# Comparative Analysis of Industrial Fused Magnesia from Natural and Flotation-Processed Magnesite: Associations Among CaO/SiO2 Ratio, Silicate Phase Formation, and Microcracking

## TL;DR

This study compares industrial fused magnesia products from natural and processed magnesite, finding that higher CaO/SiO2 ratios correlate with C2S formation and microcracking.

## Contribution

The study reveals new associations between CaO/SiO2 ratio, silicate phase formation, and microcracking in industrial fused magnesia.

## Key findings

- Reverse flotation increases the CaO/SiO2 ratio from 0.68 to 2.85.
- Higher CaO/SiO2 ratios correlate with C2S dominance and increased microcracks.
- Controlling oxide balance, not just impurities, may improve magnesia production.

## Abstract

What are the main findings?
Reverse flotation coincided with higher CaO/SiO2 ratio (0.68 to 2.85).Higher CaO/SiO2 coincided with C2S dominance; a lower ratio coincided with CMS.More C2S coincided with more microcracks and slightly lower densification.

Reverse flotation coincided with higher CaO/SiO2 ratio (0.68 to 2.85).

Higher CaO/SiO2 coincided with C2S dominance; a lower ratio coincided with CMS.

More C2S coincided with more microcracks and slightly lower densification.

What are the implications of the main findings?
Beneficiation may benefit from controlling oxide balance, not only impurities.Tailoring CaO/SiO2 may help avoid conditions linked to C2S and microcracking.The findings are derived from industrial comparison; causality requires controlled experiments.

Beneficiation may benefit from controlling oxide balance, not only impurities.

Tailoring CaO/SiO2 may help avoid conditions linked to C2S and microcracking.

The findings are derived from industrial comparison; causality requires controlled experiments.

In view of the depletion of high-grade magnesite resources in China, this study presents a comparative analysis of two industrial fused magnesia products produced via a flotation–fusion route. A low-grade magnesite (DSQLM-3, MgO 41.48 wt.%) was upgraded by reverse flotation to a concentrate (FDSQLM-3, MgO 47.55 wt.%) with >97% SiO2 removal. Two fused magnesia samples (FM-1 from natural high-grade ore DSQLM-1; FFM-3 from concentrate FDSQLM-3) were produced under identical arc-furnace melting (2800 °C, 4 h), followed by natural cooling. Although FFM-3 showed higher MgO (97.61 vs. 97.25 wt.%), its bulk density was comparable to FM-1 (3.45 vs. 3.46 g/cm3). XRD/Rietveld refinement and SEM-EDS indicated that CMS dominated the Ca–silicate assemblage in FM-1, whereas β/γ-C2S was observed in FFM-3, coinciding with a higher CaO/SiO2 (C/S) ratio (2.85 vs. 0.68). Image analysis further showed higher grain boundary microcrack metrics in FFM-3. These observations are consistent with reports in the literature stating that the β → γ transformation of C2S during cooling involves ~12% volume expansion that can contribute to cracking; however, cooling history and composition were not independently controlled in this industrial comparison, so the relationships are interpreted as data-supported associations rather than isolated causality. The results suggest that beneficiation strategies may benefit from managing residual oxide balance (especially C/S ratio) in addition to reducing total impurities. Mechanical and thermomechanical properties were not measured and should be evaluated in future work.