Publications

The filtration of tailings becomes more and more an indispensable part of the environmental management system of preparation plants. This requires powerful, reli­ able and economical filter technology. The BOKELA BoVac disc filter represents a new generation of high performance disc filters, which have set a new standard in the alumina industry, in the dewatering of coal slurries and which are operated in many applications of tailings dewatering such as gold/copper, zinc or gold/silver tailings (Hahn et al. 2015). This modern vacuum disc filter type is in approximately 80% of all applications the most economical technology for tailings dewatering – both in CAPEX and OPEX (Hahn et al. 2017 and 2014). However, running disc filters of older design are often not operated under optimal conditions and the results do not meet expectations because they are oper­ ated up to their capacity limit or beyond. In this case, it must be decided whether the operation target should be achieved with a new filters or by optimizing the existing filter system. To answer this question it is necessary to evaluate the potential for improvement and to have ideas as to which concrete measures are to be taken for an effective filter modification. The optimization of running filters with the BOKELA filter revamp pro­ gram is a very economical alternative to new investments. With this revamping program inadequate performance, excessive maintenance and high operating costs of existing filters can be quickly and inexpensively eliminated by transferring advanced design features of the BOKELA disc filter design to disc filters of old design. Benefits include: a 30% to 135% increase in filtration capacity, improved cake moisture, improved filter operation and reduced maintenance. However, the costs amount only some 20% to 30% compared to a new investment.

Mine backfill is typically placed in stopes with drawpoints or access drifts at the bottom of the stope. To contain the fluid backfill, barricades are required to prevent the flow of backfill out into the access drift. Typically barricades are constructed of muck or reinforced shotcrete; however, there are some disadvantages with typical barricade design and this paper examines some theoretical possibilities for a new barricade design that may improve safety, productivity, cycle time and the mines economics.

Prior to backfilling, fibrecrete barricades (which for the purpose of this paper refers to both barricades and bulkheads utilised for Minefill purposes) are typic­ ally cured to achieve a target strength. However, due to sensitivity of early age fibre­ crete strength caused by variations in mix properties, curing environments and spraying techniques, the rate of strength development can be quite varied. Challenges associated with conventional curing, coring transportation, and destructive strength testing methods and mine location generally prevent early age quality control testing of fibrecrete barricades and the consequence is often conservative cure periods leading to extended fill cycle times. This paper further develops a novel technique where laboratory testing is used to develop a unique relationship between strength and the shear wave velocity (or small strain stiffness) of the fibrecrete. The inves tigation considers a range of different vari­ ables encountered during the manufacture of fibrecrete to illustrate the unique relationship. The presented non-destructive test method provides a practical method to define the rele­ vant barricade strength and shear wave velocity relationship. Implementation of improved quality control techniques such as that proposed can reduce fill cycle times without comprom­ ising safety.

The paper presents the use of hydraulic backfill in the Velenje Coal Mine and the development of some procedures and devices for optimizing the basic properties of backfill mixtures. The technical, economic and environmental aspects of the hydraulic transportation of thick backfill mixtures (pastes) may be estimated only if the rheological properties are pre­ viously determined. For this purpose we developed the ball-pull test device, the tube viscosim­ eter and the pressure leaching test (PLT) equipment. A brief outline of tests of plastic and leaching characteristics and the method for determining the pressure gradient required for the specific flow of a time-independent non-Newtonian backfill mixtures and its application in the Velenje Coal Mine will be also presented.

To dispose of the smelting slag and reduce backfill cost in the mine, the aggre­ gate mixed with smelting slag was selected as the filling aggregate, and then the filling indus­ trial test of smelting slag was carried out in the stopes. Through the geological coring and strength test, the in-situ cemented backfill mass had been evaluated by the comparative ana­ lysis of RQD、P-wave velocity and UCS, which proved that the gradation of filling aggregate was optimized, and the quality of in-situ cemented backfill was improved by adding smelting slag. Based on internal links of physicomechanical parameters of cemented backfill, a relation between UCS and P-wave modulus was established from the perspective of dimensional bal­ ance. According to the test data of dry density, P-wave velocity and UCS of in-situ cemented backfill, the UCS prediction formula was obtained by the linear fitting method, which pro­ vided a strong research basis for the comprehensive quality evaluation of subsequent backfill.

The possible application of using fiber-reinforced frozen (–15°C) mine backfill was investigated using a series of laboratory experiments. Sisal fiber, Basalt fiber, and Bio­ filament were added to the tailings and water that constituted primary backfill, which served as the reference material. Samples differed in terms of fiber type, fiber content, and curing temperature. The mechanical properties of samples were investigated using the uniaxial com­ pression strength (UCS) test. The UCS of fiber-reinforced frozen backfill exceeded that of pri­ mary backfill and reached as high as 5.95 MPa. The UCS stress-strain behavior of mine backfill was markedly affected by freezing and fiber addition. Frozen backfill exhibited more ductile behavior and a higher elasticity modulus than unfrozen backfill, which showed brittle behavior. Fiber-reinforced backfill could absorb more energy before total failure.

Tailings have exhibited self heating behaviour due to exothermic sulphide oxi­ dation. Self-heating in paste backfill has caused dangerous temperatures and SO2 concentra­ tions. Self-heating potential is commonly evaluated using a laboratory test in which heated air is forced through crushed material. However, due to the monolithic nature of backfill, includ­ ing a very low permeability to oxygen and moisture, laboratory tests using a pulverized sample may be conservative and conducting tests with monolithic samples may be more repre­ sentative. Field trials were conducted at Voisey’s Bay Mine, Canada.

The paper presents the results of the numerical DEM analysis of the extrac­ tion of coal by longwall system both with roof caving and with hydraulic backfilling. The exploitation of the most productive in the basin coal seam 510 was undertaken by the Mysło­ wice colliery in a very rockburst prone strata at the depth of app. 600 m. The successful extraction with backfilling of the last longwall panel in the section of the mine was a key to any other future mining activity in the area as the stress concentration and resulting rock- bursts would prevent it otherwise. The deformation of boreholes measurements as well as geo­ physical monitoring was widely applied by the mine. The UDEC numerical model of the extensive section of the mine was built and all the extraction of coal activities ranging the period of nearly 45 years were simulated. The changes of the state of stress and strain as well as movements of the blocks in the vicinity of the longwall workings were analyzed. The strain changes in the numerical model were determined at the positions corresponding to the loca­ tion of borehole measurements in-situ. The rate of advance and productivity of the longwall face turned out to be directly related to the changing geomechanical conditions just as they were determined by the numerical simulation.

In Polish conditions of conducting underground hard coal mining in the past, in order to limit the negative impacts of conducted mining, systems with gobs filling with dry or hydraulic backfill were used. In recent years, this method of managing the floor has been abandoned, while as part of fire prevention and in order to enable waste placement in old gobs, caving mining with sealing gobs is used. It seems that this solution also results in a reduction in the amount of surface deformation. The authors presented in the article the results of own research on the subject matter. The research covered the area of one of the mines conducting exploitation in the area of the Upper Silesian Coal Basin. It was determined that the use of exploitation with sealing caving gobs reduces the subsidence coefficient, and the values of the subsidence observed in the analyzed area may be even 25% lower than when conducting exploitation without sealing and the strain extreme values over time can be up to 40% smaller.

The article discusses geomechanical aspects and numerical simulations associ­ ated with the mining methods dedicated for flat or flatly dipping orebody, i.e. room-and-pillar and longwall mining systems with regard to development of hypothetical mining panel. It was assumed that the overburden strata consists of several homogeneous rock plates reflecting the typical lithology in the Lower Silesia area. The results of the computer 3D simulations permit­ ted elastic-plastic rock mass stability analysing, identifying the areas being more susceptible to damage. Each model has been analysed from the point of view of different methods of roof control. The geomechanical risk assessment procedure utilized so called safety margins which were defined as a distance between the point characterized by the actual local strain/stress con­ ditions and the instability (limit) surface(s) which location in the 3D stress/strain space could be determined using different strength theories. The obtained results have proved that in the considered geological conditions, room-and-pillar approach has a significant advantage from point of view geomechanical safety, over the mechanized longwall excavation system.

In hard coal mines in Poland, the use of filling of caving is widespread. Mix­ tures of water and fly ash from coal combustion in power plants are used for this purpose. In addition to many other benefits, attention has been paid to this technology’s usefulness in reducing water hazards. For this purpose, laboratory tests have been undertaken on fly ash- water mixtures samples conductivity using a falling-head permeameter. The results showed that the mixtures achieve permeability values range from 8x10-7 m/s to 1,2x10-9 m/s. Addition­ ally, caved zone structure and flow of fill mixtures in longwall cavings have been discussed.

For years, environmental protection has been struggling with the problem of water contamination in Poland, especially salinity in surface water. The main source of water salinity in Poland is mining, so the problem of water salinity most affects the region of Silesia, which is characterized by a large number of hard coal mines and industrial plants. The hard coal mines located in Upper Silesia, during mining operations, pump large quantities of highly saline waters from the drainage of mine workings to the surface. Therefore, the problem of environmental protection is nowhere else on such a large scale. However, due to the fact that hard coal mines in our country constitute the main source of energy resources, solving the problem of saline water is difficult. The first part of the article presents the negative impact of salinity on water quality and resources in Poland and and it also indicates the economic effects associated with excessive salinity of rivers, which mainly include corrosive effects. The second part of the article will indicate the method of reclamation of the minefilling sand excavation, from which the leachate is dis­ charged into surface water. As the reclamation takes place by filling the excavation with post-mining waste, there is a risk that saltwater may enter the surface water. This article also presents the example how to properly reclaim areas with post-mining waste and main­ tain good water status, to which leachate from the reclaimed area is discharged. The art­ icle specifies how much water from post-mining waste can be safely discharged into surface water, without creating the risk of excessive salinity. In the event of an imminent threat, there is an obligation to immediately take preventive measures, including immediate control, containment, removal or reduction of pollution or other harmful factors e.g. by controlling leachate effluent flows.

The article presents the results of research on the physico-mechanical proper­ ties of Cemented Paste Backfill mixtures (CPB) produced from low-calcium fly ash from a conventional boiler and from slag taken from a fluidized bed boiler with the addition of metallurgical cement in the amount of 5-15 wt%. Fly ash and slag were mixed in big quantities in various proportions. The tested mixtures with a constant concentration of solids to water of 62 wt% were characterized by a wide range of consistency: from paste to very liquid. The conducted research demonstrates that the best results were obtained for the mixtures with ash to slag ratio of 75:25 wt%.

The most common method to eliminate post-mining voids created after hard coal mining consists in natural filling them with rock rubble from the strata forming the roof the mining heading. Such rubble is characterized by free spaces that allow uncontrolled flow of air. The said flow is unfavorable due to disturbances in the distribution of airflow in the ventilation network, and it poses the risk of endogenous fire. One way to reduce such adverse phenomena is to fill the rubble with fine-fraction hydraulic mixtures, most fre­ quently fly ash-water mixtures. The first part of the paper presents the method for determin­ ing the theoretical porosity of caving rubble. In the second part, the possibility of various degree of sealing of the numerically modelled caving rubble with a fine-fraction hydromix­ ture was investigated in terms of assessing its impact on the ventilation parameters of a longwall working ventilated with the “Y” method. The presented numerical model was used to calculate the airflow distribution at various filling degrees of the rubble. The obtained knowledge involving the changes in the airflow distribution parameters, depending on the sealing degree of the rubble allows to define the possibility to slow down or to stop the development process of endogenous fire. In addition, it also allows to forecast the venti­ lation conditions of workings in the longwall area, limiting the development of other ventila­ tion-related hazards, such as methane or climate hazards.

The “Regis” shaft is one of the key workings which ensure the safety and smooth flow of tourist traffic in the historic Wieliczka salt mine. Its fault-free operation requires the moni­ toring of the technical condition of the supports and the surrounding rock mass. The results of the conducted monitoring and macroscopic observations of the lining in the shaft and of the adjacent workings have exhibited gradual and progressive degradation of the rock mass structure. In order to assess the impact of these processes on the shaft and on the nearby workings, a spatial numer­ ical model of the rock mass has been created using the FLAC 3D software. The model geometry was determined after analysing the geological documentation of the area in the form of maps, cross-sections, and on the basis of visitations in the workings located in the vicinity of the shaft. On this basis, it was determined that the behaviour of the “Regis” shaft is primarily affected by a large post-mining chamber (the “Kloski” chamber) located in its immediate vicinity, on the north-eastern side. The tool used for the simulation (FLAC 3D software) allowed for the mapping of the behaviour of the continuous medium and the simulation of the destruction of the material by assigning to it (after reaching the limit stress state) the features of a plastic medium. On the basis of conducted calculations and simulations, it was determined that leaving the rock mass without any protective works may pose a threat to its stability and the stability of the “Regis” shaft lining. To protect the shaft and the rock mass, it was proposed to fill the “Kloski” chamber and the shaft below level IV. Such solution would stop the propagation of damage zones and min­ imise the rock mass displacement. Creating a stress and deformation state in the model, achieved as a result of backfilling a part of the shaft and the chamber, is highly likely to ensure the stability and safe operation of the workings located above it, in particular the section of the “Regis” shaft from the surface to level IV. The presented example showing, that backfilling used even many years after excavation of chamber can bring good results in terms of improving rock mass stability.

A zinc, copper and lead mine located in Canada has recently restarted oper­ ations after several years under care and maintenance. The mine had an existing paste plant that was historically used for surface tailings deposition. The existing paste plant was over­ hauled and retrofitted to be able to handle full plant tailings and produce cemented pastefill that will achieve the required target strengths underground. In this case study, the various design challenges faced and lessons learned are documented which led to the successful retrofit of the paste plant in 2019.

A mine in northern Ontario Canada has been in operation for several years. The mine produces 1.2 Mtpa of nickel and copper ore. The facility contains a sand plant that has been in operation for 15 years. The current sand plant combines local alluvial sands, classified tailing and reclaim tailings to produce a cemented sandfill that is sent underground via gravity. The current underground distribution system has been expanded and modified many times throughout the history of the mine and now has a total length of several kilometers. The mine operator has concerns regarding the pressure profile and flow regime of the fill throughout the reticulation system. This paper will provide an overview and evaluation with regards to the operation of the reticulation system as well as the flow model and layout. It will highlight the pressure trends and indicate where the system can be optimized and modernized.

Newmont Goldcorp’s Tanami Operations consists of the Dead Bullock Soak underground mine (DBS) and the Granites Processing Plant. DBS is currently undergoing an expansion which has created a surplus of underground (UG) waste rock. In order to deal with this surplus of waste rock a paste-waste project was initiated. The goal of this project was to develop and implement a design methodology of maximizing waste rock disposal by deposit­ ing the waste rock in primary stopes (usually only filled with 100% cemented paste backfill [CPB]). This paper presents the details of how the design methodology was developed. This includes an analysis of rock chute placement, waste rock versus CPB fill rates, and backfill strength design. Finally, the paper also presents a case study of a paste-waste stope. This study includes an economic analysis of paste-waste, highlighting the importance of paste- waste to DBS in the future.

Newmont Goldcorp Australia’s Tanami Operations consists of the Dead Bul­ lock Soak underground mine (DBS) and the Granites Processing Plant. The Backfill Group at DBS has recently introduced a number of improvements to benefit the UG reticulation system. These improvements focused on three areas: reduction of major blockage downtime, continuous monitoring of tight filling operations, and paste plant automation. The first part of the paper will cover the installation of dump/diversion valves throughout the DBS reticula­ tion system. This paper will present why these valves were installed, the design behind deter­ mining where they were placed, and several case studies showing how their installation has benefited DBS. The second part of the paper will detail the changes that allow for continuous monitoring of tight filling and present case studies on how this has benefited DBS. The third part of the paper present the results of a trial paste plant automation project which was run in conjunction with NGA’s Process Control Group. This section will detail how this automation works and present case studies on how this automation has benefited DBS.

Cemented paste backfill (CPB) is increasingly applied in underground mines world-wide and has a broad prospect considering its benefits in environmental protection and ground control. During the paste production, a well-graded aggregate is critical for the achievement of CPB. Mine tailings from the outcome of ore-dressing plant are commonly used as the fill aggregate. However, it is difficult to obtain an ideal particle size distribution for the mine tailings which are roughly mixed with final residuum in ore concentration processes. In this study, a novel industrial method is proposed to select fill aggregates from different parts of ore-dressing processes. With combined design of concentration plant and backfill plant, the tailings with desired particle sizes and proportions during the mineral processing are chosen to produce CPB without disturbing the regular ore concentration. The problem of passively accepting final tailings from ore-dressing plant has been improved.