Study on high-temperature absorption of potassium by ilmenite oxygen carrier

The synergistic alkali metals fixation potential of Oxygen Carrier Aided Combustion (OCAC) technology has attracted increasing attention. Using tailings from natural ilmenite after titanium extraction and its individual components Fe₂TiO₅ and TiO₂ as absorbents, and KCl and CH₃COOK as simulated alkali sources, the high-temperature absorption characteristics of alkali metal potassium by ilmenite tailings were studied in a static absorption experimental setup. The effects of various factors such as time, particle size, temperature, mass ratio, and gas-solid components on the absorption performance were systematically explored. Techniques such as X-ray diffraction, inductively coupled plasma optical emission spectrometry scanning electron microscopy and X-ray energy dispersive spectroscopy were used to reveal the micro-mechanisms of K enrichment on the surface and bulk phase migration within ilmenite. The results show that ilmenite tailings possess good potassium absorption capabilities at high temperatures, with the absorption rate displaying a trend of rapid increase followed by a slow decline over time. Under certain conditions, reducing particle size, increasing reaction temperature, and the concentration of K in the gas phase can further enhance the alkali fixation performance of ilmenite tailings. At temperatures and alkali metal concentrations like those of actual industrial flue gases, ilmenite tailings can achieve a K capture rate of over 40%. The primary phase of ilmenite tailings has a unique lamellar structure composed of iron-rich and titanium-rich layers arranged alternately. Compared to single-component model substances, it has a more complex morphology and superior alkali fixation capabilities. The process involves initial deposition of K on the ilmenite surface, forming an enriched layer, followed by solid-phase diffusion inward and migration deep into the particle along the titanium-rich layers. Fe in the titanium-rich layers migrates synchronously outward, doubly impacting the absorption of K in ilmenite. Additionally, Cl can further promote the absorption of K in ilmenite by reacting with Fe on the surface to form volatile FeCl₂. Minerals such as almandine calcian in ilmenite tailings also show significant synergistic absorption of K. The findings further confirm the synergistic alkali metals fixation potential of OCAC technology, while also offering new insights into the resource utilization of low-grade ilmenite.