ADVANCES IN FRACTIONATION AND CHARACTERIZATION OF NATURALLY OCCURING

ORGANO-CLAY COMPLEXES

Sankhadip DasRoll No -10538

Division of Soil Science and Agricultural Chemistry

Indian Agricultural Research InstituteNew Delhi-110012

1.Introduction

2.Nature of organo-clay complexes

3.Fractionation of organo-clay complexes

4.Characterization of organo-clay complexes

5.Research Findings

6.Conclusion

7.Path ahead

Contents

IntroductionThe soil clay-humus complex plays an important role in forming the structure and fertility of agricultural soils Stevenson (1982)

“Clay-associated organic matter as all organic matter present in the clay-sized fraction, both free organic particles and organic matter bound to minerals

Wattel-Koekkoek & Buurman (2004)

‘Primary structure of soils as defined by the soil texture resulting from the association of organic matter (OM) with primary mineral particles, and as complexes that are isolated ‘after complete dispersion of soils’

Christensen (1996)

Secondary organo-clay complexes were defined as the aggregation of several primary organo-mineral complexes

Nature of Organo Clay Complexes

Clay-organic complexes enriched in top soils are the main reservoirs of plant nutrients.

Organo-clay complexes are the adsorption products between the organic cations anions or molecules transfered from solutions , liquid or gaseous states to clay surfaces generally due to the physical or chemical bonds ( long or short range respectively).

Organo-clay complexes are conglomerate soil colloid in which clay, oxides/hydroxides (including sesquioxides and allophanes) and humic material remain associated.

The types and amount of layer silicates, intercalation of OM, content of pedogenic oxides, soil properties, vegeatation , etc are decisive in the formation of clay-organic bonds.

Fractionation of Naturally Occurring Organo - clay

complexes

Physical Fractionation Techniques

Density Fractionation

Aggregate fractionation

Particle size fractionation

Centrifugation

Gravity sedimentation

High-gradient magnetic separation (HGMS)

Size exclusion chromatography

Physical fractionation methods in the strict sense include size and density separation of primary organo–mineral complexes in whole soil, which means that aggregates are not considered (Christensen, 1992).

Chemical fractionation techniques

Extraction of Soil Organic Matter in aqueous solutions with and without electrolytes

By use of organic solvents

By hydrolysis of organic matter

By oxidation of organic matter

Characterization of Organo- clay complexes

13C nuclear magnetic resonance spectrocopy (13C-

NMR) X ray diffraction analysis

Transmission electron microscopy analysis

Scanning electron microscopy analysis Near -edge X ray absorption fine structure spectroscopy

Fourier transform infrared spectroscopy (FTIR)

Thermal analysis .

Nuclear magnetic resonance spectroscopy

The first attempt to use nuclear magnetic resonance (NMR) spectroscopy for structural characterization of soil humic substances was reported by Barton and Schnitzer (1963) and Neyroud and Schnitzer (1972).

13C-NMR can used to determine the number of non-equivalent carbons and to identify the types of carbon atoms(methyl, methylene, aromatic, carbonyl….) which may present in compound.

When energy in the form of radiofrequency is applied

When applied frequency is equal to precessional frequency

Absorption of energy occurs

Nucleus is in resonance

NMR signal is recorded

Principle of NMR

Thermal Analysis

Thermal method of analysis are group of techniques in which changes in physical and /or chemical properties of a substance are measured as a function of temperature, while substance is

subjected to controlled temperature programmed

Mass

ΔT ΔH

Deformation

Gas decompose

Thermal diffusivity

Volume

PhysicalPropertie

s

Differential Scanning Analysis

Differential Thermal Analysis

Dynamic Mechanical

Analysis

Laser Flash Analysis

Dilatometry

Evolved Gas Analysis

Thermo Gravimetric Analysis

Techniques most commonly used :

1. Thermo-microscopy2. Differential thermal

analysis

3. Differential scanning calorimetry 4. Thermo-gravimetry

Thermo gravimetric analysis (TGA)

It is an analysis, the mass of sample is recorded continuously as its temperature is increased linearly from ambient to high temperature.

Mass of material a functions of temperature.

Processes occurring without change in mass (e.g.- Physical transitions ) cannot be studied by TG

Differential Thermal Analysis(DTA)

Heat absorbed or emitted by sample is observed by measuring the temperature difference between that sample and reference compound as temperature of both are increased.

ΔT =TS -Tr as function of Temperature.

Temperature of furnace

The technique was developed by E.S. Watson and M.J. O'Neill in 1960, and introduced commercially at the Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy in 1963

Differential scanning calorimetry

X-ray diffraction is based on constructive interference of monochromatic x-rays and a crystalline sample.

The interaction of incident rays with the sample produces constructive interference when conditions satisfy Bragg’s law.

X ray Diffraction

nλ=2dsinθ

Fourier Transformed Infra-Red Spectroscopy

FTIR collects all wavelengths

simultaneously and scans at once. FTIR works based on Michelson

Interferometer which having Beam splitter Fixed mirror Movable mirror

Transmission electron microscopy

Transmission electron microscopy (TEM) has seldom been used in soil organic matter research, although it showed the variety of OM morphology found in the clay-sized fraction of soils (Feller et al., 1991; Chotte et al., 1993)

The first TEM was built by Max Knoll and Ernst Ruska in 1931, with this group developing the first TEM with resolution greater than that of light in 1933 and the first commercial TEM in 1939.

Scanning electron microscopy

The first scanning electron microscope (SEM) debuted in 1938 ( Von Ardenne) with the first commercial instruments around 1965. Its late development was due to the electronics involved in "scanning" the beam of electrons across the sample

SEMs use an electron beam instead of a beam of light, which is directed towards the specimen under examination

RESEARCH FINDINGS

Study on Differential thermal analysis of Humic acids, clay and clay humus complexes from various soils

hbkk

(Ahmed et al., 2002)

DTA curves of a) Humic acids, b) clay, and c)clay –humus complexes from various soils.

Effect of rhizosphere on Organo-clay complexation

(Mandal & Datta ,2005)

DRXD analysis of vertisols and Alfisols of Rhizosphere and Non-rhizosphere

(Ahmed et al., 2002)

Study on the comparision of X-ray diffraction patterns of clay fractions and clay-humus complexes of different soils

Entisol clay

Entisol clay-humus complex

Mollisol ΙΙ clay-humus complex

Molliso ll clay

Mollisol Ι clay-humus complex

Mollisol Ι clay

Alfisol clay

Vertisol clay

Vertisol clay-humus complex

Alfisol clay-humus complex

XRD patterns of different soils

Impact of tillage and puddling operations on the stability and physico-chemical properties of clay-humus complexes

Effect of thermal activation (35oC) on changes in organic carbon content of clay –humus complexes of surface(0-15 cm) and subsurface soil(15-30 cm ) as affected by long term NT and T treatments

(Vennila and Datta .,2008)

Contd….

Effect of thermal activation (35oC)on changes in organic carbon content of clay–humus complexes of surface(0-15 cm) and subsurface soil(15-30 cm ) as affected by long term NP and P treatments.

Solid state 13C NMR spectra of the source HA (SHA) and the unadsorbed HA (humic acid) fractions after coatingon kaolinites (HAKs), montmorillonites (HAMs) and goethites (HAGs). (Ghosh et al ., 2009)

Study of fractionation behavior of Humic Acid upon sorption on mineral surfaces with varying surface properties.

Study of organo clay complexes obtained from various soils by Transmission electron microscopy

(Ahmed et al., 2002)

TEM images of clays and clay-humus complexes of Entisol (a,b,c) & Mollisol Ι (d,e,f) respectively

Contd…

TEM images of clays and clay-humus complexes of Alfisol(g,h), Vertisol (i,j) & Mollisol ΙΙ (k,l) respectively

Scanning electron microscopy (SEM) images of (a) natural bentonite and (b) HDTMA-bentonite.

Effect on natural bentonite on modification with Hexadecyltrimethylammonium(HDTMA) bromide

(Ikhtiyarova et al., 2012)

Study on the structural arrangement of Humic acids isolated from different soils of China

SEM images of the HAs samples.(Xu et al., 2006)

ConclusionDXRD analysis helped in the better study of stability of the organo-clay

complexes not possible by conventional XRD techniques

The NMR results show a semi quantitative distribution of different carbon

moieties in the original HA and HA fractions obtained after coating.

SEM micrographs was able to show the surface changes of natural

bentonite on application of surfactant resulting in rough appearance of

surface

TEM micrographs helped in the identification of clay minerals of various

nature in different typesof soils

Stability of organo-clays was seen to be increased with depth in both

puddling and tillage conditions.

Path AheadMore studies on the nature of natural organo -clay complexes are to be conducted in comparision to synthetic ones

Surfactant studies of humic acids fractions of organo-clay complexes have to be carried out on a large scale

Studies regarding the influence of soil micro-organisms on the complexity mechanism between organic matter and clay minerals will help in greater understanding of the nature of organo-clay complexes

Modern techniques are to be used by replacing the conventional and traditional techniques in order to get a good understanding on the characteristics of organo-clay complexes