Green Low-Carbon Technology for Metalliferous Minerals

Metalliferous minerals play a central role in the global economy. They will continue to provide the raw materials we need for industrial processes. Significant challenges will likely emerge if the climate-driven green and low-carbon development transition of metalliferous mineral exploitation is not managed responsibly and sustainably. Green low-carbon technology is vital to promote the development of metalliferous mineral resources shifting from extensive and destructive mining to clean and energy-saving mining in future decades. Global mining scientists and engineers have conducted a lot of research in related fields, such as green mining, ecological mining, energy-saving mining, and mining solid waste recycling, and have achieved a great deal of innovative progress and achievements. This Special Issue intends to collect the latest developments in the green low-carbon mining field, written by well-known researchers who have contributed to the innovation of new technologies, process optimization methods, or energy-saving techniques in metalliferous minerals development

Development and Characterization of Sustainable Geomaterial Using Mining and Industrial Wastes

The rapid growth of infrastructure needs a vast amount of natural resources to be used as an engineering material; on the other, industries and mining sectors are facing difficulty in managing their by-products. Hence, research needs in the alteration of the industrial wastes that can overcome the above challenges with minimum or no adverse effect on the geoenvironment, which especially can be termed as a sustainable material. In the present study attempts have been made to develop sustainable materials, (i) controlled low strength material (CLSM), (ii) biopolymer based cementitious material and (iii) alkali activated material (AAM) from industrial and mining wastes. The controlled low strength materials are developed using (i) less explored industrial waste ferrochrome slag (FS) and (ii) coal mine overburden with fly ash and cement as the binder for both the cases. Experimental investigations like flowability, bleeding, compressive strength, California bearing ratio (CBR), settlement, ultrasonic pulse velocity and slake durability index are made on developed CLSM. Use of optical microscope to characterise the granular material FS in terms of sphericity and workability of the material is another aspect of the present work. The developed CLSM material can be used for different structural fill works with “Low flowability, to “High flowability” with the bleeding value less than 3.5%, with water content varying from 25 to 32%. The 28 days’ density varies from 15.7 kN/m3 to 16.5 kN/m3 with ultrasonic pulse velocity values close to 2000, and the water absorption values less than 3%. The unconfined compressive strength (UCS) value upto 2.75 MPa and CBR value more than 100% was obtained. Biopolymer-based cementitious materials are made using (i) fly ash and (ii) fine fraction of coal mine overburden for wind and water erosion control using three types of biopolymers; xanthan gum (XG), guar gum (GG) and carboxyl methyl cellulose sodium (CMC) salt. The wind erodibility of the materials are studied using water retention, surface resistance and wind tunnel test, similarly pinhole test, cylindrical dispersion tests are conducted to know the water erosion resistance. For water erosion, the CMC is more effective followed by GG and XG for both shale and fly ash. The surface strength of CMC and XG treated shale and fly ash increased with increase in concentration of solution upto 2%, but optimum percentage of GG treated samples observed at 1%. Higher surface strength of CMC and GG showed better wind erosion resistance. The surface strength of biopolymer treated cohesive material shale is more than that of non-cohesive material fly ash, with the denser microstructure of treated samples due to the bonding of particles. The other sustainable material, alkali activated material using mine overburden and mine tailing is discussed in terms of compressive strength after 7 and 28 days of curing under ambient, alkali and sulphate solution to simulate different environmental conditions. Development of CLSM using AAM and use of slake durability index to assess the durability of developed sustainable material are some of the novelty of the present work. The AAM using mine overburdens are found to have 28 days compressive strength varying from 25.58MPa to 59.00 MPa depending upon the curing conditions and the base materials. The slake durability test indicates the developed AAM is “medium-high durable” to “high durable material”, similar to that of sandstone. The leachate analyses on the developed sustainable materials show no adverse effect on the geoenvironment. The scanning electron microscope (SEM), x-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), electrical conductivity, zeta potential, etc. are also used for the characterization of basic material and the developed sustainable material to correlate with their macro properties. The present work will help in the possible utilisation of the developed sustainable material in infrastructure. But, the future challenges are (i) development of suitable machinery and equipment for implementation of CLSM process, (ii) pilot project study on the implementation of biopolymers for erosion control at the site and (iii) identification of cost-effective activators, possibly from industrial wastes

Development of co-disposal methods for coal discards and fine waste for the prevention of acid mine drainage

The dependence on coal ores for energy supply has led to the considerable increase in coal discards (CD) and fine waste (FW) arising from mining and processing operations. These wastes typically contain sulphide minerals, which when oxidised may lead to the generation of acidic and toxic discharge. A deficit of naturally occurring neutralising minerals to counteract this acidic discharge results in acid rock drainage (ARD). Far reaching consequences on water systems, vegetation, people and wildlife ensue as a result. To minimise the environmental burden, the acidic water resulting from the oxidation of sulphide minerals present in wastes from both active and abandoned mines is often treated with alkaline materials and is further processed to remove metals. Indefinite maintenance and operational activities emanate from these treatment processes. Further, accumulating sludge from processing streams presents post-closure liabilities. To reduce the environmental footprint, mine waste management strategies have been developed to minimise the risk of ARD formation and proliferation. In this study, the co-disposal of CD and FW was investigated as a means to prevent the initiation of oxidation reactions at source. The CD fraction is sulphide rich with high acid producing potential but can be effectively utilised to construct structurally stable beds. In these beds, large voids are formed between the particles that facilitate the transport of oxygen and water to the sulphide mineral surfaces. Co-packing FW with sulphide-rich CD provides a sustainable approach to ARD prevention. The FW has a high-water retention capacity and can be used to encapsulate, seal or cap the sulphide bearing mineral surfaces. Apart from providing a physical barrier and decreasing voids, FW typically have low sulphide content and high specific surface area that result in increased release rates of any acid neutralising minerals present in these waste materials. Co-disposal techniques thereby provide a longterm end-of-pipe approach to ARD mitigation that may offset indefinite, resource intensive, treatment options. The co-disposal of CD with FW, however, is challenging particularly at large bed cross-sectional areas, as the incidence of high percolation rates increases. This is attributed to decreased inter-particle contact that emerge in packed beds with high void ratios, decreased packing density and increased susceptibility to deformation. This undesirable packing behaviour impacts negatively on bed stability culminating in particle displacement and increased likelihood for sulphide mineral oxidation. Fine wastes conceal these sulphide minerals by either filling voids between coarse particles or forming covers with capillary barriers and acid-neutralising effects. Consequently, the generation of ARD is inhibited. At increased scale, however, the ARD prevention efficiency of covers is enhanced by increasing the CD to FW proportion to result in a structure with high load and acid buffering capacity. The approach adopted in this study entails developing packing arrangements of co-mingled CD and FW in dry-mass ratios of 3:2 and 2:3, respectively, to improve bed stability and hence prevent ARD formation with scale up. In addition to mixture ratios, improved co-packing of CD and FW is contingent on the material geochemical properties and geotechnical parameters of the resulting packed structure. As such, geochemical analyses were performed to determine the acid producing and neutralising potential of the CD and FW through acid base accounting, net acid generating and biokinetic tests followed by geotechnical assessments. The static test results indicated that the high sulphur CD (2.16% S) was potentially acid forming and the low-sulphur FW (0.84% S) was non-acid forming with high acid neutralising capacity. The co-mingled CD and FW samples (ca. 1.5% S) were deemed uncertain as the net acid producing potential was near zero and the NAG pH was less than 4.5. Accordingly, biokinetic tests were conducted over 120 days to fully understand the acid generating and neutralising rates of the inoculated and uninoculated co-mingled samples. Near-neutral conditions were sustained for prolonged periods (> 90 days) in FW dominant samples (2CD:3FW) after which a transition to acidic conditions ensued. This highlighted the limited role of acid neutralising minerals in sustaining near neutral conditions. As ARD mitigation is contingent on preventing the rapid percolation of water and exclusion of oxygen from sulphide mineral surfaces, means to prevent the rapid depletion of neutralising minerals by either dilution or washout are essential in flow through systems. This can be achieved by decreasing voids to result in increased packing density and improved bed stability. Bed stability was shown to be dependent on several interrelated factors that included the degree of saturation of the particles (water to solid ratio, W/S), CD to FW ratio, packing configuration (layers or blends), and the extent of material compaction (assisted versus unassisted packing approach). These factors were integrated to produce 16 packing arrangements. The efficiency of these configurations was compared using packing density, slump and compressibility tests. Packing densities of ca. 0.8 m3solids. m-3mould coupled with low slump spread values (600 s) were noted. The large compressive extensions and the delay to achieving maximum compressive strains signalled the low particle consolidation and decreased bed stability of unassisted wet packings. As engineered co-disposal approaches are associated with long-term bed stability and hence prolonged ARD prevention, select packings were further analysed to validate their efficacy using kinetic column tests of increasing scale. An acidic feed of pH 2 was continuously introduced to the test columns at a flow rate of 3.5 L.m-2.h-1 to expedite the oxidation process and to assess the efficiency of the packing arrangements for ARD mitigation. Segregated disposal of CD in small scale columns (D = 0.19 m, H/D = 1.12) with inherent large voids allowed unrestricted access of the aqueous oxidants to the exposed sulphide minerals leading to rapid discharge of highly acidic effluent (ca. pH 2). For the wet, unassisted co-packed systems, structural instability was observed with the wash out of FW and subsequent fast effluent discharge rates. With the loss of the neutralising and reactive barrier due to migration, acidic conditions presented earlier in these wet packed beds (after 30 days) than in dry packed beds (after 90 days). The loss in geotechnical stability was more prevalent in blended systems than in layered configurations, with a rapid loss of geochemical stability following soon thereafter, despite similar neutralising characteristics in both packing configurations. In these blended arrangements, non-functional migration of the fine waste particles transpired to result in unhindered access of the oxidants with the acid generating minerals. With dilution and wash out of the neutralising components, acidic reactions dominated. In multi-layered systems, a cascading effect prevailed despite breakthrough in some layers such that a fail-safe condition resulted. Consequently, near-neutral effluent discharge at low flow rates transpired. This further emphasised the importance in preventing the displacement of particles to maintain bed stability in co-disposal prevention strategies. Assisted dry packings of blends and layers were anticipated to result in improved bed stability at large scale. As such, CD dominant blends (3CD:2FW) and FW dominant blend and layered (2CD:3FW) systems were investigated in large scale columns (D = 0.32 m, H/D = 1.12). These columns were similarly exposed to aggressive leach conditions over 120 days. As with the smaller scale columns, the packing efficiency in multi-layered arrangements were higher than for the blends. In the blended systems, evolving geochemical and geotechnical conditions were similar regardless of the CD:FW ratio demonstrating the complexity in achieving homogenously packed matrices at large scale. In multi-layered configuration, bed structural stability was sustained for extended periods as the stress imposed on the packed bed was uniformly distributed across the moisture retaining FW layers and dissipated within the matrix. Correspondingly, particle displacement was minimised, and with the cascading phenomena, ARD was successfully prevented over extended periods. A dry cover system composed of multi-layers of CD and FW is therefore recommended for pilot scale studies. Dry cover systems can be easily constructed and present a cost-effective approach to sustainable mine waste management. Further evaluation of the structural stability of multi-layers at large scale is required as changes in bed geometry, particle size and environmental conditions can alter the dump geotechnical properties and hence geochemical stability

Static and Dynamic Properties of Controlled Low-Strength Materials Incorporating Treated Oil Sands Waste

Controlled Low-Strength Materials (CLSM) is a self-compacted self-leveling cementitious material with compressive strength of 8.3 MPa or less. It is used as an alternative of soil backfill materials in geotechnical and infrastructure applications. This study investigates the effects of incorporating treated oil sand wastes (TOSW) as a partial replacement of sand or fly ash on fresh and hardened properties of CLSM. In addition, the environmental impact of the proposed new mixtures was evaluated. The results show that CLSM mixtures incorporating TOSW had satisfied the limits and requirements of ACI committee 229 for CLSM with no environmental hazards. The incorporation of TOSW has increased the flowability of all mixtures and consequently reduced the water demand to reach the required flowability which consequently increased the compressive strength of mixtures containing TOSW and fly ash. Replacing fly ash with TOSW on the other hand, reduced the strength of CLSM slightly, but the strength remains within CLSM acceptable range of strength. In addition, this produced a more re-excavatable mixture, adequate for applications that may require future re-excavation. To investigate the effects of incorporating TOSW in CLSM as a replacement of fly ash and partial replacement of sand on its dynamic properties, shear wave velocity and geo-mechanical properties were evaluated. The piezoelectric ring actuator (PRA) technique was employed for measuring Vs of CLSM and an empirical equation was suggested to estimate Vs based on mixture proportions of CLSM. The results suggest that the shear wave velocity was affected primarily by the cement content, while TOSW had minimal impact on it. However, TOSW improved the flowability of the mixture and could totally replace fly ash for that function. It is concluded that TOSW can be successfully incorporated in CLSM mixtures, offering an application to reduce the landfill disposals of oil sands waste while reducing the demand on natural resources

Evaluation of flow and in-place strength characteristics of fly ash composite materials

Of the seven hundred and fifty millions of metric tons of fly ash that are produced annually worldwide, only a small portion e.g., 20% to 50% of the fly ash is used for productive purposes, such as an additive or stabilizer in cement, bricks, embankments, etc. The remaining amount of fly ash produced annually must either be disposed off in controlled landfills/ mine fills or waste containment facilities, or stockpiled for future use or disposal. As a result of the cost associated with disposing these vast quantities of fly ash, a significant economical incentive exists for developing new and innovative, yet environmentally safe applications for the utilization of fly ash. The main aim of the present investigation was designed to develop an engineered backfill material to be placed in mine voids using fly ash as the major component. Experimental set up was designed and fly ash samples from seven numbers of thermal power plants situated at different parts of the country were collected. Investigation into detail physical, chemical, morphological, and mineralogical characterizations have been carried out to choose the most favorable fly ash source for slurry transportation.Flow parameters such as viscosity, shear stress, shear rate (25s-1 to 1000s-1), temperature (200C to 400C), and solid concentration (20% to 60%), etc. were determined. Flow behavior was influenced with addition of additives as cationic surfactant cetyltrimethyl ammonium bromide (CTAB) and a counter-ion sodium salicylate (NaSal). As the fly ash concentration in the slurry increased an increase in viscosity was observed. Addition of surfactants (0.1% to 0.5%) modified the flowing attributes from shear thickening to shear thinning/Newtonian pattern and eliminated yield stress completely/partially compared to that of untreated fly ash slurry. Temperature of the slurry environment was also observed to influence the flowing behavior

Investigation of the Geomechanical Behavior of Mine Backfill and its Interaction with Rock Walls and Barricades

RÉSUMÉ Les rejets solides produits par les mines comprennent les rejets de concentrateur (résidus miniers) et les roches stériles. Ces rejets sont usuellement entreposés en surface, ce qui peut engendrer divers risques environnementaux et géotechniques. Une autre option consiste à remblayer les chantiers miniers avec des stériles ou des résidus miniers. Cette pratique permet de réduire les quantités de rejets entreposés en surface, et aussi d'améliorer la stabilité du terrain, de diminuer la dilution et d’augmenter la récupération de minerai. Le remblayage est utilisé avec diverses méthodes d'exploitation souterraine, pour différentes fonctions. Les préoccupations majeures associées à cette pratique sont la stabilité des structures de support (barricades) peu après le versement du remblai dans le chantier et la stabilité du remblai cimenté exposé après un certain temps après le remblayage. L'état des contraintes dans les chantiers remblayés a été largement étudié au cours des dernières années. Cependant, plusieurs incertitudes existent encore en lien avec des préoccupations majeures, notamment sur le peu de solutions disponibles afin d’évaluer l'évolution des contraintes dans les chantiers, pour concevoir les barricades et le remblai cimenté exposé, ainsi que sur pour estimer la valeur du coefficient de pression des terres K (= ζ’h/ζ’v). L'objectif principal de ce projet est d'évaluer l'état des contraintes dans le remblai confiné et ses interactions avec les barricades peu après sa mise en place et avec les trois parois latérales pour le remblai exposé à plus long terme. De nouvelles solutions analytiques sont proposées pour évaluer l’évolution du niveau d’eau dans un chantier remblayé d’un remblai hydraulique. Ces solutions sont vérifiées à l'aide de simulations numériques réalisées avec le logiciel d'éléments finis SEEP/W. Ces analyses indiquent que l’eau accumulée sur le remblai hydraulique peut induire des pressions interstitielles plus élevées et ainsi compromettre la sécurité des barricades----------ABSTRACT Solid wastes produced by mines include tailings and waste rock. These wastes are usually stored on the surface, which may raise various environmental and geotechnical risks. Another option is to backfill underground mine stopes with waste rock or tailings. This practice can reduce the surface disposal, and also improve ground stability and ore recovery in mining operations. Backfill is widely applied in different underground mining methods for various purposes. The associated major concerns are the stability of the support structure (barricades) at very early time and that of the exposed cemented fill at longer time. In recent years, the stress state in backfilled stopes has been extensively investigated. However, there are uncertainties regarding the major concerns including limited solutions for stress evolution in stopes and for design of barricades and exposed backfill, as well as the actual value of earth pressure coefficient K (= ζ’h/ζ’v) in confined fills. The main objective of this project is to evaluate the stress state within confined backfill and its interactions with barricades at very early time (shortly after the filling) and remaining three sidewalls upon exposure at longer time (typically a few weeks after the filling). New analytical solutions for evaluating the transient seepage are proposed for stopes filled with hydraulic fill. These solutions are verified using simulations conducted with the finite element code SEEP/W. These analyses indicate that ponding, generated on the top of the settled hydraulic fill, can induce higher pore water pressures and jeopardize the barricade safety

Effect Of Aggregate Propertıes On The Mechanıcal And Absorptıon Characterıstıcs Of Geopolymer Mortar

Üretiminde önemli çevresel sorunlara neden olan Portland çimentosunun imalatı için çeşitli doğal kaynaklar tüketilmektedir. Jeopolimerizasyon adı verilen yeni bir teknolojik süreç bu konuda yenilikçi bir çözüm getirmektedir. Jeopolimerler karbon emisyonu potansiyelini düşürmenin yanı sıra, uçucu kül, öğütülmüş yüksek fırın cürufu, metakaolin, vb. gibi birçok endüstriyel atık ürünü veya doğal puzolan ile sentezlenebilir. Bu çalışmada, uçucu kül esaslı jeopolimer harcın agrega özellikleri ile bazı mühendislik özellikleri arasındaki ilişkiyi ortaya koymak amacıyla deneysel bir çalışma yürütülmüştür. Bu amaç doğrultusunda, agrega olarak iki tür kum ve dört farklı gradasyon kullanılmıştır. Jeopolimer bağlayıcı, alkalin sıvılar ve uçucu kül karışımından oluşmaktadır. Kırma kireç taşı, karışık kum ve doğal kum için sırasıyla basınç dayanımı değerleri 47.83-40.25 MPa, 44.93-38.09 MPa, ve, 39.37-28.25 MPa aralığındadır. Ayrıca, su emme ve kılcal su emme deneyleri ile jeopolimer harçların geçirimlilikleri değerlendirilmiştir. Elde edilen test sonuçlarına göre uçucu kül esaslı jeopolimer harcın su emme kapasitesinin karışık agregalı olanlarda (%50 kırma kireç taşı ve %50 doğal kum), tek tip agregalı olanlara kıyasla iyileştiği gözlenmiştir