Preparation of red mud-based zero-valent iron materials by biomass pyrolysis reduction: Reduction mechanism and application study

Zero-valent iron (ZVI) materials have been developed and applied to treat various pollutants due to their strong reducing properties and large specific surface area. Red mud contains a large amount of iron oxide and therefore can be used as a source of iron base for the preparation of ZVI materials. Industrial reduction of iron oxides to prepare ZVI materials requires high temperatures resulting in high energy consumption and high costs. Biomass can be pyrolyzed at low temperatures to release large amounts of reducing gas, which can efficiently reduce red mud to obtain ZVI at lower temperatures. Therefore, this paper studied the pyrolysis of five biomasses, corn straw, wheat straw, rice husk, pine wood and coffee grounds, and compared the reduction of iron oxide in red mud at different temperatures for different biomass feedstocks. The results showed that the biomass could reduce most of the iron oxide in red mud to ZVI at 800 °C, which was at least 100 °C lower than the conventional iron reduction temperature. The reducing gas greatly facilitated the conversion of iron oxide to ZVI in this process. Moreover, the material has a good removal effect on both gentian violet and methylene blue. A low-energy and low-cost method was explored for the preparation of ZVI materials, and the resource utilization of biomass and red mud was realized.