Views:34 Author:Site Editor Publish Time: 2019-08-29 Origin:Site
Scientists refer to the number of vibrations per second as the frequency of the sound, and its unit is Hertz (Hz). The frequency of sound waves that we can hear in human ears is 20 to 20,000 Hz. Therefore, we call sound waves with frequencies above 20,000 Hz "ultrasonics". Ultrasonic waves are elastic mechanical waves (sound waves) in a matter medium that, like electromagnetic waves, refract, focus, and reflect, but ultrasonic waves are different from electromagnetic waves. When the ultrasonic wave is propagating, it relies on the elastic medium to cause the particles in the elastic medium to oscillate and transmit the energy in the direction of propagation of the ultrasonic wave through the elastic medium. When a certain intensity of ultrasound propagates through the medium, it produces a series of thermal, optical, electrical, and chemical effects that alter some of the physicochemical properties of the medium.
As we all know, the "three pass and one reverse" in the metallurgical process is the essential factor affecting the process efficiency, speed and capacity, and also summarizes the whole process of metallurgical chemical production. The so-called "three passes" refers to mass transfer, momentum transfer and heat transfer, and "one anti" refers to the chemical reaction process. How to improve the metallurgical process, in essence, should start from how to improve the efficiency and speed of "three pass and one reverse".
From this perspective, ultrasonic technology has a good role in promoting the transfer of mass, momentum and heat, and these promotion effects are mainly determined by the inherent characteristics of ultrasonic technology. In summary, when ultrasonic technology is applied in metallurgical processes, the following three main effects occur:
The cavitation effect refers to the dynamic process of growth and collapse that occurs when the micro-nuclear cavitation bubbles present in the liquid phase (melt, solution, etc.) vibrate under the action of sound waves when the sound pressure reaches a certain value. The tiny bubbles generated in the liquid phase, the manager grows up, ruptures, and annihilates the process, and hot spots appear in the tiny space around the bubble machine, thus appearing in the high temperature and high pressure zone, and promoting the reaction.
The mechanical effect is the effect that ultrasound produces as it advances through the medium. The high frequency vibration and radiation pressure of the ultrasonic wave can form an effective agitation and flow, so that the medium pointing into the vibration state in the propagation space, thereby accelerating the diffusion and dissolution process of the substance. The mechanical effect combined with the vibration of the cavitation bubble, the strong jet and local micro-flushing generated on the solid surface can significantly weaken the surface tension and friction of the liquid, and destroy the boundary layer of the solid-liquid interface, thus achieving the ordinary low-frequency mechanical agitation. Can not achieve the effect.
Thermal effect refers to the amount of heat released or absorbed by a system during a change at a certain temperature. When ultrasonic waves propagate through the medium, their energy is continuously absorbed by the medium particles, which is converted into heat energy and promotes heat transfer during the reaction process.
Through the unique effects of ultrasonic technology, the efficiency and speed of “three pass and one reverse” in the metallurgical process can be effectively improved, the mineral activity can be improved, the amount of raw materials can be reduced, and the reaction time can be shortened, thereby achieving the purpose of energy saving and consumption reduction.
At present, the application of ultrasonic waves is very extensive: ultrasonic non-destructive testing; ultrasonic liquid level measurement; ultrasonic solidification fine crystal technology, improving the properties of alloy or molten steel; ultrasonic leaching. In particular, ultrasonic leaching is of great significance for achieving high efficiency, energy saving and environmental protection of metallurgical processes.
Ultrasonic enhanced technology for processing gold mines
The study found that the use of ultrasonic enhanced leaching of gold can achieve better results, with appropriate conditions, can significantly increase the leaching speed by several times, the leaching time is shortened to several hours, and the leaching rate after 5 hours reaches 82.7%, so the production cycle is short. Ultrasonic destruction of the cover layer of mineral passivation accelerates the flow and exchange of the solid-liquid interface, thereby accelerating the chemical and electrochemical reactions, which may be the main mechanism of the effect of ultrasonic enhanced leaching. Under normal temperature and pressure, the ultrasonic pretreatment of gold ore reaches the pretreatment and gold extraction effect of autoclave acid leaching and autoclave alkali leaching at high temperature and pressure. But the cost is low, the operation is simpler, and the management is more convenient. The process is short, easy to implement, and the gold leaching rate is high.
Ultrasonic enhanced technology for treatment of uranium-containing wastewater
The uranium-containing wastewater mainly includes ore mining mine wastewater and uranium ore production and processing wastewater. In view of the removal of uranium from the tailings wastewater of a nuclear industry company in China, the removal of U(VI) and its compounds in wastewater by ultrasonic deep demineralization is a new method. The results show that the uranium removal rate is 99% compared with the conventional method. In the above case, the reaction time is shortened by 20%, the amount of additives is reduced by 75%, and no static treatment is required, and the process continuity is good.
The process utilizes the new ultrasonic deep demineralization technology to treat uranium-containing wastewater. Compared with other traditional methods, the uranium removal effect is remarkable. The treated liquid has a minimum uranium content of 4.8 μg/L, which is better than the standard 50 μg/L. Strong, safe and environmentally friendly, easy to operate in industry.