UDC 631.436

Thermal analysis of humic acids of sapropels of the Kondinsky lakes of Khanty-Mansi Autonomous Area 

Shpynova N. V., Chumak V.A. Sartakov M.P. 

Ugra state university, Khanty-Mansiysk, Russia

Results of the thermal analysis of the humic acids emitted from sapropels of various lakes, executed with use of modern devices of the synchronous thermal analysis are given.

Keywords: sapropel, humic acid, thermal analysis. 

Use of the modern synchronous thermal analysis allows with high precision and at a small expense of a sample to obtain important data on process of thermal decomposition of humic acids of various genesis [2].

Samples of sapropels for receiving humic preparations were selected from the top layers of ground deposits of five various lakes of Khanty-Mansi Autonomous Area located in the Kondinsky area. Extraction of humic acids was carried out by earlier described technique [1]. The ash-content of preparations doesn't exceed 2,28%.

The thermal analysis was carried out on the thermogravimetric TGA/SDTA 851e analyzer (firm METTLER TOLEDO STAR, Germany) at a free access of air to oven space.

The Differential Scanning Curves (DSC) of the chart of humic acids of sapropels, apparently from figure 1, give an idea of the thermal effects which are taking place at high-temperature oxidizing decomposition of these samples.

Рисунок 1 – the DSK-chart of humic acid of sapropel

It is easy to notice that thermal destruction causes a row ekzo-and the endothermic effects testifying to gradual destruction of a molecule. In its structure two sharply various parts on thermal stability are distinctly allocated: the nuclear aromatic (is steadier) also lateral aliphatic chains for which smaller heat stability is characteristic considerably. High intensity of exothermic reactions between 500 and 600 0C is caused by destruction of nuclear part, endothermic and exothermic effects in the field of low temperatures (60 – 400 0C) are connected with changes and gradual destruction of peripheral part.

Sizes of warmth of combustion depend on degree of a benzoidnost of humic acids of sapropels. The division of thermal reactions of destruction of humic acids on the low-temperature and high-temperature areas, Z which were characterized by an indicator, allows to reveal structural features of humic acids of a various origin (tab. 1).

Table 1 - Data of TGA, set of humic acids of sapropels of Srednego Priobya

sample No.	Weight loss in low-temperature area (0 - 400^0С)	Weight loss in high-temperature area (400-700^0С)	Z	Ash-content, %
1	35,14	62,83	0,56	2,20
2	39,53	59,13	0,67	1,50
3	38,81	60,03	0,65	1,21
4	35,28	62,74	0,56	2,28
5	36,10	62,81	0,57	1,12

Note: Z – the relation of loss of weight in low-temperature area to weight loss in high-temperature area.

Apparently from given tables, this indicator for group of companies of sapropels changes from 0,56 to 0,67 with increase in extent of decomposition of an initial organic substratum that is more expressed at sample No. 3 group of companies.

Reduction of coefficient of Z happens at humic acids to smaller molecular weight at the expense of intensive destruction of mostikovy groups at relative accumulation of stable groups. Thus stable groups of low-molecular fractions become much less steady.

As on термограммах by us the average maximum temperature of thermoeffect in high-temperature area which made 535,4 ⁰C, and average maximum temperature in the low-temperature area, equal 346,4 ⁰C is noted.

It should be noted that with a various molecular weight the general principle of a structure of humic acids remains. from the point of view of heat stability separate fractions of. To. are presented by identical fragments for various soils and substrata of the Ob-Irtysh flood plain.

Using data thermoweight humic acids, probably, would be to present in details process of thermal destruction and experimentally to prove each of its stages if idea of a structural structure of humic acids were fuller.

According to charts ascertaining of changes in chemical structure is possible only, and about the direction of process it is possible to assume, considering data of structural chemistry in a complex with other spectral and chemical methods.

Conclusions

1. For the first time data on thermal stability of humic acids of sapropels of the Kondinsky Area of Khanty-Mansi Autonomous Area created on lakes of various type are obtained.

2. Thermal stability of humic acids of the studied objects differs, but, generally, this is characterized by existence typical for all preparations and экзо thermoeffects that confirms presence of identical structural fragments.

Literature

1. Commissioners I.D.Vliyaniye of a way of extraction of humic acids from raw materials on a chemical composition of received preparations / I.D. Commissioners, I.N.Streltsova//Nauchn. Тр. Tyumen SHI. – Tyumen, 1971. - T.14. – Page 34-48.

2 . Tikhova V.D. Use of the modern thermal analysis for research of humic acids of peat / EL of Tikhov, L. S. Sartakov, I.D.Komissarov//Humic substances in the biosphere: сб. науч. works IV of the All-Russian conference. – M: Moscow State University publishing house, 2007. – Page 203-207.