The tailings of gold mines contain a large amount of cyanide. However, the ferrous ions in ferrous sulfate can react chemically with the free cyanide in the tailings, and generate ferrous cyanide and other substances. This reaction may affect its reaction results under certain external conditions. For example, the treatment of cyanide-containing wastewater with ferrous sulfate under high temperature, low pH value, and ultraviolet irradiation will affect the reaction. Ferrous cyanide is extremely unstable, and during the backfilling process, the ferrous cyanide solution easily seeps out, causing severe pollution of groundwater. Let’s specifically analyze the reaction process and results of adding cyanide to ferrous sulfate. Let’s do an experiment to add cyanide when there is a lot of ferrous sulfate. That is to say, when excess ferrous sulfate is added to the cyanide solution, Cyanide will turn into an insoluble precipitate Fe4[Fe(CN)6]3, which we usually call Prussian blue. Of course, in the process of tailings treatment in gold mines, some companies do not choose to add ferrous sulfate for treatment, but choose to add ferrous sulfide. Some companies choose to add iron and copper at the same time to produce white insoluble ferrous cyanide. Ferrous iron quickly absorbs oxygen from the air, turns dark blue, and forms ferric ferricyanide.
It can be concluded through experiments that the best condition for removing cyanide from solution with ferrous sulfate is to find a process that generates soluble and insoluble compounds. During the experiment, we calculated the molar ratio of the reaction results of ferrous sulfate and CN-. First, the ratio calculated according to stoichiometry was 0.39, but the optimal molar ratio we obtained through calculation was 0.5. . The optimal pH for precipitating Prussian blue is 5.5 to 6.5. Generally speaking, oxygen can oxidize iron ions to form ferricyanide and ferricyanide ions, which is more unfavorable for the removal of cyanide. Because ferricyanate ion is quite unstable under acidic conditions, it will react to form ferrous pentacyano complex [Fe(CN)5H2O]3-, which is rapidly oxidized to ferricyanate ion Fe(CN). ) 63-. These reactions basically occur at pH values below 4. After experiments, we finally came to a conclusion: when the ferrous sulfate treatment method is used for gold mine tailings treatment, the best environmental condition for using ferrous sulfate to remove cyanide from the tailings is a pH value of 5.5 to 6.5. The numerical value is the most appropriate, and the ratio of Fe to CN-0.5 is the most suitable for processing.
Post time: Sep-03-2024
