Investigating the Interaction between Ilmenite and Zinc for Chemical Looping

The iron and titanium oxide ilmenite is a benchmark oxygencarrierfor chemical looping combustion (CLC) and oxygen carrier-aided combustion(OCAC). Both of them are combustion technologies for biomass and wastefuels with lower emissions and low costs for carbon capture. Here,the interaction between the ash component zinc and oxygen carrierilmenite is studied in a two-staged vertical tube reactor. Three typesof ilmenites Norwegian rock ilmenite, synthesized ilmenite,and ilmenite extracted after 200 h of OCAC in a full-scale fluidizedbed unit were exposed to gas-phase Zn and ZnCl2.Following the exposure, samples were analyzed concerning morphology,chemical distribution, composition, and crystalline phases. The observationswere complemented with thermodynamic equilibrium calculations. Itis observed that the iron-rich layer formed on the external surfaceof rock ilmenite after activation promotes the reaction with bothgaseous zinc compounds, with zinc ferrite formed in the external Fe-richlayer. In contrast, ilmenite with no segregation of Fe and Ti showedto interact less with zinc species. Metallic Zn penetrated the particles,while the interaction depth was shallow with ZnCl2 forall investigated ilmenite oxygen carriers. The gaseous conditions,particle ash layer composition, and iron availability are shown toplay an important role in the interaction between zinc compounds andilmenite particles. Based on these results, interaction mechanismsfor Zn and ZnCl2 are proposed. This interaction could haveenvironmental implications for the toxicity of ash streams from wastecombustion in addition to possibilities for Zn recycling.

Automated summary

In this study, the interaction between zinc compounds and ilmenite particles was investigated by exposing three types of ilmenites to gas-phase Zn and ZnCl2. The results showed that the gaseous conditions, particle ash layer composition, and iron availability played an important role in the interaction between zinc compounds and ilmenite particles.