Microwave Acid Digestion Efficiency Of Landfill Composites Determined By ICP-MS Analysis

Microwave acid digestion of solid samples combined with inductively coupled plasma – mass spectrometry (ICP-MS) provides a viable approach to quantification of heavy metals within landfill waste. The efficiency of Aqua regia and HNO3 in microwave digestion of both closed and active landfill composites was compared, with a view to relating heavy metals distribution to the particle size of the landfill composites.

Landfill sites were systematically gridded into seven cells according to RCRA USEPA guidelines. Three samples were obtained from each cell at upper (0-15cm), mid (16-35cm) and low- (36-50cm) depths. The particle size was determined using the sieving method and grouped as less degraded (S> 0.63mm) and more degraded (S<0.63mm) components and homogenised.

Microwave digestion of samples was carried according to the EPA3052 method using a CEM MARS Xpress digester. An Agilent 7500 ICP-MS was used to determined metal concentrations in digested samples.

For 77% of the eleven USEPA toxic heavy metals investigated, microwave digestion with Aqua regia resulted in higher concentration of metals than with HNO3. Extraction precision for both acids was within acceptable limit for more degraded samples (RPD<20%), except for Ag and Zn. Both acids indicated (>10%) a higher burden of heavy metals in closed landfill samples than active landfill samples, except for Ag and Zn. The more degraded component of both landfills had elevated concentrations of heavy metals (>4% for HNO3 and >6% for Aqua regia). Sample recoveries based on CRM analysis showed that both acids were within the same accuracy (between 88% and 95%)