Analysis of the titanium-bearing pellets prepared by a waste titanium-based catalyst and vanadium titanomagnetite

Abstract

NH3-selective catalytic reduction of NOx over a V2O5–WO3/TiO2 catalyst is the major control method of NOx and has been successfully promoted and applied in various large steel enterprises in China. The production of waste catalysts (hazardous waste) from flue gas denitrification in iron and steel enterprises increases annually. Harmless landfills and wet purification are widely-employed methods for the treatment of waste catalysts. However, these methods pose environmental problems such as resource wastefulness, excessive amounts of acid/alkali, and considerable secondary pollution. Optimizing the effective use and disposal of such waste catalysts has become a key common problem in the industry. In this work, a novel method for producing titanium-bearing pellets by adding waste catalysts to pellet material was introduced. The feasibility of using waste catalysts to prepare titanium-bearing pellets was comprehensively evaluated by comparing the preparation process and metallurgical properties of the resulting pellets with those of commercially available titanium-containing pellets. The findings of this study reveal that the addition of 5.0% waste catalyst to the raw material can substantially improve the overall comprehensive performance of green pellets. Moreover, the drop number (dropped from 0.5 m height), average compressive strength, and burst temperature of the green pellets increased from 3.8 times, 16.5 N, and 487 ℃ (without waste catalyst addition) to 7.7 times, 21.5 N, and 553 ℃, clearly outperforming the ordinary titanium-bearing pellets prepared using vanadium–titanium magnetite (1.4 times, 15.0 N, and 542 ℃). These results could be attributed to the physical properties of the waste catalyst, which is a porous material with abundant hydrophilic groups on the surface. These hydrophilic groups, comprising hydroxyl groups, lead to the presence of more capillary water on the catalyst particle surfaces. Furthermore, the capillary force played an important role in various interactions in the pelleting process, thus improving the performance of mixtures. After roasting, the average compressive strength of the pellets containing the waste catalyst was 3083 N, higher than the 2630 N for ordinary titanium-bearing pellets. However, the short preheating and roasting time resulted in partially unreacted TiO2 being present in the internal pores of the pellets as rutile-type particles. The consolidation mechanism of pellets containing waste catalysts demonstrated that TiO2 in the waste catalyst reacts with iron oxide to form a Fe2TiO5 bond, while unreacted TiO2 reduces the compressive strength of the pellets. The metallurgical properties of the two titanium-bearing pellets are virtually identical to those of ordinary oxidized pellets, indicating that the pellets containing waste catalysts can be used in blast furnace protection smelting. This study offers a new approach for recycling waste catalysts generated by flue gas denitrification in iron and steel enterprises.

Keywords

• flue gas denitrification
• waste catalyst
• vanadium titanomagnetite
• titanium-bearing pellet
• metallurgical performance