1、Designation: D7237 15D7237 15aStandard Test Method forFree Cyanide and Aquatic Free Cyanide with Flow InjectionAnalysis (FIA) Utilizing Gas Diffusion Separation andAmperometric Detection1This standard is issued under the fixed designation D7237; the number immediately following the designation indic
2、ates the year oforiginal adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope*1.1 This test method is used to establish the
3、concentration of free cyanide in an aqueous wastewater, effluent and in-stream freecyanide concentrations after mixing treated water with receiving water. The test conditions of this test method are used to measurefree cyanide (HCN and CN-) and cyanide bound in the metal-cyanide complexes that are e
4、asily dissociated into free cyanide ionsat the pH of 6. Free cyanide is determined at pH 6 at room temperature. The aquatic free cyanide can be determined by matchingthe pH to the water in the receiving environment in the range of pH 6 to 8. The extent of HCN formation is less dependent ontemperatur
5、e than the pH; however, the temperature can be regulated if deemed necessary for aquatic free cyanide to furthersimulate the actual aquatic environment.1.2 The free cyanide test method is based on the same instrumentation and technology that is described in Test Method D6888,but employs milder condi
6、tions (pH 6-868 buffer versus HCl or H2SO4 in the reagent stream), and does not utilize liganddisplacement reagents.1.3 The aquatic free cyanide measured by this procedure should be similar to actual levels of HCN in the original aquaticenvironment. This in turn may give a reliable index of toxicity
7、 to aquatic organisms.1.4 This procedure is applicable over a range of approximately 5 to 500 g/L (parts per billion) free cyanide. Sample dilutionmay increase cyanide recoveries depending on the cyanide speciation; therefore, it is not recommended to dilute samples. Higherconcentrations can be anal
8、yzed by increasing the range of calibration standards or with a lower injection volume. In accordancewith Guide E1763 and Practice D6512 the lower scope limit was determined to be 9 g/L for chlorinated gold leaching barreneffluent water and the IQE10 % is 12 g/L in the gold processing detoxified rev
9、erse osmosis permeate waste water sample matrix.1.5 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.1.6 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsib
10、ilityof the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatorylimitations prior to use. Specific hazard statements are given in 8.6 and Section 9.2. Referenced Documents2.1 ASTM Standards:2D1129 Terminology Relating to WaterD1193
11、Specification for Reagent WaterD1293 Test Methods for pH of WaterD2036 Test Methods for Cyanides in WaterD2777 Practice for Determination of Precision and Bias of Applicable Test Methods of Committee D19 on WaterD3856 Guide for Management Systems in Laboratories Engaged in Analysis of WaterD4841 Pra
12、ctice for Estimation of Holding Time for Water Samples Containing Organic and Inorganic ConstituentsD5847 Practice for Writing Quality Control Specifications for Standard Test Methods for Water AnalysisD6512 Practice for Interlaboratory Quantitation Estimate1 This test method is under the jurisdicti
13、on of ASTM Committee D19 on Water and is the direct responsibility of Subcommittee D19.06 on Methods for Analysis forOrganic Substances in Water.Current edition approved Feb. 1, 2015June 1, 2015. Published March 2015June 2015. Originally approved in 2006. Last previous edition approved in 20102015 a
14、sD7237 10.D7237 15. DOI: 10.1520/D7237-15.10.1520/D7237-15A.2 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refer to the standards Document Summary page on the ASTM website.T
15、his document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Becauseit may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior edit
16、ions as appropriate. In all cases only the current versionof the standard as published by ASTM is to be considered the official document.*A Summary of Changes section appears at the end of this standardCopyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959
17、. United States1D6696 Guide for Understanding Cyanide SpeciesD6888 Test Method forAvailable Cyanide with Ligand Displacement and Flow InjectionAnalysis (FIA) Utilizing Gas DiffusionSeparation and Amperometric DetectionD7365 Practice for Sampling, Preservation and Mitigating Interferences in Water Sa
18、mples for Analysis of CyanideD7728 Guide for Selection of ASTM Analytical Methods for Implementation of International Cyanide Management CodeGuidanceE691 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test MethodE1601 Practice for Conducting an Interlaboratory Study
19、 to Evaluate the Performance of an Analytical MethodE1763 Guide for Interpretation and Use of Results from Interlaboratory Testing of Chemical Analysis Methods (Withdrawn2015) (Withdrawn 2015)33. Terminology3.1 DefinitionsFor definitions of terms used in this test method, refer to Terminology D1129
20、and Guide D6696.3.1.1 aquatic free cyanide, nfree cyanide measured when the buffer or temperature is adjusted to mimic the receiving-waterenvironment.3.1.2 free cyanide, nsum of the free cyanide (HCN and CN-) and cyanide bound in the metal-cyanide complexes that are easilydissociated into free cyani
21、de under the test conditions described in this test method at pH 6 and room temperature.4. Summary of Test Method4.1 The test is generally performed at room temperature, but temperature of the sample and flow injection reagents can beregulated to match the aquatic environment if necessary to measure
22、 aquatic free cyanide.4.2 The sample is introduced into a carrier solution of the flow injection analysis (FIA) system via an injection valve andconfluence downstream with a phosphate buffer solution at pH 6 to measure free cyanide or in the range of pH 6 to 8 to measureaquatic free cyanide. The rel
23、eased hydrogen cyanide (HCN) gas diffuses through a hydrophobic gas diffusion membrane into analkaline acceptor stream where the CN- is captured and sent to an amperometric flowcell detector with a silver-working electrode.In the presence of cyanide, silver in the working electrode is oxidized at th
24、e applied potential. The anodic current measured isproportional to the concentration of cyanide in the standard or sample injected.4.3 Calibrations and sample data are processed with the instruments data acquisition software.5. Significance and Use5.1 Cyanide and hydrogen cyanide are highly toxic. R
25、egulations have been established to require the monitoring of cyanide inindustrial and domestic wastes and surface waters.45.2 It is useful to determine the aquatic free cyanide to establish an index of toxicity when a wastewater is introduced into thenatural environment at a given pH and temperatur
26、e.5.3 This test method is applicable for natural water, saline waters, and wastewater effluent.5.4 Free cyanide measured using this test method is applicable for implementation of the International Cyanide Code Guidancein accordance with Guide D7728.6. Interferences6.1 Sulfide will diffuse through t
27、he gas diffusion membrane and can be detected in the amperometric flowcell. Oxidizedproducts of sulfide can also rapidly convert CN- to SCN- at a high pH. Refer to 11.3 for sulfide removal.6.2 Refer to 6.1 of Test Method D6888 and Test MethodMethods D2036 for elimination of cyanide interferences.6.3
28、 Residual flotation reagents have been shown to interfere,5 which is indicated by failure of the amperometric signal to returnto baseline compared to the standards. This effect is attributed to the formation of volatile carbon disulfide. If this interference isencountered, verify by comparing with a
29、nalysis using Test Method D6888 including bismuth nitrate in the acidification reagenton a solution without sodium hydroxide preservation, which should provide confirmation due to lower results.7. Apparatus7.1 The instrument must be equipped with a precise sample introduction system, a gas diffusion
30、 manifold with hydrophobicmembrane, and an amperometric detection system to include a silver working electrode, a Ag/AgCl reference electrode, and a Ptor stainless steel counter electrode. An example of the apparatus schematic is shown in Fig. 1. Example instrument settings areshown in Table 1.3 The
31、 last approved version of this historical standard is referenced on www.astm.org.4 40 CFR Part 136.5 Solujic, L., and Milosavljevic, E., Flotation Reagents Testing and Analyses of Cyanide Spiked Samples, Report to Newmont Mining Corporation, July 30, 2011.D7237 15a2NOTE 1The instrument and settings
32、in Fig. 1 and Table 1 are shown as examples. The analyst may modify these settings as long as performance ofthe method has not been degraded. Contact the instrument manufacturer for recommended instrument parameters.7.2 An autosampler is recommended but not required to automate sample injections and
33、 increase throughput.Autosamplers areusually available as an option from the instruments manufacturer. If the sample is to be analyzed at a constant temperature otherthan the temperature of the room, manual injections may be required unless the autosampler is equipped to maintain constanttemperature
34、.7.3 If aquatic free cyanide at a temperature other than room temperature is required, a constant temperature bath capable ofmaintaining the temperature of the aquatic environment within 60.5C should be used to regulate the temperature of the flowinjection reagents and samples.7.4 Data Acquisition S
35、ystemUse the computer hardware and software recommended by the instrument manufacturer tocontrol the apparatus and to collect data from the detector.7.5 Pump TubingUse tubing recommended by instrument manufacturer. Replace pump tubing when worn, or when precisionis no longer acceptable.7.6 Gas Diffu
36、sion MembranesA hydrophobic membrane which allows gaseous hydrogen cyanide to diffuse from the donorto the acceptor stream at a sufficient rate to allow detection. The gas diffusion membrane should be replaced when the baselinebecomes noisy, or every 1 to 2 weeks.7.7 Use parts and accessories as dir
37、ected by instrument manufacturer.C = carrier (water), R = reagent buffer (variable: pH 6 for free cyanide and pH 6-8 for aquatic free cyanide, 0.2 M phosphate buffer),A= acceptor solution (0.1 M NaOH),S = sample, P = peristaltic pump (flow rates in mL/min), I = injection valve (200 Lsample loop), MC
38、 = mixing cool (3060 cm 0.5 mm i.d.), positioned in optional constanttemperature manifold, D = gas-diffusion cell, FC = amperometric flow cell, PO/DAT = potentiostat/data collection device running data acquisition software, W = waste flows.FIG. 1 Example of Flow Injection Manifold for the Determinat
39、ion of Aquatic Free CyanideTABLE 1 Flow Injection Analysis ParametersFIA InstrumentParameterRecommendedMethod SettingPump Flow Rates 0.5 to 2.0 mL/minCycle period (total) Approximately 120 secondsSample load period At least enough time to completely fill thesample loop prior to injectionInjection va
40、lve rinse timebetween samplesAt least enough time to rinse thesample loopPeak Evaluation Peak height or areaWorking Potential 0.0 V vs. Ag/AgClD7237 15a38. Reagents and Materials8.1 Purity of ReagentsReagent grade chemicals shall be used in all tests. Unless otherwise indicated, it is intended that
41、allreagents shall conform to the specifications of the American Chemical Society, where such specifications are available.6 Othergrades may be used, provided it is first ascertained that the reagent is of sufficiently high purity to permit its use without lesseningthe accuracy of the determination.8
42、.2 Purity of WaterUnless otherwise indicated, references to water shall be understood to mean reagent water that meets thepurity specifications of Type I or Type II water, presented in Specification D1193.8.3 Sodium Hydroxide Solution (1.00M NaOH)Dissolve 40 g NaOH in laboratory water and dilute to
43、1 L.8.4 Sodium Hydroxide and Acceptor Solution (0.10 M NaOH)Dissolve 4.0 g NaOH in laboratory water and dilute to 1 L.NOTE 2Acceptor solution concentration of 0.025 M NaOH has also been found to be acceptable.8.5 CarrierWater, as described in 8.2.NOTE 3Carrier solution containing 0.025 M NaOH has al
44、so been found to be acceptable.8.6 Stock Cyanide Solution (1000 g/mL CN-)Dissolve 2.51 g of KCN and 2.0 g of NaOH in 1 L of water. Standardize withsilver nitrate solution as described in Test Methods D2036, 16.2. Store the solution under refrigeration and check concentrationapproximately every 6 mon
45、ths and correct if necessary.7 (WarningBecause KCN is highly toxic, avoid contact or inhalation.)8.7 Intermediate Cyanide Standards:8.7.1 Intermediate Standard 1 (100 g/mL CN-)Pipette 10.0 mL of stock cyanide solution (see 8.6) into a 100 mL volumetricflask containing 1 mL of 1.0 M NaOH (see 8.3). D
46、ilute to volume with laboratory water. Store under refrigeration. The standardshould be stable for at least 2 weeks.8.7.2 Intermediate Cyanide Solution 2 (10 g/mL CN-)Pipette 10.0 mL of Intermediate Cyanide Solution 1 (see 8.7.1) intoa 100 mL volumetric flask containing 1.0 mL of 1.00 M NaOH (see 8.
47、3). Dilute to volume with laboratory water. The standardshould be stable for at least 2 weeks.8.8 Working Cyanide Calibration StandardsPrepare fresh daily as described in 8.8.1 and 8.8.2 ranging in concentration from2 to 500 g/L CN-.8.8.1 Calibration Standards (20, 50, 100, 200, and 500 g/L CN-)Pipe
48、tte 20, 50, 100, 200, and 500 L of IntermediateStandard 1 (see 8.7.1) into separate 100 mL volumetric flasks containing 1.0 mL of 0.10 M NaOH (see 8.4). Dilute to volume withlaboratory water.8.8.2 Calibration Standards (2, 5, and 10 g/L CN-)Pipette 20, 50, and 100 L of Intermediate Cyanide Solution
49、2 (see 8.7.2)into separate 100 mL volumetric flasks containing 1.0 mL of 0.10 M NaOH (see 8.4). Dilute to volume with laboratory water.8.9 Cyanide Electrode Stabilization Solution (Approximately 5 ppm as CN-)Pipette 500 L of Stock Cyanide (see 8.6) intoa 100 mL volumetric flask containing 1.0 mL of 0.10M M NaOH (see 8.4). Dilute to volume with laboratory water. The solutionshould be stored under refrigeration.8.10 Acetate BufferDissolve 410 g of sodium acetate trihydrate (NaC2H3O23H2O) in 500 mLof laboratory water.Add glacialacetic
