The effect of copper on iron reduction and its application to the determination of total iron content in iron and copper ores by potassium dichromate titration

• Published in: Talanta (Oxford) Vol. 125; pp. 425 - 431
• Main Authors: Hu, Hanjun, Tang, Yang, Ying, Haisong, Wang, Minghai, Wan, Pingyu, Jin Yang, X.
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 01.07.2014
• Subjects: Borohydrides; Colorimetry; Copper; Copper ores; Dichromate titration; Iron; Iron and copper ores; Potassium; Potassium borohydride; Potassium dichromate; Reduction; Total iron content; Total iron content; Iron and copper ores; Potassium borohydride; Colorimetry; Dichromate titration
• ISSN: 0039-9140; 1873-3573
• DOI: 10.1016/j.talanta.2014.03.008

The International Standard Organization (ISO) specifies two titrimetric methods for the determination of total iron content in iron ores using potassium dichromate as titrant after reduction of the iron(III) by tin(II) chloride and/or titanium(III) chloride. These two ISO methods (ISO2597-1 and ISO2597-2) require nearly boiling-point temperature for iron(III) reduction and suffer from copper interference and/or mercury pollution. In this study, potassium borohydride was used for reduction of iron(III) catalyzed by copper ions at ambient temperatures. In the absence of copper, iron(III) reduction by potassium borohydride was sluggish while a trace amount of copper significantly accelerated the reduction and reduced potassium borohydride consumption. The catalytic mechanism of iron(III) reduction in sulfuric acid and hydrochloric acid was investigated. Potassium borohydride in sodium hydroxide solution was stable without a significant degradation within 24h at ambient conditions and the use of potassium borohydride prepared in sodium hydroxide solution was safe and convenient in routine applications. The applicability of potassium borohydride reduction for the determination of total iron content by potassium dichromate titration was demonstrated by comparing with the ISO standard method using iron and copper ore reference materials and iron ore samples. Copper ion has an catalytic effect on Fe(III) reduction by potassium borohydride and the generation of red-brown metallic copper particles ensure a full reduction of Fe(III). [Display omitted] •Reduction of Fe(III) with KBH4 is rapidly catalyzed by Cu2+ at ambient conditions.•Completion of Fe(III) reduction is indicated by red-brown metallic copper particles.•Milligram Cu is sufficient to catalyze the reduction and does not interfere with iron determination.•The proposed method for determination of total iron in iron and copper ores is simple and rapid.•The proposed method is of similar accuracy and precision with the ISO standard methods.