Optimization of an accurate and precise analysis procedure for metallurgical VOD slags with ICP-OES

Silicate-containing geological or related samples (e.g., slags, chrome ores , ilmenites) are commonly prepared for chemical analysis with inductively c oupled plasma optical emission spectrometry (ICP-OES) with state-of-the-art microwave digestion using a multi-step procedure with nitric, hydrochloric , hydrofluoric, and boric acid. However, the length of the dissolution proc edure and the complexity of the resulting matrix can obstruct accurate and continuous ICP-OES analysis. In this work, two alternative procedures were developed for the multi-eleme ntal analysis of metallurgical Vacuum Oxygen Decarburization (VOD) slags by ICP-OES. Accurate analysis of VOD slags is required for environmental reas ons and for optimal process control during the secondary refining of stainl ess steel. Standard reference slags were used to validate the accuracy and the precision of the proposed methods. Procedure A consisted of microwave-a ssisted leaching, utilizing an acid mixture of nitric and hydrochloric acid , with subsequent ICP-OES determination of Mg, Al, Ca, Mn, Fe, and Cr. Proc edure B was performed by hot phosphoric acid digestion, resulting in clear solutions, which were further diluted and analyzed with ICP-OES. This proce dure allowed the determination of Mg, Al, Ca, Mn, Fe, Cr, and also Si. The advantages and disadvantages of the two methods are discussed. Phosphor ic acid digestion is the preferred method due to its speed, simplicity, and low cost. The method resulted in RSD values (n = 6) of 0.4 to 1.6% for the major (Mg, Al, Ca, Si) and less than 5% for the minor components (Fe, Mn, Cr). The accuracy was excellent as recoveries between 98 and 101% were foun d for Mg, Al, Ca, Mn and Fe. Only the result for Si was slightly inferior ( 92% recovery), whereas the accuracy for Cr could not be determined as no re ference values were available.