Shewanella oneidensis and the dissolution of Calcite at neutral pH
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Common Ion Effects In Zeoponic Substrates: Dissolution And Cation Exchange Variations Due to Additions of Calcite, Dolomite and Wollastonite
c1inoptilolite-rich tuff-hydroxyapatite mixture (zeoponic substrate) has the potential to serve as a synthetic soil-additive for plant growth. Essential plant macro-nutrients such as calcium, phosphorous, magnesium, ammonium and potassium are released into solution via dissolution of the hydroxyapatite and cation exchange on zeolite charged sites. Plant growth experiments resulting in low yield for wheat have been attributed to a Ca deficiency caused by a high degree of cation exchange by the zeolite. Batch-equilibration experiments were performed in order to determine if the Ca deficiency can be remedied by the addition of a second Ca-bearing, soluble, mineral such as calcite, dolomite or wollastonite. Variations in the amount of calcite, dolomite or wollastonite resulted in systematic changes in the concentrations of Ca and P. The addition of calcite, dolomite or wollastonite to the zeoponic substrate resulted in an exponential decrease in the phosphorous concentration in solution. The exponential rate of decay was greatest for calcite (5.60 wt. % -I), intermediate for wollastonite (2.85 wt.% -I) and least for dolomite (1.58 wt.% -I). Additions of the three minerals resulted in linear increases in the calcium concentration in solution. The rate of increase was greatest for calcite (3.64), intermediate for wollastonite (2.41) and least for dolomite (0.61). The observed changes in P and Ca concentration are consistent with the solubilities of calcite, dolomite and wollastonite and with changes expected from a common ion effect with Ca. Keywords: zeolite, zeoponics, common-ion effect, clinoptilolite, hydroxyapatite
Beiersdorfer, R. E.↗
Lab-Scale Study of the Calcium Carbonate Dissolution and Deposition by Marine Cyanobacterium Phormidium subcapitatum
Suggestions that calcification in marine organisms changes in response to global variations in seawater chemistry continue to be advanced (Wilkinson, 1979; Degens et al. 1985; Kazmierczak et al. 1986; R. Riding 1992). However, the effect of [Na+] on calcification in marine cyanobacteria has not been discussed in detail although [Na+] fluctuations reflect both temperature and sea-level fluctuations. The goal of these lab-scale studies therefore was to study the effect of environmental pH and [Na+] on CaCO3 deposition and dissolution by marine cyanobacterium Phormidium subcapitatum. Marine cyanobacterium P. subcapitatum has been cultivated in ASN-III medium. [Ca2+] fluctuations were monitored with Ca(2+) probe. Na(+) concentrations were determined by the initial solution chemistry. It was found that the balance between CaCO3 dissolution and precipitation induced by P. subcapitatum grown in neutral ASN III medium is very close to zero. No CaCO3 precipitation induced by cyanobacterial growth occurred. Growth of P. subcapitatum in alkaline ASN III medium, however, was accompanied by significant oscillations in free Ca(2+) concentration within a Na(+) concentration range of 50-400 mM. Calcium carbonate precipitation occurred during the log phase of P. subcapitatum growth while carbonate dissolution was typical for the stationary phase of P. subcapitatum growth. The highest CaCO3 deposition was observed in the range of Na(+) concentrations between 200-400 mM. Alkaline pH also induced the clamping of P. subcapitatum filaments, which appeared to have a strong affinity to envelop particles of chemically deposited CaCO3 followed by enlargement of those particles size. EDS analysis revealed the presence of Mg-rich carbonate (or magnesium calcite) in the solution containing 10-100 mM Na(+); calcite in the solution containing 200 mM Na(+); and aragonite in the solution containing with 400 mM Na(+). Typical present-day seawater contains xxmM Na(+). Early (Archean) seawater was likely less saline. The division of marine cyanobacterium P. subcapitatum is associated with periodic deposition and dissolution of CaCO3, the rhythms and intensity of which are dependent on concentrations of both OH(-) and Na(+). Thus, the role of present-day marine cyanobacteria in the global carbonate cycle might be reduced to aggregation and recrystallization of available CaCO3 particles in marine water rather than long-term precipitation and accumulation of CaCO3 deposits. For lower Na(+) concentrations, precipitation of carbonates by cyanobacteria would be even less significant. These results suggest that the lack of calcified cyanobacteria in stromatalite-bearing Precambrian sequences can be explained not only by high dissolved inorganic carbon concentrations but also by lower salinity, as well as possible lower pH compared to present-day oceans.
Karakis, S. G.↗
Calcium Solubility In Zeolite Synthetic-Apatite Mixtures
Life support systems at a lunar or martian outpost will require the ability to produce food growing in 1) treated lunar or martian regolith; 2) a synthetic soil, or 3) some combination of both. Zeoponic soil, composed of NH4 (-) and K-exchanged clinoptilolite (Cp) and synthetic apatite (Ap), can provide slow-release fertilization via dissolution and ion-exchange. Equilibrium studies indicate that KNH4, P, and Mg are available to plants at sufficient levels, however, Ca is deficient. Ca availability can be increased by adding a second Ca-bearing mineral: calcite (Cal); dolomite (Dol); or wollastonite (Wol). Additions of Cal, Dol, and Wol systematically change the concentrations of Ca and P in solution. Cal has the greatest effect, Dol the least, and Wol is intermediate.
Beiersdorfer, R.↗
Calcium Solubility and Cation Exchange Properties in Zeoponic Soil
An important aspect of a regenerative life support system at a Lunar or Martian outpost is the ability to produce food. Essential plant nutrients, as well as a solid support substrate, can be provided by: (1) treated Lunar or Martian regolith; (2) a synthetic soil or (3) some combination of both. A synthetic soil composed of ammonium- and potassium-saturated chinoptlolite (a zeolite mineral) and apatite, can provide slow-release fertilization of plants via dissolution and ion-exchange reactions. Previous equilibrium studies (Beiersdorfer, 1997) on mixtures of synthetic hydroxyapatite and saturated-clinoptilolite indicate that the concentrations of macro-nutrients such as ammonium, phosphorous, potassium, magnesium, and calcium are a function of the ratio of chinoptilolite to apatite in the sample and to the ratio of potassium to ammonium on the exchange sites in the clinoptilolite. Potassium, ammonium, phosphorous, and magnesium are available to plants at sufficient levels. However, calcium is deficient, due to the high degree of calcium adsorption by the clinoptilolite. Based on a series of batch-equilibration experiments, this calcium deficiency can be reduced by (1) treating the clinoptilolite with CaNO3 or (2) adding a second Ca-bearing mineral (calcite, dolomite or wollastonite) to the soil. Treating the Cp with CaNO3 results in increased Ca in solution, decreased P in solution and decreased NH4 in solution. Concentrations of K were not effected by the CaNO3 treatment. Additions of Cal, Dol and Wol changed the concentrations of Ca and P in solution in a systematic fashion. Cal has the greatest effect, Dol the least and Wol is intermediate. The changes are consistent with changes expected for a common ion effect with Ca. Higher concentrations of Ca in solution with added Cal, Dol or Wol do not result in changes in K or NH4 concentrations.
Beiersdorfer, Raymond E.↗
Cycling phosphorus on the Archean Earth: Part II. Phosphorus limitation on primary production in Archean ecosystems
Several lines of evidence point to low rates of net primary production (NPP) in Archean oceans. However, whether Archean NPP was limited by electron donors or nutrients, particularly phosphorus (P), and how these factors might have changed over a billion years of recorded Archean history, remains contentious. One major challenge is to understand quantitatively the biogeochemical cycling of P on the early Earth. In Part I of this series (Hao et al., 2020), we estimated the weathering flux of P to the oceans as a function of temporally increasing continental emergence and elevation through Archean time. In Part II, we conduct thermodynamic and kinetic simulations to understand key processes of P cycling within the Archean ocean, including seafloor weathering, recycling of organic P, the solubility and precipitation of secondary phosphate minerals, and the burial diagenesis of P precipitates. Our calculations suggest low solubilities of apatite minerals in Archean seawater, primarily due to nearly neutral pH and high levels of Ca. This low solubility, in turn, implies a negligible contribution of apatite dissolution to P bioavailability in Archean seawater. We also simulate the solubility limits of common secondary P-bearing minerals, showing that vivianite would have been the least soluble P mineral in ferruginous Archean seawater (0.1–0.3 µM), even at moderate supersaturation states (Ω = 100 or 1000). If vivianite precipitation was kinetically favorable by microbial activities and mineral adsorption, the sinking flux of P as vivianite in Archean seawater could have reached the modern sinking flux, implying that vivianite precipitation was a potentially major sink for P in Archean oceans. During burial diagenesis, however, vivianite in porewater would have become less stable than Ca-phosphates of lower solubility. At elevated temperatures (>100 °C) associated with burial diagenesis and low-grade metamorphism, vivianite is predicted to react irreversibly with calcite to form apatite. Optimistic assumptions about the recycling efficiency of P on the Archean Earth lead us to estimate that by the end of the eon the total flux of P (continental weathering + recycling) could have supported NPP at levels up to 7% of the modern. The total flux of P would have been much lower on the early and middle Archean Earth, whereas fluxes of electron donors could have been higher, suggesting very low productivity and P-limitation of marine ecosystems during much of the eon. Comparing our estimates of NPP as limited by P supply with the estimate by Ward et al. (2019), in which NPP was limited by electron donors and metabolic efficiency, there could have been a transition between P-limited productivity in the early to middle Archean to electron donor-limitation closer to the eon’s end (assuming no oxygenic photosynthesis). Once oxygenic photosynthesis reached ecological significance, probably near the end of the Archean, our estimated flux of P would allow rapid oxidation of atmosphere.
Vivianite↗