فصلنامه مهندسی معدن
پیاپی 27 (تابستان 1394)

In Chador-Malu processing plant، reverse flotation is used for dephosphorization of hematite concentrate. Sodium silicate is used as iron depressant and a mixture of Alke and Dirol as collector. The phosphorus content of the concentrate is at an acceptable level (0. 047%) but the silica content is relatively high (3. 5%). The flotation circuit is designed to remove apatite but not silica. Chemical and mineralogical studies of the samples and mass balance of the flotation circuit showed that the silica content of the iron concentrate was mainly in the form of free quartz particles in the size range of minus 45 micron. The main objective of this research was to investigate the possibility of floating silica in the apatite- iron oxide- silica flotation system. Flotation experiments on samples with high silica content، showed that using 800 grams per tones of sodium silicates with silica modulus of 2. 5، at pH of 10، gave better results but the silica contents of iron concentrate (4. 5%) was still high. Addition of Ca++ to the sodium silicate solution، at pH of 11، reduced the silica contents from 4. 5% to 2%، while the iron grade was increased by 1% and the concentrate recovery was reduced by 1%.

In this paper، the removal of heavy metals، arsenic and lead by modified nano-bentonite (coated with chitosan and carboxymethyl chitosan) has been studied. First، efficiency of removal of heavy metals، arsenic and lead، under the conditions fixed by nano-bentonite and modified nano-bentonite were compared. Following، Effective parameters such as pH، dose of the nano-adsorbent، contact time and initial concentration of lead and arsenic were studied. To determine the optimal parameters and to achieve the highest level of removal، experimental design method was used. Based on the results obtained، nano-bentonite chitosan was found to be more effective for the removal of Pb and As. Also results shows that pH has an effective result on lead removal and also pH and adsorbent dosage has an effective result on arsenic removal. also، according to the results obtained under the optimal conditions: pH=6، contact time of 30 min، the initial concentration of 1000 ppb and dose of adsorbent= 1. 2 g/l for lead، pH=4، contact time of 30 min، the initial concentration of 1000 ppb and dose of adsorbent= 1. 8 g/l for arsenic، the highest value of lead and arsenic removal 92. 50% and 94. 63%، respectively by Nano-bentonite chitosan is achieved.

Since the true Earth is three-dimensional (3-D) in nature، 3-D interpretation of these structures can be more efficient relative to the one or two-dimensional (1-D or 2-D) interpretation of them. The purpose of this paper is to investigate the probable geothermal source of the northern area of Sabalan in Iran using 3-D modeling of the Magnetotelluric (MT) data. For obtaining this purpose using various techniques it was indicated the subsurface structures of the area is complex and the structural dimensionality particularly at the long periods (>2sec.) is 3-D in overall and 3-D modeling of the data is necessary. Then by designing the appropriate mesh and applying the 3-D inverse modeling algorithm، the suitable model of resistivity for the MT data was obtained. Using 3-D modeling results، geological information map and existence 2-D modeling results، the geothermal area was investigated and interpreted and the geometry location of the hotter zone as the geothermal source was identified. Also the location of the alteration zones relevant with the geothermal source were detected and delineated using the 3-D results and geological information.

Well bore stability analysis is a procedure with the view to economically improving the drilling operation. Identification of diverse types of rupture in the well bore is crucial in stability analysis. Due to reduction I reservoir pressure and index of per، hydraulic fracturing well be performed in order to increase the permeability and production from well. During the aforementioned procedure، fluid is injected inside the well to induce the fracture in the walls. Hydraulic fracturing has received much recognition as a reliable method for the stimulation of oil reservoir. In this study، conducted on 400 m of limestone in fahlyian reservoir in darkhovein oil field، pressure of shear and compressional failure is determined by virtue of parameters including rock mechanic and information on well logging as well as in situ stress of vertical and maximum and minimum horizontal. Safety mud window was defined between 0. 84 and 4. 2. The minimum allowable mud pressure for preventing the shear failure was between 33. 51 and 52. 89 and the maximum range was determined between 47. 4 and 97. 55. Furthermore، minimal required mud pressure for inducing compressional rupture and hydraulic fracturing was estimated between 108. 87 and 151. 38.

Constructing underground spaces causes chaos in the ground stress field and its deformation. Due to settlement، construction of such urban underground spaces as subway tunnels is of utmost importance. In this research، the boring process of Tehran subway tunnel، line 7، has been studied and ground settlements، under Greenfield conditions، have been estimated for 2 sections (km 5+100 and km 9+900). The numerical analyses of the settlements of these 2 sections have been done with the Plaxis 3D software and compared with those recorded on the tunnel axis. It has been shown، through measuring ground settlement of the tunnel nearby buildings، that a relatively symmetrical settlement has been occurred around the tunnel axis. Settlements in these 2 sections، estimated by analytical and numerical methods، were not found to be in the permissible range. Therefore، to control settlement، it is necessary that improving measures be taken; at km 5+100، a coefficient of 1. 6 for the chamber room pressure would suffice and at km 9+900، the tunnel route needs regional improvement to make the work face stable and cause settlements to occur in the permissible limits. The values found by infography confirm those found by this research

Wet separation circuit of the Golgohar iron ore plant includes comminution by overflow ball mills and separation by low intensity magnetic separators. The average sulfur content of the concentrate is more than 1. 2 %، which is higher than allowable limits for de-sulfurization and pelletizing plants (0. 8 % and 0. 1%، respectively). This problem is due to the low liberation degrees of sulfur bearing minerals (Pyrite) discharging the ball mills. In this research، the optimum product size (P80; 80% passing size) to achieve the acceptable level of sulfur in the product by Davis tube test was found to be 100 microns. In order to increase the grinding efficiency and to achieve the desired degrees of freedom، the ball charge level and percent solids were used as the main manipulated variables. At the 33% ball charge and percent solids of 68، mill product size reached 106 microns from the original value of 137 microns. Changes، which were implemented in whole circuit، included increasing percent solids from 47 to 65، increasing ball charge level from 27 to 33 volumetric percent and adding 20 mm diameter steel balls in to mill No. 2 with the usual 30mm balls. Mean residence time of materials in ball mill were determined by tracing method to be about 8 minutes and was used to determine the time needed to achieve stability. Sampling over a period of a few months in the plant indicated that the product size decreased to 110 microns with 95 % confidence. After implementation of changes in the plant، due to finer mill discharge، the sulfur reduction criterion (ratio of feed sulfur content and wet concentrate) increased by 19% (relative).

The shear strength parameters of rock mass fall among the most important information required for designing and stability analysis of structures excavated in the rocks. Based on this fact، Hoek and Brown suggested a method to estimate the strength and deformability parameters of jointed rock masses. In rock engineering designs، the mean values of Hoek and Brown parameters are often used. In these cases، probability analysis of rock mass properties is highly important. In this paper، based on the results obtained from rock mechanics tests carried out on rock samples of Gol-e-Gohar iron ore mine، the uncertainties in determining the shear strength parameters of the mine rock masses were modeled according to Hoek and Brown failure criteria and using Monte Carlo simulation method. Since determination of shear strength parameters of rock mass based on a specific confidence level results in the required designs of the following steps to be done based on a specific confidence level، the values of these parameters were determined with a specific confidence level. The simulation results showed that the coefficient of variation and consequently، the sparsity of the simulated data can be caused by the equations used for calculating the output parameters. Using the same inputs، higher uncertainties are present in the mathematical model of the equation that produces outputs of greater coefficient of variation compared to other equations. Therefore، the coefficient of variation and thus، the sparsity of the simulated data is smaller for the internal friction angle (due to the trigonometric equation) compared to the cohesion data. Moreover، the advantage of using distribution functions with the limits of 0 to +∞ rather than distribution functions with two infinite limits for fitting the data with small numerical values and high sparsity was shown while applying the Monte Carlo simulation method.

Extensive development of the data mining methods via the artificial intelligence implementation and machine learning algorithms that the nature has inspired، have become an important challenge to the classical statistical analysis. Some constraints in the statistical assumptions are not made in these methods and just by defining the initial conditions and proper training، acceptable results can be achieved. Self organizing map (SOM) is a way that can unsupervisedly reduce the high dimensional complicated spaces to a 2 or 3D space and recognize the principal components without any difficult and almost impossible assumptions. Despite all the transformations applied to geochemical data، they intrinsically do not suit any statistical analysis and this is a serious factor for so many ifs and buts before analyzing the data. In this study، while introducing SOM as one of the most important approaches based on artificial intelligence، its usage in geochemistry has been demonstrated in a case study of stream sediment sampling carried out in Khusf geological 1:100000 sheet. Comparing the results of applying SOM on the compositionally scaled data and compositional univariate transformed data with exploratory compositional dendrogram of the data showed a favorable conformity of the dendrogram to the SOM clustering on the compositionally scaled data.

The purpose of this research is to investigate the applicability of counterweight balance on stabilizing undercut slopes with potential plane failure in open pit mines. For this purpose، the phenomenon of arch action in geomaterial and undercut slopes was reviewed briefly. It was confirmed that by excavation at the toe of an undercut slope، the load transfers from the central undercut part to sides to produce some areas of load concentration. Therefore، making stronger the load concentrated areas beside the undercut part، by counterweight balance، leads to more stable undercut slopes. Because the main focus of this research is on open mines where always a huge amount of waste rock is available which can be used as counterweight balance، the technique of counterweight balance is suggested as an appropriate technique for stabilizing undercut walls. Some advantages of using counterweight balance are reducing the risk of slope failure during operation as well as reducing the transportation cost of waste rock. The proposed technique was applied to the Mae-Moh lignite mine of Thailand as a case study. The existence of a shearing zone at the interface between under-burden layers at the northeast area made some slope stability problems from 1990 to 1996. In 1998 occurrence of a huge slope failure in this wall leads to a mining operation suspension in the area for about 10 years. Because of the huge size of the unstable area none of the common stabilizing methods such as anchoring or grouting were economically applicable. Finally in 2010 the technique of counterweight balance was accepted by authorities and applied to the unstable area through 2011 to 2013 successfully.