Sodium sulfide manufacturing methods and applications
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Sodium sulfide production methods:
No commercial process for the production of sodium sulfide containing neither water nor iron is known. The commercially available sodium sulfide is in every case produced by reduction of sodium sulfate, usually by means of carbon, but also by means of hydrogen and other reducing gases. Reduction with carbon yields a crude melt, which contains, in addition to sodium sulfide, considerable amounts of impurities and by-products such as unreacted carbon, ash constituents, impurities from the carbon, carbonates, sulphites, sodium thiosulfates, and iron compounds. This crude melt is usually extracted with water so that the water-soluble part of the impurities and considerable amounts of iron pass into the extraction liquor. Other reactions take place subsequently in the aqueous solution, and these lead to undesirable by-products. by evaporating the extraction liquor, either crystals of the composition Na S.9H O are obtained or with further evaporation, a product containing 60% of Na S solidifies from the melt. Both hydrates, namely the hydrate crystallising from the solution and containing 32% of Na S, contain considerable amounts of soda, sulfite, thiosulfate, sulfate, and iron salts. The commercially available substance containing 60% Na is colored a dark reddish brown by the iron and can scarcely be used for certain purposes such treatment of textiles. It is not technically or economically possible to reduce the residual 40% of water content by further evaporation on account of the extraordinarily steep rise in the melt temperature above 60% of Na-S and since a suitable material for use in making the necessary apparatus which is resistant to concentrated sodium sulphite melt is unknown. Even evaporation to only 60% of Na S necessitates the use of apparafus made from expensive special alloys or causes heavy wear on other materials.
A process has now been discovered for obtaining a sodium sulphide of excellent purity by reduction of sodium sulphate with carbon or other reducing agents, which sulphide is in particular free from iron and water. The process is based on the fact that anhydrous sodium sulphide, unlike the hydrate, dissolves readily in alcohols.
Claim1: In a process for the production of pure anhydrous sodium sulfide free from iron, the step which comprises heating the melt obtained by reduction of sodium sulfate with carbon and which contains impurities resulting from the reduction process, with an alcohol, filtering the sodium sulfide solution thereby formed and recovering the sodium sulfide from the said solution by evaporating the alcohol.
It is known that sodium hydroxide may be reacted with H2S to form Na2S which may be treated with more H2S to convert Na2S to NaHS, and it has been proposed to make sodium hydrosulfide by gassing an Na2S-NaHS liquor with pure hydrogen sulfide.
In processes of the type to which the invention relates, the source of sodium is commercial caustic soda which contains appreciable quantities of impurities, such as iron, copper, nickel, manganese and silicon. These impurities do not discolor caustic soda to any great extent, and hence their presence in commercial caustic is unobjectionable. However, during H2S gassing of commercial caustic liquor, such impurities pass thru the process and are carried into the resulting NaHS liquor. Such impurities may be present in the NaHS liquor as soluble salts or suspended in finely divided condition. While probably largely sulfides, exact compositions of the impurities are not known, and whatever their nature, these subtances are referred to herein as metallic impurities. The presence of even small amounts of these impurities in Na2S or NaHS solutions results in products of very poor appearance because of the highly colored nature of the impurities after having been subjected to H2S gassing. Accordingly, a major problem presented in manufacture of relatively pure sodium hydrosulfide has been the elimination of such impurities.
Commercially available hydrogen sulfide gases contain appreciable amounts of carbon dioxide as an impurity.
Claim2: the method for producing purified sodium sulfide from a sodium hydrosulfide liquor containing (a) at least one metallic impurity of the group consisting of iron, copper, nickel, manganese, and silicon, and (b) an amount of available carbonate of sodium equivalent to more than 0.06% by weight of CO3 radical, which method comprises treating said liquor with an alkaline earth compound so as to react with available carbonate of sodium to precipitate combined CO3 thereof as alkaline earth carbonate, the amount of said alkaline earth compound being at least sufficient to reduce the available carbonate of sodium content of said liquor to an amount equivalent to not more than 0.06% by weight of CO3 radical, controlling the composition of the resulting liquor so that such liquor contains not more than 5% by weight of sodium sulfide, thereby effecting coagulation and precipitation of metallic impurities, and separating said metallic impurities from such liquor.
Claim3: The method for producing purified sodium sulfide from a sodium hydrosulfide liquor containing (a) metallic impurities of the type present in commercial sodium hydroxide, and (b) an amount of available carbonate of sodium equivalent to more than 0.06% by weight of COA radical, which method comprises treating said liquor with an alkaline earth compound so as to react with available carbonate of sodium to precipitate combined Cos thereof as alkaline earth carbonate, the amount of said alkaline earth compound being at least sufficient to reduce the available carbonate of sodium content of said liquor to an amount equivalent to not more than 0.06% by weight of Cos radical, controlling the composition of the resulting liquor so that such liquor contains not more than 5% by weight of sodium sulfide, thereby, effecting coagulation and precipitation of metallic impurities, and separating said metallic impurities from such liquor.
Sodium sulfide is one of the main chemicals and raw materials in so many industries such as mining industry, leather industry, metallurgy industry, textile industry, dyes and intermediates, pulp and paper, soda ash manufacturing, metal refining industry.
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