Effects of Acid Environment on Mechanical Properties of Cemented Tailings Backfill

Geotechnical and Geological Engineering - The characteristics of cemented tailings backfill (CTB) in the underground acidic environment under the corrosion of sulfuric acid solution were studied....     

Flow Characteristics of Cemented Paste Backfill

Cemented paste backfill (CPB) is primarily used for backfilling underground voids at George Fisher Mine (Mount Isa, Australia). The objective of this paper is to summarise the geotechnical characterisation of the tailings and the rheological properties of the CPB as determined from a laboratory testing program undertaken at James Cook University. Two binders were examined [a General Purpose cement and a slag blend cement] over a range of dosages from 0 to 6% and CPB mix solids content in the range of 72–78%. The slump tests were carried out using the standard cone (ASTM C 143) used for concrete and a cylinder with 110 mm (diameter) × 110 mm (height), whereas the yield stress was measured using a shear vane (Brookfield vane spindle V-73). The index characteristics of the tailings including the grain size distribution, liquid limit, plastic limit, specific gravity were determined as per ASTM standards. This paper will then discuss the interrelationships among the solid content, slump, saturated density and the yield stress of the CPB. It is shown that there is strong correlation between the two different slump test devices used in this study. The smaller cylindrical device appears to have good potential for slurries like mine tailings or dredged mud that have high water content for slump test. There is also strong inter-relationship among solid content, slump, yield stress, and bulk density. Increasing the solid content increases the bulk density and yield stress, but reduces the slump. While there is hardly any difference between the two binder types used in this study in terms of flow parameters, namely the yield stress and slump, the binder dosage has an effect. At any specific solid content, higher binder dosages lead to a drop in the slump and increase in the yield stress. The difference is more pronounced in dense slurries. It is also strongly believed that the trends and relationships developed in this study may be valuable for the other mining operations using CPB.     

Research on the Mechanical Properties of 3D Printing Polymer Reinforced Cemented Tailings Backfill Under Uniaxial Compression

Geotechnical and Geological Engineering - The brittle damage of the cemented tailings backfill (CTB) seriously threatens the safety of underground workers and equipment. To improve the toughness...     

Mechanical Behaviour of the Interface Between Cemented Tailings Backfill and Retaining Structures Under Shear Loads

Understanding the shear behaviour of the interface between cemented tailings backfill and retaining wall structures (barricades, bulkheads) is important for the optimal design of barricades or bulkheads, and for mine operators to balance strength and safety against cost. However, our understanding of the shear behaviour of the aforementioned interface is limited. This paper is aimed at investigating the interfacial behaviour and properties of cemented tailings backfill-retaining wall structures, including stress–strain behaviour, cohesion, friction angle and shear stiffness through direct shear tests. Two different types of barricade or bulkhead materials (brick and concrete) are used in this study. Interface shear tests are performed at various curing times of the cemented backfill. Valuable results are obtained with regards to the interface shear behaviour of backfill-retaining structures. Based on these results, interfacial properties between cemented tailings backfill and barricades or bulkheads show a significant time-dependent variation.     

Coupled Modeling of Temperature Distribution and Evolution in Cemented Tailings Backfill Structures that Contain Mineral Admixtures

Cemented paste backfill (CPB, a mixture of tailings, water and binder) is widely utilized to fill underground mine voids. To achieve a good, economical performance, one approach is to proportionally use mineral admixtures such as fly ash and slag as partial substitutes for Portland cement. Binder hydration is one of the most significant factors that can generate heat within hydrating CPB structures, which in turn, influences the mechanical and hydraulic properties of CPB, as well as the pore structure within CPB. However, the temperature evolution due to the hydration of Portland cement that contains fly ash or slag is different from that of hydration with solely Portland cement. Hence, in consideration of the heat generated by both binder hydration and transferred between CPB and its surrounding media, a numerical model is developed to predict and determine the temperature development within CPB that contains mineral admixtures. After that, data from field and laboratory studies are employed to validate the developed model. The validation results demonstrate a good consistency between the model and the field and laboratory studies. Consequently, the proposed model is applied to simulate and determine the temperature evolution with time via mineral admixtures, binder content, initial rock and CPB temperatures, stope geometry, backfilling rate, curing time and backfilling strategy. The obtained results will contribute to better designs and preparation of CPB mixtures, as well as predict the temperature distribution within CPB structures.     

Impact Energy Absorption Behavior of Cemented Coal Gangue-Fly Ash Backfill

A drop hammer test device is employed to conduct impulse tests on the cemented coal gangue-fly ash backfill (CGFB) samples which have different solid concentrations, dimensions and curing ages. The impacting time of the drop hammer on the CGFB and the maximum rebound height of the hammer are investigated. The acoustic energy loss induced by the impact of the drop hammer on the CGFB and the impact energy absorption power of the CGFB are obtained. The results indicate that, the impact energy absorption power of the CGFB increases with the increases of its solid concentration and dimension. The impact energy also exerts influence on the energy absorption power of the CGFB. When the impact energy is lower than a critical value, the energy absorption power of the CGFB increases with the increase in the impact energy. But when the impact energy exceeds the critical value, the energy absorption power of the CGFB decreases with the increase of the impact energy. The obtained results can provide theoretical and practical guidance for preventing rock burst.     

Relevance of SEM to Long-Term Mechanical Properties of Cemented Paste Backfill

This paper is an attempt to relate the microstructure to long-term mechanical properties of the cemented paste backfill produced from a hard rock mine tailing from North Queensland in Australia bound with flyash-based geopolymer (geopolymer), flyash-blended cement (FBC), and general purpose cement (GPC). A relatively high slump (260 mm) paste backfill mix with 74 wt% solids has been used to prepare cylindrical paste backfill samples with a diameter of 50 mm and a height of 100 mm. The uniaxial compressive strength tests were conducted on all samples after curing for 112 days to obtain their strength, failure strain and Young’s modulus. Fractured samples were examined under scanning electron microscope to understand the failure mechanisms at the microstructural scale. The results show that binders significantly affected the mechanical properties of paste backfills (ANOVA, p < 0.05). The paste backfill bound with geopolymer gave the lowest strength and Young’s modulus, while the paste backfills bounded with FBC and GPC showed comparable higher strength and modulus values. This was attributed to the relatively well-packed paste backfills with less cracks and smaller pore sizes in these paste backfills bound with FBC and GPC binders. In particular, needle-shaped particles, which were originally identified in GPC, highly influenced the mechanical property of paste backfills. These results indicate that fly ash can be used to partially replace the cement as a binder for paste backfills to achieve economic and environmental benefits.     

Influence of Load Path and Effective Stress on One-Dimensional Deformation of Cemented Paste Backfill (CPB) During Deposition and Curing

Geotechnical and Geological Engineering - Pore water pressure and effective stress development within cemented paste backfill (as one of the most popular local and regional underground mining...     

Development of Specimen Curing Procedures that Account for the Influence of Effective Stress During Curing on the Strength of Cemented Mine Backfill

Paste backfill used to provide ground support in underground mining is generated from full-stream tailings and is almost always placed underground with cement. For the backfill, both the rate of strength development and the final strength are important considerations for design, particularly when the backfill is subsequently exposed in the stope-mining sequence. There is strong evidence that strengths measured on specimens obtained from coring the in situ cemented backfill are much greater than laboratory-cured specimens with the same cement content. The paper reviews some of the experimental evidence showing that one of the major reasons for the different strength is the difference in effective stress acting on the backfill during curing. Laboratory specimens are (almost) always cured under zero total stress, so no effective stress develops. In contrast, backfill in a stope may cure under high effective stress, which develops due to either “conventional” consolidation in free-draining backfills, or to the so-called “self-desiccation” mechanism in fine-grained fills. Evidence is presented showing how the final strength is affected by applying stress to specimens at different stages of curing and at different rates. It is shown that a fully-coupled analysis of the filling behaviour is required to determine the appropriate effective stress regime to apply in curing laboratory specimens, where “fully-coupled” in this context means taking account of the interaction of consolidation/drainage rate, filling rate and cement hydration rate. Curing protocols for laboratory specimens are proposed, which would ensure that the strengths obtained are representative of in situ conditions.     

Predicting the Isotropic Volumetric Compression Response of Hydrating Cemented Paste Backfill (CPB)

Geotechnical and Geological Engineering - Deep and high-stress mining results in stress transfers onto the previously placed backfill, and mines have recorded several MPa induced backfill stresses....     

铝土矿选矿尾矿特性

运用X射线衍射、N2吸附实验、扫描电子显微分析、等离子光谱等多种测试方法对铝土矿选矿尾矿特性进行了研究,揭示了尾矿一些不被关注的性质,诸如铁矿物的嵌布粒度、比表面积随煅烧温度的变化、煅烧对尾矿及其中各矿物化学反应活性的影响以及各主要矿物对磷酸根离子的吸附能力等。这些性质可望在研究废水处理、尾矿增白时得到应用。     

Laboratory Characterization of Cemented Tailings Paste Containing Crushed Waste Rocks for Improved Compressive Strength Development

This paper aims at investigating some physical and mechanical characteristics of cemented tailings paste incorporating different amounts of crushed waste rocks (hereinafter called paste aggregate fill, PAF) for underground stope filling. Different mixture formulations were prepared with three classes of crushed waste rocks (or aggregate) grain size, namely 0/10, 0/15 and 0/20 mm. The amount of crushed waste rocks in the PAF mixtures ranges from 10 to 50% by volume (% v/v) (or 8–45% by mass, %m) of dry mill tailings and crushed waste rocks. The results show that the addition of crushed waste rocks in cemented tailings paste mixtures allows a significant unconfined compressive strength (UCS) development after 28 and 90 days of curing. The highest UCS was obtained from the mixtures containing 50% v/v of crushed waste rocks of class of size 0/15 mm. The PAF mixtures with the coarser crushed waste rocks (class of size of 0/20 mm) exhibit some particles segregation.     

Influence of Water Pressure on the Stress State in Stopes with Cohesionless Backfill

The rapid increase of backfill use in underground mines requires a better understanding of the interaction between the fill material and the surrounding rock mass. This is a fairly complex issue as backfill materials are weak compared to the rock mass. This difference in the mechanical behavior induces a stress transfer along the contact area. Previous work conducted on backfilled trenches and mining stopes has shown that basic arching theory can be used to estimate earth pressures in narrow, vertical openings. In this regard, most existing solutions have been developed for dry backfills. However, in many cases, water is present in mine stopes, so its effect should be assessed. In this paper, the authors present a solution to evaluate the stress state in submerged or partially submerged backfilled stopes. The proposed analytical solution is validated against numerical modeling results.     

Acidithiobacillus ferrooxidans-硫酸酸溶联合浸出金川铜镍硫化矿尾矿砂实验研究

金川铜镍硫化矿尾矿砂富含Cu、Ni和Co等金属,为对其进行回收,对新尾矿库不同深度的尾矿砂分别进行了直接硫酸酸溶浸出与A.f.-硫酸酸溶联合浸出实验,利用ICP-AES分析了不同阶段浸出液中Cu2+、Ni2+、Co2+含量。实验结果表明,A.f.-硫酸酸溶联合浸出工艺对尾矿砂中有价金属Cu、Ni和Co的浸出效果优于单独酸溶浸出工艺。其中,A.f.-硫酸酸溶联合浸出法对1m深度的尾矿砂中Cu、Ni、Co的浸出率最高,分别达到95.78%、98.01%和75.13%,而单独硫酸酸溶作用的离子浸出率分别为75.69%、74.33%和42.33%。     

煅烧条件对石棉尾矿酸浸出率的影响及机理研究

为提高石棉尾矿的酸浸出率,采用静态加热法对石棉尾矿样品进行了煅烧处理,研究了煅烧条件对石棉尾矿煅烧产物酸浸出率的影响及机理。采用热分析、XRD、红外光谱分析对原样及煅烧产物的结构、物相及分子振动吸收光谱的变化进行了分析和表征。揭示了煅烧温度、煅烧时间对石棉尾矿煅烧产物的结构、物相和酸浸出率的影响及机理。结果表明,在煅烧过程中,石棉尾矿中的纤蛇纹石先失去氢氧镁石层的外羟基,然后失去内羟基,同时伴随着镁橄榄石的结晶作用,至纤蛇纹石结构整体分解达到完全后,产物的酸浸出率才达到最高。获得最高酸浸出率的煅烧活化条件为煅烧温度680℃,煅烧时间40 min。     

Geotechnical Characteristics of Copper Mine Tailings: A Case Study

Waste management issue in mining industry has become increasingly important. In this regard, construction of tailings dams plays a major role. Most of the tailings dams require some kinds of remedial actions during their operational lifetime, among which heightening is the most common. In the first stage of the remedial provisions for Sarcheshmeh Copper Complex tailings dam in Iran, it has been decided to use hydrocyclone method to provide suitable construction material due to the high cost associated with using borrow materials for heightening of the dam. To undertake this project a series of laboratory experiments was performed to determine the copper ‘original tailings’ and ‘cycloned materials’ geotechnical characteristics to evaluate the applicability of the cycloned materials for construction purposes. Different laboratory experiments were conducted to determine the grain-size distribution, Atterberg limits, specific gravity, maximum density, shear strength parameters, consolidation coefficient, and hydraulic conductivity. The results were compared with those of similar mines to check whether they follow the trends observed in other copper tailing materials elsewhere. Variation of the cohesion and internal friction angle versus different compaction ratios were studied in order to determine realistic shear strength parameters for tailing dam stability analysis. In this study, using oedometer test, a mild linear relation between void ratio and the consolidation coefficient has been found for tailings materials. By considering the effects of void ratio and weight of passing sieve #200 materials, a new relationship is proposed that can be used for estimating the copper slimes hydraulic conductivity in seepage analysis of tailings dams.     

恬矿库周围土壤中重金属存在形态特征研究

通过对大冶铜绿山铜铁矿尾矿库周围土壤中重金属形态分析实验,研究了重金属各种形态在土壤中的分布特征。由对比实验可知,尾矿库周围土壤中Ｃｕ、Ｐｂ、Ｚｎ、Ｃｄ等重金属含量都显著地高于对照样品,书经受到重金属的严重污染。土壤中重金属形态分布征为：ｗ（Ｃｒ、Ｚｎ、Ｆｅ）;可变换态〈碳酸盐态〈有机态〈铁锰氧化态〈残渣态;ｗ（Ｃｕ、Ｐｂ）：可变换态〈碳酸盐态〈有机态〈残渣态〈铁锰氧化态;ｗ（Ｃｄ）：残渣态,有机     

城市杂填土土工特性的研究及常用地基处理方法

分析了杂填土的组成特点、沉降和变形机理及在设计中应特别考虑的几个方面，阐述了城市杂填土的浅层处理法、桩基处理法和复合地基处理法等常用的几类地基处理方法。     

Analyzing the Characteristics and Available Attributes of Skarn Gold Deposit Tailings

Skarn gold deposit tailings is a kind of tailings which is difficult to be utilized effectively. Taking a skarn gold deposit tailings from Hubei province, in China, as an example, the paper has tested and analyzed the tailings, and studied the characteristics and available attributes of the tailings, and provided scientific and efficient utilization approaches of tailings in the area of building materials further. The results showed that major mineral phases in the tailings is quartz, particle sizes of the tailings mainly exist in 10–100 μm, and the tailings has no pozzolanic activity. As a result, this kind of tailings can be used for building sand, and can be used as supplementary cementing material of concrete based on mechano-chemistry