# Effect of Na2O, MgO, CaO, and Fe2O3 on Characteristics of Ceramsite Prepared from Lead–Zinc Tailings and Coal Gangue

## TL;DR

This study explores how adding specific compounds improves the properties of ceramsite made from industrial waste, making it stronger and safer for use.

## Contribution

Systematic investigation of Na2O, MgO, CaO, and Fe2O3 effects on ceramsite made from lead–zinc tailings and coal gangue.

## Key findings

- Na2O, MgO, and CaO improved mechanical properties and reduced water absorption in a dose-dependent manner.
- Fluxes slightly increased Pb and Zn leaching, but levels remained below Chinese safety standards.
- Fluxes altered mineral composition, forming labradorite, cordierite, and hematite.

## Abstract

High-temperature sintering for ceramsite preparation is a safe and effective approach to recycle solid waste. Flux components are critical in ceramsite sintering, as they can reduce sintering temperature, modulate the viscosity and content of the liquid phase, and ultimately optimize ceramsite performance. However, existing studies on lead–zinc tailings (LZTs) and coal gangue (CG)-based ceramsite lack systematic exploration of key fluxes (Na2O, MgO, CaO, Fe2O3), limiting the high-value utilization of these wastes. Under fixed sintering conditions (preheating at 400 °C for 30 min, sintering at 1250 °C for 30 min, heating rate of 10 °C/min), this work systematically investigated the effects of these fluxes (in the forms of carbonates, except for Fe2O3) on LZTs-CG ceramsite. The mechanical properties, mineral composition, microstructure and heavy metal leaching of samples were analyzed using various methods, including uniaxial compression, X-ray diffraction (XRD), scanning electron microscopy (SEM), and inductively coupled plasma optical emission spectrometry (ICP-OES). Results showed that, while Fe2O3 exerted a non-monotonic influence, Na2O, MgO, and CaO improved apparent density and compressive strength, concurrently reducing water absorption, with these effects enhancing in a dose-dependent manner. Na2O, MgO and Fe2O3 facilitated the formation of labradorite, cordierite and hematite, respectively. All fluxes weakened the diffraction peaks of quartz and mullite. ICP-OES results indicated that the fluxes slightly increased Pb and Zn leaching, yet the highest values (0.1975 mg/L for Pb, 0.0485 mg/L for Zn) were well below the limits specified in the Chinese national standard GB 5086.2-1997 (Leaching Toxicity of Solid Waste—Horizontal Vibration Extraction Procedure). This work shows optimized flux composition enables high-performance, eco-safe LZTs-CG ceramsite, supporting LZTs and CG high-value utilization and sustainable development.