Dissolution Of Aluminosilicate Minerals Research Articles

Source of quartz cement and its impact on reservoir quality in Jurassic Shaximiao Formation in central Sichuan Basin, China

Quartz cement is an essential authigenic mineral in the tight sandstones of the Shaximiao Formation in the Sichuan Basin, China. Accurately identifying its sources and investigating its impact on reservoir quality is important for understanding diagenetic fluid evolution and pore development in these reservoirs. To address this, we conducted a systematic analysis of the silicon sources in quartz cement employing mineralogical, fluid inclusion, and geochemical data. Quartz cement is characterized by two phases of quartz overgrowth and pore-filling authigenic quartz. Homogenization temperatures of fluid inclusions range from 60 to 150 °C, indicating that quartz cementation occurred from the early diagenetic phase (B stage) to the late mesodiagenetic phase. During the early diagenetic stage, volcanic material was dissolved by meteoric water, resulting in the formation of the earliest quartz cement and smectite. At temperatures of approximately 70–100 °C, smectite illitization, accompanied by K-feldspar consumption and SiO2 precipitation. In the mesodiagenetic stage (temperature approximately 100–130 °C), organic acids led to the dissolution of minerals like feldspar and laumontite, releasing SiO2. In the deep burial stage, clastic quartz grains experienced dissolution due to high stress, providing a limited source of SiO2. Smectite alteration and the dissolution of aluminosilicate minerals represent the primary sources of silicon for quartz cementation, while contributions from volcanic material hydrolysis and pressure solution are relatively minor. The presence of chlorite films inhibits the development of quartz overgrowths, and the limited precipitation of authigenic quartz within the primary porosity has a minimal impact on reservoir quality. Consequently, sandstones rich in chlorite films represent a favorable lithology for the development of high-quality reservoirs.

Full process of calcium silicate hydrate decalcification: Molecular structure, dynamics, and mechanical properties

C-S-H gel is the origin of cohesion of cement and deteriorates with decalcification. However, the molecular process underlying its complex chemical reactions and structure/properties evolution is mostly unexplored. Herein, the influence of decalcification on calcium silicate hydrate (C-S-H) is studied by molecular dynamics and experiments. The results show, during the decalcification, the transformation of C-S-H molecular structure from lamellar crystal into cross-linked glassy structure, transformation from bound water into -OH groups, and transformation of dynamics characteristics from lattice vibration at fixed sites into diffusion, which would be exacerbated by the dissociation of intralayer calcium. Mechanically, for both nano and micro/macro scale, tensile property of C-S-H depends on interlayer bonding and so is weakest at complete dissociation of interlayer calcium, whereas compressive property decreases continuously with decalcification. The interlayer bonding basically determines the threshold of micro/macro mechanical properties of C-S-H gel. This study provides a well example for molecular-scale exploration of the full process of aluminosilicate mineral dissolution.

Potential recharge sources and origin of solutes in groundwater in the central Qinghai–Tibet Plateau using hydrochemistry and isotopic data

Study regionThe Nagqu River Basin in the central part of the Qinghai–Tibet Plateau, China. Study focusGroundwater flow systems in permafrost regions are characterized by a unique circulation. Understanding the groundwater circulation mechanism is essential for studying the hydrological effect of permafrost degradation in alpine regions. In this study, potential water sources and origin of solutes in the groundwater of a typical alpine region were studied using hydrochemistry, 18O, 2H and 3H analyses. This research is essential for studying the hydrological effects of permafrost degradation. New hydrological insights for the regionUpon moving from the mountainous region to the plains, the renewal rate decreases from 10.5% to 0.6% and the mean transit time increases from 5–30 to 20–32 years. Groundwater is mainly recharged by ground ice meltwater and infiltration of glacier meltwater, snow meltwater and precipitation in mountainous areas, and by deep groundwater near faults. Discharge to surface water, evaporation, and overflow into springs are the main drainage modes. Water/ice–rock/soil interactions, such as dissolution of aluminosilicate minerals, are the main factors affecting the hydrochemical evolution. This study provides a data-driven approach for understanding groundwater recharge and evolution in similar systems.

Spatiotemporal variability in groundwater chemistry of a mountainous catchment with complex geologic and climate gradients in south west India

Mountainous catchments are one of the world’s important water sources that sustains a major portion of global population and a rich biodiversity. The groundwater quantity and quality of mountainous watersheds depend generally on the geologic characteristics and climate gradients. Although many groundwater studies have been carried out in the midlands and lowlands of many river basins, not enough focus has been paid to the mountainous catchments of tropical watersheds. Here we report a case study on groundwater quality and controlling factors of a mountainous catchments of the Western Ghats mountain ranges of peninsular India—the Bhavani river basin, which is identified as a testbed for long-term monitoring of the Critical Zone process. A total of 88 water samples were collected seasonally for assessing various physico-chemical parameters, solute contents and scaling properties. Standard methods were followed for the estimation of various hydrochemical parameters in the open and borewell samples. The results of the study revealed that higher pH and Total Dissolved Solids (TDS) are noticed in the talc-tremolite dominated central zone whereas low values are recorded in the charnockite dominated areas. The major cations in the water samples are of the order Ca2+ > Mg2+ > Na+ > K+ and the anions are of the order HCO3− > Cl− > SO42−. The content of Cl− shows higher values in areas close to agricultural/settlement areas. An overall evaluation shows that the hydrochemistry of groundwater in the study area is influenced by both silicate and carbonate weathering. Mineral stability indices computed for the groundwater reveal that about 52% of the samples are supersaturated with carbonate minerals and often exhibit scaling due to solute overloading. Saturation Index and mineral stability diagram also support that the incongruent dissolution of aluminosilicate minerals (silicate weathering) is an important hydrochemical process controlling the chemistry of groundwater. Langelier saturation index (LSI) and Puckorius scaling index (PSI) show that a significant number of open well and borewell samples exhibit scaling tendency. Among the contributing factors that determine water quality of groundwaters, chemical weathering and anthropogenic activities play a significant role.

Biogeochemistry of holocene peatlands in the baraba forest-steppe (southern West Siberia)

Postdepositional diagenetic processes and behavior of biogenic and other elements in Holocene peatlands have been studied in Ubinskoe and Sherstobitovo bogs of the Baraba forest-steppe zone. Peat contains relatively high concentrations of Fe, Mn, Pb, Hg, Sb, Cd, Cu, and Zn in the upper part of the two sections and S, N, Ca, and Sr in the middle. Microbially mediated processes in peat affect the behavior of pH and Eh and cycles of biogenic elements. Depth-dependent distribution patterns of microorganisms in the two bogs record active cycles of carbon and nitrogen but limited sulfur exchange. Bog waters have Ca-group bicarbonate major-ion chemistry and high concentrations of Al, Fe, Cu, and Zn, due to low pH. High contents of NH4+, NO3−, and Corg and chemical oxygen demand (COD) in the bog waters are implicit indicators of rapid biochemical decomposition and oxidation of organic matter. The low pH of the water and an oxic environment in peat were favorable for the formation of goethite and hydrogoethite in upper peat layers. The formation of hematite and andhydride may be related with past wild fires. Early diagenetic processes lead to precipitation of authigenic minerals, especially, pyrite or less often siderite, calcite, and kaolinite. Reduced conditions maintained the formation of metallic Ni and intermetallic Ni–Cr nanometer particles, as well as precipitation of amorphous silica upon dissolution of aluminosilicate minerals in upper peat intervals.

Kyanite far from equilibrium dissolution rate at 0–22 °C and pH of 3.5–7.5

Kyanite is an important and slow-dissolving mineral. Earlier work has measured its dissolution rate at high temperature and acidic pH, but experimental measurements at low temperature and near neutral pH were lacking. The rate equation by Palandri and Kharaka (A compilation of rate parameters of water–mineral interaction kinetics for application to geochemical modeling. US Geological Survey, Open File Report 2004-1068, 2004) indicates that the rate of kyanite dissolution at room temperature and near neutral pH is on the order of 10−17 mol m−2 s−1, orders of magnitudes slower than most common silicate minerals such as albite and quartz. This study used an externally-stirred mixed-flow reactor, which allows high solid:solution ratios, to measure the dissolution rate of kyanite at 0–22 °C and pH of 3.5–7.5. The measured dissolution rate of kyanite is 4.6–7.6 × 10−13 mol m−2 s−1 at 22 °C, and the apparent activation energy is 73.5 kJ mol−1. This dissolution rate is close to the rate of quartz dissolution and four orders of magnitude faster than the prediction by rate equation of Palandri and Kharaka (2004). Based on our new experimental data, we recommend the following rate equation for modeling the dissolution of kyanite at ambient temperatures. $$r = ke^{{\frac{{ - E_{a} }}{R}\left( {\frac{1}{T} - \frac{1}{298.15}}\right)}}$$ where k = 5.08 × 10−13 mol m−2 s−1, and Ea = 73.5 kJ mol−1. Review of literature data (Carroll in The dissolution behavior of corundum, kaolinite, and andalusite: a surface complex reaction model for the dissolution of aluminosilicate minerals in diagenetic and weathering environs. Dissertation, Northwestern University, 1989) led to a recommended rate equation for andalusite as for T = 25 °C and pH = 2–10: $$r = k_{1} a_{{{\text{H}}^{ + } }}^{{n_{1} }} + k_{2} + k_{3} a_{{{\text{H}}^{ + } }}^{{n_{3} }}$$ where k1 = 4.04 × 10−10 mol m−2 s−1, k2 = 7.95 × 10−10 mol m−2 s−1, k3 = 1.01 × 10−17 mol m−2 s−1, n1 = 1.2 and n3 = − 0.6.

Occurrences of evaporitic salts in Bugesera region (Burundi) and relation to hydrogeochemical evolution of groundwater

Several studies conducted on occurrences of evaporitic salts in various parts of the world often interpret the formation of such salts as the result of the evaporation of subsurface brines, saline lake waters and sea water-contaminated groundwater, on one hand, and the deposition of sea sprays and wind-transported salts, on the other hand. This study seeks to understand processes governing the formation of evaporitic salts in a humid tropical context and to establish a link between the occurrence of these salts and the different processes controlling the hydrogeochemical evolution of groundwater in Bugesera region, in north-eastern Burundi. Unlike previous studies, salt occurrences in the study area occur in a continental and humid tropical environment where chemical analyses of water samples from several small lakes reveal rather fresh water. While salt incrustations reported in the western Burundi occur in a sedimentary basin which is made up of a mixture of lacustrine and fluviatile sediments, the evaporitic salts in the depression of Bugesera appear in the upper layers of the weathered overburden developed on Precambrian basement rocks. These facts suggest that the lithological nature and setting of the area may not be the key factor controlling the formation of these salt deposits. X-ray diffraction (XRD) analyses performed on saline soils from two quarries in Bugesera region confirm the presence of salt minerals including particularly gypsum (CaSO4·2H2O), halite (NaCl) and thenardite (Na2SO4). Other minerals identified such as goethite, kaolinite, muscovite and quartz may be part of the soil matrix. Chemical analyses on leachates of soil samples from the 2 quarries in Bugesera region confirm their saline nature as evidenced by high TDS (1826–17,679 mg/l) and pH values (8.3–8.5). The predominance of Na+, Mg2+, Ca2+, K+, SO42−, Cl− in the chemical composition of the dissolved salts clearly reflects their mineralogical composition. This study clearly demonstrates that these evaporitic salts originate from the combination of three processes, namely the dissolution of aluminosilicate minerals which enrich groundwater in different salt-forming ions, the capillary rise which lifts the shallow groundwater and the dissolved ions up to the reach of evaporation and ultimately the evapoconcentration which precipitates the salts following well-established pathways. These findings are well supported by the results of the simulation of the evapoconcentration process with the PHREEQC hydrochemical model.

Latent disciplinal clashes concerning the batch dissolution of minerals, and their wider implications

Environmental contextMineral dissolution kinetics are important to understand natural processes including those increasingly used to store waste carbon dioxide and highly radio-active nuclides, and those involved in the amelioration of climate change and sea-level rise. We highlight a mistake made in the fundamental science that has retarded progress in the field for over 40 years. Its removal suggests improved ways to approach dissolution studies. AbstractMineral dissolution kinetics are fundamental to biogeochemistry, and to the application of science to reduce the deleterious effects of humanity’s waste products, e.g. CO2 and radio-nuclides. However, a mistake made in the selection of the rate equation appropriate for use at the macro-scale of the aquatic environment has stymied growth in major aspects of the subject for some 40 years. This paper identifies the mistake, shows how it represents a latent disciplinal clash between two rate equations, and explores the misunderstandings that resulted from it. The paper also briefly explores other disciplinal clashes. Using the example of calcite dissolution, the paper also shows how the phenomenon of ‘non-ideal’ dissolution, which is prevalent in alumino-silicate mineral dissolution, as well as with calcite, has obscured the clash. The paper provides new information on plausible mechanisms, the absence of which has contributed to the problem. Finally, it argues that disciplinal clashes need to be minimised so that a rigorous description of dissolution at the large scale can be matched to findings at the atomic, or near-atomic, scale.

Acid rock drainage in Nevado Pastoruri glacier area (Huascarán National Park, Perú): hydrochemical and mineralogical characterization and associated environmental implications.

The generation of acid rock drainage (ARD) was observed in an area of Nevado Pastoruri as a result of the oxidative dissolution of pyrite-rich lutites and sandstones. These ARDs are generated as abundant pyrite becomes exposed to atmospheric conditions as a result of glacier retreat. The proglacial zone contains lagoons, springs, streams and wetlands, scant vegetation, and intense fluvioglacial erosion. This work reports a comprehensive identification and the results of sampling of the lagoons and springs belonging to the microbasin, which is the headwaters of the Pachacoto River, as well as mapping results based on the hydrochemical data obtained in our study. The physical properties and water chemistry of 12 springs and 22 lagoons from the proglacial zone are also presented. Water springs are far from being chemically uniform, with pH and EC values ranging between 2.55-6.42 and 23-1110μS/cm respectively, which suggests a strong geologic control on water chemistry. Fe-SO4-2 concentrations confirm the intense process of pyrite oxidative dissolution. Many of the lagoons are affected by ARD, with low pH (~3), and high EC (256-1092μS/cm) values when compared with unaffected lagoons (EC between 7 and 59μS/cm), indicating a high degree of mineralization. The affected lagoons show higher concentrations of SO42- and SiO2, and elements as Fe, Al, Mg, Mn, Zn, Co, and Ni, which are related to the alteration of pyrite and the dissolution of aluminosilicate minerals. Schwertmannite-goethite appears to be the most important mineral phases controlling the Fe solubility at a pH of 2-3.5. Moreover, they act as a sorbent of trace elements (As, Sb, V, Pb, Zn, Cr), which is an efficient mechanism of natural attenuation. Despite of this, the water flowing out from the basin is acid (pH3.1) and contains significant concentrations of Fe (0.98mg/L) and Al (3.76mg/L) that confer mineral acidity to water. The Pachacoto River located 5.5km downstream from this point showed a strong natural attenuation, with a pH of 6.9 and low concentration of metals. This mitigating process is possible due to (i) the formation of precipitates that retain toxic elements and (ii) the mixing with natural waters that promote dilution, which favor the increase of pH until circumneutral conditions.

The Thermal Water Geochemistry in Jiangxi Province (SE-China)

The chemical and isotopic compositions of Jiangxi Province thermal waters are considered. It is shown, carbon dioxide thermal waters are more mineralized (TDS=0.3–3.9g/l) than nitric thermal waters (TDS=0.3-0.4 g/l), in addition, the carbon dioxide thermal waters, in general, are weak acid and neutral (pH=5.70-7.77), the nitric thermal waters – alkaline (pH=8.5-9.25). It should be noted, the content of Na+, Si, HCO3-, CO32-, sometimes SO42− Ca2+ and K+ is predominant in the carbon dioxide thermal waters, the content of Na+, Si, F-, HCO3− is predominant, but concentrations of Ca2+, Mg2+, Cl− are quite low in the nitric thermal waters. It has been identified that the Jiangxi Province thermal waters have meteoric origin. It has been established, the main factor responsible for low concentrations of some chemical elements and high content of others is equilibrium-nonequilibrium state of water-rock system, which can be determined by continuous dissolution of aluminosilicate minerals and simultaneous precipitation of secondary minerals.

Using surface geopolymerization reactions to strengthen Athabasca oil sands mature fine tailings

AbstractThis paper describes a novel method to address the oil sands tailings reclamation problem using surface geopolymerization reactions. Geopolymerization involves dissolution of aluminosilicate minerals and re‐solidification reactions that result in the formation of three‐dimensional inorganic polymers of significant strengths. Since the fines present in oil sands mature fine tailings (MFT) mainly consist of aluminosilicate minerals, or clay minerals, it is hypothesized that by adding appropriate reagents, the surface of the clay minerals can be activated and go through geopolymerization reaction under ambient conditions. The resulting geopolymeric species formed on the clay minerals will bind the clay particles together and strengthen the tailings even without further dewatering.Geopolymerization was tested on 0.51 g/g (51 wt%) solids centrifuged MFT and its shear strength was observed to increase from 115 to 4880 Pa in 90 days when treated with 40 kg of sodium hydroxide and 60 kg sodium silicate per tonne of dry MFT solids. Similarly, the shear strength of 0.48 g/g (48 wt%) solids polymer flocculated MFT increased from 395 to 3950 Pa 90 days after the addition of the same dosages of sodium hydroxide and sodium silicate. Tests conducted on a geopolymerized model kaolinite sample showed that under the test conditions, the geopolymerization reaction only occurs on the surface of the kaolinite at the indicated dosages. The surface geopolymers held the kaolinite particles together, leading to an increase in its shear strength.

Geochemical peculiarities of nitric thermal waters in Jiangxi Province (SE-China)

The chemical composition of nitric thermal waters in Jiangxi Province, SE-China, is considered. It is shown that the studied thermal waters are characterized by low TDS (293-412 mg/l), but they always have alkaline or highly alkaline pH values. It should be noted that the content of Na+, Si, F-, HCO3-, CO32-, sometimes SO42- is predominant, on the other hand, the content of Ca2+, Mg2+, Cl- is low. It has been established that the main factors responsible for low concentrations of some chemical elements and high concentrations of others are continuous dissolution of aluminosilicate minerals and simultaneous precipitation of the secondary minerals.

The study of soil acidification of paddy field influenced by acid mine drainage

The acidification of paddy fields was studied in Guizhou Province, China. Affected by acid mine drainage, the pH value of irrigation water was 2.9 with the concentrations of iron and aluminium above 40 mg/L. Based on the pH(H2O) of topsoil, the paddy fields studied were classified spatially into three zones, the natural zone (pH value from 6.2 to 5.5), the acidified zone (pH value from 5.5 to 4.5), and the seriously acidified zone (pH value from 4.5 to 3.2), respectively. Comparing to the natural zone, the buffering processes for acidification of paddy soil were discussed by considering the changes of calcium, magnesium, potassium and aluminium in soils. The Ca, Mg and K were leached from the soil by the decomposition of carbonate and kaolinite. The leaching of Mg became less with the enrichment of iron in topsoil layer. When the soil pH was below 5.0, aluminium was leached from soil because of the dissolution of alumino silicate minerals. In addition, the hydrolysis of iron and aluminium in soil provided more protons to promote the soil acidification. Furthermore, the buffer capacity of paddy soil was discussed by the results of buffer experiment, based on which the pH buffer curve was drawn and the empirical formula for calculating the acidification rate was developed. Because pH buffer capacity of soil is about 2.78 cmolc/kg pH for the pH(H2O) value above 5.0, it is estimated that only another 50 years are needed for the pH(H2O) of the paddy soil decrease to 3.5 in the acidified zone if the acid water is used for irrigation continuously.

Geochemical characteristics of waters in mineralised area of Peloritani Mountains (Sicily, Italy)

Abstract This paper presents the results of a study on the geochemistry of waters circulating in the mineralised area of the south-eastern sector of Mt. Peloritani (north-eastern Sicily, Italy), aimed at basic understanding of the geochemical processes influencing their chemical composition. Chemico-physical parameters and data on 26 major and minor chemical elements are reported for 103 water samples. Water chemistry is mainly dominated by dissolution of carbonates and hydrolysis of aluminosilicate minerals. Total dissolved salts (TDS) range from 80 to 1398 mg/L. All the waters exhibit E H characteristic of an oxygenated environment. Excluding two samples, which show very high H + activity (pH = 3.0 and 2.7), all the waters have pH values in the range 6.2–8.6. Cluster analysis based on major ion contents defined three main chemical water types, reflecting different hydrochemical processes. The first, group I, has low salinity (average TDS = 118 ± 30 mg/L) and abundance orders (meq/L) Na > Ca ≈ Mg > K and Cl ≈ HCO 3 > SO 4 . With increased water–rock interaction, waters in groups II and III become more saline, changing composition towards SO 4 –Cl-alkaline earth and HCO 3 -alkaline earth types. Weathering of carbonate minerals causes waters to become saturated with respect to calcite and dolomite, whereas the incongruent dissolution of aluminosilicate minerals causes the solution to reach equilibrium with kaolinite and to form smectites. Trace element geochemistry in the analysed waters reflects interactions between waters and existing mineralisation, with elemental concentrations showing highly variable values, and higher concentrations of As, Pb, Sb and Zn near known mineralisation. Lead–Zn and As–Sb statistical associations, probably distinguishing interactions with different mineralogical phase paragenesis, were revealed by factor analysis. The main aqueous chemical forms of trace elements predicted by chemical speciation calculations are also reported. As most of the analysed spring waters provide the main source of freshwater for domestic purposes, attention should be given to As and Sb, whose concentrations exceed the recommended limits.

Acid drainage generation and seasonal recycling in disturbed permafrost near Eagle Plains, northern Yukon Territory, Canada

Acidic SO 4–Ca–Fe waters are discharging from sandstone bedrock overlying pyrite-rich shales along the Dempster Highway near Eagle Plains, northern Yukon Territory. Although evidence of acid drainage was present prior to the construction of the Dempster Highway in the 1970's, the removal of surficial sediments during its construction amplified the release of acidity by allowing the active layer to penetrate into the freshly exposed pyrite-rich shale. Acid drainage originating from the excavated area has a pH value averaging 3.1 ± 0.3 and over 5 g/L of dissolved solids (SO 4 2− = 3915 mg/L, Fe total = 459 mg/L, Ca 2+ = 418 mg/L and Al total = 83.6 mg/L) whereas the unaffected drainage has a pH greater than 4.4 and total dissolved solids in the 100 to 200 mg/L range. Geochemical modeling of the surface waters and active layer pore water using PHREEQC hydrogeochemical computer code predicted saturation in Fe-hydroxide and Fe-sulfate minerals, which is confirmed by the observation of abundant ferrihydrite precipitates along the acidified stream. The solute concentrations of the acidified stream and active layer soluble ions versus SO 4 plot on very similar slopes, suggesting a recycling of solutes. It is suggested that the effect of seasonal freeze-thaw of the active layer plays an important role in sustaining acidity in the stream. Freeze-back of the acid waters in the active layer produces both Fe-sulfate minerals and residual sulfuric acid. During the thaw season, this acidity is released, thus enhancing further dissolution of alumino-silicate minerals. The release of these contaminants, including acidity, not only causes a perturbation of the water quality, but also has a negative impact on the sensitive Arctic ecosystem, by disturbing the local permafrost conditions.

Hydrogeochemical evaluation of groundwater in the lower Offin basin, Ghana

Alumino-silicate mineral dissolution, cation exchange, reductive dissolution of hematite and goethite, oxidation of pyrite and arsenopyrite are processes that influence groundwater quality in the Offin Basin. The main aim of this study was to characterise groundwater and delineate relevant water–rock interactions that control the evolution of water quality in Offin Basin, a major gold mining area in Ghana. Boreholes, dug wells, springs and mine drainage samples were analysed for major ions, minor and trace elements. Major ion study results show that the groundwater is, principally, Ca–Mg–HCO3 or Na–Mg–Ca–HCO3 in character, mildly acidic and low in conductivity. Groundwater acidification is principally due to natural biogeochemical processes. Though acidic, the groundwater has positive acid neutralising potential provided by the dissolution of alumino-silicates and mafic rocks. Trace elements’ loading (except arsenic and iron) of groundwater is generally low. Reductive dissolution of iron minerals in the presence of organic matter is responsible for high-iron concentration in areas underlain by granitoids. Elsewhere pyrite and arsenopyrite oxidation is the plausible process for iron and arsenic mobilisation. Approximately 19 and 46% of the boreholes have arsenic and iron concentrations exceeding the WHO’s (Guidelines for drinking water quality. Final task group meeting. WHO Press, World Health Organization, Geneva, 2004) maximum acceptable limits of 10 μg l−1 and 0.3 mg l−1, for drinking water.

Dissolution of aluminosilicate minerals and by-products in alkaline media

In this work, the leaching behaviour of six aluminosilicate industrial minerals and by-products (kaolin, metakaolin, fly ash, natural pozzolana from Milos, zeolite and furnace slag) in alkaline solutions is investigated. The variables studied are the kind of alkali metal (K, Na), the concentration of the alkaline solution (2.5, 5 and 10 M) and the time of dissolution (5, 10 and 24 h). The solid residue after the leaching was examined by means of XRD and FTIR. As it is concluded, the leaching ability of Al and Si is according to the following descending order: Metakaolin > Zeolite > Slag > Fly Ash > Pozzolana > Kaolin. The extent of dissolution is higher in NaOH than in KOH solutions, especially when the most reactive materials are concerned. Finally, Si and Al seem to have a synchronized leaching behaviour in both alkaline solutions.

Preliminary modeling of the long-term fate of CO2 following injection into deep geological formations

The injection of CO2 into deep saline aquifers is a potential option for greenhouse gas mitigation. However, several key issues, such as underground storage time and the fate of the injected CO2, must be studied before this option becomes economically and socially acceptable. In the current study, a one-dimensional reactive mass-transport model was used to predict the long-term chemical behavior of a deep saline aquifer following CO2 injection, far away from the injection site and representative of basin-scale migration and long-term fate. The dissolution of the injected CO2 into brine causes a sharp drop in pH, and consequently, the acidic brine aggressively reacts with aquifer minerals. Our model also predicts the dissolution of aluminosilicate minerals with the formation of secondary minerals and the precipitation and dissolution of carbonate minerals and is consistent with laboratory-scale CO2 core-flooding experiments. However, the extent and development of reaction fronts depend on the reaction rates used. For example, our modeling results indicate that the transport of carbon can be significantly retarded with respect to the flow of the brine itself, and a significant amount of injected CO2 is immobilized because of mineral trapping. The precise locations and patterns of the carbon reactive transport are sensitive to the reaction rates used, illustrating the need for improved knowledge of reaction kinetics, particularly the in-situ rates of dissolution and precipitation of aluminosilicate minerals, in evaluating mineral trapping of CO2 in deep geological formations.

Quantification of mineral dissolution rates and applicability of rate laws: Laboratory studies of mill tailings

Reliable quantification of mineral weathering rates is a key to assess many environmental problems. In this study, the authors address the applicability of pure mineral laboratory rate laws for dissolution of mill tailings samples. Mass-normalised sulfide and aluminosilicate mineral dissolution rates, determined in oxygenated batch experiments, were found to be different between two samples from the same ∼50-year-old, carbonate-depleted mill tailings deposit. Consideration of difference in particle surface area and mineralogy between the samples resolved most of this discrepancy in rates. While the mineral surface area normalised dissolution rates of pyrite in a freshly crushed pure pyrite specimen and a sulfide concentrate derived from the tailings were within the range of abiotic literature rates of oxidation by dissolved molecular O 2, as were rates of sphalerite and chalcopyrite dissolution in the tailings, dissolution rates of pyrite and aluminosilicates in the tailings generally differed from literature values. This discrepancy, obtained using a consistent experimental method and scale, is suggested to be related to difficulties in quantifying individual mineral reactive surface area in a mixture of minerals of greatly varying particle size, possibly due to factors such as dependence of surface area-normalised mineral dissolution rates on particle size and time, or to non-proportionality between rates and BET surface area.

Mineral/water interactions in tailings from a tungsten mine, Mount Pleasant, New Brunswick

The pore-water geochemistry and mineralogy of tailings derived from a granitic tungsten deposit were characterized by collecting pore-water samples at discrete depth intervals throughout the tailings for the analysis of major and minor element concentrations. Mineralogical samples from the oxidation zone were analyzed by X-ray diffraction, scanning electron microscopy combined with energy dispersive X-ray spectroscopy (SEM/EDS), electron microprobe (EMP) combined with wavelength dispersive X-ray spectroscopy (WDS), and transmission electron microscopy (TEM). The oxidation of sulfide minerals in the near-surface tailings leads to a decrease in pore-water pH and elevated SO 4, As, and metal concentrations. The unusual mineralogy of this deposit, compared with that of commonly studied base-metal and gold deposits, results in several unique geochemical characteristics. The dissolution of fluorite releases F into the pore water; the F forms strong complexes with Al and enhances the dissolution of aluminosilicate minerals within the oxidation zone. As a result, high Al concentrations (up to 151.7 mg/L) are detected in the near-neutral pore water in the oxidation zone. The combined dissolution of aluminosilicates and carbonate minerals maintains the pH near 10 in the pore water at depth. Elevated concentrations of W (up to 7.1 mg/L) are detected in the pore water throughout the tailings, likely as a result of the dissolution of wolframite. Consistent with geochemical model calculations, results from SEM/EDS, EMP/WDS and TEM/EDS analyses indicate that secondary minerals, which occur as orange-brown coatings on grains of primary-minerals, are Fe oxyhydroxides. Examples of these secondary minerals display a fibrous habit at high resolution in the TEM. One of these minerals, which contains substantial amounts of Al, As, and Si as impurities, was identified by selected-area electron diffraction (SAED) analyses to be goethite. Another mineral contains relatively high amounts of Si, Pb, Bi, and As, and SAED analyses suggest that the mineral is two-line ferrihydrite.