Determination of lead in household refuse fly-ash by X-ray fluorescence spectrometry and a modified standard-addition technique

Lead in fly-ash from a garbage incinerator has been determined by X-ray fluorescence spectrometry (XRFS) and a modified standard-addition method. To keep the attenuation properties of the spiked samples constant, decreasing amounts of an attenuation modifier mercury (II) acetate] were added together with increasing amounts of the standard (lead nitrate). Linearity between fluorescence intensity and amount of lead was thus obtained, so the amount of lead in the sample could be evaluated by linear regression. The amount of modifier needed could be calculated from a simple expression. The method was validated by comparison with the results obtained by applying atomic-absorption spectrometry (AAS) to solutions made by leaching the fly-ash with strong acid. For 8 fly-ash samples, containing between 0.8 and 1.35% lead, the largest absolute difference between the two sets of results was 0.03%. Theoretical calculations based on a simplified version of the Sherman equation were performed to confirm the linearity of the modified standard-addition curves.