Consolidation and Strength Characteristics of Densified Polymer-Paste Tailings Mixture as Waste Containment Barrier Materials

Abstract

During mining operations, substantial quantities of ore undergo processing to extract valuable metals. However, this extraction process inevitably generates a significant amount of waste, commonly known as tailings. These tailings, upon exposure, can pose considerable environmental risks due to their toxicity. Specifically, the high sulfur and heavy metal content of many tailings render them susceptible to acid generation, thus presenting a hazard to the surrounding environment. Consequently, tailings are often classified as hazardous materials. Recognizing the environmental challenges posed by conventional tailings disposal methods, particularly the risks associated with exposure and contamination, the mining and civil engineering sectors have endeavored to develop alternative strategies for managing and utilizing this waste material. One such strategy that has garnered attention is cemented paste backfilling (CPB). Cemented Paste Backfilling (CPB) is an engineered material composed of approximately 2-7% binder, 15-30% water, and 70-85% tailings. CPB offers a compelling alternative to traditional tailings disposal methods, providing both environmental and operational advantages. By managing tailings in a manner that reduces their hazardous properties, CPB promotes more sustainable and safer mining practices. However, despite its broad adoption and numerous benefits, CPB technology has its limitations. Specifically, it can only utilize up to 60% of the tailings produced by mining activities for underground backfilling. To further minimize tailings from the mining industry, their conversion into barrier material (liner, cover), known as SAP-paste tailings or SAP-pastefill, for waste containment facilities, is an effective strategy after CPB. This involves blending dewatered tailings with water and a superabsorbent polymer (SAP), creating a material with low hydraulic conductivity due to the nature of paste tailings and the high swelling capacity of SAP. Compacted SAP-paste tailings (PP) exhibit hydraulic conductivity below the required minimum for barrier design in waste containment facilities. Utilizing non-acidic, cement-free paste tailings for barrier materials (liners or covers) in these facilities, whether municipal, mining, or industrial, also necessitates a thorough evaluation of their mechanical properties, such as consolidation behavior and shear strength, by mining and civil engineers. While compacted PP shows promising hydraulic properties, its mechanical characteristics essential for barrier functionality are not well understood, as no studies have assessed these aspects. Effective waste containment facility design is crucial for managing and reducing the environmental risks associated with industrial waste disposal. Therefore, this study investigates the consolidation behavior and shear strength properties of an innovative tailings barrier made of Superabsorbent Polymer (SAP) designed for waste containment facilities. Different percentages (0.0, 0.2, 0.5%) of a superabsorbent polymer (SAP) were incorporated into the tailings. The study also explores the impact of freeze and thaw cycles on consolidation and shear strength behavior (0, 1, 2, 3, 5, and 10 cycles) of the SAP-paste tailing. To enhance the barrier properties, the SAP-paste mixture undergoes comprehensive laboratory testing. Oedometer tests are conducted to examine settlement over time under various stress conditions, revealing the consolidation behavior. Additionally, direct shear tests assess shear strength characteristics, providing insights into the material's resistance to sliding and deformation under different normal stresses. Results indicate that increasing SAP content accelerates the consolidation process and affects the shear strength characteristics of the compacted SAP-paste tailings mixture. Initially, the material's shear strength rises with increasing SAP content up to 2% but declines when SAP content reaches 5%. This demonstrates that the shear strength of SAP-paste tailings fill is highly dependent on SAP concentration. Specifically, the cohesion angle increases with higher SAP content, whereas the friction angle decreases as SAP content rises. Therefore, careful testing and optimization of SAP content are essential to achieve the desired performance of SAP-paste tailing barriers in waste containment. Furthermore, when subjected to freeze/thaw cycles, the SAP paste tailing mixture exhibits increased strength and solid content initially, followed by a decrease in strength and solid content after a certain number of cycles. The lower solid content influences material compressibility, leading to higher initial void ratios with increasing cycles. In conclusion, this study suggests that SAP paste tailing barrier materials have promising performance properties for barrier construction in waste containment facilities. The result of this study can help to further optimize mixtures and further reduce waste in mining. This study is also intended to open windows to new recycled materials and thus reduce harmful impacts on the environment. However, when using SAP paste tailings as a barrier, careful consideration of the climate is essential, particularly in cold regions, given their long-term application.