Calcium cations in low-rank coals – Reexamination of quantification method and the transformation of the cations during coal processing

摘要

In order to determine the content of ion-exchanged metals in low rank coals, the selective leaching with aqueous ammonium acetate solution has been generally used. However, we have found that this method is unsuitable as quantification method. Instead of this, we would like to propose a new method using CCSEM. The transformation these metal cations upon heat-treatment of low rank coals are also studied by CCSEM. Even in the low temperature ashing, which is generally believed not to modify mineral matter, we observed that calcium ions were converted to calcite, bassanite and other compounds. CCSEM also gives us very useful information on the transformation of these metal cations upon heating at higher temperatures, as well as during liquefaction and gasification processes.