Showing papers on "Silicate minerals published in 2022"

Silicate weathering contributed to arsenic enrichment in geotherm-affected groundwater in Pliocene aquifers of the Guide basin, China

Abstract: High arsenic (As) groundwater in reduced shallow Holocene and Pleistocene aquifers has been intensively investigated, but the occurrence and the genesis mechanisms of high As groundwater in deep Pliocene aquifers affected by geothermal activity still remain unclear. To address these issues, geochemical characteristics of groundwater and aquifer sediments in both middle-Pliocene aquifers and Quaternary aquifers of the Guide basin were investigated to clarify groundwater-sediments interaction and the causes of As enrichment in groundwater from middle-Pliocene aquifer. Higher As and Na+ concentrations were observed in groundwater from middle-Pliocene aquifer (GPA) than those in groundwater from Quaternary aquifer (GQA), while GPA had lower Ca2+ concentrations than GQA. Results showed that middle-Pliocene aquifer sediments had low contents of carbonate minerals, and water-soluble Ca-bearing minerals relative to Quaternary aquifer sediments, which explain higher concentration of Ca2+ in GQA than in GPA. Na+ from weathering of silicates (i.e. (Na+)*), being calculated based on mass balance, accounted for high proportion of dissolved Na+ (up to 68%) in GPA. Weathering of silicates was related to As accumulation in GPA, which was proved by a positive correlation between As and (Na+)* in GPA, and high proportion of As bound to unweathered silicates (up to 65.7%) in middle-Pliocene aquifer sediments. The weathering of silicate minerals directly released As bound to silicates into GPA, and indirectly led to As desorption from solid surfaces by increasing pH, HCO3– and CO32–. Both (Na+)* and As in groundwater increased with the increasing groundwater temperature, showing that high temperature was conducive to weathering of silicates and As enrichment. This paper establishes a bridge between high groundwater temperature and high As concentration with weathering of silicates in aquifers.

Mineral-Supported Photocatalysts: A Review of Materials, Mechanisms and Environmental Applications

Abstract: Although they are of significant importance for environmental applications, the industrialization of photocatalytic techniques still faces many difficulties, and the most urgent concern is cost control. Natural minerals possess abundant chemical inertia and cost-efficiency, which is suitable for hybridizing with various effective photocatalysts. The use of natural minerals in photocatalytic systems can not only significantly decrease the pure photocatalyst dosage but can also produce a favorable synergistic effect between photocatalyst and mineral substrate. This review article discusses the current progress regarding the use of various mineral classes in photocatalytic applications. Owing to their unique structures, large surface area, and negatively charged surface, silicate minerals could enhance the adsorption capacity, reduce particle aggregation, and promote photogenerated electron-hole pair separation for hybrid photocatalysts. Moreover, controlling the morphology and structure properties of these materials could have a great influence on their light-harvesting ability and photocatalytic activity. Composed of silica and alumina or magnesia, some silicate minerals possess unique orderly organized porous or layered structures, which are proper templates to modify the photocatalyst framework. The non-silicate minerals (referred to carbonate and carbon-based minerals, sulfate, and sulfide minerals and other special minerals) can function not only as catalyst supports but also as photocatalysts after special modification due to their unique chemical formula and impurities. The dye-sensitized minerals, as another natural mineral application in photocatalysis, are proved to be superior photocatalysts for hydrogen evolution and wastewater treatment. This work aims to provide a complete research overview of the mineral-supported photocatalysts and summarizes the common synergistic effects between different mineral substrates and photocatalysts as well as to inspire more possibilities for natural mineral application in photocatalysis.

Recovery of Rare Earth Elements Minerals from Iron-Oxide-Silicate-Rich Tailings: Research Review

Abstract: The rapid depletion of high-grade rare earth elements (REE) resources implies that future supplies may be augmented with low-grade ores, tailings, and other unconventional resources to meet cut-off grades and, subsequently, supply demands. This paper presents an amalgamation of studies conducted on selected complex low-grade iron-oxide-silicate-rich tailings, with the overall aim of developing efficacious methods and associated process mineralogy characterization for enhanced REE minerals recovery and upgrade. To this end, a summary of the overarching key results from froth flotation, magnetic separation, and gravity separation studies of the tailings and their implications are presented in this review. Reconciliation of all the findings reveals lucid links between feed ore properties, mainly mineralogy and particle size distribution, as the key influential factors that affect the beneficiation of real complex low-grade tailings, although distinct differences in physicochemical properties of the valuable and gangue minerals may exist. It is clearly established that the unliberated association between REE and gangue minerals within the ore can lead to either synergistic or antagonistic effects on the quality of concentrates produced. Furthermore, the limitations presented by the poorly liberated minerals are exacerbated by their “fine” nature. With appreciable recoveries obtained using such readily available conventional separation methods, the tailings provide additional REE value to the primary commodities; hence, such material could be considered a potential resource for REE beneficiation. The learnings from the respective beneficiation studies are significantly important as they provide the knowledge base and greater understanding of the mineralogical characteristics and beneficiation response of REE minerals in typical complex, low-grade tailings.

Hydrogeochemical characteristics and risk evaluation of potential toxic elements in groundwater from Shanmughanadhi, Tamilnadu, India

Abstract: Hydrogeochemical and Health Risk Assessments of trace elements are integral to groundwater resource assessment, utilization, and human health. Investigation of groundwater chemistry and trace elemental impact on local inhabitants were attempted in Shanmuganadhi basin, Tamilnadu, India. About 60 groundwater samples were collected during the pre-monsoon period and analyzed for hydrochemical composition, including major and trace elements (Fe, Cr, Ni, Cu Pb, Mn, and As) to isolate chemical characteristics and human health risk assessment. Groundwater geochemistry is prejudiced by geochemical reactions uniting cation exchange, dissolution and precipitation, adsorption, and anthropogenic contributions. About thirty-two percent of groundwater samples recorded higher F-(>1.5 mg/L) than the prescribed limit suggests sources from rock weathering and silicate dissolution. Nitrates (>45.0 mg/L) suggest sources from agricultural influences. Water types indicate alkalis (Na+ + K+) dominating alkali earth (Ca2+ - Mg2+) and strong acids (Cl- and SO42-) looming weak acid (CO32- and HCO3-) irrespective of water samples. The geochemical stability diagram suggests precipitation of silica, carbonate, and magnesium and dissolution of sulphate minerals along the groundwater flow path. Significant correlation between major ions and trace elements (Pb, Mn, Ni, and Cu) suggests origin from rock weathering, human impacts, and cultivation practices. Non-carcinogenic human risk for trace elements was higher in children compared with adults via ingestion and dermal exposure. The carcinogenic result suggests that Cr in CHK (7.1 × 10-2) and HBG (4.3 × 10-2) have the most excellent chance of cancer risk. The environmental risk category attempted using Comprehensive risk factor (CRI) suggests Pb (3.2-CHK, 2.6-HBG) with potential cancer risk. The comprehensive evaluation index recommends environmental damage between mild to moderate, indicating continuous exposure of traceable elements might result in cancer cause to the inhabitants. The study suggests water quality seems to be prejudiced by various geological and anthropogenic causes and endorses counteractive measures and proper execution of existing laws to protect groundwater resources in the study area.

Some Remarks on the Electrical Conductivity of Hydrous Silicate Minerals in the Earth Crust, Upper Mantle and Subduction Zone at High Temperatures and High Pressures

Abstract: As a dominant water carrier, hydrous silicate minerals and rocks are widespread throughout the representative regions of the mid-lower crust, upper mantle, and subduction zone of the deep Earth interior. Owing to the high sensitivity of electrical conductivity on the variation of water content, high-pressure laboratory-based electrical characterizations for hydrous silicate minerals and rocks have been paid more attention to by many researchers. With the improvement and development of experimental technique and measurement method for electrical conductivity, there are many related results to be reported on the electrical conductivity of hydrous silicate minerals and rocks at high-temperature and high-pressure conditions in the last several years. In this review paper, we concentrated on some recently reported electrical conductivity results for four typical hydrous silicate minerals (e.g., hydrous Ti-bearing olivine, epidote, amphibole, and kaolinite) investigated by the multi-anvil press and diamond anvil cell under conditions of high temperatures and pressures. Particularly, four potential influence factors including titanium-bearing content, dehydration effect, oxidation−dehydrogenation effect, and structural phase transition on the high-pressure electrical conductivity of these hydrous silicate minerals are deeply explored. Finally, some comprehensive remarks on the possible future research aspects are discussed in detail.

Effect of second Si–O vibrational overtones/combinations on quantifying water in silicate and silica minerals using infrared spectroscopy, and an experimental method for its removal

Abstract: Infrared spectroscopy (IR) is the most widely used analytical tool to quantify trace water in silicate and silica minerals. A prerequisite for highly accurate IR measurements of trace water is a good understanding of the effect of the second Si–O vibrational overtones/combination bands (2nd Si–O VOCBs) on the water peaks. Silicate and silica minerals can be divided as isolated (Q0), paired (Q1), ring (Q2), chain (Q1 or Q2), sheet (Q3) and framework (Q4) structures according to the polymerization of their SiO4 tetrahedral units, and the 2nd Si–O VOCBs of these different structural types attain different vibrational features which are expected to affect the water peaks to different extents. Here, we selected olivine (Q0) and α-quartz (Q4) as two endmember-like structural examples, performed extensive IR measurements on both pristine and heat-treated thin sections prepared for these two minerals, and explored the vibrational features of the 2nd Si–O VOCBs. We have found that the 2nd Si–O VOCBs are well separated from the water peaks in olivine, but severely overlap with the water peaks in α-quartz, confirming the different roles that the 2nd Si–O VOCBs play in quantifying trace water in silicate and silica minerals with different structural polymerizations. To remove the influence of the 2nd Si–O VOCBs (or any other species rather than water), an experimental protocol has been successfully developed, as approved by some fundamental equations and verified by the data of α-quartz in the literature. This development should lead to significant accuracy improvement in quantifying trace amounts of water in Earth and planetary materials.

Recovery of Rare Earth Elements Minerals in Complex Low-Grade Saprolite Ore by Froth Flotation

Abstract: This study presented the first in a series of investigations currently underway to develop efficacious, cost-effective, and benign processing opportunities to produce rare earth elements (REE)–rich concentrate from an Australian complex low–grade saprolite ore [1.14% total rare earth oxides (TREO) grade], which is primarily exploited for its gold and copper values. This work specifically presented a preliminary flotation investigation carried out on the ore using sodium oleate as a collector. The relative effects of pulp pH, desliming, and depressants were investigated to ascertain any chance of recovering and upgrading REE minerals in saprolite ore using three different processing configurations. Based on the experimental results, flotation processes carried out on raw feed allowed the recovery of the majority of REE minerals (>50%), but the process was unselective, where clay and silicate gangue minerals reported into the flotation concentrate along with the REE minerals. However, desliming before flotation in the presence of depressants (starch and sodium silicate) improved REE minerals flotation selectivity, which produced concentrates assaying 5.87% and 4.22% TREO grades, with corresponding recoveries of 45% and 50% at pulp pH 9 and 10.5, respectively. Mineralogical analysis conducted on selected flotation concentrate indicated that silicate and clay gauge minerals were recovered via the synergistic act of surface activation and entrainment due to their fine to ultrafine nature. A comparison of all the test results revealed a haphazard grade–recovery relationship suggesting that there is an opportunity to further maximize both REE recovery and grade through further flotation studies where other process parameters may be investigated and optimized. The prospect of using magnetic separation has also been suggested.

Mineral stabilities in soils: how minerals can feed the world and mitigate climate change

Abstract: Abstract Mineral reactions in soils demonstrably take place on a human timescale. The weathering of silicate ‘rock-forming’ minerals releases nutrients that are essential for plant growth, including silica. This process consumes CO2, which is ultimately derived from the atmosphere, through enhanced rock weathering. From a human perspective, the weathering process has two beneficial functions – crop nutrition and climate mitigation – through the removal of atmospheric CO2. By considering these as a coupled process, the release of silica during weathering can be matched to what is taken from the soil by a crop (e.g. wheat). A simple analysis shows that the amount of silica that accumulates in wheat during a 4 month growing period is readily released by the weathering of pyroxene and plagioclase, minerals that commonly occur in basaltic igneous rocks. In contrast, the dissolution rate for quartz is so low that it cannot supply the silica taken up by the crop and is inert. Similarly, dissolution of clay minerals releases sufficient silica for plant uptake. Rapid weathering of silicate minerals within soils is evident from images of surfaces of grains exposed in soils for periods of 10–100 years. The evidence for silicate rock weathering as part of the soil system that sustains humanity is provided by the vegetation that we see around us.

Magnesium Isotope Fractionation During Silicate Weathering: Constrains From Riverine Mg Isotopic Composition in the Southeastern Coastal Region of China

Abstract: Mg isotopic composition of river water is dominantly controlled by the dissolution of both silicate and carbonate sources and a series of biogeochemical processes. However, the relative importance of source and isotopic fractionation control at basin/global scale is poorly constrained. This study presents the Mg isotopic composition of river water and suspended load in river draining silicate rocks in the southeastern coastal region of China. The fractionation effect of silicate weathering on Mg isotopes is documented in both dissolved and solid phases. Mg isotopic composition of rivers draining silicate rocks exhibit ∼0.3‰ δ26Mg difference, the release of Mg from Mg-rich minerals and formation of clays are the dominant processes controlling Mg isotopic composition of river water. The variation of Mg isotopic compositions of suspended load is closely related to the species of secondary clays (illite and chlorite); the fractionation direction during illite and chlorite formation contrasts, isotopically heavy Mg preferentially incorporates into illite while light Mg incorporates into chlorite. Furthermore, the negative correlation between Mg concentration and Mg isotopic compositions of river water indicates the Mg re-distribution and isotope fractionation between weathering solutions and secondary clays during silicate weathering. Such isotope fractionation-induced Mg isotope variations could be employed to estimate the contribution of Mg from silicate weathering at basin/continental scale and also have implications for exploring seawater δ26Mg evolution. This article is protected by copyright. All rights reserved.

Base cations release in soils along the 127‐year Hailuogou glacial retreat chronosequence

Abstract: At the Hailuogou glacial retreat chronosequence, a mature forest has surprisingly fast developed in ∼120 yr, although the glacial debris is dominated by nutrient-poor granite with a small contribution of carbonate minerals. In previous work, we hypothesized that the fast vegetation development is synchronized with initial fast carbonate weathering followed by slow silicate weathering. To test this hypothesis, we (a) characterized the composition of the glacial debris to elucidate the sources of base cations and (b) determined the base cation release kinetics from topsoils (0–10 cm) along the chronosequence with a weathering experiment at a constant pH value (pHstat). Besides granitic rocks, the glacial debris contained some meta-sedimentary and meta-volcanic calc-silicate rocks, amphibolite, mica schist, and quartzite. Although the total Ca concentration of the glacial debris was only about double that of Mg, K, and Na, during the 1st day of the pHstat experiment, the released mass of Ca was >10 times higher than that of Mg and K, and even about 100 times higher than that of Na. The size of the fast-reacting Ca-carbonate pool decreased quickly in the first approximately 40 yr, after which a slow-reacting Ca-silicate pool matched the fast-reacting pool with a size of 1.9 ± 0.6 g kg–1 Ca. In contrast, for Mg, K, and Na the slow-reacting pool dominated from the beginning, suggesting that these elements mainly originated from silicate weathering. Our findings support the view that the well-synchronized interplay between carbonate and silicate weathering facilitated the fast vegetation succession.

Silicate Minerals Induced by Microorganisms

Abstract: AbstractRocks are made up of minerals and they form the Earth’s crust. Nearly 90% of Earth’s solid material are silicate minerals. Rocks and minerals are the source and sink of most essential elements, without which the living forms cannot survive. This nutrient source has to be mineralized from the parent rock. The biological agents such as bacteria, fungi, algae, cyanobacteria, etc. effectively act on this mineralization process. Bioweathering is the destruction or decomposition of rocks by the ubiquitous microbial source. By this biomineralization, transformation of silicate minerals takes place by varied microbial metabolic activities. Biodissolution mechanism comprises acidolysis, extracellular polysaccharide production, pH fluctuation, chelation, organic acid secretion, and organic ligand production. These mechanisms vary with the variety of bioagents that trigger the silicate mineral formation. Biomineralization of silicate minerals leads to various biogeochemical processes, viz., soil formation, mineral transformation, and nutrient mobilization to plants and microbes itself which are streamlined naturally by this ‘bio-miners’ or biological agents, which balance nutrient cycling and maintain equilibrium. Such natural phenomenon supports the living forms in varied ecosystem. Exploration and bio-intervention of such novel microbes leads to more advantages in mineral formation and its allied processes. In this chapter, the author presents a critical review of mineral formation from silicate minerals, mechanisms, and its application aspects collected from existing literatures. An advancement and extensive research in this field would no doubt nourish the environment in ecofriendly approaches.

Hydrochemical and environmental isotopes characteristic of groundwater and controlling factors for waters’ chemical composition in the iron–copper mine area of Elazığ, SE Turkey

Abstract: Environmental context Predicting the hydrodynamic structure of water resources based on water chemistry and isotope results is important for understanding their transport and effects on the hydrogeological system. According to the results of this study, hydrogeological characteristics of ground and surface water resources in the Zeryan Stream sub-basin in the iron–copper mining area and their geochemical evolution are mainly controlled by the weathering of silicate and carbonate minerals, and ion exchange. Rationale and hypothesis Groundwater is generally the most important water resource in mine areas, and its circulation processes need to be studied in detail for rational resource exploitation. This work tested the hypothesis that the evolution of groundwater chemistry and recharge by using hydrogeochemical indicators and isotope tracers together are affected by the hydrogeochemical processes that may have taken place during the water-rock interactions in the Zeryan Stream Sub-basin, where the Iron-Copper mine is located. Methodology It used approaches such as hydrochemistry, Piper diagrams, saturation index, ionic ratios, and environmental isotopes to analyze groundwater origin and hydrochemical processes affecting water chemistry. Fifty-seven water samples were collected from 19 points during wet and dry periods. Results Results indicated that the dominance of cations and anions in the mine water follows the trend Mg2+ > Ca2+ > Na+ > K+ and SO42− > HCO3− > Cl−, and most of the water samples are Mg-Ca-HCO3-SO4, Mg-Ca-SO4-HCO3, and Ca-HCO3. Discussion Evaluation of analyzed groundwater chemical data showed that dissolution or precipitation of silicate minerals dominated in the hydrochemical evolution of groundwater, dissolution of carbonate minerals was a secondary process and to a lesser extent, ion exchange processes played a role. The δD and δ18O isotopic contents indicated that the water samples were controlled by local atmospheric precipitation, and affected by secondary evaporation during the recharge process. Tritium levels indicated some well waters are recharged from older groundwater resources from water-rock interaction and residence time. Findings The findings of this study were provided to decision-makers in order to design sustainable implications for groundwater utilization based on the sub-basin.

Exploration of Hydrogeochemical Characterization and Assessment of Organic Pollution Characteristics of Shallow Groundwater near a Chemical Plant That Discharged Sewage Illegally

Abstract: Groundwater plays a significant role in domestic use and agricultural irrigation in rural areas of northern China. The untreated wastewater from the chemical plant was directly discharged into a seepage well, resulting in the pollution of groundwater. Assessing characteristics of groundwater organic pollution and identifying evolutionary mechanisms of hydrogeochemistry are beneficial for groundwater protection and sustainable management. Statistical methods (correlation analysis (CA) and principal component analysis (PCA)) combined with hydrogeochemical methods including Piper, Gibbs, Gaillardet, and ions binary diagrams and the chloride alkalinity index were employed to explore hydrogeochemical characteristics and evolutionary mechanisms. The results showed that cations were predominantly located at the Ca2+ end and anions were mostly close to the SO42− and Cl− end. The ion concentrations of groundwater were mainly affected by water–rock interactions. The weathering or dissolution of silicate (i.e., aluminosilicate minerals), evaporite (i.e., halite and gypsum), carbonate minerals (i.e., calcite and dolomite), cation exchange, and anthropogenic activities contribute to the chemical compositions of groundwater. Based on CA and PCA, the dissolution of halide minerals and the use of pesticides and fertilizers were the main factors controlling water chemistry. Additionally, the dissolution of sulfur-bearing minerals and gypsum was the key factor controlling the concentrations of Ca2+ and Mg2+. Application of mathematical statistical methods characterized that the exceedance rate of seven organic compounds with high detection rates were as follows: carbon tetrachloride (39.83%) > 1,1,2-trichloroethane (28.81%) > chloroform (10.17%) > trichloroethene (6.78%) > 1,1,2,2-tetrachloroethane (5.93%) > perchloroethylene (5.08%) > trichlorofluoromethane (0.85%). Simultaneously, pollution under the influence of volatilization and diffusion was significantly less than that in the direction of groundwater runoff.