فصلنامه مهندسی معدن
پیاپی 31 (تابستان 1395)

The accurate prediction of rock mass cavability is one of the key factors in block caving mines. Today, the industry interest in application of caving methods in the strong rock masses, the reliable prediction of rock mass cavability will be much more important. If the cavability of the orebody is not assessed with a reasonable accuracy, expensive and time-consuming measures may be required subsequently to initiate or sustain caving. Therefore, it is of great importance to identify the effective parameters and interactions between them. Here, the effective parameters on cavability are introduced and then, by using RES method the level of dominant or subordinante of each parameter is assessed. In-situ stress, caving rate and fragmentation are the most dominant factors. Joint orientation is the most dominate parameter in the system (Max C-E) and potential of cavability is the most subordinate parameter (Min C-E).

Accurate detection of changes in geological layers and boundaries between them using petrophysical logs, is a fundamental problem in the petrophysical data processing. In this study, the boundaries of geological layers in a carbonate reservoir was determined in two different ways and petrophysical parameters and concentrations of minerals and fluid volume due to the boundaries specified for the interval studied were calculated layer by layer. In the first method, using blocking algorithm, effects of noise and shoulder beds of petrophysical logs readings were taken and sudden changes on these logs was used as the indication of boundary layer. In the second method, using a log clustering (MRGC method), the number of 9 electrofacies in the interval was determined and the facies boundary was defined as a geological boundary layer. The log entry contains both common method GR, RHOB, NPHI, DT and the PEF. In the next step, the petrophysical parameter and volumetric concentration of minerals and fluids in both methods were calculated set by applying the boundaries layer by layer and was compared with conventional petrophysical evaluation method. The calculations showed that, unlike commonly used petrophysical evaluation methods that calculate reservoir parameters in a mean and continuous manner across a reservoir, by specifying the boundaries of the layers in the sequence of a reservoir, petrophysical parameters can be calculated on a layer-by-layer basis with a much higher accuracy. As a result, with this method, the strongest and weakest layers in a reservoir can be identified precisely, and also a better view of the other layers can be obtained. The layer by layer study is more important in reservoirs with alternating and thin layers.

One of the solutions to reduce the transmission of blast-induced ground vibration may be application of open discontinuity as a barrier to the seismic wave path. In this study, the slot effect on the attenuation of blast-induced vibration by the numerical methods is investigated. Modeling the blasting environment has been done through creating a blast hole and recording particle velocity in the four different zones within close to far from blasting. Also by creating a slot and changing its depth, the effect of slot's position and depth is achieved. The effectiveness of the slot position in two states of active and passive isolation has also been investigated. The results of the study show reduction of ground vibration up to 85% by employment of slot. However, the effect of this attenuation at surface is higher than the deep position. Also the biggest change in attenuation is created in the first step of creating a slot (equal to half the length of the hole) that it is about 40% in near zones and about 10% in far zones. In this this investigation, analysis of the data sets resulted in best fitting relationship between the slot depth and attenuation with excellent determination index (R2=0.9). This study shows that the passive method in attenuation of surface vibrations is more effective than active method. However, as the slot depth increases, the effectiveness of both methods gets close together.

Tunnel Boring Machines (TBMs) are considered as the major boring machines in tunnels and underground spaces. Regarding the high cost of TBMs, performance assessment in a boring method using these machines is of paramount importance. Penetration rate and utilization coefficient are the major performance assessment indices of a TBM. There are various methods and equations for predicting the utilization coefficient, each having specific features and developed based on parameters of rock masses and machine specifications. Employing multivariate linear regression method and taking the key parameters of rock masses and TBM into consideration, this study proposed some relations for utilization factor in Zagros 1 tunnel (located near Hirvi village on the route Paveh- Nowsud, about 10 km to Nowsud, near Paveh city in Kermanshah Province, and about 120 km northwest of Kermanshah Province). To validate the developed equations, utilization factor was calculated in some sections of Ghomroud tunnel as well. Errors of the obtained results from regression method are lower than the ones obtained from NTH and CSM methods. In some cases, they exceed the ones obtained from NTH method and become lower than CSM method. In fact, regression method is ranked between the two methods. The results indicate that the equation proposed in this project predict utilization coefficient with an appropriate approximation as compared with the real condition.

At the rougher flotation circuit of the Miduk copper concentration plant (Kerman, Iran) five column cells (CISA) have been installed with 4m of diameter and 12m of height using static mixer type (MicrocelTM) spargers. Based on the initial design, columns should accept a feed rate of 625 t/h with 80% passing size of 90 µm and solids concentration of 28% and produce 88% of the plant concentrate (i.e., 22 t/h) containing 32% copper. Due to the mechanical and processing problems this objective was never achieved and theses columns were remained out of operation from the commissioning time (2005). The results of an extensive study indicated that spargers plugging is due to the entrance of small amount (2 kg) of coarse particles (up to 2.5 cm) and it is the main reason of columns non functionality. It was proposed in order to have a stable operation of the columns at the rougher stage the feed rate for each column should be reduced from 125 (design) to 70 t/h. The air superficial rate had to be also reduced from 1.9 (design) to 0.6 cm/s. A period of 10 days of continuous operation showed that the carrying capacity was 0.23 g/min/cm2 which was significantly lower than the design value (i.e., 0.58 g/min/cm2). The gas hold up was found to be lower than 10% beyond which columns started to move to the turbulent state indicated by “boiling” froth. The average life time of spargers was determined to be 20 days. The average recovery and concentrate grade of these columns were found 68 and 32%, respectively. The high wear rates of spargers, high level of maintenance and supervision needed and instability of the operation made the plant managers not to use the column cells as the roughers.

The prevention of water wastage in mineral processing plants, especially in desert and arid regions is the present and future serious priorities of this industry. To fulfil this goal, Gol-E-Gohar mining and industrial company has defined water recovery projects, including the investigation on the factors affecting the filterability of the tailings of magnetite and hematite processing plants using membrane chamber filter press. In this research, based on the literature review and given the limitations of the process, 10 factors including pH of the pulp, filter aid, flocculent, solid percentage of the pulp, filter medium, time and pressure of squeezing stage, time and pressure of air blowing stage, and finally chamber thickness were selected for investigation of their influence in three steps: initial experiments, one factor tests and designed experiments. It is found the effect of four factors are significant on the "final moisture" of cake including time and pressure of air blowing stage, solid percentage of the pulp and chamber thickness. Also, the major parameters affecting the "throughput" of filtration were defined as the time of air blowing stage, the chamber thickness, the time of squeezing stage, solid percentage of the pulp and interaction effect of the time of air blowing and squeezing stage and the interaction effect of the time of air blowing stage and solid percentage of the pulp. Finally, optimization of the factors based on three objectives was performed, obtaining the minimum moisture content of 14.32 %, the maximum throughput of 0.27 tons per hour per square meter, and a combination of 17% moisture and 0.147 tons per hour per square meter throughput when both moisture and throughput were optimized simultaneously. The optimized conditions were tested and verified in laboratory and pilot scale.

Industrial wastewaters are hazardous to natural ecosystems and can pollute surface and groundwater. Management and treatment of wastewaters are important in order to preserve the environment. For this purpose, recently, combination of different methods are employed to meet the emission standards. Electrochemical method has been considered as a proper technique for treatment of various industrial wastewaters due to its environmental versatility and compatibility. Also, Zero-valent Fe nanoparticles are used as oxidizing, reducing and catalyst agents for removal of a wide range of pollutants. In this study, performance of a combination of electrocoagulation/electroflotation methods with Fe nanoparticles has been studied in a two-stage removal of Acid Red 14 and the parameters of nanoparticles concentration and duration of electrochemical method usage were optimized. Quality of the synthetized bimetallic Fe-Ni nanoparticles through chemical precipitation of iron salt with a strong reductant (sodium borohydride) was examined by XRD and SEM tests. The results showed that with the concentration of 0.3 gr/L Fe nanoparticles, dye and COD removal efficiencies of 100% were obtained for the wastewater that had been treated 90 min by electrochemical method. Electrochemical method is advantageous due to simple operation whereas takes more time for complete removal of contaminants. Accordingly, the combined treatment by electrochemical and Fe nanoparticles methods can be utilized to provide higher qualities, and in load shocks.
Industrial wastewaters containing dyes are hazardous to natural ecosystems and can pollute surface and groundwater. Management and treatment of wastewaters are important in order to preserve the environment. For this purpose, recently, combinations of different methods are employed to meet the emission standards. Electrochemical method has been considered as a proper technique for treatment of various industrial wastewaters due to its environmental versatility and compatibility. Also, Zero-valent Fe nanoparticles are used as oxidizing, reducing and catalyst agents for removal of a wide range of pollutants. In this study, performance of a combination of electrocoagulation/ electroflotation with Fe nanoparticles has been studied in a two-stage removal of Acid Red 14 and the parameters of nanoparticles concentration and duration of electrochemical method usage were optimized. Quality of synthetized bimetallic Fe-Ni nanoparticles through chemical precipitation of iron salt with a strong reductant (sodium borohydride) was examined by XRD and SEM tests. The results showed that with the concentration of 0.3 gr/L Fe nanoparticles, dye and COD removal efficiencies of 100% were obtained for the wastewater that had been treated 90 min by electrochemical method. Electrochemical method has advantages such as simple operation whereas takes more time for complete removal of contaminants. Accordingly, the combined treatment by electrochemical and Fe nanoparticles methods can be utilized to provide higher qualities, and in load shocks.

Dynamic fracture toughness is an important fracture parameter for investigating the cracked rock masses under impact loading such as earthquake, rock bursts, rock blast and projectile penetration. The experimental results showed that the dynamic fracture toughness of rocks is strongly dependent on the size of the specimen. Therefore, here, a criterion is proposed for considering the size effect on the dynamic fracture toughness of rocks. The proposed method is based on the modified maximum tangential stress (MMTS) criterion which has been established recently for size effect analysis on the crack specimens under static loading. In the proposed criterion, the required parameters such as tensile strength and critical distance are obtained from specimens subjected to the dynamic loads. Some experimental data reported for holed-cracked flattened Brazilian disk (HCFBD) specimen with different sizes are used for evaluating the proposed criterion. It is shown that the proposed simple approach can predict the dynamic fracture toughness of the large specimens in a good agreement with the experimental data. Dynamic fracture toughness is an important fracture parameter for investigating the cracked rock masses under impact loading such as earthquake, rock bursts, rock blast and projectile penetration. The experimental results showed that the dynamic fracture toughness of rocks is strongly dependent on the size of specimen. Therefore, in this paper, a criterion is proposed for considering the size effect on the dynamic fracture toughness of rocks. The proposed method is based on the modified maximum tangential stress (MMTS) criterion which has been established recently for size effect analysis on the crack specimens under static loading. In the proposed criterion, the required parameters such as tensile strength and critical distance are obtained from specimens subjected to the dynamic loads. Some experimental data reported for holed-cracked flattened Brazilian disk (HCFBD) specimen with different sizes are used for evaluating the proposed criterion. It is shown that the proposed simple approach can predict the dynamic fracture toughness of large specimens in good agreement with the experimental data.

During different stages of a mine lifespan, planning the location of additional drill holes, based on the objective of that stage is necessary. Most of the previous algorithms proposed for this purpose aim to reduce the block model uncertainty and enhance the value of the drilling information as their objective functions, and have paid little or no attention to improve the precision of the ore/waste classification. In this investigation, effort has been made to define, based on the misclassification probability parameter, an objective function for the optimization of the location of additional drill holes. Using the simulated annealing method in the Angouran mineral deposit, the efficiency of the proposed objective function has been validated and proved in optimally locating the additional drill holes. An advantage of this objective function, compared with the common ones, is that in addition to having a direct relationship with the kriging variance, it depends highly on the estimated and cut-off grades; the more is the difference between these grades, the less will be the misclassification probability. Since these two grades remain unchanged with an increase in the number of the drill holes, the only way to reduce the misclassification probability is to reduce the estimation variance by drilling the additional drill holes in appropriate locations.