Arrangement and method for stacking

Abstract

The invention relates to a method for treating tailings. In the method, a tailings slurry comprising tailings and water, formed as a side stream to a concentration process of a mine, is treated, at least one binder is added to the tailings to form hardenable tailings, In the method, the hardenable tailings are used for stabilization of a pond in the mine area, and / or for stabilization of soil in the mine area and / or to at least partially cover a pond in the mine area and / or the tailings and the binder are mixed in a mixer of a paste plant and the hardenable tailings are selectively conveyed for use in paste backfill and dry stacking.

Description

[0001] Arrangement and method for stacking

[0002] Background of the invention

[0003] The invention relates to a new arrangement for the treatment of tailings in a mine area .

[0004] Further, the invention relates to a method for treating tailings in a mine area and utili zation of the tailings outside the mine area .

[0005] The subj ect matter of the invention is described in more detail in preambles of independent claims of the application .

[0006] In mining industry, a large amount of gangue is always extracted with the valuable component in connection with the mining of ore . The ore is crushed and comminuted before a concentration process in which the valuable minerals are processed out of the comminuted rock material . Large amounts of tailings , the remaining fine-grained gangue , are thus formed as a side stream to the concentration process . A large quantity o f water is typically used in the concentration process , whereby the material leaving the process is a tailings slurry formed by the water and the tailings . In the mine area there is a tailings stacking area where the tailings slurry is pumped and stacked in huge tailings ponds . This type of wet stacking of the tail ings is in many ways di f ficult and comprises many risks such as dust problems during a dry period, a risk of dam collapses , and leakage of the harmful mine water into the environment and groundwater . Also the traditional non-stabili zed dry stacking includes risks of the tailings being carried in the form of dust into the environment and the harmful substances being dissolved and ending up in groundwaters and / or water systems in the environment . Brief description of the invention

[0007] The idea of the invention is to provide a new and improved arrangement and method for the treatment of tailings of a mine .

[0008] The characteristic features of the arrangement according to the invention are presented in the characteri zing part of the independent device claim .

[0009] The characteristic features of the method according to the invention are presented in the characteri zing part of the independent method claim .

[0010] The idea of the proposed solution is that tail ings formed in a mine area are di sposed of safely in the mine area or placed and / or utili zed outside the mine area .

[0011] In the arrangement , a binder is mixed with the tailings to be disposed of , whereby the tailings produced as a side stream of a concentration plant in the mine area may be disposed of as a hardened structure or material in the mine area or used outside the mine area . The hardened material for disposal is solid and non- fluid material , whereby its treatment and storage is signi ficantly easier and safer than with a liquid or other fluid material .

[0012] Before adding a binder, a tailings slurry formed in a concentration process of the mine is solidi fied for example in a thickener, a filter device or other corresponding solidi fier that removes excess water . One or more binders are mixed into the tail ings fraction having a higher solid matter content and still being filtration-moist to form a hardenable mixture . Finally, the hardenable mixture is disposed of at a stacking site , where it forms a hardenable structure . Alternatively, the hardenable tai lings are used to form and stabili ze di f ferent kinds of structures in the mine area or outside the mine . I f extraction in the mine is carried out as underground mining, the corresponding method and apparatus may be used in cemented paste backfill . The advantage of the proposed solution is that tailings can be hardened simply and cost-ef fectively in the manner described in this document .

[0013] A further advantage is that the hardened materials may be disposed of in heaps and clamps . The use of these types of above-ground storages and disposal sites is signi ficantly more advantageous than placing tailings in slurry form in ponds .

[0014] When the number and si ze of di f ferent types of ponds may be reduced in the operated area, signi ficant space and cost savings will also be achieved .

[0015] Further, the storage , treatment and disposal of solid and hardened tailings is signi ficantly safer than the storage of tailings in slurry form in a pond . Hazards of overflowing caused by rain waters and breaking of the pond structures may be reduced in the storage and disposal of a solid material .

[0016] In traditional dry stacking, tai lings are dried to a solid state and stacked into clamps . Problems of the above-mentioned method are high investment and operating costs , dust issues with the clamps , high contents of harmful substances in seepage waters flowing through the clamps , and potential reslurrying of the material .

[0017] The idea of one embodiment is that tailings are conveyed from a processing plant to a tailings thickener, where they are dewatered . The treated tailings comprising higher solids are trans ferred to a mixer, where a binder is fed into the mass . The mixer and the binder feeding device may al so be cal led a paste plant from which the hardenable tailings may be conveyed in paste form to dry stacking ( SDS ) and paste backfill (U / G CPB ) . The same paste plant comprising the mixer and binder feeding may thus be used for the needs of two di f ferent applications . The idea of one embodiment is that water is removed from the tailings slurry by one or more thickener and / or filtering apparatuses , whereby the solid matter content of the tailings may be increased . Di f ferent types of solid - liquid separation apparatuses such as , for example , belt filter , belt f ilter press and disc filter are suitable for this purpose .

[0018] The idea of one embodiment is that the binder or a mixture thereof binds water and creates a colloidal viscous pore fluid, changing the viscosity of the tailings and permitting the tailings to be dry stacked at a pumpable moisture content . Binder reactions in the stabili zation harden the tailings in the stacking area .

[0019] The idea of one embodiment is that i f extraction in the mine is carried out as underground mining, the corresponding method and the same or corresponding apparatus may also be used alternately in cemented paste backfill .

[0020] Binder

[0021] The idea of one embodiment is that tailings comprising pyrite or other sulphidic sulphuric acid producing minerals are treated, whereby the binder may be for example alkali- and magnesium and calcium- as well as silicon- , aluminium-containing binders , such as aluminium refining aluminium or alkali aluminate precipitates , red mud, converter slags , sewage sludge incineration ash, di f ferent types of steel slags , blast furnace slag, coal ash, green liquor dregs , bioash or other alkali-activatable binders acting as geopolymer precursors . Portland cement , Portlandbased cements or mixtures thereof or di f ferent kinds o f aluminate cements may also be used as the binder or part of the binder .

[0022] The idea of one embodiment is that tailings comprising quartz and feldspar containing minerals are treated, whereby the binder may be for example alkali- and magnesium and calcium- as well as silicon- , aluminium-containing binders , such as aluminium refining aluminium or alkali aluminate precipitates , red mud, converter slags , sewage sludge incineration ash, di f ferent types of steel slags , blast furnace slag, coal ash, green liquor dregs , bioash or other alkali-activatable binders acting as geopolymer precursors . Portland cement , Portland-based cements or mixtures thereof or di fferent kinds of aluminate cements may also be used as the binder or part of the binder .

[0023] The idea of one embodiment is that tailings comprising alkaline earth metals , calcium and magnesium containing mica spar minerals or other silicate minerals activatable by acid and / or al kali treatments are treated . In this case acids , for example carbonic acid, act as the activator, or alkalis and tailings act as part of the binder . In this case the binder or supplementary binder may be for example alkali- and magnesium and calcium- as well as silicon- , aluminium-containing binders , such as aluminium refining aluminium or alkali aluminate precipitates , converter slags , red mud, sewage sludge incineration ash, di f ferent types of steel slags , blast furnace slag, coal ash, green liquor dregs , bioash or other alkali-activatable binders acting as geopolymer precursors . Portland cement , Portland-based cements or mixtures thereof or di f ferent kinds of aluminate cements may also be used as the binder or part of the binder .

[0024] The idea of one embodiment is that the binder properties of the tailings themselves are utili zed .

[0025] The idea of one embodiment is that the binder is alkali-activatable material .

[0026] The idea of one embodiment is that the binder is geopolymer material .

[0027] The idea of one embodiment is that the binder is poz zolanic material .

[0028] The idea of one embodiment is that the binder is made of one or more industrial side-stream materials . The idea of one embodiment is that the binder is made of one or more side-stream materials present in the mine area .

[0029] The idea o f one embodiment is that the binder comprises at least one type of ash .

[0030] The idea o f one embodiment is that the binder comprises at least one type of slag, such as for example blast furnace slag formed in the steel industry .

[0031] The idea o f one embodiment is that the binder comprises at least one activator .

[0032] Mixing and trans fer

[0033] The idea of one embodiment is that the binder is added at a paste plant o f the mine into the tailings . The paste plant is a type of tailings treatment plant , where the addition and mixing of the binder may be carried out . The hardenable tailings produced at the paste plant may be carried to the site of utili zation, where they may be used for soil stabili zation, stabili zation of ponds , dry stacking and paste backfill or other disposal site .

[0034] According to one embodiment , the tailings are transferred to the stacking area by pumping through a discharge pipe . During trans fer , the hardenable binder is mixed with the tailings , whereby the tai lings will harden at the di sposal site .

[0035] According to one embodiment , the trans ferring device is a conveyor, belt conveyor, slat conveyor, screw conveyor, or some other corresponding continuously-operated mechanical conveyor .

[0036] According to one embodiment , the trans ferring device is alternatively a vehicle or a mobile work machine that comprises a carrying space for conveying a filtered tailings fraction batch to a di sposal site . During conveying, the binder may be mixed into the batch, whereby hardening can start already during conveying or immediately thereafter, when the batch is unloaded from the carrying space to the disposal site . Alternatively, the binder may be already mixed beforehand in a separate mixer or at the paste plant before starting conveying .

[0037] According to one embodiment , fibres may be added to the hardened tailings to increase the tensile strength and prevent layer cracking .

[0038] Applications

[0039] The idea of one embodiment is that the hardenable tailings are used as a building material of a construction in the mine area, whereby the construction formed is at the same time a waste material disposal site .

[0040] The idea of one embodiment is that the hardenable tailings are used as a building material of a construction outside the mine area, whereby the construction formed is at the same time a waste material disposal site .

[0041] The idea of one embodiment is that an upwardly rising rigid and independent construction is formed of the hardenable tailings .

[0042] According to one embodiment , the above-mentioned construction is one of the following : heap, clamp, elevation, hill , arti ficial rock, bank, protective embankment , wall , dam structure or a corresponding stable and sel f- supporting construction .

[0043] According to one embodiment , the construction is founded directly on a flat field . Thus , the construction does not necessarily need to be formed in a space surrounded by any protective structure , such as for example a protective pond .

[0044] According to one embodiment , the construction comprises surfaces having an angle of repose , i . e . a slope angle , greater than 2 . 5 % .

[0045] According to one embodiment , the construction comprises vertical surfaces or surfaces having a steep angle of inclination . According to one embodiment, a height difference between a highest point of the construction and a surface surrounding the construction is at least 10 m.

[0046] According to one embodiment, the construction is cast from the hardenable waste material by mould casting, slip casting or 3-D casting.

[0047] According to one embodiment, an artificial rock or boulders which are crushed are cast from the hardenable tailings, and a construction as required is assembled from the crushed material by earth-moving methods and equipment.

[0048] According to one embodiment, infrastructure to be used in basic production of the mine is built from the hardenable tailings.

[0049] According to one embodiment, the hardenable tailings are stacked into an upwardly rising heap. Stabilization of the heap is thus carried out continuously during stacking, i.e. stabilization of the heap is continuous. The entire heap is thus made of the hardenable tailings. In this case, a separate final stabilization of the heap is not necessarily needed. The advantage of continuous stabilization is that it minimizes the open time of the heap during which the outermost surface is exposed to rain, moisture and wind.

[0050] When the heap is stacked of the hardenable tailings, it may be stacked higher than a heap stacked of a non- hardenable material. Due to higher heaps, less land area is needed to store the same volume. The reduced need of space simplifies the space utilization in the mine area and may also reduce costs.

[0051] According to one embodiment, the hardenable tailings are stacked into an upwardly rising heap. When the heap has reached the designed height and size, it may be covered with yet one or more shell layers. In this embodiment, a further final stabilization is thus carried out in addition to continuous stabilization. The shell layer is also made of the hardenable tailings, but its properties may differ from the properties of the stacked hardenable tailings , at least in terms of compressive strength . Further, additives may be added to the hardenable tailings o f the shell layer such that its properties , for example according to water transmission, solubility, dust binding, scaling resistance , colour and other desired properties , may be adj usted . In case there are several shell or structural layers one on top of the other, the properties of each of them may be adj usted to best suit di f ferent purposes .

[0052] According to one embodiment , a base structure or a structural layer of the base structure may be formed in the disposal area by the method with the hardenable tailings , such that the structure has suf ficient strength and suf ficiently low water permeability considering environmental requirements of the waste area or the disposal site .

[0053] According to one embodiment , a heap stacked from the hardenable tailings may be finally stabili zed in part already during stacking . In this case , the amount of the binder, the binder to be used and the possible addition of additives may be adj usted in the middle of stacking in such a way that a shell layer as desired can be formed at selected points of the heap . The above-mentioned stabili zed tailings and the shell layer formed therefrom act as a final or temporary surface and protective structure of the stacking area or the disposal area .

[0054] According to one embodiment , an existing heap stacked from non-hardenable tailings may be f inally stabili zed with a surface layer formed of the hardenable tailings . This way, the existing tailings heaps may be treated to make them more environmentally friendly, as dusting and dissolution may be reduced . Further, safety of the stacking area may be improved, as collapses may be prevented by means of the stabili zed surface layer .

[0055] According to one embodiment , the hardenable tailings may be used to stabili ze and cover a gangue heap with a shel l layer . The above-mentioned stabili zed tailings and the shell layer formed therefrom act as a final or temporary surface and protective structure of the stacking area or the disposal area .

[0056] According to one embodiment , fibres that are detrimental to health and the environment or other hazardous waste may be encapsulated by the method by forming a leakproof stabili zed capsule having a base and surface structure of the hardenable tailings .

[0057] According to one embodiment , a tailings slurry in an existing stacking pond is stabili zed with the hardenable tailings . The stabili zation may be applied selectively to critical or otherwise selected points of the pond . Further, the stabili zation may be applied to selected depths . By means of the stabilization, properties and behaviour of the pond and the tailings slurry therein may be controlled . Further, the stabili zation may be applied to a portion where protective embankments delimiting an edge of the pond or other structures have weakened or are at risk of weakening, such that the formation o f larger damages may be prevented and the risk of leakage reduced . It is also possible to stabili ze all edge areas of the pond with the hardenable tailings and thus ensure in advance already that dam structures of the pond will not collapse under any circumstances .

[0058] According to one embodiment , a tailings slurry of an existing stacking pond is stabili zed with the hardenable tailings . In this solution, the pond becomes a disposal site for the tailings . After the treatment , the pond comprises hard solid material instead of flowing material . This may substantially reduce environmental risks of the pond .

[0059] According to one embodiment , a cover or a protective layer i s formed of the hardenable tail ings for an existing tailings slurry stacking pond . This way, the ef fect of rainwaters and other natural phenomena on the pond may be prevented .

[0060] According to one embodiment , one or more bed-type layers or raised portions are formed in a central part of the stacking pond from the hardenable tailings . Thereby, accumulation of percolated fluid into the central part of the pond and the formation of puddles may be prevented . Elevation of the central part thus forms a kind of inclination by which the possible percolated fluid and rainwater can be directed in a controlled manner to edges of the pond, where it may be recovered and properly treated .

[0061] According to one embodiment , one or more sti f feners , such as for example rebars , meshes , rods , ropes , fibres , etc . , are arranged in the construction .

[0062] According to one embodiment , the construction formed from the hardened tailings is used as a foundation of an energy production apparatus . The construction may act as a base of for example a solar electricity plant or a wind power plant .

[0063] The idea of one embodiment is that the hardenable tailings are used as an earthworks material in the mine area .

[0064] According to one embodiment , the hardenable tailings are used as a mine road or field surfacing material . The hardenable tailings may act , for instance , as a substitute for asphalt or a surface layer formed from compacted natural stone aggregate . This substituting surface material may also be used outside the mine area, for example in maintenance , renovation and building of roads leading to the mine area and other roads in the nearby area .

[0065] According to one embodiment , the hardenable tailings are used in structural layers underneath the surface of a mine road or field . The structural layers may be frost- protected and protected from run-of f waters . This substituting material may also be used in road structures outside the mine area, for example in maintenance , renovation and building of roads leading to the mine area and other roads in the nearby area .

[0066] According to one embodiment , the hardenable tailings are used in the mine area for soil stabili zation . According to one embodiment , the tailings stacking or disposal area may be put to any construction use , for example as a residential area, by hardening the stacked tailings to a suf ficient strength .

[0067] According to one embodiment , the hardenable tailings are used for filling mineshafts , tunnels , open-pit mines or other spaces formed during removal of rock material with the hardenable tailings either entirely or at least partly .

[0068] According to one embodiment , the hardenable tailings described in this document may be utili zed in so-cal led paste backfill in which a filling material is placed into disused mine galleries , shafts or passages or spaces required for the mining method to strengthen their structure . I f necessary, the processing and strengthening properties of a mixture thus produced may be adj usted by further adding yet one or more additives to the mixture formed by the tailings and the binder . Paste backfill may also be used in situations where rock adj acent to a site to be mined next needs to be strengthened before starting the mining .

[0069] The method in said paste backfill may be combination filling utili zing both of mined gangue and the hardenable tailings .

[0070] Use of the hardenable tailings described in this application as the paste backfil l material is advantageous because the hardening may be very quick . Thus , long waiting times are avoided and mining may be continued next to the filled cavity or space only after a short interruption . A further advantage is that a material formed in the mine area from the mine ' s own process may be used as the binder and it is not necessarily required to bring in any external components for production of a backfill paste . Thi s is logistically very ef ficient .

[0071] According to one embodiment , the hardenable tailings are cast inside a lightweight formwork structure , such as for example inside a geotube . Thereby the geotube or a corresponding membrane structure can keep the cast hardenable tailings stable until the quickly-hardening material reaches a suf ficient mechanical durability .

[0072] According to one embodiment , a structure or material reserved for later closure and covering of the mine area is cast from the hardenable tailings . This type of solid material may be temporarily stored in a suitable place close to a site that is to be landscaped later . When the time of covering comes , a covering layer may be formed from this temporarily stored material for example over slurry or tailings ponds , gangue heaps , tailings heaps and other by-product storages and disposal sites in the mine area . Because the covering material is solid and has mechanical strength, it may also be used to easily form desired surface shapes in connection with landscaping . The material may be for example crushed material having a desired size, by means of which ditches and inclined surfaces as desired may be shaped in the covering layer to manage surface and rain waters . In addition to said covering material , for the covering it may be necessary to form layers slowing down the flow of water and insulating against frost over the site to be covered .

[0073] Properties

[0074] According to one embodiment , the hardenable tailings described in this document are insoluble or substantially insoluble in water . The hardened material also binds well possible heavy metals and other harmful substances present in the starting materials and thus reduces their dissolution and migration into the environment .

[0075] According to one embodiment , the hardenable tailings described in this document have a compressive strength of at least 0 . 05 Mpa .

[0076] According to one embodiment , the hardenable tailings described in this document have a compressive strength of at least 1 Mpa . According to one embodiment , the hardenable material described in this document or a material or structure hardened by means thereof have a compressive strength of at least 2 Mpa .

[0077] According to one embodiment , the hardenable material described in this document or a material or structure hardened by means thereof have a compressive strength of at least 3 Mpa .

[0078] According to one embodiment , the hardenable material described in this document or a material or structure hardened by means thereof have a compressive strength of at least 4 Mpa .

[0079] According to one embodiment , the hardenable material described in this document or a material or structure hardened by means thereof have a compressive strength of at least 5 Mpa .

[0080] According to one embodiment , the hardenable material described in this document or a material or structure hardened by means thereof have a compressive strength of at least 10 Mpa .

[0081] According to one embodiment , the hardenable material described in this document or a material or structure hardened by means thereof have a compressive strength of at least 40 Mpa .

[0082] Increasing the dry matter content

[0083] The idea of one embodiment is that the dry matter content of a tailings slurry is increased before adding the binder . This way, water or other fluid in the tail ings slurry can be separated and recovered . The recovered water may be circulated back for use in the concentration process . Further, the hardening of thickened or filtered tailings i s quicker and the amount of binder needed may be lower when there is only a small amount of water in the tailings . Moreover, the treatment of f iltered and less fluid tail ings is substantially easier than that of a tailings slurry . The following techniques and equipment, and combinations thereof, may be used for increasing the dry matter content and remove water in the tailings slurry:

[0084] - Mechanical dewatering or drying, for example by centrifuging, to remove water from solid matter by means of the centrifugal force.

[0085] - Mechanical separation of water, wherein free water is removed by vibrating, pressing or compacting .

[0086] - Equipment for mechanical dewatering include the above-mentioned centrifuge and screw press, belt filter press.

[0087] - Drying may also be carried out by the following equipment: wire-type filter (belt filter) , vibrating sieve, gravitational filter, pressure filter, centrifugal filter (spinning filter) , reverse osmosis filter, membrane filter, pressure filter, vacuum dryer or some combination thereof.

[0088] - Dewatering by filtration using filter cloths or strainers of filter equipment. Filter equipment encompasses belt filters, disc filters, drum filters pan filters and filter equipment used in the paper and mining industry. The filter equipment utilizes pressure difference, typically vacuum.

[0089] - Drying may also be carried out by means of geotubes or geobags. In this case, a material to be treated is arranged inside the tube or the bag and fluid is gradually removed and the solid matter remains inside.

[0090] - Separation of water may also be carried out by means of ultrasound. Water and solid matter can be separated by applying ultrasound to a slurry or precipitate. Increasing the solid matter content by some acoustic technique . For example an acoustic resonance tank or a belt filter based on acoustic filtration may be considered . Acoustic resonance may also be utili zed below ultrasonic frequencies .

[0091] - Dewatering may also be carried out by means of flocculants or other chemicals that bind particles from water into more easily separatable agglomerates for example in a thickener .

[0092] The embodiments described above and their features may be combined to provide desired solutions .

Claims

Claims1. A method for treating tailings, in which method: a tailings slurry comprising tailings and water, formed as a side stream to a concentration process of a mine, is treated, at least one binder is added to the tailings to form hardenable tailings char ac t e r i z e d in that the hardenable tailings are used for stabilization of a pond in the mine area, and / or for stabilization of soil in the mine area and / or to at least partially cover a pond in the mine area and / or the tailings and the binder are mixed in a mixer of a paste plant and the hardenable tailings are selectively conveyed for use in paste backfill and dry stacking.

2. The method according to claim 1, c h a r a c t e r i z e d in that the hardenable tailings are stacked at a stacking site into a heap.

3. The method according to claim 1, c h a r a c t e r i z e d in that the hardenable tailings are used for paste backfill.

4. The method according to claim 1, c h a r a c - t e r i z e d in that the hardenable tailings are used to at least partially cover a heap in the mine area.

5. The method according to claim 1, c h a r a c t e r i z e d in that the hardenable tailings are used to build infrastructure .

6. An arrangement for treating tailings of a mine according to the method of claim 1-5, char ac t e r i z e d in that the arrangement comprises : at least one water separating device for treating a tailings slurry and raising the solid matter content by removing fluid; at least one transferring device for transferring the separated tailings to a site of utilization; and at least one feeding device for adding at least one binder to the tailings, whereby the binder and the tailings are arranged to form a hardenable mixture.

7. The arrangement according to claim 6, c h a r a c t e r i z e d in that the feeding device for feeding the binder is arranged in connection with the transferring device.

8. The arrangement according to claim 6, c h a r a c t e r i z e d in that the feeding device for feeding the binder is arranged in a separate paste plant comprising a mixer.

9. The arrangement according to any preceding claim 6 - 8, c h a r a c t e r i z e d in that the transferring device comprises at least one conveyor .

10. The arrangement according to any preceding claim6 8, c h a r a c t e r i z e d in thatthe transferring device comprises a high-pressure pump and at least one transferring pipe.

11. The arrangement according to any preceding claim 6 - 10, c h a r a c t e r i z e d in that the water separating device is a thickener.

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