Combustion and leaching behavior of elements in the USGS coal standard CLB-1

Abstract

A series of heating and leaching experiments were conducted on a split taken from the coal used to create the U. S. Geological Survey's CLB-1 coal standard. The behaviors of approximately 30 elements were monitored by a variety of analytical procedures, including instrumental neutron activation analysis, inductively coupled plasma optical emission specroscopy, atomic absorption spectroscopy, and ion chromatography. Br, Se, and Hg were the only elements to exhibit volatilization at temperatures up to 1000 C. At this temperature virtually all of these elements had been volatilized. Leaching of the coal with hot (80 C) distilled water generally removed no more than a few percent of the elements monitored. Hot water leaching of the low-temperature ash was more effective, removing from 10 to 50 percent of many elements. A split of the coal was subjected to sequential leaching by ammonium acetate, hydrochloric acid (HC1), hydrofluric acid (HF), and nitric acid. Ammonium acetate, which was used to remove ion-exchangeable cations, removed 40 to 50 percent of the Ca. HCl (1:3) was effective in removing 20 to 40 percent of the chalcophile elements (As, Sb, Zn, and Fe); elements that are generally acid soluble when associated with monosulfides. HF (48%) removed 20 to more than 80 percent of the elements (K, Na, Cs, Sc, Hf, U, and Mg) commonly associated with silicate and oxide minerals. Nitric acid (10%) was generally ineffective in leaching elements from this coal sample. The responses of the various elements in the Lower Bakerstown coal during the combustion and leaching experiments were similar to the behavior reported for the elements in other Appalachian basin coals.