Reutilisation of spent SCR catalyst powder in the direct reduction process

Abstract

With the widespread adoption of selective catalytic reduction (SCR) denitrification technology and the enforcement of ultra-low emissions regulations, the annual production of spent SCR catalyst, classified as hazardous waste, has been increasing. This study presents an innovative method of integrating spent SCR catalysts into carbon-containing pellets processed in a rotary hearth furnace. The research examines the impact of the addition of spent catalyst on the comprehensive performance and reduction characteristics of carbon-bearing pellets. The results indicate that the drop number for both green and dry pellets peaks at 5.0 wt-% spent catalyst addition. When the addition of spent catalyst reaches 7.5 wt-%, both the number of drops for dry pellets and the compressive strength reach their peaks. Additionally, the compressive strength of direct reduction iron (DRI) gradually increases from 1794 N/pre to 3476 N/pre. The metallisation and zinc removal rates of DRI are maintained at high levels, exceeding 90% and 99%, respectively. The interaction between TiO₂ and FeO in the spent catalyst forms titanium–iron compounds, reducing low-melting eutectic formation. The catalyst's active sites also promote CO production, which enhances iron oxide reduction and leads to the early formation of iron grains, contributing to increased DRI compressive strength. This process not only provides an effective way to manage spent SCR catalysts but also improves pellet performance.