EA044795B1 - WASTE MANAGEMENT - Google Patents

Description

Field of technology

The invention relates to a method for extracting water and forming sustainable landscape elements from mining waste.

State of the art

The bulk of the water consumed in hard rock mining operations used to recover base or precious metals is contained in very finely ground waste products resulting from flotation or leaching. Fine grinding is necessary to release the valuable component of the ore to ensure acceptable extraction results. The resulting waste is thickened to partially extract water, and since the thickened pulp remains susceptible to liquefaction, this waste is hydraulically stored in special storage facilities, referred to as tailings ponds.

Waste particles are typically less than 150 microns in diameter and, due to their low permeability, cannot be easily drained or filtered to remove trapped water.

Even when waste filtration is used, stacking and storing the filtered product can be problematic because the filtered waste is difficult to handle and lacks structural integrity. Filtration and stacking by mechanical means are expensive operations and also generate waste, which poses storage problems in many areas.

So, two long-standing goals of the mining industry, such as the mining industry of base metals, copper, gold or platinum group metals (PGM, from the English Platinum Group Metals), are, firstly, to recover the water contained in the waste, and, - secondly, to develop an economical method of storing waste in a dry and sustainable form.

The agricultural, construction and soil stabilization industries have long used the concept of channels with capillary (wick) properties for dewatering soils with low hydraulic conductivity.

Capillary drainage (vertical or horizontal) is achieved by introducing a continuous layer of material with higher hydraulic conductivity into poorly draining soil to allow water to flow from areas of soil with low hydraulic conductivity into zones with a more porous structure, from which water can flow to places from which it may be withdrawn. Most capillary drainage systems use a permeable geotextile wrapped around a central porous core to allow water to selectively flow from the saturated soil into the porous wick.

Sand is also used as a capillary drainage material (often referred to as French drain or French drain) because it has high hydraulic conductivity (about two orders of magnitude greater than poorly drained soils). The sand channel provides a stable flow of water from soil with low hydraulic conductivity (for example, from clay) into a sand drain, from which it can flow to the water outlet. The effect of capillary drainage of water-unsaturated sand is manifested in the extraction of water from the surrounding water-saturated soil.

These principles of capillary drainage can also be applied to the dewatering of mining waste.

However, the size distribution of mining waste particles is such that they have low hydraulic conductivity (usually 10-4 - 10-6 cm/s), and therefore in the case of large volumes they remain constantly above the saturation level; water content at which waste liquefaction can occur when exposed to external pressure.

The final water content of the waste after settling is usually approximately 0.5-0.55 m ³ of water per ton of waste.

The reality is that in many jurisdictions, authorities insist on the use of an impervious cover on the base and sides of a tailings pond to prevent water from leaking from it into the environment.

Due to the large volumes, accidental destruction of the boundary (enclosing) walls of tailings ponds used to contain mining waste can have catastrophic consequences. Such destruction caused loss of life and widespread environmental pollution.

The idea of using vertical wick drainage using geotextile materials to dewater waste has been successfully tested to compact old waste to allow movement of partially dried material (Proceedings of the Tailings and Mine Waste Conference, Vancouver, British Columbia, October 26-28, 2015) . However, the cost of installing a large number of vertical drainage channels with capillary properties, with a pitch of 1-3 meters, on a large tailings pond is beyond acceptable. The material cost of each traditional geotextile capillary drainage channel is significant, approximately equal to the installation cost of each channel.

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The commercially acceptable application closest to the idea of wick drainage in a tailings pond is a layer of sand or constructed drainage channels placed at the base of the tailings pond to allow water to flow horizontally to the sump pump location. However, over a long period of time, the effective flow rate of water from the sand located at the bottom of the tailings pond is very limited. Only tailings located a few meters from the sand are dewatered due to the low hydraulic conductivity of more distant tailings and the inability of air to replace the water they contain.

Thus, capillary drainage has not found widespread use in the mining industry, even in regions where the water that could be recovered from a tailings pond is of significant value.

A similar idea of providing a high permeability layer to assist in dewatering the thinner low permeability tailings layer above is belt filtration as stated by Bentley et al. (US3767050A). Filtration of low permeability tailings slurry is accelerated by placing the tailings on an underlying layer of sand.

Another similar solution (US 9188389 B2, Ren et al.) used continuous parallel layers of fine oil sand tailings distributed by gravity over layers of other high permeability base material, such as sand from the oil sands refining process, to increase structural integrity of thin tails.

To preserve these parallel layers of tailings and sand, which are placed hydraulically and spread by gravity over an extended area, the corresponding slurries are treated with chemicals before placement. This chemical treatment provides appropriate deposition angles (tailings beach angles) of the sand fraction and the tailings fraction to maintain a constant depth of these two fractions of the structure and to ensure that this angle matches the slope of the area where the waste is to be disposed. This deposition angle typically exceeds 1%, with upper and lower limits limited by adjustments achievable by chemical modification of the respective suspensions. The achievable layer thickness of a multilayer structure is typically less than 1 meter and is limited by the threshold dewatering time required to achieve the required shear strength before adding the next layer. During this dewatering time, the higher permeability layer is partially drained, thereby providing an unsaturated base that is suitable for partially draining the overlying lower permeability layer, so that the shear strength of the composite structure is increased.

It should be noted that technologies for enriching the coarse particle fraction are being refined in such a way that larger particles are discarded. These coarse fraction beneficiation technologies include techniques such as coarse particle flotation (CPF) and leaching of very large particles remaining after CPF to recover the valuable ore component in a more concentrated form, in the case of larger particles, obtained as a result of grinding.

This sand, remaining after CPF or sand heap leaching (SHL), contains approximately the same amount of metal as traditional tailings, and, accordingly, this sand is sent to long-term storage rather than further storage. grinding to obtain fine particles. This ability to produce larger particle size residues without compromising the recovery of the valuable component opens up the possibility of partially extracting water from the resulting sand residues. For example, increasing the size of the crushed particles in the case of CPF results in a separate waste rock stream that can be disposed of as a free-draining, high-permeability sand residue.

CPF sand residues can be stockpiled separately and drained to dewater to 90% solids (WO2017/195008), or they can be mixed in some proportion with conventional tailings to incorporate as much of the tailings into the sand as possible so that at the same time, the stability of the dump was still maintained (WO2018/234880).

Since CPF beneficiation still relies on partial exposure of valuable minerals and release of waste rock through the grinding process, sufficient exposure of the target mineral occurs only when the ore is crushed to produce particles smaller than average sand particles (typically on the order of 3 -500 microns). If the upper limit of the particle distribution is at the size range where high recovery can be achieved using the CPF process, then approximately 50-70% of the crushed ore has already been crushed to the size of traditional tailings. Thus, even when mixing CPF sand with tailings as specified in WO2018/234880, either a reduction in product yield will have to be made to ensure a free-draining mixture, or such mixing may only result in partial tailings disposal. Thus, the problem of tailings storage remains unresolved.

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The essence of the invention

The present invention relates to a method for disposal of waste after grinding and processing of ores, including the following stages:

separation of processing waste into a permeable sand fraction and a tailings fraction;

laying the tailings fraction and the sand fraction to form a multi-layer structure, limited by at least one bounding wall, with the sand fraction forming continuous sand channels passing through the tailings fraction to allow water contained in the tailings and sand to flow under the influence of gravity through sand channels to water outlets; and removal of water from water outlets.

A boundary wall is an artificial or natural barrier, made of permeable or impervious materials, that encloses the stacked tailings layers so as to permit subsequent sand channels and dewatering of the tailings layer.

After laying the sand channels, they are covered with a layer of tailings, which are laid hydraulically.

A typical sand fraction contains sand particles with p80 sizes greater than 150 microns, preferably greater than 300 microns, and even more preferably greater than 400 microns, up to 3000 microns, and the sand fraction is free-draining.

By free draining it is meant that the sands will drain to a saturated state by gravity alone and preferably have the ability to be hydraulically stacked to any height with water flowing out of them by gravity to form a saturated sand typically containing less than 15% water by weight. %.

A typical tailings fraction contains particles with p80 sizes less than 200 microns, usually less than 150 microns, and its water content usually ranges from 30 to 70 wt.% (0.55-0.90 m ³ water per 1 m ³ suspension tailings), depending on the upstream tailings handling systems.

The tailings fraction may be treated with chemical additives, such as flocculating agents, before disposal to increase the permeability of the tailings layer or to change the angle of natural deposition (the slope of the tailings beach).

Preferably, at least 50% of the sand residue contains particles in the size range from 0.1 to 1 mm, preferably more than 70% and even more preferably more than 90%.

Preferably, the sand residues contain less than 25% of material with particle sizes less than 0.75 mm, preferably less than 15%, and even more preferably less than 10%.

The tailings and/or sand may be partially dewatered before placement.

In the method of the present invention, a layer of tailings is hydraulically laid and water flows from them into sand channels until the tailings layer reaches a structural integrity suitable for laying a sand channel or sand channels on top of the tailings layer, after which the next layer of tailings is hydraulically laid on top sand channel(s) and the process continues to form a multi-layer structure.

Sand channels can be laid hydraulically or laid by mechanical means in the form of drainable solids.

Sand channels may be placed on top of the previous tailings layer as a base to allow mechanical equipment to complete sand placement over the entire surface of the tailings.

Before laying further sand channels, the previous layer of tailings may be partially dewatered, either by drainage through previous sand channels or by using mechanical extrusion equipment.

Sand channels can be installed from a floating vehicle on the surface of a tailings pond covered with water.

In one embodiment, the boundary wall located at the water extraction end of the structure is permeable and water flows through the wall from the outlets.

In another embodiment, the boundary wall at the water extraction end of the structure is not permeable to water, and water is removed from the structure by pumping from the central water outlet.

Preferably, sand channels are provided with air inlet points, either at the end of the laying structure or by any other means of connection to the air.

Typically, sand channels are placed so that the maximum distance from any point in the tailings to the nearest sand channel is less than 10 meters, preferably less than 3 meters, and even more preferably less than 2 meters.

Sand channels can be connected vertically and horizontally to form a three-dimensional matrix of permeable channels within the tailings.

Sand channels can have a thickness ranging from 0.05 to 2 meters, preferably from 0.2 to

- 3,044,795 meters and even more preferably from 0.3 to 0.7 meters.

To create the structure, continuous sand channels are laid across the top surface of the tailings layer.

The tailings fraction is typically placed hydraulically to provide a tailings beach slope of about 0.5 to 2%, typically 0.5 to 1%, preferably of the order of 0.5%, to provide an appropriate slope for water flow, flowing under the influence of gravity through sand channels into the outlet.

According to one option, sand fractions and tailings fractions are laid in successive layers to form tailings layers with a thickness of 1 to 10 meters, and sand channels with an average thickness of 0.05 to 2 meters.

In another embodiment, the sand fractions are laid in separate, spatially spaced rows, and the tailings fractions are laid in sequential layers to form tailings layers having a thickness of 1 to 10 meters, and sand channels having a thickness of 0.05 to 2 meters, usually from 0.05 up to 1 meter, and spaced at a distance of 2 to 10 meters, usually from 2 to 5 meters.

In another embodiment, sand is placed to form vertical geotextile capillary drainage channels in the tailings layers between the upper and lower sand channels. This can be achieved, for example, during the formation process by blocking some or all of the sand channels so that they form a continuous vertical column of sand passing through the tailings. This can also be achieved by introducing geotextile based capillary drainage channels to connect the sand channels to each other.

In another embodiment, sand is used to create internal and external sand banks. The shafts can be divided to form separate compartments which are hydraulically filled with tailings to an appropriate height, allowing water to flow into the underlying sand channels and then pass through the permeable sand shafts to the water outlets. Then the entire process of laying sand channels and building up shafts is repeated to ultimately form the required height and shape of the structure consisting of sand and tailings.

Preferably, during the laying process, at any given time, only the top three layers of tailings, more preferably the top two layers of tailings, and even more preferably the top layer of tailings, are saturated with water, that is, tailings in which air has not yet occupied the pore space between the solid particles, so that they remain susceptible to liquefaction if pressure is applied. Saturated (water-saturated) soil is soil in which the pore space is filled with water.

Sand channels can be incorporated into existing tailings ponds to encourage compaction of tailings near the boundary wall.

Sand is preferably obtained from a separate coarse beneficiation process, and tailings are obtained from a conventional ore flotation process.

The coarse fraction enrichment process includes coarse particle flotation, screening, gravity separation, electrostatic separation and magnetic separation, typically coarse particle flotation.

In other embodiments, sand is produced by leaching sand dumps and tailings are produced by traditional stir leaching.

The invention also relates to a site (landfill) for dewatering mining waste, containing:

at least one bounding wall;

a multilayer structure defined by a bounding wall, the multilayer structure comprising tailings fractions and sand fractions forming continuous channels through the tailings fractions to allow water contained in the tailings and sand to flow by gravity through the sand channels; and water outlets.

A typical sand fraction contains sand particles with p80 sizes greater than 150 microns, preferably greater than 300 microns, and even more preferably greater than 400 microns, up to 3000 microns, and the sand fraction is free-draining.

By free draining it is meant that the sands will drain to a saturated state by gravity alone and preferably have the ability to be hydraulically stacked to any height with water flowing out of them by gravity to form a saturated sand typically containing less than 15% water by weight. %.

A typical tailings fraction contains particles with p80 sizes less than 200 microns, usually less than 150 microns, and its water content usually ranges from 30 to 70 wt.% (0.55-0.90 m ³ water per 1 m ³ suspension tailings), depending on the upstream tailings handling systems.

Preferably, at least 50% of the sand residue contains particles in the size range from 0.1 to 1 mm, preferably more than 70% and even more preferably more than 90%.

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Preferably, the sand residues contain less than 25% material with particle sizes smaller than

0.75 mm, preferably less than 15% and even more preferably less than 10%.

In one embodiment, the boundary wall located at the water extraction end of the structure is permeable and water flows through the wall from the outlets.

In another embodiment, the boundary wall at the water extraction end of the structure is not permeable to water, and water is removed from the structure by pumping from the central water outlet.

Preferably, sand channels are provided with air inlet points, either at the end of the laying structure or by any other means of connection to the air.

Typically, sand channels are laid so that the maximum distance from any point in the tailings to the nearest sand channel is less than 10 meters, preferably less than 3 meters, and even more preferably less than 2 meters.

Sand channels can be connected vertically and horizontally to form a three-dimensional matrix of permeable channels within the tailings.

The sand channels may have a thickness ranging from 0.05 to 2 meters, preferably from 0.2 to 1 meter and even more preferably from 0.3 to 0.7 meters.

To create the structure, continuous sand channels are laid across the top surface of the tailings layer.

A typical tailings fraction is hydraulically placed to provide a tailings beach slope angle in the range of about 0.5 to 2%, typically 0.5 to 1%, preferably on the order of 0.5%, to provide an appropriate slope for the flow of water flowing out. by gravity through sand channels into the outlet.

According to one option, sand fractions and tailings fractions are laid in successive layers to form tailings layers with a thickness of 1 to 10 meters, and sand channels with an average thickness of 0.05 to 2 meters.

In another embodiment, the sand fractions are laid in separate, spatially spaced rows, and the tailings fractions are laid in sequential layers to form tailings layers having a thickness of 1 to 10 meters and sand channels having a thickness of 0.05 to 2 meters, typically 0.05 up to 1 meter, and spaced at a distance of 2 to 10 meters, usually from 2 to 5 meters.

In yet another embodiment, sand is placed to form vertical geotextile capillary drainage channels in the tailings layers between the upper and lower sand channels.

In another embodiment, sand is used to create internal and external sand banks. The shafts can be divided to form separate compartments which are hydraulically filled with tailings to an appropriate height, allowing water to flow into the underlying sand channels and then pass through the permeable sand shafts to the water outlets. Then the entire process of laying sand channels and building up shafts is repeated to ultimately form the required height and shape of the structure consisting of sand and tailings.

Sand channels can be incorporated into existing tailings ponds to encourage compaction of tailings near the boundary wall.

Sand is preferably obtained from a separate coarse fraction beneficiation process, and tailings are obtained from a traditional ore flotation process.

The coarse fraction enrichment process includes coarse particle flotation, screening, gravity separation, electrostatic separation and magnetic separation, typically coarse particle flotation.

In other embodiments, sand is produced by leaching sand dumps and tailings are produced by traditional stir leaching.

Brief description of drawings

In fig. 1 is a schematic view of a multilayer structure according to a first embodiment of the invention;

in fig. 2A, 2B are schematic views of a multilayer structure according to a second embodiment of the invention;

in fig. 3A, 3B are schematic views of a multilayer structure according to a third embodiment of the invention;

in fig. 4A, 4B are schematic views of a multilayer compartment structure according to a fourth embodiment of the invention;

in fig. 5 is a graph illustrating the results of laboratory measurements of head height and material compression for copper ore tailings in Chile, illustrating the permeability/porosity ratio relationship in relation to estimating the release of water from compacting tailings.

Detailed Description of the Invention

The present invention utilizes the sand fraction of ore beneficiation residues in a new waste disposal and storage structure to recover most of the contained water and to improve the geotechnical stability of the composite structure while allowing existing practices of low-cost hydraulic waste storage.

By placing coarse and fine grain residues in a structure containing continuous channels of permeable sand through the tailings layers, most of the water contained in the tailings can flow into the sand in a manner similar to that of traditional gravity filtration. Sand channels are laid to allow gravity to move water to the outlet.

Continuous channels of permeable sand are located so that the average path length for water from any point in the tailings to the nearest sand channel facilitates the movement of water at an acceptable speed from the tailings into the sand channel, from where it can be discharged. This distance from any point of the tailings to the nearest sand channel does not exceed 10 meters, usually not more than 5 meters, and allows the tailings to be effectively dewatered in weeks to months. The shorter the distance from the tailings to the drainage sand channel, the faster dewatering occurs.

The invention uses ore that has been crushed to extract the valuable mineral it contains, and the residue is separated into a sand fraction and a tailings fraction. There is no need for additional materials, since the material necessary for the structure of the residues can be obtained as a result of the enrichment process. Although additional permeable material such as waste rock, or materials such as clay or geotextile may be used to supplement boundary walls or sand channels.

Water is removed from the structure by moving through these sandy drainage channels and then flowing out through the permeable walls of the embankment or by pumping it out of a central outlet. Water is removed for return and reuse, or it is released in a controlled manner to the environment, provided that the quality of the water meets applicable discharge standards.

Before storing tailings with low water permeability, chemical flocculating agents can be added to them to increase hydraulic conductivity and, accordingly, the rate of dewatering of the tailings.

The rate of water flow into the sand channel is greater during the initial stages of tailings drainage, and then decreases over months and even years as the water in the surrounding tailings is gradually replaced by air.

The initial rapid dewatering allows each tailings layer to achieve structural integrity suitable for laying sand channels on the surface of the tailings layer. A further layer of tailings can then be laid on the sand channels and the process continues to create a multi-layer structure.

Final drainage of the structure provides strength comparable to that of water-unsaturated soil.

With appropriate bunding to retain the top layers of the deposited tailings, the structure of the waste deposit can be adapted to the terrain, so that increased flexibility in the choice of waste disposal location is provided.

As already noted, when producing sand from ore using technologies for enriching the fraction of large particles, a high recovery rate of valuable elements can be maintained. Examples of such technologies for enriching the coarse fraction are coarse particle flotation (CPF) or sand dump leaching (SHL). These technologies ensure that sufficient quantities of sand are produced with suitable particle sizes.

For example, when using CPF technology to beneficiate ores containing copper, PGM metals, gold or iron, depending on the release characteristics of the particular ore during the grinding process, sand residues constitute approximately 20-50% of the original ore (sand/(sand + tailings)) . Sand particles from the upgrading process typically have coarse particle sizes in the range of 100-600 microns, and smaller particles that would reduce hydraulic conductivity are removed from the sand by fluidization used in the CPF process. Thus, the residual sand of the CPF process is a permeable and free-draining residue.

20-50% permeable sand from the CPF process provides enough material to allow water to move to the outlets and to provide such tailings dike as may be necessary.

The particle size of the sand obtained after enrichment of the coarse particle fraction and placed in the channels is well suited for use as a material with capillary properties for tailings dewatering.

Sand has high hydraulic conductivity and good permeability to air, which replaces interstitial water. It can move water over long distances, even under moderate hydrostatic pressure.

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The sand particles are small enough that the sand can be placed hydraulically, and it settles quickly enough that it can be placed in a planned channel position or simply spread to form a continuous, although not necessarily uniform, layer on the surface of the tailings.

The bulk density of sand is approximately the same as the density of tailings, so there is limited mixing of layers of sand and tailings during placement and drainage (for example, the bulk density of sand or tailings for copper ore, measured at the saturation point, is typically 2.1 tons /m ³ to 2.5 tons/m ³ ).

The relative sizes of sand particles and tailings are such that fine tailings particles have difficulty penetrating into the voids between sand particles, so that mixing of the two materials is limited during placement and subsequent drainage.

The interface between sand and tailings forms an effective filter zone. This filter allows water to selectively flow into the sand, just as it would through a layer of sand in a mechanical filtration device (eg US3767050A).

Although sand is preferably produced in a separate coarse fraction beneficiation process, it is also possible to coarse the crushed particles of an existing beneficiation or leach process, and then separate the desired sand fraction from the rest of the process residue to form sand and tailings fractions.

The sand channels are laid to allow a constant supply of air to assist the flow of water by gravity from the disposed tailings into a controlled number of conveniently located internal water collection and disposal openings or through a permeable bund into external catch basins. The continuous drainage of submerged tailings layers in the structure is maintained by the pressure of the overlying tailings and sand layers.

At the end of the mine's life, the structure can be hermetically sealed to stop the flow of air to avoid any long-term acidification.

It should be noted that in the method proposed by Ren et al., nothing is provided to provide air access or water outlets to facilitate water extraction, or other mechanisms to continuously displace water from submerged layers within the structure. Due to the low permeability of the overlying tailings, further continuous displacement of water from the high permeability layers will be limited as they are closed. So, while the chemical treatment and parallel layer composite structure proposed by Ren et al. will increase the ultimate shear stress of the oil sands tailings structure to meet the requirements of Canada Directive 74, the recovery of water from mining waste is much lower in this case. than can be achieved with other technologies such as filtration and dry stacking of tailings. Further, a method generally similar to that proposed by Ren et al. would not be applicable to conventional hard rock mining because sand of suitable permeability would not be produced by grinding and further processing. If sufficiently coarse grinding was used to obtain sufficient quantities of sand, traditional recovery of valuable minerals would be reduced.

The method of the present invention can reduce water losses in tailings from current levels of about 0.5-0.55 m ³ /ton of tailings, most often to levels of about 0.1-0.15 m ³ /ton of residues. Since tailings water losses represent the majority of all water consumed in hard rock processing operations, this ability to recover water from tailings represents a dramatic change in overall water consumption in mining operations.

Methods for developing and preparing storage.

The present invention involves several stages that constitute a method for extracting water and creating sustainable landscape elements from waste:

obtaining a separate sand residue from the processed ore with a suitable particle size and tailings fraction;

separate placement of fractions of sand residue and tailings to form continuous sand channels within the entire volume of tailings;

structuring sand channels to allow water to flow by gravity to water outlets;

diverting water from these outlets to ensure continuous drainage of the tailings;

gradually building up a structure consisting of sand channels and tailings, and using the weight of the overlying sand and tailings to accelerate the dewatering of stacked tailings at lower levels.

Various examples are provided below (without limiting the invention to specific embodiments) to illustrate some possible structure solutions and various methods by which the structure can be created.

The boundary walls/shafts that surround the entire structure can take different shapes.

In one embodiment, the invention can be used with a dam-type enclosing structure, which has long been used in tailings ponds. This option allows for a high degree of water recovery. Only a small portion of all tailings undergo liquefaction at any time, thereby reducing the possibility of water entering the dam wall so that the possibility of catastrophic failure of the wall is eliminated. This option improves the safety of the upstream dam wall structure. Upon final closure of the mine, the tailings within the containment dam will dewater and the tailings impoundment will be comparable to water-saturated soil behind a stable retention slope.

Alternatively, excess sand can be used to create internal and external sand banks. These shafts can be separated to form separate storage compartments for the structure. Such compartments are hydraulically filled with tailings to an appropriate height, allowing water to flow into underlying sand channels and then pass through permeable sand banks to water outlets. Then the entire process of laying sand channels and building up shafts is repeated to ultimately form the required height and shape of the landscape element consisting of sand and tailings.

The use of compartments makes it possible to give the waste storage shafts a shape that matches the topography of the territory to be reclaimed. For example, a permanent landscape feature may be revegetated to reclaim a mined-out area or for another use that may be useful or aesthetically pleasing to the local population.

In both options, water is collected both in the form of surface runoff during hydraulic storage and from outlets in sand channels. The water can then be pumped to a suitable reservoir for reuse or disposal.

To create the structure, continuous sand channels are laid across the top surface of the tailings layer. A natural tailings deposition angle (slope of the tailings beach), for example 0.5%, provides sufficient slope for subsequent gravity flow of water through the sand channel. The top surface of the laid sand channels should not be parallel to the bottom surface, which is formed with the angle of deposition of the laid tailings.

Continuous sand channels can also take different shapes.

In one embodiment, the sand can be laid in separate rows located at a distance of several meters from each other and covering about 20% of the surface of the tailings, or in another embodiment, the sand is laid so that the channels connect and, accordingly, form a continuous, but not necessarily uniform, sandy layer on the surface of the tailings.

A key design feature for either option is the continuity of the sand channels to allow water to flow smoothly through the sand channel to the outlet.

There are also possible variations in the thickness of both sand channels and tailings layers within the structure.

The preferred option for a particular mine will depend on the hydraulic conductivity of the sand and fine tailings, as well as the area where the waste will be deposited.

The thickness of the sand in each channel will generally be greater than 0.05 meter and preferably greater than 0.5 meter to ensure sufficient drainage through the sand to the outlet and to prevent siltation of the sand channel. This thickness of the sand channel can be easily achieved within the amount of sand obtained in the coarse fraction enrichment process, and there is no upper limit on the thickness of the sand in the channel.

The depth of each layer of tailings will depend on the hydraulic conductivity of the tailings and the time available before adding the next layer of tailings. The rate of compaction is dependent on hydraulic conductivity and in most cases it determines the minimum acceptable time for tailings drainage before the next set of sand channels is added. This in turn sets the maximum rate of growth of the structure, which can operate without the need for a fully constructed containment dam wall.

Pressure from overlying tailings can cause water to flow into sand channels located above, below, or to the side of the tailings.

For typical copper ore tailings, the minimum distance from any point in the tailings to the nearest sand channel will typically be in the range of 1 to 4 meters. However, for tailings with finer particles for which rapid dewatering is desired, the thickness of the tailings layer may be reduced. Conversely, for tailings that dewater much more easily, the optimal thickness of the tailings layer can be increased, for example, to 10 meters or even more.

A typical structure proposed by the invention will be such that for most of the dewatering time the rate of water removal will be limited to its movement within the tailings layer rather than passing through the sand channels to the catch basin.

To ensure the continuity of sand channels, one possible alternative is to lay these sand channels in a sandwich structure bounded by a sand wall until

- 8 044795 shown schematically in Fig. 1. The multilayer sandwich structure shown in FIG. 1, contains tailings laid in layers 10, with sand placed in sand channels 12 located between the layers of tailings, with a bounding porous wall 14 of sand or waste rock. Water 16 flows through sand channels 12, then passes through a porous sand wall 14 and is collected in a catch basin 18. The tailings in the layer 10A located at the base of the structure are completely compacted, while the tailings in the layer 10B located at the top are saturated with water.

In the second option, a group of separate horizontal sand channels can be laid through the middle part of the tailings dump. This option is schematically illustrated in Fig. 2. As shown in FIG. 2A, tailings layers 10 are laid on top of porous sand layers 12, with air flow points 22 into the sand layers 12. As shown in FIG. 2B, the sand is laid in separate rows spaced several meters apart, resulting in the formation of individual channels 12 in the tailings layers 10. As shown in FIG. 2A, water 20 flows from the tailings layers 10 into the sand channels 12, and then, under the influence of gravity, a water flow G flows from the stacking end D to the water extraction end W of the multilayer structure.

The third option, shown in FIG. 3 involves the use of additional vertical drainage channels with capillary properties to connect sand channels or layers in three dimensions to promote faster transfer of water through the sand. As shown in FIG. 2A, tailings layers 10 are laid on top of porous sand channels 12, with air flow points 22 into the sand layers 12. As shown in FIG. 3B, the sand is laid in separate rows spaced several meters apart, resulting in the formation of separate channels 12 with vertical drainage channels 24 with capillary properties in the tailing layers 10. As shown in FIG. 2A, water 20 flows from the tailings layers 10 into the sand channels 12, and then, under the influence of gravity, a water flow G flows from the stacking end D to the water extraction end W of the multilayer structure. At the water extraction end D, a pump 26 is located to remove the water 20 from the multilayer structure. This three-dimensional structure is particularly useful for very large tailings pond areas or where the sand channels are thin and the time required for horizontal water flow through the sand channels to the catchment area may be excessive. Vertical drainage channels 24 facilitate the passage of water through the dump and through a plurality of sand channels 12 into a sand layer located at the base of the dump, which can then be dewatered.

For any possible geometric design, the effective filtration area for removing water from the tailings into the sand channels is large compared to any conceivable mechanical filtration method.

In other embodiments, laying sand channels on the tailings layer can be accomplished by various means.

Sand channels can be laid hydraulically, whereby the transport water ensures the sand is laid and then flows freely to the lowest point from which it can be discharged. The low hydraulic conductivity of the underlying tailings minimizes any impact of hydraulic placement on the total water content of the tailings in the partially dewatered underlying structure.

Placing outlet pipes or hydraulic sand throwers at strategic points throughout a large tailings pond and then advancing them allows the underlying tailings layer to be hydraulically covered at the angle of natural sand deposition. When the tailings sand beach is at the required thickness, the discharge pipe or hydraulic sand thrower is moved to form the next portion of the integrated sand channel network. The sand channels installed last provide the necessary ground stability for the equipment needed to move the outlet pipes or hydraulic sand thrower. Continuous placement of tailings may continue in other parts of the tailings surface such that the tailings will eventually be deposited on top of the sand channels.

The mentioned hydraulic sand throwers are available in the market. Sand with a particle size of 350 microns for p80 and a water content of about 40% can be discharged to lay sand channels over distances of about 50 meters.

In other embodiments, sand placement may be accomplished by mechanical means such as dump trucks and bulldozers, or by the use of mechanical sand throwers.

Once formed, the sand channels are covered with a layer of hydraulically laid tailings to minimize disruption of the sand channels during the early stages of tailings placement.

For any installation method, it is advisable to provide safe access to the surface of the most recently laid tailings layer to facilitate installation of sand channels.

To achieve this, the entire tailings area can be divided into compartments so that the tailings can be placed in the first compartment while the second compartment is drained of surface water to prepare it for mechanical sand placement. This drainage can be accelerated using equipment such as Amphirol (Refs. 7, 8). In the third compartment, sand is laid.

- 9 044795

In fig. 4 shows a schematic example. As shown in FIG. 4A, this embodiment uses three compartments P1, P2 and P3. In compartment P1, sand has been laid and shafts have been erected. In compartment P2, water drains and a stable surface of the tailings is prepared, and in compartment P3 the tailings 10 are laid. As shown in FIG. 4B, the structure includes tailings layers 10, porous sand channels 12 with air inflow points 22, and water 20 flowing out of the channels 12. As shown in FIG. 4A, compartment P3 discharges surface water 30, compartment P2 discharges surface water and channel water (32 in total), and compartment P1 discharges channel water 34. Once the laying or drainage cycle is completed in each compartment, the work can alternate one after another.

Another laying option is usually used in cases where the surface of the laid tailings is flooded with water. The sand is placed using a floating vehicle so that the sand falls in the overlying water onto the surface of the tailings to form sand channels. Once a continuous sand channel is formed up to the catchment area, the sand can be covered with another layer of tailings. Once placed, the tailings isolate the dam surface from water, and the submerged sand channel can be dewatered along with the underlying and overlying layers of tailings. Although this option does not achieve complete dewatering, it does increase the density of the underlying tailings under water.

In all applications, within stacked tailings and sand layers, the pore water from the tailings is effectively filtered at the tailings/sand layer interface so that the water is treated for reuse or disposal.

There may also be options in which the structure is used to solve additional problems beyond the basic tasks of extracting water in a sustainable form.

The tailings facility can use advanced information acquisition technologies, such as fiber optics and remote sensing from drones, to monitor the moisture content of the tailings facility in real time, resulting in a level of reliability regarding geotechnical integrity.

This improved control means that the waste storage area can also be used as a water buffer by regulating the rate at which water is purified from the catch basins.

In a second embodiment of this type, the invention can be used to fill mined-out areas or in cases where it is necessary to form a certain landscape for aesthetic or practical applications. Examples include incorporation into the natural landscape, or the formation of agricultural land, or the creation of recreational areas for use by local residents.

The invention can also be used to complement existing tailings management techniques or to ensure the stability of old tailings facilities. Critical locations of old tailings ponds are located adjacent to or within dam walls, where areas of water-unsaturated tailings can cause the dam wall to fail, releasing large quantities of contained tailings.

Excess sand from the coarse fraction upgrading process can be selectively placed in dewatering channels running through the old tailings pond, for example by drilling and filling wells with permeable sand. By dewatering these channels, the water content of tailings located close to the wall can be reduced.

If more extensive dewatering and compaction is required in an old tailings pond, a sand curtain of capillary action drainage channels located further from the dam wall can be duplicated in the third dimension.

For an existing tailings pond, the sand channels described in the present invention can simply be laid in dewatering channels located near the wall. In the case of a two-dimensional curtain of capillary-action sand drainage channels near the dam wall, water will flow from any water-saturated areas into a catchment area where it can be removed from the tailings impoundment. Thus, the present invention can provide dewatering of the most critical areas for the safety of a tailings dam, so that upstream dam construction methods can be safely applied.

As already indicated, the preferred process for upgrading the coarse particle fraction is coarse particle flotation (CPF).

During the flotation of large particles:

the ore is crushed in a grinding device;

the crushed ore is sorted in a screening device to obtain a screened fraction suitable for further grinding, a screened fraction suitable for coarse particle flotation and a screened fraction suitable for fine particle flotation;

the fraction suitable for coarse particle flotation is subjected to coarse particle flotation to obtain an intermediate concentrate and residual coarse sand;

residual coarse sand is used as a sand fraction for the formation

- 10,044,795 continuous channels passing through the tailings fraction;

the intermediate concentrate is crushed to particle sizes suitable for fine particle flotation;

the screened fraction suitable for fines flotation and the crushed intermediate fraction are then subjected to fines flotation to produce tailings containing fines, which are compacted and disposed of as already described.

Using this coarse fraction beneficiation process, high levels of recovery of the valuable ore component are maintained and residual sand is produced in sufficient quantities and of suitable particle sizes.

Advantages of the present invention

The advantages of the present invention can be assessed in comparison with filtration and dry storage, or with the traditional method of storing tailings in tailings ponds.

In warm and very dry climates, dry waste storage is accomplished by hydraulically laying thin layers (usually less than 30 cm) of unseparated waste from a high density thickener or paste thickener, allowing it to dry over a period of weeks by evaporation, after which the following are added: thin layer of waste. With this technology, the water does not return and the height of the structure is limited. When using the method of the present invention, the height of the multi-layer waste structure can be tens of meters high, more than 50 meters or more than 100 meters.

Another method of dry storage is to filter the waste to an acceptable water content level (usually about 15 wt.%) and then mechanically transport the solids to the storage area and place the partially dewatered waste. With this technology, most of the water is returned, but the capital costs are high, and the filtered waste may still be squeezed out if the evaporation rate is insufficient. For such filtered waste, flat land surfaces with a large area are required, or a dam must be built to contain the filtered waste.

Compared to any dry storage method, the present invention provides numerous advantages. These benefits include: low-cost hydraulic waste storage; return of most of the water; increased speed of growth of dump heights; the geotechnical stability required to construct a higher waste structure and a method that is less sensitive to changes in operating and climatic conditions.

Compared to traditional tailings ponds, the present invention also provides numerous advantages.

The first benefit is a reduction in total water consumption. Interstitial water contained in waste is the primary form of water loss in any mine. Depending on the evaporation losses, the water consumption of the waste using the present invention will be reduced by at least half, and most likely will be reduced to about 20% of the water losses in traditional tailings ponds. Particularly in regions where water is scarce, the present invention makes it possible to design and operate a mine with much less water consumption per unit of metal output.

The second advantage is the height of water-unsaturated waste present at any time during the storage process, which eliminates the possibility of wall destruction and catastrophic liquefaction of the contained mass of waste. This ability to produce water-saturated waste reduces the amount of land that would be disturbed in the future for waste disposal, and for some mines it is possible to locate the tailings pond much closer to the processing plant. There is also increased safety when using upstream limiting shafts.

The third benefit is the long-term sustainability of the tailings pond. The moisture content and drainage characteristics of the method of the present invention allow access and restoration of vegetation to the surface of the structure. The waste is drained sufficiently so that its characteristics are similar to those of other water-unsaturated soils around the mine. The sulfide content in the sand residues will be reduced during the enrichment process of the coarse particle fraction. At the end of a mine's life, any possibility of acidic mine water escaping can be prevented by shutting off the air flow into the sand channels in the tailings.

The fourth advantage is the possibility of backfilling mined-out areas. In this case, open-pit mining will allow for a consistent process of ore mining and storage of sand channels and layers of tailings in old or recently mined areas. In deep pit mining, it is possible to extract and return sand and tailings that have been stored separately to the mined-out pit at the end of the mine's life.

The fifth advantage is the ability to store tailings, and possibly tailings and sand, hydraulically without prior filtration and transportation and provide

- 11 044795 this tailings storage facility with efficient water conservation (water in the form of dry water). The capital and operating costs of hydraulic storage, which is possible with the present invention, are significantly lower than the costs of filtration and storage using conveyors or dump trucks.

The sixth advantage is the creation of valuable landscape elements while simultaneously storing mining waste while maintaining safety measures and preserving the environment. This may take the form of re-creating original vegetation, or creating agricultural or recreational areas, or simply creating more aesthetically pleasing landscape features.

The seventh advantage is the flexibility of choosing a waste storage site in the area adjacent to the processing plant, in contrast to traditional tailings ponds, for which it is necessary to find a suitable valley (basin) for waste storage. This eliminates the need for a costly waste containment wall, which must be designed to retain the liquefiable slurry indefinitely.

The eighth advantage is the use of part of the sand channels to store water for later use and, accordingly, to dampen seasonal climate changes or other changes in water access.

Experimental data

Experiments have been conducted to recover valuable ore components using a combination of coarse flotation and conventional flotation, such that sand fractions are obtained from coarse flotation and tailings fractions are obtained from conventional flotation for Chilean copper ore and for South African PGM metal ores.

For both ores, coarse fraction flotation tests were conducted at particle sizes for which overall metal recovery was comparable to that achieved by finer grinding and conventional flotation.

25% of the PGM metal ore was recovered from the sand fraction, and 35% of the copper ore was recovered in sand form.

The particle size distribution of the two fractions, as shown in the table below, illustrates the effective removal of fines from the sand component that is produced by flotation of the coarse fraction, resulting in both sand fractions having high permeability.

The interdependence of the sizes of the two fractions meets the Terzaghi filter criterion for coexistence as separate zones, without compromising the permeability of the sand by the penetration of excessive amounts of fine particles.

Particle sizes (in microns) for copper ore Particle sizes (in microns) for PGM ore Sand, р80 600 280 Sand, р10 150 120 Tails, p80 200 100 Tails, p!0 3 3 Permeability for copper ore (m/sec) Permeability for PGM ore (m/sec) Tails 4.4* ^10'z 7.2*10' ⁸

Compression, drainage settlement, compaction and head measurements were performed to characterize the sand components and tailings of both ores.

The effect of copper ore tailings porosity on permeability determined from these measurements is shown in FIG. 5.

Simulations of the measured results were performed to calculate the maximum thickness of the tailings layer that could be laid while maintaining an acceptable compaction time for dry laying the structure hydraulically.

This modeling shows that 90% compaction should occur within 3 months, for a 3 meter thick layer of copper ore tailings and a 10 meter thick layer of PGM metal ore tailings.

Continuous dewatering will reduce the water saturation of the sand and tailings, turning the structure into a geotechnically stable soil.

Experimental verification was also carried out for the 3D structure at an enlarged scale to validate the laboratory simulation.

Three layers of 0.35 m thick tailings and 2 layers of 0.2 m thick sand from PGM metal ore processing waste were placed in a plexiglass square tank with an area of 1 m ² and allowed water to flow out from 4 outlets located at each edge of each sand layer. Compaction rates, pore pressures, water contents, and water outflow rates were measured to validate the simulation results at a slightly larger scale.

This experiment demonstrated, on a larger scale, the possibility of retaining tails

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Claims (30)

in certain areas during the installation process. This experiment also demonstrated the release of water from the adjacent tailings into the sand layer, as well as its movement towards the water outlets to achieve compaction rates consistent with the above model. The water removed from the sand layer did not contain sediment. Links 1. Proceedings of the conference on tailings and mine waste, Vancouver, British Columbia, 2015, October 26-28. 2.WO2018/234880 3.WO2017/195008 4. US3767050A 5. ICOLD (International Committee on Large Dams), 121 (2001), Tailings Dams, Risk of Hazardous Incidents ((Part 2, p. 17 - The closed drainage filtration system is a critical asset that has often been overlooked in the past, resulting which resulted in very dangerous groundwater levels within the tailings dam. As is well known, the outer slopes of a tailings dam are very sensitive to groundwater levels. Capillary rise of water above the measured groundwater level position can result in tailings in this area being wetted to levels close to full saturation. This condition can lead to unexpectedly large rises in groundwater levels even from small rains.) 6. US 9188389 B2. The contents of the above referenced materials are incorporated by reference into this application. CLAIM 1. A method for extracting water from waste after grinding and processing of ores, including the following stages: separation of processing waste into a permeable sand fraction and a tailings fraction; laying sand fractions hydraulically or mechanically to form sand channels; and covering the sand channels with hydraulically laid tailings fractions such that the tailings fractions and sand fractions form a multi-layer structure defined by at least one bounding wall, with the sand fraction forming continuous sand channels passing through tailings fraction, characterized in that water outlets are formed at the edge of said channels, while air inflow points are provided for the sand channels, either by forming inflow points at the end of the laying of the structure, or by any other means of connection with air, allowing air to enter to facilitate the flow water in canals under the influence of gravity; allow the water contained in the tailings and sand to flow under the influence of gravity in a horizontal direction through the sand channels to the water outlets; and extract water from the water outlets. 2. The method according to claim 1, in which the sand fraction contains sand particles whose dimensions for p80 exceed 150 microns, or exceed 300 microns, or exceed 400 microns. 3. The method according to claim 1, in which the sand fraction is freely drained. 4. The method according to claim 3, in which water flows out of the sand fraction under the influence of gravity to form water-unsaturated sand that contains water in an amount of less than 15 wt.%. 5. The method according to claim 1, in which the tailings fraction contains particles whose size for p80 is less than 200 microns or less than 150 microns. 6. The method according to claim 1, in which the tailings fraction contains water in an amount from 30 to 70 wt.%. 7. The method according to claim 1, in which the tailings fraction is treated with chemical additives before placement to form a layer of more permeable tailings or change the angle of natural deposition. 8. The method according to claim 1, wherein at least 50% of the sand residues contain particles whose sizes are in the range from 0.1 to 1 mm, or at least 70% of the sand residues contain particles whose sizes are in the range from 0.1 to 1 mm, or at least 90% of sand residues contain particles whose sizes range from 0.1 to 1 mm. 9. The method of claim 1, wherein the sand residue contains less than 25% of material with particle sizes less than 0.75 mm, or the sand residue contains less than 15% of material with particle sizes less than 0.75 mm, or the sand residue contains less than 10% material with particle sizes less than 0.75 mm. 10. The method according to claim 1, wherein at the water extraction end of said structure, a limiting wall is provided which is permeable to water, and water flows out from the wall through the outlet holes. 11. The method according to claim 1, wherein at the water extraction end of said structure there is a limiting wall that is not permeable to water, and water is removed from the structure by pumping out - 13 044795 from the central water outlet within the specified structure. 12. The method according to claim 1, in which the sand channels are placed so that the maximum distance from any point in the tailings to the nearest sand channel is less than 10 meters, or the sand channels are placed so that the maximum distance from any point in the tailings to the nearest sand channel was less than 3 meters, or sand channels are placed so that the maximum distance from any point in the tailings to the nearest sand channel is less than 2 meters. 13. The method of claim 1, wherein the sand channels are connected vertically and horizontally to form a three-dimensional matrix of permeable channels within the tailings. 14. The method of claim 1, wherein the tailings fraction is hydraulically placed to provide a deposition angle in the range of about 0.5 to 2%, or the tailings fraction is hydraulically placed to provide a deposition angle in the range of about 0.5 to 1%, or The tailings fraction is placed hydraulically to provide a deposition angle of approximately 0.5%. 15. The method according to claim 1, in which the sand fractions and tailings fractions are laid sequentially in layers to form layers of tailings with a thickness of 1 to 10 meters and sand channels with an average thickness of 0.05 to 2 meters. 16. The method according to claim 1, in which the sand channels have a thickness of from 0.05 to 2 meters, or from 0.2 to 1 meter, or from 0.3 to 0.7 meters. 17. The method according to claim 1, in which the sand fractions are laid in separate rows spaced apart in space and the tailings fractions are laid sequentially in layers to form tailings layers having a thickness of 1 to 10 meters, and sand channels having a thickness of 0.05 to 2 meters and spaced in space at a distance of 2 to 10 meters, or to form layers of tailings having a thickness of 1 to 10 meters, and sand channels having a thickness of 0.05 to 1 meter and spaced in space at a distance of 2 to 5 meters . 18. The method according to claim 1, in which the sand is placed so as to form vertical drainage channels with capillary properties in the tailings layers between the upper and lower sand channels. 19. The method of claim 1, wherein sand is used to form internal and external sand banks, which are separated to form separate compartments, then each compartment is filled by hydraulically stacking the tailings to an appropriate height, and the water can be diverted into underlying sand channels and flow out through permeable sand banks into the drainage basin. 20. The method according to claim 19, wherein at any given time during the layering process, only the top three layers of the tailings are saturated with water. 21. The method according to claim 19, wherein at any given time during the layering process, only the top two layers of the tailings are saturated with water. 22. The method according to claim 19, in which at any time during the laying of the layers only the top layer of the tailings is saturated with water. 23. The method according to claim 1, wherein the sand is obtained from a coarse fraction beneficiation process, and the tailings are obtained from a conventional ore flotation process, and the coarse fraction beneficiation process includes coarse particle flotation, screening, gravity separation, electrostatic separation and magnetic separation. 24. The method of claim 1, wherein the sand is produced by a sand dump leaching process and the tailings are produced by a conventional stir leaching process. 25. A system for extracting water from waste after grinding and processing of ores, containing: a multilayer structure defined by a boundary wall, the multilayer structure comprising tailings fractions and sand fractions forming continuous channels through the tailings fractions; water outlets located on the edge of the mentioned channels; and air supply points on the sand channels, either at the end of the laying structure or by other means of connection with air, allowing air to flow to assist the flow of water in the channels under the influence of gravity and allowing water contained in the tailings and sand to flow, in a horizontal direction under the influence of gravity through sand channels to water outlets. 26. The system according to claim 25, in which the sand fraction contains sand particles whose size for p80 exceeds 150 microns, or exceeds 300 microns, or exceeds 400 microns. 27. The system according to claim 25, in which the sand fraction is freely drained. 28. The system according to claim 25, in which the tailings fraction contains particles whose size for p80 is less than 200 microns or less than 150 microns. 29. The system of claim 25, wherein at least 50% of the sand residue contains particles whose size ranges from 0.1 to 1 mm, or at least 70% of the sand residue contains particles whose size ranges from 0.1 to 1 mm, or at least 90% of sand residues contain particles whose sizes range from 0.1 to 1 mm. 30. The system of claim 25, wherein the sand residue contains less than 25% material with particle sizes less than 0.75 mm, or the sand residue contains less than 15% material with particle sizes less than -