Optimization and application of an analytic system for Al4C3 quantification in recycling material

Stefan Rudolf Niedermayer

Research output: ThesisDoctoral Thesis

Abstract

Recycling of MgO-C refractories is highly recommendable from an economic and environmental point of view. However, Al4C3 formed in MgO-C refractories containing Al is a risk for using recycling material as secondary raw material. Energy intensive inactivation treatments cause formation of CO2 and dust or the loss of the critical resource graphite. Currently there is no viable way of monitoring Al4C3 in spent MgO-C bricks in plant environments, giving information about treatment necessity and potential of utilization as secondary raw material. This thesis aims to close this gap. The method was based on an autoclave for digestion. A non-dispersive infrared detection system with optopneumatic detection of CH4 enabled reproducible quantification of Al4C3 in synthetic mixtures and MgO-C bricks. The method was developed and optimized by Design of Experiment. The final version proofed reproducible and complete conversion when utilizing water at 150 °C. Further simplification by partial least square regression of pressure measurements was not feasible. Evaluation of method performance with real brick samples showed the methods ability to quantify Al4C3 reliably and repeatable. The method¿s limit of quantification and limit of detection (both < 1 mg) were sufficient. Linearity (R2 = 0.9994) and precision (¿ 5 % rel. std. dev.) in a working range of 1 to 50 mg Al4C3 were considered good. The method was robust against changing liquid volumes and the presence of potentially interfering ions, consisting of commonly used antioxidants and residues. Kinetical measurements showed a strong temperature dependence. However, no simple shrinking core model was able to accurately describe obtained data. Analysis of Al4C3 converted in distilled water indicated a mainly temperature dependent transition to mixtures of Al(OH)3 and AlO(OH). Case studies conducted by RHI Magnesita showed the duplicability of the device, enabling to build a comprehensive screening system. They also proved the correlation of measured Al4C3 content in MgO-C bricks and degree and probability of structural damage when utilized as secondary raw material. Based on the findings in this thesis, the developed device and method was a suited extension of GC-based quantification methods for monitoring of Al4C3 in MgO-refractory intended for recycling. This enables the recycling of MgO-C bricks in a more secure and efficient way, resulting in enhanced sustainability of refractory production.
Translated title of the contributionOptimierung und Anwendung eines analytischen Systems zur Al4C3 Quantifizierung in Recyclingmaterial
Original languageEnglish
QualificationDr.mont.
Awarding Institution
  • Montanuniversität
Supervisors/Advisors
  • Weiß, Christian, Assessor A (internal)
  • Prohaska, Thomas, Assessor B (internal)
  • Lehner, Markus, Supervisor (internal)
  • Ellersdorfer, Markus, Supervisor (internal)
  • Meisel, Thomas C., Co-Supervisor (internal)
Publication statusPublished - 2023

Bibliographical note

embargoed until 21-08-2028

Keywords

  • Al4C3
  • NDIR
  • gas-analytics
  • recycling

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