Crushed Waste Rock Research Articles

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.

Geotechnical Performance of Recycled Glass-Waste Rock Blends in Footpath Bases

Laboratory and field experiments were undertaken to investigate the possible application of recycled crushed glass blended with crushed basaltic waste rock as a footpath base material. The laboratory experimental program included basic and specialized geotechnical tests including particle size distribution, modified Proctor compaction, particle density, water absorption, California bearing ratio (CBR), Los Angeles abrasion, pH, organic content, and triaxial shear tests. A field demonstration footpath comprising two sections of recycled glass-waste rock blends with 15% and 30% recycled glass content and a third control section with only waste rock was subsequently constructed on the basis of the outcomes of the initial laboratory tests. Subsequently field tests with a nuclear density gauge and Clegg impact hammer were undertaken, as well as laboratory testing of field samples to assess the geotechnical performance of the trial sections. The field and laboratory test results indicated that adding crushed glass may improve the workability of the crushed waste rock base material but subsequently results in lower shear strength. The blend with 15% glass content was found to be the optimum blend, in which the material presented good workability and also had sufficiently high base strength. Higher recycled glass content (30%) resulted in borderline, though still satisfactory, performance. The research findings indicate that recycled crushed glass in blends with crushed waste rock is a potential alternative material to be used in footpath bases. A separate study is recommended to evaluate the environmental risks associated with the usage of these recycled materials.

UTILIZATION OF WASTE ROCK FROM OIL SHALE MINING

The paper deals with utilization of oil shale mining waste rock in Estonia. Crushed waste rock is utilized as an aggregate in civil engineering in frostfree environmental conditions and in road building in unbound mixtures where required resistance to fragmentation LA ≤ 35%. This study determines areas of utilization of waste rock and shows that waste rock aggregate produced using selective mining or selective crushing technology is usable in civil engineering in partially saturated conditions and in unbound mixtures where aggregates require resistance to fragmentation LA ≤ 30%. Waste rock is usable for backfilling the already mined areas.

菱刈鉱山におけるＳｕｂｌｅｖｅｌ Ｏｐｅｎ Ｓｔｏｐｉｎｇ（ＳＬＯＳ）導入に関する研究

The Hishikari Mine is the only major gold mine operating in Japan, whose production rate in 2008 was around 184,000 tonnes with the average gold grade of 42.8 g/t. The gold veins are extracted mainly by drifting and bench stoping with backfill. Blasted waste rocks are generally used as backfill materials and crushed waste rocks with cement (cemented rock fill) are used for larger stopes. In order to extract the KE-2 vein with wider mineralization and lower grade, being closely located to the narrower KE-3 vein with higher gold grade, we have studied the applicability of the sublevel open stoping (SLOS) with cemented rock fill through in-situ measurements of rock mass displacements and numerical stress analyses for evaluating the stability of the KE-2 large SLOS stopes and interaction with the KE-3 bench stopes.We have used a bi-linear stress-strain characteristics of backfill for modeling the nonlinear compaction of cemented rock fill, whose stiffness increases with wall displacements of the backfilled stopes. The non-linear compaction may affect support characteristics of backfill, the present paper, therefore, incorporates the two-stage/bi-linear compaction modeling of backfill in FLAC3D in order to analyze the supporting effects of the cemented rock fill and to investigate the required backfill quality and mining sequence for more stable and steady operations of the KE-2 and KE-3 stopes.

菱刈鉱山・採鉱切羽における充填の支保効果

The Hishikari Mine consists of epithermal vein type Au-Ag deposits. The veins are extracted mainly by drifting and bench stoping with backfill. Blasted waste rocks are generally used as backfilling materials and crushed waste rocks with cement are used for larger stopes. Although backfilling controls the displacement of excavation surface and increases the stope stability, practical evaluation for stope dimension in conjunction with backfilling effects is not established. In this study, supporting effects of stope ends were evaluated and available support lines were drawn by using a three-dimensional elastic finite element analysis. Based on available support lines, the properties of backfilling materials were evaluated. The behavior of rock mass in bench stoping was compared with a two-dimensional elasto-plastic finite element analysis. The results indicated more remarkable influence on the stope stability with the backfill stiffness. The Young's modulus of the backfilling materials containing cement at the Hishikari Mine changed from 10 MPa to 1 GPa by numerical analyses and field measurements.

Recycling of Waste Rock as a Filler to Prevent Ground Subsidence

In this study, we investigate to use waste rock as a filler for filling the cavity of abandoned mines. We discuss that waste rock can be used as a filler in the side of environmental and structural stability. Waste rocks from four mines, such as Samgi, second Yeonwha, Dongwon and Dogye, are used. Leaching tests are conducted to check the environmental stability by four methods of Soil Leaching Test, MALT, TCLP and KSLT. According to the results, Cu, Cd, Cr and As were not detected and other metals leached below 0.5 ppm. Compressive strength of waste rock and crushed waste rock are measured to evaluate the structural stability. Mixtures of crushed waste rock are used to evaluate the possibility of enhancing compressive strength. Mixture 1 is composed of 11.1% of above 13.2mm, 22.2% of 9.5-13.2mm, 33.3% of 6.7-9.5mm, 22.2% of 3.5-6.7mm and 11.1% of 2.0-3.5mm. And mixture 2 is composed of 50% of above 13.2mm and 50% of 9.5-13.2mm. Compressive of the latter was more than that of the former. Waste rock can be probably used as a filler, considering the compressive strength of commercialized filler, or 40 Kg/cm2.

Physical dispersion of radioactive mine waste at the rehabilitated Radium Hill uranium mine site,South Australia

The Radium Hill uranium deposit, in semiarid eastern South Australia, was discovered in 1906 and mined for radium between 1906 and 1931 and for uranium between 1954 and 1961 (production of 969 300 t of davidite ore averaging 0.12% U3O8). Rehabilitation was limited to removal of mine facilities, sealing of underground workings and capping of selected waste repositories. In 2002, gamma-ray data and samples of tailings, uncrushed and crushed waste rock, stream sediment, topsoil and vegetation were collected to assist in examining the current environmental status of the mine site. The data indicate that capping of tailings storage facilities did not ensure the long-term containment of the low-level radioactive wastes due to the erosion of sides of the impoundments. Moreover, wind erosion of waste fines (phyllosilicates, ore minerals) from various, physically unstable waste repositories has caused increasing radiochemical (from a background dose of 35 – 70 nSv/h to max. 0.94 μSv/h) and geochemical (Ce, Cr, La, Lu, Rb, Sc, Th, U, V, Y, Yb) impacts on local soils. Plants (saltbush, pepper tree) growing on waste dumps display evidence of biological uptake of lithophile elements, with values being up to 1 – 2 orders of magnitude above values for plants of the same species at background sites. However, radiation doses associated with the mine and processing site average 0.67 μSv/h; hence, visitors to the Radium Hill site will not be exposed to excessive radiation levels. Although rehabilitation procedures have been partly successful in reducing dispersion of U and related elements into the surrounding environment, it is apparent that 20 years after rehabilitation, there is significant physical and limited chemical mobility, including transfer into plants. Additional capping and landform design of the crushed waste and tailings repositories are required in order to minimise erosion and impacts on surrounding soils and sediments.

Evaluation of the effect of a cover layer on radon exhalation from uranium mill tailings: transient radon flux analysis

An experimental study concerning the transport of 222 Rn in uranium mill tailings (UMTs) and in the cover layer was launched in 1997 with the participation of the French uranium mining company (COGEMA). Evaluation of the cover layer’s effectiveness in reducing 222 Rn flux emanating from UMTs was one of its objectives. In the first phase, the 222 Rn flux densities were measured regularly on a UMT layer. In the second phase, the UMT was covered with a one-meter layer of compacted material consisting of crushed waste rock derived from mining activities. Radon-222 flux was then measured at the surface of this cover layer. Observations were compared with radon flux calculated using TRACI, a model for vertical water and gas flow and radon transport. The results show that the calculations bear a fair resemblance to the observations in both cases. They also show that the effectiveness of the cover layer calculated with TRACI, using the thickness and textural properties of the cover material, is very close to the measured effectiveness.

Controlling acid drainage in a pyritic mine waste rock. Part II: Geochemistry of drainage.

Mine waste rock can produce acid rock drainage (ARD) when constituent sulphide minerals (for example, pyrite) oxidize upon exposure to the atmosphere. Outdoor experiments were performed to test techniques for preventing and controlling ARD in a pyritic mine waste rock. The experiments involved lysimeter (plastic drum) experiments in which the crushed (25–50 mm particle sizes), amended and unamended waste rock was exposed to natural weather conditions (rain, drying, freezing and thawing) for 125 weeks. The amendments consisted of separately covering the waste rock with compacted soil, wood bark and water and mixing with limestone and phosphate rock at 1 and 3%. Waters draining the various rocks were collected and analyzed for acidity, pH, sulphate and metals. In general, concentrations of SO4 2-, Fe, As, Cu, Al and Mg in the drainage from the control rock increased gradually in the first year, peaked in the second year and increased further in the third year, reflecting increasing acid generation with time. SO4 2- displayed strong positive correlation (0.91 to 0.98) with Al, As, Cu, Fe and Mg.Concentrations of Zn, Mn and Cd reached their maximumin the second year. Geochemical analysis of thecomplete water quality data using the equilibriumspeciation model WATEQ4F suggested waste rockoxidation was most likely controlled by Fe3+. Al, SO4 2- and Fe concentrations in thecontrol rock appeared to be controlled by alunite(KAl3(SO4)2(OH)6), jarosite(KFe3(SO4)2(OH)6) and amorphousferric hydroxide [(am)Fe(OH)3] during the firstyear. Ion activity product data (log IAP) forFe3+ and OH- generally ranged between –37and –34 in the first two years but decreased to –39and –40 in the third year, suggesting that amorphousferric hydroxides were beginning to crystallize intomore stable forms such as ferrihydrite (Fe[OH]3)and goethite (FeOOH) in the third year. The addedlimestone lost its effectiveness after a while,probably because of precipitation of secondaryminerals on the limestone particles. The phosphaterock could not sustain the drainage pH above 6 andlost its effectiveness before the limestone did. Underthe conditions of the experiments, the soil cover didnot work as expected, probably because of sidewallpassage of oxygen and water. The water cover was themost effective control method, reducing the acidproduction rate data from 41 to only 0.08 mgCaCO3 week-1 kg-1 waste rock. The wood bark was theworst performer and accelerated acid production by 170%.

Geology of Johannesburg, Republic of South Africa

Payable gold was discovered in 1886 on the farm Langlaagte some 5 km to the west of what is now the Central Business District (CBD) of Johannesburg. A village grew around the diggings and in 1897 the Johannesburg Municipality was constituted. Johannesburg is now by far the largest city in South Africa. It is the centre of the world9s largest gold-mining industry and has become the biggest engineering and manufacturing centre on the African continent. The rocks of four major stratigraphic sequences are represented in Johannesburg. The oldest rocks in the area comprise some of the most primitive assemblages on earth. These are isolated remnants of greenstones which survived assimilation by the Archaean Basement granitic rocks. The residual and transported soils derived from greenstones are often highly expansive. The Archaean Basement granitic rocks occur in the northern suburbs of Johannesburg and on weathering have produced soils with a collapsible fabric. Sediments of the Witwatersrand Supergroup partly cover the granitic rocks and associated greenstones. The major portion of the Central Business District and adjacent areas are occupied by this east-west-striking and southward-dipping succession of shales, quartzites and conglomerates. A characteristic geotechnical problem associated with the Witwatersrand rocks is the extreme variability over relatively short distances in a north-south direction. There are two occurrences of rocks of the Ventersdorp Supergroup in the Johannesburg area. The northern-most one is in the form of a graben, down-faulted between Witwatersrand rocks to the north and south of it. Residual soils within the graben are regarded as some of the most highly compressible soils on the Highveld. The second occurrence of the Ventersdorp Supergroup is on the southern boundary where transported and residual soils derived from the andesites are highly expansive. Mafic dykes, generally deeply weathered, occur in abundance in all rock types in the city. A variety of transported soils of the Quaternary Period occur as an ubiquitous blanket covering the underlying residual soils or bedrock. Aggregates from crushed waste rock from the mine dumps account for 74 percent of the total aggregate consumption in the Johannesburg area. The quartzite, however, contains very small amounts of pyrite which, under certain conditions, gives rise to an aggregate with potentially deleterious chemical properties. Granite and andesite are the remaining aggregate sources. Mining residue deposits in the form of slimes dams and sand dumps are common in many residential and industrial townships of Johannesburg. They pose severe and complex environmental problems such as water and dust pollution as well as long term erosion and slope stability problems. Restrictions have been imposed by the Government Mining Engineer on the development of sites which have been undermined to depths less than 244 m. This has affected a strip of ground 500 m wide, very close to the CBD. There is, however, a move by property owners, developers and consultants towards a relaxation of this constraint on development.