[Fluoride emission from different soil minerals at high temperatures]

Area of Science:

• Geochemistry
• Environmental Science
• Materials Science

Context:

• Brick and tile manufacturing involves high-temperature processing of soil-derived minerals.
• Understanding fluoride emission mechanisms is crucial for environmental protection.
• Soil minerals like montmorillonite, kaolinite, vermiculite, geothite, and allophane are common raw materials.

Purpose:

• To investigate the fluoride emission characteristics of various soil minerals at high temperatures (300–1000 °C).
• To elucidate the mechanisms controlling fluoride release during thermal processing.
• To evaluate the effectiveness of calcium compounds in mitigating fluoride emissions.

Summary:

• Fluoride emission rates are dependent on temperature, mineralogy, heating duration, surface area, and added cations.
• The release of crystalline water due to crystal lattice collapse at elevated temperatures significantly impacts fluoride emission.
• Calcium compounds, particularly CaCO3 and CaO, effectively reduce fluoride emission from montmorillonite, with a 59.6% decrease observed at 800 °C with Ca-treated montmorillonite.

Impact:

• Provides insights into controlling fluoride pollution from industrial processes like brick making.
• Identifies specific soil minerals and temperature ranges associated with high fluoride emissions.
• Offers practical solutions using calcium compounds to minimize environmental fluoride release.