Quick and Easy Dissolution of Chromite Ores, Ferrochromes, and Chromium Slags for ICP-OES without Using HF or HClO4

Apr 30, 2014

The traditional method for the dissolution of chromite ore, ferrochrome, and chromium slag samples is time-consuming and requires the use of hydrofluoric (HF) and perchloric (HClO 4 ) acids. A new sodium peroxide fusion method offers a quicker, safer, and more efficient alternative to working with these high-risk acids. Various samples and reference materials were used to validate the new method. This installment of "Atomic Perspectives" describes the fusion method, provides the conditions for inductively coupled plasma–optical emission spectrometry, and lists the accuracy and precision measurements for all prepared samples.

Although there are more than 10 known chromium minerals, only one remains a source of commercial interest. This mineral is known as chromite and has a theoretical composition of FeCr2O4 containing 68% of chromic oxide (Cr2O3), in which the proportions of Mg2+, Fe2+, and Cr3+, Al3+, and Fe3+ may vary considerably (1).

The main product generated by chromite is ferrochrome, a major component in the steel industry (2). In particular, the stainless steel industry uses more than 90% of the world's chromite output. The mining and steel industries must assess the quality of the chromite ore to optimize the grade of their stainless steel product. For this reason, the chemical analysis of the chromite ore as well as its final and waste products are mandatory. Metal analysis traditionally uses atomic absorption (AA) or inductively coupled plasma–optical emission spectrometry (ICP-OES) to measure the metal content in the ores and industrial products. However, the traditional dissolution method for chromite and ferrochrome is a multistep, multiacid digestion that requires the use of hydrofluoric (HF) and perchloric (HClO4) acids and can take 1–3 h (3,4). In the context of a laboratory handling many samples per year, this method would not be very appealing or efficient.

In this installment of "Atomic Perspectives," we present a new peroxide fusion technique that overcomes the problems incurred using the classic approaches for the preparation of chromite ores, ferrochromes, and chromium slags for ICP-OES analyses. This technique yields good analytical results for the broad range of elements found in these samples.