فصلنامه مهندسی معدن
پیاپی 13 (زمستان 1390)

Convergence in the galleries of underground tunnels, caused by the displacement of the ceiling, floor and walls, strongly affects the time-dependent stability of the gallery. By estimating the displacement value, the load that will be induced to the support system can be determined. By calculation of the gallery convergence caused by displacement of floor, ceiling and walls, the pressure applied on the support system can be predicted and by thus appropriate design of support system can be done. Yet, analytical and numerical models to determine the convergence of mine galleries have been presented. Nonetheless, presentation of a simple and empirical model able to predict the convergence of galleries of coal mines, far from complexities of numerical equations, can be focused by miners. In rock galleries, two kinds of instabilities often occur. In the first case, gallery instability occurs with a sudden destruction. In this case, discontinuities divide the rocks surrounding the gallery into particles and these particles can move or rotate. In the second case, instabilities often occur in very deep layers and with high initial stresses and with progressive convergence. In this paper, field studies and measurements showed that present numerical relations for prediction of final convergence, ceiling heave and wall convergence of galleries of coal mines are not applicable for convergence determination of the galleries of Tazareh Mine. Thus, a relation for more accurate estimation of galleries of Tazareh Mine, specially the gallery K21 (because of data accessibility of this gallery and similarity of geometrical-mechanical properties of this gallery to other galleries) has been presented. For this purpose, at first, effective parameters in such convergences as depth, coal layer thickness and slope, conditions of gallery floor rocks, mining time and destruction conditions were determined. In addition to parameters effective in convergence, a criterion for the estimation of the convergence value in underground coal mines galleries is presented by means of simulation of the K21 gallery of Tazareh Mine parameters. The multiple linear regression analysis was used to find the coefficients of the independent parameters by considering all effective parameters in convergence in a way that a linear relation existed between the independent and the relative parameters. The presented equation was validated by investigating the data being normal, constancy, variance and linearity of the relation between the independent and the relative parameters. A comparison between the values calculated by using the presented criteria and the real measured values in the monitoring stations showed that the presented model is highly capable of assessing of the mentioned gallery. By this empirical relation, estimation of convergence of coal galleries, in which the coal layer has different slopes, can be done.

Maximizing Net Present Value (NPV) is the most common goal in cut-off grade optimization of open-pit mining operations. In the case, price of product has a critical effect on the optimum value of cut- off grade. In this paper, the relationship between optimum cut-off grade and price was investigated in different mining, processing and marketing capacities. In order to visualize this relationship, an illustrative mine was employed. For determining the optimum value of cut-off grade in different cases, a nonlinear programming model was formulated, and then all models were solved with Solver in Excel. The main decision variables of the model are g (cut-off grade), and T (mine life-time). the objective function of the model is maximizing NPV of mining operation, and the constraints are related to the capacity of mining, processing, and market activities, as well as the relationships between tonnage and grade in the pit. The outcomes of this paper can be summarized as follows: 1- When objective of cut-off grade optimization is maximizing the present value, increasing of price may cause increasing or decreasing of the cut-off grade, or even it may have no effect on it. This is due to the fact that when objective of optimization is maximizing the present value, the cut-off grade will be subject to two opposite forces. Increasing of price increases the value of less valuable material and so decreased the cut-off grade. on the other hand, it increases the value of the material remained in the pit, so the opportunity cost grows, tending to upper cut-off grades. When the price increases, the result of these two opposite forces determines direction of optimum cut-off grade variation. When capacities of activities (mining, processing and market) change, sometimes the force resulted from the opportunity cost overcomes other force, so optimum cut-off grade increases when the price arises, and sometimes vice versa. So optimum cut-off grade decreases when the price arises. In addition, sometimes the two forces are equal, and so increasing of the price has no effect on optimum cut-off grade. 2- Variation of maximum present value versus price in all capacities is absolutely ascending.

In this paper, we introduce a method for estimating the structural index. This method is used from analytic signal, a function in which defines as energy envelope of the three Cartesian gradients. The efficiency of this method was tested using a synthetic sphere model in 500 m depth.also the applicability of the Euler method was demonstrated on various synthetic models such as prism, dipping dike and vertical cylinder. The results have broad correlation with the assumed parameters used in constructing the models. Findings further showed that if the Euler method would be used correctly, it is able to determine the body regions. In other words, this method produces reasonable results about depth to top of the bodies on the boundaries of the subsurface body. The results of the depth estimation were plotted on a magnetic map by employing the circles with proportional diameter to the estimated depths. The Euler method was tested on real magnetic data from a ground magnetic surveying in North of Iran (Semnan province). In this region, 28 magnetic profiles with 300 m length an N-S direction were acquired. The profile spacing was selected equal to 20m based on the geological and field conditions. The dominant magnetic minerals are Magnetit and Hematit, in which in some portions are altered. The magnetic data was collected using Proton magnetometer model GM19. As the causative body geometry is unknown in this region, then we used from the combination of the analytic signal and Euler in order to estimate the structural index. The estimated value for the structural index was, which can be dedicated to thin dike body. Further, we run the Euler method for estimating the depth to top of the causative body using the estimated structural index. The Euler method determined the depth to top of the body in the studied area as 15-35m

Physical and chemical properties of crude oil, including viscosity and API gravity, are commonly inherited from the early organic matter, environmental conditions in which they were deposited and depth of burial of the source beds. API gravity increases in deeper burial due to higher thermal maturation of organic matter in the source rocks and consequently, generation of lighter saturated hydrocarbons. Mansouri Oil Field in the Dezful Embayment in northern Zagros, SW Iran, consists of three successive reservoir horizons including: Asmari Limestone (Oligo-Miocence), Ilam and Sarvak Formations (Bangestan Group) of Late and Mid Cretaceous age. API gravity variations do not follow the international depth order in these horizons, i.e., decrease from 25.83 in the upper reservoir (Asmari) to 21.46 in the lower (Ilam) and to 25.01 in the lower reservoir (Sarvak). Geochemical analysis of 5 crude samples from 3 reservoir horizons indicated that frequency distribution of saturated and non-saturated hydrocarbons, as well as polar compounds (resins and asphaltens) in the Asmari and Sarvak formations are rather close to each other, but they differ remarkably within the Ilam formation, e.g., saturated hydrocarbons maximize to 60.51% in Asmari, 50.36% in Sarvak, and 37.22% in Ilam. However, aromatics decrease to a minimum of 28.64% in Asmari and 33.84% in Sarvak, but maximize to 41.8% in Ilam. On the other hand, crude materials in the Ilam reservoir contains 20.98% of polar compounds, while in Asmari reservoir; it decreases to a minimum of 10.89%. Gas-chromatography analysis of crude samples from the Mansouri Oiled Field-showed that CPI results are rather similar and close to 1, indicating that oils in the Sarvak, Ilam and Asmari resevoirs are generated from one source rock, which belongs to th Kazhdomi Formation. Other source potential, i.e., Pabdeh Formation, was not mature thermally and therefore, did not reach the stage of oil generation. It is concluded that the Oil Field consists of only one petroleum system. Mansouri is an under-saturated oil field and lacks gas cap. Consequently, its gas-oil ratio is low and the lowest value is found in the Ilam reservoir. Minimum frequency distribution of paraffinie hydrocarbon and maximized content of aromatics and polar compounds in this reservoir could be probably due to strong variation of porosity and permeability in the Ilam Formation.

Annually 20000 t of Ni-Cd filter cake is produced in Iran zinc processing plants. For recovery of remained metals, filter cake is leached with sulphuric acid, and cadmium is cemented by zinc powder, thus it is separated from the solution easily. The remained purified solution contains about 20-25 g/L Zn, 1-1.5 g/L Ni and minor amounts of other impurities with pH 3. Separation of Ni and Zn separation is not easy due to very similar properties. The most important factor in solvent extraction is extrctant type. In alkyl phosphoric acid types, nickel transportation mechanism to organic phase is cationic exchange. In this study, the possibility of Ni and Zn separation from real and synthetic solutions by co-extraction of Ni and Zn and selective stripping of Ni by D2EHPA extractant was investigated and co-extraction of Ni and Zn results was considered. By using D2EHPA that was diluted with Kerosene in different volume ratios of 20, 30 and 40%, Zn and Ni were co-extracted in pH at 5.2, and then Ni was stripped at pH 2.8 - 3. By increasing the D2EHPA concentration from 20% to 40%, maximum Ni extraction increased from 85% to 93%. Phase ratio (A/O) and extractant concentration were optimized as 1.1 and 40% (v/v).The results showed that with D2EHPA 40%, the maximum A/O ratio for co-extraction of Zn and Ni was 1.25/1 and in higher ratios, the organic phase was destroyed. A full fractional design of the experiments was used to study the effects of variables such as pH, phase ratio and extractant concentration in the process. The optimum values of O/A and stripping pH were obtained as 3/1 and 2.8, respectively. It was found that in the optimum conditions, extraction and stripping recovery were 93% and 95%, respectively.

Nowadays different methods are being applied to improve scientists’ knowlage regarding the concept and mechanism of processes. One of these methods is mathematical modeling of processes, which is supposed to define and determine the parameters affecting the process. In mineral processing, the specific rate of grinding is one of the most important parameters for modeling and simulation of grinding circuits. Since high percent of energy is often consumed by the comminution circuit in a mineral processing plant, thus it needs to be properly investigated. The rate vareis with changing of the grinding conditions and the equipments selected for a specific task. There are several parameters affecting on the efficiency, effectiveness and on the model to be developed for energy consumption in a grinding circuit, the optimization of which should be conducted through a suitable modeling and simulation process. The material of this investigation was provided from the Sangan placer iron ore deposit, located 1000 km far from Tehran(Iran). This study aimed to investigate the effect of mills and balls diameter, ball and powder filling of the mill and rotational speed on grinding kinetics. Breakage distribution function of the placer iron ore of Sangan with a 10-millimeter maximum particle size was determined in the laboratory by a 200 millimeter mill. Values of the laboratory selection function were scaled up for a pilot mill with a diameter of 1200 millimeter. Austin's equations were used as a basis for the scale-up process. For validation of the models and checking the correctness of the scale-up process, BMCS simulator v. 1.3 was used for prediction of particle size distribution of the pilot mill discharge. The simulation results were found to be in a good agreement with the pilot test measured data. The good agreement between the discharge measured and the predicted particle size distributions confirms validity of the scale-up relationships and procedure. Therefore, the scaled-up selection function can be used confidently for design goals.

The run-of-mine ore of Aghdarreh gold mine is comminuted through crushing and grinding stages to achieve the required degree of liberation of gold particles. The comminution circuit consists of a SAG mill equipped with a discharge trommel and a hydrocyclone package which is operated in closed circuit with the SAG mill. The hydrocyclone package, is used to classify the particles ground by the SAG mill. The overflow of hydrocyclone package is fed to the gold recovery circuit at downstream. Gold extraction is carried out by leaching process and cyanidation within the stirred tanks. In this research, optimization study of the grinding circuit of Aghdarreh gold processing plant was done by modeling and simulation using MODSIM software to reduce P80 of the closed SAG circuit to less than 70 microns in order to increase the degree of liberation of gold particles at the same current circuit capacity. Plant sampling campaigns were scheduled to determine the required parameters of SAG mill model, i.e., breakage distribution function, selection function, calibrating Plitt's model and validation of models. Breakage distribution function was defined by the MODSIM software based on t10 vs. ECS model parameters (A and b) and abrasion parameter (ta) provided by the user. Selection function was also defined by the simulation software based on the given Austin model parameters (a, α, μ and Λ). Two plant surveys were done to collect the samples from various grinding circuit streams. In both sampling surveys, incremental sampling from all circuit streams including trommel undersize and oversize (ore scats), hydrocyclone feed, underflow and overflow were done at steady state for a time period of two hours. The SAG mill fresh feed was also sampled by temporarily stopping the conveyor belt and collecting enough ore material from a cut with two meters length. Operating conditions during the sampling were recorded based on the control room readings. The final sample for each stream was prepared by combining the incremental samples taken every ten minutes. Particles size distribution and solid percent of all samples, except SAG mill feed, were determined in the laboratory and then balanced by NorBal data reconciliation software. The balanced particle size distributions and flow rates were used in the MODSIM software for models’ calibration and subsequent simulations. After validating the calibrated Plitt's model based on the second sampling survey, circuit simulations were done for internal overflow and underflow diameters equal to 82 and 70 mm, respectively, six hydrocyclones in operation, increasing the charge volume from 21 to 35 % and increasing the ball charge volume from 10 to 12 %. Based on the mentioned input data, the prediction showed that P80 of the circuit product can be reduced to approximately 51 microns.

Determination of rock mass deformation modulus is one of the main requirements of any civil engineering project. Deformation modulus can be determined by in situ tests such as dilatometer, plate loading and flat jack tests. However, these methods are time consuming and expensive. Analytical methods can be also used to estimate the deformation modulus. These methods can easily evaluate factors affecting the deformation modulus. Analytical methods are based on summing of all displacements of intact rock and joints, which finally predict the deformation modulus of rock mass. In this paper, the effect of lateral stresses on the deformation modulus of jointed rock mass is taken into account. This parameter has not been considered in the previous analytical methods. In order to control and evaluate the analytical equations and to estimate the reliability of these methods, the results of laboratory tests carried out by Pinto on three schist samples were used. Moreover, the results of analytical methods were compared with the numerical methods using 3DEC software. Based on this comparison, it can be stated that: - The shear force of the lateral pressure increases the deformation modulus whereas its normal force decreases the deformation modulus of jointed rock mass. Totally, an increase of the lateral pressure will increase the total modulus of the rock mass. - Increasing of the joint normal angle, with σ1, joint spacing, joint normal stiffness (kn), joint shear stiffness (ks) and the ratio of in situ principal stresses and confining stresses results in increasing of the deformation modulus of the jointed rock mass. by increasing of these parameters from certain values, the rate of modulus increasing significantly decreases so that the rock mass modulus equals to intact rock modulus. - In the blocks containing one and three joint sets, a good correlation was obtained between the modulus calculated from the mathematical equations and the numerical modeling in the absence of the confining pressure. Their maximum error obtained as 2.5% and 2.2%, respectively. - Having applied the lateral pressure in a block containing one and three joint sets, the analytical approach and the numerical modeling estimated an error around 7% and 14%, respectively. - The results obtained from the suggested analytical method, the numerical modeling and the laboratory tests showed that there is a good agreement among them, which reveals the high accuracy of the analytical model.

Open pit mining is one of the most important methods of surface mining in which extraction of mineral deposit is carried out in benches. Ultimate limits of an open pit which define its size and shape at the end of the mine’s life must be designed before to start the operation. Manual and computer methods can be used to determine optimum ultimate pit limits. Manual methods of designing pit limits are based on stripping ratios and involve determining break even pit limits. The objective of computer methods is to determine the optimum ultimate pit outline for which the net profit is maximized. A number of algorithms such as floating or moving cone method, the Korobov algorithm and the corrected form of this method and the Lerchs and Grossmann algorithm based on graph theory have been developed to find out the optimum final pit limits. Each of these methods has special advantages and disadvantages. The designers of the corrected form of Korobov algorithm claim that this method is able to yield the true optimum pit in all the cases. The aim of this paper is to examine this method for being as a true optimum pit algorithm. This method is compared with the Lerchs-Grossmann algorithm which is the only method that can be proved, rigorously, always to yield the true optimum pit. The results show that the corrected form of Korobov algorithm is not always able to find out a true optimum pit outline.