Determination\nof the Redox Ratio of Iron in a Diamagnetic\nMatrix Using Low-Field NMR Relaxometry

Proton nuclear magnetic resonance (NMR) relaxometry is\nproposed\nto determine the iron redox ratio of slag samples. It depends on the\nparamagnetic effect on bulk water relaxation times. Experiments have\nbeen carried out to calibrate the relationship between the concentration\nof Fe<sup>3+</sup> and Fe<sup>2+</sup> ions and the measured relaxation\ntimes on prepared standard samples. It is shown that Fe<sup>2+</sup> ions have very different effects on the relaxation times than Fe<sup>3+</sup> ions. For the solid slag samples, digestion in an acid was\nused to produce solutions with a pH of 1.0. Hydrogen peroxide (H<sub>2</sub>O<sub>2</sub>) was then added to the digested samples to oxidize\nFe<sup>2+</sup> ions to Fe<sup>3+</sup> ions. The concentration of\nFe<sup>2+</sup> and Fe<sup>3+</sup> ions in solution can be calculated\nby measuring the relaxation times before and after oxidation. The\nFe<sup>3+</sup>/∑Fe ratio of slag samples was also investigated\nby wet chemistry and <sup>57</sup>Fe Mössbauer spectroscopy\nand calculated by FactSage at the equilibrium state. The results obtained\nfrom different methods are consistent, indicating that this NMR relaxometry\nmethod is reliable.