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).

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).

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).