Jo Jan 30, 2026
Mixing is an important technique for improving product quality in various manufacturing processes. Various mixers are used in the mixing processes of many fields including iron works, food industry, cosmetics and construction.
Among various types of mixers, a twin spiral mixer has the advantage of small volume and continuous mixing. In a twin spiral mixer, the left and right spiral wings attached to two axes rotating in opposite directions alternately work by advancing the material in one direction. First, the left spiral wing rotates and contacts material particles, advancing them and sending some of them toward the right spiral wing. The right spiral wing then approaches the position where it can contact the particles. Next, the left spiral wing releases the particles, and the right spiral wing comes into contact with them, advancing them and sending some toward the left spiral wing. Thus, in the twin spiral mixer, mixing is achieved by a simple cross action of the spiral wings that send some particles toward each other. From this mixing principle, the mixing degree in the twin spiral mixer is determined by the number of wings that interact with particles. In addition, due to the single mode of mixing, the attainable mixing degree is not high, and therefore, the length of the mixer must be long inevitably to increase the mixing degree.
Generally, various methods of structural and working parameters optimization have been widely used to improve the performance of machines and equipment. However, these methods are not sufficient to fundamentally change the performance characteristics and they have certain limitations. In the twin spiral mixer, it is also difficult to achieve the improvement in the mixing degree by optimizing the structural parameters, since the mixing process is realized by a simple cross action of the spiral wings.
Ri Song, a researcher at the Faculty of Mining Engineering, evaluated the mixing degree by simulating the mixing process of a twin spiral mixer by DEM (discrete element method) and then, based on this, he proposed a plan of increasing the mixing degree by installing inverse spiral wings at regular intervals in a twin spiral mixer to change the mixing mode.
Comparing the mixing degree for the conventional twin spiral mixer and the twin spiral mixer with inverse spiral wings, it was 0.779 7 for the conventional mode, 0.801 3 for the 2:1 mode, 0.81 for the 3:1 mode and 0.790 7 for the 4:1 mode, which means the 3:1 mode was the best, and the outputs from simulations were 89.1W, 429.7W, 287.8W and 151.5W, respectively.
You can find more details in his paper “Study on improving the mixing degree of a twin spiral mixer by changing the mixing mode using inverse spiral wings” in “Journal of the Brazilian Society of Mechanical Sciences and Engineering” (SCI).
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Jo Jan 29, 2026
Scattering of elastic waves by inclusions or local topography in elastic half-spaces has been an important research topic in the fields of seismology, geotechnical engineering and acoustics. Analysis of the response and potential damage to underground structures under different kinds of loadings, especially strong earthquakes, is of great importance for the design and construction of deep underground tunnels.
The propagation and scattering of elastic waves around underground tunnels located under the surface of an infinite half-space have recently been studied using two methods: analytical method and numerical method.
The analytical method mainly focuses on the models of regular shape embedded in an infinite half-space. Although this method is only suitable for relatively simple and regular models, it has an advantage over the numerical method in revealing the essence of problems.
Ri Song Chol, a section head at the Faculty of Mechanical Science and Technology, investigated the influence factors on the dynamic response of a lined tunnel embedded in an inhomogeneous half-space under the conditions of incident SH waves.
He derived an analytical solution for the scattering of plane SH waves by a lined tunnel embedded in an inhomogeneous half-space by employing the complex function method and the conformal mapping technique. The analysis focuses on the treatment of straight and circular boundaries by proper coordinate transformation and by the conversion of the physical plane to the corresponding image plane.
For more information, you can refer to his paper “Analysis of the Influence Factors on the Dynamic Response of a Lined Tunnel Embedded in an Inhomogeneous Half-Space Subjected to SH Waves” in “Russian Journal of Nondestructive Testing” (SCI).
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Jo Jan 28, 2026
Slurry electroleaching, which produces manganese dioxide from low grade manganiferous raw materials, is noteworthy.
Studies on slurry electroleaching made a start in the latter half of 1960s. Since then, in-depth researches based on slurry electroleaching have been carried out on the treatment of galena, copper sulfide ores and manganese ores. As a result, many successes have been made so far.
However, few studies and applied cases with regards to the industrial method of processing low grade manganiferous raw materials (below Mn 10%) into manganese dioxide have been reported.
DPRK has little amount of Mn raw materials of over 20%. Instead, it has a great deal of wad clay. In order to meet the domestic demands, the problem of processing wad clay must be solved. In addition, the wad clay in our country contains lots of slime. According to some preliminary experiments, slime leaked into the anode diaphragm during the process of slurry-electroleaching, thus dramatically decreasing the rate of the content of manganese dioxide.
Based on the preceding research results, Jon Yong Nam, a researcher at the Faculty of Metallic Engineering, applied slurry electroleaching method (diaphragm electrolysis) to the low-grade wad clay (Mn 4~6%) which is deposited in the central region of DPR Korea in order to obtain high-grade manganese dioxide of over Mn 40%.
He observed the effects of the temperature, current density, ratio of liquid to solid (L/S), time and coagulant agent through the basic experiment on slurry electro leaching of the wad clay. He determined the optimum conditions as follows: current density 150~200 A/m2, temperature > 65℃, L/S = 10 : 1, time 1.1 times the theoretical leaching time and amount of the coagulant agent 50 g/t. Under these conditions, the leaching rate was above 95% and the content of Mn in anodic electrodeposits was 45%.
You can find the details in his paper “A Study on the Extraction of Manganese from Wad Clay by Slurry Electrolysis” in “Russian Journal of Non-Ferrous Metals” (SCI).
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Jo Jan 27, 2026
The arsenic bearing gold concentrate is known as refractory gold concentrate and the direct cyanide leaching produces very low gold extraction. It is because gold particles are extremely fine and encapsulated in sulfides (pyrite and arsenopyrite) and the exposure of gold particles is difficult by the mechanical method only.
Oxidation roasting, bio-oxidation and autoclave oxidation are used for pretreatment of refractory gold ore. The method of autoclave oxidation for this purpose has certain advantages in production cost and environmental protection, but it needs huge investment in equipment. Bio-oxidation is another choice in view of low cost and environmental friendliness. However, it is inefficient and too sensitive to the environment. Compared to these methods, oxidation roasting is brief in operation and the period of production is short. And the amount of treatment is large and the cost is low. In roasting processes, pyrite and arsenopyrite are oxidized to reduce the cyanide and dissolved oxygen consumption, and porous calcine is formed to increase gold extraction.
Two-stage roasting process is commonly used to pretreat arsenic bearing gold concentrate. The first stage is carried out in weakly oxidative atmosphere to release arsenic in the gaseous phase as As2O3. The second stage roast is performed in oxidative atmosphere to produce porous hematite.
Kim Yong Min, a section head at the Faculty of Metallic Engineering, investigated the effect of protective alkali and pH on gold extraction in the cyanide leaching process of two-stage roasting calcine of arsenic bearing gold concentrate.
The results showed that gold extraction was independent of protective alkali such as caustic soda, sodium carbonate and lime, and the effect of pH on gold extraction was obvious. If the pH of pulp is high, the arsenic concentration of cyanide leaching solution is increased to decrease gold extraction.
He also investigated the effect of arsenic concentration of solution on gold extraction. He found that when the leaching solution has no lead ion, the arsenic has no effect on gold extraction, but when the arsenic and lead exist in solution simultaneously, the effect of arsenic on gold extraction is remarkable.
For more information, please refer to his paper “Effect of Protective Alkali and pH on Gold Extraction in Cyanide Leaching Process of Two Stage Roasting Calcine of Arsenic Bearing Gold Concentrate” in “Russian Journal of Non-Ferrous Metals” (SCI).
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Jo Jan 26, 2026
Today, the application range of nanofibers are widening day by day because of their excellent properties that are different from conventional materials.
Nowadays, electrospinning is widely used as a versatile and convenient method for the production of nano-sized fibers. However, the difficulty in the production of nanofibers by single-needle electrospinning is that it has low production efficiency. To solve this problem, several types of electrospinning methods have been developed, which can be divided into two broad categories. One is needleless electrospinning and the other is multi-needle electrospinning. Between them, multi-needle electrospinning plays an important role in preparing specific structures because it is able to control the properties of fibers.
So, when the number and density of nozzles are increased in the multi-needle electrospinning, the intended electric field of the nozzles gets more distorted due to electrical interactions between the nozzles, which destabilizes the flow of the polymer solution jet and negatively affects the quality of the obtained fibers. Therefore, the uniformity of the electric field distribution at the spinneret needle tip in the multi-needle electrospinning process is a key factor for producing good quality fibers.
Jang Kum Chol, a researcher at the Institute of Nano Science and Technology, proposed a trapezoidal wave (TW) arranged multi-needle electrospinning spinneret with auxiliary electrodes (AEs), and conducted a study to further enhance the electric field uniformity by optimizing the AE parameters by Taguchi method.
The optimization results showed that the uniformity of electric field was best when the distance between the spinneret and the auxiliary electrode was equal to 21 mm, the arrangement angle of auxiliary electrode 120゜, the spacing between two adjacent needles of auxiliary electrode 18 mm, the needle length of auxiliary electrode 13 mm, the needle diameter of auxiliary electrode 2.5 mm.
For more information, please refer to his paper “Optimization of parameters of auxiliary electrodes for electric field uniformity around spinneret needles in multi-needle electrospinning by using Taguchi method” in “Journal of Electrostatics” (SCI).
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Jo Jan 25, 2026
With the rapid development of economy, energy consumption increases gradually every year, and coal slurries are used in various thermal machines, especially in internal combustion engines, in accordance with the global strategy of saving and replacing oil.
In the production of CWS fuel, the ration of raw coal and additives and the relevant process are important for improving the quality and saving the cost.
Pak Song Chol, researcher at the Faculty of Physics, conducted an experimental study to convert coal-water-oil slurry (CWOS) into an alternative fuel (AF) for internal combustion engines by high-voltage discharge (HVD) and dielectric barrier discharge (DBD) plasmas.
He prepared CWOS by adding oil to the coal-water mixture in a relevant ratio. Then, he converted the CWOS to AF by passing high-voltage discharge and DBD plasma with gas emission and liquefaction reactions through it.
The result showed that after HVD and DBD plasma treatments, the CWOS has the average coal size reduced from 12.95 to 8.26㎛, improved dispersibility, less deposits, and calorific value enhanced by 35%.
The plasma-treated CWOS is similar to other liquid fuels in terms of rheological property and calorific value. It is therefore concluded that it can be directly employed to fuel combustion in the internal combustion engines with a little design modification.
The details can be found in his paper “Enhancement of calorific value and dispersion stability of coal-water-oil slurry by discharge plasmas: application of high voltage discharge and dielectric barrier discharge” in “International Journal of Coal Preparation and Utilization” (SCI).
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