Methods for Quantitative Determination of Iron Sulfides in Rocks

Area of Science:

• Materials Science
• Geochemistry
• Civil Engineering

Background:

• Iron sulfides in concrete aggregates can oxidize, forming sulfates that cause acid corrosion and internal sulfate attack (ISA).
• Existing quantification methods for iron sulfides in aggregates are inaccurate and often overlook pyrrhotite.
• Lack of standardized methods and guidelines limits the use of sulfide-containing aggregates.

Purpose of the Study:

• To develop and validate an on-site, cost-effective quantification procedure for pyrite and pyrrhotite in aggregates.
• To optimize selective chemical dissolution conditions for accurate sulfide measurement.
• To facilitate the practical application of sulfur-bearing aggregates in concrete production.

Main Methods:

• An orthogonal experiment was designed to optimize dissolution conditions (particle size, temperature, acid concentration, time).
• A selective chemical dissolution process was employed for quantifying pyrite and pyrrhotite.
• Quantitative results were verified using the XRD internal standard method for pyrite.

Main Results:

• The developed method achieved high accuracy for pyrrhotite (RSD 3.60%, error 3.19%) and pyrite (RSD 3.11%, error 4.70%).
• Pyrite quantification error was less than 0.6% when verified by XRD.
• The procedure was optimized for on-site application, reducing costs and complexity.

Conclusions:

• The proposed on-site quantification procedure accurately determines pyrite and pyrrhotite content in aggregates.
• This method enables effective monitoring and management of sulfide content, improving concrete durability.
• The study promotes the wider and safer use of sulfur-bearing aggregates in construction.