Study on application and environmental effect of phosphogypsum-fly ash-red mud composite cemented paste backfill

Area of Science:

• Materials Science
• Environmental Engineering
• Waste Management

Background:

• Phosphogypsum (PG) and fly ash (FA) are industrial byproducts requiring sustainable disposal solutions.
• Developing effective cementitious paste backfill (CPB) materials is crucial for mine safety and resource utilization.
• Valorizing waste materials like PG, FA, and red mud (RM) into functional products aligns with circular economy principles.

Purpose of the Study:

• To investigate the properties of cementitious paste backfill (CPB) utilizing phosphogypsum (PG) and fly ash (FA) as primary components.
• To evaluate the influence of Portland cement (OPC), red mud (RM), and silica fume (SF) on the performance of PG-based CPB.
• To assess the environmental implications and mechanical suitability of the developed CPB for mine filling applications.

Main Methods:

• Preparation of CPB samples using PG, FA, OPC, RM, and SF with varying ratios.
• Characterization of slurry flowability using water/binder ratio and superplasticizer (SP) content.
• Assessment of mechanical properties (strength) and water resistance after 28-day curing.
• Monitoring of ion dissolution (Ca2+, SO42-) during immersion to understand hydration mechanisms.
• Microstructural analysis (AFt, C-S-H) and leaching tests for environmental compliance.

Main Results:

• Optimal slurry flowability achieved with a water/binder ratio of 0.2 and 0.7% SP.
• Mechanical strength exceeded 22 MPa after 28 days, meeting mine filling requirements.
• Increased OPC, RM, and SF content significantly enhanced mechanical properties and water resistance.
• RM promoted continuous hydration, crucial for improved water resistance.
• Leaching tests confirmed compliance with Chinese environmental standards (GB/T 14848-2017) for metal ions.

Conclusions:

• The developed PG-FA based CPB, activated by RM and bound with OPC, is a viable and environmentally sound material for mine backfilling.
• This technology effectively utilizes industrial wastes (PG, FA, RM), transforming them into a high-performance construction material.
• The CPB demonstrates excellent mechanical strength, durability, and low environmental impact, supporting safe mining operations and waste resource recovery.