فصلنامه مهندسی معدن
پیاپی 39 (تابستان 1397)

This study uses multiple indicator kriging estimator based on assayed data acquired from 48 exploration boreholes in Tabas coal mine in order to predict gas content of coal seams. Results of the estimated block models showed that approximately 12% of the total area has the gas content of less than 5 (m3/ton) (Low risk), 11% has 5-10 (m3/ton) (Medium Risk) and 15% has 10- 15 (m3/ton) (High Risk), while about 62% of total area has the gas content of more than 15(m3/ton) which is of a high risk. Therefore, according to the experiences from mined panels, in the zones with lower to median gasification risk, it is possible to keep the mining operation running with management and optimization of the ventilation system. However, in the zones with higher gasification rate, demethanization process is mandatory.

Achieving the optimal size distribution and fragmentation of blasted muck-pile, has an important role on the controlling of mining processes and mineral processing as well as production costs reduction. In order to optimize the production process and to have rapid and reliable evaluation of blasting results, one of the common modern methods in size distribution of rock fragmentation is image processing method. Despite of numerous advantages of this method, the associated inherent limitations and errors affect the precision, accuracy, and reproducibility of measured results. Understanding such limitations and errors and decrease their effectiveness will improve the results of image processing. In this study, while introducing different types of image processing errors, errors of inappropriate imaging angle (perspective distortion) analyzed and reduction procedures have been suggested. The results of studies on 240 digital images of blasted fragmented rocks, show an average of 97% and standard deviation of 4.5% for elimination of perspective errors. Also, when the distance factor is 0.8 to 1. 5, the results are more reliable. Moreover, with a smaller particle size, optimal results can be achieved when the distance factor is reduced to 0.2 to 0.4. Furthermore, the frequency of distance factor in a state of lognormal distribution of data, is in the range of 0.5 to 1.5 with the average of 1.48, has the range of frequency error with an average of 3%. Also, the comparison of sieve size distribution curve of muck-piles with the size distribution curve of images taken from it, before and after perspective error elimination using auto mode of Split Desktop software, showed that after perspective error elimination, mean of size distribution error, depend on the amount of perspective distortion, were decreased 5 to 25 %.

Schedules are major concerns in construction planning and management. The mutual interferences among construction activities of tunnels are complicated, which will affect scheduling to some degree. Ground condition and construction (excavation & support system) time and costs are key factors in decision making during the planning and design phase of a tunnel project.
In this work the DAT innovative methodology for the probabilistic estimation of ground condition and construction time and costs is used. As construction progresses, geologic information is checked based on the excavated part of the tunnel and, therefore, the uncertainty about this part of the tunnel will disappears. This new information can be used to update the geology condition of the tunnel in order to obtain more precise prediction for unexcavated part.
In this paper, an engineering application to Garan road tunnel is well presented to demonstrate how the ground conditions and the construction time and costs are updated during construction. Finally, the results of simulations for the initial prediction and the updated prediction will be compared in order to see how the construction time and costs distributions of the given tunnel are changed after the geologic updating.Finally, reducing of uncertainty about the construction time and costs is resulted. It facilitates both the owners and the contractors to be aware of the risk they should carry before construction of unexcavated part, and it is useful for both tendering and bidding.

Mining is among the most dangerous activities around the world, which is always associated with various incidents, injuries, loss of life, and property damage. There are many safety, health and environmental hazards in the workplace that neglecting them and not planning to control them can have irreparable consequences. Therefore, risk assessment is important in these mines. The purpose of this study is to provide a model for the analysis of the hazards associated with wire cutting machine using fuzzy fault tree analysis in stone dimensional mines. In the present study, after conducting studies and collecting information about the causes of the risks associated with the wire cutting machine, judging through the questionnaire by the relevant experts and identifying the risks associated with the cutting wire, then analyzing has occurred and rooting the causes of the hazards using fault tree analysis method. Considering the tree model that was created with this method, used fuzzy theory to weigh the root causes identified as Basic Events in order to eventually obtain the probable occurrence of any Basic events. The results show that the highest probability of occurrence among Intermediate Events is respectively for the dangers of maintenance, the dangers of geological issues and the dangers of improper design and the highest probability of occurrence among Basic Events is respectively for the dangers of move and whipping caused by the rupture of wire, the dangers of diversion of wire cutters and the dangers of existence Lakarty (mud) inside the stone blocks. Finally, due to the control methods, an appropriate response to these risks is presented.

Ojat-Abad Iron mine is located in northern Iran, about 73 km east of Semnan, in the iron metallogenic belt of Semnan Province. Hematite is the main ore mineralization in the studied area, with 4 main forms of Fe mineralization; hard and compact hematite with magnetite, fine hematite, concretion hematite inside fine hematite matrix, and ocher. Limestone and sandstone adjacent to andesite and basalt-andesite are the host rock of the Fe mineralization. Ca and Mg carbonates, quartz, and feldspar are the most important gangue minerals. Carbonate minerals are in the form of cement in hematitic concretion, calcite veins and also as limestone and limestone-dolostone host rock. Quartz and feldspar are associated with ocher hematite and are also the main rock-forming minerals in sandstone host rock. Based on the chemical analysis, hard hematite has the highest content of Fe2O3 and ocher has the highest content of SiO2.The sum of P2O5, MnO and SO3 are less than 1 % in the ore minerals. Arsenic concentration was determined up to 1200 ppm in the hematite by EPMA.

Surface dissolution is one of the mineral surface modification methods. In this study, the effect of surface dissolution on isotherm and kinetic of sodium oleate as a collector on the surface of ilmenite, olivine-pyroxene and quartz were investigated. Parameters of conditioning time, pH, temperature, activation energy, specific area and contact angle were studied before and after surface dissolution. The results of adsorption isotherms of Langmuir, freundlich and temkin and kinetic models of elovich, lagergerin and psedo second order showed that the collector adsorption on the minerals can be described by Langmuir isotherm and pseudo second-order kinetic model. The collector adsorption on the studied minerals is occurred based on adsorption capacity from solution and mainly single layer. The results indicated that surface dissolution result in increasing the collector adsorption on ilmenite surface and decreasing it about the gangue minerals. Also, after surface dissolution, the activation energy of ilmenite is decreased form 57255.4 J/mol to 42437.9 J/mol which indicates the collector adsorption on ilmenite is more favorable. Furthermore, after surface dissolution the activation energies of quartz and olivine-pyroxene are increased from 5746.5 J/mol to 5816.5 J/mol, and from 8326.6 J/mol to 12523.3 J/mol, respectively. The results of contact angle measurement showed that after surface dissolution the contact angle of ilmenite is increased and it is decreased for gangue minerals. These results were in good agreement with the results of Uv-Vis spectroscopy, collector adsorption and ICP analysis.

Power draw estimation plays a vital role in sizing, control and optimization of grinding mills. As a result, power draw is considered to be one of the key control parameters in grinding circuits. Most of the equations presented to determine the power draw make use of the torque created by the charge inside the mill. In this research, effect of filling, mill speed, and liner shape on power draw were studied using a 1-m diameter laboratory mill, considering the amount of free flight materials with varying torque arm. The amount of inflight material and mill charge were calculated by image analysis of pictures taken from the transparent end of the mill during operation. The center of mass and the length of torque arm were calculated using Solidworks© software. Results indicated that for 45% filling, due to a reduction in the amount of materials in contact with mill shell, the maximum inflight material was obtained at speed of 100% (relative to the critical speed); whereas, for 15% filling this occurred at speed of 85%. Furthermore, the maximum torque arm for 15% filling was observed when mill speed was 45%; in case of 45% filling, the same obtained at a speed close to 80%. The power draw for a new and a worn liner (5184 h of operation) in Sarcheshmeh copper concentrator were compared. It was observed that at all mill speeds, the mill power draws for worn liners were higher than that of the new liners. For example, for 25% filling and 70% mill speed, the power draw of the worn liner was 10% higher than the new liner.