scholarly journals Sorption and Desorption of Vanadate, Arsenate and Chromate by Two Volcanic Soils of Equatorial Africa

Soil Systems ◽  
2021 ◽  
Vol 5 (2) ◽  
pp. 22
Author(s):  
Sara Gonzalez-Rodriguez ◽  
Maria Luisa Fernandez-Marcos

Sorption of oxyanions by soils and mineral surfaces is of interest due to their role as nutrients or pollutants. Volcanic soils are variable charge soils, rich in active forms of aluminum and iron, and capable of sorbing anions. Sorption and desorption of vanadate, arsenate, and chromate by two African andosols was studied in laboratory experiments. Sorption isotherms were determined by equilibrating at 293 K soil samples with oxyanion solutions of concentrations between 0 and 100 mg L−1 V, As, or Cr, equivalent to 0−2.0 mmol V L−1, 0−1.3 mmol As L−1, and 0−1.9 mmol Cr L−1, in NaNO3; V, As, or Cr were determined by ICP-mass spectrometry in the equilibrium solution. After sorption, the soil samples were equilibrated with 0.02 M NaNO3 to study desorption. The isotherms were adjusted to mathematical models. After desorption with NaNO3, desorption experiments were carried out with a 1 mM phosphate. The sorption of vanadate and arsenate was greater than 90% of the amount added, while the chromate sorption was much lower (19–97%). The sorption by the Silandic Andosol is attributed to non-crystalline Fe and Al, while in the Vitric Andosol, crystalline iron species play a relevant role. The V and Cr sorption isotherms fitted to the Freundlich model, while the As sorption isotherms conformed to the Temkin model. For the highest concentrations of oxyanions in the equilibrating solution, the sorbed concentrations were 37–38 mmol V kg−1, 25 mmol As kg−1, and 7.2–8.8 mmol Cr kg−1. The desorption was low for V and As and high for Cr. The comparison of the sorption and desorption isotherms reveals a pronounced hysteresis for V in both andosols and for Cr in the Silandic Andosol. Phosphate induced almost no V desorption, moderate As desorption, and considerable Cr desorption.

PeerJ ◽  
2018 ◽  
Vol 6 ◽  
pp. e5820 ◽  
Author(s):  
Sara Gonzalez-Rodriguez ◽  
Maria Luisa Fernandez-Marcos

Volcanic soils cover 1% of the Earth’s surface but support 10% of the world’s population. They are among the most fertile soils in the world, due to their excellent physical properties and richness in available nutrients. The major limiting factor for plant growth in volcanic soils is phosphate fixation, which is mainly attributable to active species of aluminium and iron. The sorption and desorption of phosphate is studied on the surface horizons of two African agricultural soils, a silandic Andosol (Rwanda) and a vitric Andosol (São Tomé and Principe). Both soils are slightly acid. The silandic Andosol is rich in active aluminium forms, while the vitric Andosol has high amounts of crystalline iron and aluminium oxides. Sorption isotherms were determined by equilibrating at 293K soil samples with phosphate solutions of concentrations between 0 and 100 mg P L−1 in NaNO3; phosphate was determined by visible spectrophotometry in the equilibrium solution. To study desorption, the soil samples from the sorption experiment were equilibrated with 0.02 M NaNO3. The isotherms were adjusted to mathematical models. In almost all the concentration range, the adsorption of phosphate by the silandic Andosol was greater than 90% of the amount added, being lower in the vitric Andosol but always higher than 65%. The high sorption by the silandic Andosol is attributed to its richness in non-crystalline Fe and Al, while in the vitric Andosol crystalline iron species seem to play a relevant role in the adsorption. The sorption isotherms of both soils fitted to the Temkin model, the adjustment to the Langmuir or Freundlich models being unsatisfactory; throughout the range studied, the sorption increases with increasing phosphorus concentration, a maximum sorption is not predictable (as occurs when the sorption is adjusted to the Langmuir model). For an added P concentration of 100 mg L−1 (3.2 mmol L−1), the sorption is 47.7 µmol P g−1 in the silandic Andosol and 41.6 µmol P g−1 in the vitric Andosol. The desorption is low and the comparison of the sorption and desorption isotherms reveals a pronounced hysteresis, that is, the irreversibility of the sorption. The high phosphate sorption and its irreversibility are comparable to those published for other volcanic soils with high contents of allophane, active aluminium and free iron. The strong phosphate adsorption is a serious limiting factor for plant growth, which requires a careful management of phosphorus fertilization.


Author(s):  
Adrian Valdez ◽  
Sergio Covarrubias

The Andes range in Ecuador presents high biodiversity and characteristic altitudinal gradients, which are frequently threatened by deforestation and farming. In particular, forest have developed in the high inter-Andean alley on volcanic soils forming a unique ecoregion. Little is known on the fungal biodiversity of soil in such high Andean gallery forest submitted to strong degradation pressures. Therefore, in this study we evaluated wether the soil mycobiome was associated with altitudinal gradients during the dry season. Three representative locations were selected based on altitude: A (3,309 meters above the sea level, masl), B (3,809 masl) and C (4,409 masl). High performance sequencing (NGS) of the ITS region of ribosomal DNA genes with Illumina technology was used to explore the fungal taxonomic composition in the soil samples. Our results showed changes in the structure of fungal communities in the different locations, related to the relative abundance of Amplicon Sequence Variants (ASV). Higher fungal diversity was related with the altitudinal gradient with average taxa ranging from 675, 626 and 556 ASVs, respectively from location A to C. The results highlight the complexity and diversity of fungal communities in high Andean forest and the need to protect these unique mycobiomes. The findings in this ecosystem of Ecuador will improve our understanding of distribution, diversity, ecology, and biological perspectives for the restoration of terrestrial microbiomes.


1999 ◽  
Vol 65 (6) ◽  
pp. 2307-2311 ◽  
Author(s):  
R. R. de Moraes ◽  
J. E. Maruniak ◽  
J. E. Funderburk

ABSTRACT Two methods, phenol-ether and magnetic capture-hybridization (MCH), were developed and compared with regard to their sensitivities and abilities to extract the DNA of the insect baculovirus Anticarsia gemmatalis nucleopolyhedrovirus (AgMNPV) from soil and to produce DNA amplifiable by PCR. Laboratory experiments were performed with 0.25 g of autoclaved soil inoculated with different viral concentrations to optimize both methods of baculovirus DNA extraction and to determine their sensitivities. Both procedures produced amplifiable DNA; however, the MCH method was 100-fold more sensitive than the phenol-ether procedure. The removal of PCR inhibitors from the soil appeared to be complete when MCH was used as the viral DNA isolation method, because undiluted aliquots of the DNA preparations could be amplified by PCR. The phenol-ether procedure probably did not completely remove PCR inhibitors from the soil, since PCR products were observed only when the AgMNPV DNA preparations were diluted 10- or 100-fold. AgMNPV DNA was detected in field-collected soil samples from 15 to 180 days after virus application when the MCH procedure to isolate DNA was coupled with PCR amplification of the polyhedrin region.


2019 ◽  
Vol 98 ◽  
pp. 04008
Author(s):  
Christelle Latrille ◽  
Aubéry Wissocq ◽  
Catherine Beaucaire

To predict Zn behaviour in soil, the retention properties of clay minerals plays a relevant role. In a continental environment, Ca is the main cation in solution. Soil reactivity may be reduced to sorption properties of Zn and Ca on illite and smectite, the major clay minerals in soil. With this assumption, a multi-site ion exchanger model has successfully been applied to the Zn sorption on Ca-illite and Ca-smectite. New batch experiments performed in this study enabled to collect sorption data for Zn on Ca-illite by concentration and pH isotherms. Zn sorption reversibility was then verified. These sorption data were modelled successfully with a multi-site ion exchanger (MSIE) formalism by using four sorption site types. Zn sorption isotherms on smectite were retrieved from literature and interpreted following the MSIE formalism. The obtained selectivity coefficients may be thereafter put into ion exchange models to describe the Zn sorption in natural environments.


1991 ◽  
Vol 35 (1) ◽  
pp. 116-129 ◽  
Author(s):  
Charles E. Jones

AbstractThe characteristics of a new type of rock varnish from the hyperarid coastal deserts of northern Peru, combined with laboratory experiments on associated soil materials, provide new insights into the formation of rock varnish. The Peruvian varnish consists of an Fe-rich, Mn-poor component covering up to 95% of a varnished surface and a Fe-rich, Mn-rich component found only in pits and along cracks and ridges. The alkaline soils plus the catalytic Fe oxyhydroxides that coat much of the varnish surfaces make the Peruvian situation ideal for physicochemical precipitation of Mn. However, the low Mn content of the dominant Fe-rich, Mn-poor component suggests that such precipitation is minor. This, plus the presence of abundant bacteria in the Mn-rich varnish and the recorded presence of Mn-precipitating bacteria in varnish elsewhere, suggests that bacteria are almost solely responsible for Mn-precipitation in rock varnish. A set of experiments involving Peruvian soil samples in contact with water-CO2 solutions indicates that natural fogs or dews release Mn but not Fe when they come in contact with eolian materials on rock surfaces. This mechanism may efficiently provide Mn to bacteria on varnishing surfaces. The lack of Fe in solution suggests that a large but unknown proportion of Fe in varnish may be in the form of insoluble Fe oxyhydroxides sorbed onto the clay minerals that form the bulk of rock varnish. The results of this study do not substantively change R. I. Dorn's paleoenvironmental interpretations of varnish Mn:Fe ratios, but they do suggest areas for further inquiry.


2014 ◽  
Vol 79 (1) ◽  
pp. 89-100 ◽  
Author(s):  
Marijana Kragulj ◽  
Jelena Trickovic ◽  
Bozo Dalmacija ◽  
Ivana Ivancev-Tumbas ◽  
Anita Leovac ◽  
...  

In this study, the sorption behaviour of 1,3-benzothiazole (BT) and 2-(methylthio)benzothiazole (MTBT) was investigated on Danube geosorbent under equilibrium and nonequilibrium conditions. All sorption isotherms fitted well with the Freundlich model (R2=0.932-0.993). The results showed that organic matter of the Danube geosorbent has a higher sorption affinity for the more hydrophobic MTBT compared to BT. However, sorption-desorption experiments showed that MTBT was more easily desorbed than BT molecules, which indicates the importance of absorption relative to adsorption in the overall sorption mechanism of MTBT. In general, molecules of BT and MTBT were more easily desorbed in the lower concentration range, which resulted in an increase in the hysteresis indices with increasing concentrations. Column experiments revealed that retention of the investigated compounds on the aquifer material followed the compound?s hydrophobicity. BT showed a lower retention, in accordance with its lower sorption affinity obtained in the static experiments, while MTBT showed a greater sorption affinity, and thus had a longer retention time on the column. Thus during transport BT represent greater risk for groundwaters than MTBT. These results have increased our understanding of benzothiazoles sorption and desorption process which represent one of the most important factors which influence the behaviour of organic compounds in the environment.


Author(s):  
S.M Adeyinka

The effects of palm oil contaminant on the soaked California Bearing Ratio (CBR) of subgrade was investigated. The following objectives were set out in accordance with BS 1377: 1-8 (1990) and BS 1924 (1990); Particle Size Distribution, Atterberg Limits, Compaction and California Bearing Ratio for oil-palm contaminated and uncontaminated subgrade. Palm oil and four soil samples are used in this research work. The air-dried samples were contaminated with oil-palm at 0, 2,4, 6, 8 & 10% of the dry weight of the samples for 7 days thereafter air-dried for another 7 days. Laboratory experiments on the control (0%) and palm oil-contaminated subgrade samples were conducted after 24 hours of soaking the samples in accordance with BS 1924 (1990). It was found that the soaked CBR for the contaminated soil showed a lower values (17.45%, 24.80%, 49.50% and 21.50%) than the control CBR values (48.20%, 138.40%, 160.00 and 132.10%) for sample A, B, C and D respectively. It is therefore concluded that palm oil has a negative effect on the geotechnical properties and the mechanical strength of the soil hence it is not suitable in any Civil Engineering work.


2011 ◽  
Vol 64 (8) ◽  
pp. 1716-1722 ◽  
Author(s):  
J. M. Tapia ◽  
J. A. Muñoz ◽  
F. González ◽  
M. L. Blázquez ◽  
A. Ballester

The aim of this study was to assess the sorption of Fe(III) by extracellular polymeric substances (EPS) of the Acidiphilium 3.2Sup(5) bacterium, which has promising properties for use in microbial fuel cells (MFC). The EPS of A. 3.2Sup(5) was extracted using EDTA. The sorption isotherms were determined using aliquots of purified EPS. The exosubstances loaded with metal were characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction spectroscopy (XRD) and Fourier transform infrared spectroscopy (FTIR). The sorption uptake approaches to 536.1 ± 26.6 mg Fe(III) (g EPS)−1 at an initial ferric concentration of 2.0 g l−1. The sorption of Fe(III) by EPS can be fitted to the Freundlich model. The sorption process produces hydrated iron (III) oxalate [Fe(OH)(C2O4) × 2H2O] by a reversible reaction (log K = 1.06 ± 0.16), indicating that a shift in the sorption of the cation can be easily achieved. Know the magnitude and form of iron sorption by EPS in MFC can foresee the potential impact on the metabolism of iron-reducing and iron-oxidazing bacteria and, therefore, on the feasibility of the system.


2017 ◽  
Vol 13 ◽  
pp. 393-404 ◽  
Author(s):  
Elisa Biondi ◽  
Yoshihiro Furukawa ◽  
Jun Kawai ◽  
Steven A Benner

The prebiotic significance of laboratory experiments that study the interactions between oligomeric RNA and mineral species is difficult to know. Natural exemplars of specific minerals can differ widely depending on their provenance. While laboratory-generated samples of synthetic minerals can have controlled compositions, they are often viewed as "unnatural". Here, we show how trends in the interaction of RNA with natural mineral specimens, synthetic mineral specimens, and co-precipitated pairs of synthetic minerals, can make a persuasive case that the observed interactions reflect the composition of the minerals themselves, rather than their being simply examples of large molecules associating nonspecifically with large surfaces. Using this approach, we have discovered Periodic Table trends in the binding of oligomeric RNA to alkaline earth carbonate minerals and alkaline earth sulfate minerals, where those trends are the same when measured in natural and synthetic minerals. They are also validated by comparison of co-precipitated synthetic minerals. We also show differential binding of RNA to polymorphic forms of calcium carbonate, and the stabilization of bound RNA on aragonite. These have relevance to the prebiotic stabilization of RNA, where such carbonate minerals are expected to have been abundant, as they appear to be today on Mars.


1990 ◽  
Vol 212 ◽  
Author(s):  
Hanskarl Brühl ◽  
Asaf Pekdeger ◽  
Andreas Winkler

ABSTRACTIn laboratory experiments immobilisation of Tc under oxic conditions was observed. The transport behaviour of redox-sensitive elements is not only controlled by the geochemical “frame conditions” which can be measured within the macro environment. Immobilisation behaviour of Tc strongly depends on micro environments and on microbial metabolism. Micro environments which may develope on the mineral surfaces can detoriate the mobility of Tc, furthermore the fixation of Tc is influenced by microbial activities.


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