WO2025083059A1

WO2025083059A1 - Silanol-functionalized compounds for the inhibition of silica-containing scale in single stream slurries in bayer process

Info

Publication number: WO2025083059A1
Application number: PCT/EP2024/079205
Authority: WO
Inventors: Airong Song; Dannon STIGERS; Xia Zhang; Ashley OBLON; Joseph Calbick
Original assignee: Cytec Industries Inc
Current assignee: Cytec Industries Inc
Priority date: 2023-10-17
Filing date: 2024-10-16
Publication date: 2025-04-24
Anticipated expiration: 2026-04-17

Abstract

A method of inhibiting silica-containing scales in an industrial process comprising contacting a process slurry with a scale inhibitor, the process slurry having a solids concentration of at least 0.5 g/L, wherein the scale inhibitor comprises a compound comprising recurring units covalently bound to at least one pendant silanol group.

Description

SILANOL-FUNCTIONALIZED COMPOUNDS FOR THE INHIBITION

OF SILICA-CONTAINING SCALE IN SINGLE STREAM SLURRIES IN BAYER PROCESS

BACKGROUND

[0001] The Bayer process is used for the production of alumina from bauxite. Bauxite is composed primarily of three aluminum minerals: gibbsite (Al(0H)3), boehmite (y- A10(0H)) and diaspore (a-AlO(OH)). In the Bayer process, the bauxite ore is heated with caustic to a temperature to dissolve the aluminum in an extraction (also referred to as digestion) process where aluminum oxide is converted to soluble sodium aluminate.

[0002] Among the types of minerals present in bauxite, gibbsite is the most easily digestible, requiring lower digestion temperatures (100-145 °C). Boehmite is more difficult to digest than gibbsite, due to its mineralogy, with a typical digestion temperature range of 225-245 °C. Diaspore is the most difficult ore to digest among all bauxite types. The digestion temperature of diaspore is usually above 250 °C. Lime is usually added to help diaspore digestion, and a longer residence time is also required.

[0003] In the Bayer refining process, two major industrial flow designs exist: double stream and single stream. In double stream refining, strong Bayer liquor for digesting bauxite is heated in heat exchangers to target temperatures prior to addition of ore. Bauxite is then added and mixed with the heated strong liquor in the digester. In single stream refining, the strong Bayer liquor is mixed with the bauxite first and then heated together in the heat exchangers as a slurry.

[0004] Single stream designs are more efficient than double stream designs in terms of energy recovery, water balance, caustic corrosion, and powerhouse cogeneration efficiency. The majority of alumina global production (>70%) is made using single stream designs, and prospective new plants are being designed with single stream flows. The main drawbacks for single stream processes are formation of scale, particularly sodalite scale and titanate scale (particularly in high temperature sections at temperatures greater than 160 °C) on heat exchanger walls, which influences the heat transfer coefficient to the slurry and lowers the digestion efficiency. There is scale formation in double stream flow design, but scale can be inhibited with antiscalant products.

[0005] In addition to the aluminum ores of interest, bauxite also contains other constituents or gangue minerals, considered “impurities.” The main impurities are minerals of silica, iron and titanium, as well as organic matter. The silica present in Bauxite is typically found as a clay, a natural form of an aluminosilicate. Upon addition of the Bauxite to the high concentration of NaOH-containing liquor found in the Bayer process, these clays readily react with NaOH at moderate operating temperatures and form soluble sodium silicate and sodium aluminate. While this process starts immediately upon contacting the Bauxite with the Bayer liquor, a stage in the Bayer process known as pre-desilication, is inserted in the flowsheet where continued heating (typically 70- 90 °C) of the bauxite slurry, for typically 24 hours, allows for near complete reaction of these clays, followed by the precipitation of a desilication product (DSP), an insoluble sodium aluminosilicate. Once complete, this slurry is diluted with additional Bayer liquor then subsequently heated through heat exchangers (-50-400 g/L pre-desilicated bauxite), to digestion temperatures of 140 to 180 °C, allowing for the alumina ore to react with NaOH to form soluble sodium aluminate. During the course of this heating, additional DSP is formed, both on the Bauxite solids themselves, as well as on the walls of the heat exchangers. Due to its insulating nature, the DSP formed on the heat exchanger surfaces negatively affects the energy recovery efficiency of the refinery and can cause production bottlenecks.

[0006] Several silanol-containing, aluminosilicate inhibitors for use in the Bayer process have been disclosed and are commercially available. In all cases, the antiscalant performance of these inhibitors are measured in conditions that closely mirror the conditions of scale growth in the evaporators of the Bayer process (solids level typically < 10-20 mg/L solids). This is strongly contrasted with the performance of such inhibitors under the conditions of single stream heaters, where solids levels are routinely at and above 100 g/L. A further improvement on these inhibitor structures was disclosed, where hydrophobically modified silanol-containing polyamines displayed an improved antiscalant performance, relative to previously disclosed structures, including in the presence of low levels of added solids (0.05 - 0.15 g/L). However, in those examples, the solids concentrations are approximately 4 orders of magnitude lower than the solids concentrations found in typical single stream heaters (> 90 g/L) and are used in processes that form scale rather than in process where scale is already present. Furthermore, examples in the art often require frequent treatment of process equipment surfaces with the antiscalant to see the antiscalant benefits. However, this approach requires costly and significant downtime of processes.

[0007] Hence, there remains a need for practical solutions that can prove to mitigate the large accumulation of scale that is deposited during industrial processes that suffer from the accumulation of silica-containing solids such as sodalite.

SUMMARY

[0008] This summary is provided to introduce a selection of concepts that are further described below in the detailed description. This summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used as an aid in limiting the scope of the claimed subject matter.

[0009] In one aspect, embodiments disclosed herein related to a method of inhibiting silica- containing scales in an industrial process that includes contacting a process slurry with a scale inhibitor, the process slurry having a solids concentration of at least 0.5 g/L, wherein the scale inhibitor comprising a compound comprising recurring units covalently bound to at least one pendant silanol group.

[0010] In another aspect, embodiments disclosed herein related to use of a scale inhibitor for silica-containing scale in an industrial process, the scale inhibitor comprising a compound comprising recurring units covalently bound to at least one pendant silanol group.

[0011] Other aspects and advantages of the claimed subject matter will be apparent from the following description and the appended claims.

DETAILED DESCRIPTION

[0012] Embodiments disclosed herein relate to use of a scale inhibitor in industrial process having a high solids content. In particular, embodiments disclosed herein relate to the prevention of silica-containing scale (such as sodalite, cancrinite etc.) formation in a Bayer single stream process.

[0013] As mentioned, silica-containing scale tends to accumulate in higher temperature sections of the heat exchangers in alumina refineries. Thus, a scale inhibitor, which was designed for single stream Bayer processes, may result in improved alumina production and reduced costs.

[0014] Use of the scale inhibitor in an industrial process, such as a Bayer process, may reduce or even inhibit the formation of scale, particularly sodalite scale, in at least the process heat exchangers. By reducing scale formation such as sodalite scale formation on the heat exchangers, the Bayer process may maintain high heat transfer from the heat exchanger to a slurry of Bayer liquor mixed with bauxite.

[0015] Scale Inhibitor

[0016] In one or more embodiments, the scale inhibitor comprises a compound comprising recurring units covalently bound to the at least one pendant silanol group according to the following formula (I):

wherein T is a hydrocarbon group having from 1 to 40 carbon atoms, A¹ is an organic connecting group comprising a C1-C20 hydrocarbon group, a polyalkyleneimine or a direct bond between the nitrogen atom and the adjoining pendant silanol group, and M is independently chosen from H, NH4, K, or Na.

[0017] According to one or more embodiments, the compound may be a homopolymer or a copolymer. Thus, the compound may be comprised solely of recurring units according to formula (I) resulting in a homopolymer. However, in at least one embodiment, the compound may further comprise recurring units not covalently bound to at least one pendant silanol group, thereby forming a copolymer. The recurring units that are not covalently bound to at least one pendant silanol group is shown in formula (II):

wherein E is selected from a hydrocarbon group having from 1 to 40 carbon atoms, and A² is H or polyalkyleneimine.

[0018] In a preferred embodiment, either A¹ or A² or both A¹ and A² represent either a linear or branched polyalkyleneimine, particularly a polyethyleneimine. It is also envisioned that, according to one or more embodiments, the compound may be a homopolymer where both recurring units of formula (I) and (II) comprise the same polyalkylenimine backbone. However, in other embodiments, the compound may be a copolymer comprising recurring units that have different polyalkyleneimine backbones.

[0019] Compounds useful as scale inhibitors according to embodiments disclosed herein may be prepared via any suitable method known in the art for preparing such compounds.

[0020] Recurring Units

[0021] As mentioned above, the scale inhibitor may comprise a compound comprising recurring units covalently bound to at least one pendant silanol group according to Formula (I). According to one or more embodiments, the recurring unit covalently bound to at least one pendant silanol group may comprise linear or branched polyethyleneimines as the backbone to the recurring units. In one or more embodiments, the compound may further comprise recurring units not covalently bound to at least one pendant silanol group according to Formula (II).

[0022] According to one or more embodiments, the compound may comprise recurring units that are covalently bound to at least one pendant silanol group in an amount from more than 0 to 100 mol%, such as from a lower limit of any one of 1, 2, 5, 10, 15, and 30 mol% to an upper limit of any one of 35, 40, 45, 50, 55, 60, 70, 80, 90 and 100 mol% where any lower limit may be mathematically paired with any upper limit, for example from 1 to 80 mol% or from 2 to 60 mol%. The compound may further comprise recurring units not covalently bound to at least one pendant silanol group in an amount such that m of Formula II is from 0 to less than 100 mol%, such as from a lower limit of any one of 0, 10, 20, 30, 40, 50, and 65 mol% to an upper limit of any one of 70, 75, 80, 85, 90, 99 and 99.99 mol% where any lower limit may be mathematically paired with any upper limit, for example from 10 to 99 mol% or from 40 to 99 mol%.

[0023] The recurring units of polyamines may be made by a variety of methods, such as ring opening polymerizations of aziridine or similar compounds, or by condensation reactions of amines with reactive compounds. Suitable amines include but are not limited to ammonia, methylamine, dimethylamine, ethylenediamine etc. Suitable reactive compounds include but are not limited to 1 ,2-dichloroethane, epichlorohydrin, epibromohydrin and similar compounds. It is also envisioned that the recurring units may be functionalized after the synthesis of polyamines.

[0024] Pendant Silanol Group

[0025] As mentioned above, the recurring units covalently bound to a pendant silanol group according to Formula (I). Thus, the silanol group may be appended to the compound backbone -[-T-N-]- by way of A¹, an organic connecting group comprising a C1-C20 hydrocarbon group or a direct bond between the nitrogen atom and the adjoining pendant silanol group.

[0026] According to one or more embodiments, compounds comprising recurring units covalently bound to at least one pendant silanol group may be obtained by polymerizing a monomer containing the group -Si(OM)3 where M is independently chosen from H, NH4, K, or Na or by functionalizing an already formed polymer backbone. It is also envisioned that the pendant silanol group may be obtained by copolymerizing a monomer with one or more co-monomers. Suitable monomers containing the group -Si(OM)3 include but are not limited to silane monomers which can be hydrolyzed by aqueous base, either before or after polymerization. Therefore, suitable silane monomers include but are not limited to vinyltriethoxysilane, gama-N-acrylamidopropyltriethoxysilane, p- triethoxysilystyrene, 2-(methyltrimethoxysilyl) acrylic acid, 2-(methyltrimethoxysilyl)- 1,4 butadiene, N-triethoxysilylpropyl-maleimide and other reaction products of maleic anhydride and other unsaturated anhydrides with amino compounds containing the - Si(OR)s group. Suitable co-monomers include but are not limited to vinyl acetate, acrylonitrile, styrene, acrylic acid and its esters, acrylamide and substituted acrylamides such as acrylamidomethylpropanesulfonic acid. The copolymers can also be graft copolymers such as polyacrylic acid-g-poly(vinyltri ethoxysilane) and poly(vinyl acetate- cocrotonic acid)-g-poly(vinyltriethoxysilane).

[0027] In at least one embodiment, the pendant silanol group may be obtained by reacting a compound containing the group -Si(OM)s where M is independently chosen from H, NH4, K, or Na as well as a nitrogen-reactive group that reacts with either a pendant group or an atom of the compound. For example, the compound -[-T-N-]- may be reacted with a variety of compounds containing -Si(OM)s and a nitrogen-reactive group to provide the aforementioned compounds. Suitable nitrogen-reactive compounds may comprise nitrogen-reactive groups including but are not limited to the following suitably configured functionalities: halide, sulfate, epoxide, isocyanate, anhydride, carboxylic acid and/or acid chloride, or a combination of hydroxy and halide groups. Examples of suitable nitrogen-reactive groups include alkyl halide (e.g., chloropropyl, bromoethyl, chloromethyl, and bromoundecyl) epoxy (e.g., glycidoxypropyl, 1 ,2-epoxyamyl, 1, 2- epoxydecyl or 3, 4-epoxycyclohexy-Iethyl), isocyanate (e.g., isocyanatopropyl or isocyanatomethyl), anhydride (e.g., malonic anhydride, succinic anhydride) and combinations of such groups, e.g. , a combination of a hydroxyl group and a halide, such as 3-chloro-2-hydroxypropyl. Triethoxysilylpropylsuccinic anhydride, glycidoxypropyl trimethoxysilane and chloropropyl trimethoxysilane are examples of nitrogen reactive compounds that comprise a Si(OR)s group and a nitrogen-reactive group which may be hydrolyzed.

[0028] According to one or more embodiments, the pendant silanol group is nitrogenreactive compound comprising an epoxide nitrogen-reactive group. In one or more embodiments, the pendant silanol group is 3-glycidoxypropyltrimethoxysilane and may be obtained by reacting a polyamine with a nitrogen-reactive compound such as 3- glycidoxypropyltrimethoxysilane. Suitable polyamines may include but are not limited to the above- described polyalkyleneimines.

[0029] In one or more embodiments, the compound may comprise a concentration of the pendant silanol group ranging from 6 mol% to 80 mol%, based on the total recurring units, such as from the lower limit of 6, 8, 10 and 12 mol% to an upper limit of 18, 21, 23, 25, 27, 29, 31, 33, 35, 60, and 80 mol%, where any lower limit may be paired with any upper limit. Preferably, the compound may comprise a concentration of the pendant silanol group ranging from 6 mol% to 35 mol%, in particular from 6 mol% to 25 mol%, for example from 6 mol% to 15 mol%, based on the total recurring units.

[0030] According to one or more embodiments, the compound has a number-averaged molecular weight in the amount greater than or equal to 200 g/mol.

[0031] Method of Scale Inhibition

[0032] As mentioned above, the scale inhibitors comprising the compound of the present disclosure may be used to treat and inhibit the formation silica-containing scales in an industrial process. In one or more embodiments, the method of inhibiting silica- containing scales in an industrial process comprises the step of contacting the process slurry with the scale inhibitor, the process slurry having a solids concentration of at least 0.5 g/L, wherein the solids are selected from bauxite, sodium aluminate, sodium silicate, clays, aluminosilicates, mineral impurities, amorphous silica and mixtures thereof, wherein the scale inhibitor comprises a compound comprising the aforementioned recurring units covalently bound to at least one pendant silanol group.

[0033] As mentioned above, the process slurry may be contacted with the scale inhibitor at a temperature in the range of 40 to 300 °C, such as a lower limit of 40, 50, 60, 70, 80, 90 and 100 °C to an upper limit of 150, 175, 200, 225, 250, 275 or 300 °C, where any lower limit may be paired with any upper limit.

[0034] As mentioned above, the method comprises the step of contacting the process slurry with a scale. According to one or more embodiments, the process slurry may comprise at least one of a liquid component and a solid component. The liquid component may be an aqueous solutions of salts such as sodium hydroxide, sodium aluminate, sodium carbonate, sodium sulfate, sodium phosphate, etc. and mixtures thereof. The solid component may be selected from the group consisting of bauxite, clays, aluminosilicates, mineral impurities, amorphous silica and mixture thereof. Additionally, other scales such as calcium carbonate, calcium phosphate, etc., are possible. At high temperatures, it is envisioned that the solids may be present in the form of dissolved salts.

[0035] According to one or more embodiments, the solid component of the process slurry is present in an amount of at least 0.5 g/L, for example at least 1.0 g/L. However, it is envisioned that the process slurry may be used in processes where the process slurry comprises a solid component that well exceeds the amount of at least 0.5 g/L, such as that of 100 to 400 g/L. Thus, the scale inhibitor described herein may be used to treat process slurries with solid component contents that are typically seen in single stream heaters.

[0036] According to one or more embodiments, the compound of the scale inhibitor is present in an amount of at least 5 ppm up to a limit of 5000 ppm, such as a lower limit of any one of 100, 250, 500, 1000, 1500 or 2000 ppm to an upper limit of 2500, 3000, 3500, 4000, 4500 or 5000 ppm, where any lower limit may be paired with any upper limit.

[0037] The scale inhibitor may be present in an amount of at least 5 ppm, 10 ppm, 25 ppm, 50 ppm, 100 ppm, 200 ppm, 300 ppm, 400 ppm, 500 ppm, 1000 ppm, or 2000 ppm and of at most 2000 ppm, 3000 ppm, 4000 ppm, or 5000 ppm where any lower limit can be used in combination with any upper limit. The scale inhibitor may be present in an amount of 100 to 2500 ppm.

[0038] According to one or more embodiments, the scale inhibiting compound may be added at a temperature of at least 40 °C and of at most 140 °C, such as from a lower limit of any of 40, 50, 60, 70, 80 or 90 °C to an upper limit of 100, 110, 120, 130 or 140 °C, where any lower limit may be paired with any upper limit.

[0039] As mentioned above, the scale inhibitor may be used in industrial processes to inhibit the formation of aluminosilicates. Furthermore, the scale inhibitor may be used to reduce the amount of aluminosilicate scale growth on surfaces. The reduced amount of scale growth on the surface results in sustained temperatures, thus minimal heat loss. Thus, the above described method and scale inhibitor may be used for a myriad of industrial processes. Of particular mention is a method for inhibiting silica-containing scales in an industrial process such as the Bayer process, wherein the heating step may comprise a process slurry that is a Bayer process liquor. According to one or more embodiments, the process slurry may also be a bauxite feed slurry. The scale inhibitor mentioned above may also be used in a Bayer process for refining alumina from bauxite ore. Thus, it is also envisioned that the industrial process may be a Bayer process wherein the scale inhibitor comprising the compound is added before and/or during digestion of the bauxite feed slurry, or a Bayer process that is a single stream process.

[0040] While the scope of the composition and method will be described with several embodiments, it is understood that one of ordinary skill in the relevant art will appreciate that many examples, variations and alterations to the composition and methods described here are within the scope and spirit of the disclosure. Accordingly, the embodiments described are set forth without any loss of generality, and without imposing limitations, on the disclosure. Those of skill in the art understand that the scope includes all possible combinations and uses of particular features described in the specifications.

[0041] EXAMPLES

[0042] Preparation of PEI-Silanol Compound

[0043] Polyethyleneimine is a commercially available branched compound from Nippon Shokubai Co., Ltd. at molar mass of 300 Da, 600 Da, 1,200 Da, 1,800 Da, 10 kDa, 30 kDa, and 70 kDa. Post-polymerization modification of the commercially available polyethylene imine (PEI) was adapted from US7999065. In a representative example, Compound A, the polyethyleneimine is preheated to 70 °C then mixed with monoglycidylether of a Cs-Cio aliphatic alcohol (a hydrophobe) in a glass vial. The mixture was heated and agitated at 80 °C for 1.5 hours to form a transparent viscous oil. The cooled viscous oil was mixed with DI water and 50% NaOH to form a transparent aqueous solution at room temperature. 3-glycidoxypropyltrimethoxysilane (GPTS) was then added into the aqueous solution under agitation at room temperature. The whole solution was stirred at 40 °C for 2 hours, followed by dilution with DI water and 50% NaOH to achieve the compound solids. Compounds B and C are made similarly to that of Compound A, however, the hydrophobe group is omitted as shown in the amounts in Table 1.

[0044] Performance Testing Procedures

[0045] Dose response performance tests were conducted using 4700-45ml-T-Alloy600 pressure reaction vessels heated with a J-KEM block heater. Prior to any testing, each pressure vessel is subjected to rigorous cleaning. The following describes the cleaning procedure. The 45 mb pressure vessels were rinsed well with DI water and vacuum dried in a desiccator for at least 1 hour. Using wire brushes and a drill press, each bomb was cleaned thoroughly, including the caps. Residue was removed using high pressure air or nitrogen gas. The inside walls of the pressure vessels were checked using a torch to ensure the surface was clean and shiny. A PEFT gasket was placed on each cap and a new/clean rare earth stir bar was placed in each of the pressure vessels.

[0046] The J-KEM block heater was adjusted to the temperature setpoint to the target reaction temperature. The performance test can be conducted within the temperature range of 150 °C to 260 °C. Residence time (from time pressure vessels were put into the block heater to the time the pressure vessels were taken out of the block heater) can vary depending on the objective of the experiment.

[0047] To perform the application test with added Bauxite solids, 30 mL of spent Bayer liquor from an alumina refinery was dosed with 1.2 g/L SiCh, 1 g/L of ground bauxite solids and added to the 4700-45ml-T-Alloy600 pressure reaction vessels. The scale inhibitors Compound A, B and C from Example 1 were then added in amounts according to the amounts shown in Table 2.

[0048] Each of the above application test vessels were sealed shut and heated for 1 hour at 150 °C. After cooling to room temperature, the slurry from the application test with added Bauxite solids, was poured out of the vessel, the vessel was rinsed with DI water, then a fresh slurry (30 mL plant liquor, 1.2 g/L added SiCh and 1 g/L added Bauxite solids, and the inhibitor) was added back to the vessel. The vessel was then heated for 1 h at 150 C a second time, cooled to room temperature, then the slurry was poured out of the vessel and it was rinsed with DI water (when 5 g/L bauxite solids were added, a third cycle of scaling was conducted in order to generate a measurable amount of scale on the walls of the pressure vessels). The rinsed vessels were dried (unsealed) in an oven for 30 min at 120 C, then cooled to room temperature. The mass was recorded and subtracted from the original mass of the cleaned pressure vessel to calculate the amount of scale grown on the walls of the vessel, as shown in Table 2. A 10% H2SO4 solution was added to the dried vessel to dissolve the scale to measure the concentration of SiCh directly via ICP-OES analysis.

[0049] Similar to the application tests using 1 g/L Bauxite solids above, tests were also performed with 5 g/L of added Bauxite solids. However, in the case of the 5 g/L Bauxite solid application test, a third cycle of scaling was conducted in order to generate a measurable amount of scale on the walls of the pressure vessel. The resulting amount of scale growth on the walls of the vessel after 5 g/L of bauxite solids were added to the test vessel are shown in Table 3.

[0050] The results shown in Table 3 demonstrate that in inhibiting scale formation, compounds A and B perform similarly, despite compound B not having a hydrophobe. This result is unexpected given the prior arts express teachings of using hydrophobes to increase the removal of wall scale.

[0051] In order to demonstrate the effect of dosage rates between Compounds A and B, the compounds performance was compared between the 1 g/L and 5 g/L tests to determine how much of each would be required to fully inhibit scale formation. As shown in Table 4, as the slurry solid content increased from 1 to 5 g/L, the performance of Compound A with added hydrophobe decreased. In contrast, Compound B demonstrates no sensitivity to the increasing solids in the test slurry.

[0052] As mentioned previously, scale formation on the walls of heat exchangers is a known drawback in single stream processes. The scale formation results in a lowering of the digestion efficiency as the scale buildup influences the heat transfer coefficient to the process slurry.

[0053] Table 5 shows the mass of scale growth inside the CFTR tests. As shown in Table 5, the addition of 500 ppm of Compound A to the CFTR test performed similarly to no compound addition, which resulted in no relative reduction in scale mass. However, the mass of scale grown by the addition of 500 ppm Compound B is significantly less than Compound A. This data suggests that under the conditions in the CFTR (50 g/L added Bauxite solids), a scale inhibiting compound that does not comprise a hydrophobe performs better than scale inhibiting compounds that do comprise a hydrophobe.

[0054] The performance of compound B was tested under conditions of CFTR at lower solids content (25 g/L). As shown in Table 6, a significant reduction in scale mass is seen after the addition of 150 ppm and 250 ppm of Compound B.

Claims

1. A method of inhibiting silica-containing scales in an industrial process comprising: contacting a process slurry with a scale inhibitor, the process slurry having a solids concentration of at least 0.5 g/L, wherein the solids are selected from bauxite, sodium aluminate, sodium silicate, clays, aluminosilicates, mineral impurities, amorphous silica, and mixtures thereof , wherein the scale inhibitor comprises a compound comprising: recurring units covalently bound to at least one pendant silanol group according to a following formula (I):

wherein

T is a hydrocarbon group having from 1 to 40 carbon atoms;

A¹ is an organic connecting group comprising a C1-C20 hydrocarbon group, a polyalkyleneimine or a direct bond between the nitrogen atom and the adjoining pendant silanol group; and

M is independently chosen from H, NEU, K, or Na.

2. The method according to claim 1, wherein the compound further comprises recurring units that are not covalently bound to at least one pendant silanol group according to formula (II):

wherein

E is selected from a hydrocarbon group having from 1 to 40 carbon atoms; and A² is H or polyalkyleneimine.

3. The method according to claim 1, wherein the compound has a polyethyleneimine (PEI) backbone.

4. The method according to any one of claims 1 to 3, wherein the pendant silanol group is obtained from reacting a polyamine with 3-glycidoxypropyltrimethoxysilane.

5. The method according to claim 1, wherein the process slurry further comprises a liquid component wherein the liquid component is an aqueous solution comprising salts selected from the group consisting of: sodium hydroxide, sodium aluminate, sodium carbonate, sodium sulfate, sodium phosphate and mixtures thereof.

6. The method according to any one of claims 1 to 5, wherein the compound has a number- averaged molecular weight of greater than or equal to 200 g/mol.

7. The method according to any one of claims 1 to 6, wherein the compound comprises the pendant silanol group in an amount of at least 6 mol% and up to 80 mol%, preferably of at least 6 mol% and up to 35 mol%, in particular of at least 6 mol% and up to 25 mol%, for example of at least 6 mol% and up to 15 mol%, based on the total recurring units.

8. The method according to any one of claims 1 to 7, wherein the industrial process is a Bayer process.

9. The method according to claim 8, wherein the scale inhibitor comprising the compound is added before and during bauxite digestion in the Bayer process.

10. The method according to claim 8, wherein the process slurry is a bauxite feed slurry.

11. The method according to claim 8, wherein the scale inhibitor is added before bauxite digestion in the Bayer process.

12. The method according to claim 8, wherein the scale inhibiting compound is added at a temperature of at least 40 °C and of at most 300 °C in the Bayer process.

13. The method according to any one of claims 1 to 12, wherein the scale inhibitor is present at an amount of at least 5 ppm.

14. Use of a scale inhibitor for silica-containing scale in an industrial process, the scale inhibitor comprising a compound comprising: recurring units covalently bound to at least one pendant silanol group according to the following formula (I):

wherein

T is a hydrocarbon group having from 1 to 40 carbon atoms;

M is independently chosen from H, NH4, K, or Na.

15. The use according to claim 14, wherein the industrial process is in a Bayer process for refining alumina from bauxite ore.

16. The use according to claim 15, wherein the Bayer process is a single stream process.

17. The use according to claims 14 to 16, wherein the compound comprises the pendant silanol group in an amount of at least 6 mol% and up to 80 mol%, preferably of at least 6 mol% and up to 35 mol%, in particular of at least 6 mol% and up to 25 mol%, for example of at least 6 mol% and up to 15 mol%, based on the total recurring units.

18. A compound consisting of: recurring units covalently bound to at least one pendant silanol group according to formula (I):

wherein

T is a hydrocarbon group having from 1 to 40 carbon atoms;

M is independently chosen from H, NH4, K, or Na, and optionally, recurring units not bound to at least one pendant silanol group according to formula (II):

wherein

E is selected from a hydrocarbon group having from 1 to 40 carbon atoms; and A² is H or a polyalkyleneimine.

19. The compound according to claim 18, wherein the compound has a polyethyleneimine (PEI) backbone.

20. The compound according to claim 18 or 19, wherein the pendant silanol group is obtained from reacting a polyamine with 3-glycidoxypropyltrimethoxysilane.