The combustion method is suitable for the determination of high and low sulfur content. After the sample is mixed with copper oxide, it is burned at high temperature (1250-1300 °), sulfur, sulfide and sulfate are condensed into sulfur dioxide, which is condensed with hydrogen peroxide and oxidized to form sulfuric acid to methyl red-sub-A The base blue is used as an indicator and titrated with a sodium hydroxide standard solution.
2CuS+3O 2 →2CuO+2SO 2 ↑
4FeS 2 +11O 2 →2Fe 2 O 3 +8SO 2 ↑
Fe 2 (SO 4 ) 3 →Fe 2 O 3 +3SO 3 ↑
2SO 3 >1000° 2SO 2 ↑+O 2 ↑
SO 2 +H 2 O 2 +H 2 O→H 2 SO 4 +H 2 O
H 2 SO 3 +2NaOH→Na 2 SO 4 +2H 2 0
If absorbed by water, sulfur dioxide combines with water to form sulfurous acid, and starch is used as an indicator to titrate with an iodine standard solution.
H 2 SO 3 +I 2 +H 2 O→H 2 SO 4 +2HI
For samples with higher sulfur content, it is more suitable to use neutralization method. For samples with lower sulfur content, the iodometric method is better.
When a large amount of molybdenum is present, molybdenum is evaporated to MoO 3 at a high temperature, and when the neutralization method is used, the alkali solution is consumed to make the result high, and the iodometric method is preferably used.
The fluorine content is high, and since the silicon fluoric acid is also consumed by the water, the alkali solution is also consumed, so it is suitable to determine by the iodometric method or the gravimetric method.
Calcium, barium sulphate higher thermal decomposition temperature (1200 ° respectively and 1500 °), so that when these minerals present, can be added to iron powder or of vanadium pentoxide as flux, calcium, barium sulphate is converted Iron salt reduces the decomposition temperature. However, in order to completely decompose the calcium and strontium sulfates, the temperature should not be lower than 1250-1300 °.
This method measures high levels of sulfur (>1%), and the results are often lower than the gravimetric results. Therefore, the calibration can be performed by using a standard sample containing a sulfur content equivalent to the sample to reduce the error. The apparatus for determining the total sulfur by the calcination method is shown in Fig. 1.
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