Direct reduction during the production of ferroniobium in an electric furnace

Abstract

At Baotou in China (situated in the province Mongolia) a complex iron ore is mined, concentrated and smelted. In addition to ca. 60% haematite the ore body contains on average 0.12% Nb 2O 5, 7–8% rare earths and up to 8% F. The smelting process route followed at Baotou at present is characterized by a low niobium recovery. The route blast furnace and subsequent converting is used for low niobium iron ore concentrates (< 0.1% Nb). Niobium containing Siemens-Martin or converter slag and niobium rich (ca. 0.5% Nb) iron ore are smelted together in a smaller niobium blast furnace to produce a slag which contains ca. 0.1% Nb and a pig iron, which is subsequently converted to produce a slag containing ca. 6%Nb. The converter slag is subsequently processed to ferroniobium (12.5% Nb) in electric furnaces. It was the objective of a project sponsored by the German Ministery of Research and Technology to investigate the feasibility of an alternative process routes for the improved recovery of niobium from niobium lean ores (< 1% Nb) from Baotou. Two routes were investigated viz. (i) direct reduction of iron ore pellets in a rotary kiln (in collaboration with Lurgi AG, Frankfurt) and the subsequent production of pig iron in an electric furnace from the reduced iron ore pellets and (ii) direct smelting of the iron ore concentrate in an electric arc furnace, the concentrate being fed through a hollow electrode. Subsequently the niobium is concentrated in the slag during converting. In this paper the various results of this investigation will be discussed as well as the application of neural nets to interpret the produced data.