محمود عبدالهی

When waste storage dams are used to store millions of tons of waste materials and a large volume of water or hazardous liquid, the sensitivity of different communities to the failure and destruction of such structures in front of earthquake vibrations is felt more strongly. USCOLD's report shows that in recent years, about 185 such incidents have occurred in tailings storage dams and have caused a lot of environmental concerns. The mechanism of dam failures caused by earthquakes in tailings ponds is mainly due to the liquefaction of tailings sands. As a case study, this article examines the effect of seismic loads on the pure silt used in the tailings dam in northwest Iran. Cyclic tests were performed under different initial static shear stresses using an automatic cyclic triaxial system. These materials are supplied from the Sungun copper mine located in the northwest of Iran. In this research, undrained compressive tests with the same relative densities with different effects of average effective stress and the effect of the primary static shear stress parameter on the mentioned materials under cyclic loading conditions have been used. In this study, cyclic tests were performed using the strain energy approach to evaluate the capacity energy and residual pore water pressure. The results of cyclic experiments were used to evaluate capacity energy and residual pore pressure based on the strain energy approach. Cyclic tests on the samples were performed considering the shear amplitude of 0.75% and frequency of 0.3 Hz. It is shown that the most energy dissipation occurs at the first cycle possessing the highest stiffness. For α = 0, energy density increased from 474 J/m3 to approximately 1.4 times, however, when α = 0.4, a stronger growth rate was measured from 682 J/m3 to approximately 7.5 times.

In the process of zinc hydrometallurgy, many impurities such as nickel, cobalt, and cadmium, are removed, but magnesium remains with zinc in the electrowinning stage and its concentration increases during the process. The aim of this study is to reduce the concentration of magnesium in zinc leaching solution. XRD analysis showed that the prepared zinc oxidised sample contains smithsonite and hemimorphite as valuable minerals and dolomite and calcite as tailings. The sample contains 8.27% zinc and 8.15% magnesium. Here, alkaline zinc sulfate precipitation was carried out to bring magnesium to the permissible level in electrowinning solution. In acidic leaching, effective factors such as pH, temperature, solid percent and leaching time optimized to achieve maximum zinc recovery. In alkaline zinc sulfate precipitation, effective factors such as pH, temperature and retention time examined for selective precipitation of alkaline zinc sulfate. Recovery of zinc in one leaching step reached to 70.81% at pH=2, temperature of 60°C, solid percent of 10% and leaching time of 120 minutes. The leach residue was then dissolved at pH=3 for 60 minutes, in which the total recovery of zinc increased to 86.32%. Under optimal conditions of 90°C, pH =6.5-7, zinc recovery was found to be 99.90% in the precipitate, while the amount of magnesium precipitation was 3.6%. After re-dissolution of alkaline zinc sulfate, the amount of magnesium in the solution found to be 1.3 g/l, which was much less than the allowable magnesium level in solution used for electrowinning (10-15 g/l).

In this study, the feasibility of improving the flotation circuit performance of a phase 1 of Sungun copper plant was investigated. For this purpose, circuit performance was first monitored ., It was found that in the rougher stage the some copper exists in fractions greater than 106 and smaller than 38 microns was lost. Final concentrate analysis taken on different days showed that the copper grade decreased due to the iron content increasing. Mineralogical studies also confirmed the maximum presence of pyrite in the final concentrate. Field surveys of the flotation circuit showed that there are many technical problem in the circuit that affect on the flotation process. These drawbacks including the presence of thick tubes at the surface of the re-cleaner cell, the lack of a standard pattern of wash water distribution and jet spraying. Measurement of pH in different points of the circuit showed a decrease of pH below 11 and so hydrophobicity of pyrite caused. Measurement of operating variables in the circuit showed that the wash water rate and gas rate used in the circuit were higher and lower than the values suggested by the researchers and the designer, respectively. Due to the deficiencies identified in the performance evaluation phase, laboratory tests were designed and performed in two stages using mechanical flotation cell and column flotation cell. Adjusting the gas rate and the wash water rate at the laboratory scale at the intervals suggested by the researchers resulted in the increase in 3% grade and 10% recovery.

One of the challenges in the rare earth elements (REE) production industry is the difficulty of separating them from each other. Therefore, in the present study, the possibility of cerium separation from carbonate concentrate of REEs containing 22.75% Ce, 9.4% La and 8.6% Nd (total REEs of 41.51%) was investigated. Two methods were used to separate Ce from other REEs. In the first method, due to the very low solubility of Ce4+, the calcination of carbonate concentrate and conversion of cerium carbonate to cerium oxide and selective dissolution of other REEs from the calcine were investigated. In the second method, prior to the carbonate precipitation of REEs, the possibility of cerium oxidation in the sulfate solution (by using potassium permanganate) and its subsequent selective separation from other REEs was investigated. Results of the calcination (first method) showed that only 35 and 45% of La and Nd were dissolved at 80⁰C after 2 hours leaching with 1 molar nitric acid, respectively. Results of the calcine leaching with 4 molar nitric acid at 80⁰C for 2 hours showed that more than 90% of the La and Nd were dissolved. In this conditions, 35% of the Ce was also dissolved and the leaching process was not selective. In the second method, using potassium permanganate with a stoichiometric ratio of 1.5 to 1 for oxidant to Ce, pH 3.5 for 1 hour, 98% of the Ce and less than 1% of La and Nd were precipitated. The resulting hydroxide was calcined at 850⁰C for 1 h to produce CeO2 and finally a Ce oxide concentrate was obtained with 99% purity.

Indigenous acidophilic bacteria separated from mine-waste can be used in return for the addition of the reagents like sulfuric acid. Among the tailings bacteria, Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans are of the most-studied ones for the bioleaching and bioremediation of elements. In this work, the isolation and characterization of the mentioned bacteria are studied by a proposed biochemical protocol. The sequential cultivation of the soil bacteria in a series of liquid media and solid culture medium cause the separation of bacteria. A biochemical method is used to characterize the isolated strains of the native bacteria. The changes in the Eh, pH, and culture medium color are checked in order to control the bacterial growth in a 9K liquid medium. At the first step of the sequential cultivation, the amount of nutrient broth is the main factor that affects the complete isolation of Acidithiobacillus bacteria. The trivial dosage of nutrient broth does not lead to the desired proliferation of the bacteria in the tailings soil. 8 g L-1of the nutrient broth is suitable to increase the initial number of bacteria in the soil significantly. In the next steps, the bacteria are separated from the soil, and pure strains of A. ferrooxidans and A. thiooxidans are isolated using a 9K medium. Final pure strains are achieved during the two steps of streak cultivation of bacteria in the soil medium of nutrient agar.

Nugget effect is a common feature of many vein-style gold deposits. This style of mineralization results in complication in many exploitation stages including resource and average grade estimation, representative sample selection, ore characterization as well as processing. Accurate and reliable ore characterization is a vital stage in any mineral processing project. Ore characterization in high nugget effect gold ores is so complex due to uncertainties associated with representativity of the selected sample. The main challenge is to provide a representative sample for identification of each process mineralogy parameter such as average grade, liberation, grinding size, mineral association, floatability, etc. Here, different protocols are collected and compared to draw a comprehensive picture of the available methods. The results are examined on a high nugget effect gold ore from Northeast of Iran, Azghad mine. Processing experiments were conducted to develop a process suitable for Azghad gold mine. To investigate the feasibility of pre-concentration, gravity methods using a Nelson separator was applied on the oxide sample as the main gold vein. 43.3% of total gold was concentrated in the gravity concentrate with only 2% weight recovery, suggesting gravity concentration can be considered as an efficient method in this ore. Gold preg-robbing experiments were performed for Shale sample due to the organic matter, clay minerals and mica. Preg-robbing potential of the shale ore was determined to be 1.1 ppm. Optimization of operating parameters was performed by central composite design method for the combined oxide and shale samples.