Molybdate in soil adsorption by manganese oxide
Molybdate (MoO42-) adsorption by manganese (Mn) oxide was investigated using a synthetic birnessite. Experiments were carried out in a batch experiment as a function of time (1 min to 28 d), pH (2-10) and the competitive anions sulphate (SO42-), phosphate (PO43-selenate (SeO42-) and selenite (SeO43-).
Furthermore, MoO42- adsorption was described as a function of equilibrium concentration at pH 4-7 and the data were evaluated with the Freundlich and Langmuir equations.
The amount of adsorbed MoO42- was strongly dependent on time and reached roughly an equilibrium after three days. An increase in the pH by 1.15 units within 28 days indicates ligand exchange of surface hydroxyls with MoO42-. Molybdate adsorption showed high sensitivity to pH and reached a maximum at pH 3, near the pK(a1) and pK(a2) for molybdic acid. The Freundlich equation adequately reconstructed the adsorption data. Molybdate adsorption also conformed to the Langmuir equation for the investigated pH values.
The competition sequence of anions for MoO42- adsorption by Mn oxide was SeO 43-> SeO42-> PO 43- > SO 42-, assuming a strong adsorption mechanism of MoO42- onto the surface of birnessite.
These results indicate that Mn oxides have a strong effect on the adsorption of MoO42- especially due to their higher specific surface area compared to aluminium or iron oxides. This is important regarding the availability of MoO42-in soils under agricultural conditions (pH 4-7) as well as for the treatment of soils and groundwater affected by elevated intake from industries. (C) 2015 Elsevier B.V. All rights reserved
Matem, K. and Mansfeldt, T., Molybdate adsorption by birnessite, Applied Clay Science, 2015, 108, 78-83.
[Birnessite: (Na, Ca)0.5(Mn4+,Mn3+)2O4 • 1.5H2O. Handbook of Mineralogy.]
Molybdate binding in soil
Metals in soils may positively or negatively affect plants as well as soil micro-organisms and mesofauna, depending on their abundance and bioavailability. Atmospheric deposition and biological uplift commonly result in metal enrichment in surface soils, but the relative importance of these processes is not always resolved. Here, we used an integrated approach to study the cycling of phosphorus and a suite of metals from the soil to the canopy (and back) in a temperate watershed.
The behavior of elements in these surface soils fell into three categories. First, Al, Fe, V, Co, and Cr showed little to no enrichment in the top soil layers, and their concentrations were determined primarily by soil production fluxes with little influence of either atmospheric inputs or biological activity.
Second, P, Cu, Zn and Cd were moderately enriched in surface soils due to a combination of atmospheric deposition and biological uplift. Among the metals we studied, Cu, Zn and Cd concentrations in surface soils were the most sensitive to changes in atmospheric deposition fluxes.
Finally, Mo and Mn showed strong enrichment in the top soil layer that could not be explained strictly by either current atmospheric deposition or biological recycling processes, but may reflect both their unique chemistry and remnants of past anthropogenic fluxes.
Mn has a long residence time in the soil partly due to intense biological uplift that retains Mn in the top soil layer.
Mo, in spite of the high solubility of molybdate, remains in the soil because of strong binding to natural organic matter.
This study demonstrates the need to consider simultaneously the vegetation and the soils to understand elemental distribution within soil profiles as well as cycling within watersheds
Kraepiel, A. M. L., Dere, A. L., Herndon, E. M., and Brantley, S. L., Natural and anthropogenic processes contributing to metal enrichment in surface soils of central Pennsylvania, Biogeochemistry, 2015, 123, 265-283.
Fractionation and release behaviors of metals (In, Mo, Sr) from industrial sludge
Little is known on the fate of rare metals in the environment and the associated risks. The fractionation and release of three metals of an industrial sludge were assessed. The average concentration ranges from 39.3 to 41.5 mg/kg for indium (In), 43.1-77.8 mg/kg for molybdenum (Mo), and 131.1-376.4 mg/kg for strontium (Sr). Sequential extraction results implied that In was mobile, while Mo and Sr were immobile. However, experimental results from effects of Eh/pH revealed that In was slightly mobile under acidic (pH 4.5) in Eh range of 210-260 mV, and immobile under alkaline conditions (9.0) in Eh range of -250 to 125 mV. The release of Mo was slightly mobile under acidic conditions. However, Mo was very mobile under alkaline conditions and it increased with decreasing Eh. The release of Sr was significant under acidic conditions; however, it was immobile under alkaline conditions. Solubility and adsorption as affected by pH, and speciation could explain their release behaviors. Discrepancy in predictions from sequential extraction and actual observation from Eh/pH experiments was discussed. (C) 2015 Elsevier Ltd. All rights reserved.
Chen, J. Y., Luong, H. V. T., and Liu, J. C.,Fractionation and release behaviors of metals (In, Mo, Sr) from industrial sludge, Water Research, 2015, 82, 86-93.
Acid extraction of molybdenum, nickel and cobalt from mineral sludge generated by rainfall water at a metal recycling plant
This study investigated the leaching yields of Mo, Ni and Co from a mineral sludge of a metal recycling plant generated by rainfalls. The investigated mineral sludge had a complex heterogeneous composition, consisting of particles of settled soil combined with the metal bearing particles (produced by catalysts, metallic oxides and battery recycling). The leaching potential of different leaching reagents (stand-alone strong acids (HNO3 (68%), H2SO4 (98%) and HCl (36%)) and acid mixtures (aqua regia (nitric + hydrochloric (1:3)), nitric + sulfuric (1:1) and nitric + sulfuric + hydrochloric (2:1:1))) was investigated at changing operational parameters (solid - liquid (S/L) ratio, leaching time and temperature), in order to select the leaching reagent which achieves the highest metal leaching yields. Sulfuric acid (98% H2SO4) was found to be the leachant with the highest metal leaching potential. The optimal leaching conditions were a three stage successive leaching at 80 degrees C with a leaching time of 2 h and S/L ratio 0.25 g L-1. Under these conditions, the achieved mineral sludge sample leaching yields were 85.5, 40.5 and 93.8% for Mo, Ni and Co, respectively. The higher metal leaching potential of H2SO4 in comparison with the other strong acids/acid mixtures is attributed to the fact that H2SO4 is a diacidic compound, thus it has more H+ ions, resulting in its stronger oxidising power and corrosiveness.
Vemic, M., Bordas, F., Guibaud, G., Joussein, E., Lens, P. N., and van Hullebusch, E. D.,Acid extraction of molybdenum, nickel and cobalt from mineral sludge generated by rainfall water at a metal recycling plant, Environmental technology, 2015, 1-33.
Solid-solution phase partitioning coefficients
The authors' aim was to develop rapid and inexpensive regression models for the
prediction of partitioning coefficients (Kd ), defined as the ratio of the total
or surface-bound metal/metalloid concentration of the solid phase to the total
concentration in the solution phase. Values of Kd were measured for boric acid
(B[OH]3 (0) ) and selected added soluble oxoanions: molybdate (MoO42- ),
antimonate (Sb[OH]6- ), selenate (SeO42-), tellurate (TeO42- ) and
vanadate (VO43- ). Models were developed using approximately 500 spectrally
representative soils of the Geochemical Mapping of Agricultural Soils of Europe
(GEMAS) program. These calibration soils represented the major properties of the
entire 4813 soils of the GEMAS project. Multiple linear regression (MLR) from
soil properties, partial least-squares regression (PLSR) using mid-infrared
diffuse reflectance Fourier-transformed (DRIFT) spectra, and models using DRIFT
spectra plus analytical pH values (DRIFT?+?pH), were compared with predicted log
Kd?+?1 values. Apart from selenate (R(2) ?=?0.43), the DRIFT?+?pH calibrations
resulted in marginally better models to predict log Kd?+?1 values (R(2)
?=?0.62-0.79), compared with those from PSLR-DRIFT (R(2) ?=?0.61-0.72) and MLR
(R(2) ?=?0.54-0.79). The DRIFT?+?pH calibrations were applied to the prediction
of log Kd?+?1 values in the remaining 4313 soils. An example map of predicted log
KKd?+?1 values for added soluble MoO4 (2-) in soils across Europe is presented.
The DRIFT?+?pH PLSR models provided a rapid and inexpensive tool to assess the
risk of mobility and potential availability of boric acid and selected oxoanions
in European soils. For these models to be used in the prediction of log Kd?+?1
values in soils globally, additional research will be needed to determine if soil
variability is accounted on the calibration. Environ Toxicol Chem 2014;9999:1-12.
Janik LJ, Forrester ST, Soriano-Disla JM, Kirby JK, McLaughlin MJ, Reimann C;
GEMAS Project Team. GEMAS: Prediction of solid-solution phase partitioning coefficients (Kd ) for
oxoanions and boric acid in soils using mid-infrared diffuse reflectance spectroscopy. Environ Toxicol Chem. 2015 Feb;34(2):235-46. doi: 10.1002/etc.2821. Epub 2015 Jan 8. © 2014 SETAC.
Effect of long-term equilibration on the toxicity of molybdenum to soil organisms
To determine if long-term equilibration may alleviate molybdenum toxicity, earthworms, enchytraeids, collembolans and four plant species were exposed to three soils freshly spiked with Na2MoO4.2H2O and equilibrated for 6 or 11 months in the field with free drainage.
Total Mo concentrations in soil decreased by leaching, most (up to 98%) in sandy soil and less (54-62%) in silty and clayey soils.
Changes in residual Mo toxicity with time were inconclusive in sandy soil.
In the other two soils, toxicity of residual total Mo was significantly reduced after 11 months equilibration with a median 5.5-fold increase in ED50s.
Mo fixation in soil, i.e. the decrease of soil solution Mo concentrations at equivalent residual total soil Mo, was maximally a factor of 2.1 only.
This experiment shows natural attenuation of molybdate ecotoxicity under field conditions is related to leaching of excess Mo and other ions as well as to slow ageing reactions. (C) 2011 Elsevier Ltd. All rights reserved
van Gestel, C. A. M., McGrath, S. P., Smolders, E., Ortiz, M. D., Borgman, E., Verweij, R. A., Buekers, J., and Oorts, K., Effect of long-term equilibration on the toxicity of molybdenum to soil organisms, Environmental Pollution, 2012, 162, 1-7.
The Mo concentration in soil of the Pamperan region of Argentina was
Lavado, R.S., Porcelli, C.A., Alvarez, iR., Concentration and distribution of extractable elements in a soil as affected by tillage systems and fertilization, Science Of The Total Environment, 1999, 232, 3, 185-191.
Average and "normal" concentration levels for various metals including molybdenum have been proposed in order to establish a base line from which to assess contamination and pollution of the environment. Suggested levels are based on experience in Canada, Great Britain and two small areas in Wisconsin, U.S.A., but the general applicability of these levels especially in the U.S.A., remains to be established. For soils an average molybdenum concentration of 1.5 ppm is suggested with a normal range of 0.2-5 ppm. Similarly, average trace element contents of some vegetables have been suggested.
Warren, H . V., Delavault, R. E., Fletcher, K. W., Geology Environ. Contr. Bull., 1971, 6, 34.
Aging reactions in soils can influence the lability and hence bioavailability of added metals in soils through their removal from labile pools into pools from which desorption is slow (non-labile pools). The aims of this study were to examine the effect of aging reactions on the lability of soluble molybdate (MoO42-) added into soils with varying physical and chemical properties and develop models to predict changes in the labile pool of MoO42- in soils with incubation time. Soils were spiked with soluble MoO42- at quantities sufficient to inhibit barley root growth by 10% (EC10) or 90% (EC90) and incubated for up to 18 months. The labile pool of MoO42- (E value) was observed to decrease in soils with incubation time, particularly in soils with high clay content. A strong relationship was observed between measures of MoO42- lability in soils determined using E value [sampling the solution phase]and L value [use of a biological component (e.g. plant or earthworm) grown directly in the labelled soil] techniques (R2 = 0.98) suggesting E values provided a good measure of the potential plant available pool of MoO42- in soils. A regression model was developed that indicates clay content and incubation time were the most important factors affecting the labile pool of MoO42- in soils with time after addition (R2 = 0.70-0.75). The aging model developed suggests soluble MoO42-will be removed into non-labile pools more rapidly with time in neutral to alkaline clay soils than in acidic sandy soils. Labile MoO42- concentrations in molybdenum contaminated soils was found to be <10% of the total molybdenum concentrations in soils. Crown Copyright (C) 2012 Published by Elsevier Ltd. All rights reserved
Kirby, Jason K., McLaughlin, Michael J., Ma, Yibing, and Ajiboye, Babasola, Aging effects on molybdate lability in soils, Chemosphere, 2012, 89, 876-883.
Metal and nanoparticle occurrence in biosolid-amended soils
Metals can accumulate in soils amended with biosolids in which metals have been concentrated during wastewater treatment.
The goal of this study is to inspect agricultural sites with long-term biosolid application for a suite of regulated and unregulated metals, including some potentially present as commonly used engineered nanomaterials (ENMs).
Sampling occurred in fields at a municipal and a privately operated biosolid recycling facilities in Texas. Depth profiles of various metals were developed for control soils without biosolid amendment and soils with different rates of biosolid application (6.6 to 74 dry tons per hectare per year) over 5 to 25 years.
Regulated metals of known toxicity, including chromium, copper, cadmium, lead, and zinc, had higher concentrations in the upper layer of biosolid-amended soils (top 0-30 cm or 0-15 cm) than in control soils.
The depth profiles of unregulated metals (antimony, hafnium, molybdenum, niobium, gold, silver, tantalum, tin, tungsten, and zirconium) indicate higher concentrations in the 0-30 cm soil increment than in the 70-100 cm soil increment, indicating low vertical mobility after entering the soils.
Titanium-containing particles between 50 nm and 250 nm in diameter were identified in soil by transmission electron microscopy (TEM) coupled with energy dispersive x-ray spectroscopy (EDX) analysis.
In conjunction with other studies, this research shows the potential for nanomaterials used in society that enter the sewer system to be removed at municipal biological wastewater treatment plants and accumulate in agricultural fields. The metal concentrations observed herein could be used as representative exposure levels for eco-toxicological studies in these soils. (C) 2014 Elsevier B.V. All rights reserved
Yang, Y., Wang, Y. F., Westerhoff, P., Hristovski, K., Jin, V. L., Johnson, M. V. V., and Arnold, J. G., Metal and nanoparticle occurrence in biosolid-amended soils, Science of the Total Environment, 2014, 485, 441-449.