Development of a sampling train for arsenic in pyrolysis vapours resulting from pyrolysis of arsenic containing wood waste

Abstract

In the present study a sampling and analysis method for arsenic emissions during pyrolysis of arsenic containing wood, such as chromated copper arsenate (CCA) treated wood, has been developed. The procedure is based on the NIOSH (National Institute for Occupational Safety and Health) standard for arsenic trioxide sampling. Validation for this specific application is needed since pyrolysis of arsenic containing wood leads to a gas stream containing sticky tar compounds and aerosols. Validation was carried out through tube furnace experiments using both CCA treated wood and arsenic trioxide powder as input. The outlet of the tube furnace was coupled to a cooling section and sampling train. The sampling train consisted of one or more filter sections and impingers. Different combinations of filters (untreated or impregnated) and impingers, as well as different combinations of washing solutions were tested. The different units of the sampling train were analysed by inductively coupled plasma mass spectrometry (ICP-MS) in order to determine the distribution of arsenic over the different units. For the working conditions considered (pyrolysis at 350 °C for 20 minutes with a nitrogen flow rate of 100 Nl h⁻¹) the combination of a quartz cooling tube and a cellulose ester membrane filter impregnated with a Na₂CO₃–glycerol solution was sufficient to capture the arsenic. Two extra impingers (the first one containing 50 ml HNO₃ 1 M in the case of CCA treated wood and 50 ml NaOH 0.1 M in the case of As₂O₃ and the second one containing 50 ml NaOH 0.1 M) were added downstream of the filter section as backup either in case of filter failure or to check whether all the arsenic released is captured by the cooling tube and filter.