{cm}}^3/\mathrm{g}$. The defect-related PL of the synthesized ZnO is represented by a broad band with a maximum at 575 nm. The crystal structure, Raman spectra, morphology, atomic charge state, and optical and photoluminescence properties of the synthesized compounds are also discussed. The photo-oxidation of acetone vapor over ZnO is studied by in situ mass spectrometry at room temperature and UV irradiation (${\lambda }_{\max }$ = 365 nm). The main products of the acetone photo-oxidation reaction, water and carbon dioxide, are detected by mass spectrometry, and the kinetics of their release under irradiation are studied. The effect of morphology and microstructure on the photo-oxidative activity of ZnO samples is demonstrated. Full article

This article presents the microstructure (SEM) and corrosion behavior of ZnAl12Mg3Si0.3 (ZAMS) coatings obtained by the double hot-dip method on Sebisty steel with increased strength. On the basis of chemical composition studies in micro-areas (EDS) and phase composition studies (XRD), structural components of the coating and corrosion products formed on the coating surface after exposure to the neutral salt spray (NSS) test (EN ISO 9227) were identified. The presence of the Fe(Al,Si,Zn)₃ intermetallic phase was found in the Fe-Al intermetallic layer, while in the outer layer, dendrites rich in Al and Zn were identified. In these dendrites, the eutectics of Zn/MgZn₂ and precipitates of the MgZn₂ phase and Si were located. The NSS test showed better corrosion resistance of ZAMS coatings compared to conventional zinc hot-dip coatings. The increase in corrosion resistance is due to the formation of favorable corrosion products: simonkolleite—Zn₅(OH)₈Cl₂·H₂O and hydrozincite—Zn₅(OH)₆(CO₃)₂, and the presence of the MgZn₂ phase in the coating, which is more anodic than other structural components. Full article

This article reviews blue shortwave-excited luminescence (BSL) in natural minerals and synthetic materials. It also describes in detail the emission of seven minerals and gems displaying BSL, as well as three references in which BSL is caused by titanate groups (TiO₆): benitoite, Ti-doped synthetic sapphire and spinel. Emission (under 254 nm shortwave excitation) and excitation spectra are provided, and fluorescence decay times are measured. It is proposed that BSL in beryl (morganite), dumortierite, hydrozincite, pezzotaite, tourmaline (elbaite), some silicates glasses, and synthetic opals is due to titanate groups present at a concentration of 20 ppmw Ti or above. They all share a broad emission with a maximum between 420 and 480 nm (2.95 to 2.58 eV) (thus perceived as blue), and an excitation spectrum peaking in the short-wave range, between 230 and 290 nm (5.39 to 4.27 eV). Furthermore, their luminescence decay time is about 20 microseconds (from 2 to 40). These three parameters are consistent with a titanate emission, and to our knowledge, no other activator. Full article

In this study, waterborne hybrid organic-inorganic zinc rich coatings (ZRC) with different aluminum flake amounts were tested at low thickness in 3 wt% NaCl aqueous solution. Open circuit potential and impedance response evolution over time were measured experimentally to evaluate their anticorrosion properties. Microstructure of the investigated coatings and composition of the corrosion products were also determined by electron microscopy, X-ray diffraction and infrared spectroscopy, while the stability of the coatings was investigated via inductively coupled plasma optical emission spectroscopy. The results showed that the absence of aluminum flakes leads to a less stable matrix, unable to retain sufficient corrosion inhibitors, resulting in a shorter protection time. For an intermediate concentration of aluminum particles, good corrosion properties were observed. Corrosion products play an important role in the protection mechanism, with simonkolleite and hydrozincite accumulating over time, forming a protective layer on the substrate for several weeks. High amounts of aluminum also lead to the formation of corrosion products, but without providing a barrier effect, while rapidly consuming zinc, leading to rapid formula failure. These results indicate that the use of a controlled amount of aluminum flakes can significantly improve the corrosion protection capability of this type of coating. Full article

Zinc oxide arouses considerable interest since it has many applications—in microelectronics, environmental decontaminations, biomedicine, photocatalysis, corrosion, etc. The present investigation describes the green synthesis of nanosized ZnO particles using a low-cost, ecologically friendly approach compared to the classical methods, which are aimed at limiting their harmful effects on the environment. In this study, ZnO nanoparticles were prepared using an extract of Mentha arvensis (MA) leaves as a stabilizing/reducing agent, followed by hydrothermal treatment at 180 °C. The resulting powder samples were characterized by X-ray diffraction (XRD) phase analysis, infrared spectroscopy (IRS), scanning electron microscopy (SEM), and electron paramagnetic resonance (EPR). The specific surface area and pore size distribution were measured by the Brunauer–Emmett–Taylor (BET) method. Electronic paramagnetic resonance spectra were recorded at room temperature and at 123 K by a JEOL JES-FA 100 EPR spectrometer. The intensity of the bands within the range of 400–1700 cm⁻¹ for biosynthesized ZnO (BS-Zn) powders decreased with the increase in the Mentha arvensis extract concentration. Upon increasing the plant extract concentration, the relative proportion of mesopores in the BS-Zn samples also increased. It was established that the photocatalytic performance of the biosynthesized powders was dependent on the MA concentration in the precursor solution. According to EPR and PL analyses, it was proved that there was a presence of singly ionized oxygen vacancies (V₀⁺) and zinc interstitials (Zn_i). The use of the plant extract led to changes in the morphology, phase composition, and structure of the ZnO particles, which were responsible for the increased photocatalytic rate of discoloration of Malachite Green dye. Full article

Zinc (Zn) coating is being used to protect steel structures from corrosion. There are different processes to deposit the coating onto a steel substrate. Therefore, in the present study, a 100 µm thick Zn coating was deposited by arc and plasma arc thermal spray coating processes, and the corrosion resistance performance was evaluated in artificial seawater. Scanning electron microscopy (SEM) results showed that the arc thermal spray coating exhibited splats and inflight particles, whereas plasma arc spraying showed a uniform and dense morphology. When the exposure periods were extended up to 23 d, the corrosion resistance of the arc as well as the plasma arc thermal spray coating increased considerably. This is attributed to the blocking characteristics of the defects by the stable hydrozincite (Zn₅(OH)₆(CO₃)₂). Full article

Corrosion behaviour of Sn (0.0, 0.5, 1.0, 2.0 and 3.0 wt.%)-doped Zn 1.6 wt.% Al 1.6 wt.% Mg alloys exposed to salt spray testing was investigated. Intergranular corrosion was observed for all alloys in both as-cast and annealed states. However, due to microstructure spheroidisation in the annealed samples, potential intergranular corrosion paths are significantly reduced. Samples with 0.5 wt.% of Sn showed the best corrosion properties. The main corrosion products identified by XRD analysis for all samples were simonkolleite and hydrozincite. Occasionally, ZnO and AlO were identified in limited amounts. Full article

The ore deposits of Bou Caïd (Ouarsenis, Algeria) occur in Jurassic and Cretaceous sedimentary rocks. The barite and Pb-Zn (Fe, Cu, and F) ore deposits of Bou Caïd belong to vein- and karst-type. The mineralization is represented in the whole area by a mixture of barite (currently still exploited) and nonsulfides consisting of hemimorphite, smithsonite, cerussite, hydrozincite, and Fe-oxy-hydroxides, with remnants of galena and sphalerite in variable proportions. Mineralogical and geochemical analyses were carried out on the Bou Caïd nonsulfides. Several samples representing nonsulfide mineralization (Grand Pic and at Srâa Abdelkader) were subjected to a multidisciplinary analytical approach, using optical microscopy (OM), powder X-ray diffraction (PXRD), Scanning Electron Microscopy with Energy Dispersive Spectrometry (SEM-EDS). Nonsulfide mineralization consists of a mixture of hemimorphite, hydrozincite, smithsonite, cerussite, and Fe-oxy-hydroxides, often with zebra-like textures. In the proposed paragenetic scheme, covellite and chalcocite are followed by cerussite, jarosite, smithsonite, and hydrozincite. Then, hemimorphite crystallizes, accompanied by mimetite, traces of malachite and clay minerals (also Zn-bearing), precipitate. Fe-(Mn)-oxy-hydroxides can form during various phases of the supergene stage. Small amounts of late barite can be related to partial remobilization and occur as reprecipitation products. Stable isotope analyses were performed on the calcites and metal carbonates of the supergene ores. Carbon and oxygen isotope values of smithsonite and hydrozincite were comparable to published supergene Zn carbonate data. The isotope values of the Bou Caïd calcites fell both into the hydrothermal carbonate and in the supergene fields. Full article

Elements in mining extracts can be potentially toxic if they are incorporated into soils, sediments or biota. Numerous approaches have been used to assess this problem, and these include sequential extractions and selective extractions. These two methods have limitations and advantages, and their combined use usually provides a rough estimate of the availability or (bio)availability of potentially toxic elements and, therefore, of their real potential as toxicants in food chains. These indirect speciation data are interesting in absolute terms, but in the work described here, this aspect was developed further by assessing the evolution of availability-related speciation in relation to the transport processes from the emission source, which are mainly fluvial- and wind-driven. This objective was achieved by characterizing tailings samples as the source of elements in soils and sediments at increasing distances to investigate the evolution of certain elements. The standard procedures employed included a sequential five-step extraction and a selective extraction with ammonium acetate. The results show that the highest percentages of Zn and Pb in tailings, soils and sediment samples are associated with oxyhydroxides, along with a significant presence of resistant mineralogical forms. In the case of Cd, its association with organic matter is the second-most important trapping mechanism in the area. The physicochemical mechanisms of transport did not transform the main mineralogical associations (oxyhydroxides and resistant mineralogical forms) along the transects, but they produced a chaotic evolution pattern for the other minor matrix associations for Zn and a decrease in exchangeable and carbonate-bound forms for Pb in soils. Interestingly, in sediments, these mobile forms showed a decrease in Zn and a chaotic evolution for Pb. The most probable reason for these observations is that Zn²⁺ can form smithsonite (ZnCO₃) or hydrozincite (Zn₅(CO₃)₂(OH)₆), which explains the retention of a carbonate-bound form for Zn in the soil transect. In contrast, Pb and Cd can appear as different mineral phases. The order of (bio)availability was Pb > Zn > Cd in tailings but Cd > Pb > Zn in soils. The physicochemical processes involved in transport from tailings to soils produce an increase in Cd (bio)availability. The trend is a decrease in bioavailability on moving away from the source (tailings), with maximum values obtained for Cd near to the source area (200–400 m). Full article

Environmental contamination due to human activities is a worldwide problem that has led to the development of different remediation techniques, including biotechnological approaches such as phytoextraction and phytostabilization. These techniques take advantage of pioneer plants that naturally develop tolerance mechanisms to survive in extreme environments. A multi-technique and multi-disciplinary approach was applied for the investigation of Helichrysum microphyllum subsp. tyrrhenicum samples, bulk soil, and rhizospheres collected from a metal-extreme environment (Zn-Pb mine of Campo Pisano, SW Sardinia, Italy). Zinc, Pb, and Cd are the most abundant metals, with Zn attaining 3 w/w% in the rhizosphere solid materials, inducing oxidative stress in the roots as revealed by infrared microspectroscopy (IR). X-ray diffraction (XRD), scanning electron microscopy (SEM), and chemical analysis coupled with synchrotron radiation-based (SR) techniques demonstrate that quartz, dolomite, and weddellite biominerals precipitate in roots, stems, and leaves, likely as a response to environmental stress. In the rhizosphere, Zn chemical speciation is mainly related to the Zn ore minerals (smithsonite and hydrozincite) whereas, in plant tissues, Zn is primarily bound to organic compounds such as malate, cysteine, and histidine molecules that act as metal binders and, eventually, detoxification agents for the Zn excess. These findings suggest that H. microphyllum subsp. tyrrhenicum has developed its own adaptation strategy to survive in polluted substrates, making it a potential candidate for phytostabilization aimed at mitigating the dispersion of metals in the surrounding areas. Full article

A preliminary C–O stable isotopes geochemical characterization of several nonsulfide Zn-Pb Tunisian deposits has been carried out, in order to evidence the possible differences in their genesis. Nonsulfide ores were sampled from the following deposits: Ain Allegua, Jebel Ben Amara, Jebel Hallouf (Nappe Zone), Djebba, Bou Grine, Bou Jaber, Fedj el Adoum, Slata Fer (Diapir Zone), Jebel Ressas, Jebel Azreg, Mecella (North South Axis Zone), Jebel Trozza, Sekarna (Graben Zone). After mineralogical investigation of selected specimens, the C–O stable isotopic study was carried out on smithsonite, hydrozincite, cerussite and calcite. The data have shown that all the carbonate generations in the oxidized zones of Ain Allegua and Jebel Ben Amara (Nappe Zone), Bou Jaber, Bou Grine and Fedj el Adoum (Diapir Zone), Mecella and Jebel Azreg (North South Zone) have a supergene origin, whereas the carbonates sampled at Sekarna (Graben Zone) (and in limited part also at Bou Jaber) precipitated from thermal waters at moderately high temperature. Most weathering processes that controlled the supergene alteration of the Zn-Pb sulfide deposits in Tunisia had probably started in the middle to late Miocene interval and at the beginning of the Pliocene, both periods corresponding to two distinct tectonic pulses that produced the exhumation of sulfide ores, but the alteration and formation of oxidized minerals could have also continued through the Quaternary. The isotopic characteristics associated with the weathering processes in the sampled localities were controlled by the different locations of the sulfide protores within the tectonic and climatic zones of Tunisia during the late Tertiary and Quaternary. Full article