An effective method for removing desulfurization ions from ammonia solutions

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This post was last edited by Refinery Operator on 2015-6-26 08:24. 1. Purpose: To convert the divalent sulfur ions in ammonia water into elemental sulfur or ions in a higher valence state, with the concentration to be below 0.01 g/L. 2. Water quality: It is a 3% ammonia solution, which mainly contains water, ammonia, and ammonium sulfide; the concentration of sulfur ions is between 1 g/L and 2 g/L. 3. Experimental procedure: First, the hydrogen peroxide method was tried in the laboratory. Theoretically, S2- + 4H2O2 === SO42- + 4H2O, and this reaction should enable a removal efficiency of over 99.9%. However, in practice, no matter how much hydrogen peroxide was added, the aqueous solution turned yellow. After thorough mixing, samples were taken and analyzed using the iodometric method to determine the concentration of divalent sulfur ions, but no detection was possible. But if it’s left for over a day, it will appear again. II. Desulfurization is carried out using chemically pure ferrous sulfate heptahydrate. Fe2+ + S2- === FeS (precipitate); however, in an alkaline environment, Fe2+ + 2 OH- === Fe(OH)2 (precipitate). Both substances are black. Therefore, I found information on forums regarding a method for measuring the concentration of divalent sulfide ions in solutions using back-titration. The first part of this method describes that if there are no hydrolyzable metal ions, the solution can be adjusted to an ammoniacal condition using ammonia (which has an ammonia smell, with a pH of 10–11). A certain excess of soluble cadmium salt solution (such as cadmium chloride) is then added, and the mixture is stirred thoroughly. Only cadmium sulfide will precipitate, while the excess cadmium ions form ammine complexes that remain in the solution. Filter and wash the precipitate (wash the precipitate until no chloride ions remain, as all the main ions have been washed away, and thus the reducing sulfite and thiosulfate ions are also gone); discard the waste liquid. Therefore, it was decided to use cadmium chloride to verify whether ferrous sulfate achieves desulfurization. The procedure for the experiment is as follows: 100 ml of the ammonia solution to be tested is taken, and the concentration of divalent sulfur ions is determined using the iodometric method to be 1 g/L. The theoretical amount required is 0.87 g of ferrous sulfate heptahydrate, which is sufficient to precipitate all the divalent sulfur in the ammonia solution. However, since hydroxide ions can also consume ferrous ions, twice the theoretical amount of ferrous sulfate heptahydrate was used. Considering that ferrous sulfide is easily oxidized, after complete reaction, it is quickly filtered using filter paper; the supernatant is collected, cadmium chloride solution is added, and any white precipitate that forms in the solution under test is observed. (Since cadmium sulfide is yellow), it can be concluded that all divalent sulfur in the raw water was completely removed by ferrous sulfate heptahydrate. However, when tested using the iodometric method, there was still 0.6 g/L of divalent sulfide ions. (The testing was done with someone else’s help) It crashed. I would like to ask the experts here: is it a problem with my experimental method or something else? If you have any good methods, please share them with me! I’m not a professional in this field; I’ve researched various materials and conducted experiments over several weeks, but still haven’t found a good method. Thank you again! ! !