A machine learning technique for estimating the zeta potential of clay minerals under various brine conditions

Laboratory and in situ test results show that electrokinetic decontamination is a promising subsurface decontamination method. However, it has also been reported that several problems arise, such as reverse flow and pH gradient across the anode and the cathode during the electrokinetic decontamination process. Variation in pH alters the zeta (ζ) potential of soils, which is one of the factors affecting the efficiency of contaminant removal by the electrokinetic method. The magnitude of the ζ potential controls the fluid flow rate, whereas its sign controls the flow direction. However, research on how the ζ potential of soils changes under various chemical conditions is limited. In this paper, the effect of pore-fluid chemistry on the ζ potential of kaolinite, montmorillonite, and quartz powder is determined with NaCl, LiCl, CaCl2·2H2O, MgCl2·6H2O, CuCl2, CoCl2, ZnCl2, AlCl3, and Pb(NO3)2. The test results reveal that the ζ potential of the minerals with alkali and alkaline-earth metals changes according to the diffuse electrical double-layer theory. The hydrolyzable metal ions produce two points of zero charge (PZCs), one of which is that of the soil; and the other, that of hydrolyzable oxide. The ζ potential of minerals with hydrolyzable metal ions becomes increasingly positive and reaches its maximum value at neutral pH. It then decreases and again reaches very negative values at alkaline pH values (pH ∼ 10), depending on ion concentration and the bulk precipitation pH of hydrolyzable metals as hydrolyzable oxides. On the basis of the results of this study, it is recommended that the ζ potential of the soils be determined before electrokinetic decontamination.Key words: alkaline-earth metals, electrokinetic decontamination, heavy metals, zeta potential.

Mineral potential mapping with a restricted Boltzmann machine

Swelling of clay minerals in ammonium leaching of weathered crust elution‐deposited rare earth ores

Porphyry Cu-Au prospectivity modelling using semi-supervised learning algorithm in Dehsalm district, eastern Iran

The capacity of soil to sequester carbon (C) is a key process that promotes the reduction of CO2 in the atmosphere. Soils can absorb as much as 20% of anthropogenic carbon emissions, which can contribute to mitigate climate change. This capacity relies on the organo-mineral association, which includes different minerals, Fe and Al oxides, which have a critical soil organic carbon (SOC) sorption surface. Based on an equation of the potential C saturation deficit of fine soil particles (<20 μm/silt and clay fractions) for tropical regions, this study investigated the SOC sequestration potential of the clay fraction for soils in Piracicaba region, São Paulo State, Brazil as influenced by the clay minerals. This potential was fitted to a spatial regression model for soil depths 0–20 cm and 80 to 100 cm. In the surface layer, the sequestration potential was mostly explained by the relative abundance of soil minerals (Kaolinite, Hematite, Goethite and Gibbsite) determined using vis-NIR-SWIR spectroscopy. A direct relationship was observed with Goethite and Gibbsite, indicating that low concentrations would reduce the sequestration potential. At 80 to 100 cm depth, Kaolinite and Hematite explained most variation in SOC sequestration potential. Additionally, the C associated with the mineral fraction and the C saturation potential as a function of minerals were modeled and a strong importance of hematite in the C sequestration and stabilization cycle was identified at both depths. The individual mineral contribution to SOC sequestration potential was also mapped, which identified high contributions of goethite and gibbsite for deep soil layers. The influence of land use on the carbon sequestration potential of minerals was observed, with the greatest potential being found in areas with pasture and cropping mosaics and grassland and forest mosaics, with a high presence of kaolinite and hematite. These minerals have a greater potential for carbon sequestration at greater depths and, therefore, could be critical in climate change mitigation strategies.

In various geosciences branches, including mineral exploration, geometallurgical characterization on established mining operations, and remote sensing, the regionalized input variables are spatially well sampled across the domain of interest, limiting the scope of spatial uncertainty quantification procedures. In turn, response outcomes such as the mineral potential, mining throughput, metallurgical recovery, or in situ estimations from remote satellite imagery are usually modeled from a highly restricted subset of testing samples, collected at certain locations due to accessibility restrictions and high acquisition costs. Our limited understanding of these functions, in terms of the multidimensional complexity of causalities and hidden dependencies on inaccessible inputs, may lead to observing changes in such functions based on their geographical location. Pooling different response functions across a domain is critical to correctly predicting outcome responses, the uncertainty associated with these inferred values, and the significance of inputs in such predictions in under-explored areas. This paper introduces the notion of a dual random field (dRF), where the response function itself is modeled as a regionalized variable. In this way, different established response models across the geographical domain are considered observations of a dRF realization, enabling the spatial inference and uncertainty assessment of both response models and their predictions. We explain how dRFs inherit all the properties from classical random fields, allowing the use of standard Gaussian simulation procedures to simulate them. Additionally, the application of dRFs is demonstrated through a mineral potential mapping case study on which different local binary response models are calibrated on the domain using support vector classification. These models are combined to obtain a mineral potential response, providing an example of how to rigorously integrate machine learning approaches with geostatistics.

Mineral exploration employing drones, contemporary geological satellite remote sensing and geographical information system (GIS) procedures: A review

Recognition of mineralization-related anomaly patterns through an autoencoder neural network for mineral exploration targeting

A geological and mineralogical review of clay mineral deposits and phyllosilicate ore guides in Central Europe – A function of geodynamics and climate change

Simple SummaryAdverse weather conditions and harvesting technique have broad effects on forage quality including contamination with soil particles, e.g., clay minerals. Clay minerals are organised in a layered structure which enables adsorption of bivalent cations. Accordingly, ingested clay minerals may interact with dietary bivalent trace elements, such as Cu, Fe, Mn, and Zn. This study aimed to assess the relationship between clay mineral ingestion and the solubility of dietary trace elements along the digestive tract in vitro. In the presence of clay minerals, we found a reduction of solubilised Zn, Cu, and Mn under ruminal, abomasal, and duodenal conditions. However, clay minerals led to an increase in dissolved Fe under abomasal and duodenal conditions. Therefore, ingested clay minerals may be assumed to alter the solubility of essential dietary trace elements in the digestive tract of ruminants.Ruminants ingest large quantities of clay minerals along with inorganic soil constituents in roughages. The layered structure of clay minerals, however, may adsorb cations and may, thus, interfere with the ruminants’ supply of essential trace metals, such as Zn, Mn, Cu, and Fe. As quantitative knowledge about interactions between clay ingestion and essential trace metal metabolism are largely lacking, this in vitro study focussed on the effect of clay on the solubility of dietary Zn and other bivalent trace metals in the digestive tract of ruminants. Therefore, buffered rumen fluid was used for the simulation of ruminal conditions (RC), acidified rumen fluid (pH 2) was used for abomasal conditions (AC), and duodenal chyme was used for duodenal conditions (DC). These media were added with gradient levels of zinc and incubated at 39 °C for 24 h in the absence or presence of clay minerals. Soluble Zn, Cu, Mn, and Fe were derived by centrifugation (10,000× g) of incubated media, and the supernatants were analysed. Clay depressed the solubility of added Zn in ruminal (65.3% vs. 16.5%), abomasal (97.7% vs. 33.7%), and duodenal conditions (41.3% vs. 21.1%), the results of which were statistically significant (p < 0.001). Moreover, clay reduced dissolved Cu (µg/mL) (RC: 0.13 vs. 0.10; AC: 0.16 vs. 0.13; DC: 0.10 vs. 0.08) and Mn (µg/mL) (RC: 3.00 vs. 1.80; AC: 5.53 vs. 4.80; DC: 3.18 vs. 1.77) (p < 0.05 in all cases). The presence of clay minerals increased the concentrations of solubilised Fe (µg/mL) in abomasal (1.80 vs. 2.86, p < 0.05) and duodenal conditions (1.76 vs. 2.67; p < 0.05). In total, the present in vitro study demonstrates the potential of clay minerals ingested with ruminant feeds for depressing the solubility of dietary Zn, as well as the depression of dietary Cu and Mn along the passage of the digesta from the rumen until the duodenum. Additionally, clay minerals may release Fe into the digesta.

To strengthen the rare earth leaching process and weaken the hydration of clay minerals for preventing landslides, it is of great importance to adopt a green and sustainable leaching agent in the industry. In this work, the leaching process of weathered crust elution-deposited rare earth ores with formate salts (ammonium formate, potassium formate, and sodium formate) was investigated. The effects of formate salts on the linear swelling ratio and zeta potential of the clay minerals were studied. The experimental results showed that ammonium formate could effectively recover the rare earth elements from weathered crust elution-deposited rare earth as well as inhibit the leaching of impurity aluminum. At room temperature, when the ammonium formate concentration was 1% wt, the leaching efficiencies of rare earth and aluminum were 87 and 37%, respectively. Compared with traditional inorganic ammonium salts, the inhibition effect of impurity aluminum was obvious. In addition, the results of the linear swelling ratio in the clay minerals showed that the inhibit ability of formate salts on the hydration of clay minerals enhanced with the increase of the formate concentration, and the order of the inhabitation on the clay minerals followed: 1% ammonium formate > 1.5% potassium formate > 2.5% sodium formate > distilled water. Based on the double layer theory, ammonium formate and potassium formate could effectively compress clay mineral particles to avoid water intake, which could increase the interaction between clay mineral particles and greatly reduce the electronegative property of the clay minerals, so as to effectively reduce the surface hydration of clay minerals to decrease the swelling of rare earth ore. The results of this experiment have important and practical significance in guiding the prevention of landslides, promoting the in-situ leaching technology, and effectively protecting the ecological environment in mining areas.

To reveal the repair potential and effect of clay minerals on heavy metal contaminated soil, this paper summarizes the application of common clay minerals such as kaolinite, montmorillonite and zeolite in the repair of heavy metals, and repairs heavy metals with clay minerals and biochar, lime and chelating agents. Correlation analysis illustrates the potential and mechanism of clay minerals for heavy metals. For one thing, clay minerals have a large specific surface area and a negative charge on the surface, which greatly increases their adsorption properties for heavy metals. for another, clay minerals have high nutrient elements and rich organic matter, Which increase soil fertility and trace elements, as well as crop yield. Clay minerals have been widely used in soil heavy metal pollution repair, but most of them still stay at the laboratory level. In the future, more attention should be paid to the application of clay minerals in practical engineering.

Iron-bearing clay minerals are ubiquitous in the environment, and the clay-Fe(II)/Fe(III) redox couple plays important roles in abiotic reduction of several classes of environmental contaminants. We investigated the role of Fe-bearing clay minerals on the bioreduction of nitrobenzene. In experiments with Shewanella putrefaciens CN32 and excess electron donor, we found that the Fe-bearing clay minerals montmorillonite SWy-2 and nontronite NAu-2 enhanced nitrobenzene bioreduction. On short time scales (<50 h), nitrobenzene reduction was primarily biologically driven, but at later time points, nitrobenzene reduction by biologically formed structural Fe(II) in the clay minerals became increasingly important. We found that chemically reduced (dithionite) iron-bearing clay minerals reduced nitrobenzene more rapidly than biologically reduced iron-bearing clay minerals despite the minerals having similar structural Fe(II) concentrations. We also found that chemically reduced NAu-2 reduced nitrobenzene faster as compared to chemically reduced SWy-2. The different reactivity of SWy-2 versus NAu-2 toward nitrobenzene was caused by different forms of structural clay-Fe(II) in the clay minerals and different reduction potentials (Eh) of the clay minerals. Because most contaminated aquifers become reduced via biological activity, the reactivity of biogenic clay-Fe(II) toward reducible contaminants is particularly important.

Clay minerals are usually regarded as an important factor affecting the results of low salinity water (LSW) flooding. However, experiments on clay minerals are mainly in qualitative stage, the mechanism of clay minerals has not been studied completely. In this paper, Zeta potential of four kinds of clay minerals (montmorillonite; chlorite; illite; kaolinite) in different brine was measured, microscopic models of these clay minerals were made to measured wetting angle in different brine, and montmorillonite and kaolinite were chosen to conduct microscopic displacement experiments through customized micro-glass etching models. From experiment results, the following conclusions can be get: 1). With the decrease of salinity of injected water, the negative zeta potential of clay minerals increases and the wetting angle decreases. 2). Clay minerals are more sensitive to monovalent Na+ than bivalent Ca2+. 3). The results of microscopic experiments show that LSW can effectively improve oil recovery, whether kaolinite or montmorillonite. The recovery of montmorillonite is better with a relatively high salinity of LSW and kaolinite is better with a relatively low salinity of LSW. The mechanism of LSW improves kaolinite recovery factor is the change of wettability while that of montmorillonite is the increase of water phase wettability. However, a lot of droplet-like residual oil cannot be displaced in the montmorillonite throat. In filed production, both kaolinite-rich and montmorillonite-rich reservoirs are suitable for LSW flooding to improve oil recovery. However, for kaolinite reservoirs, a lower salinity of injected water would produce a better result, while for montmorillonite reservoirs, residual oil droplets in the throat are noteworthy.

A study on soil conditioning for cohesive soils with high content of clay minerals: Microscopic simulation and laboratory experiment