Molybdate Blue Method Research Articles

Experimental and computational evidence of U(VI)–OH–Si(OH)4 complexes under alkaline conditions: Implications for cement systems

The complexation of uranyl hydroxides with orthosilicic acid was investigated by experimental and theoretical methods. Spectroluminescence titration was performed in a glovebox under argon atmosphere at pH 9.2, 10.5 and 11.5, with [U(VI)] = 10−6 and 5 × 10−6 mol kgw−1. The polymerization effects of silicic acid were minimized by ruling out samples with less than 90 % monomeric silicic acid present, identified via UV–Vis spectrometry using the molybdate blue method. Linear regression analysis based on time-resolved laser-induced fluorescence spectroscopy (TRLFS) results yielded the conditional stepwise formation constants of U(VI)–OH–Si(OH)4 complexes at 0.05 mol kgw−1 NaNO3. The main spectroscopic features – characteristic peak positions and decay-time – are reported for the first time for the UO2(OH)2SiO(OH)3− species observed at pH 9.2 and 10.5 and UO2(OH)2SiO2(OH)22− predominant at pH 11.5. Quantum chemical calculations successfully computed the theoretical luminescence spectrum of the complex UO2(OH)2SiO(OH)3− species, thus underpinning the proposed chemical model for weakly alkaline systems. The conditional stability constants were extrapolated to infinite dilution using the Davies equation, resulting in log10β°(UO2(OH)2SiO(OH)3−) and log10β°(UO2(OH)2SiO2(OH)22−). Implications for U(VI) speciation in the presence and absence of competing carbonate are discussed for silicate-rich environments expected in certain repository concepts for nuclear waste disposal.

High-frequency soluble reactive phosphorus in-situ analysis in lakes

High-frequency in-situ monitoring of nutrients in lakes is increasingly becoming relevant to understand event-driven nutrient pulses better. These pulses are essential for phytoplankton development but are usually not captured during conventional sampling programs. In-situ monitoring of nutrients in lakes has been lagging despite the role of nutrients in eutrophication. We evaluated an in-situ wet chemistry soluble reactive phosphorus (SRP) analyzer to establish a methodological basis for high-frequency measurements of SRP. The device (based on the molybdate blue method) was evaluated in laboratory and field tests by comparing it with conventional laboratory analysis. The results of the in-situ analyser during laboratory were similar to the conventional analysis (R2 > 0.995, NSE = 0.989, PBIAS = 8.4 %). Repeated measurements by the in-situ analyzer in a 0.1 mg L-1 test solution had a mean and standard deviation of 0.1005 ± 0.0047 and a MAPE of 3.39, indicating the stability of the measurements. During field tests in a hypertrophic lake with anoxic hypolimnion, the in-situ analyzer SRP concentrations were lower and divergent from the laboratory analysis; due to potential interference of the in-situ analyzer's reagents by sulfides. Under aerobic conditions during field tests, the in-situ P results of a eutrophic, mixed shallow lake were similar to those from water samples analyzed in the laboratory (R2 = 0.562 – 0.812, NSE = 0.397 – 0.707, PBIAS = -8.5 – 24.6 %). There was no difference in SRP concentration among the unfiltered, 0.2 µm, and 10 µm pore size filtered samples; filter pore size did not play a role in the measured SRP concentrations. The in-situ SRP analyzer revealed previously unobserved phenomena, e.g., multiple strongly discontinuous SRP peaks reaching almost 0.1 mg L-1; it therefore, offers a solid methodological basis for high-frequency monitoring of SRP. Incorporating high-frequency in-situ nutrient analysis in lake monitoring provides insights into lakes' short-term nutrient dynamics. Such information is essential for understanding the effects of extreme events like droughts, storms, and heat waves.

Characterizing bioavailable phosphorus concentrations in an agricultural stream during hydrologic and streambed disturbances.

In freshwater ecosystems, phosphorus (P) is often considered a growth-limiting nutrient. The use of fertilizers on agricultural fields has led to runoff-driven increases in P availability in streams, and the subsequent eutrophication of downstream ecosystems. Isolated storms and periodic streambed dredging are examples of two common disturbances that contribute dissolved and particulate P to agricultural streams, which can be quantified as soluble reactive P (SRP) using the molybdate-blue method on filtered water samples, or total P (TP) measured using digestions on unfiltered water reflecting all forms of P. While SRP is often considered an approximation of bioavailable P (BAP), research has shown that this is not always the case. Current methods used to estimate BAP do not account for the role of biology (e.g., NaOH extractions) or require specialized platforms (e.g., algal bioassays). Here, in addition to routine analysis of SRP and TP, we used a novel yeast-based bioassay with unfiltered sample water to estimate BAP concentrations during two storms (top 80% and > 95% flow quantiles), and downstream of a reach where management-associated dredging disturbed the streambed. We found that the BAP concentrations were often greater than SRP, suggesting that SRP is not fully representative of P bioavailability. The SRP concentrations were similarly elevated during the two storms, but remained consistently low during streambed disturbance. In contrast, turbidity and TP were elevated during all events. The BAP concentrations were significantly related to turbidity during all disturbance events, but with TP only during storms. The novel yeast assay suggests that BAP export can exceed SRP, particularly when streams are not in equilibrium, such as the rising limb of storms or during active dredging.

Inoculación de hongos solubilizadores de fósforo y micorrizas arbusculares en plantas de jitomate

La necesidad de reducir el uso de fertilizantes químicos demanda la creación de estrategias alternativas que mantengan una producción vegetal competitiva sin deterioro del ambiente. En este estudio, se evaluó la efectividad de la inoculación de hongos micorrícicos y solubilizadores de fósforo (solos y en consorcios) sobre la micorrización, el contenido de fósforo en la parte aérea, la altura, y longitud de la raíz de las plantas de jitomate. Los tratamientos incluyeron tres cepas de hongos solubilizadores (Aspergillus niger, Penicillium brevicompactum y Penicillium waksmanii), un consorcio de micorrizas y todas sus posibles combinaciones incluyendo un testigo (sin hongos). Después de cuatro meses, se cuantificó la colonización micorrícica, el contenido de fósforo de la parte aérea por el método del azul de molibdato y las variables altura y longitud de raíz. Los resultados obtenidos demostraron un rango de colonización del 48-66%; los valores más altos se detectaron con los tratamientos de HMA y HMA + An. Los tratamientos consorcios de HSF y HSF + HMA exhibieron 191% de incremento del fósforo foliar respecto a los testigos. La altura de las plantas de jitomate fue significativamente mayor en todos los tratamientos con respecto al testigo. Para la longitud de raíz el tratamiento HMA y el testigo presentaron los valores más altos. Los consorcios de hongos solubilizadores de fósforo en combinación con el consorcio de hongos micorrícicos tienen un alto potencial para ser utilizados como biofertilizantes de jitomate en invernadero.

Screening of Soil Bacteria for Phytase Activity

The aim of the present papaer was to realize a screening for phytase producing bacteria isolated from soil where pig manure was stored. It was used PSM, PKA media and the molybdate-blue method in order to determine the presence of phytase- phosphate solubilizing- and proteaze- producing bacteria. About half of the bacterial isolates were phytase producers

On the colorimetric measurement of aqueous Si in the presence of organic ligands and common pH buffering agents

The effects of the presence of ten organic ligands and common pH buffering agents – acetate, oxalate, tartrate, citrate, phthalate, EDTA, carbonate, TRIS, phosphate and borate – on aqueous Si concentration measurements made using the common molybdate blue method were quantified. The concentrations of these additives ranged from 0.01 to 0.1 mol/kg in the measured aqueous solutions. Whereas measured Si concentrations were not affected by the presence of up to 0.1 mol/kg acetate, hydrogen phthalate or TRIS, the presence of 0.1 mol/kg of all other selected additives altered substantially the measured Si concentrations using the molybdate blue method. For example the presence of 0.1 mol/kg of citrate, EDTA, and hydrogen phosphate decreased the ratio of measured to true Si concentrations to ~0.05. These variations are interpreted to stem from the formation of competing aqueous complexes in the aqueous phase limiting the formation of the characteristically blue SiMo12O404– complex.

Solubility and dissolution kinetics of quartz in NH 3–H 2O system at 25 °C

Understanding of the solubility of quartz in aqueous ammonia solutions is crucial to our knowledge of many hydrometallurgical processes. The solubilities of natural quartz and ground quartz with particle size from 45 μm to 75 μm were measured in the NH 3–H 2O system at 25 °C, with ammoniacal concentrations up to 2.93 mol/kg H 2O. Solubilities were determined by molybdate blue method. Quartz and amorphous silica solubilities in the NH 3–H 2O system were also calculated by geochemical modeling code. The experimental and predicted results indicate that the two minerals have fundamentally different dissolution behavior. Natural quartz solubility undergoes large enhancement with ammonia, rising rapidly from a silica concentration of 6.83 mg/L in pure water and leveling off at 419 mg/L in 2.92 mol/kg NH 3 solutions. Ground quartz solubility lies between natural quartz and amorphous silica, which shows monotonically increasing from m SiO2 = 690 mg/L in 0.26 mol/kg NH 3 solution to 1530 mg/L in 2.74 mol/kg NH 3. The rate of dissolution of ground quartz far from equilibrium was also studied in the NH 3–H 2O system. The effects of particle size and duration time on dissolved silica were investigated. The results showed that ammonia concentration has no great impact on the rate of dissolution of ground quartz with particle size of 45–75 μm. Our findings clearly imply the degree of particle surface damage by grinding and the reaction time are the most important factors for the ammonia leaching of quartz.

Phosphorus Sorption Characteristics of Red Soils from Lampung, West- and Central Java

Phosphorus Sorption Characteristics of Red Soils from Lampung, West- and Central Java (S.A. Siradz and R.J. Gilkes): Red soil is a common name used to identify any soil showing yellowish to reddish colour, these soils mainly occur in tropical and subtropical regions. The term is frequently used to convey an image of red, infertile, acid soils in the tropics and is associated with tropical and subtropical climates which are characterized by high temperature and humidity. Major soil constraints to crop production may include low pH, low available P and high P fixation capacity, toxicity due to Al and sometimes Mn and Fe, deficiencies of N, Ca, Mg, K, and micronutrients e.g. Mo, Zn and Cu, low CEC and low base saturation, and very low content of weatherable minerals. The aim of this study was to determine the phosphorus sorption characteristics of red soils from Lampung, West Java and Central Java. Soils were sampled at depth of 0-20 cm from minimally disturbed sites after discarding the uppermost few cm consisting of an accumulation of litter. The samples were air-dried, crushed using a ceramic mortar and pestle and then passed through a 0.5 mm stainless steel sieve. Measurements of P sorption were conducted by equilibrating 200 mg of air dry soil (<0.5 mm) in 20 mL 0.2 M KCl containing 0-30 mg PmL-1. P concentrations in filtrate were determined by the molybdate blue method. Phosphorus sorption data for soils were fitted to simple Langmuir and Freundlich isotherm equations and both equations described the data equally well. Langmuir P sorption maximum (xm) for soil ranged from 719-2747 µg Pg-1, with median values of 1.825 µg Pg-1. There were systematic decreases in the values of Langmuir sorption maximum (xm) for soils from Lampung > West Java and Central Java. Values of pH(NaF), Ald, and exchangeable Ca were most predictive of P sorption in these soils.

Release of Colloids from Injection Grout Silica Sol

AbstractNon-cementitious grouts have been tested in Olkiluoto for the sealing of fractures with the small hydraulic aperture. A promising non-cementitious inorganic grout material for sealing the fractures of the apertures less than 0.05 mm is commercial colloidal silica called silica sol. The use of colloidal material has to be considered in the long-term safety assessment of a spent nuclear fuel repository. Objective of this work was to determine colloid release from the silica sol gel and stability of silica colloids in different groundwater conditions. To use silica sol as a grout, the injected colloids have to aggregate and form a gel within a predictable time by using a saline solution as an accelerator. Silica sol gel samples were stored in contact with medium salinity and low salinity groundwater simulates. Release of silica colloids and colloid stability was followed by analyzing the colloid concentration, particle size distribution, concentration of reactive silicon, solution pH and zeta potential after one month, half a year and one year. Malvern Zetasizer Nano ZS equipment was used to determine colloidal particle size distributions applying the dynamic light scattering method and zeta potential based on dynamic electrophoretic mobility. The colloidal particle concentration was estimated from Zetasizer measurements applying a standard series. Dissolved reactive silica concentration was determined using the molybdate blue method and total silica concentrations were determined using ICP–MS. The release and stability of silica colloids were found to be dependent significantly on groundwater salinity. Zeta potential values near zero and the increase in particle size at first and then the disappearance of large particles indicated particle flocculation or coagulation and instable colloidal dispersion in a saline groundwater simulate. In low salinity ground water simulate high negative zeta potential values, small particle size and constant size distribution indicate the existence of stable silica colloids. The concentrations of the released colloids were slightly higher than determined in natural granitic ground waters. Under prevailing saline groundwater conditions in Olkiluoto no significant release of colloids from silica sol is expected but the possible influence of low salinity glacial melt waters has to be considered.

Enzymatic characterization of organic phosphorus in animal manure.

Information on the forms of P present in animal manure may improve our ability to manage manure P. In most investigations of manure P composition, only inorganic and total P are determined, and the difference between them is assigned as organic P. In this study, we explored the possibility of identifying and quantifying more specific organic P forms in animal manure with orthophosphate-releasing enzymes. Pig (Sus scrofa) manure and cattle (Bos taurus) manure were first sequentially fractionated into water-soluble P, NaHCO3-soluble P, NaOH-soluble P, HCl-soluble P, and residual P. The fractions were separately incubated with wheat phytase, alkaline phosphatase, nuclease P1, nucleotide pyrophosphatase, or their combinations. The released orthophosphate was determined by a molybdate blue method. Part of the organic P in those fractions could be identified by the enzymatic treatments as phytate (i.e., 39% for pig manure and 17% for cattle manure in water-soluble organic P), simple phosphomonoesters (i.e., 43% for pig manure and 15% for cattle manure in NaOH-soluble organic P), nucleotide-like phosphodiesters (2-12%), and nucleotide pyrophosphate (0-4%). Our data indicate that the enzymatic treatment is an effective approach to identify and quantify the organic P forms present in animal manures.

Variation in Phosphorus Sorption with Soil Particle Size

Phosphorus (P) is considered a primary cause for surface water eutrophication that leads to anoxia. Understanding the relationships between soil particle size and P sorption helps devise effective best management practices (BMPs) to control P transport by erosion, leaching, and overland flow from agricultural land. Consequently, this study examined the effect of surface soil particle size on the sorption of P in five soil series (four Ultisols and one Entisol) from the Mid-Atlantic region. The sorption of P in each soil was assessed by equilibrating (after shaking for 24 h) 5 g soil containing varied amounts of KH2PO4 in 20 mL of 0.01 M KCl solution. Phosphorus in solution was determined by the molybdate blue method of Murphy and Riley. The P adsorption characteristics of these soils were described using the Langmuir isotherm. Results indicated that variability in P sorption was related to particle size and soil type. Soil organic matter content contributed a great deal to P sorption in the Entisol. However, soil clay had influence on the P sorption characteristics of each soil. The maximum P retentive capacities of soils (as determined by Sm from Langmuir equation) and P sorbed at 500 mg P kg−1 addition showed a linear relationship (r2 = 0.94). Therefore, based on the results obtained, the single point method of Bache and Williams may be appropriate to describe the maximum P sorption capacity of non-sandy soils, as observed in this study.