Environ. Scl. Technol. 1983, 17, 439-441
Keyser, T. R.; Natusch, D. F. S.; Evans, C. A,, Jr.; Linton, R. W. Environ. Sci. Technol. 1978, 12, 768-773. Natusch, D. F. S.; Wallace, J. R. Science (Washington,D.C.) 1974,186,695-697. Morrison, G. H.; Slodzian, G. Anal. Chem. 1975, 47, 933A-944A. Wechsung, R.; Hillenkamp, F.; Kaufman, R.; Nitze, R.; Unsold, E.; Vogt, H. Microsc. Acta, Suppl. 1978, No. 2, 281-296. Denoyer, E.; Van Grieken, R.; Adams, F.; Natusch, D. F. S. Anal. Chem. 1982,54, 26A-41A. Van Dyck, P.; Markowicz, A.; Van Grieken, R. X-Ray Spectrom. 1980, 9, 70-76. Van Craen, M.; Natusch, D. F. S.;Adams, F. Anal. Chem. 1982,54, 1786-1792. Ganjei, J. D.;Leta, D. P., Morrison, G. H. Anal. Chem. 1978, 50, 285-290. Plog, C.; Wiedmann, L.; Benninghoven, A. Surf. Sci. 1977, 67, 565-580. Fisher, G. L.; Natusch, D. F. S. “Analytical Methods for Coal and Coal Products”; K m , C., Jr., Ed.; Academic Press: New York, 1979; Vol. 111, Chapter 54.
vironment but are also apparently quite soluble and therefore available. Acknowledgments
We thank Peter Van Dyck for performing the XRF measurements. Registry No. Na, 7440-23-5; Al, 7429-90-5; Si, 7440-21-3;C1, 22537-15-1; K, 7440-09-7; Ca, 7440-70-2; Ti, 7440-32-6; V, 744062-2; Cr, 7440-47-3;Mn, 7439-96-5; Fe, 7439-89-6;Co, 7440-48-4; Cu, 7440-50-8; Zn, 7440-66-6; Ba, 7440-39-3; Pb, 7439-92-1; Mg, 7439-954; P, 7723-140; S, 7704-34-9; Br, 10097-32-2;Sr, 7440-246.
Literature Cited Davison, R. L.; Natusch, D. F. S.; Wallace, J. R.; Evans, C. A., Jr., Environ. Sci. Technol. 1974, 8, 1107-1113. Kaakinen, J. W.; Jorden, R. M.; Lawasani, M. H.; West, R. E. Environ. Sci. Technol. 1975, 9, 862-869. Klein, D. H.; Andren, A. W.; Carter, J. A.; Emery, J. F.; Feldman, C.; Fulkerson, W.; Lyon, W. S.; Ogle, J. C.; Talmi, Y.; Van Hook, R. I.; Bolton, N. Environ. Sci. Technol. 1975, 9,973-979. Smith, R. D.; Campbell, J. A.; Nielson, K. K. Environ. Sci. Technol. 1979, 13, 553-558. Taylor, D. R.; Tompkins, M. A,; Kirton, S. E.; Mauney, T.; Natusch, D. F. S.; Hopke, P. K. Environ. Sci. Technol. 1982, 16, 148-153. Bertine, K. K.; Goldberg, E. D. Science (Washington,D.C.) 1971,173, 233-236. Linton, R. W.; Williams, P.; Evans, C. A., Jr.; Natusch, D. F. S. Anal. Chem. 1977,49, 1514-1521.
Received for review March 16,1982. Revised manuscript received February 23, 1983. Accepted March 7, 1983. D.F.S.N. acknowledges the support of a Guest Professorship from the Belgian NFWO and a period of study leave from Colorado State University, Fort Collins, CO, during which time this work was performed. M.J.V.C. acknowledges the assistance of IWONL, Belgium. This work was carried out under Grant 80-85/10 of the Interministrial Commission for Science Policy, Belgium.
Practical Method for Determination of Total Cyanide in Metal-Containing Wastewaters Takashl Yoshlda NEC Environment Engineerlng, Ltd., Mlyamae-ku, Kawasaki, Japan
Yutaka Tamaura” and Takashl Katsura Department of Chemistry, Tokyo Instltute of Technology, Ookayama, Meguro-ku, Tokyo 152, Japan
w A new procedure for total and latent cyanide in metal-containing wastes is reported. The method employs gas chromatographic measurement of BrCN extracted from brominated aqueous samples with ethyl ether. Alternate use of excess arsenite and permanganate permits measurement of total and latent cyanide values apparently free of interferences common to the present Japanese standard method. The regulated value of cyanide in effluents discharged to a municipal sewer or to a river in Japan is 1 mg/L of total cyanide (1,2). The total cyanide is determined by distilling a strongly acidified sample in the presence of EDTA (ethylenediaminetetraacetic acid) into a sodium hydroxide solution, followed by analysis of the distillate by colorimetry, titration, or cyanide-sensitive electrode (1, 3,4). The total cyanide method measures simple cyanide, weakly complexed cyanides (with Zn2+,Cd2+),and strongly complexed cyanide such as hexacyanoferrate(I1) ( 4 ) . A problem in the present total cyanide analysis is the distillation of H2S, which interferes with the analysis of the distillates by the colorimetric and titrimetric methods. In the colorimetric analysis of distillate, sulfide consumes chromophoric reagent, and in the titrimetric method, sulfide consumes silver nitrate titrant. Another problem is that otherwise unresponsive cyanide forms (e.g., thiocyanate) can be broken down to free cyanide (“latent 0013-936X/83/0917-0439$01.50/0
cyanide”) when oxidizing substances are present in the sample. Usually, metal-containing wastes from laboratories of universities or research institutes include interfering substances such as sulfide and latent cyanide, as well as various oxidizing and reducing substances. This paper describes a practical gas chromatographic method for the determination of total cyanide in metal-containing wastes from the laboratories. Experimental Section
Chemicals. All chemicals used were analytical grade, and all chemical solutions were prepared with distilled water. Instruments. A Shimazu GC-4CM gas chromatograph equipped with an electron capture detector (63Ni)was used. A Toha Electric Wave TCN-1B total cyanide analyzer was used for the distillation of the samples. Distillation in Total Cyanide Determination. A sample solution (50 mL) was neutralized and transferred to a distillation flask, and then 10 mL of an EDTA solution (10 m/v), 2.5 mL of a NaAsOa solution (0.9 M), and 3 mL of phosphoric acid were added successively. For the studies on the effect of the reducing substances and on the removal of sulfide interference by arsenite, the addition of the arsenite solution was omitted, and the concentrations of the reducing substances and arsenite in the sample were varied. The resultant solution was boiled for 20 min
0 1983 American Chemical Society
Environ. Sci. Technol., Vol. 17, No. 7, 1983 439
Table I. Effects of Sulfide, Thiosulfate, and Sulfite on the Analysis of Total Cyanide by Gas Chromatography and b y Colorimetry and the Removal of Sulfide Interference by Arsenite recovery of cyanide (0.3 mg/L of CN- added) foreign ion added, mg/L none
SaI
0
I
I
2
4 R e t e n t i o n Time
6
8
10
( rnin )
Figure 1. Gas chromatogram of cyanogen bromide generated from cyanide: CN-, 0.3 mg/L glass column (3 mm 0.d. X 1 m) packed wlth Porapak QS (80-100 mesh); carrier gas, N2 (30 mL/min); column temperature, 130 OC; detector and injectlon temperatures, 160 OC.
to distill cyanide into 40 mL of a 0.2 N NaOH, while nitrogen gas was passed through the solution (0.2 L/min). Latent Cyanide Determination. A KMn04 solution (0.6 mM) was used instead of the arsenite solution described in the total cyanide determination. The total cyanide value was obtained as the difference between the total cyanide value determined when adding the excess permanganate and the value determined when using excess arsenite. Analysis of Distillate by Gas Chromatography. The cyanide in the distillate was analyzed by gas chromatography according to the method described by Nota et al. (5) and Honma et al. (6),but with modifications. The volume of the distillate was made up to 50.0 mL, and 2.0 mL of the solution was transferred to a 20-mL test tube that could be closed with a glass stopper. Into the test tube, 2 mL of H3P04solution (20 v%) and several drops of a bromine water (3 w/v%) were added; the bromine water was added dropwise until its color remained. The resultant solution was allowed to stand for 5 min to complete the transformation of cyanide to BrCN, and then 1 drop of a phenol solution (5%) was added to decompose the excess bromine. Subsequently, ethyl ether (16.0 mL) was added, and the test tube was shaken for 2 rnin to extract BrCN into ether. Two pL of the ether extract was injected into the gas chromatograph. A glass column (3 mm X 1m) packed with Porapak QS (80-100 mesh) was used. The temperatures of the column and the detector (and injector) were controlled to 130 and 160 OC, respectively. The flow of Nz carrier gas was adjusted to 30 mL/min. Figure 1 shows the gas chromatogram for a standard cyanide solution (0.3 mg/L) in which a peak of BrCN appears at 5.6 min of retention time; BrCN gives the peak at the retention time. The assignment of the peak to BrCN by mass spectrometry was reported by Honma et al. (6). The concentration was estimated from the peak area. The calibration curve was linear at 0.01-0.08 mg/L but slightly nonlinear in the range 0.1-0.4mg/L. An estimate of the precision was ascertained from the results of four samples each containing 0.1 mg/L of cyanide. The relative standard deviation was 6.8%.
Results and Discussion Effect of Reducing Substances during Distillation. Free cyanide was completely distilled in 20 min by this simple distillation process. Table I shows the recoveries of the free cyanide determined by colorimetry (pyridine440
Environ. Sci. Technoi., Vol. 17, No. 7, 1983
s,o:so;Sa-
+ As0,-
-I-As0,-b As0,-
1 10 50 1000 5000 1000 5000 1000 0
5000 10000
by GC, % 102 99 95 88
100 93 88 81
by colorimetry, % 99 83 86 0 0 0 0 0
81 89 100
pyrazolone) ( I ) and by gas chromatographyfor the samples containing the chemicals indicated in the table. Here, we use the term “gas chromatography” in the sense that it includes the reaction step transforming cyanide into BrCN and the ether extraction step. In the gas chromatograms for the results of Table I, only the BrCN peak appeared. The colorimetric analyses were strongly affected by the presence of sulfide, thiosulfate, and sulfite (S2-,50 mg/L; SZO3’-, greater than 1000 mg/L). However, as seen in Table I, the interference was very small when the distillates were analyzed by gas chromatography. Thus, cyanide in samples containing sulfide, thiosulfate, and sulfite (S2-,50 mg/L; Sz02- and S032-,1000 and 5000 mg/L) can be determined by gas chromatography, although the distillates are contaminated with the reducing substances such as sulfide during the distillation. In the conventional standard methods,(l, 7), sulfide in the sample solution or in the absorption solution is removed by treating the samples with lead carbonate or by redistilling after treating the distillate with potassium permanganate. Removal of Sulfide Interference by Arsenite. As seen in Table I, the recovery of free cyanide decreased significantly at high sulfide concentration (1000 mg/L), by using the total cyanide gas chromatographic procedure. However, when the distillation step was omitted, the cyanide was completely recovered at the high sulfide concentration. Thus, the sulfide at high concentration values interferes with the distillation step. To remove the sulfide interference in the distillation step, arsenite was included in the samples. Arsenite and sulfide form a precipitate, As2S3,which is relatively stable in the solution acidified with phosphoric acid, and distillation can be performed without removing the As2S3precipitate. As a routine procedure, 2.5 mL of NaAsO2 solution (0.9 M) was added to 50 mL of the sample (AsOz-, 4800 mg/L). However, as seen in Table I, when the sulfide concentration is around 1000 mg/L, an additional arsenite should be added. The metal-containing waste from laboratories is sometimes an oxidizing media and contains Clz, NO3-,Mn04-, and Cr2OT2-.Strongly complexed cyanide in the metallic waste is little decomposed with these oxidizing substances during storage. However, being not reduced prior to the distillation, the oxidizing substances decompose the cyanide during the total cyanide analysis or form free
Table 11. Liberation of Free Cyanide by the Reaction between Formaldehyde and Hydroxylamine during the Total Cyanide Analysis CNfound, chemicals added, mg/L mg/L formaldehyde 10 0.00 hydroxylamine 100 0.03 formaldehyde 10 0.14 hydroxylamine 100
Table 111. Determination of the Latent Cyanide Using Thiocyanate as a Latent Cyanide chemicals added to the SCN- sample solution,Qmg/L As0,-
1.1
5000
cyanide from latent cyanide. We have to check the presence of oxidizing substances. However, the check is actually impossible, since the waste includes many substances and metal ions with varying oxidation potentials, e.g., the potassium iodide test paper for checking the interfering oxidizing substances cannot be used for the Cu2+-containingsample. The addition of the excess arsenite seems to overcome this problem. In this case, when reducing substances such as S2-, S2032-,and SO3,- are contained instead of the oxidizing substances, they interfere with the colorimetry. But they do not interfere with the gas chromatography; therefore, we can analyze by the gas chromatography after the simple distillation. If we do analyze by colorimetry, we have to redistill the absorption solution after decomposing the reducing substances in it. ASTM standard recommends the use of arsenite to reduce the oxidizing substances, and Japanese Industrial Standard (JIS) recommends the use of both arsenite and hydroxylamine (1, 7). However, as seen in Table 11, when hydroxylamine was used instead of arsenite in the present method, an additional cyanide was determined for the formaldehyde-containing sample. This is due to the liberation of free cyanide by the decomposition of formaldoxime, which is formed by the reaction of formaldehyde and hydroxylamine during the distillation (4). Formaldehyde is commonly used in laboratories, and its presence in laboratory wastes is highly probable. Arsenite is the preferable reducing chemical for the total cyanide determination of the laboratory waste. This chemical also can remove the sulfide interference in the distillation step as described above. Latent Cyanide. When an excess oxidizing chemical such as permanganate is added into the sample instead of arsenite, the analytical value will be the sum of the total and latent cyanides. As seen in Table 111, when an excess permanganate was added into the samples containing thiocyanate (as a latent cyanide), thiocyanate was determined as free cyanide, but little cyanide was determined, excess arsenite being added. Thus, latent cyanide values can be obtained from the difference between the total cyanide value determined in the presence of excess permanganate and that in the presence of excess arsenite. A big problem in the treatment of the metallic wastes from laboratories is the presence of latent cyanide. If its concentration is high, with a fear of much cyanide generation, the waste should not be mixed with the wastes containing oxidizing substances. Thus, the determination of the latent cyanide concentration in the metallic wastes is important from the viewpoint of safety in the treatment.
Mn0,-
a
2.6 27 270 270
CNfound, mg/L 0.05
0.07 0.11 0.11
0.002
SCN- 0.12 mg/L as CN-.
Table IV. Total Cyanide in the Metallic Sample Solution
metal ions added
total cyanide, mg/L
none Fe3+ (100 mg/L) metal ionsQ (900 mg/L)
0.30 0.27 0.27
a CdZ+,Cuz+,Cr3+,Znz+,MnZ+,PbZ+,Fe3+,Niz+,and Hgz+ (each metal ion concentration was 100 mg/L).
Total Cyanide in the Metal-ContainingWastes. JIS describes the use of sufficient EDTA to decompose cyanometal complexed into the free cyanide (1). As seen in Table IV, when 10 mL of 10% w/v EDTA solution was added, about 90% of the cyanide was recovered for the sample containing 900 mg L of metal ions (Cd2+,Cu2+ Cr3+,Zn2+,Mn2+,Pb2+,Fe +,Ni2+,and Hg2+;each metai concentration was 100 mg/L). ASTM standard recommends the use of MgC1, as a decomposition catalyst. In the present method, however, the addition of MgC1, did not give a marked effect on the recovery of the cyanide from the metal-containing sample solution. This seems to be due to the difference in the acids used in the JIS and ASTM standard methods; H3P04is used in the JIS, while H2S04is used in the ASTM standard.
d
Registry No. CN-, 57-12-5;Fe, 7439-89-6;water, 7732-18-5.
Literature Cited (1) "Testing Methods for Industrial Waste Water"; Japanese Standards Association: Tokyo ("Total Cyanide"; Japanese Industrial Standard JIS K 0102, 1981; pp 110-115). (2) "Quality of Environment in Japan"; Japan Environmental Agency, 1979; p 309. (3) "Testing Methods for Industrial Waste Water"; Japanese Standards Association: Tokyo ("Total Cyanide"; Japanese Industrial Standard JIS K 0101, 1979; p 107-115. (4) Owerbach, D. J.-Water Pollut. Control Fed. 1980, 52, 2647-2654. ( 5 ) Nota, G.; Palombari, R. J . Chromatogr. 1973, 84, 37-41. (6) Honma, H.; Suzuki, K.; Yoshida, M.; Yanashima, H. Bunseki Kagaku, 1979, 28, T56-T60. (7) Annu. Book ASTM Stand. 1981, 31, 701-721.
Received for review August 30,1982. Revised manuscript received February 18, 1983. Accepted March 10, 1983.
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