Method for separating iron-containing impurities from a host matrix - Patents.com

Abstract

A method for separating iron-containing impurities from silica sand is described. The method includes subjecting a silica sand slurry to froth flotation in the presence of a collector, a foaming agent, and an inhibitor selected to concentrate the iron-containing impurities of the silica sand in the flotation foam, thereby producing silica sand having reduced iron-containing impurities in the tail product. The collector comprises ≧60 to ≦70 w / w% tall oil acid, ≧10 to ≦30 w / w% poly-α-hydroxyl alkyl ether, and up to 3 w / w% tall oil rosin. The foaming agent is a non-ionic surfactant, in particular one or more alkyl polypropoxy C n P m and / or Polyethoxy C n E m The foaming agent includes n=0 to 6 and m=1 to 3. The suppressor includes sodium silicate.

Description

[Technical field]

[0001] The present disclosure relates to methods for separating iron-containing impurities from a host matrix, and in particular to a froth flotation process for separating iron-containing impurities from silica sand. [Background technology]

[0002] The discussion of the background of the present disclosure is intended to facilitate understanding of the present disclosure, but it should be understood that this discussion is not an admission or admission that any of the material referred to was publicly known or part of the common general knowledge as of the priority date of this application.

[0003] Silica sand is the primary raw material for glass manufacturing and serves growing demand from the construction market, rising automotive production and sales, abrasives, and hydraulic fracturing. There is also growing global demand for specialty glass for photovoltaic cells and mobile phones, as well as lithium-ion batteries, resulting in a demand for high-purity silica sand with minimal contamination from aluminum-, iron-, titanium-, calcium-, magnesium-, and potassium-containing impurities.

[0004] Iron-containing impurities are generally a) liberated and free iron mineralogically contained in fine particles (approximately 106 um); b) a silica particle surface coating that can be mechanically removed; and c) coarse grained, individual heavy minerals, e.g. hematite, magnetite, or ilmenite They can be of any one of three types, including:

[0005] The first type of iron-bearing impurity may be managed and removed via simple screening and cycloning techniques, the second type may be addressed via particle attrition, and the third may be removed by spiral gravity techniques.

[0006] However, some silica sand deposits contain very little individual and more variable iron speciation. In particular, potassium aluminum silicates such as feldspar and muscovite can contain significant iron variation in the mineral matrix. For example, low-content feldspar (LF) may contain up to 3000 ppm Fe2O3, medium-content feldspar (MF) may contain 3000-5000 ppm Fe2O3, and high-content low-content feldspar (HILF) may contain >5000 ppm Fe2O3. The conventional separation processes discussed above can reduce the iron grade to about 700 ppm Fe2O3, but cannot produce a final product with iron grades below 500 ppm Fe2O3 to meet high purity silica specifications.

[0007] The process described herein seeks to provide an alternative process for separating iron-containing impurities from silica sand, and in particular to reduce the iron-containing impurity content to <500 ppm Fe2O3. Summary of the Invention

[0008] The present disclosure provides a method for separating iron-containing impurities from a host matrix, such as silica sand.

[0009] One aspect of the present disclosure is a method for separating iron-containing impurities from silica sand, comprising the steps of: subjecting a silica sand slurry to froth flotation in the presence of a collector, a foaming agent, and an inhibitor selected to concentrate iron-containing impurities of the silica sand in the flotation foam, thereby producing a silica sand having reduced iron-containing impurities in the tail product, wherein the collector comprises ≧60 to ≦70 w / w% tall oil acid, ≧10 to ≦30 w / w% poly-α-hydroxyl alkyl ether, and up to 3 w / w% tall oil rosin. A method is provided.

[0010] In one embodiment, the collector may be present in an amount of from 200 to 800 g / t.

[0011] In one embodiment the inhibitor comprises sodium silicate. The inhibitor may be present in an amount of 25 to 250 g / t.

[0012] In another embodiment, the foaming agent is a non-ionic surfactant, in particular one or more alkyl polypropoxy C n P m and / or Polyethoxy C n E m It comprises a foaming agent, n=0-6 and m=1-3. The foaming agent may be present in an amount of 5-100g / t.

[0013] In one embodiment, the silica sand slurry has a solids content of 25-45% by weight solids, particularly 28-40% by weight solids.

[0014] In one embodiment, the foam flotation is carried out at a neutral pH range, particularly from about pH 7.2 to about pH 7.5. In some embodiments, a buffer may be added to maintain the pH in this neutral pH range. Suitable buffers include sodium carbonate. The buffer may be present in an amount of 10 to 150 g / t.

[0015] In one embodiment, before subjecting the silica sand slurry to froth flotation, the silica sand may be subjected to particle size reduction and classification to obtain a top size in the range of 250-1200 μm. The particle size reduction step may be carried out in a high pressure grinding roll (HPGR) with a compressive force of 20-40 bar and a roll speed of 10-20 rpm. The operating parameters of the HPGR may be appropriately selected to provide a desired top size product that meets the specification requirements.

[0016] Advantageously, the froth flotation process may be used to separate iron-containing impurities from coarse silica sand, including fine silica sand, including silica sand particles >425 μm, or silica sand particles <425 μm.

[0017] It will be appreciated that coarse particles have a tendency to cause the flotation cell to pack down and become jammed, impairing the performance of the flotation cell and the separation and removal of iron impurities from the silica sand. Thus, although the froth flotation process described herein may be carried out in a conventional tank or Denver flotation cell when the particle size of the flotation feed is <425 μm, the inventors recommend using a HydroFloat cell when 20% or more of the flotation feed is >425 μm.

[0018] A further aspect of the present disclosure provides a silica sand having less than 500 ppm Fe2O3, the silica sand being produced according to the froth flotation process defined above.

[0019] Notwithstanding any other forms that may fall within the scope of the processes outlined in the summary, specific embodiments will now be described with reference to the accompanying drawings, in which: [Brief description of the drawings]

[0020] [Figure 1] 1 is a flowsheet according to one embodiment of a process for separating iron-containing impurities from silica sand. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] The present disclosure relates to a method for separating iron-containing impurities from silica sand.

[0022] [General terminology] Throughout this specification, unless specifically stated otherwise or the context requires otherwise, reference to a single step, composition, group of steps, or group of compositions should be construed to include one or more (i.e., one or more) of those steps, compositions, group of steps, or group of compositions. Thus, as used herein, the singular forms "a," "an," and "the" include plural aspects unless the context clearly indicates otherwise. For example, reference to "a" includes the single as well as two or more; reference to "an" includes the single as well as two or more; reference to "the" includes the single as well as two or more, etc.

[0023] Each embodiment of the disclosure described herein applies mutatis mutandis to each and every other embodiment unless specifically stated otherwise. The disclosure is not limited in scope by the specific embodiments described herein, which are intended for illustrative purposes only. Functionally equivalent products, compositions, and methods are clearly within the scope of the disclosure described herein.

[0024] The term "and / or", e.g., "X and / or Y", shall be understood to mean either "X and Y" or "X or Y" and shall be interpreted as providing explicit support for both meanings or for either meaning.

[0025] It will be understood that throughout this specification the word "comprise" or variations such as "comprises" or "comprising" imply the inclusion of a stated element, integer, or step, or group of elements, integers, or steps, but not the exclusion of any other element, integer, or step, or group of elements, integers, or steps.

[0026] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this invention belongs. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, suitable methods and materials are described below. In case of conflict, the present specification, including definitions, will control. Furthermore, the materials, methods, and examples are merely illustrative and not limiting.

[0027] The term "about" as used herein means within 5% of a given value or range, more preferably within 1%. For example, "about 3.7%" means 3.5 to 3.9%, preferably 3.66 to 3.74%. When the term "about" is associated with a range of values, such as "about X% to Y%, the term "about" is intended to modify both the lower (X) and upper (Y) values ​​of the recited range. For example, "about 20% to 40%" is equivalent to "about 20% to about 40%".

[0028] [Specific term] The term "foam flotation" as used herein refers to a hydrometallurgical process for selectively separating solid particles of hydrophobic minerals from non-hydrophobic minerals in a slurry mixture. It is particularly useful for separating fine solids from other solids in a liquid mixture by selective attachment of the hydrophobic solid particles to gas bubbles contained in the liquid mixture. A gas, typically air, is passed through the liquid mixture at a velocity that results in the accumulation of sustained "foam" or bubbles at the liquid-surface interface. The density difference between the gas bubbles and the liquid provides the attached hydrophobic solid particles with buoyancy, lifting these particles to the surface while the hydrophilic solid particles are trapped within the slurry. The hydrophobic solid particles concentrated at the surface may then be separated from the slurry by draining the slurry or by mechanically skimming the surface.

[0029] The term "foaming agent" as used herein refers to a chemical or chemical composition (i.e., a mixture of chemicals) used in froth flotation to stabilize gas bubbles that carry hydrophobic solid particles to their surface. Foaming agents may contain polar (i.e., hydrophilic) and non-polar (i.e., hydrophobic) chemical moieties, whereby in use the foaming agent increases the surface tension at the liquid-air interface, thereby stabilizing the gas bubbles in the foam.

[0030] The term "collecting agent" as used herein refers to a chemical or chemical composition (i.e., mixture of chemicals) used in froth flotation that can be physically or chemically adsorbed onto the surface of particles to increase the wetting ability of the particles, thereby increasing their attachment to the gas bubbles and their concentration in the foam.

[0031] As used herein, the term "inhibitor" refers to a chemical or chemical composition (i.e., a mixture of chemicals) used in froth flotation that is capable of selectively inhibiting the interaction of mineral particles with air bubbles so that the mineral particles remain in the slurry rather than being concentrated in the foam.

[0032] Surfactants are amphiphilic organic compounds that contain a hydrophobic (i.e., water-insoluble) portion and a hydrophilic (i.e., water-soluble) portion, thereby allowing the interfacial tension between two fluids, such as a gas and a liquid, to be reduced. The hydrophobic portion extends from the bulk aqueous phase into the gas, while the hydrophilic portion remains in the aqueous phase. The term "nonionic surfactants" as used herein refers to surfactants that have an uncharged hydrophilic portion. Typically, the hydrophilic portion will contain oxygen groups that participate in hydrogen bonds in the aqueous phase. Examples of nonionic surfactants include, but are not limited to, fatty alcohol ethoxylates, alkylphenol ethoxylates, fatty acid ethoxylates, ethoxylated amines, and / or fatty acid amides, fatty acid esters of polyhydroxy compounds, fatty acid esters of glycerol, fatty acid esters of sorbitol, fatty acid esters of sucrose, and alkyl polyglucosides.

[0033] As used herein, the term "alkyl" refers to a substituted or unsubstituted saturated hydrocarbon group including straight-chain alkyl and branched-chain alkyl groups containing from 1 to 22 carbons in the chain.

[0034] The term "alkoxy" refers to an alkyl group having an oxygen attached thereto. Representative alkoxy groups include methoxy, ethoxy, propoxy, n-butoxy, i-butoxy, tert-butoxy and the like.

[0035] The term "alkyl ether" refers to two hydrocarbon groups linked by an oxygen. The term "alpha hydroxy ether" refers to an alkyl ether in which the hydrocarbon group is substituted with a hydroxyl group on the carbon adjacent to the oxygen ether bond.

[0036] The term "tall oil acids" as used herein refers to a mixture of oleic, linoleic, and rosin acids derived from the hydrolysis of tall oil, a by-product of wood pulp. The term "tall oil rosin" as used herein refers to the distillation product of crude tall oil. Tall oil rosin is a mixture of resin acids, including but not limited to abietic acid, ihydroabietic acid, palustric acid, neoabietic acid, isopimaric acid, and may contain up to 6% nonsaponifiable material.

[0037] [Process for separating iron-containing impurities from their host matrix] SUMMARY OF THE DISCLOSURE The embodiments described herein generally relate to processes for separating iron-containing impurities from a host matrix, particularly silica sand or quartz.

[0038] The iron-containing impurities separated by the processes described herein may include free iron, iron oxides such as magnetite, hematite, ilmenite, and limonite; iron sulfides such as pyrite, marcasite, and pyrrhotite; iron silicates such as chamosite, silomelan, greenite, minesotite, grunerite; iron rust feldspar and muscovite, among others.

[0039] Referring to the Figure, a process flowsheet is shown for producing silica sand having less than 500 ppm Fe2O3 from as-mined silica sand feedstock containing iron-containing impurities.

[0040] The as-mined silica sand passes through a scrubber 10 to clean clay contamination, gangue mineralization, and organic matter therefrom. Coarse particles of +1 mm may also be rejected. The scrubber 10 may be any suitable conventional scrubber, such as a trommel scrubber, a drum washing scrubber, or a rotary scrubber.

[0041] The washed and screened silica sand may then be passed to a constant density tank 12, if desired. The separated overflow (fines) from the constant density tank 12 is then pumped at a constant density and feed rate to a thickening tank 14. The underflow (or coarser materials) is fed to a hydrocyclone 16, where the overflow (fines) is fed back to the constant density tank 12, and the underflow is passed through one or more atritioners 18 arranged in series.

[0042] The one or more abraders 18 clean the particle surfaces of the silica sand, thereby increasing the removal of iron-containing impurities. Typically, the silica sand may be abraded for about 20 minutes. The abraders 18 may be configured with one or more upflow classifiers to reject fine particles. Typically, fine particles have a particle size <100 μm, although one skilled in the art will understand that the definition of particle size of fine particles may vary depending on the desired sales product specifications. It will be readily apparent to one skilled in the art to select an appropriately sized upflow classifier to reject fine particles depending on the desired sales product specifications.

[0043] The attrited sand is then passed through a size classification screen 20. The coarse oversize is passed through a high pressure grinding roll (HPGR) 22 where the sand is pulverized and classified to a maximum size in the range of 250-1200 μm. The HPGR may be operated to generate a compaction force of 20-40 bar and a roll speed of 10-20 rpm. The operating parameters of the HPGR may be appropriately selected to provide a desired maximum size product meeting specification requirements.

[0044] The maximum size product from the HPGR 22 continues through the sizing screen 20 to a mixing tank 24 where it is mixed with water to produce a silica sand slurry having a solids content of about 25-45% by weight solids, specifically about 28-40% by weight solids. The mixing tank 24 may conveniently operate as an equalization tank where one or more of a collector, foaming agent, retarder, and buffering agent may be added to the slurry. Alternatively, one or more of a collector, foaming agent, retarder, and buffering agent may be added to the slurry in the equalization tank 26. The slurry may remain in the equalization tank 26 for a suitable residence time of about 30 to 120 seconds.

[0045] The conditioned slurry may then be passed through a flotation cell 28, particularly a plurality of flotation cells 28a, 28b, 28c, 28d arranged in series. The flotation cells 28a, 28b, 28c, 28d may be conventional flotation tanks or Denver flotation cells, particularly when the particle size of the flotation feed is <425 μm. Coarse particles tend to pack and jam the flotation cells, impairing the performance of the flotation cells and the separation and removal of iron impurities from the silica sand. Therefore, when 20% or more of the flotation feed is >425 μm, we recommend using a flotation cell 28 that includes a HydroFloat cell.

[0046] It will be appreciated that the foaming agent may be added either to the conditioning tank 26 prior to flotation or directly to the first flotation cell 28a, depending on the duration and agitation required to disperse it in the slurry.

[0047] The foaming agent acts to facilitate the generation of a stable foam to aid in the recovery of fine particles. The iron-bearing particles are concentrated through the attachment of these particles to stabilize the air bubbles that rise to the top of the flotation cell. Other reagents can assist in the selective collection of the desired iron-bearing particles and the settling of the silica sand.

[0048] The foaming agent is alkyl polypropoxy C n P m and / or alkylpolyethoxy C n E m Foaming agents, such as C4H9O(C2H4O)1H, C4H9O(C2H4O)3H, C1H3O(C3H6O)2H, C4H9O(C2H4O)2H, C6H 13 The foaming agent may be selected from the group including O(C2H4O)2H, (C3H6O)3H, C3H7O(C3H6O)3H, C4H9O(C3H6O)3H. In particular, the foaming agent includes a propoxylated butanol such as Polyfroth® H27.

[0049] The foaming agent may be present in the slurry in an amount of 5 to 100 g / t. In embodiments where the flotation cell comprises a HydroFloat cell, the foaming agent may be present in the slurry in an amount of 50 to 100 g / t. In alternative embodiments where the flotation cell comprises a conventional flotation tank or a Denver flotation cell, the foaming agent may be present in the slurry in an amount of 5 to 30 g / t.

[0050] The inhibitor maximizes silica recovery by preventing bulk mass of silica sand from being floated with the target particles. One suitable example of an inhibitor includes sodium silicate. Sodium silicate functions well as an inhibitor at neutral pH. Other inhibitors such as sodium and calcium lignosulfonates can also behave as silica inhibitors at neutral pH, but those inhibitors that have a tendency to contribute to excessive foaming behavior are less desirable.

[0051] The amount of inhibitor present in the slurry is primarily dependent on the particle size distribution, therefore finer flotation feed particle size distributions require higher inhibitor dosages. The inhibitor may be present in an amount of 25 to 250 g / t.

[0052] The collector adheres to and activates the surfaces of the iron-bearing impurities, particularly the iron rust feldspar species, through surface activation of highly cationic species. The silica sand (mainly quartz) remains somewhat inert and unaffected by the collector, thereby enhancing the separation of the targeted iron-bearing impurity particles into a foam and retention of the silica sand particles in the slurry.

[0053] The scavenger may comprise ≧60 to ≦70 w / w% tall oil acid, ≧10 to ≦30 w / w% poly-α-hydroxyl alkyl ether, and up to 3 w / w% tall oil rosin. The scavenger may be present in an amount of 200 to 800 g / t.

[0054] The scavenger may have additional suppression and foaming properties. Furthermore, it will be appreciated that the concentration of the suppressor and foaming agent may be reduced when the scavenger is present at higher dosages of >600 g / t.

[0055] Froth flotation is carried out in the neutral pH range, particularly from about pH 7.2 to about pH 7.5. The inventors have noted that the process is sensitive to pH as it moves away from neutrality. In particular, the effectiveness of collector performance decreases in acidic conditions. Therefore, a buffer may be added to maintain the pH in the neutral pH range. Suitable buffers include, but are not limited to, sodium carbonate.

[0056] Advantageously, conducting the froth flotation in the neutral pH range alleviates environmental concerns frequently associated with obtaining approval for processes that operate at high or low pH. The froth flotation process described herein is therefore much more environmentally friendly than prior art processes used to separate iron impurities from silica sand.

[0057] The scavenger generates acid as it dissolves in water, so the amount of buffer will be related to the amount of collector present in the slurry. The buffer may be present in an amount of 10 to 150 g / t.

[0058] The iron-containing particle-rich foam concentration is then collected from the top of the flotation cell, either by passively overflowing into a collection washer or by mechanically skimming. The underflow, which is a slurry containing quartz sand with reduced iron-containing impurities, then flows to a surge tank 30 and undergoes classification in a product screen 32 according to desired consumer specifications.

[0059] The following table describes the resulting products produced from the froth flotation process described herein by subjecting various feed materials to the process.

[0060] [Table 1]

[0061] It will be understood by those skilled in the art that numerous variations and / or modifications may be made to the above-described embodiments without departing from the broad general scope of the present disclosure, and the present embodiments are therefore to be considered in all respects as illustrative and not restrictive.

[0062] Unless the context requires otherwise due to descriptive language or necessary implication, in the following claims and the preceding description, the word "comprise" or variations such as "comprises" or "comprising" are used in their inclusive sense, i.e., used to specify the presence of mentioned features, but do not exclude the presence or addition of further features in various embodiments of the invention.

Claims

1. A method for separating iron-containing impurities from silica sand, comprising: subjecting a silica sand slurry to froth flotation in the presence of a collector, a frother, and a depressant selected to concentrate the iron-containing impurities in the silica sand in the froth flotation foam, thereby producing silica sand with reduced iron-containing impurities in the tail product, wherein the collector comprises ≧60 to ≦70 w / w% tall oil fatty acid, ≧10 to ≦30 w / w% poly-α-hydroxyl alkyl ether, and up to 3 w / w% tall oil rosin.

2. The foaming agent is a nonionic surfactant, particularly one or more alkyl polypropoxy C ｎ P ｍ and / or polyethoxy C ｎ E ｍ The method according to claim 1, comprising a foaming agent, where n = 0 to 6 and m = 1 to 3.

3. The method according to claim 1 or 2, wherein the depressant comprises sodium silicate.

4. The method according to claim 1, wherein the collector is present in an amount of 200 - 800 g / t.

5. The method according to claim 1, wherein the depressant is present in an amount of 25 - 250 g / t.

6. The method according to claim 1, wherein the frother is present in an amount of 5 - 100 g / t.

7. The method according to claim 1, wherein the silica sand slurry has a solids content of 25 - 45 wt%.

8. The method according to claim 1, wherein the froth flotation is carried out in a neutral pH range of about pH 7.2 to about pH 7.

5.

9. The method according to claim 8, wherein a buffer is added to maintain the pH in the neutral pH range.

10. The method according to claim 9, wherein the buffer is present in an amount of 10 - 150 g / t.

11. The iron-containing impurity is Fe ２ O ３ reduced to less than 500 ppm in the separated silica sand product, the method according to claim 1.

12. The method according to claim 1, wherein the silica sand is subjected to micronization and classification before being subjected to froth flotation, and the maximum size is in the range of 250 - 1200 μm.

13. The method according to claim 12, wherein the micronization step is carried out with a high pressure grinding roll (HPGR) applying a compressive force of 20 - 40 bar and having a roll speed of 10 - 20 rpm.

14. Silica sand having less than 500 ppm of Fe ２ O ３ Silica sand produced by the froth flotation process according to claim 1, the silica sand having

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