Silica Reservoir Research Articles

Synergistic effect of silica/polypyrrole nanocomposites synthesized by hydrothermal method using rice husk as a silica source for corrosion protection

Rice husk, a plentiful agricultural waste, is a natural and environmentally friendly silica reservoir. In this study, a hydrothermal synthesis was employed to produce silica/polypyrrole nanocomposites, with the primary objective of developing corrosion-resistant materials. The nanocomposites are comprehensively characterized using XRD, FTIR, FESEM, and electrochemical studies. The results confirmed the successful formation of a silica/polypyrrole nanocomposite and revealed that the adsorption of polypyrrole molecules onto silica clusters controls the formation of larger silica nanoparticles. Pure silica exhibits spherical particles ranging from 500 to 1 μm. A low concentration of polypyrrole results in nanoparticles with dimensions ranging from 100 to 200 nm, while a higher concentration leads to reduced silica nanoparticles with sizes 10–20 nm. Aggregation of spherical nanoparticles is more prominent in silica/polypyrrole nanocomposites than pure silica nanoparticles. The nanocomposites of silica/polypyrrole, namely SP-1, SP-2, and SP-3, demonstrated significantly higher corrosion resistance (Rct) values of 36613 Ω, 44536 Ω, and 49060 Ω, respectively, in comparison to the pure silica (19540 Ω). The corrosion rates of pure silica, SP-1, SP-2, and SP-3 were determined to be 1.2687 mm/yr, 0.4715 mm/yr, 0.4681 mm/yr, and 0.3042 mm/yr, respectively. Silica exhibits remarkable chemical stability and exceptional corrosion resistance, whereas polypyrrole is a conducting polymer endowed with distinctive electrical characteristics. These constituents can be synergistically combined within a nanocomposite matrix, enhancing corrosion resistance. The synthesized nanocomposite exhibits considerable promise as a corrosion-resistant coating agent, presenting a sustainable remedy for corrosion mitigation in different industrial contexts.

Electrosynthesis of Silica Reservoir Incorporated Dual Stimuli Responsive Conducting Polymer-Based Self-Healing Coatings

The current work describes a unique corrosion-protective self-healing coating approach. Porous silica reservoirs were synthesized by the Stober process. The silica reservoirs were preloaded with a corrosion inhibitor (oxalic acid) (dopant) and simultaneously covered with polyelectrolytes layers. Using the cyclic-voltammetry approach, a silica reservoir was dispersed into the aniline oxalate solution to successfully produce the poly(aniline-silica reservoir) (PASR) coatings on a steel electrode. The number of cycles had a major influence on the development and thickness of the PASR coating. The presence of a reservoir during the repeating cyclic voltammetry scans limits the polymer oxidation process. The composite coatings adhered well to the steel electrode and had excellent electroactive properties. The corrosion performance of PASR-coated steel was evaluated using electrochemical impedance spectroscopy and Tafel studies in 1% NaCl solutions. The enhanced corrosion prevention and self-healing function of this newly developed PASR coating was confirmed by a simulated corrosion process using the scanning vibrating electrode technique (SVET). The results imply that a dopant release caused by the corrosion process results in an anticorrosion/inhibition effect.

Emerging action of corrosion prevention based on sustained self-healing coatings

The present study reports the mechanism of a silica-based novel self-healing/defect inhibiting coating for the efficient renewal of defects and corrosion on metal substrates, effective from sub-micron to mm dimensions. The coating predominantly employs silica nanoparticles that act as tiny containers evidencing a homogeneous mesoporous surface morphology. The containers were preloaded with the dopant of oxalic acid. After loading the container, aniline monomers were introduced to be preferentially adsorbed on the surface of the silica containers. The aniline on being doped by oxalic acid with electrons joins to form long chains of polyaniline (PANI), covering the entire surface of the silica containers, forming a protective sheet thereby forming sphere-like PANI-SiO2 reservoirs (PSR). The oxalic acid-PANI acts as a charge transfer complex where acid acts as a donor due to the oxalate and an inhibitor at the onset of corrosion, serving the original purpose. Also, Polyaniline (PANI) detects simultaneously and frequently to release the doping ion, and these ions passivate the metal, plus PANI back to the original position getting doping ions from the silica reservoir. The superior corrosion protection of this developed active system compared to traditional epoxy coating was confirmed by electrochemical impedance spectroscopy (EIS) and an imitated corrosion process by the scanning vibrating electrode technique (SVET) in 3% NaCl solution. The observations affirm that the sustained release behavior of the acid dopant is triggered by surface corrosion, revealing self-healing phenomena.

Hydrothermal Origin of Early Permian Chert Nodules in the Central North China Craton Linked to Northern Margin Cratonic Activation

AbstractSedimentary chert phases from the Archean to the present are widely used to trace sedimentary environments and tectonic settings. Recently, chert nodules occurring within carbonates have been the subject of possible hydrothermal or biogenic origin, in lieu of a diagenetic origin. However, chert nodules from a vast cratonic basin represent extremely rich silica accumulations but less noted is how they respond to submarine hydrothermal activity (and/or surface siliceous organism productivity). The links between the cratonic‐type chert depositions and environmental changes regarding cratonic evolution need to be revisited at a large temporal‐spatial scale. The chert nodules are widespread throughout the Lower Permian Taiyuan Formation in the North China Craton (NCC). Several Taiyuan chert‐rich successions across the NCC have been selected to study possible links between chert deposition and cratonic evolution in scenario of partial cratonic activation of the northern NCC margin during the Late Paleozoic. Based on stratigraphic correlation, the chert nodules are ubiquitously, evenly distributed throughout the Taiyuan Formation at a large craton‐basin scale from the northern to southern interior NCC. Petrological results, elemental abundances, together with silicon and oxygen isotopic compositions of chert samples infer significant hydrothermal contributions for the silica accumulations. Therefore, the cratonic‐scale chert depositions of hydrothermal origin infer a giant and remote silica reservoir, linking to the large igneous province and magmatism in the NCC northern margins. The Taiyuan chert nodules could be unique marine sedimentary archives recording the Late Paleozoic NCC partial activation, which also generated continental records of igneous rocks, bauxites and tuffs. The strong tectonics of the northern margin, south‐dipping topography and northward transgression of the Early Permian NCC facilitated the chert deposition on the shallow marine platform in the cratonic interior.

Early silica crust formation in planetesimals by metastable silica-rich liquid immiscibility or cristobalite crystallisation: the possible origin of silica-rich chondrules

The formation and differentiation processes of planetesimals—small bodies in the solar system—remain actively debated. Planetesimal differentiation is known to have occurred early (<1.5 Myr after the formation of Ca-Al-rich inclusions), as attested by the ages of iron meteorites. Metal-silicate segregation implies global-scale melting, induced by heat released from short-lived radiogenic isotopes, and the consequent generation of a silicate magma ocean. Thermodynamic calculations show that silicate magma crystallisation would have induced silicate-silicate differentiation, leading to the formation of a thick olivine-dominated “mantle” and a thin basaltic “crust”. However, thermodynamic modelling of magma ocean crystallisation does not produce any silica phases. Here I experimentally show that crystallisation of a chondritic liquid does not follow the thermodynamically predicted path. Silica phases are generated early (before 55% differentiation) as a function of initial magma ocean temperature. As cristobalite or liquid silica phases are less dense than residual liquids or olivine, silica phases could have formed proto-crusts that would have acted as buoyant lids at the surfaces of planetesimals, allowing the eventual accretion and preservation of debris (chondrites). Moreover, the destruction of such a crust by impacts could provide an explanation for the origin of the silica reservoir that condensed around some chondrules.

Paragenesis of silicified mid-Paleozoic and mid-Cenozoic corals based on petrography and silicon isotopic analyses

Petrographic analyses of silicified coral fossils from the Upper Ordovician Cutter Formation and Silurian Fusselman Formation of New Mexico, and the Paleogene-Lower Neogene Tampa Member and Suwannee Limestone of Florida show that septal voids of these coral fossils are filled with megaquartz and septal walls are replaced by chalcedonic microspherulites and microquartz. The boundaries of the microquartz and spherulites of the septal walls conform to accommodation space left by the megaquartz that filled the septal voids. These textures suggest that megaquartz filled the septal voids prior to silicification of the septal walls. The measured δ30Si compositions of silica defining the septal walls and silica that fills the septal voids range from −5.23‰ to +1.03‰. The void-filling silica has isotopically light Si and the septal wall replacement Si is isotopically heavier. The silicon isotopic data are consistent with distillation of a finite silica reservoir which favors incorporation of lighter silicon isotopes in earlier-formed silica by Rayleigh fractionation. Distillation of light isotopes during progressive silica precipitation is also documented in vug-filling silica. Thus, silica replacement textures and silica isotopic compositions of samples from different geologic ages and locations, regardless of crystal sizes or degree of cementation of the primary porosity in the corals, support early void-filling silica precipitation followed by septal wall silica precipitation in essentially closed system environments.

Origin of spherulitic and cone-in-cone concretions in Cambro-Ordovician black shales, St Lawrence Estuary, Quebec, Canada

AbstractSpherulitic concretions are very rare among carbonate concretions that generally consist of micritic carbonate. The occurrence of spherulitic concretions in Cambro-Ordovician black shales of unknown stratigraphic age on a mid-channel island in the St Lawrence Estuary in Quebec is a new example in addition to only three hitherto reported occurrences of spherulitic carbonate concretions. Their origin is still poorly understood. These concretions occur in close association with, and show various transitions to, cone-in-cone structure. The spherules, measuring 0.5 to 12 mm in diameter, consist of intergrown fine fibres of ferroan calcite and quartzine, pointing to the formation of the concretions below the sulfate-reduction zone. A phenomenological theory of spherulitic crystallization relates the thickness δ of an impurity-rich layer in front of impurity-rejecting growing crystals to the impurity-diffusion coefficient D and the growth velocity G of the crystal by δ = D/G. In spherulite-forming environments, extremely small values of δ (in the order of &lt;10−4 cm) in conjunction with cellulation lead to spherulitic fibre growth. The theory of spherulitic crystallization is here applied to sedimentary deposits for the first time. The intimate association of calcite and quartzine in the concretions requires a chemical change from alkaline to acidic conditions, which occurs below the carbonate-reduction zone owing to the dissolution of sponge spicules or radiolarians. The transition from spherulite to the silica-free cone-in-cone structure occurs when the silica reservoir that acted as an impurity is exhausted in the crystallization process.

Biogenic silica accumulation varies across tussock tundra plant functional type

Abstract Silica (SiO2) accumulation by terrestrial vegetation is an important component of the biological silica cycle because it improves overall plant fitness and influences export rates of silica from terrestrial to marine systems. However, most research on silica in plants has focused on agricultural and forested ecosystems, and knowledge of terrestrial silica cycling in the Arctic, as well as the potential impacts of climate change on the silica cycle is severely lacking. We quantified biogenic silica (BSi) accumulation in above and below‐ground portions of three moist acidic tundra (MAT) sites spanning a 300 km latitudinal gradient in central and northern Alaska, USA. We also examined plant silica accumulation across three main tundra types found in the Arctic (MAT, moist non‐acidic tundra and wet sedge tundra (WST)). Biogenic silica concentrations in live Eriophorum vaginatum, a tussock‐forming sedge that is the foundation species of tussock tundra, were not significantly (p &lt; .05) different across the three main sites. Concentrations of BSi in live above‐ground tissue were highest in the graminoid species (0.55 ± 0.07% BSi in sedges from WST, and 0.27 ± 0.01% in E. vaginatum across the three MAT sites). Both inter‐tussock tundra species and shrubs contained substantially lower BSi concentrations than E. vaginatum. Our results have implications for how shifts in vegetation cover associated with climatic warming may alter silica storage in tussock tundra vegetation. Our calculations suggest that shrub expansion via warming will increase BSi storage in Arctic land plants due to the higher biomass associated with shrub tundra, whereas conversion of tussock tundra to WST via permafrost thaw would produce the opposite effect in the terrestrial plant BSi pool. Such changes in the size of the terrestrial vegetation silica reservoir could have direct consequences for the rates and timing of silica delivery to receiving waters in the Arctic. A plain language summary is available for this article.

Controlling the bio-inspired synthesis of silica

The influence of different parameters on the silicification procedure using lysozyme is reported. When polyethoxysiloxane (PEOS), an internally crosslinked silica reservoir, is used, regular structures with a narrow size distribution could be obtained only via introducing the silica precursor in two steps including initial dropping and subsequent addition of residual oil phase in one portion. We found that mixing sequence of mineralizing agents in the presence of a positively charged surfactant plays a key role in terms of silica precipitation when tetraethoxyorthosilicate (TEOS) is the oil phase. In contrast, well-mineralized crumpled features with high specific surface area could be synthesized in the presence of PEOS as a silica precursor polymer, regardless of mixing sequence. Moreover, introducing sodium dodecyl sulfate (SDS) as a negatively charged surfactant resulted in regular silica sphere formation only in combination with hexylene glycol (MPD) as a specific co-solvent. Finally, it is demonstrated that by inclusion of different nanoparticles even more sophisticated hybrid materials can be generated.

Investigation into the Controlled-Release Kinetic Models of Rose Perfume in SBA-15 and KIT-6

A new system for the controlled release of rose perfume is presented. Mesoporous SBA-15 and KIT-6 materials as controlled-release agent are synthesized via hydrothermal method. Rose perfume was introduced into the pores of SBA-15 and KIT-6 via the incipient wetness impregnation method. This silica reservoir maintained a slow release of rose perfume over more than 10h. Rose perfume release was controlled by configurational diffusion in the SBA-15 and KIT-6 pores having free diameters of less than 12 nm. The release of rose perfume was tuned by adapting pore diameter and temperature. By fitting the release data, the results show that the release actions of rose perfume in SBA-15 and KIT-6 are consistent with Korsmeyer-Peppas model and First-order’model respectively.

Controlled release of chlorhexidine from amorphous microporous silica

A new system for the controlled release of the antiseptic chlorhexidine is presented. Amorphous microporous silica (AMS) excipient material was synthesized via an acid catalyzed sol–gel method and shaped as powder or coating. Chlorhexidine diacetate was introduced into the pores of the AMS silica via the incipient wetness impregnation method. This silica reservoir maintained a slow release of chlorhexidine over more than 7 days. Chlorhexidine release was controlled by configurational diffusion in the AMS pores having free diameters of less than 1 nm. The release of chlorhexidine was fine tuned by adapting particle size and pore diameter. Controlled release of chlorhexidine from an AMS coating on silicon wafer was demonstrated.

Mesostructured silica based delivery system for a drug with a peptide as a cell-penetrating vector

A drug delivery system using mesostructured silica as a reservoir has been developed for the storage and controlled release of a drug with a cell-penetrating peptide (CPP) as a vector. We use fluorescein isothiocyanate (FITC) as the drug model and octaarginine (R8) as a vector to endow the drug with cell-penetrating property. The mesostructured silica reservoir system was prepared by using a one-pot liquid–crystal templating method, which is suitable for the encapsulation of intact FITC-R8 conjugates and sustained release of drugs without hampering their properties. The hydrophobic poly(propyl oxide) (PPO) shell of the pore-filling Pluronic F127 and the electrostatic interaction between R8 and siloxide ions on the pore walls act as the diffusion-limiting factors of the FITC-R8 conjugate. A sigmoidal in vitro release of FITC-R8 from mesostructured silica into phosphate buffered saline (PBS, pH 7.4) was observed and the typical release duration was 5 days at 37 °C. Release from the reservoir yielded significant elongation in duration of the FITC signals in DU145 cells by confocal microscopic analysis, compared with a single administration of FITC-R8.

Widespread formation of cherts during the early Eocene climate optimum

Radiolarian cherts in the Tethyan realm of Jurassic age were recently interpreted as resulting from high biosiliceous productivity along upwelling zones in subequatorial paleolatitudes the locations of which were confirmed by revised paleomagnetic estimates. However, the widespread occurrence of cherts in the Eocene suggests that cherts may not always be reliable proxies of latitude and upwelling zones. In a new survey of the global spatio-temporal distribution of Cenozoic cherts in Deep Sea Drilling Project (DSDP) and Ocean Drilling Program (ODP) sediment cores, we found that cherts occur most frequently in the Paleocene and early Eocene, with a peak in occurrences at ∼ 50 Ma that is coincident with the time of highest bottom water temperatures of the early Eocene climatic optimum (EECO) when the global ocean was presumably characterized by reduced upwelling efficiency and biosiliceous productivity. Cherts occur less commonly during the subsequent Eocene global cooling trend. Primary paleoclimatic factors rather than secondary diagenetic processes seem therefore to control chert formation. This timing of peak Eocene chert occurrence, which is supported by detailed stratigraphic correlations, contradicts currently accepted models that involve an initial loading of large amounts of dissolved silica from enhanced weathering and/or volcanism in a supposedly sluggish ocean of the EECO, followed during the subsequent middle Eocene global cooling by more vigorous oceanic circulation and consequent upwelling that made this silica reservoir available for enhanced biosilicification, with the formation of chert as a result of biosilica transformation during diagenesis. Instead, we suggest that basin–basin fractionation by deep-sea circulation could have raised the concentration of EECO dissolved silica especially in the North Atlantic, where an alternative mode of silica burial involving widespread direct precipitation and/or absorption of silica by clay minerals could have been operative in order to maintain balance between silica input and output during the upwelling-deficient conditions of the EECO. Cherts may therefore not always be proxies of biosiliceous productivity associated with latitudinally focused upwelling zones.

An implantable sol–gel derived titania–silica carrier system for the controlled release of anticonvulsants

A sol–gel derived titania–silica reservoir has been synthesized and characterized. These materials can be used as an implantable carrier for controlled anticonvulsant delivery (sodium phenytoine and valproic acid). Xerogel characteristics, biocompatibility and in vitro release properties were obtained. FT-IR and UV–Vis spectroscopy were used to obtain information regarding the interaction between anticonvulsants and the mesoporous titania–silica ceramic. For the in vitro biocompatibility study, titania–silica reservoirs were surgically implanted into the basolateral amygdale of a rat. Following an implantation for a period of 8 months, the structure of the brain parenchyma and reservoir interface appears to be preserved. There was no evidence of inflammation or gross tissue reaction. Phenytoine was slowly released in vitro from the binary TiO 2–SiO 2 xerogel over a period of 500 h. We envision that this sol–gel derived titania–silica system might play a significant role in the development of a new generation of controlled release biomaterials.

Stratigraphy and sedimentology of a chert reservoir at the Precambrian-Cambrian Boundary: the Al Shomou Silicilyte, South Oman Salt Basin

ABSTRACT The Al Shomou Silicilyte is a unique source and reservoir rock found in the South Oman Salt Basin, where up to 400 m thick and several kilometers wide slabs of silicilyte are entrapped in salt domes at depths of 4 to 5 km. Discovered in the early 1990s, the play is characterized by light and sour oil, high overpressures (19.8 kPa/m), and a high-porosity, low-permeability microcrystalline silica matrix rich in organic matter, deposited around the Precambrian-Cambrian boundary. The palaeogeographic setting during the Al Shomou Silicilyte deposition was a restricted, marine intra-cratonic basin, surrounded by carbonate platforms. The basin was most likely segmented into structural highs and lows, with potential relief of more than 200 m. The deposits of the Al Shomou Silicilyte are stratigraphically ‘sandwiched’ by two regionally extensive shale units, the underlying ‘U’-Shale Formation and the overlying Thuleilat Shale Member. The basinal Al Shomou Silicilyte and the time-equivalent platform carbonates were deposited during a TST to HST in sea-level characterised by reduced siliciclastic input. Silicilyte formation was replaced by the regionally extensive lower Thuleilat Shale and Thamoud Carbonate. The Al Shomou Silicilyte is typically organic-rich, finely laminated and consists of 80–90% microcrystalline quartz with a crystal-size of 2–3 microns. Commonly, the silica crystals form sheet-like aggregates with high intercrystalline microporosity (up to 30%). Other authigenic phases in the silicilyte are pyrite, apatite, magnesite and illite/smectite clay minerals. Minor silt- and sand-sized detrital components are mica/illite flakes, K-feldspar, quartz and sedimentary rock fragments. The organic material averages 7% of the bulk rock volume and is finely disseminated and/or concentrated in laminae. No identifiable macro- or microfossils have been found to-date in the silicilyte. The textural and chemical characteristics suggest formation in a reducing, probably anoxic environment below wave base. The 300–400 m thickness and uniform character of the silicilyte indicate relatively stable conditions during deposition. The lack of recognizable biogenic components and only traces of detrital particles, suggest that the silicilyte is mostly composed of chemically formed silica. The microcrystalline silica could well be the result of a rapid inorganic nucleation of silica gel. The large volumes of silica necessary for silicilyte formation require a silica reservoir of reasonable magnitude, i.e. sea water. A model with a stratified water column is proposed, in which the oxic surface waters probably represented the site of organic productivity and carbonate deposition, and the deeper water at the thermocline/chemocline, the site of silica formation and bacterial mat growth. Silica gel formation may well have been linked to the biological cycle, i.e. mediated by sulfate-reducing bacteria (chemoautotrophs). Comparison with other siliceous deposits indicates that there are no known analogues. Models proposed for banded iron formations are probably the closest approximation to the type of processes involved in the formation of the silicilyte. Given its apparent chronostratigraphic position at the Precambrian-Cambrian boundary, it may well represent a global deepwater facies related to key events which are suggestive of extinction and faunal turnover at the Precambrian-Cambrian boundary.

Middle Eocene to early Miocene environmental changes in the sub-Antarctic Southern Ocean: evidence from biogenic and terrigenous depositional patterns at ODP Site 1090

During Leg 177 of the Ocean Drilling Program (ODP), a well-preserved middle Eocene to lower Miocene sediment record was recovered at Site 1090 on the Agulhas Ridge in the Atlantic sector of the Southern Ocean. This new sediment record shows evidence of a hitherto unknown late Eocene opal pulse. Lithological variations, compositional data, mass-accumulation rates of biogenic and lithogenic sediment constituents, grain-size distributions, geochemistry, and clay mineralogy are used to gain insights into mid-Cenozoic environmental changes and to explore the circumstances of the late Eocene opal pulse in terms of reorganizations in ocean circulation. The base of the section is composed of middle Eocene nannofossil oozes mixed with red clays enriched in authigenic clinoptilolite and smectite, deposited at low sedimentation rates (≤2 cm ka −1). It indicates reduced terrigenous sediment input and moderate biological productivity during this preglacial warm climatic stage. The basal strata are overlain by an extended succession (100 m, 4 cm ka −1) of biosiliceous oozes and muds, comprising the upper middle Eocene, the entire late Eocene, and the lowermost early Oligocene. The opal pulse occurred between 37.5 and 33.5 Ma and documents the development of upwelling cells along topographic highs, and the utilization of a marine nutrient- and silica reservoir established during the pre-late Eocene through enhanced submarine hydrothermal activity and the introduction of terrigenous solutions from chemical weathering on adjacent continents. This palaeoceanographic overturn probably was initiated through the onset of increased meridional ocean circulation, caused by the diversion of the Indian equatorial current to the south. The opal pulse was accompanied by increased influxes of terrigenous detritus from southern African sources (illite), mediated by enhanced ocean particle advection in response to modified ocean circulation. The opal pulse ended because of frontal shifts to the south around the Eocene/Oligocene boundary, possibly in response to the opening of the Drake Passage and the incipient establishment of the Antarctic Circumpolar Current. Condensed sediments and a hiatus within the early Oligocene part of the section possibly point to an invigoration of the deep-reaching Antarctic Circumpolar Current. The mid-Oligocene to lower Miocene section on long time scale exhibits less pronounced lithological variations than the older section and points to relatively stable palaeoceanographic conditions after the dramatic changes in the late Eocene to early Oligocene.

An exsolution silica-pump model for the origin of myrmekite

Myrmekite, as defined here, is the microscopic intergrowth between vermicular quartz and modestly anorthitic plagioclase (calcic albite-oligoclase), intimately associated with potassium feldspar in plutonic rocks of granitic composition. Hypotheses previously invoked in explanation of myrmekite include: (1) direct crystallization; (2) replacement; (3) exsolution. The occurrence of myrmekite in paragneisses and its absence in rocks devold of discrete grains of potassium feldspar challenge those hypotheses based on direct crystallization or replacement. However, several lines of evidence indicate that myrmekite may in fact originate in response to kinetic effects associated with the exsolution of calcic alkali feldspar into discrete potassium feldspar and plagioclase phases. Exsolution of potassium feldspar system projected from [AlSi2O8] involves the exchange CaAlK-1Si-1, in which the AlSi-1 tetrahedral couple is resistant to intracrystalline diffusion. By contrast, diffusion of octahedral K proceeds relatively easily where it remains uncoupled to the tetrahedral exchange. We suggest here that where the ternary feldspar system is open to excess silica, the exchange reaction that produces potassium feldspar in the ternary plane is aided by the net-transfer reaction K+Si=Orthoclase, leaving behind indigenous Si that reports as modal quartz in the evolving plagioclase as the CaAl component is concomitantly incorporated in this same phase. Thus silica is “pumped” into the reaction volume from a “silica reservoir”, a process that enhances redistribution of both Si and Al through the exsolving ternary feldspar.

Biogeochemical silica mass balances in Lake Michigan and Lake Superior

Silica budgets for Lake Michigan and Lake Superior differ in several respects. Mass balance calculations for both lakes agree with previous studies in that permanent burial of biogenic silica in sediments may be only about 5% of the biogenic silica produced by diatoms. Because dissolution rates are large, good estimates of permanent burial of diatoms can not be obtained indirectly from the internal cycle of silica (silica uptake by diatoms and subsequent dissolution) but must be obtained from the sediment stratigraphy. The annual net production of biogenic silica in Lake Michigan requires 71% of the winter maximum silica reservoir which must be maintained primarily by internal cycling in this large lake whereas the comparable silica demand in Lake Superior is only 8.3%. The greater silica demand in Lake Michigan is the result of phosphorus enrichment which has increased diatom production. It is hypothesized that steady-state silica dynamics in Lake Michigan were disrupted by increased diatom production between 1955 and 1970 and that a new steady state based on silica-limited diatom production developed after 1970. Mass balance calculations for Lake Michigan show in contrast with previous work that the hypothesized water column silica depletion of 3.0 g · m−3 could have occurred even though 90% or more of the biogenic silica production is recycled.