Key to improve the recovery of heap leaching is enhanced permeability of the heap, so that with the free gold ore leaching solution in sufficient contact and reaction occur. How to increase the oxygen content in the immersion gold process is also an important condition for improving the leaching rate. Therefore, in order to improve the technical indexes in the heap leaching process, especially for the treatment of refractory gold ores, such as fine granules and multi-lime ore, In the dip process, the process of ore granulation, adding wetting agent and oxygen leaching is carried out to achieve the purpose of improving the gold recovery rate.
Granulation heap leaching
The core problem of heap leaching is how to ensure that the immersion gold liquid is in full contact with the valuable components in the ore and reacts effectively. It is more difficult for ore containing more ore and clay . Around this core, a lot of research work has been carried out in the past ten years and a breakthrough has been made. In 1975, Holmes and Naruer company proposed TL law and the US patent (US Pat.No.4017309), this method is further improved by the Chilean company and SMP in 1980 for industrial production in Lo Aguire copper mine, so as to overcome the heap The inherent shortcomings of dip find an effective way.
The full name of the TL method should be a granulation-pretreatment-thin layer heap leaching method. The essence of the TL method is: 1 to improve the permeability of the ore itself and the heap by granulation; 2 to add a leaching agent to the ore during the granulation process. Advance contact and pre-reaction to accelerate the leaching speed; 3 points thin layer heap immersion to ensure uniform liquid and favorable oxygen.
The comprehensive result is that the kinetic process and the internal and external diffusion processes are effectively promoted by improving the permeability of the leaching, greatly improving the leaching recovery rate, shortening the heap leaching period, and reducing the consumption of the leaching agent. This is the key technical problem to be solved by the heap leaching method.
1) Granulation process In order for the heap leaching production to be successful, the heap leaching material must have good permeability to allow the cyanide solution to pass uniformly through the heap. Therefore, some refractory gold ore can be successfully processed by granulation heap leaching. .
Most of the precious metal-containing ores and materials need to be broken up to 25.4 mm or fine before granulation in order to expose the precious metals contained in the ore and increase the total yield of the precious metals.
During the granulation process, the powder ore in the clay and ore adheres to the coarse particles, forming a layer of fine-grained inclusions. This type of ore has sufficient wet strength and is rarely broken when cured and then wetted. Since granulation can produce porous and permeable raw materials, it can overcome the main problems caused by ore particle size segregation during pile-up, such as migration of fine particles and channeling of solution during leaching.
Three important granulation parameters were determined through research, namely: 1 the amount of binder added to the dry feed; 2 the amount of water added to the binder and ore mixture; 3 required to form the calcium silicate linkage Curing time. Reasonable determination of these three parameters will successfully pretreat the poorly permeable broken ore, contain a large amount of clay minerals and fine tailings and other materials.
Practice and research have shown that most of the broken ore (-25mm) can be effectively leached through the following procedures. First, mix 4kg of Portland cement into each ton of material, then wet it with water or cyanide solution until the final moisture is about 12%, mechanically roll the wet mixture to achieve the purpose of the agglomeration, and then solidify for more than 8h, then carry out the conventional heap. Dip treatment. [next]
The cement added during the granulation process provides a protective base for cyanide leaching. After the pile is piled up, leaching is carried out by a conventional process. When a small amount of fine particles is contained, it is only necessary to add a solution to adhere the fine particles to the coarse particles. However, when the content of fine particles, i.e., -200 mesh, exceeds 10%, it is necessary to add a binder to granulate. A loosely bonded (not dense) similar ore-like polymer is produced. These polymers have high permeability and are stable in mechanical strength during leaching. The test result is the best for Portland special cement. The addition amount is generally 0.9-4.4kg per ton of ore; the lime is second. But both binders provide the required protective base, and lime is better in this regard.
The binder must be added to the relatively dry ore and mixed with the ore to rewet. The binder should be added to the crushing circuit and mixed with the ore as the ore breaks. Moreover, it can absorb excess water in the ore, making it easy for the ore to pass through the crushing equipment without clogging the screen to block the drain. The binder is added to the crushing circuit, which is intimately mixed with the ore, especially the lime fills the entire heap, ensuring alkalinity.
The mixture of ore, binder and solution must be cured for 8 h. A large amount of fine ore is required for a large amount of binder, and the curing time takes about 2-3 days. If the solution is only used for solution, no curing time is required and no special curing equipment is required.
2) Granulation 1 By granulation, those ore containing a large amount of fine particles and clay can be treated by a low-cost heap leaching process, and those large low-grade gold ore bodies are likely to be exploited.
2 Increased the total recovery rate of gold. Because fine grinding increases the exposure of free gold without segregation. Otherwise, the granulation-free material will undergo delamination during the pile-up process, causing the fine-grained material to concentrate locally and hinder the penetration of the immersion liquid (see Figure 1).
3 increased penetration speed and shortened leaching time. This is more economical for mines that can expand their production capacity while the infrastructure investment in preparing the dip pad does not increase significantly.
4 The porous nature of the ore makes the heap "breath", which provides the necessary oxygen for gold dissolution and accelerates the reaction between gold and cyanide. This opens up the possibility of increasing the height of the heap, which reduces the cost of the per-ton of ore to be treated, and the land can be used more efficiently. [next]
5 The ore heap consisting of ore bodies has a high porosity and, therefore, can effectively wash cyanide remaining in the immersed ore heap. When the dip is discarded, stable pellets can minimize dust contamination problems.
6 The precious metal content in the precious liquid obtained by heap leaching is high, and the recovery rate of gold can be improved by using the replacement or activated carbon adsorption method.
However, crushing systems and agglomeration systems are expensive and should not be placed in industrial production unless absolutely necessary. Before starting industrial production, it is first necessary to determine the technical and economic conditions for granulation heap leaching.
3) Granulation equipment 1 cylindrical granulator. The most common granulation equipment is a cylindrical granulator (see Figure 2). Most cylindrical granulators rotate at only 20% to 60% of the critical speed. The ratio of barrel length to diameter is 5:2.5. This device is superior to other types of devices because of its large capacity. The granulator has three operating parameters: one is the rotation speed of the cylinder, which can be adjusted by a sprocket, a pulley or a variable speed drive; the second is that the inclination of the cylinder should be maintained between 1 ° and 4 °; The appropriate residence time in the cylindrical granulator is 1-4 min. The conveyor should be at right angles to the length of the barrel to prevent material spillage or build-up. A rubber blade is mounted in the barrel along its length to prevent material from sticking to the wall.
2 disc granulator. This granulator has several job control parameters that can be varied to suit the material to be processed. The slope of the disc is generally 40°-65° from the horizontal, the depth is 0.46~0.91m, and the number of revolutions of the disc is 30~50r/min, depending on the diameter and slope of the disc, and also depends on the ore size and the disk. Diameter (see Figure 3). A 6.3 m diameter disc granulator can process ore 90 tons per hour. Driving such a large-scale granulator requires about 95 kW of power.
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The cylindrical granulator can be used outdoors, while the disc granulator can be placed indoors to avoid problems such as sand dust.
3 pile granulation. As shown in Figure 4, this is the simplest granulation method suitable for handling finer materials. The discharge end of the conveyor belt connected to the crushing equipment is about 4.6~6.1 m above the ground. This pile will have sufficient height to allow the material to roll down and mix along its stack; the ore flow from the conveyor belt can be wetted from the front or rear. The supply or rubber tube is attached to the frame of the conveyor. The jet produces thicker droplets and does not require a wetting device. Below the spray there is one or more heavier mixing rods suspended in the falling ore stream. Its role is to mix the outer layer of wet ore with the dry ore inside.
Use the front-end loader to load the material of the pile into the truck and send it to re-pile or directly pile up, so that the ore can be mixed again; the material can also be discharged into a storage bin and piled up by the stacker.
4 belt transfer mechanism pellets. Spray water onto the sieve - 9.5mm ore. All products under the sieve are sent to a common conveyor belt. The four conveyor belts are then passed through, and a heavy metal rod at the transfer point is suspended in the falling ore stream (as shown in Figure 5).
The number of conveyor belts to be mixed depends on the amount of fines in the ore. -100 mesh 5% of hard siliceous ore requires only two or three conveyor belts, but a ratio of 10% or 15% requires four or five conveyor belts. If it exceeds 15%, it needs to be treated with a cylinder or disc granulator. .
A spray head and mixing rod are required for each transfer point. The conveyor speed of the conveyor belt is 76~91m/min. An ore of 136 tons per hour with a bandwidth of 0.61 m and 227 tons of ore per hour at 0.76 m width. Note that the spray does not wet the belt directly. All solutions should be sprayed onto the ore. The angle of inclination of the conveyor belt is 1500. The vertical space between the pulley at the discharge end of the 1500 and the end of the conveyor belt is about 1.8 m. This allows the nozzle and mixing rod to be installed, giving the ore a chance to mix. As long as the ore does not slip under the belt, its slope can be steeper.
5 inclined vibration step type chute granulation. The granulation equipment has 12 steps of about 7.6 cm high, and the ore rolls down from the steps and mixes. Each step is at an angle of about 35 to the horizontal. The amplitude and frequency of the vibration of the slot can vary. Water is added through the spray bar at the top of the vibrating trough, and the ore is granulated with the step or sliding down the chute. It is important for this granulation equipment to maintain a constant rate of ore supply. The residence time of the material on the tank is less than 10s. If a binder is required, it must first be mixed with dry ore with a separate unit and then sent to a step chute granulator.
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