فصلنامه مهندسی معدن
پیاپی 23 (تابستان 1393)

Today، full face tunnel excavation is usually performed by TBMs and based on ground properties، different machines are used. In urban areas with soft ground، Earth Pressure Balance (EPB) machines are widely employed to excavate tunnel with a variety diameter from small to very large. One of the most important parameters in EPB tunneling is face pressure. In fact، in EPBs، the magnitude of advance rate and discharging of excavated material from chamber by screw cause a pressure in chamber that is called face pressure. Low face pressure leads to tunnel face instability and subsequently ground surface settlement. In contrast، high face pressure، especially in shallow tunnels cause blowout. There are several methods to calculate face pressure in which can be categorized as: empirical، analytical and numerical methods. Numerical methods are used to confirm the result of analytical methods as well as where tunnel influence on important structures. In numerical model، water table was assumed as a horizontal plain and natural and saturated unit weights were considered above and under the water table، respectively. In numerical model، all parts of excavation، shield drive، grout injection and segment installation were considered. In addition، some important items such as gap between shield and tunnel perimeter was modeled exactly as it is. The loads acting on the tunnel face were estimated according to the active and passive earth pressure principles. The optimal face pressures for EPB shield was proposed in different soil strength parameters and adjacent structure type. The result showed that، face pressure is the most parameter in the shield tunneling. Also the obtained results show that، decreasing and increasing face pressure cause the stress state to be closer to the soil mass failure envelope.

This study examines the potentiality of quarry rehabilitation of Gol-e-Gohar in Sirjan and converting it into a tourist attraction and recreational place. Therefore، sampling of water، soil and air was done. By designing via Gemcom software and calculating the volume and the area of the quarry at the end of mining، and water inlet flow rate and moving water into the pit for several years، the pit has been turned into a lake. By planting trees and plants on the steps that are above the static water surface، the landscape will be changed and the pit is converted into a beautiful surrounding. According to the sampling of water containing electrical conductivity and high salinity and soil of the quarry which has low nutrients، Tamarisk and Palm trees were selected for planting in the mine، due to shortage of suitable water and soil.

In this study، the efficiency of alkali method for the enrichment of ilmenite concentrate of Kahnooj titanium complex was examined to produce titanium dioxide pigment. For this purpose، the effect of operating time، alkali to ilmenite mass ratio and stirring speed on titanium extraction rate was investigated and analyzed on the basis of a full factorial design and ANOVA test. Results showed that temperature has the most significant effect on the extraction rate. Under optimal conditions، i. e. temperature of 220 oC، ilmenite to alkali mass ratio of 9 and agitation speed of 800 rpm، the extraction rate of 97% for titanium was achieved. The obtained potassium titanate was then leached with hydrochloric acid and the solution was hydrolyzed to produce titanium dioxide with a purity of 95%. The successful results of this study، proved the potential of alkaline decomposition process for the production of titanium dioxide from ilmenite concentrate of Kahnooj complex.

Ash content of concentrates of cyclone-spiral units at the Zarand coal washing plant was higher than the allowable limit (11%) mainly. The main reason was due to the presence of particles smaller than 150 µm containing high amount of ash. The removal of this size fraction by installing a screen with aperture of 0. 5 mm increased the quality of the concentrate. The stream passing the screen (removed fraction) used to be sent to the cyclone-spiral unit at the flotation section for further processing. Since the spiral concentrate of this unit had low quality (ash content of 18%) it was sent to the screening unit. The under screen stream used to be sent again to the cyclone-spiral unit at the flotation section. This procedure created a non-beneficial circulating load with the amount of 56% of the spiral concentrate. By modification in the dewatering process، this amount was reduced to 5%. In order to increase the quality of the final concentrate، a two-stage separation unit where the spiral concentrate instead of entering the screening unit was fed to another spiral was installed. Finally، by determining optimum values of 40 for solids concentration and 2 t/h for the feed to spiral، the amount of final concentrate and capacity were increased by 11 and 14 t/h، respectively. Furthermore، the final spiral concentrate ash decreased from 18 to 11%.

Steady-State simulation of grinding circuit is an efficient tool for achieving reasonable estimates of the process and improving its performance. In this study، along with coding the grinding simulator for a closed circuit and providing applicable sub-routins for calculation of breakage and selection functions and etc in MATLAB and creating a user friendly interface، it was attempted to calibrate the models of this software using sampling data of Zarshuran gold processing pilot plant. Models’ Calibration was done using raw، average and also reconciled data using bilinear method and in each stage، simulation results and measured data were compared. Results of simulations showed that selecting valid models for the units and using reconciled data in model calibration process، leads to calculating true parameters for selected models and consequently، resulting in better simulations. Maximum error reduced from 153. 16 percent in water flowrate of hydrocyclone underflow calculated using raw data down to 4. 57 percent while reconciled data were used. In addition، it was shown that repetitive sampling of every sapmling point and averaging the data could reduce the errors to some extent.

Mineral processing operation at the Sarcheshmeh porphyry copper mine has produced huge quantities of tailings materials containing sulfide minerals mainly pyrite and chalcopyrite. The tailings have been geochemically and mineralogically characterized to evaluate and gain insight into pyrite and chalcopyrite oxidation processes، acid mine drainage generation (AMD)، and transportation of the oxidation products. Five vertical trenches up to 4. 2 m deep were excavated from the tailings surface، and altogether 70 solid samples were taken in 0. 3 m intervals. The results show that pyrite with a content range of 4-6% was the main sulfide mineral found in the tailings which has major role in AMD generation. The lowest pH values were 2. 9، 3. 3، 3. 3، 3. 9 and 3. 0 which were determined at profiles A، B، C، D and E، respectively. The depth of oxidation zone in tailings varies between 1. 8 and 2 m at all five profiles. This paper also presents a numerical finite volume model to simulate sulfide minerals oxidation، AMD generation and transportation of the oxidation products. A shrinking core concept describes oxidation process. Gaseous diffusion was the main mechanism for oxygen transport through the tailings. The governing equations of the model were numerically solved using PHOENICS software. The role of Thiobacillus ferrooxidans bacteria was also considered in the oxidation and leaching processes. A close agreement was achieved between the field data and modeling results for pyrite and chalcopyrite oxidation. In this paper، capping the tailings as a reclamation scenario is further simulated to gain insight into how pollutants produced by pyrite oxidation in the tailings disposal site could be reduced if a cap is used to limit oxygen diffusion and surface recharge infiltration. The simulated results of scenario with cap show that oxygen source removal limited the oxidation process. However، transportation of the oxidation products continued for long time.

The Geophysical and geochemical approaches have been used widely for investigation of environmental contaminations. The main goal of this research is the study of heavey metal accumulation in soil and also investigation of the penetrating depth of drainage in soil in Qaleh- Zari Copper Mine which located at the 180 km of south west of Birjand. To achieve the goal، 2 dimensional electrical resistivity tomography method has been used. For determination of penetrating depth، a 2D electrical resistivity tomography profil has been designed with length of 520 m perpendicular to the study area. In following، 210 point has been picked. The obtained results indicate that the electrical resistivity in affectin area has been reduced up to 3 ohm-meters whereas the resistivity of surrounding formation is above 2000 ohm-meter. The geoelectric sections show that the penetrating depth of drainage is approximately 30m. The existence of joints and fractures within the bed rock which results in groundwater penetration and probably contamination from tailings dam can be the reason of decrease in resistivity of bed rock. Geotechnical studies in the study area imply to the existence of shear zone in the site. Consequently، environmental geochemistry using of enrichemnt index (EI)، geo-accumulation index (GAI) and pollution index (PI) have been performed. For this purpose، the some samples from soil (3 samples) and drainage (1 sample) have been collected. Data analusis using above indexes show that the concentration of heavy metalts (V، Cr، Mn، Fe، Co، Ni، Cu، Mo، Hg، As، Ag، Pb، Cd، Zn) have been increased by increasing of depth. So، the solis have been polluted in area. This leads to a decreation in formations resistivity that verify the results obtained from the electrical Tomography. The results of such studies can be used to manage the environmental impacts in mine.