TSO 1620 NTERNATIONAL STANDARD INTERNATIONAL ORGANIZATION FOR STANDARDIZATION MEKIYHAPOIHA OPrAHW3ALM IO CTAHIAPTW3ALIH.ORGANISATION INTERNATIONALE DE NORMALISATION Cryolite, natural and artificial -- Determination of silica content -- Reduced molybdosilicate spectrophotometric method Cryolithe, naturelle et artificielle - Dosage de la silice -- Methode spectrophotométrique au molybdosilicate reduit First edition - 1976-09-15 ANsr internat Doc Sert Ref. No. ISO 1620-1976 (E) UDC 553.634 : 546.284 : 543.42 Descriptors : aluminium ores, cryolite, chemical anaiysis, determination of content, silicon dioxide, spectrophotometric analysis. Copyright international Organizationfor Standardization Price based on 5 pages tted without license from IHS Not for Resale FOREWORD ISO (the International Organization for Standardization) is a worldwide federation of national standards institutes (IsO Member Bodies). The work of developing Internationa! Standards is carried out through ISO Technical Committees. Every Member Body interested in a subject for which a Technical Committee has been set up has the right to be represented on that Committee. Internationai organizations, governmental and non-governmental, in liaison with IsO, aliso take part in the work. Draft International Standards adopted by the Technicail Committees are circuiated to the Member Bodies for approval before their acceptance as International Standards by the Iso Council. Prior to 1972, the results of the work of the Technical Committees were pubished as Iso Recommendations; these documents are now in the process of being transformed into International Standards. As part of this process, Technical Committee iSO/TC 47 has reviewed ISO Recommendation R 1620 and found it replaces 1S0 Recommendation R 1620-1970 to which it is technically identical. isO Recommendation R 1620 was approved by the Member Bodies of the following countries : Australia Hungary Romania Austria India South Africa, Rep. of Belgium Iran Spain Brazil Israel Sweden Chile Italy Switzerland Thailand Czechoslovakia Netherlands Egypt,Arab Rep.of New Zealand Turkey Norway United Kingdom France Germany Peru U.S.S.R. Greece Poland Yugoslavia The Member Body of the following country expressed disapproval of the Recommendation on technical grounds : Canada International Standard. International Organization for Standardization, 1976 : Printed in Switzerland Copyright International Organization for Standardization nse from IHS Not for Resale ISO 1620-1976 (E) INTERNATIONAL STANDARD Cryolite, natural and artificial - Determination of silica content -- Reduced molybdosilicate spectrophotometric method 1 SCOPE AND FIELD OF APPLICATION 4.3 Nitric acid, approximately 8 N solution. International Standard specifies reduced Dilute 540 ml of nitric acid, p approximately 1,40 g/ml, This molybdosilicate spectrophotometric method for the deter- about 68 % (m/m) solution, with water to 1 000 ml. mination of the silica content of natural and artificial cryolite and of naturai and synthetic materials having a 4.4 Sodium motybdate, 195 g/l solution (0,8 M approxi- molar ratio (NaF/AiF3) between 3 and 1,7 approximately. mately). The method is applicable to products the phosphorus(V) content of which does not exceed oxide(P205) 0,02 % (m/m). of sodium molybdate dihydrate (Na2MoO4.2H20) in hot water and, after cooling, dilute to 100 ml. 1.1 Special case (under study) Transfer the solution to a bottle made of silica-free material and, if necessary, filter before use. Phosphorus(V) oxide contents greater than 0,02 % (m/m). 4.5 Tartaric acid,100 g/l solution. 2 REFERENCE IsO 1619, Cryolite, natural and artificial -- Preparation and storage of test samples. 4.6 Sulphuric acid, approximately 16 N solution. Carefully add 450 ml of sulphuric acid, p approximately 3 PRINCIPLE 1,84 g/ml, about 96 % (m/m) solution, to about 500 mi of water: Cool, dilute to 1 000 ml and mix. Alkaline fusion of a test portion by means of a mixture of sodium carbo