Sodium Sulfide

Sodium sulfide is an organic chemical that has attained an important position in the organic industry. It is consumed as a reducing agent in the manufacture of amino compounds, and it enters into the preparation of many dyes. It is also employed extensively in the leather industry as a depilatory. Sodium polysulfide is one of the important are the rayon, metallurgical, photographic, and engraving fields. This product usually is a side product of other industry.

This chemical may be obtained as 30% crystals of sodium sulphide or as 62% flakes. Solutions of it may be shipped in steel. One disadvantageous property of sodium sulphide is its deliquence. It crystallizes wit nine molecules of water, Na2S.9H2O. The oldest method of production is the reduction of sodium sulphate with powdered coal in a reverberatory furnace. Another similar process is the reduction of barite in the same manner, leaching and double decomposition with soda ash. For the reaction involving the reduction of salt cake, very drastic condition are needed. The reaction must be carried out about 900oC. The reaction are:

Na2SO4 + 4 C -->  Na2S + 4 CO
Na2SO4 + 4 CO  
-->  Na2S + 4 CO2

Specially designed small reverberatory furnace seem to give the least difficulty, because they avoid overheating the charge. The reaction takes place in the liquid phase and is very rapid. Rotary kiln of the type used for calcining limestone have been applied with some success to this reaction. The reduction of barium sulphate is very similar. Newer plants use nickel or nickel clad equipment to reduce iron contamination. The substance issuing from the furnace is known as black ash.

Another method of production involves the saturation of a caustic soda solution with hydrogen sulphide and the addition of another molecule of sodium hydroxide according to the reaction:

H2S + NaOH
--> NaHS + H2O

NaHS + H2O
--> Na2S + H2O

Heavy metal sulphide are filtered from the solution of sodium hydrosulfide. The solution is concentrated and then reacted with sodium hydroxide to give a high purity product. Stainless steel is used as a construction material.

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