Weathering Of Silicate Minerals Research Articles

Authigenic dolomites in the Eocene–Oligocene organic carbon-rich shales from the Polish Outer Carpathians: Evidence of past gas production and possible gas hydrate formation in the Silesian basin

Eocene–Oligocene dolomite concretions and beds from the Grybów and Dukla units of the Polish Outer Carpathians were studied. These rocks occur in the organic carbon-rich, marine and fine-grained deposits of hemipelagic or turbiditic origin. Mineralogic, elemental and stable C and O isotopic composition of the dolomites was determined. Results indicate that the rocks were formed by precipitation of predominantly Fe-rich dolomite cement close to the sediment-water interface prior to significant compaction. The main source of bicarbonate for dolomite formation was bacterial methanogenesis as evidenced by the high δ13C values up to 16.6‰. The main source of alkalinity was probably weathering of silicate minerals which might have also liberated Ca and Mg ions for the dolomites to form. The distribution of these dolomites indicates that microbial methane production was widespread in the Silesian basin. Moreover, formation of some dolomites in the Eastern part of the Dukla unit was probably associated with gas hydrates as suggested by the elemental and oxygen isotopic composition of dolomitic matrix. Therefore, the dolomites may serve as a proxy of areas where biogenic methane was produced, where the rocks had high hydrocarbon potential, and where hydrates could have existed.Detailed mineralogic and petrographic analyses allowed for the reconstruction of the diagenetic sequence and the evolution of pore fluids. Textural relationships between successive cement generations indicate that the central parts of the composite dolomite crystals experienced corrosion and that the latest ankerite cement filled the secondary intragranular cavities within those crystals. This observation shows that reconstructions of pore fluid evolution based on core-to-rim analyses of such composite crystals may lead to wrong interpretations. Septarian cracks developed in the dolomites are often filled with multistage cements. The earliest generations are ferroan dolomite and ankerite cements which precipitated within the cracks simultaneously to the ferroan dolomite and ankerite cements from the matrix of the dolomitic rocks which shows that septarian cracking occurred very early, during the final stages of concretionary formation. These cements were followed by the late-diagenetic precipitates, mainly quartz, kaolinite and blocky calcite. This calcite is commonly associated with bitumen which shows that it precipitated during or after oil migration in the decarboxylation zone.

Hydrogeological processes controlling the release of arsenic in parts of 24 Parganas district, West Bengal

A study was conducted to understand the hydrogeological processes dominating in the North 24 Parganas and South 24 Parganas based on representative 39 groundwater samples collected from selected area. The abundance of major ions was in the order of Ca2+ > Na+ > Mg2+ > K+ > Fe2+ for cations and HCO3 − > PO4 3− > Cl− > SO4 2− > NO3 − for anions. Piper trilinear diagram was plotted to understand the hydrochemical facies. Most of the samples are of Ca-HCO3 type. Based on conventional graphical plots for (Ca + Mg) vs. (SO4 + HCO3) and (Na + K) vs. Cl, it is interpreted that silicate weathering and ion exchange are the dominant processes within the study area. Previous studies have reported quartz, feldspar, illite, and chlorite clay minerals as the major mineral components obtained by the XRD analysis of sediments. Mineralogical investigations by SEM and EDX of aquifer materials have shown the occurrence of arsenic as coating on mineral grains in the silty clay as well as in the sandy layers. Excessive withdrawal of groundwater for irrigation and drinking purposes is responsible for fluctuation of the water table in the West Bengal. Aeration beneath the ground surface caused by fluctuation of the water table may lead to the formation of carbonic acid. Carbonic acid is responsible for the weathering of silicate minerals, and due to the formation of clay as a product of weathering, ion exchange also dominates in the area. These hydrogeological processes may be responsible for the release of arsenic into the groundwater of the study area, which is a part of North 24 Parganas and South 24 Parganas.

Rare earth element cycling in the pore waters of the Bering Sea Slope (IODP Exp. 323)

We studied the diagenetic behavior of rare earth elements (REEs) in a highly productive passive margin setting of the Bering Sea Slope. Site U1345 was drilled during the Integrated Ocean Drilling Program Expedition 323 at a water depth of 1008m currently in the center of an oxygen minimum zone. Pore water concentrations of fourteen REEs were determined down to ~140meters below the seafloor (mbsf). The REE concentrations were higher in the pore water than the deep seawater, indicating that there was significant liberation from the sediments during diagenesis. There was a major peak at ~10mbsf that was more pronounced for the heavy REE (HREE); this peak occurred below the sulfate-methane transition zone (6.3mbsf) and coincided with high concentrations of dissolved iron and manganese. At ~2mbsf, there was a minor peak in REE and Mn contents. Below ~40mbsf, the REE concentration profiles remained constant. The Ce anomaly was insignificant and relatively constant (PAAS-normalized Ce/Ce*=1.1±0.2) throughout the depth profile, showing that the Ce depleted in seawater was restored in the pore water. HREE-enrichment was observed over the entire 140m except for the upper ~1m, where a middle REE (MREE)-bulge was apparent. REE release in shallow depths (2–4mbsf) is attributed to the release of light REEs (LREEs) and MREEs during the organoclastic reduction of Mn oxides in anoxic sediments. The high HREE concentrations observed at ~10mbsf can be attributed to the reduction of Fe and Mn minerals tied to anaerobic oxidation of methane or, less significantly, to ferromagnesian silicate mineral weathering. The upward diffusion flux across the sediment-water interface was between 3 (for Tm) and 290 (for Ce) pmolm−2y−1.

Using correlation and multivariate statistical analysis to identify hydrogeochemical processes affecting the major ion chemistry of waters: a case study in Laoheba phosphorite mine in Sichuan, China

Prior to mining, the water in and around the mine is rarely influenced by human activities, and hydrogeochemical processes are the major factors influencing and controlling water chemistry. To identify these natural hydrogeochemical processes in Laoheba phosphorite mine (Sichuan Province, China), correlation and multivariate statistical techniques were used. Results show that water quality in the area is generally good before the Laoheba phosphorite mine goes into construction and production. The cluster analysis classified water samples into 4 clusters (C1–C4). Samples from C1 and C2 are of HCO3−Ca·Mg and HCO3−Ca type, while those from C3 and C4 are of HCO3−Ca·Mg type. Most parameters except Cl− and pH show an increasing trend in the order of C1 to C4. Three principal components were extracted, and PC1 represents the ion exchange and the weathering of calcite, dolomite, and silicate minerals. PC2 and PC3 indicate the process of water recharge from upstream waters and the process of evaporation, respectively. The hydrochemistry of waters in the area is a result of multiple factors, and natural mineral weathering and ion exchange are the most important ones.

Statistical analysis of hydrochemistry of groundwater and its implications for water source identification: a case study

Hydrochemistry of groundwater is important for inrush water source identification in coal mines. For determining the source of inrush water from the 8101 working face in the Wolonghu coal mine, Northern Anhui Province, China, a total of 22 groundwater samples from three aquifer systems (loose layer—LA, coal bearing sandstone—CA, and the underlying limestone—TA), and eight samples from the 8101 working face were collected for analyzing major ion concentrations. The results suggest that major ion concentrations of the aquifer systems were different from each other, and they can be subdivided into Na–HCO3, Na–SO4, and Ca–SO4 types. Factor analysis indicates that their chemical compositions are mainly originated from two kinds of contributions: dissolution of soluble minerals (e.g., calcite, dolomite, and gypsum) and weathering of silicate minerals (e.g., plagioclase). Plots of factor scores and cluster analysis imply that LA was connected with CA, whereas TA was an isolated aquifer system. Moreover, the source of 8101 working face water was finally determined to be LA by using discriminant analysis.

Characterization of Rhizobium sp. Q32 Isolated from Weathered Rocks and its Role in Silicate Mineral Weathering

One mineral-solubilizing strain was isolated from weathered potassic trachyte surfaces and identified as Rhizobium sp. Q32 based on the 16S rRNA gene sequence analysis. The mineral (feldspar and biotite) dissolution potential and the physiological characteristics of the bacterium were investigated. Laboratory mineral dissolution experiments indicated that inoculation with the live bacterium significantly increased feldspar and biotite dissolution by a factor of 1.2–4.7 for Si and 1.2–1.5 for K in comparison with the dead bacterium inoculated controls. In addition, extracellular polysaccharide production by the bacterium increased with time but the bacterium produced small pH changes (6.0–6.5) in the course of mineral dissolution experiment. The bacterium was found to produce siderophores and have the characteristics of acid or alkali and salt tolerance and temperature resistance. The result suggested that feldspar and biotite dissolution may be mainly caused by extracellular polysaccharide and/or siderophores produced by the bacterium.

Retraction Note: The hydrochemical framework of surface water basins in southern Ghana

Surface water resources play a crucial role in the domestic water delivery system in Ghana. In addition, sustainable food production is based on the quality and quantity of water resources available for irrigation purposes to supplement rain-fed agricultural activities in the country. The objective of this research was to determine the main controls on the hydrochemistry of surface water resources in the southern part of Ghana and assess the quality of water from these basins for irrigation activities in the area. R-mode factor and cluster analyses were applied to 625 data points from 6 river basins in southern Ghana after the data had been log transformed and standardized for homogeneity. This study finds that surface water chemistry in the south is controlled by the chemistry of silicate mineral weathering, chemistry of rainfall, fertilizers from agricultural activities in the area, as well as the weathering of carbonate minerals. A Gibb’s diagram plotted with total dissolved solids (TDS) on the vertical axis against (Na+ + K+)/(Ca2+ + K+ + Na+) on the horizontal axis indicates that rock weathering plays a significant role in the hydrochemistry. Activity diagrams for the CaO–Na2O–Al2O–SiO2–H2O and CaO–MgO–Al2O3–SiO2–H2O systems suggest that kaolinite is the most stable clay mineral phase in the system. In addition, an assessment of the irrigation quality of water from these basins suggests that the basins are largely low sodium—low to medium salinity basins, delivering water of acceptable quality for irrigation purposes.

Using hydrochemical data and modelling to enhance the knowledge of groundwater flow and quality in an alluvial aquifer of Zagreb, Croatia

The Zagreb alluvial aquifer system is located in the southwest of the Pannonian Basin in the Sava Valley in Croatia. It is composed of Quaternary unconsolidated deposits and is highly utilised, primarily as a water supply for the more than one million inhabitants of the capital city of Croatia. To determine the origin and dynamics of the groundwater and to enhance the knowledge of groundwater flow and the interactions between the groundwater and surface water, extensive hydrogeological and hydrochemical investigations have been completed. The groundwater levels monitored in nested observation wells and the lithological profile indicate that the aquifer is a single hydrogeologic unit, but the geochemical characteristics of the aquifer indicate stratification. The weathering of carbonate and silicate minerals has an important role in groundwater chemistry, especially in the area where old meanders of the Sava River existed. Groundwater quality was observed to be better in the deeper parts of the aquifer than in the shallower parts. Furthermore, deterioration of the groundwater quality was observed in the area under the influence of the landfill. The stable isotopic composition of all sampled waters indicates meteoric origin. NETPATH-WIN was used to calculate the mixing proportions between initial waters (water from the Sava River and groundwater from “regional” flow) in the final water (groundwater sampled from observation wells). According to the results, the mixing proportions of “regional” flow and the river water depend on hydrological conditions, the duration of certain hydrological conditions and the vicinity of the Sava River. Moreover, although the aquifer system behaves as a single hydrogeologic unit from a hydraulic point of view, it still clearly demonstrates geochemical stratification, which could be a decisive factor in future utilisation strategies for the aquifer system.

Is orogenesis a net sink or source of atmospheric CO2?

In global carbon cycle models, orogenesis is often viewed as a sink for atmospheric CO2, acting on tectonic timescales. However, recent attempts to quantify fluxes for CO2 produced by metamorphic reactions and released to the atmosphere suggest that these are an order‐of‐magnitude greater than CO2 uptake by chemical weathering of silicate minerals, and that metamorphic CO2 is released on millennial timescales. These hypotheses have gained support from both measurements of CO2 emissions from present‐day orogenic hot springs and chromatographic modelling of carbonation reactions in metamorphic rocks from ancient orogens. In this article I review research that attempts to quantify metamorphic CO2 release fluxes, focussing specifically on studies conducted in the SW Scottish Highlands.

Hydrochemical and isotopic characteristics of groundwater in the Yanqi Basin of Xinjiang province, northwest China

In this study, hydrochemical and isotope investigations were conducted in the Yanqi Basin to determine the chemical composition, and to gain insight into the groundwater recharge process in the Yanqi Basin. It mainly used hydrochemistry, environmental isotopes, and a series of comprehensive data interpretation, e.g., statistics, ionic ratios, and Piper diagram to obtain a better understanding of the functioning of the system. The following hydrochemical processes were identified as the main factors controlling the water quality of the groundwater system: weathering of silicate minerals, dissolution, ion exchange, and to a lesser extent, evaporation, which seemed to be more pronounced down gradient of the flow system. As groundwater flows from the recharge to discharge areas, chemical patterns evolve in the order of Ca2+–HCO3 −, Ca2+/Mg2+–HCO3 − to Ca2+–Mg2+–Cl−–SO4 2−, Na+–K+–Cl−–SO4 2− and Na+–Cl− according to lithology. The environmental isotope (δ 18O, δ 2H, 3H) measurements further revealed that precipitation was the main recharge source for the groundwater system; some local values indicated high levels of evaporation. Tritium and CFC analysis were used to estimate the ages of the different groundwater; the tritium values of the groundwater samples varied from 2.82 to 29.7 TU. The age of the groundwater at depths of <120 m is about 30–50 years. CFC values obtained for six samples to determine groundwater age; the age of the groundwater is about 20–50 years.

Microbial Communities in Antarctic Subglacial Aquatic Environments

Glaciological processes under ice masses, including ice sheets, produce conditions favorable for microbes by forming subglacial aquatic environments (SAE) through basal melting and providing nutrients and energy for microbes from bedrock comminution. The abundance and interconnectivity of water beneath the Antarctic Ice Sheet, largely demonstrated through remote sensing techniques, indicates significant and varied SAE including lakes, saturated sediments and channelized and linked cavity drainage systems. Microbes have been detected in the two Antarctic SAE sampled to date; accreted ice from Vostok Subglacial Lake in East Antarctica and saturated till from beneath ice streams draining the West Antarctic Ice Sheet. Heterotrophic activity has been measured in these samples at temperatures close to freezing in the laboratory, demonstrating that in situ microbial activity in subglacial environments is plausible. Phylogenetic analysis of 16S rRNA gene sequences suggests that organisms with Fe and S oxidizing metabolisms may also be important members of the microbial community in these environments. This is consistent with the geochemistry of the accreted ice and till pore waters that indicates biologically driven sulfide oxidation coupled to carbonate and silicate mineral weathering as a significant solute source. Exploration of Antarctic SAE is in its infancy, and in a number of the unexplored SAE, the lack of connectivity between oxygenated surface waters and the subglacial environment and the extended water flow paths and water-rock residence times may lead to anoxic conditions. Such anoxic conditions would favor anaerobic microbial metabolisms similar to those documented in other deep terrestrial subsurface environments.

The effect of pedological conditions on the sources and sinks of silicon in the Vertic Planosols in south-western Ethiopia

As a dynamic source and sink of elements, the secondary Si-bearing solid phases in soil partly govern transfer of elements and pollutants. Terrestrial plants affect silicate mineral weathering and make Si readily soluble through the formation of phytoliths, a biogenic form of amorphous silica, which return on topsoil through litterfall. Besides phytoliths, other readily-soluble Si components, such as pedogenic opal, volcanic glass, adsorbed Si onto Fe oxides and poorly crystalline aluminosilicates take part in the regulation of the Si balance. The aim of this paper is to assess the impact of pedological conditions on the sources of dissolved Si and its dynamics in a Vertic Planosol characterized by contrasting bleached and vertic horizons. The Si-containing readily soluble phases were quantified by specific extractions (Na2CO3: Sialk, oxalate: Siox, DCB: Sidcb and CaCl2: SiCaCl2) performed on samples of the bleached and vertic horizons. Moreover, amorphous silica (ASi) from the soil (including phytoliths and volcanic glass) was extracted by gravimetric separation. In the bleached horizon, phytoliths are the main Si-bearing readily soluble phases of the silt-sized fraction, while Si in the sand-sized fraction is largely controlled by volcanic glass and feldspars. The higher SiCaCl2 concentration and the significant increase of (Si/Al)CaCl2 ratios in soil solution of the vertic horizon attest for a marked difference in terms of Si dynamics. The activity of dissolved Si as H4SiO4 in the aqueous phase of the Vertic Planosols in south-western Ethiopia seems to be controlled in the bleached E horizon by the balance between the dissolution of feldspars and volcanic glass, active uptake by grasses (formation of phytoliths), neoformation of kaolinite and intense lateral leaching. In the vertic Bw horizon the sources and sinks of Si are governed by the dissolution of phytoliths, the adsorption on and desorption from Fe oxides and slow leaching. Our results clearly indicate that the contrasting pedological conditions in the bleached and vertic horizons impact the sources and sinks of Si in the Vertic Planosols in south-western Ethiopia, and as such could partly control terrestrial Si fluxes.

The sources and fluxes of dissolved chemistry in a semi-confined, sandy coastal aquifer: The Pingtung Plain, Taiwan

Groundwater chemical fluxes from the Pingtung Plain in SW Taiwan to the ocean were determined by analysing waters from 43 wells at varying depths through a 237m deep window across the Pingtung Plain, for major dissolved cations, anions, dissolved SiO2, and stable isotopic composition of O and H, and computing their subsurface water fluxes from measurements of hydraulic heads and formation permeabilities. The results show that between 1.5% (SO42-) and 12.3% (Ba2+) of the total chemical weathering flux discharged to the ocean (Kaoping River combined with groundwater) can be attributed to the groundwater. Estimated propagated errors at 1σ on subsurface fluxes are ±20%. Multi-year daily hydraulic head data give the direction of groundwater flow through the plain, and indicate that pumping has led to episodic reversals of flow, facilitating seawater intrusion in the near-coast aquifer. Tracing end-member proportions using mixing relationships shows that, in addition to seawater and meteoric water, hot-spring activity contributes to the dissolved chemistry of the groundwater. In addition to these three end-members, the weathering of carbonate and silicate minerals in the plain accounts for the remainder of the chemical budget. Hydrological connectivity exists throughout the drilled depth of the basin, but chemical gradients show that flow is stratified, with up to a twofold increase in silicate-derived Na+ seen in deeper horizons as compared to the near surface. For all ions except SO42-, the average concentrations of dissolved species in the coastal groundwaters exceed those of the river, ranging from a factor of 1.33 in the case of Li+ to 27.29 in the case of Cl−. The results suggest that submarine groundwater chemical fluxes through the drilled depth of the Pingtung Plain into the Taiwan Strait are modest in comparison to those related to surface runoff.

Groundwater quality and its suitability for drinking and agricultural use in the Yanqi Basin of Xinjiang Province, Northwest China

The Yanqi Basin in Xinjiang Province is an important agricultural area with a high population density. The extensive agricultural activities in the Yanqi Basin started in the 1950s with flood irrigation techniques. Since then, the groundwater table was raised because of the absence of an efficient drainage system. This obstacle is a crucial factor that restricts sustainable socioeconomic development. Hydrochemical investigations were conducted in the Yanqi Basin, Northwestern China, to determine the chemical composition of groundwater. Sixty groundwater samples were collected from different wells to monitor the water chemistry of various ions. The results of the chemical analysis indicate that the groundwater in the area is generally neutral to slightly alkaline and predominantly contains Na(+) and Ca(2+) cations as well as HCO3(-) and SO4 (2+) anions. High positive correlations between HCO3 (-)-Mg(2+) + Ca(2+), SO 4 (2-)-Mg(2+), SO4 (2-)-Na(+) + K(+), and Cl(-)-Na(+) + K(+) were obtained. The total dissolved solids (TDS) mainly depend on the concentration of major ions such as HCO3(-), SO4 (2-), Cl(-), Ca(2+), Mg(2+), and Na(+) + K(+). The dominant hydrochemical facies for groundwater are Ca(2+)-Mg(2+)-HCO3(-), Mg(2+)-Ca(2+)-SO4 (2-)-Cl(-), Na(+)-K(+)-Cl(-)-SO4 (2-), and Na(+)-K(+)-Mg(2+)-Cl(-)-HCO3(-) types. The hydrochemical processes are the main factors that determine the water quality of the groundwater system. These processes include silicate mineral weathering, dissolution, ion exchange, and, to a lesser extent, evaporation, which seem to be more pronounced downgradient of the flow system. The saturation index (SI), which is calculated according to the ionic ratio plot, indicates that the gypsum-halite dissolution reactions occur during a certain degree of rock weathering. SI also indicates that evaporation is the dominant factor that determines the major ionic composition in the study area. The assessment results of the water samples using various methods indicate that the groundwater in the study area is generally hard, fresh to brackish, high to very high saline, and low alkaline in nature. The high total hardness and TDS of the groundwater in several places indicate the unsuitability of the groundwater for drinking and irrigation. These areas require particular attention, particularly in the construction of adequate drainage as well as in the introduction of an alternative salt tolerance cropping.

Geochemical processes regulating groundwater chemistry with special reference to nitrate and fluoride enrichment in Chhatarpur area, Madhya Pradesh, India

The present study focuses on the hydrogeochemical composition of groundwater in Chhatarpur area with special focus on nitrate and fluoride contamination, considering the fact that groundwater is the only major source of drinking water here. Carbonate and silicate mineral weathering followed by ground water–surface water interactions, ion exchange and anthropogenic activities are mainly responsible for high concentrations of cations and anions in the groundwater in the region. The average concentration of nitrate and fluoride found in 27 samples is 1.08 and 61.4 mg/L, respectively. Nitrate enrichment mainly occurs in areas occupied with intense fertilizer practice in agricultural fields. Since the area is not dominated by industrialization, the possibility of anthropogenic input of fluoride is almost negligible, thus the enrichment of fluoride in groundwater is only possible due to rock–water interaction. The highly alkaline conditions, which favor the fluorite dissolution, are the main process responsible for high concentration of fluoride.

Saltwater intrusion and nitrate pollution in the coastal aquifer of Dar es Salaam, Tanzania

Dar es Salaam Quaternary coastal aquifer is a major source of water supply in Dar es Salaam City used for domestic, agricultural, and industrial uses. However, groundwater overdraft and contamination are the major problems affecting the aquifer system. This study aims to define the principal hydrogeochemical processes controlling groundwater quality in the coastal strip of Dar es Salaam and to investigate whether the threats of seawater intrusion and pollution are influencing groundwater quality. Major cations and anions analysed in 134 groundwater samples reveal that groundwater is mainly affected by four factors: dissolution of calcite and dolomite, weathering of silicate minerals, seawater intrusion due to aquifer overexploitation, and nitrate pollution mainly caused by the use of pit latrines and septic tanks. High enrichment of Na+ and Cl− near the coast gives an indication of seawater intrusion into the aquifer as also supported from the Na–Cl signature on the Piper diagram. The boreholes close to the coast have much higher Na/Cl molar ratios than the boreholes located further inland. The dissolution of calcite and dolomite in recharge areas results in Ca–HCO3 and Ca–Mg–HCO3 groundwater types. Further along flow paths, Ca2+ and Na+ ion exchange causes groundwater evolution to Na–HCO3 type. From the PHREEQC simulation model, it appears that groundwater is undersaturated to slightly oversaturated with respect to the calcite and dolomite minerals. The results of this study provide important information required for the protection of the aquifer system.

A Multivariate Statistical Analysis of Groundwater Chemistry Data in the Highest Bandama Basin at Tortiya (Northern Côte D’Ivoire)

The multivariate statistical tools R-mode hierarchical cluster analysis (HCA) and principal component analysis (PCA) were simultaneously applied to groundwater hydrochemical data of the Highest Bandama Basin (Northern of Cote d'Ivoire) to extract principal processes controlling water chemistry. Though the PCA proved to be more robust at unveiling the sources of variation in the hydrochemistry than the R-mode hierarchical cluster analysis (HCA), the combined use of both techniques resulted in more reliable interpretations of the hydrochemistry. They reveal three processes responsible of water chemistry which are mineralization-water residence time, oxidation process and spatial origin of water and degradation of quality. Among these processes, mineralization-water chemistry by mean of water-interaction and weathering of silicate minerals is the most important. The oxidation process underlines the influence of environment conditions and aquifers state in ions acquisition. Indeed, the probable degradation of groundwater is thus revealing.

The Influence of the Unsaturated Zone on the High Fluoride Contents in Groundwater in the Middle Voltaian Aquifers- The Gushegu District, Northern Region of Ghana

The Influence of the Unsaturated Zone on the High Fluoride Contents in Groundwater in the Middle Voltaian Aquifers- The Gushegu District, Northern Region of Ghana This study was aimed at determining the origin of elevated fluoride content of groundwater in parts of the Gushegu District of the Northern Region of Ghana. Hydrochemical data from a total of 19 groundwater samples and porewater were analyzed to establish hydrochemical trends which would indicate the major causes of variation in the hydrochemistry. R-mode factor and hierarchical cluster analyses were jointly applied to the data. Three major sources of variation, accounting for over 76% of the total variance in the dataset were revealed. This study establishes that silicate mineral weathering may be the major factor influencing groundwater hydrochemical variation in the area.

Tuning the dissolution kinetics of wollastonite via chelating agents for CO2 sequestration with integrated synthesis of precipitated calcium carbonates

Carbon mineralization has recently received much attention as one of the most promising options for CO2 sequestration. The engineered weathering of silicate minerals as a means of permanent carbon storage has unique advantages such as the abundance of naturally occurring calcium and magnesium-bearing minerals and the formation of environmentally-benign and geologically stable solids via a thermodynamically favored carbonation reaction. However, several challenges need to be overcome to successfully deploy carbon mineralization on a large scale. In particular, the acceleration of the rate-limiting mineral dissolution step along with process optimization is essential to ensure the economic feasibility of the proposed carbon storage technology. In this study, the effect of various types of chelating agents on the dissolution rate of calcium-bearing silicate mineral, wollastonite, was explored to accelerate its weathering rate. It was found that chelating agents such as acetic acid and gluconic acid significantly improved the dissolution kinetics of wollastonite even at a much diluted concentration of 0.006 M by complexing with calcium in the mineral matrix. Calcium extracted from wollastonite was then reacted with a carbonate solution to form precipitated calcium carbonate (PCC), while tuning the particle size and the morphological structure of PCC to mimic commercially available PCC-based filler materials.

A linear regression model (LRM) for groundwater chemistry in and around the Vaniyambadi industrial area, Tamil Nadu, India

A linear regression model in conjunction with cluster analysis was applied to the groundwater quality parameters for the Vaniyambadi industrial area, Tamil Nadu, India. These physico-chemical parameters were collected from 25 wells by intensive groundwater sampling conducted during January 2010. All the major ions, pH and electrical conductivity were analyzed. The abundances of cations were in the order of Na <Ca <Mg <K and those of anions were in the order of Cl <HCO3 <SO4 <CO3, respectively. This was in agreement with the water types, Na-Cl and Na-Ca-HCO3, determined by the Piper plot. High concentrations of the ions Na, Cl and SO4 were recorded near the tanneries that operate within the study area. While the elevated concentrations of HCO3 and F were observed away from the tanneries. This peculiar hydrochemical behaviour suggests that the chemistry of water is predominantly influenced by tannery effluents and weathering of silicate minerals. Results of the linear regression model yielded 11 regression equations for the 5 most correlated parameters. A dendrogram from the cluster analysis showed 2 major clusters representing the influence of tanneries and geological formations in the study area, which confirmed the results of major ion chemistry.