Research on Rare Earth Tailings-Based Slag Used for Dephosphorization of Hot Metal Containing Moderate Amounts of Chromium

The utilization of rare earth tailings still has various disadvantages such as high energy consumption, low utilization ratio and serious pollution, which severely restricts the industrialization. As a result, it is difficult to solve the solid waste treatment problems of rare earth tailings fundamentally. To achieve bulk utilization in a way of energy conservation and environmental protection, a novel technology of dephosphorization using rare earth tailings-based slag was proposed to realize both dephosphorization and chromium retention of hot metal containing moderate amounts of chromium. To develop this new technology, a series of equilibrium experiments between slag and hot metal containing moderate amounts of chromium was carried out using a molybdenum disilicide resistance furnace at 1723 K. The effect of slag composition on the oxidation of phosphorus and chromium in hot metal was investigated, and the commercial software FactSage 7.2 was also utilized for analyses. The effective dephosphorization and recycle of rare earth tailings were realized via optimizing chemical composition of slag. In addition, the addition of Cr 2 O 3 inhibits the chromium loss significantly, resulting from increased activity of Cr 2 O 3 . When the CaO/Fe 2 O 3 ratio in the initial slag increases, the chromium loss ratio shows a continual declining tendency, while the dephosphorization efficiency first increases and then decreases. With the increase of rare earth tailings proportion (abbreviated as RETP), both the dephosphorization efficiency and chromium loss ratio fall. Both the dephosphorization efficiency and chromium loss ratio show a decreasing tendency with increasing CaF 2 content.