Solidification/Stabilization of Arsenic-Containing Tailings by Steel Slag-Based Binders with High Efficiency and Low Carbon Footprint.

Wei Gao,Zifu Li,Siqi Zhang,Xiaoqi Li,Yuying Zhang,Wen Ni,Guoxiang Teng

doi:10.3390/ma14195864

Abstract

The disposal of nonferrous metal tailings poses a global economic and environmental problem. After employing a clinker-free steel slag-based binder (SSB) for the solidification/stabilization (S/S) of arsenic-containing tailings (AT), the effectiveness, leaching risk, and leaching mechanism of the SSB S/S treated AT (SST) were investigated via the Chinese leaching tests HJ/T299-2007 and HJ557-2010 and the leaching tests series of the multi-process Leaching Environmental Assessment Framework (LEAF). The test results were compared with those of ordinary Portland cement S/S treated AT (PST) and showed that the arsenic (As) curing rates for SST and PST samples were in the range of 96.80–98.89% and 99.52–99.2%, respectively, whereby the leached-As concentration was strongly dependent on the pH of the leachate. The LEAF test results showed that the liquid–solid partitioning limit of As leaching from AT, SST, and PST was controlled by solubility, and the highest concentrations of leached As were 7.56, 0.34, and 0.33 mg/L, respectively. The As leaching mechanism of monolithic SST was controlled by diffusion, and the mean observed diffusion coefficient of 9.35 × 10−15 cm2/s was higher than that of PST (1.55 × 10−16 cm2/s). The findings of this study could facilitate the utilization of SSB in S/S processes, replacing cement to reduce CO2 emissions.

Highlights

Nonferrous metals are an important basic material for the development of the Chinese economy [1]
All leached-As concentrations of S/S treated AT (SST) samples were below the type IV water threshold of the Chinese standard as published in the Standard for Groundwater Quality (GB/T 14848-2017) (50 μg/L, transverse solid line) with the exception of T-4-7d (52 μg/L), while the leached-As concentrations of the Portland cement S/S treated AT (PST) samples were below the type III water threshold (10 μg/L, transverse dotted line)
Accounting for the complete exposure of the tailings into acid rain and acid mine wastewater caused by pyrite oxidation, the applicable pH domain of 4–9 for arsenic-containing tailings (AT) was chosen rather than the default 5.5–9 used for the natural pH of soil, while the pH domain for T-3 sample cured for d (T-3-90d) and PST-90d was chosen as 7–13 to capture the natural pH and anticipated environmental processes that may occur over time (Figure 3a,b)

Summary

Introduction

Nonferrous metals are an important basic material for the development of the Chinese economy [1]. The mining, processing, and smelting industry of non-ferrous metals is the most significant source of heavy metal and metalloid emissions in China (e.g., Hg, 53.6%; Cd, 88.9%; Pb, 81%; As, 61.8%) [2]. It is imperative to develop effective and economically viable technologies to reduce pollution from the non-ferrous metal industry. Backfilling is an ecological solidification/stabilization (S/S) method for the safe disposal of non-ferrous metal tailings, which could support underground goaf to prevent surface collapse, improve the recovery rate of resources, and prevent the release of contaminants from the tailings [4]. Ordinary Portland cement (OPC) is a traditionally used binder in backfilling S/S processes, but in the production of clinker, the raw materials need to be calcined in a rotary kiln at temperatures up to 1500 ◦ C, leading to abundant emissions of CO2 in the process of decomposing the calcium carbonate into calcium oxide (CaO) and CO2.

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Discussion

Conclusion