Inorganic Precipitation Research Articles

Oxygen isotope fractionation in phosphates: the role of dissolved complex anions in isotope exchange†

Oxygen isotope fractionation factors for phosphates were calculated by means of the increment method. The results suggest that Ag3PO4 and BiPO4 are enriched in 18O relative to AgPO4, and the three phosphates are consistently depleted in 18O relative to Ba3[PO4]2; fluorapatite and chlorapatite exhibit a similar behaviour of oxygen isotope fractionation with consistent enrichment of 18O relative to hydroxyapatite. The valence, radii and coordination of metal cations play a quantitative role in dictating the 18O/16O partitioning in these phosphates of different compositions. The calculated fractionation factors for the Ag3PO4–H2O system are in agreement with experimental determinations derived from enzyme-catalysed isotope exchange between dissolved inorganic phosphate and water at the longest reaction durations at low temperatures. This demonstrates that the precipitated Ag3PO4 has completely captured the oxygen isotope fractionation in the dissolved inorganic phosphate. The calculated fractionation factors for the F/Cl-apatite–water systems are in agreement with the enzyme-catalysed experimental fractionations for the dissolved phosphate–water system at the longest reaction durations but larger than fractionations derived from bacteria-facilitated exchange and inorganic precipitation experiments as well as natural observations. For the experimental calibrations of oxygen isotope fractionation involving the precipitation of dissolved phosphate species from aqueous solutions, the fractionation between precipitate and water is primarily dictated by the isotope equilibration between the dissolved complex anions and water prior to the precipitation. Therefore, the present results provide a quantitative means to interpret the temperature dependence of oxygen isotope fractionation in inorganic and biogenic phosphates.

Last Glacial droughts and fire regimes in the central Mexican highlands

ABSTRACTOver the last glacial cycle, climate variations in the Neotropics were related to diverse forcing mechanisms whose understanding has been limited because of the scarcity of continuous long records. Here we use high‐resolution charcoal particle accumulation, inorganic carbon precipitation and magnetic susceptibility data from Lake Chalco, located in high‐altitude tropical central Mexico, to assess the fire regimes and drought periods between ∼85 and 10.8k cal a BP. Overall, drought intervals were characterized by high carbonate deposition and were contemporary with high spring insolation. Most of the high fire activity periods were coupled with droughts, whereas some of them seem to have responded to volcanic activity in the basin. Periods of more fire activity during the latest part of Marine Isotope Stage 3 were associated with a long interval of higher spring insolation. Increase in drought frequency during 47–27k cal a BP were possibly linked to a more active Laurentide Ice Sheet influencing the oceanic and atmospheric controls of the tropical climatic system. In fact, Chalco and Cariaco records show similar millennial‐scale trends, suggesting a role of the Intertropical Convergence Zone in modulating moisture availability in the region.

Profound “turn-off” effects of anionic polymers on the inhibitory activity of cationic polyallylamine in the prevention of silica scale

Colloidal/amorphous silica (SiO2nH2O, n is variable) is considered as the most undesirable inorganic precipitate that forms during various processes in silica-supersaturated industrial waters. In this paper we present how certain polymeric chemical additives can prevent silicic acid polymerization to form colloidal silica, which may lead to deposition onto industrial equipment. More specifically, stabilization of silicic acid is accomplished by using a cationic polymer, polyallylamine hydrochloride (PALAM), in supersaturated silica solutions (starting silica concentration in the form of silicate 500 ppm, or 8.3 mM sodium orthosilicate, Na2SiO3·5H2O, expressed as SiO2) at pH = 7. PALAM is a linear homopolymer that carries one amine side functional group every two carbon atoms, so it becomes protonated at circumneutral pH, rendering the molecule cationic. Its blends with anionic polymers such as carboxymethylinulin (CMI), poly(acrylamide-co-acrylic acid) (PAM-co-AA) and phosphonomethylated chitosan (PCH) are also studied for their silica scale inhibition efficiency.

Colour origin of Tortonian red mudstones within the Mersin area, southern Turkey

Fluvial red mudstones of Tortonian age (overbank deposits) are widespread in the Mersin area in southern Turkey. The XRD analysis reveals that the mudstones consist predominantly of smectite, containing 3.0 to 6.6wt.% Fe2O3, of which ≤1% is present as hematite. However this is evidently sufficient hematite to yield a red colour to the whole rock. SEM images show that very fine hematite crystals are disseminated in the mudstones as pore-filling cement between smectite flakes. After reddening, some of the clay and hematite were most likely leached and accumulated with smectite in the shrink–swell fractures as infill. Reddening in the mudstone took place in a terrestrial environment and the hematite pigment formed from intrastratal water by inorganic precipitation at the initial stage of diagenesis. The free Fe2+ was most likely released from the Fe-bearing minerals in an aqueous reducing environment, with hematite being precipitated as cement during the dry periods.

Effect of food wastewater on biomass production by a green microalga Scenedesmus obliquus for bioenergy generation

Effect of food wastewater (FW) on the biomass, lipid and carbohydrate production by a green microalga Scenedesmus obliquus cultivated in Bold’s Basal Medium (BBM) was investigated. Different dilution ratios (0.5–10%) of BBM either with FW or salt solution (NaCl) or sea water (SW) were evaluated. S. obliquus showed the highest growth (0.41gL−1), lipid productivity (13.3mgL−1dayL−1), carbohydrate productivity (14.7mgL−1dayL−1) and nutrient removal (38.9mgTNL−1 and 12.1mgTPL−1) with 1% FW after 6days of cultivation. The FW promoted algal autoflocculation due to formation of inorganic precipitates at an alkali pH. Fatty acid methyl ester analysis revealed that the palmitic and oleic acid contents were increased up to 8% with FW. Application of FW improved the growth, lipid/carbohydrate productivity and biomass recovery efficiency of S. obliquus, which can be exploited for cost effective production of microalgae biomass.

Identifying vital effects in <i>Halimeda</i> algae with Ca isotopes

Abstract. Geochemical records of biogenic carbonates provide some of the most valuable records of the geological past, but are often difficult to interpret without a mechanistic understanding of growth processes. In this experimental study, Halimeda algae are used as a test organism to untangle some of the specific factors that influence their skeletal composition, in particular their Ca-isotope composition. Algae were stimulated to precipitate both calcite and aragonite by growth in artificial Cretaceous seawater, resulting in experimental samples with somewhat malformed skeletons. The Ca-isotope fractionation of the algal calcite (−0.6‰) appears to be much smaller than that for the algal aragonite (−1.4‰), similar to the behaviour observed in inorganic precipitates. However, the carbonate from Halimeda has higher Ca-isotope ratios than inorganic forms by approximately 0.25‰, likely because of Rayleigh distillation within the algal intercellular space. In identifying specific vital effects and the magnitude of their influence on Ca-isotope ratios, this study suggests that mineralogy has a first-order control on the marine Ca-isotope cycle.

Effect of temperature and calcium ion concentration on permeability reduction due to composite barium and calcium sulfate precipitation in porous media

In the oil industry, water injection is used as a secondary recovery technique for pressure maintenance and efficient oil and gas production. Injected water may be incompatible with water that occurs naturally within the pores of reservoir rock. When these two incompatible waters mix, inorganic scales precipitate within porous media. Many studies have been conducted to investigate the effect of scale formation on the ability of reservoir rock to transmit fluids. Most of these studies have focused on single salt precipitation. This paper is intended to investigate the permeability reduction of porous media due to composite BaSO4–CaSO4 precipitation. Since pure BaSO4 scaling tendency decreases with increasing temperature, while pure CaSO4 scale formation potential increases with increasing temperature, the effect of temperature on the co-precipitation of BaSO4 and CaSO4 was questionable. This paper presents the results of an experimental study which performed by injection of two incompatible solutions into the pack of glass beads at temperatures of 50 and 70 °C to exhibit the effect of temperature on the composite BaSO4–CaSO4 scaling potential. The experimental results and Scanning Electron Microscopy images indicated that even minute amounts of calcium ions combined with barium ions clearly affected the scale nature, morphology, particle size and intensity of scale formation.

Chemical waves in heterogeneous media.

Formation of precipitation patterns and wave propagation in excitable media have attracted considerable scientific interest in the context of nonlinear chemical kinetics because of a new approach to micro and nanofabrication, in addition to some biological aspects. All precipitation patterns share common morphological characteristics, namely the formed patterns are stationary and no dynamical patterns can be observed in these classical precipitation systems (e.g., Liesegang phenomenon). However, it has been recently shown that in several circumstances dynamic patterns (chemical waves) can exist in purely inorganic precipitation systems similar to the well-known and studied (excitable) waves in Belousov-Zhabotinsky reaction. In this study, we show how to fine-tune the pattern characteristics in precipitation systems, such as the wavelength and the pattern morphology by changing the concentrations of the reagents, and we demonstrate chemical waves on a moving 3D spherical precipitation layer. We show that such precipitation waves have anomalous transport property, specifically superdiffusive nature, and it can be controlled by the initial concentration of the inner electrolyte. Moreover, we present several precipitation systems in which chemical wave propagation inside a moving precipitation layer can emerge. This observation points out the generality and robustness of similar behavior in diffusion-precipitation systems.

Experimental evidence for kinetic effects on B/Ca in synthetic calcite: Implications for potential B(OH)4− and B(OH)3 incorporation

The boron to calcium ratio (B/Ca) in biogenic CaCO3 is being increasingly utilized as a proxy for past ocean carbonate chemistry. However, B/Ca of cultured and core-top foraminifers show dependence on multiple physicochemical seawater properties and only a few of those have been inorganically tested for their impacts. Accordingly, our understanding of the controls on foraminiferal B/Ca and thus how to interpret B/Ca in fossil shells is incomplete. To gain a clearer understanding of the B incorporation mechanism, we performed inorganic calcite precipitation experiments using a pH-stat system. As previously reported, we confirm that B/Ca in calcite increases with both fluid pH and total B concentration (denoted as [BT], where [BT]=[B(OH)3]+[B(OH)4−]). We provide the first evidence that B/Ca also increases with the concentration of total dissolved inorganic carbon (DIC) and calcium ion. With the exception of the [BT] experiments, these chemical manipulations were accompanied by an increase in calcite saturation, and accordingly precipitation rate (denoted as R). But when pH and [Ca2+] were jointly varied at a fixed saturation level to maintain relatively constant R at different pH and [Ca2+] combinations, B/Ca was insensitive to both pH and [Ca2+] changes. These experimental results unequivocally suggest kinetic effects related to R on B/Ca. Furthermore, with a suite of chemical manipulations we found that the B/Ca variability is explicable by just R and the [BT]/[DIC] ratio in the parent fluids. This observation was particularly robust for relatively rapidly precipitated samples, whereas for relatively slowly precipitated samples, it was somewhat ambiguous whether the [BT]/[DIC] or [B(OH)4−]/[HCO3−] ratio provides a better fit to the experimental data. Nonetheless, our experimental results can be considered as indirect evidence for incorporation of both B(OH)4− and B(OH)3 into calcite. We propose a simple mathematical expression to describe the mode of B incorporation into synthetic calcite that depends only on the fluid [BT]/[DIC] ratio and the precipitation rate R. This novel finding has important implications for future calibrations and applications of the B/Ca proxy as well as the δ11B paleo-pH proxy.

Preparation, characterization and kinetics of ion exchange studies of Ni2+ selective polyaniline–Zr(IV)molybdophosphate nanocomposite cation exchanger

Polyaniline–Zr(IV)molybdophosphate (PAZMP) was synthesized by sol–gel mixing of polyaniline (PANI) into the inorganic precipitate Zr(IV)molybdophosphate (ZMP). The physico-chemical properties of the material were characterized by using XRD, TGA, FTIR, SEM and TEM. Distribution studies for various metal ions revealed that the composite is highly selective for Ni2+. Its selectivity was examined by achieving some important binary separations of metal cations which indicates its utility in environmental pollution control. Ion-exchange kinetics for few divalent metal ions was evaluated by particle diffusion-controlled ion-exchange phenomenon at different temperatures. Some physical parameters like D0, Ea and ΔS0 have been evaluated under favoring a particle diffusion-controlled mechanism.

Calibration of stable isotope composition of Thoracosphaera heimii (dinoflagellate) calcite for reconstructing paleotemperatures in the intermediate photic zone

AbstractIn this study we investigate the temperature dependence of oxygen isotope ratios preserved in calcite formed by the dinoflagellate Thoracosphaera heimii, focusing primarily on the development of a geological proxy. Geochemical analysis of the calcite shells produced by this species represents a valuable proxy for reconstructing environmental conditions in the intermediate photic zone. Calibration is based on isotopic analysis from culture experiments performed in very dilute batch conditions, as well as from near‐monospecific T. heimii assemblages separated from core top sediments. Results are similar for both approaches and indicate that T. heimii shells have oxygen isotope compositions close to equilibrium values predicted for inorganic calcite precipitation. This calibration of the isotopic composition of dinoflagellate calcite indicates that monospecific assemblages of T. heimii can be used to unravel paleotemperatures in the intermediate photic zone by applying isotopic transfer functions for equilibrium calcite. In culture, however, a δ18O offset of −1‰ is observed at temperatures <17°C, which falls below the natural temperature range of this species. Culture analyses also reveal a relationship between temperature and carbon isotope composition of calcite. The mechanisms behind this relationship remain to be explored, but their identification may provide a better understanding of carbon isotope systematics from both biogeochemical and geological perspectives. Comparison of the oxygen isotope composition of T. heimii shells with that of shallower dwelling organisms, such as the coccolithophores, represents a valuable proxy for determining temperature gradients within the photic zone and may enable reconstruction of the evolution of the depth of the thermocline.

Submerged Membrane Bioreactor for Vegetable Oil Wastewater Treatment

AbstractA bench‐scale submerged membrane bioreactor (SMBR) was employed to treat vegetable oil plant wastewater with complete sludge retention. Treatment performance and membrane fouling of the SMBR were investigated. The system stably removed high amounts of total organic carbon, oil, and ammonia from vegetable oil wastewater and reduced the chemical oxygen demand, demonstrating the great potential of the SMBR in removing pollutants. The membrane fouling layer was not only governed by deposition of organic substances composed of extracellular polymeric substances like proteins, polysaccharides etc., and oil substances but also by inorganic elements. Organic foulants coupled to inorganic precipitation enhanced the formation of a gel layer and triggered severe membrane fouling in the SMBR.

Technologies to Recover Nutrients from Waste Streams: A Critical Review

Technologies to recover nitrogen, phosphorus, and potassium from waste streams have undergone accelerated development in the past decade, predominantly due to a surge in fertilizer prices and stringent discharge limits on these nutrients. This review provides a critical state of art review of appropriate technologies which identifies research gaps, evaluates current and future potential for application of the respective technologies, and outlines paths and barriers for adoption of the nutrient recovery technologies. The different technologies can be broadly divided into the sequential categories of nutrient accumulation, followed by nutrient release, followed by nutrient extraction. Nutrient accumulation can be achieved via plants, microorganisms (algae and prokaryotic), and physicochemical mechanisms including chemical precipitation, membrane separation, sorption, and binding with magnetic particles. Nutrient release can occur by biochemical (anaerobic digestion and bioleaching) and thermochemical treatment. Nutrient extraction can occur via crystallization, gas-permeable membranes, liquid–gas stripping, and electrodialysis. These technologies were analyzed with respect to waste stream type, the product being recovered, and relative maturity. Recovery of nutrients in a concentrated form (e.g., the inorganic precipitate struvite) is seen as desirable because it would allow a wider range of options for eventual reuse with reduced pathogen risk and improved ease of transportation. Overall, there is a need to further develop technologies for nitrogen and potassium recovery and to integrate accumulation–release–extraction technologies to improve nutrient recovery efficiency. There is a need to apply, demonstrate, and prove the more recent and innovative technologies to move these beyond their current infancy. Lastly, there is a need to investigate and develop agriculture application of the recovered nutrient products. These advancements will reduce waterway and air pollution by redirecting nutrients from waste into recovered nutrient products that provides a long-term sustainable supply of nutrients and helps buffer nutrient price rises in the future.

Synthesis and characterization of polyaniline-titanium tungstophosphate; Its analytical applications for sorption of Cs+, Co2+, and Eu3+ from waste solutions

Crystalline phases of polyaniline-titanium tungstophosphate composite material were synthesized via sol-gel procedure by incorporating the organic polymer polyaniline into the matrix of an inorganic precipitate of titanium tungstophosphate. The physicochemical properties of this hybrid material were determined using atomic absorption spectrophotometry, CHN elemental analysis, X-ray diffraction and X-ray fluorescence analysis, IR spectroscopy, thermal analysis, and scanning electron microscopy. According to the data obtained, the chemical formula of polyaniline-titanium tungstophosphate can be presented as [(WO3)(TiO2)4(H3PO4)3 + (-C6H4NH-)]·8H2O. The material shows monofunctional ion-exchange characteristic and exhibits enhanced resistance to HNO3, HCl, and alkaline media. The ion-exchange capacity of polyaniline-titanium tungstophosphate for Cs+, Co2+, and Eu3+ ions was found to be 3.63, 1.55, and 1.30 mg-equiv g−1, respectively, exceeding the ion-exchange capacity of other composite and inorganic ion exchangers. The material was found to be highly selective to Eu3+, with the following selectivity series: Eu3+ > Cs+ > Co2+. The thermodynamic functions (ΔG0, ΔS0, and ΔH0) of the adsorption of Cs+, Co2+, and Eu3+ ions onto polyaniline-titanium tungstophosphate were calculated. They show that the overall adsorption process is spontaneous and endothermic.

Catalytic destruction of chlorobenzene over mesoporous ACeOx (A = Co, Cu, Fe, Mn, or Zr) composites prepared by inorganic metal precursor spontaneous precipitation

Mesostructured ACeOx (A=Co, Cu, Fe, Mn, or Zr) composites with large specific surface area and developed mesoporosity were prepared by inorganic metal precursor spontaneous precipitation (IMSP) method. Influences of catalyst surface area, pore structure, reducibility, and active oxygen concentration on catalytic performance were studied. Both preparation route and metal precursor type affect metal active site dispersion, and the IMSP is a desirable approach for synthesis of metal composites with homogeneous active phase distribution. The original crystalline structure of CeO2 is well maintained although parts of transition metal cations are incorporated into its framework. The forming of An+–O2−–Ce4+ connections in ACeOx catalysts could reduce the redox potential of metal species, allowing effective redox cycles during oxidation reactions. CuCeOx demonstrates powerful catalytic efficiency with 99% of chlorobenzene (CB) destructed at 328°C, which is much lower than the other ACeOx oxides and Cu-doped catalysts synthesized via the incipient impregnation and coprecipitation methods (T99>405°C). The active site reducibility is the foremost activity determining factor for CB destruction.

Removal of Pb(II) from aqueous solution using ethylene diamine tetra acetic acid-Zr(IV) iodate composite cation exchanger: Kinetics, isotherms and thermodynamic studies

EDTA-Zr(IV) iodate was prepared via the incorporation of aqueous solution of EDTA into the inorganic precipitate of Zr(IV) iodate. Distribution coefficient values for different metals showed that EDTA-Zr(IV) iodate had the highest adsorption capacity for Pb(II). The practical applicability of EDTA-Zr(IV) iodate was explored by separating Pb(II) metal from a synthetic mixture of metal ions. Dependence of adsorption on contact time, pH of the solution, exchanger dose and temperature was studied to achieve the optimum conditions. Kinetic studies showed better applicability for pseudo-second-order model. Thermodynamic parameters viz. – entropy change, enthalpy change and Gibb's free energy change were also calculated.

Stable strontium isotope fractionation in synthetic barite

The mineral barite (BaSO4) accommodates strontium (Sr) in its crystal structure, providing an archive of Sr-isotopes (87Sr/86Sr and δ88/86Sr) in the highly stable sulfate mineral. We investigated mass dependent stable Sr-isotope fractionation (Δ88/86Sr=δ88/86Srsolid−δ88/86Srsolution) during inorganic precipitation of barite from a barium-rich solution by addition of sulfate under controlled conditions and compared this to equilibrium isotopic fractionation calculated using Density Functional Theory modeling. Sr-substituted barite is predicted to have lower 88Sr/86Sr than any other studied species, and at 25°C will be about 0.6–0.7‰ lower than the two modeled Sr(H2O)82+-bearing salts that could approximate aqueous Sr2+. This agrees in direction and order of magnitude with experimental results that estimate equilibrium Sr-isotope fractionation in barite to be 0.3‰ lower than aqueous Sr2+ at ∼20°C. The high ionic strength of some of the precipitating solutions (up to 1M) and potential differences in the average coordination number of aqueous Sr2+ add to uncertainty in a direct comparison of the calculated equilibrium isotopic fractionation values with the experimental results.Stable Sr-isotope fractionation varied along with the distribution coefficient of Sr [Kd(Sr)=[Sr/Ba]barite/[Sr/Ba]solution], which is a function of both temperature and barite saturation state. However the relationship between mass dependent isotopic fractionation and Kd(Sr) is different for conditions of changing temperature versus barite saturation state. With increasing temperature (from 5 to 40°C), the barite phase became isotopically lighter (Δ88/86Sr=−0.29‰ to −0.41‰). Conversely, with increasing saturation state (saturation index of barite=3.0–4.3) the barite phase became isotopically heavier (Δ88/86Sr=−0.25‰ to −0.10‰). These observations suggest chemical kinetic effects control isotopic fractionation rather than equilibrium temperature effects. The relationship with saturation state indicates the potential presence of a diffusive boundary layer. Barite crystal morphology appears to be affected by the diffusion rate of solute (sulfate) to the growing crystal surface relative to the overall growth rate of barite crystals during precipitation.

Allophanic and ferric root-associated stalactites: biomineralization induced by microbial activity (Galeria da Queimada lava tube, Terceira, Azores)

AbstractRoot-associated stalactites (rootsicles) in Galeria da Queimada lava tube have a mineralogical composition and developmental association with microbes that render them unique. Samples were examined by X-ray diffraction, micro-Raman spectrometry and scanning electron microscopy/X-ray energy-dispersive spectroscopy. Three types of rootsicle were defined: incipient; hard (white and red); and black spongy. The incipient rootsicles still contained rotten organic material and showed the beginning of mineralization by allophane. The white hard and black spongy types were also composed of allophane, while the red hard type was composed of hydrous ferric oxi-hydroxide minerals (HFO). The allophane and HFO in the andisol covering the cave roof precipitated out of the dripwater running along the roots to form the studied rootsicles. All three types of rootsicle showed black layers, coatings, spots or patches composed of manganese oxide minerals and, occasionally, hisingerite (iron (III) phyllosilicate). An alternation of organic precipitation caused by filamentous bacteria and inorganic precipitation (the latter facilitated by pH changes in the dripwater and the cave's temperature) built up both the porous and compact rings observed in the white and red hard rootsicles. The largely straight filaments seen in the porous rings of the white hard rootsicles may be indicative of the previous presence ofLeptothrixspp., while the helical morphologies seen in the red hard rootsicles may be indicative of that ofGallionellaspp. The manganese oxide minerals detected probably formed via microbial activity. This study reflects the important role of filamentous bacteria in rootsicle formation, independent of their mineralogy.

Electrochemistry of Inorganic Precipitates Formed in Self-Organizing Chemical Systems

The interfacing of two solutions, each containing a reactive ion (e.g. Fe+2 / HS-), produces a self-assembling mineral film or membrane at the solution interface. When one solution is injected into the other, the membrane forms as a self-organizing “chemical garden” structure that grows vertically upward according to buoyancy and internal fluid pressure. When the solutions are instead interfaced across a porous template, such as parchment paper or dialysis tubing, the precipitate forms as a mineral film on the template. In either case, the formation of self-assembling precipitates in steep chemical/pH gradients at solution interfaces produces inorganic membranes that exhibit organized structure at both macro and micro scales. Chemical garden membranes can grow as bulbs, tubes, or gelatinous ‘chimney’-like structures, and the membranes themselves are permeable to some ions, and exhibit morphological gradients from interior to exterior (e.g. a crystalline side and a smoother side). Inorganic membranes often exhibit compositional gradients from interior to exterior as well, reflecting the chemical gradients in which they precipitated. These are dynamic chemical systems and in recent work we have studied the ability of mineral membranes to generate and maintain electrical potentials (Barge et al. 2012). Inorganic membranes of iron sulfides produced on dialysis tubing templates between contrasting solutions were also found to be partially bipolar and capable of preferential ion exchange, as well as electrically conductive (Barge et al. 2014). In some ways, the self-assembling inorganic precipitates formed in solution interface experiments are similar to the ion-exchange membranes and gas diffusion layers in commercial as well as experimental fuel cells. This has led to some preliminary work in using commercially available electrode / GDL material as a template to precipitate chemical membranes that can then be used in fuel cell experiments (Barge et al. 2014) to determine if these are capable of acting as redox catalysts. Interfacial precipitates can be grown in many different reactant systems and depending on the chemistry can be useful for various materials / electrochemical applications. Natural analogs to these self-assembling membranes include the growth of chimneys at hydrothermal vents, which are formed as minerals precipitate in the chemical / pH gradient where subsurface hydrothermal fluid feeds into the chemically contrasting seawater. Hydrothermal chimneys are natural chemical gardens, and it has even been proposed that life on Earth emerged in such a system, so we can also use electrochemical studies of out-of-equilibrium chemical precipitates to understand the mechanisms that might operate in geological settings.L. M. Barge, T. P. Kee, I. J. Doloboff, J. M. P. Hampton, M. Ismail, M. Pourkashanian, J. Zeytounian, M. M. Baum, J. Moss, C.-K. Lin, R. D. Kidd, I. Kanik (2014) The Fuel Cell Model of Abiogenesis: A New Approach to Origin-of-Life Simulations. Astrobiology, 14(3):254-70.L.M. Barge, I. J. Doloboff, L. M. White, G. D. Stucky, M. J. Russell, I. Kanik. (2012) Characterization of Iron-Phosphate-Silicate Chemical Garden Structures. Langmuir, 28 (8), pp 3714-3721.

From hydrodynamic plumes to chemical gardens: the concentration-dependent onset of tube formation.

Many inorganic precipitation reactions self-organize macroscopic tubes known as chemical gardens. We study the nonequilibrium formation of these structures by injecting aqueous sodium sulfide solution into a reservoir of iron(II) chloride solution. Our experiments reveal a distinct, concentration-dependent transition from convective plumes of reaction-induced, colloidal particles to mechanically connected, hollow tubes. The transition concentration (0.1 mol/L) is widely independent of the injection rate and causes a discontinuous change from the radius of the plume stalk to the radius of the tube. In addition, tubes have lower growth speeds than plumes. At the transition concentration, one observes the initial formation of a plume followed by the growth of a mechanically weak tube around a jet of upward-moving precipitation particles. We find that the plumes' morphology and geometric scaling are similar to that of laminar starting plumes in nonreactive systems. The characterization of dried tubes by X-ray diffraction indicates the presence of greigite and lepidocrocite.