Heap immersion underlay material

The underlay material should first meet the basic requirements of the heap immersion mat, and secondly, it should be based on the specific conditions at that time. Various underlay materials are used in modern heap leaching projects. This article describes several types that are used more widely.

1. If the clay base layer has suitable clay within 2 km from the heap leaching field, a clay underlayer may be used. The usual practice is to layer the clay layer on the compacted foundation. In order to ensure the quality, the bentonite is often added and then laminated. The thickness and total thickness of the layered clay depend on the quality of the clay. The particle size of the clay is an important indicator of the quality of the clay, and the layer thickness and total thickness are generally determined by the maximum particle size of the clay.

The clay mat has a layer thickness of about 3-5 times the size of the mesh through which the clay passes.

The total thickness of the clay underlayer is generally about 10 to 12 times the size of the mesh through which 95% of the clay can pass. As shown in Table 1.

Table 1 Thickness selection of clay underlayer

The quality of the clay underlay depends not only on the quality of the clay, but also on the construction method and construction machinery. This step of layered construction is very critical. In this step, the clay is mixed with a tray tiller without adding water, and then the water is sprayed as required. After the moisture reaches the requirement, the vibratory roller is passed back and forth at least 9 times to compact the clay. Generally, the layered clay is about 150 to 180 mm thick. The construction method for each floor is basically the same. The difference is the intermediate layer, and it is often necessary to add 3% to 5% of bentonite in the amount of clay. Another important issue is to ensure a good landing of the interface between the layers, which is to loosen the compacted bottom surface portion and lay a layer of clay. It is not suitable for construction during the icing period. In the hot season, due to the influence of evaporation, attention should be paid to water conservation.

The well- ^placed clay underlayer can have a permeability as low as 3 × 10 ^{-9 cm} / s, which can fully meet the requirements of 1 × 10 ^{-7 cm} / s.

When using a front-end loader or a conveyor belt to build a pile, in order to prevent the ore from falling from a high place on the surface of the clay layer, it is generally required to cover the bottom layer with a pebble or coarse sand protective layer. The ore block is usually between 50 and 100 mm.

Second, the mulch bottom layer The mulch film referred to here includes organic synthetic materials of different kinds and thicknesses. Such as various thickness of polyvinyl chloride, high density polyethylene soft board and so on. These materials have low permeability up to 1 x l - ^{13 cm} / s. People care about its ability to resist pressure and puncture. Table 2 shows the test results of various mulch films.

Table 2 Test results of the film underlay material

Note: PVC-polyvinyl chloride; HDPE-high-density polyethylene; P is qualified, no pierced pores are found; F-damage, at least one hole appears; T-punctured from the top; B-punched from the bottom. Cover layer thickness l00mm. The pressure applied to the underlayer during the test was 80 kN. A contact stress of 2000 kPa was generated. Hold time 2min.

Table 2 shows that 1mm thick PVC is used as the underlay material, and then the coarse sand is used as protection. The effect is ok. If the -l0mm sieved conglomerate is used as the protective layer, even a 1.25mm thick PVC will not work. However, 1 mm thick high density polyethylene (HDPE) is used as the underlayer material, and the effect is good in the case of the protective layer material tested. It can be seen that the high-density polyethylene of the same thickness is superior to the pressure resistance and puncture resistance of the polyvinyl chloride.

There are more and more mulch mats for the heap immersion underlayer. Some small yards have used a layer of linoleum and two layers of PVC agricultural film, which can only be used once. Although the investment is less, the production and operation costs are large. The 719 uranium ore heap leaching used 3mm thick PVC soft board and can be reused many times. Shuangwang gold ore and Xinjiang Sal Burak large industrial heap leaching are 1.2mm thick soft PVC plate, -40mm ore particle size, high pile 7m, tests proved that can be used repeatedly. At present, most of the uranium ore heap leaching uses 1.0mm soft PVC board as the bottom cushion, and the cost is about 25 yuan/m ² . Using cyclohexanone as a binder, the construction method is simple, and it should be laid according to the slope when laying. From low to high, it is lapped one by one, the bonding width is 3~5cm, and the temperature during laying and bonding is preferably higher than 25°C. Otherwise, apply some pressure.

Third, the asphalt concrete underlay layer asphalt concrete underlay has a permeability of 10 ^-8 to 10 ^{-10 cm} / s, and its permeability is between the clay underlayer and the mulch underlayer. However, its resistance to compression and puncture is superior to that of the mulch and clay underlayer. A good quality asphalt concrete underlay can withstand the round-trip traffic of 150t trucks. Its cost or one-time investment is very large, so only large, high-heap, and long-term reused yards are used.

The construction method of the asphalt concrete underlayer is to first lay a layer of asphalt concrete on the compacted foundation, then lay a layer of asphalt-rubber mold, and finally lay a layer of asphalt concrete on the asphalt-rubber film. In order to improve the drainage capacity, a layer of coarse sand or a uniform ore layer of 0.1 to 0.2 m thick is generally added to the asphalt concrete underlayer. The size of the ore that is piled up is generally 20 to 80 mm.