1、TOTAL CYANIDE IN REFINERY WATERS BY VISIBLE SPECTROPHOTOMETRY UOP Method 682-84 SCOPE This method is for determining cyanide in aqueous solutions in the presence of large quantities of sulfide. The lower limit of detection in the presence of 1.0% or 0.1% sulfide is 0.2 or 0.02 mass-ppm cyanide, resp
2、ectively. The upper limit of detection can range from 200 ppm to 10,000 ppm cyanide depending on the size of the sample selected for analysis. Thiosulfate above a level of 0.1% will interfere with the test. Significant amounts of sulfite, thiocyanate, aldehydes, amines and other materials can also i
3、nterfere with the analysis. The instability of cyanide in the presence of air requires that the analysis be performed as soon as possible after sampling. OUTLINE OF METHOD The sulfide content of the sample is determined by UOP Method 683, or equivalent, to determine the sample size required for sulf
4、ide removal using cadmium carbonate. The cyanide released after acidification is distilled and swept into an alkaline absorption solution. After neutralization and the addition of chloramine-T and barbituric acid-pyridine, the absorbance of the solutions red-blue color is measured spectrophotometric
5、ally at 578 nm. The mass-ppm cyanide is determined from a previously prepared calibration curve. APPARATUS Balance, readability, 0.1-mg Beakers, graduated, 100-, 250- and 400-mL Cotton balls, medium size Cyanide micro distillation apparatus, fabricated and described as shown in Figs. 1 through 5, av
6、ailable from UOP Inc., or equivalent Absorber tube, with a Teflon stopcock metering valve, Lab Glass Inc., Cat. No. LG-9606T-100, Fig. 1, “C” Distillation tube, with built-in condenser and charger funnel, Fig. 1, “A” IT IS THE USERS RESPONSIBILITY TO ESTABLISH APPROPRIATE PRECAUTIONARY PRACTICES AND
7、 TO DETERMINE THE APPLICABILITY OF REGULATORY LIMITATIONS PRIOR TO USE. EFFECTIVE HEALTH AND SAFETY PRACTICES ARE TO BE FOLLOWED WHEN UTILIZING THIS PROCEDURE. FAILURE TO UTILIZE THIS PROCEDURE IN THE MANNER PRESCRIBED HEREIN CAN BE HAZARDOUS. MATERIAL SAFETY DATA SHEETS (MSDS) OR EXPERIMENTAL MATER
8、IAL SAFETY DATA SHEETS (EMSDS) FOR ALL OF THE MATERIALS USED IN THIS PROCEDURE SHOULD BE REVIEWED FOR SELECTION OF THE APPROPRIATE PERSONAL PROTECTION EQUIPMENT (PPE). COPYRIGHT 1970, 1984 UOP LLC ALL RIGHTS RESERVED UOP Methods are available through ASTM International, 100 Barr Harbor Drive, PO Box
9、 C700, West Conshohocken PA 19428-2959, United States. The Methods may be obtained through the ASTM website, www.astm.org, or by contacting Customer Service at serviceastm.org, 610.832.9555 FAX, or 610.832.9585 PHONE. 2 of 11 682-84 Filter assembly, consisting of a Millex Filter, Millipore, Type HA,
10、 0.45 m, Cat. No. SLHA0250S, inserted into a shortened Luer Lok stainless steel needle (0.065-inch OD, 16 gauge). A length of Teflon tubing (400-mm, 0.125-inch OD) connected to the needle, leads directly onto the stopcock inside the charger funnel of the distillation tube through a tight fitting nec
11、k (5-mm OD) of the ground glass joint (19/38), Fig. 3, “B”. Flow manometer, with a 300-mm length of capillary glass tubing (0.25-mm ID) immersed into a test tube. A short piece of the same tubing is used as an air flow restrictor, Fig. 2. Gas scrubber, hydrogen sulfide, Fig. 1, “B” Heating jacket fl
12、uid circulation system, Fig. 5, arranged so that a heating jacket surrounding the distillation tube is positioned higher than the circulator pump, Haake, Model D3. Make all connections using heavy wall rubber tubing secured with stainless steel clamps. Syringe assembly, consisting of a 50-mL (1-mL g
13、raduations) Plastipak Disposable Syringe with Luer Lok, Becton Dickinson, Cat. No. 5663, fitted with a stainless steel Luer Lok stopcock, Millipore, Cat. No. XX30-025-65, Fig. 3, “A” Vacuum source, consisting of a vacuum pump and a 2-liter filtering flask with side tube as a trap, Fig. 4 Flask, Erle
14、nmeyer, 250-mL capacity, narrow neck, Ts stopper, Sargent-Welch Scientific, Cat. No. S-34147-F, or equivalent Flasks, volumetric, 50-, 100-, 250-, 500-, 1000- and 2000-mL Pipets, dispensing, Eppendorf multivolume micropipet, Sargent-Welch Scientific, Cat. No. SC69721-10C & 10J, or equivalent Pipets,
15、 disposable, glass, 145-mm length, Pasteur, capillary, Sargent-Welch Scientific, Cat. No. S-69647-A, or equivalent Pipets, volumetric, 1-, 2-, 5-, 10-, 20-, 25- and 50-mL Pipets, graduated, 10- and 25-mL pH meter, Orion, Model No. 611, Sargent-Welch Scientific, Cat. No. S-30030-90, or equivalent Spe
16、ctrophotometer, with 10-mm matched silica cells, Bausch and Lomb, Model 710, or equivalent Stirring apparatus, magnetic, variable speed, Sargent-Welch Scientific, Cat. No. S-76506, or equivalent Sulfide in Refinery Waste Water test apparatus, see UOP Method 683 Timer Weighing dishes, polystyrene, di
17、sposable, capacity approximately 5.5 g, Sargent-Welch Scientific, Cat. No. S-3860-C, or equivalent REAGENTS AND MATERIALS All reagents shall conform to the specifications established by the Committee on Analytical Reagents of the American Chemical Society, when such specifications exist, unless othe
18、rwise specified. References to water shall mean deionized by polystyrene amberlite type resins. The water must meet Type II requirements described in ASTM D 1193. Unqualified references to solutions mean aqueous solutions. Acetic acid, glacial 3 of 11 682-84 Alcoholic sodium hydroxide absorber solut
19、ion. Dissolve 64 0.1 g of reagent grade NaOH pellets in approximately 1600 mL of water in a 2000-mL volumetric flask, cool and dilute to volume with methanol. Shake to mix. Barbituric acid, 98% minimum purity, Sargent-Welch Scientific, Cat. No. EK1090-100GM, or equivalent Buffer solution, sodium ace
20、tate pH of 6. Dissolve 40.0 0.1 g of anhydrous sodium acetate in 60 2 mL of water, using a 250-mL beaker. Bring to a pH of 6 as measured with a pH meter using about 6-8 mL of glacial acetic acid. Transfer and dilute to volume in a 100-mL volumetric flask. Cadmium carbonate, powder, 98% minimum purit
21、y, Sargent-Welch Scientific, Cat. No. SC16016-500GM, or equivalent Chloramine-T solution. Dissolve 1.0 0.01 g of hydrated Chloramine-T (Sargent-Welch Scientific, Cat. No. EK1022-250GM, or equivalent) in a 100-mL volumetric flask in water. Dilute to volume and mix. Prepare fresh weekly. Hydrochloric
22、acid, concentrated Lead acetate solution, 5%. Dissolve 25 0.1 g of Pb(CH3COO)23H2O (Sargent-Welch Scientific, Cat. No. SC13088-500GM, or equivalent) in approximately 300 mL of water in a 500-mL volumetric flask. Add 125 mL of glacial acetic acid, swirl to dissolve, dilute to volume with water and mi
23、x. Magnesium chloride catalyst solution. Dissolve 51 0.1 g of MgCl26H2O (Sargent-Welch Scientific, Cat. No. SC13291-500GM, or equivalent) in water in a 100-mL volumetric flask. Dilute to volume with water and mix. Methanol, HPLC grade (not more than 3 ppm acetone or aldehydes), Fisher Scientific, Ca
24、t. No. A-452, or equivalent Phenolphthalein indicator, 1% solution in methanol, Sargent-Welch Scientific, Cat. No. SC14007-500ML, or equivalent Potassium cyanide, 96% minimum purity, Sargent-Welch Scientific, Cat. No. SC17216-125GM, or equivalent Potassium Cyanide Stock Solution, 250 ppm. Dissolve 0
25、.6258 g 0.1 mg of KCN in approximately 200 mL of water containing 1.6 g of NaOH pellets in a 1000-mL volumetric flask, dilute to volume with water and mix. Prepare monthly. Potassium Cyanide Standard Solution, 10 ppm. Pipet 20 mL of the potassium cyanide stock solution into a 500-mL volumetric flask
26、, dilute to volume using the alcoholic sodium hydroxide solution and mix. Prepare weekly. Potassium Cyanide Working Solution, 1 ppm. Pipet 25 mL of the potassium cyanide standard solution into a 250-mL volumetric flask, dilute to volume using the alcoholic sodium hydroxide solution and mix. Prepare
27、on a daily basis as needed, within two hours of analysis, and protect from light. Pyridine, 99.8% minimum purity, Sargent-Welch Scientific, Cat. No. SC14376-500ML, or equivalent Pyridine-barbituric acid reagent. Weigh 15 0.1 g of barbituric acid into a 400-mL beaker. Stir with a magnetic stirrer whi
28、le wetting the powder with a little water to make a smooth paste. Carefully, in a fume hood, add 75 mL of pyridine, followed by 15 mL of concentrated HCl and stir until all lumps are dispersed. Dilute to about 200 mL with water and stir until a clear yellow solution is formed. Transfer into a 250-mL
29、 volumetric flask, allow to cool, dilute to volume and mix. Prepare fresh weekly or discard sooner if the solution severely darkens or if a precipitate forms. 4 of 11 682-84 Sodium hydroxide, 10% in water Stopcock grease, silicone Sulfuric acid, 1:1. Carefully pour 100 mL of concentrated H2SO4into 1
30、00 mL of water in a 250-mL glass stoppered Erlenmeyer flask, cool and mix. Triethylene glycol, 97% minimum purity, Sargent-Welch Scientific, Cat. No. EKP2828-001KG, or equivalent CALIBRATION To minimize the possibility of oxidation, prepare the standards for the calibration curve while distilling th
31、e last sample to be analyzed. Using a graduated 10-mL pipet, transfer 0.5, 2.0, 5.0 and 8.0 mL of the one-ppm Potassium Cyanide Working Solution into four, labeled 50-mL volumetric flasks. Using a graduated pipet add to the respective flasks 9.5, 8.0, 5.0 and 2.0 mL of alcoholic sodium hydroxide abs
32、orber solution to bring the volume in each flask to 10 mL. To a fifth flask add by pipet 10 mL of alcoholic sodium hydroxide absorber solution. Continue the procedure as described under Spectrophotometric Determination. PROCEDURE Preparation of Distillation Apparatus Assemble the apparatus as shown
33、in Figs. 1 through 5 and rinse the micro cyanide distillation apparatus with water. All ground glass joints should be greased lightly with silicone stopcock grease. Start and adjust the heater-circulator pump to maintain the triethylene glycol temperature at 120 C. Disconnect the gas scrubber (Fig.
34、1B) and prepare it by packing 3 cotton balls inside and thoroughly soaking the cotton with lead acetate solution by allowing 15 0.5 mL of the solution to drain through the packed scrubber into a 100-mL beaker. Remove the excess solution by touching the vacuum hose to the male ball joint for about 30
35、 seconds, secure the gas scrubber to the distillation tube with spring hooks and connect the ball joint with the clamp. Pipet 20 mL of water into the absorber tube and add about 50 1.0 mL of water into the charger funnel. Connect the flow manometer (Fig. 2) to the charger funnel and apply a vacuum e
36、quivalent to 100-120 mm of water (to which a few drops of food coloring has been added) in the capillary column, by adjusting the Teflon stopcock metering valve (Fig. 1C). Once the metering valve is properly adjusted, a smooth, steady and reproducible air flow is obtained for many successive distill
37、ations. Remove the flow manometer glass joint from the charger funnel. Turn off the pump circulating the triethylene glycol heating fluid around the heating jacket and by opening the pinch clamp, allow air to enter into the jacket and to gravity-drain the heater fluid into the circulator. Remove the
38、 gas scrubber and cool the interior of the distillation tube by flushing it with cold water added above the condenser while simultaneously vacuum siphoning it off from the charger funnel with a piece of plastic tubing connected to a vacuum hose. (The apparatus is cleaned out in the same manner betwe
39、en distillations.) Reconnect the gas scrubber and secure with the spring hooks. Drain the water from the absorber tube, rinse with acetone and dry using vacuum. Pipet 20 mL of alcoholic absorber solution into the absorber and reconnect the calibrated metering valve on top of the absorber tube. Conne
40、ct and clamp the ball joints, and then place the syringe/filter assembly (Fig. 3) into position on the charger funnel making sure that the Teflon sample tubing ends close above the stop-cock inside the charger funnel. When the apparatus is on stand-by or not in use, keep both the distillation and ab
41、sorber tube clean by leaving each filled with a 1:10 aqueous dilution of alcoholic absorber solution. 5 of 11 682-84 Figure 1 Cyanide Micro Distillation Apparatus NOT TO SCALE 6 of 11 682-84 Figure 2 Flow Manometer Figure 3 Syringe/Filter Assembly 7 of 11 682-84 Figure 4 Vacuum Source and Trap Figur
42、e 5 Heating Jacket Fluid Circulation 8 of 11 682-84 Sample Size Determination Determine the sulfide content of the sample using UOP Method 683, or equivalent. Determine the density of the sample using ASTM Method D 1298. Dilute the sample as specified in Table 1. Pipet the required aliquot of sample
43、 into a 100-mL volumetric flask. Add two drops of phenolphthalein and shake the flask. If the solution turns red (see NOTE), titrate with glacial acid, using a disposable pipet, to a colorless endpoint. Dilute to 100 mL with water immediately prior to sulfide removal and shake to mix Table 1 Sulfide
44、, % Sample Aliquot Diluted to 100 mL (Item C in Calculations) 2.1 - 5.0 2.0 1.1 - 2.0 5.0 0.51 - 1.0 10.0 0.21 - 0.5 20.0 0.11 - 0.2 50.0 0.1 or less 90.0 Sulfide Removal Remove the plunger from the 50-mL plastic syringe, close the stainless steel stopcock and place the syringe with the open end at
45、the top in a 400-mL beaker. Pipet 50 mL of the sample solution from the volumetric flask into the syringe. To the syringe, add 500 10 mg of preweighed cadmium carbonate from a plastic weighing dish and 2.0 mL of sodium acetate buffer solution using a volumetric pipet. IMMEDIATELY insert the plunger.
46、 Use both hands to hold the plunger firmly in line with the syringe barrel to prevent gas or liquid leakage. Vigorously shake the syringe for 2 minutes holding it horizontally so that the mixture travels along the length of the barrel. Hold the syringe upright for 20 to 30 seconds to allow most of t
47、he solids to settle onto the plunger. Connect the syringe-stopcock to the Millex filter assembly (Fig. 3) previously connected to the charger funnel. While keeping the syringe upright, open the syringe-stopcock and slowly filter-inject 40 0.05 mL of the clear filtrate through the charger tube and in
48、to the distillation apparatus. Disconnect the Teflon tubing from the Millex filter at the Luer Lok. Allow the contents of the tubing to drain into the charger funnel. Remove the remaining ground glass joint. Cyanide Distillation Following the sample injection, wash the charger funnel with 2 mL of ma
49、gnesium chloride catalyst solution followed by 10 mL of H2SO4(1:1) solution. Replace the flow manometer on the charger funnel and turn on the cooling water for the reflux condenser. Also turn on the heater fluid circulating pump with the pinch clamp closed, and set the timer to 30 minutes. The sample should be refluxing within 5 minutes. If the hot vapor zone climbs higher than 30% of the way up the condenser, immediately increase the cooling water flow. The flow manometer should indicate the proper preset vacuum air flow in the system producing a smooth bubble
