Porosity evaluation of fine particles in mine tailing based on electrical conductivity by considering surface conduction

Influence of surface conductivity on the apparent zeta potential of amorphous silica nanoparticles

Various morphologies of calcium oxalate dihydrate (COD) crystals containing cross-shaped, flower-like, thin-bipyramid, thick-bipyramid, and elongated-bipyramid structures, with a size of approximately 5 μm, were prepared by varying the reactant concentration, reaction temperature, stirring speed, and additive. X-ray diffraction (XRD) and infrared spectroscopy (FT-IR) showed that the synthesized crystals were pure-phase COD crystals. The factors affecting the morphology of COD and the mechanism of COD formation were discussed. Physicochemical properties such as specific surface area, pore structure, pore size, zeta potential, and conductivity of the crystals were identified. The cytotoxicity of five different shapes of COD crystals in human kidney proximal tubular epithelial (HK-2) cells was investigated using the Cell Counting Kit-8 (CCK-8) assay and propidium iodide (PI) staining assay. The cytotoxicity was ranked in the following order: COD-elongated-bipyramid > COD-thick-bipyramid ≈ COD-cross-shaped > COD-thin-bipyramid > COD-flower-like. The toxicity of tetragonal bipyramid COD crystals was closely correlated with the area of the Ca2+ ion-rich (100) face; the crystals with large (100) faces showed a higher toxicity to HK-2 cells. The cytotoxicity of cross-shaped COD and flower-like COD was affected by the sharpness of their crystal edges; COD-CS with sharp corners caused more serious injuries to cell membranes. These findings are helpful in understanding the effects of mineralization conditions and additives on crystal morphology as well as to identify the relationship between crystal morphology and cytotoxicity. The results also provide a reference for the injury difference of various shapes of crystals from normal subjects and stone patients to the renal epithelial cells and the formation mechanism of calcium oxalate stones.

Mine tailings contain finer particles, crushed rocks, dugout-soil, water, and organic and inorganic metals or metalloids, including heavy metals and radionuclides, which are dumped as waste or non-economic by-products generated during mining and mineral processing. These abundant and untreated materials seriously threaten the environment, human health, and biodiversity because of the presence of heavy metals, radionuclides, and associated primary and secondary toxic components, including the risk of tailings dam failures. Biocementation technology, which involves the use of mining microbes to secrete cement-like materials that bind soil particles together, is a promising approach to restore mine tailing sites and reduce their mobility and toxicity. However, there is a lack of literature on the combined interactions among mining microbes, tailings residues, biocementation, and low-carbon cement (LCC) prospects. This comprehensive review article explores the prospects of mining microbes for mine tailings restoration using biocementation technology, the key influencing factors and their impact, mechanisms and metabolic pathways, and the effectiveness of biocementation technology in restoring mine tailings sites. In addition, it reviews the utilization of mine tailings materials as an alternative source of cement or construction materials for LCC technology. Furthermore, this review highlights the important issues, challenges, limitations, and applications of biocementation technology for mine tailings rehabilitation. Finally, it provides insights for future research and implementation of biocementation for mine tailings restoration and utilization of tailing materials in the industrial sector to reduce carbon emissions/footprints and achieve net-zero goals.

This study aimed to investigate the potential of enrichment of rare-earth-bearing minerals in historic mine tailing using the froth flotation process. Characterization studies indicated that tailings contained 11,000 ppm of rare earth elements (REEs). The major mineral in the tailings was apatite at ~84%, which was associated with iron oxides (~16%). TESCAN’s integrated mineral analysis (TIMA) showed that monazite was the main REE mineral, and 69% of monazite was locked in apatite grains. Characterization studies suggested that the separation of REEs-bearing apatite from iron oxides is possible using froth flotation, wherein apatite was floated and iron oxides were depressed. Zeta potential experiments were conducted to understand the behavior of the main minerals in the feed when selected depressants of iron oxides were added. Depressants included corn starch, sodium metasilicates, polyacrylamide (PAM), hybrid polyacrylamide (HyPAM), and chitosan. Zeta potential results suggested that chitosan and polyacrylamide-based polymers had the strongest adsorption on magnetite at pH 7 and pH 9, respectively, as indicated by the large shift in the zeta potential of magnetite suspensions. Flotation results were consistent with zeta potential findings and showed that Hy-PAM and chitosan had the best depression efficiency of iron oxides at pH 9 and pH 7, respectively.

A series of modified montmorillonites including Zn2+ loaded montmorillonite (Zn/MMT), Ce3+ loaded montmorillonite (Ce/MMT) and Zn2+‐Ce3+ loaded montmorillonites (Zn‐Ce/MMT) were prepared by an ion‐exchange reaction, and characterized using X‐ray photoelectron spectroscopy (XPS), X‐ray diffraction (XRD), and scanning electron microscopy (SEM). The specific surface areas, zeta potentials and antibacterial activity of the modified montmorillonites were also investigated. Zinc and cerium were proved to be present as bivalent zinc state and trivalent cerium state in the modified montmorillonites. For the modified montmorillonites, the d001 basal spacings increased and the particles were formed of irregular shapes. The antibacterial activity of the modified montmorillonites was enhanced with the increase of specific surface areas and zeta potentials, and Zn2+‐Ce3+ loaded montmorillonites displayed obvious synergistic antibacterial effect. When Zn/Ce atomic ratio was 1.24, the Zn‐Ce/MMT showed high antibacterial efficiency and broad‐spectrum antibacterial activity, possessing the MIC against Escherichia coli, Staphylococcus aureus, Candida albicans and Mucor of 1500, 1000, 2000 and 3000 mg·L−1, respectively.

Particulate matter (PM) is a major ambient air pollutant causing millions of premature deaths each year in China. The toxicity of PM is property and size dependent. In this study, ambient PM samples collected in Beijing were divided into five size fractions with nominal aerodynamic ranges of <0.40, 0.40-1.1, 1.1-3.3, 3.3-5.8, and 5.8-10 μm. Individual size fractions were characterized for a number of properties including particle size distribution, specific surface area, zeta potential, dithiothreitol (DTT)-based redox ability, and contents of water-soluble organic carbon (WSOC), polycyclic aromatic hydrocarbons (PAHs), selected metals, and endotoxin. Human adenocarcinomic alveolar epithelial cell line A549 and small mouse monocyte-macrophage cell line J774A.1 were tested for their relative viabilities and inflammatory effects (interleukine-8 for A549 and tumor necrosis factor-α for J774A.1) after exposure to PM of various sizes. It was found that PM specific area was positively correlated with WSOC, high molecular weight PAHs, DTT-based redox ability, negatively correlated with surface zeta potential and lithophile metals. Several trace metals from combustion sources were enriched in intermediate size fractions. For both endotoxin concentrations of the PM and PM induced inflammatory cytokine expressions by the two cell lines, there were general increasing trends as PM size increased with an exception of the finest fraction, which induced the highest inflammatory effects. It seems that the size dependence of cytokine expression was associated with a number of properties including endotoxin content, zeta potential, settling velocity, metal content, and DTT-based redox ability.

Electrical conductivity models have been widely used to estimate water content and petrophysical properties of soils in hydrogeophysical studies. However, these models are typically only valid for soils with non‐expandable matrices because they were originally developed for clean sandstone reservoir rocks. Soils containing swelling clays are characterized by matrices that expand/contract upon gaining/losing water. In this laboratory study, we demonstrate that soil matrix changes affect saturation estimation using Archie's laws. A sample of a soil containing a swelling clay was fully saturated with a potassium chloride solution, then left to dry evaporatively at room temperature for 8 days. The complex resistivity of the soil, along with its weight and volume shrinkage, were measured daily during the drying period, and the surface conductivity was calculated based on previous empirical findings. Over the course of the study, the simultaneous evaporation yielded a 33% decrease in volume and caused a nonlinear reduction in saturation with decreasing water content. Accounting for surface conductivity and correcting for saturation using the calculated volume reduction resulted in a power‐law relationship with high R 2 values between resistivity and saturation along with reasonable saturation exponents. On the contrary, neglecting either surface conductivity or shrinkage caused similar underestimations of saturation exponents. These results indicate that the application of Archie's second law to soils with swelling clays leads to erroneous predictions of resistivity if saturation values are not corrected for changes in the volume of the soil and surface conductivity is neglected.

Ghezeljeh montmorillonite nanoclay or “Geleh-Sar-Shoor” (means head-washing clay) used as a native adsorbent to extraction-preconcentration mercury ions from a variety of real water and fish samples have been investigated in a batch system followed by atomic absorption spectroscopy (AAS) with vapor generation accessory (VGA) system. The clay was characterized by using FT-IR, SEM-EDS, XRF, XRD, CEC, Specific surface area and Zeta potential. The results of XRD, FT-IR, Zeta potential and CEC of the Ghezeljeh clay confirm that montmorillonite is the dominant mineral phase. On the basis of on SEM images, the distance between the layers is in nm level. The outcome of varying parameters and interfering ions were studied. Detection and quantification limits, preconcentration factor, and adsorption capacity were calculated. The Langmuir and Freundlich equations showed the finest fit to the equilibrium data. The adsorption procedure follows a pseudo-second-order reaction pattern. Calculation of ΔG0, ΔH0 and ΔS0 displayed that the nature of Hg(II) ions adsorption is endothermic and favorable at upper temperature.

This article presents the method of extraction-preconcentration of Lead, Cadmium, and Nickel ions from food samples using the Ghezeljeh montmorillonite nanoclay (Geleh-Sar-Shoor) as a new native adsorbent in batch single component systems. The extraction-preconcentration of heavy metals were carried out by applying the solid phase extraction (SPE) method followed by atomic absorption spectroscopy (AAS), and inductively coupled with plasma atomic emission spectroscopy (ICP-AES). The Ghezeljeh nanoclay was characterized by using Fourier transform infrared spectroscopy (FT-IR), Scanning electron microscopy-energy dispersive spectrometer operating (SEM-EDS), X-ray diffractometry (XRD), X-ray fluorescence (XRF), Cation Exchange Capacity (CEC) measurements, BET specific surface area and Zeta potential. According to BET theory, the specific surface areas of the Ghezeljeh nanoclay was calculated to be 19.8 m2 g-1 whereas the cation exchange capacity was measured to be 150 meq/100 g. The results of XRD, XRF, FT-IR, Zeta potential and BET surface area of the nanoclay confirmed that montmorillonite was the dominant mineral phase. Based on SEM images of this clay, it can be seen that the distance between the plates is nm level. For all three ions, the detection and quantification limits, dynamic linear range, preconcentration factor, and adsorption capacity were obtained. The effect of various interfering ions was studied. The experimental method was successfully applied for the extraction of heavy metals in different tea and rice samples.

The collapse of mining tailings produces huge disasters. The soils in mining tailing consists of solid soil and mining particles, air and water. As the mining tailing is generally fully saturated, the void in mining tailings is water. Note that the void ratio or porosity controls the strength of the mining tailings. The in-situ porosity of soils has been determined by using undisturbed samples, which produces discontinuous porosity. However, the undisturbed samples may not be easily obtained in mining tailings because mining tailings is not cohesive soils. Thus, the field velocity resistivity probe (FVRP) is used for the evaluation of the porosity profile along the depth. The FVRP generates and detects the compressional and shear wave velocities by piezoelectric disk elements and bender elements, respectively. Furthermore, the electrical resistivity is obtained by the electrical resistivity probe, which is installed at the tip of wedge. The FVRP is penetrated into the mining tailings and captures the continuous profile of shear wave velocity, compressional wave velocity, and electrical resistivity. Test results show that the porosity profile along the depth is estimated by the FVRP. This study demonstrates that the FVRP may be an effective tool for the estimation of the porosity of mining tailings.

Evaluation of mine tailings’ potential as supplementary cementitious materials based on chemical, mineralogical and physical characteristics

The adsorption mechanisms of algae-bacteria symbiotic system and its fast formation process

The chemical characteristics of mine tailings, organic amendments (doses), and plants are the critical factors that must be evaluated and monitored to ensure the sustainability of phytostabilization. The aim of this study was to evaluate the mobility of copper (Cu) in mine tailings (MT) of the Zone Central of Chile to which commercial humic substances were added, examining their effect on the uptake of Atriplex halimus. Two commercial humic substances (HS1 and HS2) extracted from leonardite (highly oxidized lignite), of different pH and total organic carbon, were evaluated by adsorption curve for Cu. In columns, soluble Cu, pH, and electrical conductivity in leachates were evaluated for MT, MT + HS1, and MT + HS2, and HS1 and HS2 in doses of 120 mg kg-1. In pot assay, seeds were germinated directly in MT and cultivated for 140 days with the addition of HS2 in 120 and 240 mg kg-1. Mine tailing presents high concentration of Cu (2016 ± 223 mg kg-1, pH 6.3 ± 0.1). The results of sequential extraction indicate that Cu is associated with the sulfide fraction of low risk of mobility. The amount of Cu sorbed by HS1 was higher than that sorbed by HS2, and both humic substances showing better fit to the Freundlich than Langmuir model. Lixiviation of Cu was significantly lower in MT + HS1 (0.166 ± 0.043 mg kg-1) and MT + HS2 (0.157 ± 0.018 mg kg-1) than in MT (0.251 ± 0.052 mg kg-1). Copper concentration in plants reached 185.8 ± 37.8 mg kg-1 in the roots and 32.6 ± 7.4 mg kg-1 in the aerial parts cultivated in MT without effect of the humic substance addition in Cu uptake nor growth. Copper concentrations in the aerial parts were adjusted to sufficient or normal levels in plant. A good management of mine tailings through phytostabilization could consider an adequate mixture of humic substances (to avoid leaching of metals) and an organic amendment that provides essential nutrients and increases biomass generation.

Effects of physico-chemical properties of ions-doped hydroxyapatite on adsorption and release performance of doxorubicin as a model anticancer drug

The influence of surface properties, including fineness, total pore volume, specific surface area and zeta potential on viscosity of TiO2 slurry were studied. The viscosity and these surface properties of TiO2 samples were respectively measured by viscometer, standard sieve, specific surface area analyzer, particle size analyzer. The results show that with increase of fineness and absolute value of zeta potential, the viscosity of TiO2 slurry decrease gradually, but with increase of total pore volume and specific surface area, the viscosity of TiO2 slurry also increase. The suitable conditions in low viscosity of TiO2 slurry are as follows: fineness and absolute value of zeta potential is respectively greater than 0.1%, 70mV; total pore volume and specific surface area is respectively less than 0.05cc/g, 7.5m2/g