Backfill material

Abstract

A backfill material for mining and tunneling applications comprising: a) tailings, b) a binder component, c) water, and d) at least one dispersant selected from the group consisting of polycarboxylic acid ethers and polycarboxylic acids. The binder component comprises a binder based on Portland cement clinker and calcined clay. The backfill material has a reduced carbon footprint by partially replacing a binder based on Portland cement clinker with calcined clay. The yield point of the material and the compressive strength of the formed backfill material are not compromised.

Description

[0001] The present invention relates to a backfill material that can be used in various mining and tunneling applications.

[0002] Backfill material is used to fill excavation pits in mining, such as in "cut and fill" mining, typically steeply inclined ore bodies or wide horizontal bodies, where the fill serves as a means of creating floor support and sidewall support. For example, a narrow excavation extending longitudinally along the impact of the ore body is driven upward or downward after the deposit. To provide support for the hanging walls, pillars are left in place. Later, the spaces between adjacent pillars can be filled with backfill to support the roof, allowing the pillars to be removed to extract the ore within.

[0003] The mined portion of a stope is typically backfilled with an aqueous slurry of tailings from the crushing and processing of the mineral ore, which is pumped into the stope. Tailings can be, for example, reduction plant tailings, mill tailings, and coal dust tailings. Tailings are typically made up of fine particles less than 150 microns, with the majority being less than 75 microns.

[0004] Typically, the slurry is pumped to a distance of several kilometers from the location where it was prepared. In order to make the slurry pumpable, a high proportion of water and / or plasticizer must be added to plasticize the solids of the slurry.

[0005] It has been proposed to add ordinary Portland cement to the slurry to improve the compression resistance of the backfill and provide improved strength.

[0006] WO 2022 / 117528 A1 relates to a method for producing a backfill paste for underground operations, the method comprising or consisting essentially of mixing a) cement, b) tailings from an underground operation, c) optionally additional water, d) at least one polycarboxylate ether, and e) calcium hydroxide. The invention also relates to a method for controlling the flow of a backfill paste for underground operations.

[0007] Portland cement is primarily made from certain clay minerals, limestone, and gypsum in a high-temperature process that drives off carbon dioxide and chemically combines the main ingredients into new compounds. Because carbon dioxide is produced both by the cement production process itself and by the energy plants that generate electricity to run the process, cement production is currently the leading source of carbon dioxide emissions to the atmosphere.

[0008] As global warming and ocean acidification become increasingly problematic, and the desire to reduce carbon dioxide gas emissions (the primary cause of global warming) continues, the cement production industry will come under increased scrutiny. Furthermore, cement plants generate other pollutants such as NOx, SOx, VOCs, particulates, and mercury. Cement plants also produce cement kiln dust, which sometimes must be landfilled, typically in hazardous materials landfills.

[0009] It would be desirable to provide backfill materials with a reduced carbon footprint without compromising key properties.

[0010] However, replacing part of the ordinary Portland cement and the uncontrolled nature of tailings mean that it is difficult to predict the behavior of the backfill material. Solutions that work reliably in other areas of technology may not necessarily produce the desired results in backfill operations.

[0011] It is an object of the present invention to provide a backfill material having a reduced carbon footprint without compromising key properties such as yield strength (so that the backfill material can also be pumped over long distances) and, for example, the strength of the formed backfill.

[0012] Therefore, the present invention provides a backfill material comprising a binder component, tailings and a dispersant, which ensures sufficient workability and open time.

[0013] The above problems are solved by a backfill material comprising: a. tailings; b. a binder component, c. water, d. and at least one dispersant selected from polycarboxylate ethers and polycarboxylic acids, wherein the binder component comprises a binder based on Portland cement clinker and calcined clay.

[0014] The term backfill refers to a reinforcing material that can be used in underground operations to fill any voids and has a flowable or pumpable consistency under standard conditions. Voids can originate from the excavation process in underground operations, or they can occur naturally, such as caves. Backfill is a settable material that hardens over time to form a solid material that provides resistance to compression. In particular, hardening of the backfill occurs through the hydration mechanism of the binder component.

[0015] Backfill material is delivered via pipelines to the underground void, where it gradually solidifies and develops strength. The hardened backfill provides support for nearby rock, reducing surface subsidence and increasing ore recovery. Flowability is critical for backfill, as the material must be pumpable to be delivered to the target space as described previously.

[0016] A backfill material is generally considered adequate for underground operations and is sufficiently pumpable when it exhibits a yield point ("YP") of 1000 Pa or less, preferably 900 Pa, more preferably 800 Pa, as measured by the constant shear rate method (0.5 rpm) using a HAAKE viscotes ter iQ rheometer and with a vane (VANE) (FL100) measuring geometry. The yield point of a backfill material can be used to obtain information about the fluidity of the backfill material. The yield point is the lowest shear stress value above which the material will behave like a fluid and below which it will behave like a solid. It is commonly seen at start-up of rakes, mixers and pumps, when higher than usual energy is required to begin rotation. The peak in energy required is due to the yield point, which causes the material to exhibit solid-like properties until the yield point is exceeded. Once the yield point is overcome, the material behaves like a liquid and will begin to flow.

[0017] The backfill material may be in the form of a slurry or a paste. A slurry is intended to mean any flowable suspension of fine particles in a liquid in which the excess liquid can be separated as a supernatant. A paste is intended to mean a homogeneous mixture of fine particles and a liquid that is substantially stable against segregation and seepage.

[0018] In the context of the present invention, tailings are a by-product of mining operations after valuable materials have been extracted from the ore in a processing plant or mill using mineral processing techniques such as flotation.

[0019] Fine grinding of ores such as copper, gold, zinc / lead, nickel, platinum group metals, etc. is required to release valuables from the gangue contained in order to selectively float the valuables in the froth flotation cell. For copper, this size range is typically p80 between 100 and 200 microns. Therefore, all gangue materials associated with the valuable minerals are crushed to a similar size. The resulting tailings can be stored as a thickened slurry or paste in a specially constructed tailings storage facility. Ponds can be used for long-term storage, as a place to allow the different components of the tailings to settle out of suspension, or for temporary holding until the tailings can be further processed. When the tailings source includes a settling pond, a dredging device can be used to remove the tailings from the settling pond as dredged tailings, which can also be called cooked fine tailings, and the tailings supplied to the mixing volume can include dredged tailings.

[0020] The chemical composition and physical appearance of tailings can vary widely. Generally, the chemical composition will depend largely on the location and chemical composition of the sediment from which the tailings were extracted. Furthermore, the chemical composition may be affected by the extraction method and subsequent storage time and conditions. The physical appearance, including particle size and shape, also generally depends on the mechanical processing of the ore and tailings. Tailings can be used directly as backfill material after valuable materials have been extracted from the ore, or they can be stored in tailings ponds, which serve as temporary storage facilities for the tailings.

[0021] Typically, tailings are a mixture of silt (<75 microns), fine sand (75-150 microns) and coarse sand (>150 microns). Tailings are typically made of fine particles, where at least 90% by weight are less than 150 microns in size and at least 50% by weight are less than 75 microns in size.

[0022] Tailings from underground operations may contain quartz and phyllosilicates. Other minerals may additionally be present, such as magnetite and gypsum. However, it is preferred that the amount of gypsum in such tailings is low. A low amount is an amount of less than 5 wt%, preferably less than 2 wt%, more preferably less than 1 wt%, relative to the total dry weight of the tailings. Phyllosilicates are layered silicate minerals, more specifically based on tetrahedral MO4 sheets (M = Si 4+ , Al 3+ ) and octahedral M(O,OH)6 sheets (M=Al 3+ , Mg 2+ , Fe 2+ / 3+ The phyllosilicates are selected from the group consisting of smectite minerals (such as montmorillonite, nontronite, beidellite, saponite, hectorite and sauconite), vermiculite, kaolinite, serpentines (such as serpentine and lizardite), palygorskite, sepiolite, talc, pyrophyllite, chlorite, micas (such as muscovite or biotite), interlayer defect micas such as illite, glauconite, chrysolite and polysilicon muscovite.

[0023] Phyllosilicates or expanded clays have been observed to hinder the performance of polycarboxylate ether superplasticizers, which are designed to adsorb onto cement particles to disperse them in aqueous slurries or pastes. Expanded clays interfere with this function. In this case, the adsorbed superplasticizer can no longer act as a plasticizer, resulting in reduced fluidity of the building composition. Quite surprisingly, it has been found that polycarboxylate ether dispersants function well in the backfill materials of the present invention, likely due to a higher water-to-binder ratio than encountered in conventional cementitious building compositions.

[0024] The backfill material of the present invention includes the use of a binder component comprising a binder based on portland cement clinker and calcined clay. The use of calcined clay material as a partial substitute for portland cement allows for a significant reduction in the overall carbon footprint of the backfill material at substantially the same strength as achieved with conventional portland cement.

[0025] In one embodiment, the weight ratio of the binder component to the tailings is from 1 to 20, preferably from 1.5 to 15, more preferably from 2 to 10.

[0026] The term "Portland cement" refers to any cementitious compound containing Portland clinker, in particular CEMI within the meaning of paragraph 5.2 of standard EN 197-1. A preferred cement is ordinary Portland cement (OPC) according to DIN EN 197-1. The phases that make up Portland cement are primarily alite (C3S), belite (C2S), calcium aluminate (C3A), calcium aluminoferrite (C4AF), and other minor phases. Commercially available OPC can contain calcium sulfate (<7% by weight) or be essentially free of calcium sulfate (<1% by weight).

[0027] In one embodiment, the Portland cement clinker is present in an amount of at least 5 wt%, preferably in an amount of 10 to 90 wt%, more preferably in an amount of 15 to 65 wt%, relative to the weight of the binder component.

[0028] Clay is a material that is abundant worldwide. Calcined clay materials are obtained by heat-treating clays containing phyllosilicates (i.e., sheet silicates). Phyllosilicates include 1:1 and / or 2:1 layered (natural) clays or mixtures thereof, containing di- and / or tri-octahedral sheets or mixtures thereof and a layer charge of 0 (e.g., kaolinite), a negative layer charge of up to 1 (e.g., mica), or mixtures thereof. Heat treatment of clays transforms the clay mineral by dehydroxylation and the release of water. For example, kaolinite can be heat-treated to obtain metakaolin (Al2Si2O7). The calcined clay materials obtained are volcanic ash of natural origin. The composition and crystal structure of the clays derived from natural deposits to prepare calcined clays can vary widely. For the purposes of the present invention, calcined clay is any material prepared by heat-treating clays that provide volcanic ash reactivity. Because the composition, crystal structure, fineness, and processing conditions, such as the temperature and time of heat application, can vary significantly, the reactivity of calcined clays can also vary significantly.

[0029] It has been found that suitable clay materials belong to the kaolin group, such as kaolinite, dickite, nacrite or halloysite. Acceptable strength can also be achieved using smectite clays, including dioctahedral smectites such as montmorillonite and nontronite and trioctahedral smectites such as saponite or vermiculite, and mixtures thereof. This opens up the possibility of using clays that are more widely available than kaolin.

[0030] These may be medium or low grade kaolin clays or non-kaolin clays.The calcined clay material may comprise less than 90 wt%, preferably less than 70 wt%, for example 30-40 wt% of calcined clay derived from kaolin.

[0031] In one embodiment, the calcined clay is present in an amount of at least 5 wt%, preferably in an amount of 10 wt% to 80 wt%, more preferably in an amount of 15 wt% to 60 wt%, relative to the weight of the binder component.

[0032] According to another embodiment, the binder component additionally comprises at least one of carbonate rock powder and a sulfate source.

[0033] The combined replacement of cement with calcined clay and carbonate rock powder allows for higher levels of substitution. The idea of ​​combining calcined clay and carbonate rock powder to replace cement is based on the observation that cement containing alumina reacts with the carbonate phase to produce a hard and crystalline carboaluminate phase and contributes to the development of the microstructure.

[0034] Carbonate rock powder consists of finely ground carbonate rock and is available in large quantities. Useful examples include limestone, such as ground limestone or precipitated limestone, dolomite, magnesite, and mixtures thereof. Preferably, the carbonate rock powder is limestone.

[0035] To prevent undersulfation and optimize early strength, it may be necessary to adjust the sulfate content in the calcined clay blend. Adequate sulfate content can be achieved by adding a sulfate source to the blend. A sulfate source is a compound that can provide sulfate ions in an alkaline aqueous environment. Typically, the sulfate source has a concentration of at least 0.6 mmol L at 30°C. -1 The water solubility of the sulfate source is suitably determined in water having an initial pH of 7. The sulfate source may be a calcium sulfate source, and the sulfate source is preferably selected from gypsum, hemihydrate, anhydrite, and mixtures thereof.

[0036] In one embodiment, the binder component further comprises, in addition to calcined clay, a supplementary cementitious material, preferably selected from the group consisting of slag, fly ash, and natural pozzolans. Slag may be metallurgical slag, which is a solid waste produced by the metallurgical industry, such as steel slag, blast furnace slag (BFS), ground granulated blast furnace slag (GGBFS), red mud (RM), and copper slag (CS), or synthetic slag. Fly ash is produced, in particular, during the combustion of coal in power plants. According to WO 08 / 012438, Class C fly ash (lignite fly ash) contains approximately 10% by weight of CaO, while Class F fly ash (hard coal fly ash) contains less than 8% by weight, preferably less than 4% by weight, and typically about 2% by weight of CaO. Natural pozzolans may be tuff, trass, or volcanic ash.

[0037] As another essential component, the backfill material of the present invention comprises a dispersant selected from polycarboxylate ethers, polycarboxylic acids and mixtures thereof.

[0038] It is known to add dispersants to aqueous slurries of hydraulic and / or mineral binders to improve their workability. This type of additive can prevent agglomeration of the particles already dispersed and of the newly formed particles by hydration, and in this way improves workability (flowability, pumpability, viscosity, self-compacting ability, sprayability, finishing ability). In order to reduce the fraction of excess water at a given processing consistency and / or to improve the processing properties at a given water / binder ratio, additives commonly referred to as water reducers or plasticizers are used. Those that allow a high level of water reduction are referred to as high-efficiency water reducers or superplasticizers. Polycarboxylate ether superplasticizers (PCEs) based on carboxyl-containing monomers and on olefin monomers containing polyethylene glycol are known per se.

[0039] Polycarboxylate ethers (PCEs) are, in particular, comb-shaped polymers having a carbon-containing backbone to which are attached pendant cement anchoring groups and polyether side chains, wherein the polyether side chains are preferably linked to the polycarboxylate backbone via ester, ether, and / or amide groups. The anionic groups are carboxyl and / or carboxylate groups. PCEs are preferably obtained by free radical copolymerization of polyether macromonomers and monomers containing anionic groups. Polycarboxylate ethers are commercially available.

[0040] Typically, the polycarboxylate ether incorporates structural units (I) comprising anionic and / or anionogenic groups and structural units (II) comprising polyether side chains.

[0041] Preferably, the structural unit comprising anions and / or anion-forming groups is one of the general formulae (Ia), (Ib) and / or (Ic):

[0042]

[0043] where R 1 is H, C1-C4 alkyl, CH2COOH, preferably H or methyl;

[0044] X is a chemical bond;

[0045] R 2 It is OM;

[0046]

[0047] in

[0048] R 5 is H or C1-C4 alkyl, preferably H,

[0049] Z is O;

[0050]

[0051] in

[0052] R 6 is H or C1-C4 alkyl, preferably H,

[0053] Q is NR 7 or O;

[0054] R 7 For H, M, (C n1 H 2n1 )-OH、(C n1 H 2n1 )-PO3M2、(C n1 H 2n1 )-OPO3M2, (C6H4)-PO3M2 or (C6H4)-OPO3M2

[0055] n1 is 1, 2, 3, or 4; and

[0056] wherein each M is independently H or a cationic equivalent.

[0057] The structural units of general formula (Ib) are believed to contain anion-generating groups that undergo hydrolysis under alkaline conditions to give structural units of formula (Ic) wherein Q is O and R 7 It is H or M.

[0058] Preferably, the structural unit comprising a polyether side chain is one of the general formulae (IIa), (IIb), (IIc) and / or (IId):

[0059]

[0060] in

[0061] R 10 、R11 and R 12 are independently H or C1-C4 alkyl, preferably H or methyl;

[0062] Z 2 is O or S;

[0063] E is C2-C6 alkylene, cyclohexylene, CH2-C6H 10 , 1,2-phenylene, 1,3-phenylene or 1,4-phenylene;

[0064] G is O, NH or CO-NH; or

[0065] E and G together are a chemical bond;

[0066] A is C2-C5 alkylene or CH2CH(C6H5), preferably C2-C3 alkylene;

[0067] n2 is 0, 1, 2, 3, 4, or 5;

[0068] a is an integer from 2 to 350, preferably from 10 to 150, more preferably from 20 to 100;

[0069] R 13 is H, an unbranched or branched C1-C4 alkyl group, CO-NH2 or COCH3;

[0070]

[0071] in

[0072] R 16 、R 17 and R 18 are independently H or C1-C4 alkyl, preferably H;

[0073] E 2 It is C2-C6 alkylene, cyclohexylene, CH2-C6H 10 , 1,2-phenylene, 1,3-phenylene or 1,4-phenylene or a chemical bond;

[0074] A is C2-C5 alkylene or CH2CH(C6H5), preferably C2-C3 alkylene;

[0075] n2 is 0, 1, 2, 3, 4, or 5;

[0076] L is C2-C5 alkylene or CH2CH(C6H5), preferably C2-C3 alkylene;

[0077] a is an integer from 2 to 350, preferably from 10 to 150, more preferably from 20 to 100;

[0078] d is an integer from 1 to 350, preferably from 10 to 150, more preferably from 20 to 100;

[0079] R 19 is H or C1-C4 alkyl; and

[0080] R 20 is H or C1-C4 alkyl;

[0081]

[0082] in

[0083] R 21 、R 22 and R 23 are independently H or C1-C4 alkyl; preferably H;

[0084] W is O, NR 25 Or N;

[0085] If W = O or NR 25 , then V is 1 and if W=N, then V is 2;

[0086] A is C2-C5 alkylene or CH2CH(C6H5), preferably C2-C3 alkylene;

[0087] a is an integer from 2 to 350, preferably from 10 to 150, more preferably from 20 to 100;

[0088] R 24 is H or C1-C4 alkyl;

[0089] R 25 is H or C1-C4 alkyl;

[0090]

[0091] in

[0092] R 6 is H or C1-C4 alkyl, preferably H;

[0093] Q is NR 10 , N or O;

[0094] If Q = O or NR 10 , then V is 1 and if Q=N, then V is 2;

[0095] R 10 is H or C1-C4 alkyl;

[0096] A is C2-C5 alkylene or CH2CH(C6H5), preferably C2-C3 alkylene; and

[0097] a is an integer from 2 to 350, preferably from 10 to 150, more preferably from 20 to 100;

[0098] wherein each M is independently H or a cationic equivalent.

[0099] The molar ratio of structural unit (I) to structural unit (II) is 1:3 to about 10:1, preferably 1:1 to 10:1, and more preferably 3:1 to 6:1. Polymeric dispersants comprising structural units (I) and (II) can be prepared by conventional methods, for example, by free radical polymerization or controlled radical polymerization. The preparation of dispersants is described, for example, in EP0894811, EP1851256, EP2463314, and EP0753488.

[0100] Polymers can be characterized by their charge density. Charge density refers to the percentage of monomers that contain charged functional groups. Charge density can affect solubility, conformation, and electrostatic interactions, and is itself sensitive to pH.

[0101] In one embodiment, the polycarboxylate ether dispersant has a charge density of at least 0.1 meq / g, preferably from 0.5 to 8 meq / g.

[0102] The polycarboxylic acid may be selected from low molecular weight polycarboxylic acids and polymeric polycarboxylic acids and their salts.

[0103] Suitable low molecular weight polycarboxylic acids and their salts have, for example, a molecular weight of 500 g / mol or less and include aliphatic polycarboxylic acids such as oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, fumaric acid, maleic acid, itaconic acid, citraconic acid, mesaconic acid, malic acid, tartaric acid, and citric acid.

[0104] Suitable low molecular weight polycarboxylic acids and their salts also include aminocarboxylic acids and their salts, such as ethylenediaminetetraacetic acid and nitrilotriacetic acid.

[0105] Suitable polymeric polycarboxylic acids can be selected from homopolymers and copolymers of α,β-ethylenically unsaturated carboxylic acids; and copolymers of at least one α,β-ethylenically unsaturated carboxylic acid and at least one sulfo-containing monomer; and salts thereof. The polymeric polycarboxylic acid can be used as a free acid or in a partially or fully neutralized form (i.e., as a salt). The cation is not particularly limited and can be selected from alkali metal (e.g., sodium or potassium) and ammonium cations.

[0106] The molecular weight of the polymeric polycarboxylic acid is 25,000 g / mol or less, preferably the molecular weight is in the range of 1000 to 25000 g / mol, most preferably 1000 to 5000 g / mol. The molecular weight can be measured by gel permeation chromatography (GPC).

[0107] Effective polymeric polycarboxylic acids have a carboxyl group density within a certain range. Preferably, the milliequivalent weight is 3.0 meq / g or higher, preferably 3.0 to 17.0 meq / g, more preferably 5.0 to 17.0 meq / g, and most preferably 5.0 to 14.0 meq / g.

[0108] The polymeric polycarboxylic acid is selected from homopolymers and copolymers of α,β-ethylenically unsaturated carboxylic acids; and copolymers of at least one α,β-ethylenically unsaturated carboxylic acid and at least one sulfo-containing monomer. Suitable α,β-ethylenically unsaturated carboxylic acids include acrylic acid, methacrylic acid, and polymaleic acid.

[0109] Suitable sulfonic acid-containing monomers include 2-propylene-1-sulfonic acid (allylsulfonic acid), 2-methyl-2-propylene-1-sulfonic acid (methallylsulfonic acid), vinylsulfonic acid, styrenesulfonic acid (i.e., 2-styrenesulfonic acid, 3-styrenesulfonic acid, and 4-styrenesulfonic acid), and 2-acrylamido-2-methylpropanesulfonic acid (AMPS).

[0110] Preferably, the polymeric polycarboxylic acid is a homopolymer of acrylic acid, a homopolymer of methacrylic acid, a copolymer of acrylic acid and maleic acid, or a copolymer of methacrylic acid and maleic acid, most preferably a homopolymer of acrylic acid.

[0111] Examples of suitable polymer components are available under the trade name Commercially available from BASF SE, e.g. PA 20, PA 15, CP 10S, PA 25CL PN, CP 12S, PA 40. "CP" usually means copolymer, while "PA" usually means polyacrylate.

[0112] In a preferred embodiment, the at least one dispersant is present in an amount of 0.05% to 15% by weight, preferably in an amount of 0.1% to 10% by weight, relative to the weight of a) and b).

[0113] In the context of the present invention, water refers to any water present in the backfill material, regardless of its source. The water in the backfill material of the present invention can originate from cement, tailings, water present when an aqueous solution or dispersion of at least one polycarboxylate ether is used, and / or any additional water that is added. The term "additional water" refers to water that is added as is. In other words, "additional water" is water that is not present in cement or tailings, but is present when an aqueous solution or dispersion of at least one polycarboxylate ether is used.

[0114] If additional water is added, this water can be any available water, such as distilled water, purified water, tap water, mineral water, spring water, well water, brine, waste water and groundwater. The use of waste water is only possible when the composition of such waste water is known and the impurities contained therein are not likely to impart a function to any other component of the composition of the present invention. The use of brine is only possible when the risk of corrosion of steel elements is low. It is particularly preferred in this context to use water extracted from underground operations, such as water pumped from mining operations. Preferably, the water extracted from underground operations is filtered to remove tailings before use.

[0115] In a preferred embodiment, the weight ratio of water to binder components is higher than 1, preferably 2 to 30, more preferably 3 to 25.

[0116] The present invention also relates to a method for backfilling comprising pumping or gravity delivering a backfill material according to any preferred embodiment, filling an excavation in an underground operation or a surface operation with the backfill material, and allowing the backfill slurry to set.

[0117] A process is preferred wherein the tailings are from an underground operation or from a tailings pond.

[0118] The present invention preferably relates to a backfill method wherein the tailings originate from the crushing of ore and mineral processing. Example

[0119] The present invention will be further described by way of illustrative examples, which however should not be construed as limiting the scope of the application in any way.

[0120] Unconfined compressive strength (UCS)

[0121] The UCS was measured with an Xforce K 150 kN force transducer on a Zwick Roell Allround Line Z 150. Before the UCS test, the dimensions of the sample were adjusted to obtain an effective pressing surface.

[0122] yield point

[0123] The yield point of the fresh backfill material was measured using a HAAKE viscotes ter iQ rheometer and measuring geometry with a blade (FL100) using the constant shear rate method (0.5 rpm).

[0124] Three calcined clays with different surface areas were used in the backfill tests:

[0125] Calcined Clay A is a blended kaolin / smectic clay with a high surface area (47 m 2 / g);

[0126] Calcined clay B is kaolin clay, calcined clay has a low specific surface area (4m 2 / g);

[0127] Calcined clay C is kaolin clay, calcined clay with medium specific surface area (22m 2 / g).

[0128] The specific surface area can be measured according to ISO 9277:2010.

[0129] Sample preparation

[0130] The mix designs of the tested backfill materials are summarized in Table 1. Four different binder components were tested, and the compositions of the different binder components are summarized in Table 2. For each binder component, three different dispersants were tested. An overview of the dispersants is given in Table 3. For each binder component, a comparative experiment was performed without the addition of a dispersant.

[0131] The backfill material was prepared by mixing the dispersant with the mixing water. Dry solids in the form of copper mine tailings and the binder component were mixed with the prepared water-dispersant mixture. The backfill material was cast into 20 mm x 20 mm x 20 mm cubes using an IKA mixer (mixing time 30 seconds, rest time 30 seconds, then 1 minute). The backfill samples were stored in a climate chamber at 30°C and 80% relative humidity.

[0132] Table 1 - General Backfill Material Mixtures

[0133] Backfill material mixture tailings Binder components Water including dispersant total Amount (in g) 300 15.79 89.07 404.89

[0134] The designs of the different binder compositions tested are summarized in Table 2.

[0135] Table 2 - Composition of the tested adhesive components

[0136]

[0137] The dispersants included low, medium, and high charge densities, as shown in Table 3.

[0138] Table 3 - Overview of dispersants used

[0139] <![CDATA[PCE I * ]]> <![CDATA[PCE II ** ]]> <![CDATA[PCE III ** ]]> Charge density [meq / g] 1.1 0.8 1.8

[0140] *PCE I is a copolymer of acrylic acid and prenyloxy polyethylene glycol ether

[0141] **PCE II and PCE II are copolymers of acrylic acid and ethyleneoxybutyl polyethylene glycol

[0142] The experimental results show that Figure 1-4The compressive strength was determined after 7, 14 and 28 days.

[0143] In all experiments, lower yield points were observed for all dispersants tested compared to the comparative examples. In other words, with the addition of dispersants, a significant improvement in yield point was observed compared to the comparative examples. For PCE II, the lowest yield point was observed for all binder components tested.

[0144] The compressive strengths obtained for the different dispersants are comparable to those obtained for the comparative example. Since high compressive strengths are required, the results clearly show that the yield point of the backfill material can be improved by adding dispersants while obtaining a favorable compressive strength.

Claims

1. A backfill material, comprising a. Tailings, b. Binder component, c. Water, d. and at least one dispersant selected from polycarboxylate ethers and polycarboxylic acids, The binder component comprises a binder based on Portland cement clinker and calcined clay.

2. The backfill material of claim 1, wherein the binder component further comprises at least one of carbonate rock powder and a sulfate source.

3. The backfill material of claim 2, wherein the carbonate rock powder is limestone and the sulfate source is selected from the group consisting of gypsum, hemihydrate, anhydrite, and mixtures thereof.

4. Backfill material according to any one of the preceding claims, wherein the binder component additionally comprises a supplementary cementitious material, preferably a supplementary cementitious material selected from slag, fly ash and natural pozzolans.

5. The backfill material according to any one of the preceding claims, wherein the weight ratio of the binder component to the tailings is 1 to 20, preferably 1.5 to 15, more preferably 2 to 10.

6. Backfill material according to any one of the preceding claims, wherein the Portland cement clinker is present in an amount of at least 5 wt. %, preferably in an amount of 10 wt. % to 90 wt. %, more preferably in an amount of 15 wt. % to 65 wt. % relative to the weight of the binder component.

7. Backfill material according to any one of the preceding claims, wherein the calcined clay is present in an amount of at least 5 wt. %, preferably in an amount of 10 wt. % to 80 wt. %, more preferably in an amount of 15 wt. % to 60 wt. % relative to the weight of the binder component.

8. Backfill material according to any one of the preceding claims, wherein the weight ratio of water to binder component is higher than 1, preferably 2 to 30, more preferably 3 to 25.

9. Backfill material according to any one of the preceding claims, wherein the at least one dispersant is present in an amount of 0.05% to 15% by weight, preferably in an amount of 0.1% to 10% by weight, relative to the weight of a) and b).

10. The backfill material according to any one of the preceding claims, wherein the polycarboxylate ether dispersant has a charge density of at least 0.1 meq / g, preferably 0.5 to 8 meq / g.

11. The backfill material according to any one of the preceding claims, having a yield point of 1000 Pa or less, measured by the constant shear rate method (0.5 rpm) using a HAAKE viscotes ter iQ rheometer with a blade (FL100) measurement geometry.

12. A method for backfilling comprising pumping or gravity delivering a backfill material according to any one of the preceding claims, filling the backfill material in an excavation in an underground operation or surface operation, and allowing the backfill slurry to set.

13. A method for backfilling according to claim 14, wherein the tailings are from underground operations or from surface ponds.

14. A method for backfilling according to claim 14 or 15, wherein the tailings originate from crushing and mineral processing of the ore.

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