ISO 157:1996 pdf download

ISO 157:1996 pdf download.Coal – Determination of forms of sulfur
1.1 Scope
This International Standard specifies methods of determining the sulfate and pyritic sulfur contents of coals, including brown coals and Iignites, and of calculating the amount of organic sulfur present.
1.2 Normative references
The following standards contain provisions which, through reference in this text, constitute provisions of this International Standard. At the time of publication, the editions indicated were valid. All standards are subject to revision, and parties to agreements based on this International Standard are encouraged to investigate the possibility of applying the most recent editions of the standards indicated below. Members of IEC and IS0 maintain registers of currently valid International Standards.
IS0 331 :I 983, Coal – Determination of moisture in the analysis sample – Direct gravimetric method.
IS0 334:1993, So/id mineral fuels – Determination of total sulfur – Eschka method.
IS0 351 :I 995, So/id mineral fuels – Determination of total sulfur – High temperature combustion method.
IS0 1015:1992, Brown coals and /ignites – Determi-nation of moisture content – Direct volumetric method.
IS0 1170:1977, Coal and coke – Calculation of analy-ses to different bases.
IS0 1988: 1975, Hard coal – Sampling.
IS0 5068:1983, Brown coals and /ignites – Determi-nation of moisture content – Indirect gravimetric method.
1.3 Principle
The procedure described in this International Standard utilizes the differential solubilities of sulfates and pyrites in dilute hydrochloric and nitric acids under reflux conditions, such that each can be taken in solution successively and determined directly. A general schematic representation of the procedure is given in figure 1.
1.4 Preparation of the test sample
The test sample is the general analysis test sample prepared in accordance with IS0 1988 or IS0 5069-2, as appropriate. Grind about 25 g of the sample to pass a sieve of aperture 75 urn and ensure that its moisture content is in equilibrium with the laboratory atmosphere, exposing it if necessary in a thin layer for the mini- mum time required to achieve equilibrium. Before commencing the determination, thoroughly mix the test sample for at least 1 min, preferably by mechanical means. If the results are to be calculated other than on an air- dried basis (see 6.1) then, after weighing the test portion (see 2.41, determine the moisture content using a further portion of the test sample by the method described in IS0 331, IS0 1015 or IS0 5068, as appropriate.
2.1 Principle
The test portion is extracted with dilute hydrochloric acid to bring both the sulfate sulfur and the non-pyritic iron into solution. The pyritic iron and sulfur remain in the residue which is separated by filtration.