PhD student Huibin Li is part of a Research Team within the Steel Research Hub whose area of research aims to develop a fundamental understanding and a capability to assess the effects of using different Australian iron ores or ferrous-based plant dusts, on the melt characteristics of raw materials in the sinter blend, particularly in relation to temperature, basicity and gas composition. The research is focused on the interaction between different components of a sinter blend, and the establishing of cost-effective, bench‐scale experimental capabilities to investigate these component interactions prior to either pilot‐scale or plant trials.  Two bench-scale methods are developed: static pressed tablet and reacting column (“millipot”) facility.

The challenge

The potential for recycling of steel plant by-products can be limited by undesirable elements such as zinc. One specific example is Basic Oxygen Steelmaking filter cake produced by wet scrubbing the steelmaking process off-gas. Although this filtercake can be incorporated back into the raw materials via the sintering process, zinc will continue to build up and cause process problems in the blast furnace unless steps are taken to remove it.

This study is investigating the behaviour of Zn in the sintering process to identify a strategy for its removal from the filter cake and allow significantly greater opportunities for recycling at low cost.

The approach

Pressed tablet and millipot sintering tests were employed to study the behaviour of zinc under controlled sintering conditions making it possible to examine zinc mass transport during sintering. It is also possible to manipulate local conditions by using tablets of specific composition in the millipot and observing the impact on the resulting zinc distribution over the sintered column.

The outcome

Zinc removal in sintering requires reduction from its oxide forms before vaporisation and gas phase transport out of the product sinter that will be charged into the blast furnace. To achieve this reduction, it was found that extra coke added to the sinter blend, as well as metallic iron in filter cake improve the local reducing conditions. Zinc removal increased with increasing sintering temperature and decreasing oxygen partial pressure.

In static tablet sintering, the base blend zinc removal was approximately 25% at 1300°C in an inert nitrogen atmosphere. With a process representative 0.5% oxygen atmosphere and the addition of 9% coke zinc removal of up to ~92% was achieved.

In millipot sintering, zinc removal of up to 67% was able to be controlled by varying the coke content in the filter cake tablets. Zinc removal improved when the tablets were positioned at the bottom of the sintering bed, shortening the distance for zinc oxidation and recapture.