Method for the determination of cyanide in wastewater - Master's thesis - Dissertation

Method for determination of cyanide in wastewater Key words: cyanide determination method; ultraviolet spectrophotometer; US analytical instrument ; UV-1800A

Total cyanide refers to cyanide which can form hydrogen cyanide by heating and distillation in the medium with pH less than 2 in the presence of phosphoric acid and EDTA, including all simple cyanide (mostly cyanide of alkali metal and alkaline earth metal, ammonium Cyanide) and most of the complex cyanide (zinc cyanide complex, ferricyanide complex, nickel cyanide complex, copper cyanide complex, etc.), excluding cobalt cyanide complex. Under neutral conditions, the cyanide in the sample reacts with chloramine T to form cyanogen chloride, which is then reacted with isonicotinic acid to form pentene dialdehyde after hydrolysis, and finally condensed with pyrazolone to form a blue dye. The chromaticity is proportional to the content of cyanide and is measured photometrically.

1 Test part 1.1 Main instruments (1) Spectrophotometer; American instrument ; UV-1800A (2) 25ml with colorimetric tube. 1.2 Reagents (1) 2% (m/V) sodium hydroxide solution. (2) 0.1% (m/V) sodium hydroxide solution. (3) Phosphate buffer solution (pH=7): Weigh 34.0 g of anhydrous potassium dihydrogen phosphate and 35.5 g of anhydrous sodium hydrogen phosphate in a beaker, dissolve in water, dilute to 1000 ml, and shake well. Store in the refrigerator. (4) 1% (m / V) chloramine T solution: Before use, weigh 0.5g of chloramine T dissolved in water, and diluted to 50ml, shake. Store in a brown bottle. (5) Isonicotinic acid-pyrazolone solution: 1 isonicotinic acid solution: 1.5 g of isonicotinic acid was weighed and dissolved in 24 ml of 2% sodium hydroxide solution, and diluted with water to 100 ml. 2 Pyrazolone solution: 0.25 g of pyrazolone was weighed and dissolved in 20 ml of N, N-dimethylformamide. Before use, the pyrazolone solution 2 and the isonicotinic acid solution 1 were uniformly mixed at 1+5. (6) Standard solution: Weigh 0.25g (note the poisonous!) dissolved in 0.1% sodium hydroxide solution, and use 0.1% sodium hydroxide solution to 100m1, shake well. Store in a brown bottle away from light. Pipette 10.00ml stock solution into the Erlenmeyer flask, add 50ml water and 1ml 2% sodium hydroxide solution, add 0.2ml test silver spirit indicator solution, titrate with silver nitrate standard solution (0.0100mol/L), the solution changes from yellow For orange-red color, record the amount of silver nitrate standard solution (V

1

). At the same time, take 10ml of experimental water instead of stock solution for blank test, record the amount of silver nitrate standard solution (V

0

), calculated by the following formula: cyanide (mg / ml) = where, c - silver nitrate standard solution concentration (mol / L); V

1

- When titrating the stock solution, the amount of silver nitrate standard solution (ml); V

0

- Blank test, silver nitrate standard solution amount (ml); 52.04 - molar mass of cyanide ion (2CN ̄) (g / mol); 10.00 - take the volume of the stock solution (ml). (7) Standard intermediate solution (1ml containing 10.00μg cyanide ion): Calculate the volume (V) of the stock solution required to prepare 500ml standard intermediate solution by the following formula: V = where 10.00-1ml standard intermediate solution contains 10.00μg CN ̄; 500—standard intermediate solution volume (ml); T—stock solution containing CN ̄ (mg). Accurately absorb the stock solution in a 500ml brown volumetric flask, dilute to the mark with 0.1% sodium hydroxide solution, and shake well. (8) Standard use solution (1ml containing 1.00μg cyanide ion): Before use, draw 10.00ml standard intermediate solution (1ml containing 10.00μg cyanide ion) in 100ml brown volumetric flask, dilute to the standard with 0.1% sodium hydroxide solution Line, shake well. 1.3 Experimental method 1.3.1 Drawing of calibration curve (1) Take 8 25ml plug colorimetric tubes and add standard solution 0, 0.20, 0.50, 1.00, 2.00, 3.00, 4.00, 5.00, respectively, and add 0.1% hydroxide. Sodium solution to 10 ml. (2) Add 5ml of phosphate buffer solution to each tube and mix. Quickly add 0.2m1 chloramine T solution, immediately cover the plug, mix and place for 3-5 min. (3) Add 5 ml of isonicotinic acid-pyrazolone solution to the tube and mix. Dilute to the mark with water and shake well. Place in a water bath at 25-35 ° C for 40 min. (4) Using a spectrophotometer, at a wavelength of 638 nm, use a 10 mm cuvette, a zero-concentration blank tube as a reference, measure the absorbance, and draw a calibration curve. 1.3.2 Determination of sample (1) Pipette 10.00ml of distillate A and 10.00ml of blank test distillate in a plug colorimetric tube, and then proceed according to the drawing steps (2)-(4) of the calibration curve. Operation, measuring absorbance. (2) Find the corresponding cyanide content from the calibration curve. Cyanide (CN ̄, mg/L) = where m

a

--Check the cyanide content (μg) of the sample from the calibration curve; m

b

- Find the cyanide content (μg) of the blank sample (distillate B) from the calibration curve; V - the volume of the sample (ml); V

1

- the volume of the sample (distillate A) (ml); V

2

- Volume (ml) of the sample (distillate A taken during colorimetry). 2 Results and discussion 2.1 The form of cyanide is readily volatile when cyanide is present in HCN. Therefore, after adding the buffer, each step should be operated quickly and the plug should be closed at any time. 2.2 The choice of the blank experiment is to reduce the test blank value. In the experiment, colorless N -2 methylformamide is preferred. 2.2 Temperature influence When the experimental temperature is low, the phosphate buffer solution will precipitate crystals and change the pH of the solution. Therefore, it is necessary to dissolve the crystals in a water bath and mix them before use. 2.3 The effect of sodium hydroxide When the absorption liquid uses a higher concentration of sodium hydroxide solution, the phenolphthalein should be used as an indicator before adding the buffer solution, and the hydrochloric acid solution is added dropwise until the red color fades. Both the water sample and the calibration curve should be the same sodium hydroxide concentration. 2.4 Precision and Accuracy The spiked water sample has a cyanide content of 0.022--0.032 mg/L. After 6 laboratory analyses, the relative standard deviations of individual laboratories are 7.4% and 1.8%, respectively. The rate is 92--99%. 3 Conclusion Under neutral conditions, the cyanide in the sample reacts with chloramine T to form cyanogen chloride, and then reacts with isonicotinic acid to form pentenedionaldehyde after hydrolysis, and finally condenses with pyrazolone to form blue dye. The chromaticity is proportional to the content of cyanide, and photometry is performed. Isonicotinic acid-pyrazolone colorimetric method, the minimum detection concentration is 0.004 mg / L; the upper limit of determination is 0.25 mg / L. The method is applicable to drinking water, surface water, domestic sewage and industrial wastewater. Key words: cyanide determination method; ultraviolet spectrophotometer; US analytical instrument ; UV-1800A