COMPARISON OF DIGESTION METHODS APPLIED FOR LEAD QUANTIFICATION IN DRINKING WATER SAMPLES

Abstract

This study evaluated the digestion efficiency of a new rigorous digestion technique: focused shortwave infrared radiation digestion (SWIR). The increases of acid concentrations to 5% v/v and extended digestion time to 2h could increase lead recovery of PbO2 digestion; however, the increase of the power intensity to 400W accompanied a decrease of lead recovery. In this thesis, the SWIR method was also compared against standard preservation (direct analysis) and hot block digestion (conventional rigorous digestion method), on different lead and iron compounds digestion, including lead (IV) oxides (PbO2), lead (II) phosphate (PbSO4), hematite (Fe2O3), magnetite (Fe3O4), and chloropyromorphite (Pb5(PO4)3Cl. For PbO2 digestion, the recovery by the SWIR method was 69.4%, exceeding the lead recovery by standard preservation and hot block digestion by factors of approximately 28 and 6, respectively. With the addition of hydrochloric acid (HCl), lead recovery of PbO2 digestion by hot block digestion and the SWIR method were both increased (102.6% and 98.1%, respectively). In terms of lead (II) sulfate digestion, lead scale digestion, and chloropyromorphite digestion, standard preservation was able to recover the highest concentrations of lead. For hematite digestion (with HNO3 only), the iron recovery by standard preservation was the lowest (1.5%), while the iron recovery by hot block digestion and the SWIR method were 17.1% and 15.2%, respectively. The iron recovery of magnetite digestion (with HNO3 only) by standard preservation remained the lowest (1.7%) among three methods, while hot block digestion recovered 45.2% of iron and the SWIR method recovered 42.3%. With addition of the reducing agent (H2O2), the iron recovery of both hematite and magnetite digestion by the SWIR method were all increased and slightly higher than the iron recovery by hot block digestion.