Asphalt recycling
PAHs (polynuclear aromatic hydrocarbons) are mixtures of organic compounds, which contain fused aromatic rings. They are ubiquitous pollutants of low solubility and high toxicity, which biodegrade very slowly. Some are known carcinogens. Crude oil contains high concentrations of PAHs and consequently they are found in coal tars used in asphalt. Phenols, another group or organic compounds found in asphalt are also toxic. The ability to accurately determine concentrations of these compounds in asphalt is essential in order to address the toxicity and the possibility for recycling. For PAHs, a method using High Performance Liquid Chromatography (HPLC) and a diode array detector was developed. Initially the asphalt sample is heated with solvent in a soxhlet extraction in order to extract the PAHs. Once extracted, the solvent is injected into the HPLC column. Under specific conditions, 16 PAHs were successfully identified. The method yielded good recoveries of between 81-99%. The method developed is therefore an efficient qualitative method, allowing the identification of 16 PAHs in asphalt. For quantitation however, a different technique, Gas Chromatography/ Mass Spectroscopy (GC/MS) was found to be more accurate. This technique however, gave results 50% lower than the results obtained by HPLC. Since MS has more selective detection and the GC/MS system gave better resolution, PAH quantification throughout the remainder of the project was carried out using GC/MS. For the quantitative determination of phenols, an HPLC method with soxhlet pre-treatment was also developed. The asphalt sample was extracted with solvent, the extract purified into an alkaline phase, neutralised and injected on the HPLC column. 10 phenols were successfully identified and quantified with external calibration, with recoveries ranging for 34-100%. The potential is thus available for the toxicity assessment of asphalt. With additional input these methods could be developed into a routine method of analysis to allow more environmental options such as asphalt recycling to be considered.
