After the immersion pile is washed, the cloth liquid leaching can be performed. In the whole liquid leaching stage, there are many working tasks, and they are influential and complicated. To be methodical, three work needs to be done: the preparation and use system of the immersion liquid, the determination of the spray intensity, the daily spray and the interval. The arrangement of time.
I. Formulation and use system of the leaching solution Firstly, it is required that the pH value, the potential, the concentration of the leaching agent and the like of the prepared immersion immersion liquid can meet the needs of the leaching chemical reaction. Secondly, since different from the agitation leaching heap leaching, the implementation of closed loop flow, the end of the recovery solution after leaching metallic return, so the end of harmful impurities accumulated liquid to be strictly controlled. To eliminate the influence of harmful impurities, acid method uranium ore heap leaching, heap leaching copper, typically occurs after the peak of the tail was once open process. Third, the concentration of the leaching agent in the heap leaching is not constant, but varies with the leaching time, generally from high to low. For example, in the 180d leaching cycle of the American Bluebird Copper Mine, the change in sulfuric acid concentration in the leaching solution is shown in the following table. The concentration of sodium cyanide also changes during gold heap heap leaching.
Relationship between Sulfuric Acid Concentration and Leaching Time in Bluebird Copper Mine Heap Leaching
Leaching time (d) | Amount of sulfuric acid in the leaching solution (g/L) |
0~l0 | 50 |
10~30 | 30 |
30~60 | 20 |
60-180 | 7 |
2. Spray strength refers to the volume of the immersion liquid applied to the unit area of ​​the mine per unit time. It is usually expressed by L/(h·m 2 ). Because of the different height of the ore heap, it is also expressed in units per unit of ore per unit time. Its unit is L/(h·t ore).
Spraying strength is a very important parameter in heap leaching. It is the main basis for determining the volume of the structure in the heap leaching project, and is also the important basic data for determining the scale of the recycling facility; it is also one of the main factors affecting the leaching cycle; The scaling phenomenon is closely related. How to determine the spray intensity, often divergent, and some advocate that the spray intensity is as small as possible, and some think that it should not be small. The data appearing in the literature is also very different. The reason, in addition to the difference in ore properties, is mainly due to the consideration of the spray intensity as an isolated factor. In fact it is related to many factors, it is the most flexible and adjustable parameter in heap leaching.
The main factors that restrict the spray intensity are as follows:
(a) The most important constraint is the permeability of the mine. Whether in theory or in practice, surface area fluids are not allowed during spraying. It can be seen that the size of the spray intensity is first determined according to the permeability of the pile.
(2) Consideration of scaling factors. In addition to the type and concentration of the leaching agent, the scaling has a large relationship with the spray strength, and the spray strength is small, and the possibility of scaling is large. This relationship is very evident when fluorite- containing uranium ore is leached with sulfuric acid.
(3) The relationship between the leaching period and the spray intensity, which is inversely proportional to a particular mine. The spray strength is large and the leaching period is short. On the contrary, the leaching period is long.
(4) The impact of climate factors. Dry, hot season or area, the leaching intensity should be larger; and the low temperature, rainy season or area spray intensity should be smaller.
(5) The constraints of economic factors, including investment and production costs. In terms of cost, the spray intensity is large, the concentration of metal ions in the leachate is low, and the post-treatment production cost is increased. In addition, when the spray strength is too large, the leach solution is not completely moved in the form of water film along the surface of the ore. At the same time, it chemically reacts with minerals, but most of the leaching solution passes through the large gap between the ore and passes through the heap. It does not play the role of leaching, which wastes pumping energy and increases the load on the spray system. And equipment wear. From the aspect of investment, the spray intensity is small, and the volume of the structure such as the rich liquid pool and the tail liquid pool, and the scale of the post-treatment can be reduced accordingly. On the contrary, the volume and post-processing scale of these structures will increase, and the investment will increase.
Although some examples have selected spray strengths with two extremes, such as greater than 100 L/(h·m 2 ) and less than 5 L/(h·m 2 ), most of the heap leaching uses the same spray strength. Fluctuations within the scope. According to the survey, 90% of the gold mine heap leaching sites in the United States use a spray intensity of 6.9 to 15 L/(h·m 2 ). For ore crushed to -20 mm, and granulated heap leaching, if the pile height is less than 6 m, the spray intensity in the above range is suitable. The spray intensity of uranium heap heap leaching should be slightly higher than that of gold mine heap leaching, generally 15~25L/(h·m 2 ). The reason is that uranium ore heap leaching uses low acid as the leaching solution. The concentration of iron and aluminum in the leaching solution is very high. They are easily hydrolyzed and precipitated. UO 2 2 + itself is also easily hydrolyzed, so that uranium ore heap leaching partially causes leaching. In the case where the uranium is deposited with the iron in the heap, increasing the spray strength is advantageous for leaching.
Third, the spray time Here are two layers of meaning, one refers to the total time of each mine spray every day, and the second refers to the interval of each spray.
The heap leaching uses intermittent spraying, one is because the heap immersion is controlled by the capillary pressure, the apparent reaction rate is very slow, and the second is based on the principle of unsaturated flow, which oxidizes the mineral by the oxygen in the air. The choice of the intermittent time between the spray time and the two sprays is only based on a rough test. Under normal circumstances, spray 8 ~ 12h every day, stop spraying for 16 ~ 12h, each spray intermittent time is about 1.0 ~ 1.5 times the spray time. Most of them use spray 1h to stop for 1~1.5h, or continuous spray for 2h, stop for 2~3h, and continuous spray for 2~4h, because it will make the structure and post-processing scale large and the capital investment is high.
For heap leaching with a long leaching period, the relationship between spray and intermittent time is usually changed in stages. Before and after the peak concentration occurs, it is similar to the above-mentioned situation, that is, spraying for 8 to 12 hours per day, to the end of leaching, stopping The spraying time can be lengthened. In order to increase the leaching rate and save money, it is often stopped for one week and then sprayed once.
The leaching period of a heap, ie the total number of leaching days, depends mainly on the nature of the ore. Some granulation heaps can be completed in 7 to 10 days, and some ore sulphide ore heap leaching can last for several hundred days. The leaching period of most heap leaching is roughly determined initially from the indoor small test, and then finally determined according to the actual situation on site. When the concentration of metal ions in the leachate is usually called the "minimum economic concentration" (C mm ), the spray is stopped and no longer leached. However, the “minimum economic concentration†is related to the spray intensity and the daily spray time, as well as the ambient temperature. Therefore, it should not be mechanically only to see the metal ion concentration value in the leachate, and should also be compared with the indoor small test and production. How close is the leaching rate? If the leaching rate has reached the expected requirement, and C mm has reached the specified index (if the uranium concentration reaches 20mg∕L, the gold concentration reaches 0.5mg∕L), the leaching can end: otherwise it should be adjusted Spray parameters, such as reducing the spray intensity, extending the interval time, or finding out the cause (such as the temperature is too low), take appropriate measures for the problem.
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