ANALYSIS OF SLAG CONTENT IN FERRO ALLOYS
FOURIER TRANSFORMED INFRARED SPECTROMETRY
PART I – FERRO MANGANESE
Slag is a partially vitreous byproduct of metal smelting to separate the metal fraction from the unwanted fraction. Ores often have unwanted minerals associated with them, like silica, and during the process of smelting this can combine with other materials in the furnace and the fuel to produce something that looks a lot like lava. This liquid rock or slag, like other industrial byproducts, actually has many uses, and rarely goes to waste. It can usually be considered to be a mixture of metal oxides and silicon dioxide. Slag appears in concrete, aggregate road materials, as ballast, and is sometimes used as a component of phosphate fertilizer.
Ferroalloys like FeMn are mostly produced in submerged electric arc furnaces. Slags in the FeMn process are Al2O3-MgO-SiO2 based with minor contents of CaO and MnOx, originating from silicate minerals but can have quite large composition range depending on the manganese ore and its gangue minerals. Characteristic of the FeMn process is that the slag is rich in manganese oxide up to above 30%. The MnOx in slag is not only divalent oxides but also of some higher valent of Mn3+. In FeMn production conditions the slag consists mainly of Mn2+.
In ferromanganese alloy, Fe and Mn are present in metallic bonding, whereas slag contains metal – oxygen and Si – O bonding having specific vibration absorption in IR region. This method recognizes this IR wavelength and utilizes it for finding out the slag contamintion in supplied FeMn alloy.
A PerkinElmer FTIR (spectrum 100) with HATR was used for this analysis. Pure FeMn slag is oven dried and absorptiogram has been taken showing a max. absorption at 870 – 875 cm-1.
Three different concentrations of slag samples (25%, 50%, 75%) and three concentrations in lower range (1%, 5%, 10%) are also prepared using Alumina as diluents and FTIR absorptiograms are taken.
ABSORPTIOGRAMS OF 25% – 75% FeMn SLAG
ABSORPTIOGRAMS OF 1% – 10% FeMn SLAG DILUTED WITH ALUMINA
ABSORPTIOGRAM OF ALUMINA (used as DILUENT)
Standard curves are drawn in the two different concentration range, both higher (25, 50 & 75%) and lower (1, 5 & 10%). Both show excellent correlations with R2 value of 0.9983 and 0.9996. Another standard curve has been drawn with 2, 5 & 7% concentration with R2 value of 0.9999.
STANDARD CURVE DRAWN WITH 25, 50 & 75% CONCENTRATION OF FeMn SLAG (R2 = 0.9983)
STANDARD CURVE DRAWN WITH 1, 5 & 10% CONCENTRATION OF FeMn SLAG (R2 = 0.9996)
STANDARD CURVE DRAWN WITH 2, 5 & 7% CONCENTRATION OF FeMn SLAG (R2 = 0.9999)
STANDARD CURVE DRAWN WITH 2, 5 & 10% FeMn SLAG AND PURE FERRO ALLOY INSTEAD OF Al2O3 (R2 = 0.9967)
RESPECTIVE SPECTRA of :
Slag : Metal = 10 : 90; Slag : Metal = 5 : 95; Slag : Metal = 2 : 98
PURE FERRO ALLOY
Analysis of a sample of FeMn for its slag content was done by this method and was found to be 0.84%.
A FeMn SAMPLE ANALYSED FOR SLAG CONTENT BY FTIR WITH HATR
Presence of slag is detrimental in Ferroalloys. Hence slag associated with ferroalloys supplied by the supplier needs estimation.
Contributed by: Nandita Das under guidance of Prof. Barun Gupta