The cyanide solution is piped to the heap and then supplied to the heap through a nozzle, dropper or cloth pool on the heap. The method of cloth liquid is divided into spraying, dripping and cloth liquid pooling, and the three kinds of methods provide leaching liquid to the ore pile. The cloth liquid pool is only used for ore with poor permeability, so it is less used. Spray nozzles and dropper drip are widely used.
1. Spraying requirements for spraying are uniform, so that the solution saturates the oxygen in the air and minimizes the loss of cyanide. For this reason, the droplet size of the spray should be appropriate. Too small misty water droplets have large evaporation losses and are easily blown away by the wind. Usually, the nozzle orifice diameter is 2 to 3 mm.
Before spraying the cyanide solution, spray lime water to the heap to neutralize the acid produced by the oxidation of iron sulfide in the ore until the desired pH is reached. This time usually takes 1~2 weeks.
The lean liquid is pumped from the lean liquid pool through the plastic pipe to the immersion pile. Cyanide can dissolve iron, steel or steel pipes, so plastic boring is used for heap leaching. Heap leaching copper or brass can not pump member, can not use copper or brass spare parts, because the solution will be dissolved cyanide. Since the plastic pipe can be peeled off from the pipe wall when it reaches a certain thickness, the plastic pipe has self-cleaning characteristics. At the same time, plastic pipes are cheap, flexible and light. High density polyethylene pipes are the most commonly used plastic pipes for heap leaching processes. The spray line is erected from the side of the immersion pile and laid on the top of the pile. The sprinklers are evenly arranged along the pipeline, and the pipelines are laid in parallel so that the spray ranges of the sprinklers overlap each other.
In the current heap leaching production, sodium cyanide solution is basically used. The concentration is generally 0.1~2.3kg/t solution. If the ore contains high amounts of silver , the concentration of the immersion liquid should be larger.
The spray is generally intermittent, which facilitates the entry of air into the heap.
Mine effluent from the flooded heap, containing gold as its volume mass reaches 1 ~ 10g / m 3, the input to the activated carbon adsorption column, the lean solution after adsorption and, where appropriate, additional alkali cyanide, return spray. The sodium cyanide mass fraction of the pre-spraying solution is controlled at 0.06% to 0.08%, the medium term is 0.04% to 0.05%, and the final phase is 0.02% to 0.03%.
The spray strength of the solution is generally 5~12 L/(m 2 Â·h). Practice has shown that by appropriately increasing the spray strength, the leaching time can be shortened. Mass transfer is accelerated because the spray intensity is increased. However, when the spray intensity is too large, the concentration of gold in the leachate is remarkably lowered.
Distribution of the immersion liquid: After adding cyanide and lime, the immersion liquid is pumped from the mixing tank to the distribution point. The immersion liquid flows from each point into the network of immersion liquid pipelines distributed at the top of the heap. The pipeline is generally a plastic pipe with a diameter of 2 to 5 cm. On the main distribution line of the liquid supply, nozzles and nozzles are connected at regular intervals. The sprinkler system is divided into fixed type and swing type. The fixed sprinkler system is the most economical and easy to install. The production operation is only to make holes at regular intervals on the distribution line to achieve the purpose of spraying. The most common solution distribution system is the rocking type (Fig. 1), known as the rain bird shower. The spray effect of this type of sprinkler is more uniform than that of a fixed sprinkler system. However, it is easy to cause the calcium salt to foul, thereby hindering the flow of the immersion liquid. When fouling severely impedes the flow of the immersion liquid, the shower must be removed and immersed in a hydrochloric acid solution to dissolve the calcium salt. [next]
In order to solve this problem, the immersion liquid is evenly distributed, and some producers have tried to improve the nozzle of the shower. Thereby avoiding the denser annular spray phenomenon that often occurs in the shower. The line pressure during the operation of the sprinkler is 1.4~2.3kg/cm 2 , which can realize the immersion coverage of the radius of 10.5~15m (see Figure 2).
The other is the Bagdade oscillating sprinkler, developed by the Cyprus'Bagdad mine in Arizona, USA. It has been widely used. The production is to cut a rubber tube of 23 cm length and 6.4 cm wall thickness, and one end is connected with the liquid supply tube and pressure is applied. When the solution passes through the pipeline, the other end oscillates and the immersion liquid is ejected in a ring shape. Swing showers are usually placed on a 3m center arch. Some people think that this oscillating sprinkler has a better liquid-sinking effect than a rain bird sprinkler. The feature is that maintenance is easier. When calcium salt scales appear in the tubing, the sprinkler can be expanded and shaped to remove fouling. The working pressure is 1.4-2.8 kg/cm 2 . [next]
The liquid storage method of the heap is the key to improve the leaching rate of heap leaching. In the past, the â€œWob-blersâ€ spraying equipment was used almost all over the world because it sprayed evenly and the droplet size was quite stable, but it The disadvantage is that the impact on the surface of the heap is large. In 1987, the Rochester Gold Mine in the United States first used drip equipment for new gold leaching technology. At present, more than 80% of gold mine heap leaching plants in the United States are using drip leaching gold.
In recent years, there has been great progress in heap leaching technology in China, but the drip method as a practical technology for gold mine heap leaching is just beginning. In 1990, the gold ore heap leaching center of the Ministry of Geology and Mineral Resources applied the drip leaching technology to the gold leaching and gold extraction practice for the first time in the Saerbulak gold mine in Fuyun County, Xinjiang, China. The experiment was a complete success.
The advantage of dripping compared to spraying is: optimal condition control with heap leaching solution; daily evaporation loss of solution is reduced from 27% to 6%; reducing reagent consumption and avoiding wind entrainment; improving drip system around Environmental safety conditions; can shorten the leaching time, dripping leaching for 23d can achieve the effect of spraying 77d, the leaching rate is 92%. In areas where conditions are appropriate, the droplet emitters can be buried in the heap in winter and continue to leach, which will extend the production cycle and allow for heap leaching and gold extraction throughout the year.
The drip is the same as the conventional spray. It is a droplet emitter installed on the capillary. Under a certain pressure, the solution is evenly and slowly dropped into the heap. Since the droplets are continuously and slowly piled into the pile, the impact on the surface of the heap is small, and the entire heap is wetted by the immersion liquid in the lateral and longitudinal directions by capillary action, thus reducing fine particle migration and channeling. at the lowest limit. Therefore, during the leaching time, the heap basically maintains its original permeability. In addition, in general, the droplet launching tube is placed on the surface of the heap, and the droplets are in contact with the air for a short period of time, which reduces the evaporation loss of the solution, reduces the reagent consumption, and avoids wind entrainment and improves the mine. Environmental conditions around the pile.
Whether drip is successful or not, it is the key to uniform penetration. This requires uniform discharge of the droplet discharge tube, adjustable flow rate, simple structure, good anti-clogging performance, easy installation and maintenance, and low price. It is best to use it repeatedly.
According to the particle size flow rate and the penetration range of the pile, the drop hole spacing should be 70cm, the capillary spacing should be 60cm, and the dripper flow adjustment range should be 2-20L/h.
In order to ensure the normal operation of the drip, and to solve the most clogging problem in the dripping leaching process, a filter should be used, the filter screen is 120 mesh, and a pressure gauge, a water meter and a backwashing device are installed.
The liquid supply pump adopts an ordinary submersible pump with a head of 25m and a flow rate of 15m3/h. The backwashing pump is connected with the conventional sprayed clean water pump, and all operations are controlled by valves. [next]
The installation arrangement of the drip system pipeline is based on the need of drip strength. The polyethylene pipe of Ð¤50mm is selected as the main pipe, and the two sides are supplied to the two sides in two directions. The capillary is selected from the special drip capillary of Ð¤10mm, and the filter is used to ensure the drop. The drenching is carried out normally, and the piping system layout is shown in Figure 3.
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