فصلنامه مهندسی معدن
پیاپی 24 (پاییز 1393)

The flotation behavior of chalcopyrite in the presence of different concentration of sodium sulphide at pHs 7، 9 and 12 was investigated for both chalcopyrite single mineral and chalcopyrite flotation concentrate samples under controlled potential conditions. The surface analytical techniques of X-ray Photoelectron Spectroscopy (XPS) has provided information on the surface of chalcopyrite particles to identify surface species which are responsible for depression or flotation of chalcopyrite at different oxidation-reduction states of pulp. It was found that changes in pulp potential resulted in dual effects of sodium sulphide on flotation behavior of chalcopyrite. In other words، both flotation and depression of chalcopyrite could be achieved via controlling the pulp potentials. It was found that elemental sulphur and sulphoxy species resulted from electrochemical interactions between sodium sulphide and pulp contents and oxidation-reduction products of chalcopyrite، strongly affect the floatability of chalcopyrite. It was also found that maximum depression of chalcopyrite occurred at pH 12، Na2S concentrations about 10-1-10-2M and potential ranges between -200 mV to -100 mV (SHE). The optimum conditions for activation (sulphidisation) of chalcopyrite were found at pH 9، Na2S concentration about 10-3M and potential ranges between +300 mV to +400 mV (SHE).

In longwall mining, the roof strata behind the stope is caved with face advancing. This is followed by a high load distribution around the panel and gob. Determination of the stress concentration, its distribution around the panel and the influencing parameters such as the stope length are of critical important to design of longwall mining. Both numerical and empirical methods can be used to investigate the effect of stope length on distribution and concentration of stress induced at the panel. In this paper, numerical modeling and analysis of a longwall panel were carried out by using a 3D numerical model for investigating the effect of stope length on stress distribution in Tabas coal mine, Parvadeh No. 1. A sensitivity analysis of the impact of six different values of stope length on abutement stress showed a nonlinear relation between the stope length and front abutment stress. The analyses results revealed that with a 30 percent increase in the stope length from 190 to 245 m, front abutment stress increases only to 10 percent (i.e. 5.55 to 6 MPa).With stopes longer than 245 meters up to 300 meters, an increase of 20 percent in stope length resulted in a 27 percent decrease of roof stress (i.e. 6 to 4.4 MPa). Also, results obtained from modeling studies revealed that the location of maximum front abutment stress increases from 5 to 15 meters in front of the face with change in stope length from 190 to 300 meters.

During tunneling in poor ground conditions or when there is shallow overburden above the tunnel crown, the rock or soil mass needs to be reinforced ahead of the face before tunnel excavation. Umbrella arch is a pre-reinforcement technique which is obtained by installing steel pipes and injecting grout inside. If pipes are perforated, there should be a reinforcing zone between pipes due to injection. So pipe, grout and reinforcing area around pipes could be considered as pipe umbrella components. In this paper three dimensional modeling of umbrella arch method by FLAC 3D finite difference method is investigated. Then, the effectiveness of umbrella arch method at Qazvin-Rasht railway tunnel, where it is located at poor and very poor rock condition, is investigated by comparing three support types. These are 1- conventional supports (steel sets and shotcrete), 2- conventional method and face cable bolts and 3- conventional method, face cable bolts and umbrella arch method. Analyses are based on crown displacement, settlement and saqurai hazard warning levels.It has shown that Pre-supports application (face bolts and umbrella method) have reduced crown displacement and settlement magnitudes 41% and 61% respectively. On the other hand, umbrella arch use (case three) has decreased crown displacement and settlement 31% and 49% in comparison to just face blot application and conventional supports (case two). According to Saqurai hazard warning levels, displacement magnitudes are just located below level two, where umbrella arch is used.

A sample from "Zaylik" exploration area were taken. Microscopic studies (polished thin sections and polished sections), XRD, XRF and SEM showed that this ore is an oxidized zone. The main mineral is quartz and other minerals consist of clay, secondary hydrous iron oxides and rarely Pyrite, Chalcopyrite, Gold, Azurite and Malachite. Due to the dispersion of fine gold, cyanidation process was conducted without any pre-processing. Cyanidation experiments with effective factors concluding pH, d80, cyanide concentration and leaching time were conducted in a CCD design using the DX8 software. The software proposed models for gold recovery and remaining free cyanide respectively with R2 values of 0.77 and 0.83. In the next step, the optimum conditions obtained from the models were validated experimentally and improved by oxidation and kinetics tests. Pre-aeration was done with flow rate 0.6 lit /min in 3 hours and this was found suitable. Periodic addition of sodium cyanide was found preferable rather than instant adding at time zero. Considering the fact that the recovery did not differ significantly in 24 hours and 12 hours, the optimum leaching time was considered 12 hours. In 12 hours, 1050 ppm sodium cyanide was consumed and in order to achieve optimum recovery of %93.93, pH of 10.15 and d80 of 106 microns should exist in the system.

In the jointed rock masses such as rock slopes، the joints considered as cracks in which their tips are the weak points for fracture initiation. Some of the numerical codes for the stability analysis of jointed rock masses have considered only blocks movement on the surfaces of the existing fractures. The tips of these rock joints may act as the fracture creation points and some new discontinuities containing high stress intensity points or plasticity situation may develop. The purpose of this research is to simulate the stable or unstable crack propagation mechanism in the rock bridge area and the cracks coalescence phenomena until the blocks can be created in the fractured rock slopes using linear elastic fracture mechanics (LEFM) theories. Thus، combining the displacement discontinuity based indirect boundary element method (called the higher order displacement discontinuity method) with the maximum tangential stress criterion and programming it by Mathematica software has been used for the crack analysis in this study. The fracture types or modes of fracturing predicted and the crack propagation and cracks coalescence estimated in the rock bridge area for several examples of typical rock slopes. After cracks propagation and coalescence، blocks velocity and shear displacement on new discontinuities obtained as high stress concentration points or plastic mode zones using a distinct element method (UDEC).

To continue drilling operation, identification of unstable zones in some parts of oil and gas wells is important. Wellbore wall collapse or swelling, in addition to stop drilling operations can lead to variety of mechanical problems. The most important factors in this process are presence of clay and clay facieses in sedimentary sequences of oil and gas fields. There are several methods to identify clay type and volume such as determination of Cation Exchange Capacity (CEC). In some minerals like smectite and vermiculite, while expanding property is noticeable, cation exchange capacity is high. This study has been done in Shurijeh Formation (Early Cretaceous) in Gonbadli gas field. First, for 20 samples, CEC has been measured applying Bower method and then by neural network estimator, based on the petrophysical logs and laboratory results, an appropriate model was fitted to estimate this parameter in well interval. The cation exchange capacity values obtained and Caliper log were used to examine the relationship between wellbore collapse and CEC. This study implied that more than 75 percent of the points in which CEC are higher than 70 in well No.1 and more than 74 percent in well No.2, have been collapsed. As a result this parameter can be used to detect and prevent collapses in clayey zones of well.

Erroneous estimation of clay volume can result in miscalculation of reservoir parameters such as effective porosity and water saturation which finally leads to false interpretation of reservoir production. Thus, volume of clay (Vcl) is the most critical parameter to determine in shaly sand reservoir quality assessments. In this study, volume of clay in Shurijeh Formation, aging Lower Cretaceous, was estimated after carrying out a sensitivity analysis between a suite of petrophysical logs and laboratory measure volume of clay, using seven different petrophysical methods from six types of well logs and combination of some of them. On each method different petrophysical corrections (such as 0.6-coefficient, Larinov-1, Clavier and Steiber) were applied and then the results were compared to the results of quantitative analysis of 76 core samples from produce well (A) and non produce well (B) in one of eastern Kopet-Dagh basin fields. Finally, based on minimum average relative error, the best log and the best correction are determined as gamma ray log and Steiber correction for volume of clay estimation in this formation. Also, an empirical equation was developed based on index of gamma ray method for evaluating the volume of clay which has the minimum relative error.