Sulphur oxidisers

When pyrites and marcasite are not distinctly crystallised it is frequently difficult to distinguish between them, as the foregoing characteristics are not clearly discernible. A convenient chemical method has been devised, however, which enables a discrimination to be made with certainty.1 It consists in boiling the mineral with iron alum, containing 1 gram of ferric iron and 16 c.c. of 25 per cent, sulphuric acid per litre. The proportion of sulphur oxidised in the case of pyrites is 60 4 per cent, of the total sulphur contained in the mineral in the case of marcasite it is only 18 per cent.2 The reaction may be considered as taking place in two stages, namely —... 

The main reaction responsible for marble decay and damage to monuments is therefore the sulphation which occurs on the surface of these materials. Oxidation of SO2 to SO3 occurs by catalytic action due to surface impurities such as FeaO. , soot, colloidal deposits, CaS04 2H 0 already formed, humidity and also to sulphur oxidising bacteria. 

Here, a simple trajectory model approach has been adopted to relate the total deposition of oxidised sulphur, oxidised and reduced nitrogen ecies to the respective emissions of sulphur dioxide, nitric oxide and ammonia. An air parcel extending from the ground surface to the top of the boundary layer is advected by the wind over the emissions grid to reach the arrival or receptor site. The pollutants within the air parcel undergo chemical transformations and are removed by dry and wet deposition. Full details of the model are given elsewhere [17]. 

Sulphate-reducing bacteria are examples of anaerobic bacteria, whereas sulphur oxidising bacteria are examples of aerobic bacteria (Figure 4.3). 

In the case of sulphur-oxidising bacteria (SOB), the colour of the corrosion products is reportedly yellow [23]. 

Phase 2 First stage of microbial succession where, provided that sufficient nutrients, moisture and oxygen exist, some species of sulphur-oxidising bacteria (e. g., Thiobacillus sp.) can attach themselves onto the concrete surface and grow. Mostly, these species of SOB are neutrophilic sulphur-oxidising bacteria (NSOM). These bacteria produce some acidic products and convert the sulphides present to elemental sulphur and polythionic acids. 

Phase 3 The second step of microbial succession, it normally follows Phase 2 where the pH has been reduced fairly. Another species of SOB known as acidophilic sulphur-oxidising bacteria (ASOM) such as T. thiooxidans colonise the concrete surface and further reduce the acidity. It has been proposed that during Phase 2 the NSOM reduces the pH to 4.0 where during Phase 3, the pH is further reduced by the ASOM to 1.0 or 2.0 [28]. 

Studies show that microbial succession can start with very low numbers of both types of the sulphur-oxidising bacteria so that MID can develop completely [27]. Quoting from Bock and Sands work, Rogers et al. reported that a cell density of chemolithotrophic SOBs such as Thiobacillus of about 10 to 10 cells per grams of concrete is required before MID is detected [27]. 

The most thoroughly studied group of sulphur oxidising organisms... 

MAHMOUD S.A.Z., ZAKI M.M. and ABD-EL-HAFEX A.E., 1977. A survey of sulphur oxidising and sulphate reducing bacteria in Egyptian soils. Journal of Microbiology, 12, 15-22. 

VITOLINS M.I. and SWABY R.J. 1969. Activity of sulphur-oxidising microorganisms in some Australian soils. Australian Journal of Soil Research, 171-183. 

He2SiCl2 via PCMe-SD P on warming. Sulphur oxidises permethyl silyl... 

The Sulphur Cycle.— Unlike phosphorus, sulphur appears in both oxidised and reduced forms in the history of life. Completely oxidised as sulphate, it enters the plant from the soil, and is converted into partially reduced organic compounds containing the thiol group —SH or the disulphide linkage —S—S—. From these, the completely reduced form, HjS, is derived by bacterial degradation either in the soil or in the alimentary tract of the animal. Hydrogen sulphide is attacked by the sulphur-oxidising bacteria, with the ultimate formation of sulphate, which is available for plant absorption. 

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