Method for dewatering mine tailings

Abstract

The present invention relates to a method for dewatering mine tailings, comprising the addition of at least one water-soluble polymer and at least one surfactant to said tailings.

Description

[0001] Description

[0002] Title of the invention: Method for dehydrating mining residues

[0003] Technical field of the invention

[0004] The present invention relates to a method for dehydrating mining residues comprising the addition of at least one water-soluble polymer and at least one surfactant to said residues.

[0005] Prior art

[0006] In the mining industry, tailings are the waste generated during the processing of ore. They are generally stored in retention basins, ponds, dams, or dikes in semi-liquid form when they are mining sludge, or in the form of spoil heaps when they are dry or solid materials. These volumes of stored tailings represent an environmental and human risk in the event of a failure of these structures.

[0007] In addition, the current development of environmental policies across the world is increasingly forcing mining companies to rehabilitate their operating sites, thus obliging these companies to treat mining residues, particularly by dehydrating them in the case of mining sludge, to form a stable soil.

[0008] Dewatering this sludge offers several advantages for mining companies:

[0009] - a reduction in the total volume of residues. In addition, the eliminated water can be recycled for the exploitation of minerals, which is crucial today, particularly in countries experiencing water stress.

[0010] - Dewatered mining sludge is lighter, making it easier to transport and dispose of. This reduces the costs associated with transporting tailings to permanent storage or further processing sites.

[0011] - Dewatering tailings sludge helps improve its geotechnical stability. By reducing the water content, the tailings become more compact and are less likely to liquefy or move uncontrolled. This reduces the risk of landslides or storage facility failures.

[0012] Specific techniques for dewatering mining sludge may vary depending on the characteristics of the sludge, the treatment objectives, and environmental constraints. Methods such as filtration, centrifugation, pressing, or thermal drying may be used, depending on the needs.

[0013] The classic steps of a sludge dewatering process by filtration are as follows:

[0014] - the sludge is generally conditioned by adding chemical reagents such as Acculants to promote the agglomeration of particles;

[0015] - The conditioned sludge is then brought into a filtration device to be dehydrated;

[0016] - the device is pressurized, the solid matter and the liquid matter of the sludge are separated. The solid matter is collected in or on the filter and forms a filter cake;

[0017] - As filtration progresses, the filter cake thickens and consolidates,

[0018] - This cake can optionally be washed to remove residual impurities;

[0019] - Once filtration is complete, the filter cake is removed from the filter and disposed of as waste.

[0020] Each mining slurry has its own specific characteristics and processing requirements, which can influence the steps and parameters of the filtration process. Filtration techniques can also vary depending on the available equipment and the specific processing objectives of each mine.

[0021] US4210531 describes the use in combination of a surfactant and an organic solvent on a slurry previously inoculated with a high molecular weight non-ionic polyacrylamide to reduce the humidity of the cake.

[0022] Document US4968435 describes the synthesis of an insoluble cationic polymer in inverse emulsion comprising non-ionic surfactants and the use of this polymer as Acculant.

[0023] Document WO2006027121 describes a method for mechanically dewatering sludge comprising hydrocarbons. The sludge is pretreated with a combination of clay, inorganic coagulant, preferably cationic acculant polymers and a preferably anionic surfactant to improve the dryness of the cake.

[0024] Document US2016310964 mentions the combination of swelling clay, an anionic polymer of low ionic charge and very high molecular weights with a cationic collector to improve the dehydration of oil sands residues after a flotation process.

[0025] Document US 2016 / 0311709 describes a process for dehydrating oil sands residues.

[0026] Document US 2011 / 0009534 describes a process for dehydrating mining residues

[0027] Document US 2002 / 0190005 describes a method of inverting an emulsion containing a flocculant and the use of this inverted emulsion in the treatment of aqueous sludge.

[0028] Although the described processes offer the possibility of dewatering mine tailings, mining companies still face long processing times that impact productivity. Industrial filtration tools have a predefined size and capacity, which limits the amount of mine tailings that can be processed simultaneously. In addition, filtration requires relatively long cycle times to ensure complete filtration.

[0029] Beyond these productivity issues, mining companies need to reduce the residual moisture in cakes in order to comply with regulatory constraints, such as in Brazil, or to recycle as much water as possible in countries where water stress is significant, such as Chile.

[0030] The Applicant has discovered that the combination of at least one specific polymer and at least one specific surfactant, applied to a mechanical dewatering system, makes it possible to improve the speed of dewatering of mining residues regardless of their origin, while reducing the quantity of residual moisture (thus increasing dryness), thus making it possible to comply with local regulatory constraints while increasing productivity. In addition to these advantages, the cake obtained is less sticky, which allows for improved overall process efficiency.

[0031] The method according to the invention is part of a principle of environmental awareness and the impact of industries and humans on the planet. The reduction in the time required to dehydrate mining residues allows a reduction in the quantity of greenhouse gases, such as CO2, produced by dehydration systems, and the reduction of residual moisture present in the filter cakes allows better recovery of water and thus recycling of a greater quantity. In addition, the present invention is advantageously implemented using materials of biological origin, for example biomass, or recycled. The synthesis of the monomers used is advantageously a biological synthesis, for example, by enzymatic catalysis.The energy used to implement the dehydration process according to the invention advantageously comes from a heat pump or from a renewable source, for example wind power, photovoltaic power, or, in particular for mobile installations, of the fuel cell or lithium battery type.

[0032] Statement of the invention

[0033] The present invention relates to a method for dehydrating a mining residue comprising the following steps: a) Adding and mixing at least one water-soluble polymer and at least one surfactant to the mining residue in order to obtain a conditioned mining residue; b) Dehydrating the conditioned mining residue by mechanical filtration in order to obtain a dehydrated mining residue; the water-soluble polymer(s) being chosen from:

[0034] - anionic water-soluble polymers having a molecular weight between 800,000 and 3,000,000 g / mol;

[0035] - cationic water-soluble polymers having a molecular weight between 10,000 and 3,000,000 g / mol;

[0036] - and their mixtures, the surfactant(s) being chosen from:

[0037] - anionic surfactants, and / or;

[0038] - non-ionic surfactants; and

[0039] - their mixtures.

[0040] Description of the invention

[0041] By "mechanical filtration" we mean filtration carried out by the input of mechanical energy.

[0042] A "polymer" means a homopolymer or a copolymer. A copolymer is a polymer made from at least two different monomers.

[0043] A "hydrophilic monomer" means a monomer that has an octanol / water partition coefficient, K ow , less than or equal to 1, in which the partition coefficient K owis determined at 25°C in an octanol / water mixture with a volume ratio of 1 / 1, at a pH between 6 and 8.

[0044] A "hydrophobic monomer" means a monomer that has an octanol / water partition coefficient, K ow , greater than 1, in which the partition coefficient K ow is determined at 25°C in an octanol / water mixture with a volume ratio of 1 / 1, at a pH between 6 and 8.

[0045] The octanol / water partition coefficient, K ow , represents the ratio of concentrations (g / L) of a monomer between the octanol phase and the aqueous phase. It is defined as follows:

[0046] [Math 1]

[0047] The term "water-soluble polymer" means a polymer that gives an aqueous solution without insoluble particles when dissolved under stirring at 25°C and with a concentration of 10 gL' 1 in deionized water.

[0048] By “anionic polymer” is meant a polymer consisting of hydrophilic anionic monomer(s) and optionally hydrophilic non-ionic monomer(s).

[0049] By “cationic polymer” is meant a polymer consisting of hydrophilic cationic monomer(s) and optionally hydrophilic non-ionic monomer(s).

[0050] By “X and / or Y” we mean “X”, or “Y”, or “X and Y”.

[0051] Also included in the invention are all possible combinations between the various embodiments disclosed, whether preferred or exemplary. Furthermore, when ranges of values ​​are indicated, the limits are part of these ranges. The disclosure also includes all combinations between the limits of these ranges of values. For example, the ranges of values ​​"1-20, preferably 5-15", imply the disclosure of the ranges "1-5", "1-15", "5-20" and "15-20" and the values ​​1, 5, 15 and 20. The molecular weight is determined by the intrinsic viscosity of the polymer.The intrinsic viscosity can be measured by methods known to those skilled in the art and can be calculated from the reduced viscosity values ​​for different polymer concentrations by graphical method consisting of plotting the reduced viscosity values ​​(y-axis) on the concentration (x-axis) and extrapolating the curve to zero concentration. The intrinsic viscosity value is plotted on the y-axis or by using the least squares method. The molecular weight can then be determined by the Mark-Houwink equation: [q] = KM“.

[0052] [q] represents the intrinsic viscosity of the polymer determined by the solution viscosity measurement method.

[0053] K represents an empirical constant.

[0054] M represents the molecular weight of the polymer, a represents the Mark-Houwink coefficient.

[0055] K and a depend on the particular polymer-solvent system.

[0056] Dehydration process

[0057] Mining waste

[0058] The mining residue used in the context of the invention includes any type of residue or waste from the exploitation of minerals, such as coal, diamond, phosphate, metal (alumina, platinum, iron, gold, copper, silver, etc.) mines. The suspensions can also come from drilling muds. The residues from the exploitation of oil sands are excluded from the scope of the invention.

[0059] Residue conditioning stage

[0060] Before filtration, the residue undergoes a conditioning step in order to improve the filtration process.

[0061] This conditioning is achieved by the simultaneous or separate addition of at least one water-soluble polymer and at least one surfactant to the residue.

[0062] The water-soluble polymer and the surfactant can be added all at once or in several batches. Preferably, they are added all at once.

[0063] Generally, they are added as a solution. The water-soluble polymer and the surfactant can be added sequentially (for example, the polymer is added first, then the surfactant, or vice versa), in parallel, or alternately (a first fraction of one of the two, followed by a first fraction of the other, then a second fraction of the first, and so on).

[0064] Preferably, they are added successively, more preferably the polymer is added first followed by the surfactant.

[0065] The water-soluble polymer and the surfactant can be added at the same injection point, or they can be added at different injection points, preferably they are added at the same injection point.

[0066] The quantity of water-soluble polymer added to the mining residue is advantageously between 0.5 and 5,000 ppm relative to the weight of dry matter of the mining residue to be dehydrated, preferably between 1 and 2,000 ppm, more preferably between 2 and 1,000 ppm, more preferably between 3 and 500 ppm, more preferably between 5 and 200 ppm, more preferably between 10 and 100 ppm.

[0067] The quantity of surfactant added to the mining residue is advantageously between 10 and 10,000 ppm relative to the weight of dry matter of the mining residue to be dehydrated, preferably between 50 and 5,000 ppm, more preferably between 200 and 2,000 ppm.

[0068] Water-soluble polymer

[0069] The water-soluble polymer according to the invention is chosen from:

[0070] - anionic water-soluble polymers having a molecular weight between 800,000 and 3,000,000 g / mol;

[0071] - cationic water-soluble polymers having a molecular weight between 10,000 and 3,000,000 g / mol.

[0072] Advantageously, the hydrophilic anionic monomer(s) are chosen from monomers having vinyl functions (advantageously acrylic, maleic, fumaric, malonic, itaconic, or allylic). They may contain a carboxylate, phosphonate, phosphate, sulfate, sulfonate group, or another anionically charged group. Examples of suitable monomers include acrylic acid; methacrylic acid; dimethylacrylic acid; itaconic acid; itaconic acid hemi-ester; itaconic anhydride; itaconamide; crotonic acid; maleic acid; fumaric acid; acrylamido undecanoic acid; 3-acrylamido 3-methylbutanoic acid; maleic anhydride;strong acid monomers having, for example, a sulfonic acid or phosphonic acid function such as vinylsulfonic acid, vinylphosphonic acid, allylsulfonic acid, methallylsulfonic acid, 2-methylidenepropane-1,3-disulfonic acid, 2-sulfoethylmethacrylate, sulfopropylmethacrylate, sulfopropylacrylate, allylphosphonic acid, styrenesulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid (ATBS), 2-acrylamido-2-methylpropane disulfonic acid; the water-soluble salts of these monomers such as their alkali metal, alkaline earth metal or ammonium salts; and mixtures thereof. Preferably, the hydrophilic anionic monomer is acrylic acid, one of its salts and mixtures thereof.;

[0073] The quantity of hydrophilic anionic monomers in the anionic water-soluble polymer is advantageously between 5 and 100 mol% relative to the total quantity of monomer in the anionic water-soluble polymer, preferably between 10 and 50 mol%, more preferably between 15 and 35 mol%, the remaining quantity of monomer to reach 100 mol% being hydrophilic non-ionic monomers.

[0074] In a particular embodiment, the hydrophilic anionic monomer(s) may be partially or totally salified.

[0075] Salified means the substitution of a proton of at least one acid function of the type - R(=O)-OH (with R= P, S or C) of the anionic monomer by a metal or ammonium cation to form a salt of the type -R(=O)-OX (X being a metal or ammonium cation). In other words, the non-salified form corresponds to the acid form of the monomer, for example RC(=O)-OH in the case of the carboxylic acid function, while the salified form of the monomer corresponds to the form RC(=O)-O' X + , X + corresponding to an alkali or ammonium cation. The salification of the acid functions of the water-soluble polymer can be partial or total.

[0076] The salified form advantageously corresponds to the salts of alkali metals (Li, Na, K. . .), alkaline earth metals (Ca, Mg. . .) or ammonium (for example the ammonium ion or a tertiary ammonium). The preferred salts are the sodium salts.

[0077] Salification can be carried out before, during or after polymerization. In a particular embodiment, the polymer advantageously comprises between 1 and 100 mol% of hydrophilic anionic monomer(s) in salified form, preferably between 50 and 100 mol%.

[0078] Advantageously, the hydrophilic cationic monomer(s) are chosen from monomers derived from vinyl-type units (advantageously acrylamide, acrylic, allyl or maleic), these monomers having a phosphonium or quaternary ammonium function.Mention may be made, in particular and without limitation, of diallyldialkyl ammonium salts such as diallyl dimethyl ammonium chloride (DADMAC); acidified or quaternized salts of dialkylaminoalkylacrylamides; acidified or quaternized salts of dialkylaminoalkylmethacrylamides, such as for example methacrylamidopropyl trimethyl ammonium chloride (MAPTAC), acrylamidopropyl trimethyl ammonium chloride (APTAC), acidified or quaternized salts of dialkyl aminoalkyl acrylate such as quaternized or salified dimethylaminoethyl acrylate (ADAME), acidified or quaternized salts of dialkyl aminoalkyl methacrylate such as quaternized or salified dimethylaminoethyl methacrylate (MADAME) and mixtures thereof. Advantageously, the alkyl groups are C1-C3. Preferably, the hydrophilic cationic monomer is diallyl dimethyl ammonium chloride.

[0079] A person skilled in the art will know how to prepare the quaternized monomers, for example using a quaternizing agent of type RX, R being an alkyl group and X being a halogen or a sulfate. The quaternizing agent may be chosen from dialkyl sulfates comprising from 1 to 6 carbon atoms or alkyl halides comprising from 1 to 6 carbon atoms. Preferably, the quaternizing agent is chosen from methyl chloride, benzyl chloride, dimethyl sulfate or diethyl sulfate. In addition, the present invention also covers monomers of type DADMAC, APTAC and MAPTAC whose counterion is a sulfate, a fluoride, a bromide or an iodide instead of the chloride.

[0080] The term “quaternizing agent” refers to a molecule that can alkylate a tertiary amine.

[0081] The amount of hydrophilic cationic monomers in the cationic water-soluble polymer is advantageously between 5 and 100 mol% relative to the total amount of monomer in the cationic water-soluble polymer, preferably between 50 and 100 mol%, more preferably between 80 and 100 mol%, the remaining amount of monomer to reach 100 mol% being hydrophilic non-ionic monomers. Alternatively, the cationic water-soluble polymer may be a polyamine obtained by condensation between epichlorohydrin and dimethylamine.

[0082] By "amine" we mean both the neutral form and the ionic form (i.e. in the form of ammonium).

[0083] The anionic water-soluble polymers and the cationic water-soluble polymers may optionally comprise at least one hydrophilic non-ionic monomer.

[0084] Advantageously, the hydrophilic non-ionic monomer(s) are chosen, in particular, from the group comprising water-soluble vinyl monomers, such as acrylamide, methacrylamide, N-alkylacrylamides, N-alkylmethacrylamides, N,N-dialkyl acrylamides (for example N,N-dimethylacrylamide or N,N-diethyl acrylamide), N,N-dialkylmethacrylamides, alkoxylated esters of acrylic acid, alkoxylated esters of methacrylic acid, N-vinylpyrrolidone, N-methylolacrylamide, N-vinylformamide (NVF), N-vinyl acetamide, N-vinyl imidazole, N-vinyl succinimide, acryloyl morpholine (ACMO), acryloyl chloride, glycidyl methacrylate, glyceryl methacrylate, diacetone acrylamide, hydroxyalkyl (meth)acrylate, thioalkyl (meth)acrylate, hydroxyalkylacrylates, hydroxyalkyl methacrylates, and mixtures thereof.Among these non-ionic monomers, the alkyl groups are advantageously C1-C5, more advantageously C1-C3. They are preferably linear alkyls. Preferably, the hydrophilic non-ionic monomer is acrylamide.

[0085] The water-soluble polymer can be partially or completely post-hydrolyzed.

[0086] The water-soluble polymer may be post-hydrolyzed. Post-hydrolysis is the reaction of the polymer after polymerization. This step consists of the reaction of hydrolyzable functional groups of advantageously non-ionic monomers, more advantageously amide or ester functions, with a hydrolysis agent. This hydrolysis agent may be an enzyme, an ion exchange resin, or an alkaline base. Preferably, the hydrolysis agent is a Bronsted base. During this post-hydrolysis step of the water-soluble polymer, carboxylic acid or amine functions are formed. Indeed, the reaction between the base and the amide or ester functions present in the water-soluble polymer produces amine or carboxylate groups respectively. In a particular embodiment, the water-soluble polymer may comprise a transfer agent.

[0087] The transfer agent is advantageously chosen from methanol, isopropyl alcohol, sodium, calcium, magnesium, potassium or ammonium hypophosphite; 2-mercaptoethanol; 3-mercaptopropanol; dithiopropylene glycol; thioglycerol; thioglycolic acid; thiohydracrylic acid; thiolactic acid; thiomalic acid; cysteine; and aminoethanethiol; n-dodecyl mercaptan; sodium, calcium, magnesium, potassium or ammonium metally sulfonate; and their mixture. Preferably, it is sodium hypophosphite.

[0088] The amount of transfer agent in the polymer is advantageously between 0 and 50,000 ppm by weight relative to the total weight of the monomers of the polymer, preferably between 1 and 10,000 ppm by weight, more preferably between 5 and 5,000 ppm by weight, even more preferably between 20 and 2,000 ppm by weight. When present, the transfer agent represents at least 10 ppm by weight, relative to the total weight of the monomers of the polymer, preferably at least 20 ppm by weight.

[0089] In a particular embodiment, the polymer does not comprise a transfer agent.

[0090] In a particular embodiment, the polymer may be structured by at least one branching agent. A structured polymer means a non-linear polymer that has side chains.

[0091] The branching agent is advantageously chosen from:

[0092] - structural agents, which may be chosen from the group comprising compounds with polyethylene unsaturation (having at least two unsaturated functions, with the exception of diallyldialkyl ammonium), such as, for example, vinyl functions, in particular allylic or acrylic. Examples that may be mentioned are methylene bis acrylamide (MBA), triallyamine, or tetraallylammonium chloride or 1,2 dihydroxy ethylene bis-(N-acrylamide),

[0093] - compounds having at least two epoxy functions,

[0094] - compounds having at least one unsaturated function and one epoxy function,

[0095] - macroinitiators such as polyperoxides, polyazos and polytransfer agents such as polymercaptant polymers and polyols,

[0096] - functionalized polysaccharides,

[0097] - water-soluble metal complexes composed of: * a metal with a valence greater than 3 such as, by way of example and in a non-limiting manner, aluminum, boron, zirconium or titanium, and

[0098] * of a ligand carrying a hydroxyl function.

[0099] When the water-soluble polymer comprises at least one branching agent, it remains soluble in water. Those skilled in the art will know how to adjust the quantity of branching agent, and possibly the quantity of transfer agent, in order to achieve this result.

[0100] The polymers used in the process of the invention are advantageously linear, in other words, the polymers do not comprise a branching agent.

[0101] The polymer can be obtained by solution polymerization; gel polymerization; precipitation polymerization; suspension polymerization; reactive extrusion polymerization; water-in-water polymerization; or micellar polymerization, preferably the polymer is prepared by aqueous solution polymerization.

[0102] In the context of the invention, the polymer is not obtained in inverse emulsion.

[0103] Within the scope of the invention, no surfactant or oil is added during the polymerization of the polymer of the invention.

[0104] Indeed, it has been observed that the presence of oil or surfactant during the preparation of the polymer leads to a loss of application performance when used in combination with the surfactant of the invention. The polymerization is a radical polymerization. By radical polymerization, we include free radical polymerization using UV, azo, redox or thermal initiators as well as controlled radical polymerization (PCR) techniques or matrix polymerization techniques.

[0105] As controlled radical polymerization techniques, we can cite, without limitation, techniques such as iodine transfer polymerization (ITP), nitroxide-mediated polymerization (NMP), atom transfer (ATRP), reversible addition-fragmentation chain transfer polymerization (RAFT), of which the MADIX technology is part.

[0106] ("MAcromolecular Design by Interchange of Xanthates" in English), various variations of polymerizations with organometallic compounds ("Organometallic Mediated Radical Polymerization" in English (OMRP)), radical polymerization controlled by heteroatomic compounds ("OrganoHeteroatom-mediated Radical Polymerization" in English (OHRP)).

[0107] The polymer can be in liquid, gel or solid form when its preparation includes a drying step such as spray drying, drum drying, radiation drying such as microwave drying, or fluidized bed drying.

[0108] The anionic water-soluble polymer advantageously has a weight-average molecular weight of between 1,000,000 and 2,500,000 g / mol, preferably between 1,500,000 and 2,000,000 g / mol.

[0109] The cationic water-soluble polymer advantageously has a weight-average molecular weight of between 20,000 and 2,000,000 g / mol, preferably between 30,000 and 1,500,000 g / mol, more preferably between 50,000 and 1,000,000 g / mol, more preferably between 100,000 and 800,000 g / mol.

[0110] In a preferred embodiment, the water-soluble polymer is cationic.

[0111] In a particularly preferred embodiment, the cationic water-soluble polymer is a polyamine obtained by condensation between epichlorohydrin and dimethylamine having a molecular weight of between 10,000 and 800,000 g / mol.

[0112] Surfactant

[0113] The surfactant according to the invention is chosen from:

[0114] * anionic surfactants, and / or;

[0115] * non-ionic surfactants.

[0116] The surfactant advantageously has an HLB of between 5 and 17, preferably between 7 and 15, more preferably between 8 and 12.

[0117] The hydrophilic-lipophilic balance (HLB) of a chemical compound is a measure of its hydrophilic and / or lipophilic properties, determined by calculating the values ​​for different regions of the molecule, as described by Griffin in 1949.

[0118] In the present invention, we have adopted Griffin's method based on calculating a value based on the chemical groups of the molecule. Griffin assigned a dimensionless number between 0 and 20 to give information on the solubility of water and oil.

[0119] The HLB value of a substance having a total molecular mass M and a hydrophilic part of a molecular mass Mh is given by: HLB = 20 (Mh / M).

[0120] The anionic surfactant(s) are advantageously chosen from the group consisting of salts of alkyl sulfates, alkyl sulfonates, alkyl aryl sulfonates, alkyl ether sulfates, alpha olefin sulfonates, alkyl aryl ether sulfates, sulfated alcohols and ethoxylated sulfated alcohols, taurates, petroleum sulfonates, alkyl naphthalene sulfonates, alkyl sarcosinates and alkyl sulfosuccinates in which the alkyl group contains from 8 to 22 carbon atoms and the aryl group is a phenyl or a naphthyl and mixtures thereof. Preferably, it is sodium alkyl sulfosuccinate, more preferably sodium dioctyl sulfosuccinate.

[0121] The non-ionic surfactant(s) are advantageously chosen from ethylene glycol monostearate, propylene glycol myristate, glyceryl monostearate, glyceryl stearate, polyglyceryl-4-oleate, sorbitan acylate, sucrose acylate, PEG-150 laurate, PEG-400 monolaurate, polyoxy ethylene monolaurate, polysorbates, polyoxy ethylene octylphenyl ether, PEG-1000 cetyl ether, polyoxy ethylene tridecyl ether, polypropylene glycol butyl ether, Poloxamer® 401, stearoyl monoisopropanolamide, hydrogenated tallow polyoxy ethylene amide, secondary alcohol ethoxylates, decyl glucoside, lauryl glucoside, octyl glucoside, ether fatty alcohol polyglycolic acid, alkylphenol polyglycolic acid ether, fatty acid polyglycolic acid ester, mixed polymers of polypropylene oxide and polyethylene oxide, N-methyl myristamide.N-sorbityl lauramide, N-methyl myristamide, N-sorbityl myristamide, and alkyl polysaccharides such as octyl, nonyldecyl, undecyldodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, penta ... Surfactant formulations may contain additional components such as alkali metal salts (such as NaCl, NaOH), alkaline earth metal salts (such as MgCl2, CaCl2), and oxidants (such as hydrogen peroxide). The relative amounts of the additional components that comprise the surfactant formulation may vary over a wide range.

[0122] Dehydration stage by mechanical filtration

[0123] The conditioned mining residue is then brought into a filtration device to be dehydrated by separating the solid residues from the liquids in the residue.

[0124] Filtration is carried out under pressure.

[0125] Preferably, the applied pressure ranges from 1 to 15 bars.

[0126] Preferably, the pressure is increased gradually during filtration, for example by 1 bar / min until a pressure of at least 15 bars is reached.

[0127] Filtration is typically carried out for a period ranging from 1 to 300 minutes, preferably from 5 to 200 minutes, more preferably from 10 to 100 minutes.

[0128] Solid residues are typically collected in the filter and form the filter cake.

[0129] The liquids are collected in a separate collector and form the filtrate.

[0130] The mechanical filtration device refers to a type of equipment for dehydrating mining residues by supplying mechanical energy and implemented under pressure. Advantageously, the mechanical filtration device is chosen from filter presses and belt filters. Preferably, these are filter presses.

[0131] The dry matter content in the dehydrated mining residue is advantageously at least 80%, preferably at least 81%, more preferably at least 82%, more preferably at least 83%, more preferably at least 84% and more preferably at least 85%.

[0132] In a preferred mode at the end of the dehydration step, the cake is subjected to post-treatment.

[0133] Post-treatment consists of washing the cake and / or drying. Drying can be carried out using air, for example under an air flow (especially compressed air) or in an oven.

[0134] Washing the cake allows the recovery of valuable dissolved elements, or the elimination of impurities and / or toxic products used during the extraction of ores (caustic soda, cyanide, etc.) and thus reduces the danger and pollution of the residues.

[0135] Drying the cake with air increases the dryness (dry matter content).

[0136] The characteristics of these treatments will be adjusted by those skilled in the art according to the final objectives to be achieved for the discharge of solid residues into nature.

[0137] The invention and the advantages arising therefrom will become more apparent from the following examples given to illustrate the invention, and not in a limiting manner.

[0138] Examples

[0139] List of abbreviations:

[0140] DADMAC: Diallyl dimethylammonium chloride (hydrophilic cationic monomer)

[0141] AMD: Acrylamide (hydrophilic non-ionic monomer)

[0142] AA: Acrylic acid (hydrophilic anionic monomer)

[0143] ADAME. Q: Chlorinated dimethylaminoethyl methyl acrylate

[0144] APTAC: Acrylamidopropyl trimethyl ammonium chloride

[0145] Example 1: Dehydration of sludge on a filter press

[0146] The tests were carried out on a filter press using a single-plate filtration cell manufactured by Choquenet (France). The cell size used for the tests is 30 mm.

[0147] The test procedure is as follows:

[0148] - 300 g of mud are placed under stirring in a beaker,

[0149] - The sludge is conditioned by adding a polymer and / or surfactant solution (5 g / L), in the case of the invention the polymer solution is added first, followed by the addition of the surfactant in solution;

[0150] - The sludge thus conditioned is brought into the feed chamber of the Choquenet cell, then injected into the cell under atmospheric pressure. - The pressure is increased by 1 bar / min until a pressure of 8 bars is reached;

[0151] - The filtration speed is measured by monitoring the volume of filtrate recovered over time using a graduated cylinder.

[0152] - The test is finished when the volume of recovered filtrate no longer increases. The time to reach this plateau corresponds to the cycle time.

[0153] - The filter cake is then recovered, weighed and dried. After this time, the dry cake is reweighed, the ratio of the mass before / after drying (oven or air) corresponds to the dryness of the cake. The cake is dried in an oven at 90 °C for 12 h (residues II to 16) or by passing compressed air through the cake (residues 17 and 18). The stickiness of the cake is assessed visually by looking at the appearance of the filter after demolding the cake. A score from 1 to 10 is given depending on the coverage of the filter by the tested sludge. For a score of 1, the cake peels off easily and no residue is observed on the filter. Conversely, for a score of 10, the cake peels off with difficulty and the filter is entirely covered with a thin film of cake. Finally, the score given corresponds to a percentage of filter coverage.

[0154] The polymers (PI to P 12) tested are commercial products sold by the company SNF and their composition is summarized in Table 1 below.

[0155] Table 1: List of polymers used in the process according to the invention

[0156] The conditioned residues (II to 115) according to the invention (i.e. sludge + polymer + surfactant) as well as the counter-example conditioned residues (CEI to CE12) are presented in table 2.

[0157] Table 2: Compositions of the polymer+surfactant system of the residues packaged according to the invention II to 115 and counter-examples CEI to CE12.

[0158] The filtration and dehydration performances between the residues conditioned according to the invention (II to 115) and the comparative conditioned residues (CEI to CE12) are presented in Table 3 below.

[0159] Table 3: Filtration and dehydration performances between the residues conditioned according to the invention (II to 115) and the comparative conditioned residues (CEI to CE12) The cationic or anionic polymers alone (CE2 and CE3) make it possible to increase the filtration speed to the detriment of the dryness of the cake and lead to the formation of a cake with a more sticky character.

[0160] Conversely, the use of surfactant alone (CE4 and CE5) allows to reduce the humidity of the cake at the expense of the cycle time and also allows to reduce the stickiness of the cake.

[0161] The combination of the polymer and surfactant system according to the invention (II to 115) makes it possible to reduce the cycle time and the stickiness of the filter cake obtained and also to improve the dryness of the latter in a synergistic manner. The choice of the best treatment depends on the expectations, whether it is the residual humidity rate or the filtration speed.

[0162] Tests demonstrate that these performances are dependent on the molecular weight of the polymer and the nature of the surfactant, which must be correctly chosen. The selection of the molecular weight depends on the overall charge of the polymer; in fact, an anionic polymer has a wider and higher operating range than a cationic polymer.

[0163] Different types of filters were then tested to demonstrate the better performance obtained by using mechanical filters in combination with the combination compared to other filters, for example vacuum.

[0164] The polymer / surfactant combinations evaluated are the IEC, 13 and 14 combinations, the composition of which is detailed in Table 2.

[0165] Example 2: Evaluation of mechanical and non-mechanical filters with respect to sludge dewatering performance

[0166] Example 2a: Sludge dewatering on a belt filter press (mechanical filter)

[0167] The tests were carried out by draining on a filter equipped with a belt filter press.

[0168] 300 g of sludge previously conditioned with the previously defined dose of polymer and surfactant are placed in the center of the filter.

[0169] A second filter is placed on top with a piece of absorbent paper to help absorb the water absorbed by the absorbent paper above.

[0170] An inflatable cushion connected to the upper part of the cell allows progressive pressure to be applied in steps of 1 bar up to 5 bars.

[0171] Each pressure increase is carried out after the flow of the pressurized filtrate has completely stopped. The filtration time is obtained by adding the flow times of each stage.

[0172] The resulting cake is then removed from the mold and dried. The dryness of the latter is measured as described in Example 1.

[0173] Example 2b: Sludge dewatering on a vacuum belt filter (non-mechanical filtration)

[0174] The tests were carried out using a Büchner filter topped with a vacuum belt filter type filtration cloth equipped with a vacuum pump.

[0175] 300 g of sludge previously conditioned with the previously defined dose of polymer and surfactant are distributed evenly on the surface of the filter.

[0176] At the end of the addition, the vacuum pump is immediately started to achieve a vacuum of 100 mbar.

[0177] The filtration speed is measured by monitoring the volume of filtrate recovered over time using a graduated cylinder.

[0178] The vacuum is applied until cracks appear on the cake surface. The duration of the vacuum application corresponds to the filtration time.

[0179] The resulting cake is then removed from the mold and dried. The dryness of the latter is measured as described in Example 1.

[0180] Example 2c: Sludge dewatering on drum or disc filters (non-mechanical filters)

[0181] The tests are carried out on the same device since disc or drum filters have a similar operating principle.

[0182] The tests were carried out using a filter developed by SNF, which consists of a vertical disc with a diameter of 300 mm connected to a vacuum pump. The disc is topped with a filter cloth of the disc or drum filter type.

[0183] The disc is immersed in a beaker containing 300 g of sludge previously conditioned with the previously defined dose of polymer and surfactant.

[0184] A vacuum of 300 mbar is then applied. The filter cake forms on the surface of the disc. Filtration is complete when the cake thickness no longer varies. The filtration time corresponds to the time between the vacuum being applied and the end of filtration.

[0185] The filtration speed is measured by monitoring the volume of filtrate recovered over time using a graduated cylinder.

[0186] The resulting cake is then removed from the mold and dried. The dryness of the latter is measured as described in Example 1.

[0187] Results

[0188] The dryness results obtained on the different compositions according to the filter used are presented in Table 4 below.

[0189] Table 4: Evaluation of dryness according to the type of filter used in a sludge dewatering process; INV = invention; CE = counter-example

[0190] The results show on the one hand that the compositions according to the invention (polymer + surfactant) make it possible to obtain a cake with a higher dryness (CEI vs 13 / 14) regardless of the type of filter used, i.e. mechanical or not. On the other hand, the use of mechanical filters also makes it possible to improve the dehydration of the residues in comparison with the use of non-mechanical filters.

[0191] The filtration speed is also evaluated according to the composition and the filter used to dewater the sludge.

[0192] The results are presented in Table 5 below.

[0193] Table 5: Performance of different types of filters on filtration speed; INV = invention; CE = counter-example.

[0194] The results show on the one hand that the compositions according to the invention (polymer + surfactant) make it possible to increase the filtration speed (CEI vs 13 / 14) regardless of the type of filter used, i.e. mechanical or not. On the other hand, the use of mechanical filters also makes it possible to improve the dehydration of the residues.

[0195] In summary, the present invention makes it possible to improve the dryness (dry matter content in the cake), but also the filtration speed, in particular by means of a mechanical filter such as a filter press or a belt filter press.

Claims

Claims 1. A method for dehydrating a mining residue comprising the following steps: a) Adding and mixing at least one water-soluble polymer and at least one surfactant to the mining residue in order to obtain a conditioned mining residue; b) Dehydrating the conditioned mining residue by mechanical filtration in order to obtain a dehydrated mining residue; the water-soluble polymer(s) being chosen from: - anionic water-soluble polymers having a molecular weight between 800,000 and 3,000,000 g / mol; - cationic water-soluble polymers having a molecular weight between 10,000 and 3,000,000 g / mol; and - their mixtures, the surfactant(s) being chosen from: - anionic surfactants; - non-ionic surfactants, and - their mixtures.

2. Method according to claim 1, characterized in that the water-soluble polymer and the surfactant are added at the same injection point, one after the other, the polymer being added before the surfactant.

3. Method according to claim 1 or 2, characterized in that the anionic water-soluble polymer consists of one or more hydrophilic anionic monomers and optionally hydrophilic non-ionic monomers.

4. Method according to claim 3, characterized in that the anionic water-soluble polymer consists of one or more hydrophilic anionic monomers chosen from acrylic acid; methacrylic acid; dimethylacrylic acid; itaconic acid; itaconic acid hemi-ester; itaconic anhydride; itaconamide; crotonic acid; maleic acid; fumaric acid; acrylamido undecanoic acid; 3-acrylamido 3-methylbutanoic acid; maleic anhydride; monomers of strong acid type having for example a sulfonic acid or phosphonic acid function such as vinyl sulfonic acid, vinylphosphonic acid, allylsulfonic acid, methallylsulfonic acid, 2-methylidenepropane-1,3-disulfonic acid, 2- sulfoethylmethacrylate, sulfopropylmethacrylate, sulfopropylacrylate, allylphosphonic acid, styrenesulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, 2-acrylamido-2-methylpropanedisulfonic acid; water-soluble salts of these monomers such as their alkali metal, alkaline earth metal, or ammonium salts; and mixtures thereof;and optionally one or more hydrophilic non-ionic monomers chosen from acrylamide, methacrylamide, N-alkylacrylamides, N-alkylmethacrylamides, N,N-dialkyl acrylamides, N,N-dialkylmethacrylamides, alkoxylated esters of acrylic acid, alkoxylated esters of methacrylic acid, N-vinylpyrrolidone, N-methylol acrylamide, N-vinylformamide, N-vinyl acetamide, N-vinyl imidazole, N-vinyl succinimide, acryloyl morpholine, acryloyl chloride, glycidyl methacrylate, glyceryl methacrylate, diacetone acrylamide, hydroxyalkyl (meth)acrylates, thioalkyl (meth)acrylates, hydroxyalkylacrylates, hydroxyalkyl methacrylates, and mixtures thereof.; 5. Method according to claim 1 or 2, characterized in that the cationic water-soluble polymer consists of one or more hydrophilic cationic monomers and optionally hydrophilic non-ionic monomers.

6. Method according to claim 5, characterized in that the cationic water-soluble polymer consists of one or more hydrophilic cationic monomers chosen from diallyldialkyl ammonium salts; acidified or quaternized salts of dialkylaminoalkylacrylamides; acidified or quaternized salts of dialkylaminoalkylmethacrylamides, acidified or quaternized salts of dialkylaminoalkyl acrylate, acidified or quaternized salts of dialkylaminoalkyl methacrylate and mixtures thereof;and optionally one or more hydrophilic non-ionic monomers chosen from acrylamide, methacrylamide, N-alkylacrylamides, N-alkylmethacrylamides, N,N-dialkyl acrylamides, N,N-dialkylmethacrylamides, alkoxylated esters of acrylic acid, alkoxylated esters of methacrylic acid, N-vinylpyrrolidone, N-methylolacrylamide, N-vinylformamide, N-vinyl acetamide, N-vinyl imidazole, N-vinyl succinimide, acryloyl morpholine, acryloyl chloride, glycidyl methacrylate, glyceryl methacrylate, diacetone acrylamide, hydroxyalkyl (meth)acrylates, thioalkyl (meth)acrylates, hydroxyalkylacrylates, hydroxyalkyl methacrylates, and mixtures thereof.; 7. Method according to one of claims 1 to 4, characterized in that the water-soluble polymer is an anionic water-soluble polymer consisting of 5 to 100 mol% of hydrophilic anionic monomer and 0 to 95 mol% of hydrophilic non-ionic monomer, relative to the total quantity of monomers in the anionic water-soluble polymer.

8. Method according to claim 5 or 6, characterized in that the water-soluble polymer is a cationic water-soluble polymer consisting of 5 to 100 mol% of hydrophilic cationic monomer and 0 to 95 mol% of hydrophilic non-ionic monomer, relative to the total quantity of monomers in the cationic water-soluble polymer.

9. Method according to one of claims 1 to 8, characterized in that the water-soluble polymer is free of crosslinking agent.

10. Method according to claim 8, characterized in that the water-soluble polymer is a cationic polyamine obtained by condensation between epichlorohydrin and dimethylamine, and has a molecular weight of between 10,000 and 800,000 g / mol.

11. Method according to one of claims 1 to 10, characterized in that the mechanical filtration is carried out by means of a filter press.

12. Method according to one of claims 1 to 11, characterized in that the mining residue comes from the exploitation of ores, drilling muds.

13. Method according to one of claims 1 to 12, characterized in that the quantity of water-soluble polymer added to the mining residue is between 0.5 and 5,000 ppm relative to the weight of dry matter of the mining residue to be conditioned; and in that the quantity of surfactant added to the mining residue is between 10 and 10,000 ppm, relative to the weight of dry matter of the mining residue to be conditioned.

14. Method according to one of claims 1 to 13, characterized in that at the end of the dehydration step, the cake is dried under a flow of air.

Images