Notes

 

1. Liquid waste containing organic mercury compounds

 Add excess potassium permanganate solution to liquid wastes and heat at 70Ž for 2-3 hours to decompose organic compounds, reduce excess potassium permanganate with sodium oxalate and treat as inorganic mercury compounds.

 

2.  Liquid waste containing hexavalent chromium [Cr(VI)]

 Add reductant (sodium hydrogen sulphite, etc.) , after acidification with sulphuric acid, until the color of liquid waste changes to green, store after ensure to achieve a concentration below 50 ppm of chromium.

 

3.  Liquid waste containing inorganic fluoride and their compounds

 Add excess calcium chloride at pH 6-11, allow to stand over 5 hours, filter off the precipitate, store the filtrates after ensure to achieve a concentration below 0.5 % of fluoride.

 

4.  Liquid waste containing inorganic phosphate and their compounds

Add excess calcium chloride at pH 10-11, allow to stand over night, filter off the precipitate, store the filtrates after ensure to achieve a concentration below 300 ppm of total phosphorus.

 

5.  Liquid waste containing heavy metals containing chelating agents

1) Decompose organic compounds with potassium permanganate. (see note 1)

2) Add sodium carbonate or sodium hydroxide to optimum pH, allow to stand and filter off, treat the precipitate as inorganic sludge, and treat the filtrate as dilute organic aqueous solutions group.

 

6.  Liquid waste containing cyanide and their compounds

 Add sodium hypochlorite solution at pH >11, allow to stand for 1 hour and store the waste after ensure to achieve a concentration below 80 ppm of total cyanide.

(If liquid waste was made acidic, toxic cyanogen gas would be released.)

 To liquid wastes containing non decomposable cyanide complexes, such as KAg(CN)2, etc., add about 25 folds amounts of iron(II) sulphate heptahydrate for cyanide, adjust to pH 5-6 and allow to stand, store at pH 9.0-9.5 after ensure to achieve a concentration below 80 ppm of total cyanide. If precipitation occurs, filter off the precipitate.

 

7.   Liquid waste containing arsenic and their compounds

 Add calcium hydroxide to over pH 11, allow to stand for over night,  filter off the precipitate and add the filtrate to about 50-folds amounts of iron(III) sulphate for arsenic, adjust to pH 7-10, allow to stand for over night, filter off the precipitate , store the filtrate at pH 9.0-9.5 after ensure to achieve a concentration below 20 ppm of arsenic.

 Organic arsenic compounds (cacodylic acid, etc.) should be decomposed with oxidizing agent (hydrogen peroxide, sodium hypochloride or potassium permanganate) and go to above treatment.

 

8.  Liquid waste containing selenium and their compounds

 Add sodium sulphide, after acidification with dilute sulphuric acid, filter off the precipitate, store the filtrate at pH 9.0-9.5 after ensure to achieve a concentration below 12.5 ppm of selenium.

 Organic selenium compounds should be decomposed with oxidizing agent (hydrogen peroxide, sodium hypochloride or potassium permanganate) and go to above treatment.

 

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