EURO-ECO 2007 Hanover 4 - 5 December 2007	Environmental and Engineering Aspects for sustainable living
	European Academy of Natural Sciences, Hanover European Scientific Society, Hanover Russian Academy of Natural Sciences, Moscow

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The rainfalls in many heavily industrialized regions of the world produce an acid reaction with a mean pH near 4,0-4,5, which is believed to have destroyed the environmental ecological balance. The widely spread precursors of acid rains are sulphur dioxide and the fine sulphate mist into which sulphur dioxide is readily transformed. The chief sources of sulphur dioxide formation are: sintering plants, heating and power plants, concentration plants.

At present time total annual sulphur dioxide emissions totaled some 300 million tons. The acid rains problem comes largely from the transport of polluted air masses, containing sulphur dioxide, over distances of thousands of kilometers from one region to another, from one country to another depending on the wind direction.

The highly efficient limestone process which has been worked out by Russian and Ukrainian specialists solves the problem of avoiding atmospheric pollution by sulphur dioxide and sulphates without any waste sludge and with considerable reduction of waste water. The general principle of gas scrubbing consists in the absorption of sulphur dioxide by limestone in a highly efficient scrubber. The absorbing suspension circulates in the system and part of it regularly withdrawn into the sludge tanks and replaced by some fresh suspension.

In this process of gas scrubbing, 85% of sulphur dioxide and up to 90% of the sulphur dust are removed from the latter. The coefficient of limestone utilization is 50%. According to the freeing process, the slurry consisting of a mixture of limestone, calcium sulphate and sulphite is pumped into the thickener and the sludge is then conveyed to the dehydration and a drying chamber.

The results of our laboratory and field investigations during several years shown clearly that the finished product of sulphur dioxide removal, i.e. the dried sludge, is an effective fertilizer-ameliorant in widely spread soil and climatic conditions. The reason of sludge action as ameliorant-fertilizer consists in the specific construction of every sludge particle which can be divided into three spherical parts. The first external part is calcium sulphite. The second intermediate part is calcium sulphate. The third internal part is unreacted calcium carbonate. Chemical investigations have shown that the open air conditions promote rapid oxidation of the calcium sulphite contained in the sludge to calcium sulphate. Thus, finally sludge particles consist of two parts – external calcium sulphate and internal calcium carbonate with the ratio of carbonates to sulphates is maintained at 1:0,6.

Every sludge particle applied in soil interactes with different chemical compounds. This interaction begins from the contact of the external part of the sludge particle (calcium sulphate) with the soil..It was found that in presence of available sulphate and ammonium ions in soil solution calcium sulphate can rapidly increase its solubility due to formation of the soluble complex compound, ammonium calcium disulphate. This process provides the liberation of the internal part of sludge particles – calcium carbonate. This compound not only executes the main function in reducing the soil acidity but allows the possibility to uptake by plants such important nutrients as ammonium and calcium. Results obtained in field experiments give the possibility to confirm stable and significant positive influence of sludge applying on crop yield levels. The yields of grain and fodder crops are increased by 25-50% during 4-5 years under the adding of sludge to the soil in optimum doses calculated dependently on soil acidity.

Thus, the desulphurization of sinter-gases enables not only to prevent acid rains and remove its results, but to create an ecologically clean industrial cycle without any waste products.