Trace element analysis of gasification plant samples by i.c.p.-m.s.: validation by comparison of results from two laboratories

In the absence of either standard methods for trace element analysis of coa l-derived chars and ash or standard reference materials for coal gasificati on samples, a comparative exercise has been undertaken to validate analyses of chars and fines recovered from a coal gasification pilot plant. Several sample digestion methods, used for converting solid samples to aqueous sol utions for trace element analysis by i.c.p.-m.s. and i.c.p.-a.e.s., have be en compared: peroxide fusion (sodium peroxide + sodium carbonate) and micro wave digestion by AEA Technology and wet-ashing (open acid digestion) and m icrowave digestion by Imperial College (IC). The aim was to analyse samples from a pilot plant scale coal gasification rig. Digestions were carried ou t using a range of sample sizes, at times as small as LD mg and analyses of small quantities of these samples were compared with results on the same s amples from a specialist contract laboratory (AEA Technology). Elements stu died were As, B, Ba, Be, Cd, Co, Cr, Cu, Ga, Hg, Mn, Mo, Ni, Pb, Sb, Se, Sn , V and Zn. For the majority of the elements studied, elemental concentrati ons (1-150 wppm range) were generally in agreement between the two laborato ries within 50%. Limitations of the various digestion methods are discussed . All the digestion techniques appeared to lose mercury and therefore a Lec o atomic absorption spectrophotometer based method was used to determine Hg . Output solid stream distributions of trace elements from the gasifier ind icate that all of the Hg in the fuels was released to the fuel gas. The pri mary cyclone fines stream contained the major part of the trace elements fr om the fuels. The causes of apparent losses of As, Mo, Pb, Sn, Zn and Se ar e discussed. (C) 2000 Elsevier Science Ltd. All rights reserved.