Abstract
Highly concentrated coal water mixtures (CWM' s) were found to display various flow properties when prepared and stored at different pH values, eventhough they con-sist of the same coal, having the same particle size distribution, and the same anionic dispersing agent. It was found that, at low pH values, much mineral matter dissolves into the dispersing medium (water), and that the resultant multi-valent cations affected the CWM rheology by changing inter-particle interactions, decreasing the degree of dispersion.The pH adjustment to higher values restored the CWM flow properties, however not completely. It was attributed to Ca2+ and/or Mg2+ ions which have higher solubility at pH values of about 8.
Cation masking reagents were examined to prevent the adverse effects of the cations. Sodium silicate was shown to be effective in masking Ca2+ ion. The reagent may be used to control the rheological properties of CWM' s using coals with higher water-dissolvable mineral matter content.
