Iron ores occur in igneous, transformed, or sedimentary rocks. The most widely distributed iron-containing minerals are oxides, such as hematite (Fe2O3), magnetite (Fe3O4), or limonite (FeO(OH) · n H2O), but carbonates such as siderite (FeCO3) are also important.

The total iron content in iron ore plays a central economic role for mining companies. The higher the iron content in the ore, the more profitable the mining operation. Therefore, a fast and accurate analysis is important to determine the most profitable areas to work.

In this Application Note, the iron determination according to ISO/TS 2597-4 is presented. A sample of iron ore is dissolved in hydrochloric acid at elevated temperatures. Afterwards, the total iron content is determined quickly and accurately by potentiometric titration using the Pt ring electrode and potassium dichromate as titrant.

The method is demonstrated for various iron ore samples. The iron ore is milled until the grain size is less than 160 µm.

905 Titrando with tiamo. Example setup for the determination of the iron content in iron ore.
Figure 1. 905 Titrando with tiamo. Example setup for the determination of the iron content in iron ore.

This analysis is carried out on a 905 Titrando equipped with a rod stirrer, combined Pt ring electrode, and temperature sensor. Additionally, a heating plate is needed.

Hydrochloric acid, deionized water, and few drops of tin(II) hydrochloride are added to a reasonable amount of prepared sample. The mixture is heated for one hour at 80 °C, followed by 10 minutes at 95 °C. Afterwards by visual inspection of a color change, iron(III) is reduced with tin(II) chloride, and then titanium(III) chloride is added with an excess, which is then oxidized.

After cooling the sample down to room temperature, deionized water and an acid mixture (phosphoric acid and sulfuric acid) are added. Then the sample is titrated with standardized potassium dichromate until after the equivalence point.

The analysis demonstrates acceptable results and well-defined titration curves. Results are summarized in Table 1. An example titration curve is displayed in Figure 2.

Table 1. Mean total iron content of various iron ore samples determined with a Titrando system (n = 4).
Sample
Mean SD(rel) in %
1 65.11% 0.21%
2 54.25% 0.27%
3 62.81% 0.41%
4 66.78% 0.32%
5
66.18% 0.45%
Figure 2. Example titration curve of iron content determination.

After sample preparation, the determination of iron content in iron ores can be performed reliably and cost-efficiently by using a Metrohm autotitrator. Fast and precise determination according to ISO/TS 2597-4 is possible.

The presented method provides an inexpensive and easily performable approach to estimate if an extraction of iron from iron ore is economically feasible or not.

Author

Metrohm AG

Ionenstrasse
9100 Herisau

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