Minimize Free Cyanide in Blast Furnace GCPl Launders?

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How can I minimize the free cyanide concentration in blast furnace GCPl launders?

Are there any technical papers addressing the issue?

Does aeration in launder reduce free cyanide?

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4 Answers

  1. Dear Manjunath,

    Experiments confirm that ozone provides the optimal means for the minimization or elimination of cyanide releases from the water-supply cycle of blast furnaces. The cyanides are completely decomposed, with no wastes and without the need for other reagents.

    Cynide formation in furnace is largely due to composition of the raw materials and the reactions occurring in the lower part of the furnace at 2000– 2500°C. Nitrogen and hydrogen from the blast, components of natural gas, and volatiles from the coke react with the hot coke to form cyanogen. The pres ence of alkalis in the raw materials and their accumulation in certain temperature zones of the furnace facilitate the formation of solid cyanides KCN and NaCN. These cyanides are captured by the ascending flux of blast furnace gas and entrained to the upper part of the furnace, where some of the cyanides break down at ≤1000°C, reducing iron oxides. Some cya nides are oxidized at 635°C, forming small solid crystals, and are deposited on the batch, with which they fall into the high temperature zone. A considerable quantity of cyanides is entrained with the blast furnace gas to the gas purification system. In the blast furnace gas, cyanides are present.

     

    Please find attached herewith article.

    Regards,

    Prem Baboo

    1 Comment

  2. Fe has tendency to react with free ammonia first due to pH range prevailing in steel industry effluent . It will work well but will increase the dose require for cyanide chelation. Lowering pH might reduce the effect of Fe dosing and though also reduce free ammonia . 6-8 ppm is manageable with properly maintained biological system plus reasonable Fe+2 dosing 

  3. Very simple but practical method is to dose with ferrous sulphate. This will eliminate the cyanide. 

    And if you don't have a reliable source of ferrous sulphate, then make your own with excess scrap metal in sulphuric acid - resulting liquid is pure ferrous sulphate. :)

    1 Comment

    1. Is presence of free ammonia have impact on ferrous sulphate ?

      1 Comment reply

      1. I would think that ammonia would have little impact, but I am not 100% sure on that. My experience with ferrous and cyanide destruction comes from my time on the Gold plants in South Africa, where we made a scrap metal/sulphuric acid ferrous plant and dosed the tailings before it wa sent underground in a backfill operation - so no ammonia involved at all.

        The best would be to run a small test to establish your ferrous dosage requirement and at the same time undertake observations of the impact of the ammonia, if any, on the destruction of cyanide.

        Good luck with this interesting problem. 

  4. Hello Manjunath 

    It seems still you are looking at answers. It is good to reduce the principle pollutant at source with resource recovery but tell you there is a limit of 2-6 ppm Cyanide at Blast Furnace and Coke Oven recovery plant and reducing it beyond this range would be a tough task . 

    As I indicated earlier that if your sole aim is to nitrify stably in the down stream biological wastewater treatment by minimizing impact of cyanide then you need to look at the whole problem holistically. the source reduction certainly help but 6-8 ppm Cyanide is manageable in biological plant if it is present at site. 

    As I understand , at lower pH cyanide will volatilize but then at 400 m3/hr reducing pH to 6-6.5 would be costly and collecting cyanide in air and dispose it of would be another challenge. 

    If liquid stream is facing treatment problems due to Cyanide then certainly We can help. You can send us details on levapor.india@gmail.com and We can have a look at the problem. 

     

    Regards

     

    Amit