Mg Concentration In Solution Research Articles

Effect of magnesium on monohydrocalcite formation and unit-cell parameters

Abstract Monohydrocalcite (MHC) is hydrated calcium carbonate, which plays an active role in many geological processes, carbonate biomineralization, and can be used for fundamental science (as a paleoenvironmental indicator) and industry (for removal of hazardous anions). Despite a great number of works, the conditions preferable for MHC formation/stabilization and MHC crystal chemical patterns in relation to Mg and H2O are not clarified yet. In the course of current work, we conducted 38 syntheses to obtain information on MHC formation at different Mg/Ca ratios (0–12), pH (~9–12), and temperature (23 and 3 °C). Newly formed carbonate precipitates were studied by means of X-ray powder diffraction, optical, and scanning electron microscopy, energy-dispersive X-ray spectroscopy, Raman, and Fourier-transform infrared (FTIR) spectroscopies. The phase diagram for MHC, calcite, aragonite, and dypingite as a function of pH and Mg concentration in solution at T = 23 °C and Ca/CO3 = 0.5 was obtained. We demonstrated that MHC could be stable in dry conditions for up to two years and that the time of crystallization is important for the transformation of amorphous calcium carbonate to MHC. Our results on synthetic MHC stability show that the widespread idea that MHC is a short-lived intermediate phase is wrong. For the first time, on the basis of a regular changes in the unit-cell parameters the possibility of significant incorporation of magnesium in MHC has been demonstrated. According to FTIR data, it is shown to be accompanied by an increase in the water content, which leads to multidirectional change in a and c MHC parameters.

Evolution of calcite growth morphology in the presence of magnesium: Implications for the dolomite problem

The effect of magnesium on calcite growth morphology was known to occur as step rounding in some cases and surface segmentation in others. What remains unknown are the conditions for and the relations between the different effects, suggesting a lack of comprehensive understanding of the fundamental cause. Here we investigated the evolution of spiral hillock morphology on calcite cleavage surfaces in solutions with increasing Ca to Mg ratios and supersaturation levels using in situ atomic force microscopy. We isolated the effects of Mg and saturation by conducting experiments under conditions of constant pH, ionic strength, and Ca2+/CO32−. Our results revealed three types of morphological variations, ranging from step rounding in one direction (type I), to all directions (type II), and finally to a mosaic-like surface segmentation associated with monolayer buckling and step bunching (type III). These results suggest that the effect of magnesium on calcite growth depends upon multiple parameters including the concentration of Mg in solution, the step speed, as well as the extensiveness of Mg for Ca substitution in calcite lattice. We propose that the morphological variation may be understood by a model taken into consideration of (1) the lifespan and flux size of Mg ions at kinks in comparison to step kinetics, and (2) the diffusion and alignment of point defects created by the substitution of Mg for Ca in the crystal lattice. Stress calculations show that the maximum amount of Mg which calcite lattice can sustain before plastic deformation is ∼40%, suggesting that lattice stress due to the mismatch between MgCO3 and CaCO3 is likely the ultimate cause for the difficulty of ambient condition dolomite crystallization.

镁缺乏对“不知火”和“椪柑”生理指标、镁分布及叶片超微结构的影响

By using sand culture, the changes of physiological and anatomical features and the characteristics of magnesium (Mg) distribution of Citrus cultivars ”shiranuhi” [Citrus reticulata × (C.reticulata × C.sinenesis)] and ”ponkan” (C.reticulata) seedlings were studied in the Mg-deficient conditions. The results showed: 1) The deficiency of Mg decreased significantly the plant biomass, root viability, leaf chlorophyll contents and superoxidase dismutase (SOD) activities of both cultivars, especially for ”shiranuhi”. Mg deficiency increased significantly peroxidase (POD) activities, malondialdehyde (MDA) contents and relative conductivity of both plant leaves. Furthermore, MDA contents and relative conductivity in ”shiranuhi” were significantly higher than those in ”ponkan”. In addition, leaf catalase (CAT) activity of ”shiranuhi” in Mg-deficient condition increased significantly, but it wasn’t observed on ”ponkan”.2) Mg contents of both cultivars' leaves increased with increasing Mg concentration in solution, and they decreased obviously with the leaf aged. Furthermore, Mg contents of ”shiranuhi” were significantly higher than that of ”ponkan” under Mg-deficient condition.3) Ultrastructural observation of leaf structure and chloroplast showed that the organelle of ”shiranuhi” was damaged seriously under Mg-deficient condition, which was revealed by the vague thylakoid lamella with less number, drastic increase of starch grain volume, and the blurred membranes of chloroplast and mitochondria. As to ”ponkan”, distortion, plasmolysis and less grana lamella of chloroplast were observed, but the starch grain and plastoglobuli numbers were increased. Thus, it is suggested that the influences of Mg deficiency on physiological and anatomical features were more obvious in ”shiranuhi” than in ”ponkan”.

Adaptation of the Ion Exchange Method for the Determination of the Free Ionic Fraction of Cadmium in Solution

The understanding of the availability of a metal in soil necessitates a minimum knowledge about its speciation in the soil solution. Here, we evaluated an alternative to the use of ion exchangers for estimating the free ionic fraction of cadmium (FCd) in solution. It is based on the exchange selectivity coefficient (VK) rather than the distribution coefficient (DK) to estimate FCd. Because VK for the Cd-Ca exchange for the used Amberlite resin was independent of the solution Ca concentration (0.5-7.5 mM) and pH (range: 4.5-6), the experiment on a solution mimicking the analyzed solution to estimate VK was not necessary. The influence of variable Ca and Mg concentrations in solution on FCd was assessed in synthetic solutions containing either citrate or malate. The best way to estimate FCd seemed to treat the exchange data as if Ca was solely present. However, neither the proposed approach nor those applying DK prevent the overestimation of FCd when Ca is partly complexed in the analyzed solution. A method intending to estimate two replicates of FCd for a given, unique solution was also studied on solutions issued from sorption-desorption experiments performed on a humic podzol. It consists of two successive supplies of a known resin mass to a unique sample. Both estimates were close and not significantly different.

Magnesium ameliorates aluminum rhizotoxicity in soybean by increasing citric acid production and exudation by roots.

Superior effectiveness of Mg over Ca in alleviating Al rhizotoxicity cannot be accounted for by predicted changes in plasma membrane Al3+ activity. The influence of Ca and Mg on the production and secretion of citrate and malate, and on Al accumulation by roots was investigated with soybean genotypes Young and PI 416937 which differ in Al tolerance. In the presence of a solution Al3+ activity of 4.6 microM, citrate and malate concentrations of tap root tips of both genotypes increased with additions of either Ca up to 3 mM or Mg up to 50 microM. Citrate efflux rate from roots exposed to Al was only enhanced with Mg additions and exceeded malate efflux rates by as much as 50-fold. Maximum citrate release occurred within 12 h after adding Mg to solution treatments. Adding 50 microM Mg to 0.8 mM CaSO4 solutions containing Al3+ activities up to 4.6 microM increased citrate concentration of tap root tips by 3- to 5-fold and root exudation of citrate by 6- to 9-fold. Plants treated with either 50 microM Mg or 3 mM Ca had similar reductions in Al accumulation at tap root tips, which coincided with the respective ability of these ions to relieve Al rhizotoxicity. Amelioration of Al inhibition of soybean root elongation by low concentrations of Mg in solution involved Mg-stimulated production and efflux of citrate by roots.

Cationic interactions in radiocaesium uptake from solution by spinach

Interionic effects on radiocaesium uptake in spinach ( Spinacia oleracea L, cv. Subito) were measured in a solution culture experiment. In total, 15 different nutrient solutions, spiked with 137Cs, were prepared in which K, NH 4, Ca and Mg concentrations were varied at four different total salt concentrations between 5.3meql −1and 21.2meql −1. The range of cationic concentrations studied was: K, 0.53 to 10.4 mmoll −1; NH 4, 0 to 8.47 mmoll −1; Ca, 0.15 to 5.0 mmoll −1; Mg, 0.08 to 2.0 mmoll −1. The plant/solution 137Cs transfer factor (TF) varied between 41 lkg −1 and 117 lkg −1. Radiocaesium levels in the plants were poorly, but positively, correlated with the K concentration in solution. However, radiocaesium levels were significantly reduced by increasing Ca + Mg concentrations in solution. Between 10.06 and 1.06moll −1 K, radiocaesium levels in 20-day-old plants were only slightly affected if K was replaced by NH 4 at almost constant Ca + Mg concentrations. The negative effect of Ca + Mg concentrations on 137Cs uptake is interpreted from their effect on 137Cs loading in the apoplast of the root cortex. A quantitative relationship is presented between the 137Cs TF and the fractional loading of 137Cs in the apoplast, which is calculated by ion exchange laws. This relationship is linear ( R 2 = 0.81) for the 15 different solutions studied.

Effect of Magnesium and Manganese Nutrition on Watermelon Growth and Manganese Toxicity

Abstract Watermelon [Citrullus lanatus (Thunb.) ‘Sugar Baby’ was grown in sand culture to evaluate Mn uptake as affected by solution concentration of Mn and Mg. Manganese toxicity symptoms were developed first on the lower mature leaves as small, distinct, blackish-brown speckling on the lower leaf surface that progressed to extensive vein browning and necrotic lesions. Leaves developed toxicity symptoms when they contained ≥1325 mg·liter−1 Mn. Growth was reduced at Mn concentrations in nutrient solution ≥22.5 mg·liter−1. Development of Mn toxicity symptoms was delayed with increasing Mg concentrations in solutions. Increasing Mg concentration in solution to 48 or 96 mg·liter-1 reduced Mn composition and Mg uptake per unit root surface at 2 and 30 mg·liter-1 Mn in solution, but had no effect at 60 mg·liter-1 Mn in solution.

Hydrothermal serpentinization of peridotite within the oceanic crust: Experimental investigations of mineralogy and major element chemistry

Mantle derived ultramafic rocks form a significant portion of lithosphere created at slow-spreading mid-ocean ridges. These rocks are ubiquitously serpentinized, due at least in part to interaction with seawater, at temperatures below approximately 500°C. To evaluate reaction pathways, primary mineral reaction rates, major element exchange between rock and solution, and alteration mineral formation, interaction of equigranular peridotites with seawater and seawater derived solutions has been investigated experimentally at 200°C and 300°C, 500 bars. Seawater chemistry changed greatly during the experiments. Initially, the concentrations of Mg, Ca, and SO 4 decreased, as did pH. During Iherzolite experiments, however, the trend of dissolved Ca concentrations reversed with time, first decreasing, then increasing. pH also increased during the latter part of the experiments. Mg, Ca, SiO 2, Fe, Cl and ΣCO 2 decreased as pH increased Fe II oxidation is shown to be affected by solution pH, being greatly enhanced under alkaline conditions. Resulting solution composition and reaction pathway are dependent on initial solution composition, particularly initial concentrations of Mg in solution. Consistent with changes in solution chemistry, the peridotites were significantly altered. Substantial amounts of olivine, relatively minor amounts of diopside and all the enstatite dissolved. Alteration products included serpentine + anhydrite ± magnesium hydroxide sulfate hydrate ± magnetite ± brucite ± tremolite-actinolite or truscottite. From the changes in solution chemistry and examination of the alteration products, the reaction rates (moles per unit time) of olivine to enstatite to diopside during 300°C Iherzolite-seawater experiments are estimated to be approximately 1.0/1.0/0.1. These rates correspond to constant surface area rates of 1.5:5:1 (moles per unit time per unit surface area), which are consistent with experimental data on the dissolution kinetics of these minerals and emphasize the importance of initial rock texture on reaction rates.

Hydrothermal alteration of basalt by seawater under seawater-dominated conditions

Fresh mid-ocean ridge basalt glass and diabase have been reacted with seawater at 150–300°C, 500 bar, and water/rock mass ratios of 50, 62, and 125, using experimental apparatus which allowed on-line sampling of solution to monitor reaction progress. These experiments characterize reaction under what we have called “seawater-dominated” conditions of hydrothermal alteration. In an experiment at 300°C, basalt glass undergoing alteration removed nearly all Mg 2+ from an amount of seawater 50 times its own mass. In the process, the glass was converted entirely to mixed-layer smectite-chlorite, anhydrite, and minor hematite. Removal of Mg from seawater occurred as a Mg(OH) 2 component incorporated into the secondary clay. This produced a precipitous drop in solution pH early in the experiment, accompanied by a dramatic increase in the concentrations of Fe, Mn, and Zn in solution. As Mg removal neared completion and the glass was hydrolyzed, pH rose again and heavy metal concentrations dropped. At water/rock ratios of 62 and 125 and 150–300°C, the mineral assemblage produced was similar to that at a water/rock ratio of 50. Solution chemistry, however, contrasted with the earlier experiment in that Mg concentrations in solution were greater and pH lower. This caused significant leaching of heavy metals. At 300°C nearly all of the Na, Ca, Cu, Zn, and CO 2 and most of the K, Ba, Sr, and Mn were leached from the silicates. H 2S, Al, Si, and possibly Co were also significantly mobilized, whereas V, Cr, and Ni were not. Little or no seawater sulfate was reduced. Although submarine hot spring solutions sampled to date along mid-ocean ridges clearly come from rock-dominated hydrothermal systems, evidence from ocean floor metabasalts and from heat flow studies indicates that seawater-dominated conditions of alteration prevail at least locally both in axial hightemperature systems and in ridge flank systems at lower temperatures.

Some effects of varied magnesium nutrition on the growth and composition of olive plants (cultivar ‘chondrolia chalkidikis’)

Olive plants ( Olea europaea cultivar ‘Chondrolia Chalkidikis’) were grown in perlite: sand (1 : 1) cultures irrigated with nutrient solutions widely varying in magnesium (Mg) levels. When calcium (Ca) concentration in solution was 4 mM, maximum fresh weight (Fw) was produced with 0.4–2 mM Mg. Above 2 mM Mg in solution, fresh weight yield declined. The ratio of Ca Mg in solution for optimum vegetative growth of olive trees was 2. Ca concentration of leaves and roots fell consistently with increasing Mg concentration in solution from 0.005 to 20 mM. When the concentration of Ca was 0.5 mM, an increase of Mg in solution from 3 to 20 mM did not further reduce Ca content of tissue. Mg concentration of leaves and roots increased, but not in proportion to the increase of Mg in the nutrient solution. An increase of Mg in solution from 2 to 10 mM was followed by a proportional increase of manganese (Mn) content of leaves. Above 10 mM Mg, a plateau in Mn concentration was reached. The zinc (Zn) content of leaves and roots was increased when Mg in solution increased up to 0.2 mM, then was reduced in the range 0.2–2 mM Mg and remained constant between 2 and 20 mM Mg. Other elements like copper (Cu) and iron (Fe) were not affected by increasing Mg concentration in solution.

Studies on the Relation between the Trolerance of Crops to Soil Acidity and that to Low pH : 16. 0n the calcium and magnesium concentration in fractions extracted from root by various solutions

Milk vetch and Italian ryegrass were cultivated in water solutions with different composition. Roots of these plants were successively extracted with 66% EtOH (Fr.1), cold water (Fr.2), O.1M acetic acid in 75% EtOH (Fr.3), 0.3% NaOH in 60% EtOH(Fr.4), 1N〓NaC1(Fr.5), 2% acetic acid (Fr.6) and with 5% HC1 (Fr.7). The residual material was ashed (Fr.8)and Ca and Mg in these fractions were determined, The results obtained were as follows : 1. When the concentration of Ca in culture solution was strongly lowered from the standard concentration, the concentration of Ca in each fraction decreased slightly indicating that the rate of Ca transport to top was reduced. At very high Ca concentration in culture solution, calcium carbonate and Ca bound to pectic acid besides water soluble Ca greatly increased. First two Ca fractions probably came from the excess Ca, being absorbed more than the amoun to be transported to the top in a short period. Italian ryegrass, which required lower Ca concentration fo culture solution for optimum plant growth, was cultivated at standard Ca concentration and low Ca concentration. The two largest Ca types of the root, Ca bound to pectic acid and tribasic calcium phosphate, were smaller in amount and on the other hand the reactive Ca soluble in alcohol was high. This pattern of distribution of Ca appeared to explain the less repuirement of Ca in root and the more translocation fo Ca to the top by this plant. In Italian ryegrass, whose plant growth was not suppressed too much at low Ca concentration, the amount in the root of calcium carbonate and Ca bound to pectic acid were reduced but no reduction was observed in both types of transportable Ca, soluble in alcohol and in water. This may be attributed to the effective transport of Ca to the top at low Ca solution. At excess Ca concentration in culture solution, Ca bound to pectic acid and especially tribasic calcium phosphate accumulated markedly in root. 2. The Ca bound to pectic acid and protein were directly depressed by increase of Mg concentration in solution caused by the competitive effect of Mg. The amount of tribasic calcium phosphate was not affected by direct competitive effect of Mg but was depressed by the decrease of concentration ot Ca in root. When the concentration of Mg in culture solution was so increased as to reduce Ca bound to pectic acid and tribasic calctum phosphate by the competitive effect of Mg, the plant growth was reduced. 3. At low Al concentration of 0.5ppm in culture solution, the binding of Ca to protein and pectic acid and accumulation as tribasic calcium phosphate were inhibited. At high Al concentration of 5ppm, accumulation of calcium carbonate was also inhibited besides the last two types. In Italian ryegrass, which was tolerant to Al toxicity, the depression of Ca in above three types at the Al concentration of 0.5-5ppm in culture solution was little. 4. At low pH solution of 4.3 in culture solution, alcohol soluble Ca in root was depressed as compared with that of pH 5.3 and resulted in the depression of translocated Ca at the top. And the accumulation of tribasic calcium phosphate in root was also inhibited in this case. In milk vetch, which was susceptible to the injury of high H ion, the amount of Ca bound to pectic acid in root also decreased as well as the above two types of Ca, at low pH of solution. At high pH value of 6.3 in culture solution, Ca concentration of tribasic calcium phosphate and Ca bound to pectic acid increased as compared with that of pH 5.3. 5. The concentration of Mg fractiond, which were bound to pectic acid, soluble in alcohol and soluble in alcohol with acetic acid, increased with increase of Mg concentration in culture solution. In milk vetch, whose growth was severely reduced by excessive Mg concentration in culture solution, the concentration of Mg in above three types easily increased at Mg concentration of 2-15ppm in solution. [the rest omitted]