TRACE MERCURY CONCENTRATIONS IN COALS AND COAL-DERIVED MATERIAL DETERMINED BY ATOMIC-ABSORPTION SPECTROPHOTOMETRY

The volatility of mercury can cause large errors during quantification when methods based on acid digestion are applied. In this study, merc ury levels in coals have been determined by an atomic-absorption-based instrument hitherto not used with coals or coal-derived materials. Th e results have been compared with 'certified' values of reference mate rials. The instrument is relatively easy to use: solid and liquid samp les may be introduced directly, without pretreatment. The range of sam ples studied included the Argonne Premium Coal Samples and other coals , coal-derived products, biomass materials, sand and kaolin. The instr ument gave correct mercury concentrations for certified reference mate rials. Samples of silver birch and forest residue contained similar co ncentrations of mercury as observed in coals; other biomass samples co ntained far smaller quantities of mercury. Thus, the use of biomass in power generation would not necessarily lead to any great reduction of mercury in emissions from power plant: careful selection appears nece ssary. Only 3% of the mercury of the original coal was detected in the filter cake (corresponding to undissolved coal and mineral matter) fr om a coal liquefaction pilot plant. Mercury in the original coal appea rs to have passed either to (i) gas formed during liquefaction (betwee n 2 and 4% daf) or to (ii) the dissolved coal extract, possibly in the form of organometallic complexes. The presence of 0.15 ppm mercury in a coal tar pitch also suggests the organometallic retention of mercur y in this fraction. All solid residue streams from a gasification pilo t plant, operating at about 930-960 degrees C, have shown nearly negli gible mercury, compared to the original coal, indicating that the bulk of the mercury in the feedstock was released into the product gas. (C ) 1998 Elsevier Science Ltd. All rights reserved.