Cemented Mine Backfill Research Articles

Corrigendum: Characterization of strength and quality of cemented mine backfill made up of lead-zinc processing tailings

Corrigendum: Characterization of strength and quality of cemented mine backfill made up of lead-zinc processing tailings

Recycling Dam Tailings as Cemented Mine Backfill: Mechanical and Geotechnical Properties

As a result of developing technology and scientific studies, employing dam tailings as critical raw material and vital economic reserve has become widespread recently. Employing dam tailings as a main ingredient of CPB (cemented paste backfill) can offer benefits to mining operations. This study deals with the use of dam tailings in CPB, considering the mechanical and geotechnical aspects. CPB was prepared at fixed solid and cement contents (72%, and 5%, respectively) and tested for different cure ages varying from 3 to 56 days. The results disclosed that the strength of filling increased over time, with the exception of 56-day cured CPB having high sulfur minerals where strength decreased sharply. The reasons behind these strength surges could be clarified by CPB’s basicity, which quickens the hydration of cement. Voids between tailings grains are also occupied by hydration products, resulting in the high strengths. Due to the fact that higher sulfate contents can cause lower pH values within CPB, this is one of the factors that should be considered for the backfill’s strength performance. The cement tends to increase the backfill’s pH in short term, but pH of long-term cured backfills decreases because of dam tailings which is inclined to acid formations and erosions. This is a sign that the deformation properties of CPB are deteriorated. Depending on curing time, CPB’s water content and void ratio decrease, but their surface areas increase. The resulting data will endow to better apprehend the effects of dam tailings on CPB quality integrating cost and quality.

Physico-chemical and micro-structural behavior of cemented mine backfill: Effect of pH in dam tailings

The tailings created during ore processing have been a serious problem for mining companies and environment since it is a challenging task to effectively manage these highly voluminous/dangerous tailings. Therefore, several tailings disposal methods like tailings dams are needed for sustainable mining operations. The tailings accumulated in the dams reflect a critical raw material source since they might contain key base/precious metals, such as Au, Ag, Co, Ni, Cu and Zn. This study deals with the use-ability of dam tailings in cemented mine/paste backfill (CMB/CPB), considering the physico-chemical and micro-structural aspects. The backfill mixtures were manufactured at 76 wt% solid and 5 wt% cement contents, exposed to cure for up to 56 days, and tested for determining their strength (UCS), geo-chemical (i.e., pH, redox potential, and conductivity) and microstructure (i.e., XRD, TGA, and SEM) characteristics. Results disclosed that the strength of backfill was improved by the augmented basicity/age while only backfills made with sulfide-rich tailings had a noticeable drop in strength. This can be enlightened by the types of tailings (aged and fresh), and the hydration products shaped owing to the interaction of these tailings mixed with cement. While the values of pH detected by chemical tests were amplified up to 14 days, some decreased up to 56 days due to acid formations and erosions. This is the key function of CPB's deterioration physically, chemically, and microstructurally. Lastly, the outcomes of this study will allow us to further explore/assess the effects of dam tailings' potential usages on quality/performance of backfill mixtures.

Strength and microstructure evolution in cemented mine backfill with low and high pH pyritic tailings: Effect of mineral admixtures

To properly dispose mining-induced tailings, diverse techniques including cemented paste fill (CPB) have been already employed. Indeed, tailings are manufactured by using different admixtures which are poisonous to the environment and need to be closely explored by considering its effects. This study dealt with the quality of CPB containing low pH (4.9) and high pH (10.8) pyritic tailings. Besides, employing ground blast furnace slag (GBFS) and fly ash (FA) in diverse rates instead of ordinary Portland cement (OPC) and their effects on fill performance were explored. Strength and microstructure of CPB made with constant solid content (72 wt%) and different OPC/GBFS-FA ratios (e. g., 90/10, 70/30 and 50/50) were carried out by several laboratory tests. Results showed that the lowest UCS performance was obtained from CPB having 50%FA and acidic tailings. It was also observed that GBFS-based backfills gave better strength than FA-based ones, irrespective of tailings, owing to the former’s high pozzolanic activity and grain shape. Regardless of additives, the highest strengths were gained from basic tailings-based backfills. pH of pyritic tailings affected fill’s performance due to its aggressive effects on cement hydration. To sum up, this study has provided relevant information and technical evidence that will subsidize the engineering design of a low-cost, zero-waste, and viable mine fill system.

Characterization of Strength and Quality of Cemented Mine Backfill Made up of Lead-Zinc Processing Tailings

Predicting the reactions of the backfill materials exposed to the effects of air and groundwater will eventually ensure an efficient and accurate mine fill system for sustainable mining operations. This paper reveals the effect of the mobility of sulfur ions within lead-zinc processing tailings on strength and quality of cemented mine backfills. Some laboratory tests such as X-ray diffraction, ion chromatography, scanning electron microscopy, combustion tests, chemical analysis, pH and zeta potential measurements were performed to better characterize the backfill’s mechanical and microstructural properties. Moreover, CEM II/A-P Portland pozzolan and CEM IV/A pozzolanic cements as ready-to-use cement products were used for cemented mine backfill preparation. To ensure the carrier of the lead-zinc tailings and to prevent the mobility of the sulfurous components, a binder content ranging from 3 to 7 wt% were employed in mine backfills. The experimental findings demonstrate that the used cement type and proportions were insufficient and some fractures are occurred in the samples due to the sulfur ion mobility. Accordingly, one can state clearly that the elemental analysis through the combustion test method can provide fast and reliable results in the determination of sulfur within lead-zinc processing tailings.

The Potential to Replace Cement with Nano-Calcium Carbonate and Natural Pozzolans in Cemented Mine Backfill

The effectiveness of mine backfilling depends on the properties of its constituents. The high cost of cement, which is commonly used as a binder in mine backfill, has led researchers to seek alternatives to partially replace it with other binders. This study investigated the potential to use nano-calcium carbonate (NCC) and natural pozzolans (zeolite and pumice) along with Portland cement (PC) in mine backfill. Two types of experimental samples were prepared: (1) gold tailings and silica sand to investigate the effect of NCC and (2) nickel tailings to investigate the effect of natural pozzolans. The unconfined compressive strength (UCS) was measured for samples cured for up to 56 days. Moreover, selected samples were subject to mercury intrusion porosimetry to investigate microstructural properties. Results show that addition of NCC did not improve the UCS of backfill prepared with gold tailings and cured for 28 days, whereas a dosage of 1% NCC in backfill samples prepared with silica sand improved UCS by 20%, suggesting that the gold tailings negatively affected strength development. Natural pozzolans, in particular, 20% zeolite, had 24% higher UCS after 56 days of curing compared to samples prepared with PC and thus have the potential to partially replace cement in mine backfill.

Effect of Air Entrainment on Cemented Mine Backfill Properties: Analysis Based on Response Surface Methodology

As part of an extensive research program exploring the potential benefits of using air-entraining admixtures in mine backfill, the experimental study presented in this paper investigates the effect of cement and entrained air dosages on mine backfill unconfined compressive strength (UCS), fresh density, and dry density. Backfill specimens were prepared using silica sand, normal Portland cement, water, and an entrained air admixture. An experimental design with response surface methodology was adopted to develop predictive mathematical models and analyze the results. The results demonstrated that an entrained air dosage of 3.5% could improve the UCS of the mine backfill owing to better dispersion of cement particles. However, a further increase in the dosage reduced the UCS as well as the fresh and dry densities by approximately 200 and 120 kg/m3, respectively. Study results imply that using air-entraining admixtures can potentially enhance mine backfill flowability and reduce the density, thus providing safer and more sustainable working conditions in an underground mining environment.

Unsaturated flow in hydrating porous media with application to cemented mine backfill

Unsaturated flow in hydrating porous media is pertinent to several engineering applications, including underground and surface use of cemented tailings. Proper description and modelling of flow is complicated by changes in material properties due to hydration as well as by the generation of suction by the net consumption of water volume by hydration, variously termed chemical shrinkage or self-desiccation. It is necessary to define changes in hydraulic properties with time; for instance, the soil-water characteristic curve (SWCC) is not unique in time in addition to being path (drying versus wetting) dependent. To address this problem, a theory for modelling unsaturated flow in hydrating materials is introduced. The theory deconstructs the SWCC into a pore-size distribution, which changes with time as hydration occurs, and the water content, which is a variable that must be tracked with space and time. Matric suction depends on the time-dependent SWCC and the water content variable. The theory is applied to a multi-layer deposition experiment performed in a column, and shows reasonable results.

Alternative by-product based binders for cemented mine backfill: Recipes optimisation using Taguchi method

In this paper, four pozzolanic by-products (waste glass, copper slag, wood bottom ash and coal fly ash) and two by-products (cement kiln dust (CKD) and anhydrite) having hydration activating potential are mixed with Portland cement and ground granulated blast-furnace (GGBS) to create low cost binders to be used in mine cemented paste backfill (CPB). The Taguchi method is used to optimise binders’ formulations in regard of mechanical strength development. Two series of experiments are implemented: optimisation tests on CPB prepared with pure silica and validation experiments on CPB prepared with real mine tailings.Globally, between 35% and 45% of expensive binders (Portland cement and GGBS) can be substituted by by-products (pozzolan and activator). Waste glass and copper slag are respectively the most and the least performing pozzolanic by-products and Wood bottom ash and coal fly ash have an intermediate cementitious potential. Nevertheless, their reactivity is insufficient to compete with GGBS which content can be adjusted to reach the strength required by mine exploitation. The strength development can be accelerated by substituting up to 30% of Portland cement by anhydrite, adding 5% of CKD and slightly increasing the amount of pozzolan.

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.

Assessment of the self-desiccation process in cemented mine backfills

During the placement of fine-grained cemented mine backfill, the high placement rates and low permeability often result in undrained self-weight loading conditions, when assessed in the conventional manner. However, hydration of the cement in the backfill results in a net volume reduction—the volume of the hydrated cement is less than the combined volume of the cement and water prior to hydration. Though the volume change is small, it occurs in conjunction with the increasing stiffness of the cementing soil matrix, and the result in certain circumstances can be a significant reduction in pore-water pressure as hydration proceeds. In this paper, the implications of this phenomenon in the area of cemented mine backfill are explored. An analytical model is developed to quantify this behaviour under undrained boundary conditions. This model illustrates that the pore-water pressure change is dependent on the amount of volume change associated with the cement hydration, the incremental stiffness change of the soil, and the porosity of the material. Experimental techniques for estimating key characteristics associated with this mechanism are presented. Testing undertaken on two different cement–minefill combinations indicated that the rate of hydration and volumes of water consumed during hydration were unique for each cement–tailings combination, regardless of mix proportions.

Numerical Modeling of Cemented Mine Backfill Deposition

In current underground mining practice, it is common to use tailings, without added cement, to fill mined-out voids (“stopes”). If fine-grained tailings are used, the high placement rates and low permeability can often result in undrained loading conditions and, hence, lower effective stress, when assessed in the conventional manner. Where cement is added, the cement modifies the consolidation characteristics in a number of ways, including increasing the strength and stiffness, reducing the permeability, and inducing volumetric changes associated with the hydration reactions leading to “self-desiccation.” As a result, conventional consolidation-analysis techniques are unsuitable for assessing the behavior. The one-dimensional mine-tailings-consolidation program (MinTaCo) has been modified, and renamed CeMinTaCo, to couple cement hydration with conventional consolidation analysis. The fundamental theory behind the modifications is presented. The model is used to undertake a sensitivity study, which highlig...

Potential of lead/zinc slag for use in cemented mine backfill

This paper gives the results of tests for the replacement of Portland cement in blended cement, by ground granulated lead/zinc slag. It is part of a wider programme to investigate the potential use of available granulated lead/zinc slag in cemented mine paste backfill. The results show that the slag gives similar compressive strength of standard mortar to granulated iron blast furnace slag. It appears to be more active requiring less grinding. On the other hand, there is evidence for the retardation of setting times and strength growth by the high zinc content in the slag. Zinc in the cement and in tailings used for the paste could limit the use of the lead/zinc slag and even iron blast furnace slag as cementing material in mine paste backfill.

Ground granulated blast-furnace slag for cemented mine backfill: production and evaluation : Douglas, E; Malhotra, V M CIM Bull V82, N929, Sept 1989 P27–36

This report presents the results of a laboratory study undertaken to evaluate ground granulated blast-furnace slag from Algoma Steel Corporation, as a replacement for Portland cement in cemented mine backfill. The evaluation was based on the results of compressive strength tests. Tests results show that, in terms of compressive strength, the slap performs as well or better than Portland cement as the binding agent in cemented mine backfill. Lime was found to be a potentially good activator