A novel iron-based phosphate cement (IPC), derived from iron-rich smelting slag (ISS), was developed as a sustainable and efficient binder for the stabilization/solidification of trivalent chromium (Cr3+). The mechanical properties, hydration behavior, microstructure, leaching toxicity, chromium chemical forms, and environmental safety of chromium-stabilized iron phosphate cement (CIPC) were thoroughly evaluated. The results showed that, with a mass ratio of ISS to ammonium dihydrogen phosphate (ADP) of 2.0, and even with the addition of 20 % chromium nitrate nonahydrate (CN), the compressive strength of CIPC reached 4.2 MPa after curing for 28 d. Furthermore, chromium leaching was well below 1 mg/L, significantly lower than the GB 5085.3-2007 standard limit of 15 mg/L, demonstrating the effective encapsulation of Cr3+ due to IPC's high early strength. In the IPC system, Cr3+ was primarily stabilized by forming CrPO4 and CrxFe1-x(OH)3 co-precipitates, which were further solidified through the physical encapsulation of IPC hydration products, such as (NH4)2Fe(PO3OH)2 center dot 4H2O, (NH4) (Mg,Ca)PO4 center dot H2O, and FePO4. This process resulted in a solidification efficiency of up to 99 %. BCR analysis confirmed that more than 98 % of the chromium in the CIPC remained in a stable residual form. Finally, the ecological risk index (PERT) was found to be 23.52, far below the safety threshold of 150, indicating the solidified material's long-term environmental safety. This study provides an innovative approach for the reutilization of ISS while effectively stabilizing/solidifying chromium.

Copper smelting slag (CSS) are waste slag obtained from smelters after reusing sulphur smelting slag. This study explores the potential of CSS to serve as a resource in cement mortar construction. Specifically, the study investigates the use of mechanical and chemical methods to enhance the volcanic ash activity of CSS, enabling them to replace up to 30 % of the cement content in cement mortar. The modified CSS was analyzed in terms of particle size and (Toxicity Characteristic Leaching Procedure) TCLP testing, while cement mortar specimens were subjected to a battery of tests including compressive strength, Freeze-thaw experiment, TCLP testing and cement stability testing. The results showed that compared with the unmodified CSS material, the copper smelting slag cement material with CaCO3 3 meets the requirements of GB/T 1596-2017 on the standard compressive strength of OPC 42.5 grade, with a compressive strength of 38.88 MPa at 10 % CaCO3 3 admixture, among which the CSS cement material with 10 % CaCO3 3 is the best and meets the leaching toxicity standard. Moreover, the modified CSS reduced energy consumption by 7.15 %, CO2 2 emissions by 27.41 %, and cost by 19.84 %. XRD, FTIR and SEM analysis showed that the mechanical activation of CaCO3 3 doping more drastically damaged the crystal structure of CSS, and local lattice distortion occurred, which induced the transformation of CSS from crystalline phase to amorphous phase and destroyed the ordered structure of minerals, resulting in the volcanic ash activity increased. Overall, this study demonstrates that CSS can serve as a viable raw material in cement mortar samples, reducing environmental impact and achieving resourceful use of slag.

As an industrial byproduct of smelter operations, smelting slag has brought certain environmental issues including without taking safety precautions or using appropriate management. Through a thorough analysis of the literature published in the last years, the latest research progress on the characteristics, resource utilization pathways, and safety utilization evaluation of non-ferrous metal smelting slag was introduced in this work. Key findings indicate that different ore concentrate materials, smelting conditions and types determine chemical and mineralogical characteristics of smelting slag. Moreover, smelting slag exhibits extremely high flexibility in various applications, not only as metal recovery and construction materials, but also as agricultural fertilizers and remediation agents. At the same time, the importance of conducting strict safety assessments under various utilization scenarios to mitigate its potential environmental risks is emphasized. In addition, this article also emphasizes the direction of future research, including creating a comprehensive and quantized environmental risk assessment method of heavy metals in soil-slag mixtures, as well as exploring more innovative utilization methods of smelting slag. Overall, this review is significant for promoting research on the use of smelting slag in environmental protection and sustainable resource utilization.