U-Mate Int. Natural Organic Humates

Potential Applications of Humates In Environmental Engineering

1.ORIGIN AND PROPERTIES OF HUMATES

1.1. ORIGIN OF HUMIC SUBSTANCES

The formation of humic substances (humus) begins when organic residues of plants and animals come in contact with microbial life in the soil. The carbon compounds contained in the residues, that were synthesized by the plant or animal when it was alive, supplying protein and energy for the various bacteria, fungi, and other microorganism involved in the decay process.

During humification of organic matter, microbes utilize Carbon compounds for their own metabolism. The assimilation of these nutrients from the original residues by microorganisms is the first stage in the process of creating humus. Much of the nutrient and energy assimilated into the bodies of microbes is re-used be other microbes when they die. Some is mineralized back into plant food and some is change not biological resist and compounds that accumulate as components of humus.

Plants create organic matter which feeds soil organisms which transform the nutrients from the residues back into plant food and nutrients for other organisms. The undigested portion of the residue accumulates as humus. Humus is, however not completely immune to decomposition. microbes will eventually recycle all elements in humus back to where they initially came from, even if it takes a millennium to do it. therefore humus never remains in a static condition and undergoes constant but very slow changes.

The properties of humus depends on the properties of the soil and weather conditions. As the temperature of a soil increases a rate of organic matter decomposition and decrease as accumulation of humus. Thus soils in warmer regions of the earth tend to have lower levels of humus than soils in colder areas.

When decomposed organic matter reaches a certain level of humification and can be referred as humus it gains colloidal properties similar to those of mineral colloids. The most important of these properties is cation exchange capacity (CEC) that allows humic substances absorb many metal cations such as potassium, calcium, and magnesium.

Humic substances are a mixture of complex organic compounds that are usually separated into three fractions that can be isolated from soil:

Humic acids: the fraction of humic substances that is not soluble in water under acidic conditions (pH<2.) but is soluble at higher pH values;

Fulvic acids: the fraction of humic substances that is soluble in water under all pH conditions;

Humins: the fraction of humic substance that is not soluble in water at any pH value.

The main fraction of humus are humic acids and their salts HUMATES. A rich soil with a near neutral pH would contain a high level of humates. Whereas the same soil with a low pH would be replete with humic acids.

Humates products that ore on the market are actually mixtures of humic acids, Humates fulvic acids and other organic and inorganic substances. The quality of these products is usually defined from a content of soluble humic acids using extractions procedures. Most sophisticated methods are also developed that examine important characteristics of humic acids, particularly content of quinine, carboxyl, phenolic, and amino groups as well as condensed aromatic nucleuses.

1.2 PROPERTIES OF HUMATES

Humic acids are defined as complex aggregates of brown to dark colored amorphous high molecular weight substances, united by general principle of structure, but have some distinctions, which depends on their origin. As chemical functions they contain corboxylic, phenolic, amino and quinone with aromatic nucleuses of low degree of condensation which are incorporate by parts of non aromatic character. The presence of aromatic nucleuses with mobile p-type electrons and various functional groups cause the ability of humic acids to ionic exchange, complex formation and oxidizing-reduction reactions.

Humic acids are collids and behave somewhat like clays, even through the nomenclature suggests that they are acids and from true salts. When the cation exchange suites on the humic molecule are filled predominantly with hydrogen cations, the material is considered to be an acid and is named accordingly. However, it has no great effect on pH because the acid is insoluble in water. When the predominant cation on the exchange sites is other than hydrogen, the material is called humate. The humates of monovalent alkali metals (e.g. sodium, potassium) are soluble in water, but humates of multivalent metals (e.g. calcium, magnesium, iron) as well as heavy metals are insoluble. apart from their effect on the solubility the materials and their absorption by clays, the different cations have little effect on the humic molecules.

Humis substances are predominantly negatively charged due to the abundance of carboxylic and phenolic groups. Due to the hydration of the charged groups and electrostatic repulsion between the charges the dissolved humic substances can be distribed by an extended conformation that adjusts itself due to changes in the environmental conditions.

Humic substances are generally seen as important soil and fresh water components. They are generally recognized as the component that is often responsible for the binding of the major part of the available metal ions. Humis substances can also be dissolved or bound to other soil components. The absorption of humic matter onto the mineral particles may influence the speciation and mobility of these dissolved entities and influence the binding of metal ions to these components.

The majority of data on humates application is related to agriculture. It has been found that humates simultaneously influence all components of future harvest: water, soil and plant. Penetrating the water, humates change is structure so that it becomes more organized and arranged like fragments of ice structure. As a result the water become more solvent of minerals and thus improving plant nutrition. Penetrating the soil, humates restore its structure: convert soluble forms of heavy metals and other harmful, radioactive and environmentally dangerous chemicals into insoluble forms. Thus preventing their introduction into the food chain. In addition, humates form complexes with phosphorus and micro elements which are easy assimilated by plants, increasing efficiency of application mineral fertilizers.

Demonstrate results of the use of humates indicate increase of harvest of all agricultural products. Practical experience of humate use in Russia and other former USSR republics has confirmed a significant harvest increase in the range 15 - 60%. It has also been found that humates increase the quality of agricultural products, increasing the content of nutritious elements.

2. ENVIRONMENTAL APPLICATIONS OF HUMATES

2.1 Interaction of Humic Substances with Environmental Contaminants.

Environmental scientists have become interested in humic substances for a long time because of their interactions with soil and water pollutants and their influence on treatment processes. There are, however very few reports on practical applications of humates in environmental engineering. Most of them utilize humates to remove metals from water or immobilized heavy metals in soil.

Interaction between humic substances and hazardous-wastes chemicals is most likely to occur when such chemicals have been disposed of underground. A major factor in considering interaction of humic substances with waste chemicals is the solubility of the humic materials,which depends predominantly on the acid-base precipitation behavior of these substances. The most likely route for mobilization of large quantities of humic material is through contact with strong caustic wastes, such as discharge from removal of sulfur from petroleum products. Humic substances in solution can be precipitated by contact with acidic wastes or by contact with multiple charged metal ions, most likely calcium or magnesium.

The ability of humic substances to act as chelating agents for metal ions is well documented. The particular effects of that humic substances have on chelatable metals in hazardous wastes depend upon the following factors:
- the nature of the humic substances
- the chemistry of soil or water environment with respect to acidity - alkalinity and oxidation - reduction
- the presence of competing species (e.g. cyanide that compete with humic ligands for metal ions)

In some cases the chelation pf ,metal ions as soluble humis species may prevent precipitation of the metals by precipitate-forming anions such as carbonate, hydroxide or sulfide. It has been reported that the presence of humic acids can increase solubility of mercury by a factor of 1000. Thus removal of metals from water with humic substances using precipitation may not be effective.

The other major influence of humic substances on metal speciation is through oxidation-reductions reactions. This can occur in two major ways.

1) humic acid can function as a reducing agent with reducing potential (E0 = 0.7 V) similar to that for ferrous cation (E0 = 0.77 V)
2) humic acid can stabilize to reduced catonic form of metal by chelation thus enhencing reduction of oxoanions (e.g. Cr2O72-: MoO42-)

Humic acid has been reported to reduce ionic mercury to elemental mercury. The accumulation of vanadium and molibdenum in peats (which are humic materials) and coals (transformed humic materials) has been attributed to the reduction of humic substance of soluble VO3- and MoO42- to chelatable catonic species.

The reduction of acidic iron (III) to iron (II) and subsequent retention of the iron (II) product in bituminous coal has also been demonstrated. This phenomenom can be utilized in remediation of chlorinated organic compounds since iron (II) is an efficient dechlorinating agent.

The transport, reactivity and fate of nonpolar organic compounds in the aquatic and terrestrial environments are influenced by their association with dissolved, colloidal, and undissolved humic substances. The degree pf association in particular compound is affected by the nature of the compound and humic material, the concentration of both, pH, calcium concentration and the presence of other organic and inorganic solutes.

2.2 Reported Applications of Humic Substances in Environmental Engineering

Based on available data on humic acids or humates the following applications of these substances are possible:

1. Neutralization of acid wastewater with humates, accompanied by the formation and settling of insoluble humic acids.

2. Removal of heavy metals by chelation or precipitation as insoluble humates.

3. Removal anions, such as phosphates, cyanide and organic anions by mixed ligand complexation.

4. Sorption of toxic organics from water in order to enhance biological treatment of wastewater streams.

5. Clarification of suspended matter by precipitation and flocculation of humic acids and insoluble metal humates.

Humates an be used as a main remedy or as a part of more complex treatment in various environmental engineering technologies applied to wastewater, groundwater, leachates and soil. They potentially can replace activated carbon and other organic and inorganic adsorbent.

Application of humates for absorption of toxic organic compounds is particularly interesting since organic compounds may not only be immobilized on humates but also incorporated into the humate chemical structure. Thus desorption would not be necessary.

Preliminary respirometric tests conducted indicate that humates can enhance removal of phenols, oils and copper in biological system. They also revealed that humates can support growth of the biomass as carbon source. The extend of this phenomenon depends however on biomas/humate ratio.

REFERENCES

Abbott, G. A. Leonardite - A Material of Industrial Promise. US Bureau of Mines Circular #8164, 1963.

Aiken, G. R., McKnight, D. M., Wershaw, R.L. and McCarthy, P. (Editors). Humic Substances in Soil, Sediment and Water: Geochemistry, Isolation and Characterization. Wiley-Interscience: New York, 1985.

Choudhry, G. C. Humic Substances: Structural, Photophysical, Photochemical and Free Radical Aspects and Interactions with Environmental Chemicals. Goedon and Breach Sci. publ., New York 1984.

Christman, R. F. and Gjessing, E. T. (Editors). Aquatic and Terrestrial Humic Materials. Ann Arbor Science, 1983.

Lesage, S., Xu., H., Novakowski, K. S. and Brown, S. The Use of Humic Acids to Enhance the Removal of Aromatic Hydrocarbons from Aquifer Contaminated with Petroleum Products. Extended Abstracts for the Special Symposium of the Industrial and Engineering Chemistry Division, September 9-11, 1996, Bringham Alabama. American Chemical Society pp.743-746

Levinsky, B. V. Humates are Guarantee of Fertility and Environmental Safety of Agricultural Products. Technical Paper at the Internet Site:

MacComish, M. P. and Ong, J. H. Mercury. In: Environmental Inorganic Chemistry. Properties, Processes and Estimation Methods. SETAC Special Publication Series, Peergamon Press, New York, 1988.

Manahan, S E. Interactions of Hazardous-Wastes Chemical with Humic Substances. In: Suffet, I.H. and McCarthy, P. (Editors). Aquatic Humic Substances. Influence on Fate and Treatment of Pollutants. American Chemical Society, Advances in Chemistry Series 21, Washington, DC, 1989, pp. 83-92.

Sachs, P. Humus: Still a Mystery. Technical PAper at the Internet Site: http://usets.ids/~nofari/tnf_hums.htm

Senn, T.L. and Kingman, A. R. A Review of Humus and Humic Acids. Research Series No. 145. South Carolina Agricultural Experiment Station, Clemson University, Clemson S.C., 1973

Suffet, I.H. and McCarthy, P. (Editors). Aquatic Humic Substances. Influence on Fate and Treatment f Pollutants. American Chemical Society, Advances in Chemistry Series 21, Washington, DC, 1989.

Vermeer, R. Interactions Between Humic Acids and Hermatite and Their effects on Metal Ion Specialization. PhD. Thesis on the Internet:

Vermeer, A. W.P., van Rjemsdijk, W.H. and Koopal, L.K. Interactions Between Humic Acid and Mineral Particles. Langmuir 14 (10) pp. 2810-2819,1998.