Silicate Source Research Articles

Hydrogeochemical characterization and geochemical modeling for the evaluation of groundwater quality and health risk assessment in the Varuna River basin, India.

This study focuses on determining significant controlling factors of chemical consequences, inverse geochemical modeling, water quality, and human health risk in the Varuna River basin of India. The study interprets that according to pH, total dissolved solids, and total hardness, the maximum number of groundwater samples are alkaline, fresh, and have substantial hardness. The abundance of major ions follows a pattern: Na > Ca > Mg > K, and HCO3 > Cl > SO4 > NO3 > F. Piper diagram shows that Ca-Mg-HCO3 facies are predominant during both seasons. Na-normalized molar ratios of HCO3/Na, Mg/Na, and Ca/Na are 0.62, 0.95, and 1.82 (pre-monsoon) and 0.69, 0.91, and 1.71 (post-monsoon), respectively, elucidating the coupled silicate and carbonate weathering (dolomite dissolution) sources. The Na/Cl molar ratio is 5.3 (pre-monsoon) and 3.2 (post-monsoon), indicating silicate alteration as the primary process rather than halite dissolution. The chloro-alkaline indices confirm the presence of reverse ion- exchange. Geochemical modeling using PHREEQC identifies the formation of secondary kaolinite minerals. The inverse geochemical modeling categorizes the groundwaters along the flow path from recharge area waters (Group I: Na-HCO3-Cl), transitional area waters (Group II: Na-Ca-HCO3), and discharge area waters (Group III: Na-Mg-HCO3). The model demonstrates the prepotency of water-rock interactions in pre-monsoon justified by the precipitation of Chalcedony and Ca-montmorillonite. The mixing analysis shows that in the alluvial plains, groundwater mixing is a significant hydrogeochemical process that affects groundwater quality. The Entropy Water Quality Index ranks 45% (pre-monsoon) and 50% (post-monsoon) of samples as an excellent category. However, the non-carcinogenic health risk assessment shows that children are more susceptible to fluoride and nitrate contamination.

Late Campanian Climatic-Continental Weathering Assessment and Its Influence on Source Rocks Deposition in Southern Tethys, Egypt

Climatic variability and silicate weathering are remarkable features throughout the Late Cretaceous period. Late Campanian black shale is considered the most significant silicate source rock in the southern Tethys. Here, we used mineralogical and geochemical data to evaluate the continental weathering intensity and climatic changes as well as their impact on the deposition of the Late Campanian black shale in the Western Desert of Egypt. The studied black shale has a relatively high concentration of Al, Fe, Mg, Ca, Sr, Ga, Co, Cr, and V when compared to the average Post-Archean Australian Shales (PAAS). The studied samples have elevated values of Ga/Rb, and low values of Rb/Sr, Sr/Cu, and K2O/Al2O3, supporting the deposition of Late Campanian shale under warm/humid conditions. Furthermore, the average chemical index of alteration (CIA, 78.6%), chemical index of weathering (CIW; 83.8%), C-value (1.26), Fe/Mn (408), and Mg/Ca (1.54) reveal the predominance of warm/humid climate. The chemical weathering proxies (CIA, CIW, PIA, LnAl2O3/Na2O) and ACNK diagram imply that the Late Campanian samples were exposed to a moderate grade of chemical alteration. The deposition of black shale occurred under high seawater salinity conditions based on Sr/Ba (Avg = 3.6). Additionally, the weathering indices are well correlated with paleoclimatic proxies, suggesting that weathering intensity is strongly affected by paleoclimate. However, chemical weathering during the Late Campanian has a weak influence on oceanic nutrient fluxes. No substantial impact of the paleoclimate during the deposition of Late Campanian black shale on water salinity was reported.

Study of mechanical properties of geopolymer mortar prepared with fly ash and GGBS

Geopolymers are a novel form of artificial polymer created when an alumino - silicate source is prompted or activated using alkaline hydroxide and a silicate solution. Geopolymeric material is gaining popularity due to their excellent mechanical behavior, environmentally friendly nature and good long term durability. The rapid growth in geopolymer binder’s research and development in recent years has indeed indicated that geopolymer has the greatest potential in solving not only waste management problems related to alumino-silicate solid waste materials generated by various industries, but also environmental degradation related to the use of OPC as a primary binder material in the construction industry.Fly ash (FA), contains significant levels of alumina and silica, which are required for the geopolymerization reaction to occur at 60 to 80 °C which restricts its application in the field. To address this issue an attempt has been made to use GGBS (20%, 30% and 50%) as an additive to reduce the curing temperature. Above mentioned percentages of GGBS have been used with FA with alkaline activator consisting of Sodium Hydroxide (6 M,8M, 10 M, 12 M) and Sodium Silicate. The effect of addition of GGBS on setting time, compressive strength and water absorption has been compared with mortar prepared with OPC. To substantiate the results, FTIR has been used to study the changes in bonding behavior of Si-O-Si and Si-O-Al due to addition of GGBS.

Self-activated rare-earth free phosphor prepared by propylene glycol-modified silane

A facile wet-chemistry method can be applied to produce efficient rare-earth-free LED phosphors. In this study, self-activated Ca2SiO4 phosphor was developed using a propylene glycol-modified silane (PGMS) as a silicate source. The structural and luminescence properties of samples were characterized using synchrotron X-ray powder diffraction and photoluminescence (PL) spectroscopy, respectively. The PGMS phosphor consists of mixed crystal phases of α′L, β, and γ, whereas the solid-state reaction (SSR) phosphor only has a β phase. The synthesized PGMS phosphor with distinctive crystal defects shows self-activated luminescence, while the SSR phosphor has no PL properties.

Properties of One-Part Alkali Activated Ground Granulated Blast Furnace Slag Using Slaked Lime as Alkali Activator – A Comparative Study with Different Silicate Sources

The paper reports the results of investigating the prospect of using slaked lime as a solid activator to activate the ground granulated blast furnace slag (GGBFS) with micro-silica as an additive. The results of the above-mentioned one-part mix are compared to that of GGBFS activated with solid sodium silicate in combination with slaked lime and quick lime, discretely. The compressive strength is found to be comparable to that of slaked lime and sodium silicate activated GGBFS; the silica fume substitution is recommended at 10% with 5% slaked lime. The main hydration products are C-S-H and C-A-S-H. Although the setting is delayed, strength development is acceptable with curing at ambient temperature. The microstructural analyses conducted through Field emission gun scanning electron microscopy (FEGSEM) and X-ray diffraction (XRD) are in good correlation with the results obtained for strength development.

Silicon improves the effect of phosphate-solubilizing bacterium and arbuscular mycorrhizal fungus on phosphorus concentration of salinity-stressed alfalfa (Medicago sativa L.)

Under salinity stress, the availability of soil nutrients to plants is reduced, leading to disruption of nutrition and the balance of plant nutrients, including phosphorus (P). The use of phosphate-solubilizing microorganisms (PSM) and silicon (Si) in alleviating salinity stress and improving the uptake of P by plants has become a global solution. However, there is limited information on the effect of phosphate-solubilizing bacteria and arbuscular mycorrhizal fungi in the combination with Si on improving the absorption of P by plants including legumes under salinity stress. In this study, the plant growth-promoting potential of an effective phosphate-solubilizing bacterial strain (R115), Microbacterium shaanxiense, and an arbuscular mycorrhizal fungus, Claroideoglomus etunicatum, alone or in the combination with Si to alleviate salinity stress in alfalfa inoculated with its rhizobial symbiosis, Ensifer meliloti N44, and improve the absorption of P by this plant was investigated by a pot-experiment in a completely randomized design with factorial arrangement in three repetitions. Experimental treatments included: Si factor at two levels of 0 and 4 mM Si from potassium silicate source, bacterial strain R115 factor at two levels of B0 (control), and strain R115 (B1), mycorrhizal fungus factor at two levels of F0 (control) and mycorrhizal fungus (F1), and salinity (saline water) factor at three levels of 0, 5, and 15 dS m−1. Salinity stress reduced plant biomass, the content of chlorophyll, the concentration of N, P and K of plant and increased the concentration of Na in shoot tissue and the activity of antioxidant enzymes (catalase and superoxide dismutase) in alfalfa plant. However, the use of PSM (M. shaanxiense R115 and C. etunicatum) and Si improved the morphological and physiological characteristics of the plant, reduced the plant Na concentration, and increased the concentration of N, P, and K of alfalfa plants. The highest improvement in plant growth indices (shoot P concentration) was recorded in plants inoculated with PSM in the presence of Si. The results of this study showed that Si fertilization can be suggested as a sustainable strategy for improving the plant growth promoting effects of PSM on the growth of alfalfa (e.g., increased shoot P concentration) and encouraging ecological adaptability of this plant under saline water irrigation.

Valorizing hazardous lead glass sludge and alumina flakes filling waste for the synthesis of geopolymer building bricks.

Geopolymer bricks from lead glass sludge (LGS) and alumina flakes filling (AFF) waste were synthesized in the present work. AFF waste was chemically treated to prepare sodium aluminate (NaAlO2) powder. Silicate source (untreated LGS and thermally treated one at 600 °C (LGS600)) and sodium oxide (Na2O) concentration (as NaAlO2) were the compositional parameters, which affected the physical and mechanical properties (compressive strength, water absorption, and bulk density) of the prepared bricks. High organic matter content inside LGS caused a retardation effect on the geopolymerization process, resulting in the formation of hardened bricks with modest 90-day compressive strengths (2.13 to 4.4 MPa). Using LGS600 enhanced the mechanical properties of the fabricated bricks, achieving a maximum 90-day compressive strength of 22.35 MPa at 3 wt.% Na2O. Sodium aluminosilicate hydrate was the main activation product inside all samples, as confirmed by X-ray diffraction and thermal analyses. Acetic acid leaching test also proved that all LGS600-NaAlO2 mixtures represented Pb concentrations in leachates lower than the permissible level of characteristic leaching procedures, indicating the mitigation of environmental problems caused by these wastes.

Nutrient fluxes in the Bons Sinais Estuary (Mozambique) – sources and sinks

ABSTRACT Estuaries are the main gateway of nutrients into marine coastal waters. Human activities and biodegradation processes in coastal freshwater and mangrove swamps are the major sources of nutrients. This study examines the sources, sinks and flux rates of nitrogen (N), phosphorus (P) and silicon (Si) through the interfaces: river estuary, mangrove estuary and ocean estuary. Measurements of the concentrations of nutrients and water velocity were made near the surface on an hourly basis, and then integrated over the flood and ebb flows over the cross-sectional area and a budget estimated over the tidal cycle, at the three interfaces. The results indicated that freshwater swamps, along the river basin, and mangrove swamps were the major source of nitrate in the estuary; the urban sewage effluent was the major source of phosphate; major sources of silicate were the freshwater swamps and coastal ocean waters. Mangrove swamp showed a tendency to retain phosphate, confirming the hypothesis that mangroves are effective sewage filters and pollutant retainers. The river exported nitrate into the estuary at a rate of 59 tons per tidal cycle, and then the estuary as a whole exported nitrate into the coastal waters at a rate of 68 tons per tidal cycle. The present study contributes to the explanation of the observed high coastal productivity of the Sofala Bank and to the development of prognostic and predictive models to quantify and predict the nutrient export to – and productivity of – coastal waters.

Preparation and characterization of a novel alkali-activated magnesite cement

The present paper focuses on synthesizing an alkali-activated binder, in which magnesium carbonate (MC) was the only precursor. MC was individually activated with sodium hydroxide (NaOH), sodium silicate (Na2SiO3) and sodium aluminate (NaAlO2). Increasing Na2O content (as NaOH) up to 10 wt% enhanced the compressive strength slightly. At constant Na2O content (10 wt%), the sample activated by (Na2SiO3) recorded the highest compressive strength. Although the hardened mixture activated by NaAlO2 showed the higher compressive strength compared to NaOH-activated sample, it still recorded strength lower than Na2SiO3-activated-mixture. XRD, TG/DTG, FTIR, and SEM techniques indicated that phase composition depends mainly on the Na2O source. 29Si MAS-NMR spectroscopy verified the formation of magnesium silicate hydrate with Q1, Q2, and Q3 silicate connectivity, when MC was activated with Na2SiO3. Incorporating lead glass sludge (LGS) as a silicate source, enhances the formation of a cross-like silicate chain (Q3) coinciding with an improvement of the compressive strength and a retardation of Pb-leachability. As proved by 27Al MAS-NMR, Al inside hydrotalcite phase, formed within NaAlO2-activated-MC, has six coordination bonds. Activating MC with NaOH produces magnesium hydroxide (Mg(OH)2) and thermonatrite Na2CO3·H2O phases. Owing to the diversity of the hydration products, a wide range of 90-day compressive strengths (9–53 MPa) was recorded. A preliminary result showed that the CO2-emission generates from optimum mixture containing 30 wt% LGS is lower than resulted from Portland cement manufacturing.

Magnesium isotopic composition of rivers draining karst-dominated regions in Southwest China

Magnesium isotopic composition (δ26Mg) could constrain sources and processes of riverine Mg, thus providing new perspectives on budgeting the global Mg cycle. Carbonate lithology displaying karst covers about one-fifth of the Earth's ice-free continental area, however, Mg isotopic composition and associated fractionation processes in rivers draining carbonate are not well constrained. This study focused on tributaries of the mid-reaches of the Xijiang River, a carbonate dominated river in southwest China. The δ26Mg value of river water shows a large range of −2.23‰ to −0.61‰. The clay formation results in a maximum δ26Mg variation of ~0.3‰ and the influence of secondary carbonate precipitation on river δ26Mg is not observed. Lithology is the primary control of Mg isotopic composition of river water. The relations of Sr/Ca ratio and 87Sr/86Sr, and Mg/Ca ratio and δ26Mg value are suggestive of silicate, limestone, and dolomite weathering sources in the river. However, in some tributaries, the solute sources indicated by Sr and Mg isotopes are different, this could be due to the heterogeneous distribution of lateritic soil and weathering of reactive minerals with distinct Sr and Mg content. Compiling data of large rivers over the world, a relationship between the solute proportion of carbonate weathering and δ26Mg of river water is observed, suggesting that isotopic composition of carbonate weathering Mg flux is −2.3‰ at the continental scale. The result might provide links between riverine δ26Mg and chemical weathering flux in geological history.

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

AbstractMg 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 1/Mg 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.

Remote silicate supply regulates spring phytoplankton bloom magnitude in the Gulf of Maine

AbstractSpring phytoplankton blooms in the Gulf of Maine (GoM) are sensitive to climate‐related local and remote forcing. Nutrient supply through the slope water intrusion has been viewed as critical in regulating the GoM spring blooms, with an assumption that nitrogen is the primary limiting nutrient. In recent years, this paradigm has been challenged, with silicate being recognized as another potential limiting nutrient, but the source of silicate and its associated water mass remain difficult to be determined. In this study, a time series of spring bloom magnitude was constructed using a self‐organizing map algorithm, and then correlated with the fluctuation of water composition in the deep Northeast Channel. The results reveal the importance of silicate supply from previously less‐recognized deep Scotian Shelf Water inflow. This study offers a new hypothesis for spring bloom regulation, providing a better understanding of mechanisms controlling the spring bloom magnitude in the GoM.

Design of Fly Ash-Based Alkali-Activated Mortars, Containing Waste Glass and Recycled CDW Aggregates, for Compressive Strength Optimization.

Alkali-activated mortars and concretes have been gaining increased attention due to their potential for providing a more sustainable alternative to traditional ordinary Portland cement mixtures. In addition, the inclusion of high volumes of recycled materials in these traditional mortars and concretes has been shown to be particularly challenging. The compositions of the mixtures present in this paper were designed to make use of a hybrid alkali-activation model, as they were mostly composed of class F fly ash and calcium-rich precursors, namely, ordinary Portland cement and calcium hydroxide. Moreover, the viability of the addition of fine milled glass wastes and fine limestone powder, as a source of soluble silicates and as a filler, respectively, was also investigated. The optimization criterium for the design of fly ash-based alkali-activated mortar compositions was the maximization of both the compressive strength and environmental performance of the mortars. With this objective, two stages of optimization were conceived: one in which the inclusion of secondary precursors in ambient-cured mortar samples was implemented and, simultaneously, in which the compositions were tested for the determination of short-term compressive strength and another phase containing a deeper study on the effects of the addition of glass wastes on the compressive strength of mortar samples cured for 24 h at 80 °C and tested up to 28 days of curing. Furthermore, in both stages, the effects (on the compressive strength) of the inclusion of construction and demolition recycled aggregates were also investigated. The results show that a heat-cured fly ash-based mortar containing a 1% glass powder content (in relation to the binder weight) and a 10% replacement of natural aggregate for CDRA may display as much as a 28-day compressive strength of 31.4 MPa.

Sediment and water geochemistry record of water-rock interactions in King George Island, Antarctic Peninsula

AbstractWe used a multidisciplinary approach integrating major, trace and rare earth element geochemistry, mineralogy of rocks and sediments along with the ionic composition of water reservoirs of Admiralty Bay, King George Island, to evaluate the record of water-rock interactions under Maritime Antarctic conditions. Our results showed that the ionic compositions of the streams and meltwaters predominantly reflect the atmospheric inputs, while lake waters have higher Na/Cl, Ca/Mg and HCO3/Cl ratios related to chemical weathering in lake sediments, but this did not allow for distinguishing purely silicate sources. Consistent with the trace and rare earth element data, various alteration indices and Index of Compositional Variability values denote the low degree of chemical weathering in the lake sediments. The records from the previously unexplored Mud Lake and Upper Lake suggest that the lakes of Admiralty Bay are better places to trace the impacts of a succession of environmental changes that have occurred in the watershed, while the stream channel sediments, when accompanied by water chemistry data, may provide a more representative composition of the source rocks than the lake sediments. These findings may help revealing the intensity of contemporary weathering in a colder climate with relatively few mineralogical changes accompanied by a lesser degree of elemental loss.

Bio‐derived sodium silicate for the manufacture of alkali‐activated binders: Use of bamboo leaf ash as silicate source

AbstractAlkali activated binders are a promising alternative to the use of Portland cement in the manufacture of concrete for curbing CO2 emissions. Novel sources of silicates have been investigated in recent years for reducing cost and environmental impacts associated with the use of chemical activators. This study describes the production of solid sodium silicate (SS) activating powder from bamboo leaf ash (BLA). Bamboo leaves were calcined at 550–800°C, mixed with NaOH pellets, and heated in an oven at 300°C. The obtained silicate powder was used for activating blended fly ash/slag samples. Mechanical and microstructural properties of BLA‐based samples were compared to those of samples made with commercially available chemicals. The strength of BLA‐activated mortars matched the commercially‐sourced activators, being 25–30 MPa at 7 days and exceeding 40 MPa at 28 days. The microstructural analysis suggested that BLA‐based SS showed a lesser degree of dissolution of precursors at 7 days, but the quality of the matrix was higher than that of NaOH‐activated samples. These results confirmed that the reactivity of BLA‐silicate powder was similar to that of commercial SS solutions, and show the potential valorization of future biomass renewable waste in the production of low carbon, alkali‐activated concretes.

Sediment provenance and silicic volcano-tectonic evolution of the northern East African Rift System from U/Pb and (U-Th)/He laser ablation double dating of detrital zircons

Detrital zircons from two major rift basins within the East African Rift System (EARS) provide a means to evaluate not only sediment provenance and landscape dynamics in sedimentary basins, but also the timing of the silicic volcano-tectonic evolution of the rift system. We sampled from drill cores collected by the Hominin Sites and Paleolakes Drilling Project (HSPDP) in Ethiopia and Kenya to study the detrital mineral records of the Northern Awash (NA; 3.3–2.9 Ma) and West Turkana (WTK; 1.9–1.4 Ma) drill cores. We performed (U-Th)/He and U/Pb analyses on detrital zircons using single crystal laser ablation double dating (LADD) techniques. Analyses of four NA samples yielded zircon 206Pb/238U dates younger than ∼45 Ma, consistent with derivation from silicic volcanic rocks associated with EARS activity. Most of these samples lack zircon 206Pb/238U dates from ∼22–13 Ma, due to a decrease in silicic volcanism and a watershed configuration limiting delivery of silicic source materials to the sample site. NA zircon 206Pb/238U dates imply a sedimentary source from the western Afar margin, with a transition to more localized sediment reworking within the Afar Depression after a major regional tectonic reorganization and formation of a disconformity at ∼2.9 Ma. The WTK sample yielded many zircons with Cenozoic 206Pb/238U dates similar to those from the NA core, but the WTK sample also sources a small population of Neoproterozoic zircons associated with rocks from the Mozambique Belt and reworked sedimentary deposits. Despite being recorders of predominantly silicic activity, the detrital zircon U/Pb dates from both drill sites track the established timing of major volcanic phases in the EARS. A subset of zircons from both sites has concordant 206Pb/238U and (U-Th)/He dates, indicating a short duration between zircon crystallization and eruption of the host volcanic rock, but the majority of zircon (U-Th)/He dates are significantly younger than the 206Pb/238U dates for the same zircon. Some (U-Th)/He dates are even younger than the depositional age of the sedimentary sample from which it was collected. The observed spread in zircon (U-Th)/He dates likely reflects partial resetting associated with late mafic volcanism and/or hydrothermal activity within this dynamic rift environment.

Definition and Classification of Bioceramic Endodontic Sealers.

The term "bioceramic" is used in endodontics to describe various products and is often used in general terms for mineral trioxide aggregate (MTA) and other hydroscopic dental cements (HDC), which creates confusion in the terminology. The aim of the study is to present a definition and an original classification of bioceramic endodontic sealers. A total of 123 articles were found by the PubMed search engine using the key phrase "bioceramic endodontic sealers". Of these 123 articles, we analyzed 20 articles that contain information about the composition, properties, definition, and classification of bioceramic endodontic sealers. In accordance with the collected data on the composition and the delivery form of calcium silicate endodontic sealers, we propose a new definition of bioceramic endodontic sealers that clarifies the specificities of these materials. In the new classification they are divided by two criteria: source of calcium silicate and form of delivery. It also contains the particular products' names in order to aid their usage in the clinical practice.Conclusions: The new definition of bioceramic endodontic sealers clears out the confusion in the terminology, which promotes the classification of these products and helps understanding their clinical application.

Lithic arrowheads: Siliceous raw material sources and technology in Southern Portugal

AbstractThis analysis focused on one hundred and fifteen lithic arrowheads recovered from the Zambujeiro and Mitra 2 dolmens, funerary monuments in Évora, Portugal. These were analyzed by noninvasive and minimally invasive analytical techniques, including handheld X‐ray fluorescence (hXRF), variable pressure scanning electron microscope coupled with energy dispersive X‐ray spectrometry (VP‐SEM‐EDS), and laser ablation inductively coupled plasma mass spectrometry (LA‐ICP‐MS) to establish the sources of the raw materials used to manufacture these arrowheads and to compare and cluster different artefacts. The raw materials used in the manufacture of the arrowheads were found to be from different sources suggesting that long‐distance trade routes extending south, east and possibly west were in place in Southern Iberia during the Neolithic and Chalcolithic periods. Whether this difference is related to the availability of raw materials throughout time, different procurement strategies, or simply by choice, remains unknown. The trade routes associated with the Mitra 2 Dolmen also seem to have a greater range than those connected to the Zambujeiro Dolmen.

Silicon supplied via foliar application and root to attenuate potassium deficiency in common bean plants

Potassium (K) deficiency affects physiological performance and decreases vegetative growth in common bean plants. Although silicon (Si) supplied via nutrient solution or foliar application may alleviate nutritional stress, research on the bean crop is incipient. Thus, two experiments were carried out: initially, a test was performed to determine the best source and foliar concentration of silicon. Subsequently, the chosen Si source was supplied in nutrient solution via roots or foliar application to verify whether Si supply forms are efficient in alleviating the effects of K deficiency. For these purposes, a completely randomized 2 × 3 factorial design was used, with two levels of K: deficient (0.2 mmol L−1 of K) and sufficient (6 mmol L−1 of K); and Si: in nutrient solution via roots (2 mmol L−1 of Si) or foliar application (5.4 mmol L−1 of Si) and control (0 mmol L−1 of Si). Our findings revealed that Si supplied via foliar spraying using the source of sodium silicate and stabilized potassium at a concentration of 5.4 mmol L−1 was agronomically viable for the cultivation of bean plant. K deficiency, when not supplied with silicon, compromised plant growth. Moreover, root-and-foliar-applied Si attenuated the effects of K deficiency as it increased chlorophylls and carotenoids content, photosynthetic activity, water use efficiency and vegetative growth. For the first time, the role of Si to mitigate K deficiency in the bean crop was evidenced, with a view to further research on plants that do not accumulate this beneficial element.

A novel alkali activated magnesium silicate as an effective and mechanically strong adsorbent for methylene blue removal

A novel, cheap, and easy-to-synthesize sepiolite-based alkali-activated material (Sep-AAM), synthesized by the reaction of a magnesium silicate source, sepiolite, with sodium silicate solution, demonstrating high mechanical strength and methylene blue (MB) removal performance is introduced. Kinetics data indicated that MB adsorption occurs through pseudo-second-order adsorption kinetics model, while the Langmuir isotherm model provided a better fit to adsorption isotherms. The Sep-AAM provided a removal capacity of 99.92 mg g−1 at 50 °C, setting a new benchmark value among the materials used for this purpose. Thermodynamical parameters indicated that the adsorption of MB onto Sep-AAM was endothermic and the interaction between Sep-AAM and MB included weak chemical bonding. Regenerability of the Sep-AAM in powder and monolith forms was confirmed up to four-cycles. Structural parameters determined by several characterization tools demonstrated that the surface hydroxyl groups are responsible for the superior MB adsorption performance. The mechanical strength measurements showed that Sep-AAM in monolith form displayed a remarkable compressive strength value of 40 MPa. To establish a new approach forward on the development of AAMs for wastewater treatment, this study shows that sepiolite can effectively be utilized and Sep-AAM provides a sustainable solution for dye removal with advanced mechanical properties.