Main applications of sodium sulfide_industrial additives

Background and overview^[1]

Sodium sulfide, also known as “alkali sulfide”, is the sodium salt of hydrogen sulfate, with the molecular formula Na₂S. Commonly known as “stinky alkali”. Pure sulfide alkali is an easily deliquescent white powder, also available in flakes and lumps. Very soluble in water, slightly soluble in alcohol, insoluble in ether, slightly corrosive to most metals. Reacts with acids to emit toxic and flammable hydrogen sulfide gas. Swallowing or inhaling its dust is harmful to the human body and corrosive to skin, eyes and mucous membranes. Relative density: 2.427 (16℃/4℃), melting point: 50℃; should be stored in a ventilated, dry place, away from light, and the container should be sealed to prevent moisture and deterioration. Keep away from heat sources and living areas, and isolate from explosives, acids, oxidants, etc. Wear protective gear and rubber gloves when loading and unloading. Use water or sand for fire protection. This product can be mixed and burned with sodium sulfate and carbon to reduce the sodium sulfate to produce sodium sulfide. Mainly used in the preparation of sulfur dyes and as reducing agents in the organic chemical industry. When the human body is poisoned, it should be quickly moved to fresh air and artificial respiration should be performed if necessary. Wash skin injuries with water and dilute acetic acid. If this product contains less than 30% crystal water, it should be classified as a Class 4.2 flammable substance. United Nations number (UNNo.): 1849/8227/8-08/225, domestic product name number: 82011, corrosive product.

Apply^[2]

1. Application of sodium sulfide in metallurgy

1) Removal of impurities from rare earth leachate. When processing weathered crust eluviation type rare earth ores, after leaching and leaching with a strong electrolyte solution, the resulting rare earth leachate often contains a large number of impurity ions, such as Al3+, Fe3+ , Ca2+, Mg2+, Cu2+, etc. When using the oxalic acid precipitation process, these impurities will inevitably form oxalate precipitation and transfer to the rare earth products, affecting the purity of the product. Moreover, in order to avoid emulsification in the subsequent extraction process, impurity ions in the feed liquid must be removed first. The solubility product constants of several metal sulfide precipitations are shown in the attached table. When Na2S is added to the rare earth leachate, the heavy metal ions Cu2+, Pb2+, Zn2+, etc. in the solution can be effectively removed. Studies have shown that controlling the pH at about 5 and adding Na2S to the rare earth leachate to remove impurities not only has a good impurity removal effect, but also does not cause loss of rare earths.

2) Treatment of mercury-containing wastewater Mercury-containing wastewater is extremely harmful to the environment and human health. In the alkali production industry, the mercury content in discharged wastewater is generally high, exceeding the international level (0.05mg/L). In weakly attenuated (pH 8-11) solutions, mercury ions can react with sodium sulfide to form a precipitate that is insoluble in water. As can be seen from the attached table, the solubility product of HgS is very small (Ksp=1.6×10-52). Through research, it has been determined that the treatment effect is best when the dosage of Na2S is constant and the pH value is controlled between 9 and 10, and the Hg2+ in the wastewater can be reduced to below the national standard (0.05mg/L). In addition, Fe(OH)2 and Fe(OH)3 colloids are generated in water by adding FeSO4. These colloids can not only absorb mercury ions, but also capture and coat suspended HgS solid particles, playing a good coagulation and precipitation effect. . The sediment is not prone to secondary pollution and is easy to dispose.

3) Using Na2S to remove arsenic Arsenic generally exists in minerals in the form of sulfide. During the pyrometallurgy process, most of the arsenic volatilizes into the flue gas and dust, especially the direct emission of low-concentration SO2 will pollute the environment. Therefore, arsenic removal treatment should be carried out before subsequent treatment or evacuation of flue gas. Use Na2S solution to absorb SO2 flue gas, causing As3+ and S2- to form As2S3 precipitation (Ksp=2.1×10-22). At higher pH (pH>8), As2S3 can be dissolved to form As3S3-6 or AsS2-3, which is relatively At low pH, the solution will produce H2S gas. Research by Yin Aijun et al. [4] shows that when the pH of the solution is controlled in the range of 2.0 to 5.5, the reaction time is 50 minutes, the reaction temperature is 30 to 50°C, and flocculants are added, arsenic can be removed better, and the arsenic removal rate can reach 90%. %above. In the production of medicinal white carbon black, in order to reduce the content of impurity arsenic in the production raw material concentrated sulfuric acid, sodium sulfide is added to the concentrated sulfuric acid to precipitate As3+ to form As2S3 and remove it. Production practice shows that arsenic removal by sodium sulfide not only has a fast reaction speed, but also removes arsenic thoroughly. The arsenic content in the sulfuric acid after arsenic removal is less than 0.5×10-6. The arsenic content of the silica produced from this raw material is ≤0.0003%, which fully complies with the regulations of the United States Pharmacopoeia.

4) Application of Na2S in electroplating

Na2S is used as a brightener in electroplating: sodium sulfide is dissolved in water and ionized into positively charged sodium ions (Na+) and negatively charged sulfide ions (S2-). During the electroplating process, S2- in the electrolyte The presence of can promote cathode polarization and speed up the cathode reaction under the same current. The deposition speed is also accelerated, the deep plating capacity is increased, the coating is refined, and the surface of the plated parts becomes brighter accordingly.

Sodium sulfide removes impurities in the electrolyte: During the electroplating production process, impurities in the raw materials will be brought into the plating solution to a greater or lesser extent. These impurities undergo different reactions under the action of electrodes. Impurities with lower potential will be deposited on the surface of the plated parts together with Zn2+, affecting the quality of the coating. After adding sodium sulfide, S2- in sodium sulfide can form a precipitate with metal impurity ions, preventing impurities from participating in the electrochemical reaction and making the coating bright.

5) Use Na2S solution for flue gas desulfurization. At present, the recovery method of SO2 in flue gas is mainly to convert SO2 into H2SO4, liquid SO2 and elemental sulfur. Because elemental sulfur is easy to handle and transport, it is also an ideal recycling product. A new process using H2S produced from Na2S solution as reducing agent to reduce SO2 to produce elemental sulfur. This process is simple and does not require the consumption of expensive reducing agents such as natural gas and low-sulfur coal like general production technology. When the pH of the solution drops to 8.5~7.5, absorbing SO2 with Na2S will produce H2SFor sodium phosphate, place the weighed raw coal and sodium sulfate into a ball mill for grinding;

(2). Place the powder obtained in step (1) into a calcining furnace for calcining. Control the calcining temperature to 1000℃-1100℃ and the calcining time to 30-50min to obtain the sodium sulfide semi-finished product;

(3). Dilute the sodium sulfide semi-finished product prepared in step (2) with water into a sodium sulfide solution, and perform 2-3 times of filtration and clarification;

(4). Pour the sodium sulfide solution treated in step (3) into the iron remover, add 0.1-0.3%wt polyferric sulfate to settle the various precipitated substances generated, and stir for 20-30 minutes. The temperature Filter at 70-80℃ to obtain sodium sulfide solution with iron content below 10ppm;

(5). Evaporate and concentrate the solution in step (4) to 60% content, and tablet it to obtain a sodium sulfide product with an iron content of less than 10 ppm;

(6). Add metal manganese powder and/or manganese-based alloy powder to the zinc sulfate solution. The temperature is 50-60°C and the pH is >4.5. Stir the reaction. After the reaction is completed, filter and separate, and then concentrate by evaporation. Crystallize to obtain high-purity zinc sulfate. Add 5-8 kilograms of zinc sulfate to each cubic filtrate of the prepared high-purity zinc sulfate to weigh the zinc sulfate. Prepare 1 cubic meter of zinc sulfate solution for each cubic meter of filtrate; add barium sulfide to each cubic meter of water. 140kg, take the clear liquid for later use; add the above two prepared solutions to the sodium sulfide filtrate at the same time, stir, control the reaction temperature above 80-90°C, precipitate, remove impurities and clarify, send to the evaporation process, and concentrate by evaporation. High purity sodium sulfide is obtained.

Main reference materials

[1] Technical Dictionary of Container Transport Business·Volume 2

[2] Application of sodium sulfide in metallurgy and mineral processing

[3] CN201810763300.3 A high-purity sodium sulfide preparation process