EA048393B1 - REMOVAL OF SI FROM WATER STREAMS OF MINERAL PROCESSING PLANTS - Google Patents

Description

Field of technology

The present invention relates to a method and a device for removing Si from an aqueous stream(s) of a mineral processing plant. In particular, the present invention relates to a method and a device for removing soluble and/or colloidal Si compounds from an aqueous stream of a mineral processing plant.

Prior art

During the various process steps of mineral raw material processing, the pH of the suspension usually decreases as a result of oxidation of sulphide minerals and the absence of carbonate minerals, which are effective pH buffers. This sulphur oxidation and the accompanying decrease in pH also continues during tailings (waste) processing, resulting in increased concentrations of dissolved ions in the liquid phase, such as SO ₄ , Mg, Fe, Ni, Ca, K, Na. In addition, as a result of dissolution of aluminosilicate/silicate minerals at low pH values, Si and Al are released into the liquid phase.

The water produced in tailings treatment operations, as well as other feedwater streams to the system, such as waste rock dump or open pit water, may contain significant concentrations of dissolved substances such as Si and metals. When the various water streams are mixed and fed to the high pH flotation stage, the solubility of the various chemical species changes. Accordingly, depending on the concentration of dissolved Si in the feedstream, and depending on the pH profile in the process, the dissolved silicates may polymerize to form gels and colloids, either by polymerization or by reaction with various metal ions or solid surfaces.

Gels and colloids formed by silicates can cause a variety of problems that can ultimately lead to losses of valuable metals as well as reduced recovery rates and quality of final products.

Accordingly, there is a need to develop a method for removing Si compounds from water streams of a mineral processing plant.

In particular, there is a need to develop a method for removing soluble and/or colloidal Si compounds from water streams of a mineral processing plant and thus preventing the formation of gels and colloids containing silicates, which will eliminate the problems they create.

The essence of the invention

The objective of the present invention is to provide a method and apparatus for removing soluble and/or colloidal Si compounds from an aqueous stream of a mineral processing plant, which will increase the degree of extraction and the quality of the extracted product and, accordingly, the overall efficiency of the plant.

One embodiment of the invention relates to a method for removing soluble and/or colloidal Si compounds from an aqueous stream of a mineral processing plant. The method comprises adding a coagulant(s) and/or a flocculant(s) and/or a flotation chemical reagent(s) to an aqueous stream to ensure the formation of flocs comprising at least some amount of Si compounds and to obtain a treated aqueous stream; performing a cleaning flotation of the treated aqueous stream to separate at least some amount of Si compounds as a top product of the cleaning flotation; and removing the top product of the cleaning flotation. The cleaning flotation comprises the use of gas bubbles, wherein at least 90% of the gas bubbles have a diameter of from 0.2 to 250 μm.

One embodiment of the invention relates to a plant for removing soluble and/or colloidal Si compounds from an aqueous stream of a plant processing mineral raw materials. The plant comprises: a mixing system designed to add a coagulant(s) and/or a flocculant(s) and/or a flotation chemical reagent(s) to the aqueous stream, and a cleaning flotation plant designed to separate at least some amount of Si compounds from the aqueous stream in the form of a cleaning flotation top product and to obtain residual process water in the form of a cleaning flotation bottom product.

Brief description of graphic materials

Fig. 1 schematically shows an example of a process flow diagram of a method according to one embodiment of the invention;

Fig. 2 schematically shows an example of a process flow diagram of a method according to one embodiment of the invention;

Fig. 3 schematically shows an example of a process flow chart of a method according to one embodiment of the invention; and Fig. 4 schematically shows an example of a process flow chart of a method according to one embodiment of the invention.

The images are schematic. The images are not to scale.

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Detailed description of the invention

Below, the technical solution is considered in more detail using the example of some embodiments, which should not be considered as limiting.

The term "including" as used in the present description and in the claims may have an open-ended meaning, however, it also includes the limiting term "consisting of".

The following numerical designations are used in this document:

100 water flow

101 processed water streams

102 cleaning flotation unit

103 top product of cleaning flotation

104 bottom product of cleaning flotation

105 dewatering equipment

200a water flow

201 treated water streams

202 cleaning flotation unit

203 top product of cleaning flotation

204 bottom product of cleaning flotation

205a tailings thickener

211 mineral raw material flotation circuit

212 suspension

213 bottom product of mineral raw material flotation circuit

214 top product of mineral raw material flotation circuit

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215 tailings thickener bottom product

216 flotation plant

300a water flow

301 processed water stream

02 Cleaning flotation unit

303 top product of cleaning flotation

304 bottom product of cleaning flotation

305a tailings thickener

311a first circuit of mineral raw material flotation

311b Second circuit of mineral raw material flotation

312 suspension

313a bottom product of the first circuit of mineral raw material flotation

313b bottom product of the second circuit of mineral raw material flotation

314a top product of the first circuit of mineral raw material flotation

314b top product of the second circuit of mineral raw material flotation

315 tailings thickener bottom product

316 flotation unit

400b water flow

401 processed water stream

402 cleaning flotation unit

403 top product of cleaning flotation

404 bottom product of cleaning flotation

405b concentrate thickener

411 mineral raw material flotation circuit

412 suspension

413 bottom product of mineral raw material flotation circuit

414 top product of mineral raw material flotation circuit

416 flotation plant

425 bottom product from concentrate thickener

In the mining industry, beneficiation is a process that increases the economic value of ore by removing gangue minerals, producing a higher-grade product (concentrate) and a waste stream, or tailings. Examples of beneficiation processes include froth flotation and gravity separation. The term gangue refers to the non-commercially valuable material that surrounds or is intimately mixed with the target mineral in an ore deposit.

Froth flotation enrichment is commonly used to extract and enrich sulphide ores. Froth flotation is a method suitable for separating minerals from gangue by using the difference in their hydrophobicity. The difference in hydrophobicity between valuable minerals and gangue is increased by using surfactants and wetting agents. The flotation process is used to separate various sulphides, carbonates and oxides prior to subsequent refining.

To perform froth flotation, the ground ore is mixed with water to form a slurry and the target mineral is rendered hydrophobic by adding a surfactant or collector chemical. The type of chemical added depends on the nature of the mineral being extracted, but most often on the nature of the non-target minerals. The slurry, which includes hydrophobic particles and hydrophilic particles, is sent to tanks called flotation cells,

- 3 048393 which are equipped with aeration devices to produce bubbles. Hydrophobic particles are captured by air bubbles, which rise to the surface, forming foam. The foam is removed from the chamber, obtaining a concentrate of the target mineral. Froth flotation is usually carried out in several stages to achieve the maximum degree of extraction of the target mineral or minerals and the maximum concentration of these minerals in the concentrate.

The amount of gangue in the ore increases. The amount of Si-containing minerals in the gangue minerals increases. Most of these _Si -containing minerals may be in the form of feldspar ( _KAlSi3O8 - _NaAlSi3O8 - _CaAl2Si2O8 ) and quartz ( _SiO4 / _SiO2 ), which are the two most common minerals in the Earth's continental crust. The basic structure of these minerals typically includes a continuous lattice of silicon and oxygen tetrahedra, usually with Fe, Al, Mn or Mg included in the structure as impurities. Due to the presence of impurities, the otherwise very stable structure may be unstable to external conditions such as pH changes. Accordingly, the structure may disintegrate into smaller parts. If this occurs during the process, the silicates may solubilize or form colloids. When the pH increases, Si-containing particles can react with various compounds, thus forming new structures. When the silicate structure is restored, for example, ribbon structures can form. These structures can cause an increase in viscosity, thus leading to problems during beneficiation/concentration.

Typically the waste rock recovered from beneficiation is sent to a tailings dam where it is expected that over a long residence time, typically 20-40 days, sediment will form, residual flotation chemicals will decompose and solids will separate from the collected and reusable process water. The collected process water can then be recycled back into the beneficiation process. The quality of the recycled process water plays a role in achieving the required recovery rates and end product quality.

Nowadays, water shortages, environmental control requirements from legal authorities and the public, cost and space requirements of traditional treatment of process water in tailings treatment processes place increasing demands on the recycling of process water, resulting in the main beneficiation processes being carried out in systems that are at least partially closed with respect to water use. In closed systems, supersaturation of process water with silicates can sometimes occur. It has been shown that the majority of the total Si content is present as colloids rather than soluble compounds.

As noted above, gels and colloids formed by silicates can cause various problems that can ultimately lead to losses of valuable metals, as well as to reduced recovery rates and final product quality. Problems can arise, for example, from the adsorption of colloids on mineral surfaces, which prevents the adsorption of the collector on the mineral surfaces. The adsorption of collectors by colloids prevents the adsorption of collectors on mineral surfaces, which is necessary for flotation, and thus impairs flotation kinetics. In addition, valuable metals can become entrapped in the gel matrix, which leads to reduced metal recovery. In addition, gels and colloids can cause problems related to thickening (non-settling colloids, their recirculation back into the flotation process) or even problems during concentrate filtration (higher moisture content in the filter cake due to the formation of an aqueous gel). It is known that silicates form hydrophilic layers on the surfaces of valuable minerals, which leads to a decrease in the flotation properties of valuable minerals.

In addition, Si tends to form complexes with Fe in aqueous solutions. The resulting complexes may be fine colloidal particles. Fine colloidal particles containing Si and Fe create an excessive fines load, which may adversely affect the froth flotation process. Si and Fe together may form coatings/layers on the ore surface, thereby changing the flotation properties of the ore and ultimately reducing the ore recovery. Complexes containing Si and Fe may cause changes in the oxidation-reduction properties of the ore, which leads to changes in the foaming ability of the ore. For example, pentlandite (iron nickel sulfide) can be oxidized by complexes containing Si and Fe. The foaming ability of oxidized pentlandite differs from its foaming ability in the unoxidized state, which may adversely affect the ore recovery.

Iron (Fe) itself can also affect Ni recovery in flotation. Excess iron in the process water can cause Fe hydroxide coatings to form on the pentlandite ore used to extract Ni, resulting in lower Ni recovery.

The amount of soluble and/or colloidal silicon compounds in water used in mineral processing can be more than 100 ppm, often even 300-400 ppm. Soluble silicon compounds can also be referred to as dissolved compounds.

- 4 048393 silicon. The existence of soluble and/or colloidal silicon compounds in water streams from a mineral processing plant has generally not been previously recognized. Typically, when performing water analyses, water samples were filtered prior to elemental analysis. Since typical filters have a pore size of 0.45 µm, colloidal silicon compounds were filtered from the samples. In addition, the problems posed by soluble and/or colloidal silicon compounds in mineral processing discussed above were not fully recognized.

The object of the present invention is to provide a method and apparatus for removing soluble and/or colloidal Si compounds from aqueous streams of a mineral processing plant and thus preventing the formation of gels and colloids containing Si compounds and the problems caused by them. Furthermore, since the aqueous streams typically include Fe in complex with Si, the method also ensures the removal of at least some of the iron contained in the aqueous streams of the mineral processing plant.

In the context of the present invention, Si compounds are compounds containing silicon and found in materials associated with the processing of mineral raw materials. Si compounds include silicates. The term silicate may refer to any member of the class of anions consisting of silicon and oxygen, to any salt including such anions, or to any ester including such anions. The term silicate also includes anions that include a continuous framework of SiO ₄ tetrahedra in the structure of which metals, typically Fe, Al, Mn or Mg, are incorporated as impurities. The term silicate also includes silicate minerals, as well as rocks comprising primarily such minerals. Silicates may also include quartz (SiO2). Silicates also include minerals in which some of the silicon atoms are replaced by aluminum or another tetravalent atom(s), such as aluminosilicates.

In the context of the present invention, a colloidal suspension or colloid is a mixture in which a substance in the form of dispersed microscopic insoluble or soluble particles is suspended in another substance. In order to form a colloid, the insoluble or soluble particles must not precipitate, or a very long period of time must be required for their noticeable precipitation. Thus, in this document, the term colloidal Si compounds refers to silicon-containing compounds that are suspended in water, forming a mixture in which the insoluble or soluble particles do not precipitate, or a very long period of time is required for their precipitation.

In the context of the present invention, the removal of soluble and/or colloidal Si compounds may be referred to as a method for the complete elimination of said compounds or a method for reducing the amount of said compounds, i.e. the amount of Si compounds in the aqueous stream sent for treatment exceeds the amount of said compounds in the stream obtained after performing the method described in this document.

In the method according to one of the embodiments, which is shown in Fig. 1, a coagulant(s) and/or a flocculant(s) and/or a flotation chemical reagent(s) are added to the aqueous stream 100 of the mineral processing plant. This leads to the destabilization of colloidal particles and suspended solids, which are collected into larger aggregates that can be separated from the aqueous solution. A treated aqueous stream 101 is obtained.

The treated aqueous stream 101 is subjected to cleaning flotation in a cleaning flotation unit 102. The cleaning flotation includes the use of gas bubbles, wherein at least 90% of the gas bubbles have a diameter of 0.2 to 250 μm. At least some of the soluble and/or colloidal Si compounds can be separated as an overhead product 103 of the cleaning flotation. The bottom product 104 of the cleaning flotation includes residual production water. The overhead product 103 of the cleaning flotation, including at least some of the soluble and/or colloidal Si compounds, can be removed as tailings. The bottom product 104 of the cleaning flotation can be recycled back into the process for use as production water.

The aqueous stream from which soluble and/or colloidal Si compounds are to be removed may comprise water from dewatering equipment 105. Dewatering equipment 105 may comprise a settling device or a filter. The settling device may be, for example, a thickener or a clarifier. The aqueous stream 100 to be processed may comprise at least a portion of the stream obtained from dewatering equipment 105. Alternatively or in addition, aqueous stream 100 may comprise mine water or water collected from a tailings pond.

According to one embodiment shown in Fig. 2, the aqueous stream 200a obtained from the dewatering equipment, in this case from the tailings thickener 205a, comes from a flotation plant 216 including a mineral flotation circuit 211 designed to process ore particles suspended in a suspension 212 by flotation to recover ore

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The mineral flotation circuit 211 is designed to separate the suspension 212 into a mineral flotation circuit underflow 213 and a mineral flotation circuit overflow 214. The mineral flotation circuit overflow 214 includes the recovered material.

The flotation unit 216 may be designed to recover Ni and/or Cu. As shown in Fig. 3, the flotation unit 316 may include a first mineral flotation circuit 311a designed to recover Cu and a second mineral flotation circuit 311b designed to recover Ni.

The first and second circuits of mineral raw material flotation can have common or separate water supply circuits.

According to one embodiment, the dewatering equipment includes a settling device, which is a thickener. The thickener is designed in such a way that it functions as a solid-liquid separator to separate the sludge, i.e., the thickener underflow, from the supernatant, i.e., the thickener overflow. The thickener underflow includes particles whose density exceeds that of the liquid, causing them to fall into the sludge.

The thickener may be a so-called concentrate thickener 405b, as shown in Fig. 4. The overhead product 414 of the mineral raw material flotation circuit may be directed to the concentrate thickener 405b. In the concentrate thickener 405b, the water absorbed by the particles and thereby increasing the density of the extracted ore may be removed, which facilitates the transportation of the concentrate and its further processing. In the concentrate thickener 405b, the overhead product 414 of the mineral raw material flotation circuit is dewatered to form an overhead product 400b from the concentrate thickener and a bottom product 425 from the concentrate thickener. The bottom product 425 from the concentrate thickener includes the extracted ore, i.e., concentrate, which is directed from the concentrate thickener 405b for further processing. The overhead product 400b from the concentrate thickener may be processed in the method described in this document.

In an alternative embodiment, the thickener may be a so-called tailings thickener 205a, 305a, as shown in Fig. 2 and 3. The underflow 213, 313b of the mineral flotation circuit may be directed to the tailings thickener 205a, 305a. In the tailings thickener 205a, 305a, the underflow 213, 313b of the mineral flotation circuit is dewatered to form a tailings thickener overflow 200a, 300a and a tailings thickener underflow 215, 315. The tailings thickener overflow 200a, 300a may be processed in the manner described herein. The tailings thickener underflow 215, 315 is recovered from the tailings thickener 205a, 305a. The underflow 215, 315 from the tailings thickener is typically recovered from the thickener as tailings (waste). The solids content of the underflow 215, 315 from the tailings thickener may be at least 80% by weight.

According to one embodiment, the aqueous stream 100, 200a, 300a, 400b, from which it is necessary to remove soluble and/or colloidal Si compounds, includes a thickener overhead product. The thickener overhead product can be obtained from the concentrate thickener 405b and/or from the tailings thickener 205a, 305a. The thickener overhead product includes process water and soluble and/or colloidal Si compounds. The thickener overhead product can further include Si-containing particles, as well as other unwanted, contaminating or unrecovered materials or compounds, such as fine particles and larger particles, starch-based anticollectors, microorganisms, etc., suspended and/or dissolved in the process water.

Prior to processing by the cleaning flotation method, the thickener overflow may be sent to a thickener overflow tank to stabilize the thickener overflow.

The coagulant(s) and/or flocculant(s) may be added to the aqueous stream 100, 200a, 300a, 400b in any suitable manner, provided that the coagulant(s) and/or flocculant(s) are properly mixed with the aqueous stream 100, 200a, 300a, 400b. For example, the coagulant(s) and/or flocculant(s) may be added in a mixing unit.

According to one embodiment, the cleaning flotation is dissolved air flotation (DAF). DAF is a flotation process widely used for clarifying water or waste streams. Solids are separated from the liquid using small bubbles of a flotation gas, which may be called microbubbles. Microbubbles may be formed, for example, by dissolving air or another flotation gas in the liquid under pressure. The bubbles are formed when the pressure drops during the release of the dispersion. The solid particles attach to the bubbles and rise to the surface. The resulting floating sludge may be removed from the surface of the liquid as a DAF overflow using sludge collectors.

The result of the described method can be a decrease in the turbidity of the water flow by 50- 6 048393

99%. Turbidity is the cloudiness or haze of a fluid caused by the presence of large quantities of individual particles that are normally invisible to the naked eye. Turbidity is caused by suspended solid matter consisting of very small particles that settle very slowly or not at all, or by colloidal particles.

According to one embodiment, the cleaner flotation bottom product 104, 204, 304, 404 or at least a portion thereof is recycled back into the flotation process or into a process preceding flotation. The cleaner flotation bottom product 104, 204, 304, 404 or at least a portion thereof can be recycled, for example via grinding, into flotation. Fig. 3 shows a plant in which the cleaner flotation bottom product 104, 204, 304, 404 or at least a portion thereof is recycled back into the flotation unit 216, 316, 416 for use in the flotation of mineral raw materials. In the case where water for flotation or for a process preceding flotation, such as grinding, is withdrawn from a tailings treatment area, the withdrawn water has a low pH, since the pH of the tailings water decreases over time. Metals contained in tailings dissolve more easily in water with a low pH. To carry out the flotation process, the pH of the suspension must be increased, which causes the previously dissolved metals to precipitate. However, precipitates cause problems during flotation. Metals and other impurities contained in the waste water can also cause a decrease in the surface quality of minerals already during milling. Therefore, the problems described above can be eliminated by recycling the underflow of the cleaner flotation back to flotation or even to a process preceding flotation, such as milling.

The coagulant may be selected from a group comprising: inorganic coagulants, aluminum salts, iron salts, organic coagulants. Preferably, the coagulant is an aluminum salt or an iron salt. The coagulant is selected in such a way that it causes coagulation. Coagulation is the process of destabilization of colloidal particles and suspended solids, as a result of which they form microflakes, which under suitable conditions can form agglomerates. Coagulation is a chemical process involving charge neutralization. Coagulation depends on the type of coagulant used, its dosage and mass, pH and initial turbidity of the treated water, as well as the properties of the undesirable substances present.

In a colloidal suspension, particles settle very slowly or do not settle at all due to the electrical charges present on the surface of the colloidal particles, which provide mutual repulsion of the particles from each other. The surface charge can be estimated by the value of the zeta potential (electrokinetic potential). To initiate coagulation, a coagulant with an opposite charge is added to the water, which reduces the repulsive charge and destabilizes the suspension. After neutralization of the repulsive charges, the particles begin to agglomerate under the action of Van der Waals forces and form flakes.

A flocculant may be a synthetic polymer or a natural polymer or derivatives of both. Flocculants are agents that promote flocculation by causing colloids and other suspended particles to aggregate in liquids, resulting in floc formation. Flocculation is the process by which destabilized particles combine to form larger aggregates called flocs, which can be separated from water by sedimentation or flotation. Many flocculants include polyvalent cations such as aluminum, iron, calcium, or magnesium. These positively charged molecules can interact with negatively charged particles and molecules, lowering the barriers to aggregation. Some flocculants can react with water to form insoluble hydroxides, which, upon sedimentation, combine with each other to form long chains or networks that physically entrap small particles into larger flocs. The natural polymer or derivative thereof may include, for example, starch or modified starch or polysaccharides. Examples of synthetic polymers include, for example, high molecular weight (with a molecular weight greater than 500,000) flocculants such as polyacrylamides (negatively or positively charged or neutral) or Mannich reaction products (positively charged), and low molecular weight (with a molecular weight less than 500,000) flocculants such as polyamines (positively charged), polyepiamine (copolymer of dimethylamine and epichlorohydrin) (positively charged), poly(diallyldimethyl ammonium chloride) (positively charged), polyethyleneimines (positively charged) or polyethylene oxide (neutral).

The flotation chemical reagent(s) that can be added to the aqueous stream to improve the formation of flocs comprising at least some amount of Si compounds to obtain the treated aqueous stream can comprise at least one substance selected from the group consisting of: collectors, activators, anticollectors, frothers, modifiers. Collectors can comprise surface-active organic reagents such as thiols, alkyl carboxylates, alkyl sulfates, alkyl sulfonates, alkyl phosphates, amines, chelating agents and alkyl phosphonic acids. Activators can comprise, for example, metal hydroxy derivatives or sodium sulfide. Anticollectors can comprise, for example, sodium sulfide or cyanide salts. Frothers can comprise, for example, alcohols, polyethers, ethylene oxide and polyglycol ethers.

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Claims (17)

According to one embodiment, before performing the cleaning flotation of the treated aqueous stream 101, 201, 301, 401, the pH value of the aqueous stream 100, 200a, 300a, 400b is adjusted to values in the range from 4.5 to 10. The pH value of the aqueous stream can be adjusted before adding the coagulant(s) and/or flocculant(s) and/or flotation chemical reagent(s) to the aqueous stream. Thus, before performing the cleaning flotation of the treated aqueous stream 101, 201, 301, 401, the pH value of the treated aqueous stream 101, 201, 301, 401 is in the range from 4.5 to 10. According to one embodiment, an iron salt is used as a coagulant. In this case, in order to increase the efficiency of coagulation, before carrying out the cleaning flotation of the treated aqueous stream 101, 201, 301, 401, the pH value of the aqueous stream 100, 200a, 300a, 400b can be adjusted in the range from 5 to 8. The pH range from 5 to 8 can be preferable, since it is known that precipitation of iron hydroxide occurs in the specified pH range. The pH value of the aqueous stream can be adjusted in any suitable way. The pH value can be adjusted, for example, in a mixing unit. The use of an iron salt as a coagulant is advantageous, since the aqueous stream already contains Fe, and thus, smaller amounts of coagulant may be required to achieve the desired coagulation. In addition, the flakes obtained by using iron salt as a coagulant can have higher stability under cleaning flotation conditions, which increases the efficiency of cleaning flotation. The result of the process described in this document is that the treated process water, i.e. the liquid obtained from the cleaning flotation unit, is clean in the sense that it does not contain soluble and/or colloidal Si compounds, and the treated process water can be reused without adversely affecting the result of the process. Depending on the composition of the treated water stream, the Si removal rate can be from 55 to 90%. In addition, since the aqueous streams typically contain Fe in complex with Si, the method also provides the possibility of removing at least some of the iron contained in the aqueous streams of the mineral processing plant. This avoids problems caused by complexes containing Si and Fe, as well as excess iron itself. Depending on the dosage of the coagulant and the composition of the aqueous stream, approximately 60-90% of the iron contained in the aqueous streams can be removed by the method described herein. CLAUSE OF INVENTION 1. A method for removing soluble and/or colloidal Si compounds from an aqueous stream (100, 200a, 300a) of a mineral processing plant, comprising adding a coagulant(s) and/or a flocculant(s) and/or a flotation chemical reagent(s) to the aqueous stream (100, 200a, 300a) to ensure the formation of flocs comprising at least some amount of Si compounds and to obtain a treated aqueous stream (101, 201, 301); performing a cleaning flotation of the treated aqueous stream (101, 201, 301) to separate at least some amount of Si compounds in the form of a cleaning flotation overhead product (103, 203, 303); and removing the cleaning flotation overhead product (103, 203, 303); wherein the cleaning flotation comprises the use of gas bubbles, wherein at least 90% of the gas bubbles have a diameter of from 0.2 to 250 μm, wherein the aqueous stream (100, 200a, 300a) comprises water obtained from dewatering equipment (105), wherein the underflow (213, 313a, 313b) from a flotation unit (216, 316) comprising a mineral flotation circuit (211, 311a, 311b) designed to process ore particles suspended in a suspension (212, 312) by flotation to recover ore is used to form the aqueous stream (100, 200a, 300a) from the dewatering equipment (105), and wherein the mineral flotation circuit (211, 311a, 311b) is designed to for separating the suspension (212, 312) into a bottom product (213, 313a, 313b) of the mineral raw material flotation circuit and an upper product (214, 314a, 314b) of the mineral raw material flotation circuit, and the water flow (200a, 300a) coming from the flotation unit (216, 316) is the bottom product (213, 313b) of the mineral raw material flotation circuit. 2. The method according to claim 1, wherein the equipment (105) for dewatering includes a settling device or filter. 3. The method according to claim 2, wherein the settling device is a thickener (205a, 305a). 4. The method according to any one of claims 1 to 3, wherein the aqueous stream (100, 200a, 300a) comprises at least a portion of the stream obtained from the dewatering equipment (105). 5. The method according to any one of claims 1 to 4, wherein the flotation unit (216, 316) is designed to extract Ni and/or Cu. - 8 048393 6. The method according to any one of claims 1 to 5, wherein the flotation unit (216, 316) includes a first mineral flotation circuit (311a) designed to extract Cu and a second mineral flotation circuit (311b) designed to extract Ni. 7. The method according to any one of claims 1 to 6, characterized in that the method further comprises recycling at least a portion of the underflow (104, 204, 304) of the cleaning flotation back into the flotation process or into the process preceding the flotation. 8. The method according to any one of the preceding claims, wherein the coagulant is an aluminium salt. 9. The method according to any one of claims 1 to 7, wherein the coagulant is an iron salt. 10. The method according to any of the preceding claims, wherein before carrying out the cleaning flotation of the treated aqueous stream (101, 201, 301), the pH value of the aqueous stream (100, 200a, 300a) is set in the range from 4.5 to 10. 11. The method according to any one of the preceding claims, wherein the aqueous stream (100, 200a, 300a) comprises Fe in a complex with Si, and the method comprises removing at least some amount of Fe from the aqueous stream (100, 200a, 300a). 12. The method according to any of the preceding claims, wherein the cleaning flotation is dissolved air flotation. 13. A system for removing soluble and/or colloidal Si compounds from an aqueous stream (100, 200a, 300a) of a mineral processing plant, comprising a mixing system designed to add to the aqueous stream (100, 200a, 300a) a coagulant(s) and/or a flocculant(s) and/or a flotation chemical reagent(s); and a cleaning flotation unit (102, 202, 302) configured to separate at least some of the Si compounds from the aqueous stream (100, 200a, 300a) as a cleaning flotation overhead (103, 203, 303) and to obtain residual production water as a cleaning flotation underflow (104, 204, 304), wherein the system further comprises dewatering equipment (105) and a flotation unit (216, 316) comprising a mineral flotation circuit (211, 311a, 311b) configured to process ore particles suspended in the slurry (212, 312) by flotation to recover the ore, wherein the mineral flotation circuit (211, 311a, 311b) is configured to separate suspensions (212, 312) into the underflow (213, 313a, 313b) of the mineral raw material flotation circuit and the overflow (214, 314a, 314b) of the mineral raw material flotation circuit, and the underflow (213, 313b) of the mineral raw material flotation circuit is intended for feeding to dewatering equipment (105) designed for dewatering the underflow (213, 313b) of the mineral raw material flotation circuit to form the underflow (215, 315) from the dewatering equipment and the overflow from the dewatering equipment, which forms the specified aqueous stream (100, 200a, 300a), intended for feeding thereto a coagulant(s) and/or a flocculant(s) and/or a flotation chemical reagent(s). 14. The system according to claim 13, wherein the dewatering equipment (105) includes a settling device or filter. 15. The system of claim 14, wherein the settling device is a thickener (205a, 305a), wherein the underflow (213, 313b) of the mineral raw material flotation circuit is intended to be fed to the thickener (205a, 305a) designed to dewater the underflow (213, 313b) of the mineral raw material flotation circuit to form an overflow (200a, 300a) from a tailings thickener and an underflow (215, 315) from a tailings thickener, where the aqueous flow (200a, 300a) includes the overflow (200a, 300a) of the thickener. 16. The system according to any one of claims 13-15, wherein the flotation unit (216, 316) is designed to extract Ni and/or Cu. 17. The system according to any one of claims 13 to 16, wherein the cleaning flotation unit (102, 202, 302) is a dissolved air flotation unit. -