Gold Tailings Research Articles

Reply to the discussion by J. Chu, W.K. Leong, and W.L. Loke on "Defining an appropriate steady state line for Merriespruit gold tailings"

Chu et al. provide a discussion of an issue that has long been a source of concern for anyone trying to characterize the potential for liquefaction of sandy material using laboratory testing, i.e., the method of specimen preparation. At the outset, we need to correct an apparent misunderstanding. In their discussion of our paper, Chu et al. query why the gold tailings is labeled as material that “would always exhibit dilative characteristics upon loading”, when our study showed that contractive behaviour was possible. The quoted phrase merely represented the conventional wisdom in South Africa prior to the Merriespruit failure and was based primarily on the results of laboratory testing carried out in commercial laboratories using slurry deposition techniques where little attention was paid to the effect of preparing specimens at a range of initial void ratios. Chu et al. question the method of moist tamping that was used in our experimental programme and quote various researchers to support their view. However, contrary to their claim, Dyvik and Hoeg (1999) found that specimens prepared by both moist tamping and by a slurry deposition technique produced contractive behaviour, whilst undisturbed specimens of the same silty fine sand showed dilative behaviour, even at a slightly higher initial void ratio. These authors attributed the difference to the existence of layering in the undisturbed specimen, which was apparently clearly evident. Vaid and Sivathayalan (2000) have shown results obtained from moist tamping preparation techniques that indicate a less uniform distribution of void ratio than was obtained from the water pluviation method and point to the large collapse settlement of moist tamped specimens upon initial flooding as evidence of the unsuitability of this technique. We would suggest that this component of settlement might be minimized by an appropriate choice of the moisture content at which the moist tamped specimen is prepared. We carry out this screening process as a matter of routine and have found large differences in the volume change upon saturation. It is thus misleading to talk about the moist tamping technique without being clear about the moisture content used. Chu et al. clearly favour the use of the water pluviation technique for specimen preparation, claiming that “water pluviation is considered to produce a soil fabric similar to that of natural sands,” despite the difficulties (which they acknowledge) of segregation that occur when fines are deposited together with sand. They also show results for “identical” specimens that were prepared using water sedimentation and moist tamping techniques and produced dilative and contractive behaviours, respectively. It is questionable whether void ratios can be determined to an accuracy of three decimal places, as implied by their results. We have certainly been unable to produce this level of accuracy. Their ‘identical” specimens may thus not be identical at all. The difference in behaviour could also be because of the almost unavoidable variation in local void ratio that occurs during specimen preparation. As shown by Frost et al. (1999), even the technique of specimen preparation by highly controlled air pluviation could not prevent some degree of nonhomogeneity of void ratio distribution. These authors suggest that global void ratio measures lead to erroneous determinations of the steady state, a problem that is exacerbated with dilative specimens. A key point that does not seem to have been addressed by Chu et al. relates to how we might explain the occurrence of extensive flow failures unless the material that flows is predominantly contractive in nature. The fact that moist tamping produces a structure that is susceptible to strain softening during undrained loading shows that such behaviour is of course possible. The primary question thus seems to be whether the structure developed by moist tamping is representative of what may occur in the field. An interesting factor that appears to have been overlooked by the proponents of water pluviation as a technique of specimen preparation is the nature of the water into which the solid particles

Discussion of "Defining an appropriate steady state line for Merriespruit gold tailings"

Discussion of "Defining an appropriate steady state line for Merriespruit gold tailings"

Dewatering of fine slurries by the Kalgoorlie Filter Pipe

Filtration of slimes is difficult due to the cake build up of fine solids. This cake has a high resistance to flow and slows the dewatering process. In the 1970’s and 80’s work on the crossflow filtration process offered improvements in the filtration of these fine solids by keeping the cake to a limited thickness. This was achieved by using a shearing force on the cake generated by a slurry flow tangential to the filter medium. Working on this principle, the Kalgoorlie Filter Pipe uses a flexible hose of a woven medium to provide dewatering of slurries under pressure. The pressure required for this dewatering can be found in any line where a slurry is being pumped from one location to another, such as a tailings discharge line. Laboratory and plant trials have shown that for some gold tailings, an increase of up to 9% can be obtained in slurry % solids over a 100 m pipe length.

Epithermal instrumental neutron activation analysis for the determination of gold and arsenic in Ghanaian gold tailings using conventional and anti-coincidence counting

Epithermal instrumental neutron activation analysis (EINAA) together with both conventional and anti-coincidence counting techniques were used to analyze six different gold tailing samples from Ghana for Au and As. The method involves the use of the epi-cadmium site of the Dalhousie University Slowpoke-2 reactor facility for the irradiation of the samples. After irradiation, the samples were counted directly on the detectors. The identification and quantification of the elements were done using 411 keV photopeak of 198Au and both 559 keV and 657 keV photopeaks of 76As. The precision and accuracy of the method were evaluated. Values for Au in the samples ranged from 2.48 ppm and 6.76 ppm and for As between 1,550 ppm and 3,460 ppm. The values obtained using the two counting systems were in good agreement while the anti-coincidence counting system gave values of higher precision and accuracy. The detection limit for Au were 20 and 10 ppb for the conventional and anti-coincidence spectrometric systems, respectively, and 50 ppb for As in both cases. Details of the method and results are presented.

Static liquefaction as a possible explanation for the Merriespruit tailings dam failure: Discussion

The authors are to be congratulated for providing the mining and geotechnical community with a well documented account explaining why a disastrous flow movement of tailings occurred from the breach of the Merriespruit gold tailings impoundment in South Africa in 1994. Lessons learned from this disaster should not be lost on the profession. Some important aspects however beg further elaboration and recognition.

Defining an appropriate steady state line for Merriespruit gold tailings

Failure of the Merriespruit gold tailings dam in 1994 in South Africa was unusual in that never before had a gold tailings dam in South Africa failed in such a catastrophic fashion. Conventional thinking was that gold tailings would always exhibit dilative characteristics upon loading, primarily because of the method of deposition which allows significant consolidation to occur due to sun-drying. This paper demonstrates that the concept of a steady state line, which separates dilative from contractive behaviour upon undrained loading, is applicable to Merriespruit tailings. Four particle-size distributions of Merriespruit tailings were tested to determine the influence of the percent finer than 75 µm on the position of the steady state line. The tailings with the greater percentage of fines gave a steady state line that plotted above all the others, which translated to the requirement that a greater relative density was necessary to produce noncontractive behaviour than for the low-fines tailings samples. The difficulty of defining a unique steady state line for a particular tailings, due to errors in measurement of initial sizes, is illustrated and it is recommended that error bands be assigned to any steady state line. In a companion paper, evidence from the post-failure investigation is combined with the test results in this paper to explore the likelihood of static liquefaction as the cause of the Merriespruit flow failure.Key words: static liquefaction, tailings, steady state, flow failure.

Static liquefaction as a possible explanation for the Merriespruit tailings dam failure

In 1994 the Merriespruit gold tailings dam in South Africa failed, resulting in 17 deaths. The post-failure investigation provided no explanation as to why the catastrophic flow failure, which contradicted all previous experiences of failures of gold tailings dams in South Africa, occurred. The documented history of the dam describes insufficient freeboard provision and often poor pool control, which is argued to have resulted in some areas of the dam having high in situ void ratios. Some of the undrained triaxial tests carried out on specimens obtained from zones adjacent to the failure scar exhibited nondilative behaviour. Laboratory triaxial tests that were conducted on reconstituted specimens and are reported in a companion paper defined a series of steady state lines that were dependent on the particle-size distribution of the tailings. Void ratios obtained from undisturbed samples taken during the post-failure investigation are compared with these steady state lines and it is shown that an appreciable percentage of the specimens were likely to have been contractant. The inference drawn is that a large volume of tailings was in a metastable state in situ and overtopping and erosion of the impoundment wall exposed this material, resulting in static liquefaction of the tailings and a consequent flow failure.Key words: static liquefaction, gold tailings, Merriespruit, failure.

Defining an appropriate steady state line for Merriespruit gold tailings

Failure of the Merriespruit gold tailings dam in 1994 in South Africa was unusual in that never before had a gold tailings dam in South Africa failed in such a catastrophic fashion. Conventional thinking was that gold tailings would always exhibit dilative characteristics upon loading, primarily because of the method of deposition which allows significant consolidation to occur due to sun-drying. This paper demonstrates that the concept of a steady state line, which separates dilative from contractive behaviour upon undrained loading, is applicable to Merriespruit tailings. Four particle-size distributions of Merriespruit tailings were tested to determine the influence of the percent finer than 75 µm on the position of the steady state line. The tailings with the greater percentage of fines gave a steady state line that plotted above all the others, which translated to the requirement that a greater relative density was necessary to produce noncontractive behaviour than for the low-fines tailings samples....

Static liquefaction as a possible explanation for the Merriespruit tailings dam failure

In 1994 the Merriespruit gold tailings dam in South Africa failed, resulting in 17 deaths. The post-failure in - vestigation provided no explanation as to why the catastrophic flow failure, which contradicted all previous experiences of failures of gold tailings dams in South Africa, occurred. The documented history of the dam describes insufficient freeboard provision and often poor pool control, which is argued to have resulted in some areas of the dam having high in situ void ratios. Some of the undrained triaxial tests carried out on specimens obtained from zones adjacent to the failure scar exhibited nondilative behaviour. Laboratory triaxial tests that were conducted on reconstituted speci - mens and are reported in a companion paper defined a series of steady state lines that were dependent on the particle- size distribution of the tailings. Void ratios obtained from undisturbed samples taken during the post-failure investiga - tion are compared with these steady state lines and it is shown that an appreciable percentage of the specimens were likely to have been contractant. The inference drawn is that a large volume of tailings was in a metastable state in situ and overtopping and erosion of the impoundment wall exposed this material, resulting in static liquefaction of the tail - ings and a consequent flow failure.

Arsenic Speciation in a Contaminated Gold Processing Tailings Dam

Gold recovery in ores containing arsenopyrite releases significant amounts of arsenic into the environment due to mineral processing and oxidation during storage. The extent of arsenic weathering in a tailings dam has been investigated. Speciation of As in surface and pore waters and pond sediments showed that for gold tailings in the dam, As enrichment took place in the pore water relative to the surface water. In pond sediments As was predominantly present as residual arsenopyrite and partly as a substance co‐precipitated with iron hydroxide. The arsenic release from the sediment results from a reductive dissolution of the arsenopyrite and Fe oxides. In the surface water, arsenate and arsenite are the main arsenic species (arsenate is dominant), but in the pore waters methylation processes play a significant role. Arsenic transport is accompanied by the transformation of As into the less toxic compounds (methylated species) co‐existing with the most toxic species (arsenite).

Speciation of As(III) and As(V) in some Ghanaian gold tailings by a simple distillation method

As(III) and As(V) in goldtailings and river-bedsediments from Obuasi were determined by distillationof arsenic as AsCl3. Results yielded 3750±426 mg kg-1 (45.2%) for As(V) and 3050±66 mg kg-1 (36.7%) for As(III) in the tailings. In the river-bed sediments, one spot yielded: As(III) 0 mg kg-1 (0%) and As(V) 1447±51 mg kg-1 (100%), whilst a second spot yielded: As(III) 0 mg kg-1 (0%) and As(V) 2976±51 mg kg-1 (100%). Using arsenic oxide standards, the recovery of As(III) and As(V) in the trioxide were 94.8 and 0.6% respectively. In a mixture of the two oxides, the recovery of As(III) was 87.6% with practically no interference from As(V). Total As content of the tailings was determined by neutron activation analysis (NAA) to be 8305±75 mg kg-1.

Engineering properties of gold tailings

ABSTRACT A comprehensive laboratory testing program has been conducted to establish the engineering properties of gold tailings from Kidston Gold Mines in North Queensland, Australia. The engineering properties of the tailings have been categorised into textural, hydraulic, and mechanical properties. The textural properties include the particle size distribution and the specific gravity. The hydraulic properties include the water characteristic curve, and the saturated and unsaturated hydraulic conductivity. Various models that describe the tailings water characteristic curve and hydraulic conductivity function have been presented. The mechanical properties include the bulk modulus, Poisson's ratio, the friction angle, the dilation angle, and the unsaturated shear strength parameters. The engineering properties of the tailings are vital to the management of the tailings both during the mine's operation, and long after its de-commissioning.

Erosion and Anti-Erosion Measures for Abandoned Gold Tailings Dams

Erosion and Anti-Erosion Measures for Abandoned Gold Tailings Dams

Environmental impact of the gold mining industry in Ghana

X-ray Fluorescence (XRF) Analysis and Atomic Absorption Spectrophotometry (AAS) have been used in assessing heavy metal pollution from some gold mines in Ghana. The presence and levels of heavy metals in gold ore, gold tailings, inland waters, and river sediments have been determined. Using these techniques, the heavy metals: Cr, Mn, Fe, Cu, Zn, As, Pb, Rb, Sr, Y, Zr, and Nb were identified in some of the solid samples within a concentration range of 0.08 ppm--4.9%. However, the inland waters showed the presence of only Fe and Zn at levels of 0.08-2.4 micrograms/mL.

Gold tailings reclamation in South Africa

Gold tailings reclamation in South Africa

Geotechnical aspects of remedial design for a gold tailings dam. Technical notes on practical applications : Sally, J P Int J Num Anal Meth GeomechV9, N6, Nov–Dec 1985, P589–598

Geotechnical aspects of remedial design for a gold tailings dam. Technical notes on practical applications : Sally, J P Int J Num Anal Meth GeomechV9, N6, Nov–Dec 1985, P589–598

Geotechnical aspects of remedial design for a gold tailings dam

AbstractRemedial measures were required for a gold tailings dam in South Africa which had undergone a minor slope failure. Information from laboratory and field measurements was used for evaluation of the present and future stability as the height of the dam increased. To aid the design process, numerical methods were used for prediction of in situ conditions. Stability analyses by computer were then used to optimize the type of remedial measure.

Pollution by arsenic in a gold-mining district in Nova Scotia

Arsenic levels were determined in arseniferous gold tailings, waters, stream sediments, plants and aquatic organisms in the vicinity of a stream draining the Montague gold mining district near Halifax, Nova Scotia. Background levels of arsenic in Mitchell Brook, upstream from the former mining activities, were high (37 ng ml −1), although below the safety limit of 50 ng ml −1. Levels did, however, decrease, due perhaps to ion exchange during passage of the water through a non-polluted swamp, but then increased to 190 ng ml −1 as the stream passed through the arseniferous gold trailings of the abandoned Montague Gold Mine. Thereafter, levels decreased again and reached 46 ng ml −1 at the outflow in Lake Charles. Arsenic levels in tailings were inordinately high and ranged from 0·38% to 0·65%, being highest in the downslope areas. In stream sediments (clay and quartz fractions), arsenic levels increased considerably in the vicinity of the mine and remained high for most of the remaining course of the stream. Arsenic levels in ashed twigs of alder Alnus rugosa growing on the stream banks correlated well with arsenic levels in water except where the latter became excessively high. The arsenic content of aquatic organisms correlated well with the arsenic content of water and ranged from 0·002 to 0·059 μg g −1 (dry weight) for mayfly larvae, 0·002 to 0·18 μg −1 (dry weight) for caddisfly larvae and 0·63 to 3·2 μg g −1 (wet weight) for the banded killifish (minnow). It is concluded that arsenic pollution from former gold mining activities in this area is appreciable and it is suggested than in future gold mining operations care should be taken to isolate arseniferous tailings from local drainage systems.