Gold is a precious metal, and therefore in any process in the production of gold, its priority must be how to ensure the highest yield, which is the lowest loss rate. At present, as a need for subsequent deep processing, etc., the production of gold into powder has become an important process. If gold is only used as a common metal for metal milling, there are several alternative milling techniques, but to ensure the highest yield on a low cost basis, it is not Process methods can be achieved. Although gas atomization can realize the production of gold powder at low cost, it is difficult to ensure the complete collection of gold powder because the system is difficult to obtain, and it is impossible to have a high yield; water atomization can achieve high yield of gold powder, but due to its The system is complicated, the equipment is expensive, and the power consumption is too large, so the production cost is too high. The author succeeded in realizing the production practice of low-cost and high-yield gold powder in a large-scale gold enterprise, and introduced the water-gas combination gold powdering process developed by the company, and specializes in the milling process of precious metals such as gold. Sexual and related technical issues have been analyzed and discussed in depth.
Second, the process
Considering the low cost and high yield, gold powder milling should adopt a new process of gas and water combined atomization. The process flow is shown in Figure 1.
As shown in Fig. 1, in the process, high-pressure gas and atmospheric water are simultaneously introduced into the atomizer, so that the molten gold can be directly atomized into the water curtain (screen formed by water) while being atomized by the effective gas. Dispose of and then use a special collection technique to collect the gold powder. The practice of gold powder production in a large gold enterprise shows that the new water-gas combination atomization process can ensure that all gold is recovered, that is, its yield is 100%. The reason why the 100% of gold in the milling process can be achieved, the key technology of the process lies in the rational design of the atomization flow field centered on the atomizer and the rational configuration of the outlet end of the spray chamber and the collection system, making the gold The powder does not have the possibility of scattering into the environment.
Third, the related technical issues in the process of gold milling
As a precious metal, gold is a priority when it is processed in any way to minimize losses. Due to the particularity of the milling process, it is simply impossible to ensure that there is no loss at all; however, this can be achieved if the process conditions and associated equipment are properly set. In the following, combined with the practice of powder production in a domestic gold enterprise, the related technical issues involved in ensuring the zero-loss problem of gold powder production are discussed.
(1) About the atomizer
The atomizer in the gold milling process is the core component of the entire milling system. Here, it is required that the atomizer can effectively atomize the molten gold to make gold powder, and at the same time, it must ensure that the atomized gold powder is not lost; this requires the atomizer to have both high atomization capacity and After the atomizing medium is ejected from the atomizer nozzle, a reasonable atomization flow field is formed together with the purified water introduced through the predetermined direction; the flow field can merge the gold powder into a rotating flow field with a fuzzy boundary to form Gas, solid, and liquid three-phase flow fields, and "downstream" down (see Figure 2). In this way, it is guaranteed that the gold powder will not scatter randomly in the atomization chamber; this is also one of the keys to ensuring high yield of gold in the milling process.
(2) About the spray chamber
The function of the atomization chamber is originally to provide sufficient space for the sufficient atomization of the metal; in the case of the cylindrical atomization chamber which is often used, the diameter and length of the cylinder are two basic parameters determining the size of the space. If it is a simple gas atomization, sufficient spray chamber space, especially the length, will be beneficial to obtain spherical powder, because the molten metal is required to be atomized when it is atomized. Sufficient time to form a sphere under the action of surface tension. But here, the shape requirements for gold powder are not important, and the important thing is still the fundamental indicator of yield. Based on this, the size of the spray chamber is not the most important, and how the shape of the spray chamber can ensure that the gold powder does not scatter into the environment is crucial. The key here is that, due to the need of gas atomization, the high-pressure gas having the pressure of P 1 introduced into the atomization chamber, once ejected from the atomizer, immediately diffuses in the atomization chamber and causes the pressure inside the atomization chamber P 2 Increased and then exported to the environment via the outlet of the spray chamber. If the ambient atmospheric pressure is P 0 , the pressure difference P 2 -P 0 and the size of the outlet area S determine the flow rate of the gas stream as it flows through the outlet. (The effect of water and powder is omitted here).
Figure 3 is a flow model of a three-phase flow field formed by atomizing gas, water, and gold powder in a spray chamber. In the figure, P 1 , P 2 and P 0 are the pressure in the atomizer, the pressure in the atomization chamber and the atmospheric pressure, respectively, and S 1 and S 2 are the areas of the outlet of the atomizer and the outlet of the atomization chamber, and 1 , 2 is the flow rate of the atomizer outlet and the spray chamber outlet, respectively.
Considering the continuity of the fluid, there is S 1 1 . Obviously, the higher the velocity of the stream at the exit of the atomizer, the more unfavorable the pooling of the gold powder stream. Because, although the gas, solid and liquid three-phase flow fields composed of high-pressure gas, water and gold powder are formed as designed in the atomization chamber as described above, under ideal conditions, the gold powder will be completely transferred into the water. It flows out from the outlet of the spray chamber, which prevents the gold powder from being emitted into the environment. But in fact, it is impossible to absolutely ensure that the gold powder is completely integrated into the water stream. There is always a part of the gold powder that will flow with the airflow to the environment. Therefore, a secondary purification device must be additionally installed at the outlet of the atomization chamber to completely block the gold powder. Escape into the air. However, the airflow speed The larger 2 , the more unfavorable the final purification; on the other hand, the airflow speed The smaller the 1 is, the larger the outlet area S 2 of the atomization chamber will be required, which in turn makes the purification device too large and complicated, which makes the purification difficult. Therefore, how to optimize the outlet size of the atomization chamber and rationally design the secondary purification device becomes another key issue for finally obtaining high yield.
(3) About system circulation
Since the gold milling process mainly uses water to purify the powder, when the water and the powder are separated, a small amount of gold powder inevitably remaining in the water must be finally recovered. However, the sedimentation speed of the fine gold powder is too slow, and some are suspended in the water for a long time and it is difficult to sink. Therefore, the water must be recycled during the production process; and the reasonable reservoir structure and the position of the inlet and outlet will be set. It is conducive to the accumulation of fine gold powder which is slowly settled, and very few of the fine gold powder which is not easy to settle will not be lost to the external environment. In fact, due to the yellow metal precious metal, it is impossible to maintain continuous production for a long time. The production time of the milling system must be much less than the time of production stoppage. In this way, there is enough time for the fine gold powder suspended in the water to sink to the bottom. It is eventually recycled, so that the gold powder can be collected to the maximum extent or even completely collected.
Fourth, the conclusion
As the gold of precious metals, when using the atomization method to prepare gold powder, the first consideration is the high yield problem, and the key factors affecting the yield are:
(1) Designing a reasonable atomizer so that after the atomizing medium is ejected from the atomizer nozzle, a reasonable gas, solid and liquid three-phase atomizing flow field is formed together with the purified water introduced through the predetermined direction, thus ensuring The prepared gold powder does not scatter randomly in the atomization chamber.
(2) Design a reasonable atomization chamber so that the structure and shape are conducive to secondary purification without causing the gold powder to scatter to the environment.
(3) The water must be recycled during the production process. The reasonable structure of the reservoir and the position of the inlet and outlet will help to collect the fine gold powder which is slowly settled, and very few of the fine gold powder which is not easy to settle will not be lost to the outside. Environment.
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