Reza Dehghan

Micaceous minerals, known as layer silicates, are counted mostly as the gangue minerals associated with valuable minerals, especially iron oxides. They mainly reject through the reverse flotation process using the cationic collectors, e.g., ether amines, to improve process sustainability. Although ether amines have been applied for floating the wide range of silicates, few investigations explored their adsorption behaviors on the micaceous minerals. In this study, flotation of phlogopite, biotite, and quartz (for comparison purposes) in the presence of Flotigam^®EDA (EDA) (commercial ether monoamine collector), at pH 10 was investigated through the single mineral micro–flotation experiments. Adsorption behaviors were explored by the contact angle, residual surface tension measurements, and zeta potential analyses. Micro–flotation outcomes indicated that the quartz floatability was more than phlogopite and biotite. In the presence of 30 mg/dm³ EDA, their recoveries were 97.1, 46.3, and 63.8%, respectively. Increasing EDA concentration made a substantial increase in micaceous minerals’ floatability. Adsorption assessments confirmed that increasing the EDA concentration resulted in higher adsorption of EDA onto the surface of micaceous minerals than the quartz (all by physical adsorption). Such a behavior could be related to the nature of micaceous minerals, including their layer structure and low hardness.

Recently, a two-stage dynamic dense medium separator, called Tri-Flo, has become more applicable for treating difficult-to-wash coals. In this study, a 70-mm diameter transparent Tri-Flo separator was manufactured using prototyping and the effects of geometrical and operating parameters were investigated. Central composite design (CCD) was used in the experimental phase. The effects of internal tubes diameter, the installation slope, and the internal flow rate on the Tri-Flo performance were analyzed. CFD simulation was also used for better understanding of the flow pattern and interpretation of the experimental results. The results indicated that the air core diameter in both stages of the separator increases with all three variables. It was also found that medium recovery to float product in rougher and cleaner stages increases with unit inclination and internal tubes diameter, while it decreases with medium flow rate. The decrease in the air core size with increasing the feed tube diameter was an outstanding finding in both experiments and simulations. On average, a 16% decrease in the air core diameter was obtained when the feed tube diameter was increased from 23 mm to 26 mm. The results of the CFD simulation showed that there is a meaningful compatibility between the experimental observations and mathematical simulations.

The production yield and clean coal quality in dense-medium coal washing equipment such as three-product cylindrical separators are mainly controlled via the back-pressure adjustment at the sink port. However, the role of the back pressure in the fluid flow in such separators has been previously assessed only to a very limited extent. This study was undertaken to investigate the effect of back pressure on the flow pattern in a 70-mm three-product cylindrical separator. Accordingly, a time-dependent, three-dimensional numerical study was conducted based on computational fluid dynamics (CFD) in a two-phase system. The turbulence was simulated by the Reynolds stress model (RSM) whereas the volume of fluid (VOF) method was used to model the water–air interface. The simulation results were validated using the experimental data. The sensitivities of the flow fields and some other hydrodynamic characteristics to the increase of back pressure were different in the first and second stages of separator. Increase in the tangential velocity, the suppression of the air core and the improvement of medium recovery were some of the consequences of increasing the back pressure.

Demand for high-quality iron concentrate is significantly increasing around the world. Thus, the development of the techniques for a selective separation and rejection of typical associated minerals in the iron oxide ores, such as phosphorous minerals (mainly apatite group), is a high priority. Reverse anionic flotation by using sodium silicate (SS) as an iron oxide depressant is one of the techniques for iron ore processing. This investigation is going to present a synthesized reagent “sodium co-silicate (SCS)” for hematite depression through a reverse anionic flotation. The main hypothesis is the selective depression of hematite and, simultaneously, modification of the pulp pH by SCS. Various flotation experiments, including micro-flotation, and batch flotation of laboratory and industrial scales, were conducted in order to compare the depression selectivity of SS versus SCS. Outcomes of flotation tests at the different flotation scales demonstrated that hematite depression by SCS is around 3.3% higher than by SS. Based on flotation experiment outcomes, it was concluded that SCS can modify the pH of the process at ~9.5, and the plant reagents (including NaOH, Na₂CO₃, and SS gel) can be replaced by just SCS, which can also lead to a higher efficiency in the plant.

Parvadeh coal preparation plant (PCPP) was installed in 2008 for the production of 750,000 TPY of clean coal. One unit of a Tri-Flo separator having 700 mm diameter and two units having a 500 mm diameter were used in the PCPP process flowsheet for the preparation of the coarse coal particles (−50 + 6 mm) and small coal particles (−6 + 0.5 mm), respectively. Two types of the raw coal having different washability characteristics were designed to be used as the plant feed from two different coal mines. In this study, sink-float experiments were performed on the representative samples of each feed types from the mechanized and conventional mining operations. Consequently, the validities of Near Gravity Material Index (NGMI), Govindarajan Washability Index (GWI), and the conventional sink-float washability data were evaluated to predict the performance of the industrial Tri-Flo separators in washing the raw coals. Two washability indices of NGMI and GWI were calculated and the results were compared. In the washability studies on both coarse and small coal fractions, both NGMI and GWI showed that the sample from the mechanized mining operation is easier to wash. However, better process yield, combustible recovery, and separation efficiency were obtained in the industrial Tri-Flo separators using the feed sample from conventional mining operation. Therefore, none of these relatively new quantitative indices have been able to predict the correct coal behavior in the Tri-Flo separators. Comparatively, there has been a good agreement between the results from conventional washability data and the actual performance of the Tri-Flo separators.