Fitomineria

total and amenable cyanide: destillation

Scope and application

1.1 this method is a reflex-distillation procedure used to extract soluble cyanide salts and many insoluble cyanide complexes from wastes and leaches. it is bases on the decomposition of nearly all cyanides by a reflux distillation procedure using a strong acid and a magnesium catalyst. Cyanide, in the form of hydrocyanic acid (HCN) is purged from the sample and captured into an alkaline scrubber solution. The concentration of cianyde in the scrubber solution is then determined by method 9014 of method 9213. This method may be used as a reflux destilation procedure for both total cyanide amenable to chlorination. The "reactive" cyanide content of a waste is not determined by this method. Refer to 40 CFR 2651.23 for information on the characteristic of reactive.

1.2 This method was designed to address the problem of "Trace" analyses (<1000 ppm). THe method may also be used for "minor" (1000 ppm - 10 000 ppm) and "major" (>10 000 ppm) analyses by adapting the appropriate sample dilution. Howerer, the amount od sodium hydroxide in the standars and the sample analyzed must be the same.

2.0 Summary of method

2.1 The cyanide, as hydrocyanic acid (HCN), is released from samples containing cyanide by means of reflux distillation operation under acidic conditions and absorbed in a scrubber containing sodium hydroxide solution. The cyanide concentration in the absorbing solution is then determined colorimetrically or titrametrically by method 9014 or by ion-selective electrode by method 9213.

3.0 Interferences

3.1 interferences are eliminated of reduced by using the distillation procedure. Chlorine and sulfide are interferences in method 9010.

3.2 Oxidizing agents such as chlorine as chlorine decompose most cyanides. Chlorine interferences can be removed by adding an excess of sodium arsenate to the waste prior to preservation and storage of the sample to reduce the chlorine to chloride which does not interfere.

3.3 sulfide interference can be removed by adding an excess of bismuth nitrate to the waste (to precipitate the sulfide) before destillation. Samples that contain hydrogen sulfide, metal sulfides, or other compounds that may produce hydrogen sulfide during the distillation should be treated by the addition of bismuth nitrate.

3.4 high results may be obtained for samples that contain nitrate and/or nitre. During the destination, nitrate and nitrite will form nitrous acid, which will react with some organic compounds to form oxides. These compounds once formed will decompose under test conditions to generate HCN. The possibility of interference of nitrate and nitrite is eliminated by pretreatment with sulfuric acid just before distillation. Nitrate and nitrite are interferences when present at levels higher than 10 mg/l and in conjunction with certain organic compounds.

3.5 Thiocyanate is reported to be an interference when present at very high levels. Levels of 10mg/l were no found to interfere.

3.6 Fatty acids, detergents, surfactants, and other compounds may cause foaming during the destination when they are present in high concentrations and may make the endpoint for the titrimetric determination difficult to detect. Refer to Sec. 6.7 for an extraction procedure to eliminate this interference.

4.0 Apparatus and materials

4.1 reflux distillation apparatus such as show in figure 1 or figure 2. the boiling flask should be of one liter size with inlet tube and provision for condenser. the gas scrubber may be a 270 ml fisher milligan scrubber or equivalent. The reflux apparatus may be a wheaton 377160 distillation unit or equivalent.

4.2 hot plate stirrer / heading mantle

4.3 PH meter

4.4 Amber light

4.5 Vaccum source

4.6 refrigerator

4.7 Erlenmeyer flask 500 ml

4.8 KL starch paper

4.9 calss a volumetric flask 1000, 250 and 100 ml

5.0 REAGENTS

5.1 Reagent grade chemicals shall be used in all test. Unless otherwise indicated, it is intended that all reagents shall conform to the specifications of the committee on Analytical Reagents of the American Chemical Society, where such specifications are available. Other grades may be used, provided it is first ascertained that the reagents is of sufficiently high purity to permit use without lessening the accuracy of the determination.

5.2 Reagents water. all references to water in this method refer to reagent water, as defined in chapter one.

5.3 Reagents for sample collection, preservation, and handling

5.3.1 Sodium arsenate (0.1N), NaAsO2 Dissolve 3.2 of NaAsO2 in 250 ml water

5.3.2 Ascorbic acid C6H8O6

5.3.3 Sodium hydroxide solution (50%), NaOH. Commercially available

5.3.4 Acetic acid (1.6M) CH3COOH Dilute one part of concentrated acetic acid with 9 parts od water

5.3.5 2,2,2-Trimethylpentane, C8H18

5.3.6 Hexane C6H14

5.3.7 Chloroform CHCl3

5.4 Reagetns for cyanides amenable to chlorination

5.4.1 Calcium hypochlorite solution (0.35M), Ca(OCl)2 Combine 5gr of calcium hypochlorite and 100 ml of water. Shake before using

5.4.2 Sodium hydroxide solution (1.25N), NaOH. Dissolve 50gr of NaOH in 1 liter of water

5.4.3 Sodium arsenite (0.1N). See sec 5.3.1

5.4.4 Potassium iodide starch paper

5.5 Reagents for distillation

5.5.1 Sodium hydroxide (1.25N) see sec. 5.4.2

5.5.2 Bismuth nitrate (0.062M), Bi(NO)3 /5H2O. Dissolve 30gr of Bi(NO)3 / 5H2O

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