Coupling effects of mineral components on arsenic transformation during coal combustion.

Exploring arsenic (As) transformation during coal combustion is beneficial for reducing its pollution. Herein, combustion experiments were developed at 1100-1300 °C in a fixed-bed experimental system with 25 types of coal samples. The occurrences of As in coal and combustion products were characterized. All the original forms of As in coal were found to be unstable during combustion. As retained in ash existed as water-soluble and ion-exchangeable and residual forms, but only as residual form at combustion temperature above 1200 °C. The distribution of As in gaseous and solid combustion products varied widely by coal types, which resulted from the coupling effects of multi-minerals in coal. Co-combustion experiments were conducted using As model compounds and pure minerals, by which the interaction of Ca, Fe, Si and Al minerals to retain As was elucidated. The As transformation during coal combustion was primarily attributed to the coupling action of Ca, Fe, Si and Al minerals in coal. As a result, As was retained as Ca-Si-Al-As and Fe-Si-Al-As composite salts in the ash, which have little environmental hazard. Utilizing the coupling effects of multi-minerals during combustion help reduce As pollution from coal-fired plants.