Inhibiting fly ash reactivity by adding N- and S- containing compounds.

Area of Science:

• Materials Science
• Chemical Engineering
• Environmental Science

Background:

• Fly ash utilization is crucial for sustainable waste management.
• Understanding fly ash reactivity is key to optimizing its industrial applications.
• The role of additives in modifying fly ash properties requires further investigation.

Purpose of the Study:

• To investigate the effect of thiourea (TUA), ammonium thiosulfate (TSA), and amidosulfonic acid (ASA) on the reactivity of a model fly ash.
• To determine the influence of these compounds on the decomposition rate of carbonaceous material in fly ash.
• To elucidate the kinetic behavior of the fly ash decomposition process in an oxidant atmosphere.

Main Methods:

• Thermogravimetric analysis (TGA) was employed to study the decomposition of a model fly ash at various heating rates (5, 10, 20 K min⁻¹).
• A model fly ash was prepared using activated carbon mixed with copper(II) chloride dihydrate (CuCl₂·2H₂O), pyrolyzed at 700°C, and washed.
• Thermogravimetric analysis coupled with mass spectrometry (TG-MS) was used to identify decomposition products.

Main Results:

• Adding CuCl₂·2H₂O to activated carbon increased the decomposition rate in air.
• TUA and TSA significantly accelerated the decomposition of the model fly ash.
• ASA also accelerated decomposition, but to a lesser extent than TUA and TSA.
• TG-MS confirmed the formation of nitrogenated and sulfur-containing compounds.
• A kinetic model (order 0.6) accurately described the decomposition process across tested heating rates.

Conclusions:

• TUA, TSA, and ASA influence the reactivity of fly ash, primarily by accelerating its decomposition.
• The acceleration is attributed to reactions between the carbonaceous material and the nitrogen and sulfur compounds in the additives.
• The study provides valuable kinetic insights into fly ash-additive interactions, relevant for industrial processes.