ASTM_D_6019_-_20.pdf

Designation:D601920Test Method forDetermination of Chromic Oxide in Basic ChromiumTanning Liquors(Ammonium Persulfate Oxidation)1This standard is issued under the fixed designation D6019;the number immediately following the designation indicates 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.Scope1.1 This test method covers the determination of chromicoxide in chrome tanning liquors,either simple,with addedaluminum or zirconium,or with the usual masking complexingagents.1.2 The values stated in SI units are to be regarded asstandard.No other units of measurement are included in thisstandard.1.3 This standard does not purport to address all of thesafety concerns,if any,associated with its use.It is theresponsibility of the user of this standard to establish appro-priate safety,health,and environmental practices and deter-mine the applicability of regulatory limitations prior to use.1.4 This international standard was developed in accor-dance with internationally recognized principles on standard-ization established in the Decision on Principles for theDevelopment of International Standards,Guides and Recom-mendations issued by the World Trade Organization TechnicalBarriers to Trade(TBT)Committee.2.Summary of Test Method2.1 The solution is oxidized with ammonium persulfateuntil the chromium is completely converted to the chromateion.The solution is boiled to complete oxidation of organicmaterials and to destroy excess ammonium persulfate;it is thencooled and acidified.Potassium iodide is added,and theliberated iodine is titrated with standardized sodium thiosul-fate.3.Terminology3.1 Definitions:3.1.1 recycled chrome(reacidified chrome),nthe mixtureobtained when spent chrome liquor is captured,filtered,precipitated with alkali and the precipitate is reacidified withsulfuric acid.4.Significance and Use4.1 The procedure described is for the quality control formanufacturing liquors and specifications for the purchase ofsuch liquors.4.2 The chromium content of the liquors determines theamount to be used to obtain the desired degree of tannage,andhence may be a matter for specification in the purchase ofleather.5.Reagents and Materials5.1 Purity of ReagentsReagent grade chemicals shall beused in all tests.Unless otherwise indicated,it is intended thatall reagents shall conform to the specifications of the Commit-tee onAnalytical Reagents of TheAmerican Chemical Society,where such specifications are available.2Other grades may beused,provided it is first ascertained that the reagent is ofsufficiently high purity to permit its use without lessening theaccuracy of the determination.5.2 Purity of WaterUnless otherwise indicated,referenceto water shall be understood to mean distilled water,deionizedwater or water of equal purity.5.3 Ammonium Persulfate20%solution 100 g of persul-fate into 500 mL water.5.3.1 Alternatively,ammonium persulfate may be added in6.6 as solid form using plastic scoopula.5.4 Starch Indicator,2%Make a paste of 2 g of solublestarch in about 10 mL of water,add 90 mL water,and boil for1 min with stirring.Cool.Refrigerate after use.The solution issubject to decomposition and should be renewed if a deep bluecolor is not obtained on addition of one drop of indicator to asolution of 1 drop tincture of iodine in 100 mL of water.5.5 Sodium Thiosulfate Solution,0.1 NDissolve 24.85 gof Na2S2O35H2O in water,add 1 g Na2CO3,and dilute to 1 L.5.5.1 StandardizationDrypotassiumdichromate(K2Cr2O7)in an oven at 130C for 2 h and cool in a desiccator.1This test method is under the jurisdiction of ASTM Committee D31 on Leatherand is the direct responsibility of Subcommittee D31.06 on Chemical Analysis.Current edition approved April 1,2020.Published May 2020.Originallyapproved in 1996.Last previous edition approved in 2015 as D6019 15.DOI:10.1520/D6019-20.2Reagent Chemicals,American Chemical Society Specifications,AmericanChemical Society,Washington,DC.For suggestions on the testing of reagents notlisted by the American Chemical Society,see Analar Standards for LaboratoryChemicals,BDH Ltd.,Poole,Dorset,U.K.,and the United States Pharmacopeiaand National Formulary,U.S.Pharmacopeial Convention,Inc.(USPC),Rockville,MD.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United StatesThis international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for theDevelopment of International Standards,Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade(TBT)Committee.Weigh into a glass stoppered Erlenmeyer flask(500 mL)about0.2 g of potassium dichromate to an accuracy of 0.1 mg.Dissolve in 250 mLwater,add 15 mL1:4 hydrochloric acid,20mL of 10%potassium iodide solution,sto