A filter aid for reducing the moisture content of iron ore slurry and a method of making the same

Abstract

The application discloses a kind of filter aids for reducing iron ore pulp moisture content and preparation method thereof, belong to filter aid technical field.The filter aid is with starch as matrix, cooperate bromoalkane, bromo quaternary ammonium salt and other raw materials, by pre-oxidation, alkaline activation, double bromination grafting and post-processing are obtained;Among them, bromoalkane is the normal monovalent alkyl bromide of carbon chain length 8-14, and bromo quaternary ammonium salt is 2-bromoethyl trimethyl ammonium bromide or 6-bromoethyl trimethyl ammonium bromide.The present application realizes the synchronous grafting of hydrophobic alkyl chain and cationic quaternary ammonium salt through covalent bond, which can not only destroy the mineral surface hydration film and convert attached water, but also flocculate fine particles and impurities, and optimize the pore structure of filter cake.The filter aid solves the defects of single function and poor synergy of traditional technology, significantly improves the filtration efficiency, reduces the moisture content of filter cake and the turbidity of filtrate, and the raw materials are environmentally friendly, the preparation process is simple, suitable for industrial production, and suitable for iron ore pulp solid-liquid separation filtering scene.

Description

Technical Field

[0001] This invention relates to the field of filter aid technology, and in particular to a filter aid for reducing the moisture content of iron ore slurry and its preparation method. Background Technology

[0002] In the iron ore beneficiation industry, a combined process of "stage grinding-magnetic separation-anion reverse flotation" is typically used to achieve efficient separation of valuable minerals and gangue impurities. Fine grinding is a crucial step in improving the liberation of individual mineral particles and ensuring the accuracy of subsequent separation. As the grade of iron ore resources declines year by year, the grinding particle size needs to be further refined to meet the concentrate grade requirements for smelting. This leads to a significant increase in the proportion of -200 mesh fine particles in the slurry and a substantial increase in the specific surface area of ​​the particles. Simultaneously, inhibitors, collectors, and reagents such as sodium silicate (water glass) added during flotation adsorb onto the surface of iron ore particles, forming a stable colloidal system in the slurry. This increases the thickness and strengthens the hydration film on the surface of the mineral particles, resulting in increased slurry viscosity and decreased fluidity, posing a severe challenge to subsequent solid-liquid separation and filtration. Currently, in industrial production, the filtration process generally suffers from problems such as high filter cake moisture content, slow filtration rate, and high turbidity of filtrate. Excessive filter cake moisture not only increases energy consumption in subsequent pellet sintering processes but may also lead to insufficient pellet strength and poor sintering permeability, affecting smelting efficiency. Meanwhile, impurities such as residual fine silica mud and organic agents in the filtrate increase water treatment costs and pose a risk of loss of fine iron ore particles, resulting in resource waste.

[0003] To improve the filtration performance of iron ore slurry, various solutions have been proposed in existing technologies. Some technologies employ inorganic-organic composite coagulant systems such as polyaluminum chloride (PAC), polyacrylamide (PAM), and polyferric aluminum sulfate (PAFS) to increase particle size and reduce slurry viscosity by neutralizing the colloidal charge of the slurry and bridging flocculation. Other technologies use single cationic modified starch as a filter aid, utilizing the adsorption and neutralization effects of cationic groups to achieve flocculation and agglomeration of fine particles. Still other technologies attempt to enhance the hydrophobicity of mineral surfaces by hydrophobically modifying starch, thereby disrupting the hydration film. These existing solutions alleviate the slurry filtration problem to some extent; for example, compound coagulants can effectively reduce slurry viscosity, cationic modified starch can improve particle agglomeration, and hydrophobic modified starch can reduce water adhering to the mineral surface.

[0004] However, existing technologies still have significant shortcomings: the components in compound coagulant systems are merely physically mixed, lacking chemical bonding, resulting in poor synergistic stability. Furthermore, these systems lack hydrophobic functional groups, failing to fundamentally disrupt the robust hydration film on the mineral surface, thus limiting the removal of attached water, and the filter cake moisture content remains insufficient for industrial applications. Single cationic modified starch can only achieve particle flocculation, failing to address the problem of residual attached water caused by the hydration film, resulting in insufficient dehydration depth. While single hydrophobic modified starch can disrupt the hydration film, it lacks cationic flocculation capabilities; fine particles struggle to aggregate due to electrostatic repulsion, leading to a densely packed filter cake with high filtration resistance and slow filtration rates. In addition, inorganic salts in some compound systems may affect subsequent smelting processes, and corrosive reagents or recalcitrant components introduced during filter aid preparation can pose production safety and environmental risks. Therefore, developing a filter aid that combines efficient hydrophobic film disruption, strong flocculation and impurity removal functions, good synergistic stability, and environmental safety has become a key requirement for solving the iron ore slurry filtration problem and improving the economic efficiency of the mineral processing industry. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of existing technologies by proposing a filter aid for reducing the moisture content of iron ore slurry and its preparation method.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: a filter aid for reducing the moisture content of iron ore slurry, comprising the following components by weight: starch: 100 parts, bromoalkanes: 12-25 parts, bromoquaternary ammonium salts: 8-15 parts, sodium hydroxide: 8-12 parts, deionized water: 950-1050 parts, and ethanol: 80-120 parts.

[0007] Preferably, the bromoalkane is a normal monoalkyl bromide with a carbon chain length of 8-14, selected from one of 1-bromooctane, 1-bromodecane, 1-bromododecane, and 1-bromotetradecane;

[0008] Preferably, the brominated quaternary ammonium salt is selected from 2-bromoethyltrimethylammonium bromide or 6-bromoethyltrimethylammonium bromide.

[0009] Preferably, the starch is selected from corn starch, wheat starch, tapioca starch or potato starch.

[0010] More preferably, the starch is selected from corn starch.

[0011] Furthermore, the present invention also provides a method for preparing a filter aid to reduce the moisture content of iron ore slurry, comprising the following steps:

[0012] (1) Add starch and deionized water to the reactor and stir at room temperature for 10-30 min. Then add ammonium persulfate, keep stirring and heat to 90-100℃, and keep the reaction at this temperature for 50-70 min to obtain pre-oxidized starch paste. The chemical reaction is shown below:

[0013] ;

[0014] (2) After the pre-oxidized starch paste cools to 45-55℃, add sodium hydroxide and stir at 300-400r / min for 10-30min to obtain sodium starch alcohol paste; the chemical reaction is shown below:

[0015] ;

[0016] (3) Prepare an aqueous solution of the quaternary ammonium bromide salt for later use;

[0017] (4) Maintain the system temperature at 45-55℃, add bromoalkanes dropwise, and after the addition is complete, keep the reaction at this temperature for 2-4 hours. Then add an aqueous solution of bromoquaternary ammonium salt dropwise, and after the addition is complete, react for 14-18 hours to obtain the grafted modified starch paste. The chemical reaction is illustrated below:

[0018]

[0019] Where R represents octylene: ,

[0020] Zheng Gui Ji: ,

[0021] n-Dodecyl: ,

[0022] tetradecyl: ,

[0023] Trimethylpropylammonium bromide: ,

[0024] n-Hexyltrimethylammonium bromide: One of them;

[0025] (5) After the grafted modified starch paste cools to room temperature, adjust the pH of the system to neutral with dilute hydrochloric acid solution, add ethanol, stir for 30-60 min, and then collect the filter cake through plate and frame filtration. Wash the filter cake 1-2 times with deionized water, dry the filter cake and pulverize it to 80-120 mesh to obtain a filter aid that reduces the moisture content of iron ore slurry; the chemical reaction that occurs after adjusting the pH to neutral with dilute hydrochloric acid is shown in the following diagram:

[0026] .

[0027] Preferably, the weight ratio of starch to ammonium persulfate in (1) is 1:0.0003-0.0006.

[0028] Preferably, the stirring rate in (1) is 300-400 r / min.

[0029] Preferably, the sodium hydroxide in (2) is an industrial-grade flake alkali with a purity of ≥96%.

[0030] Preferably, the concentration of the brominated quaternary ammonium salt aqueous solution in (3) is 30-50 wt%.

[0031] Preferably, the bromoalkane in (4) is added at a time of 10-20 min.

[0032] Preferably, the dripping time of the brominated quaternary ammonium salt aqueous solution in (4) is 20-40 min.

[0033] Preferably, the concentration of the dilute hydrochloric acid solution in (5) is 0.1-0.5 mol / L.

[0034] Preferably, the drying method in (5) is one of atmospheric pressure hot air drying, vacuum drying or paddle drying, the drying temperature is controlled at 60-80℃, and the material is dried until the moisture content is ≤5%.

[0035] More preferably, the drying method in (5) is atmospheric pressure hot air drying at a temperature of 60-80℃, until the moisture content of the material is ≤5%.

[0036] Preferably, the mechanism of action of the filter aid for reducing the water content of iron ore slurry according to the present invention is explained as follows:

[0037] This invention relates to a filter aid for reducing the moisture content of iron ore slurry. Its mechanism of action is based on starch, where hydrophobic alkyl chains grafted with covalent bonds form a dual synergistic effect of "dehydration + impurity removal" with cationic quaternary ammonium salt groups. Combined with the supporting effect of the starch skeleton, it achieves both deep dehydration and efficient removal of various impurities from the iron ore slurry. The specific process is as follows:

[0038] After starch undergoes ammonium sulfate pre-oxidation treatment, some α-1,4 glycosidic bonds are selectively broken, reducing the system viscosity while preserving the polymer chain backbone. This provides a structural basis for the uniform discrete grafting of hydrophobic alkyl chains and cationic quaternary ammonium salts. The two functional groups are randomly distributed in the starch backbone, without overlapping or canceling each other out, each performing its specific function. Among them, the grafted 8-14 carbon chain length n-alkyl bromides (such as 1-bromooctane, 1-bromododecane, etc.) act as strongly hydrophobic side chains. Due to the strong hydrophobicity and hydrophobic association effect of long-chain aliphatic hydrocarbons, they spontaneously aggregate in the slurry to form continuous hydrophobic microdomains. These microdomains are directionally adsorbed on the surface of iron ore particles, precisely covering the hydrophilic sites on the mineral surface, destroying the originally firm hydration film, significantly increasing the contact angle between the mineral and water, and transforming the tightly attached hydration film on the particle surface into free water that can be easily removed under filtration force. This fundamentally weakens the hydrophilicity of the mineral and lays the foundation for rapid water separation.

[0039] Meanwhile, the cationic quaternary ammonium salt groups of the grafted 2-bromoethyltrimethylammonium bromide or 6-bromoethyltrimethylammonium bromide, relying on their strong positive charge characteristics, play a dual core role: on the one hand, they rapidly dissolve and disperse in the slurry, efficiently neutralizing the negative charge on the surface of fine iron ore particles, eliminating electrostatic repulsion between particles, and then, through the bridging effect of starch polymer segments, agglomerating the dispersed fine particles into loose, interconnected flocs, avoiding the decrease in permeability caused by dense particle accumulation in the filter cake, and creating a smooth channel for the rapid discharge of free water; on the other hand, they target various impurities in the iron ore slurry that affect filtration efficiency ( For impurities such as fine silica mud, residual flotation reagents (collectors, inhibitors), and sodium silicate (water glass), the strong positive charge of cationic quaternary ammonium salts can strongly neutralize and adsorb these negatively charged impurities. After the fine colloidal impurities such as silica mud are neutralized, they lose their stable suspension ability and tightly bind to iron ore particle flocs. Residual organic flotation reagents bind to the hydrophobic alkyl microregions on starch chains through hydrophobic interactions, and are then fixed inside the flocs through the bridging effect of cationic groups. Sticky impurities such as sodium silicate are neutralized by cationic quaternary ammonium salts, eliminating the high viscosity problem of the slurry caused by them, and significantly improving the fluidity of the slurry liquid phase.

[0040] Two functional groups are bonded to the starch backbone through stable covalent bonds, forming an "organic-inorganic synergistic" macromolecular structure: the hydrophobic alkyl chain focuses on disrupting the hydration membrane at the solid-liquid interface, while the cationic quaternary ammonium salt group handles both particle flocculation and impurity neutralization and adsorption. The rigid framework of the starch matrix itself further optimizes the filter cake pore structure and reduces the filter cake specific resistance, while firmly locking the adsorbed impurities in the filter cake to prevent them from clogging the filter cloth pores. Ultimately, under the triple synergistic effect of "hydrophobic membrane disruption and dehydration + cationic flocculation and impurity removal + framework support and efficiency improvement," the iron ore slurry not only achieves a significant reduction in filter cake moisture but also efficiently removes various impurities, extends the filter cloth's service life, and simultaneously improves filtration efficiency and filtrate clarity. This completely solves the technical pain points of traditional filter aids, such as single dehydration, impurity residue, poor physical compound synergy, and slurry viscosity.

[0041] Compared with the prior art, the beneficial effects of the present invention are:

[0042] 1. This invention achieves a triple synergistic function of "hydrophobic membrane disruption + flocculation and impurity removal + skeletal support" through a bivalent covalent graft modification design of hydrophobic alkyl chains and cationic quaternary ammonium salts. The hydrophobic groups can directionally disrupt the hydration film on the surface of iron ore particles, converting attached water into free water; the cationic groups can efficiently neutralize the negative charge of fine particles and impurities, forming loose flocs through bridging and reducing filtration resistance; the rigid skeletal structure of the starch matrix further optimizes the pore structure of the filter cake, reducing filter cloth clogging. The synergistic effect of these three components fundamentally solves the limitations of traditional filter aids with their single function, achieving a unified approach of deep dehydration and efficient impurity removal, significantly improving filtration efficiency and filtrate clarity, and extending the service life of the filter cloth.

[0043] 2. This invention uses natural starch as the base material, combined with bromoalkanes and bromoquaternary ammonium salts. The raw materials are widely available, cost-effective, and environmentally compatible. The starch-based materials are non-toxic and easily degradable, will not introduce harmful impurities into the slurry, and will not affect subsequent pelletizing and smelting processes. The preparation process adopts an atmospheric pressure aqueous phase process, without corrosive reagents or high-risk reaction steps, resulting in a high production safety factor. Ethanol and production wastewater can be recycled after distillation and neutralization, reducing resource waste and environmental pressure, which is in line with the concept of green industrial production.

[0044] 3. The preparation process of this invention has strong industrial adaptability, requiring no high-precision equipment or complex operating procedures. The temperature and time parameters in the starch pre-oxidation, alkaline activation, double grafting reaction, and post-treatment stages are mild and controllable. The equipment used for stirring, filtering, and drying are all conventional equipment in the mineral processing industry, facilitating large-scale continuous production. The quaternary ammonium bromide salt is pre-prepared as an aqueous solution and added dropwise to ensure uniform and complete reaction; conventional drying methods are suitable for wet filter cake treatment, avoiding process inconsistencies. The overall process is simple, highly stable, and has low production costs, making it easy to rapidly promote and apply in mineral processing enterprises.

[0045] 4. The filter aid of this invention has broad applicability to complex iron ore slurry systems, especially suitable for slurries with high viscosity and a high proportion of fine particles after fine grinding. The cationic groups effectively neutralize the polarity of viscous impurities such as sodium silicate and residual flotation reagents, significantly reducing slurry viscosity and improving fluidity. The synergistic effect of the hydrophobic and cationic groups efficiently removes harmful impurities such as fine silica mud, preventing them from affecting concentrate grade. After use, no additional adjustments to the beneficiation process parameters are required to simultaneously optimize filter cake moisture and filtrate turbidity, reducing energy consumption and improving efficiency in subsequent processes, demonstrating significant economic benefits and practical value. Detailed Implementation

[0046] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with existing known technologies. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0047] Example 1: A specific preparation method of a filter aid for reducing the moisture content of iron ore slurry, comprising the following steps:

[0048] (1) Add 1 kg of corn starch and 9.5 kg of deionized water to the reactor, stir at 300 r / min for 10 min at room temperature, then add 0.3 g of ammonium persulfate, keep stirring and heat to 90 °C, keep the temperature for 50 min to obtain pre-oxidized starch paste;

[0049] (2) After the pre-oxidized starch paste is cooled to 45°C, add 80g of sodium hydroxide (industrial flake alkali with a purity ≥96%) and stir at 300r / min for 10min to obtain sodium starch alcohol paste;

[0050] (3) Prepare an aqueous solution of 80g of 2-bromohexyltrimethylammonium bromide with a concentration of 30wt% for later use;

[0051] (4) Maintain the system temperature at 45℃, add 120g of 1-bromododecane dropwise over a time of 10min, and after the addition is complete, keep the temperature for 2h, then add the brominated quaternary ammonium salt aqueous solution dropwise over a time of 20min, and after the addition is complete, react for 14h to obtain the grafted modified starch paste.

[0052] (5) After the grafted modified starch paste cools to room temperature, adjust the pH of the system to neutral with a 0.1 mol / L dilute hydrochloric acid solution, add 800 g of ethanol, stir for 30 min, and then collect the filter cake through plate and frame filtration. Wash the filter cake with deionized water 1-2 times, dry the filter cake with hot air at 60℃ until the moisture content is ≤5%, and then crush it to 80-120 mesh to obtain a filter aid that reduces the moisture content of iron ore slurry.

[0053] Example 2: A specific preparation method of a filter aid for reducing the moisture content of iron ore slurry, comprising the following steps:

[0054] (1) Add 1 kg of corn starch and 10 kg of deionized water to the reactor, stir at 350 r / min for 20 min at room temperature, then add 0.5 g of ammonium persulfate, keep stirring and heat to 95 °C, keep the temperature for 60 min to obtain pre-oxidized starch paste;

[0055] (2) After the pre-oxidized starch paste is cooled to 50°C, add 100g of sodium hydroxide (industrial flake alkali with a purity ≥96%) and stir at 350r / min for 20min to obtain sodium starch alcohol paste;

[0056] (3) Prepare an aqueous solution of 120g of 2-bromohexyltrimethylammonium bromide with a concentration of 40wt% for later use;

[0057] (4) Maintain the system temperature at 50℃, add 200g of 1-bromododecane dropwise over a time of 15min, and after the addition is complete, keep the temperature for 3h, then add the brominated quaternary ammonium salt aqueous solution dropwise over a time of 30min, and after the addition is complete, react for 16h to obtain the grafted modified starch paste.

[0058] (5) After the grafted modified starch paste cools to room temperature, adjust the pH of the system to neutral with a 0.3 mol / L dilute hydrochloric acid solution, add 1 kg of ethanol, stir for 45 min, and then collect the filter cake through plate and frame filtration. Wash the filter cake with deionized water 1-2 times, dry the filter cake with hot air at 70℃ until the moisture content is ≤5%, and then crush it to 80-120 mesh to obtain a filter aid that reduces the moisture content of iron ore slurry.

[0059] Example 3: A specific preparation method of a filter aid for reducing the moisture content of iron ore slurry, comprising the following steps:

[0060] (1) Add 1 kg of corn starch and 10.5 kg of deionized water to the reactor, stir at 400 r / min for 30 min at room temperature, then add 0.6 g of ammonium persulfate, keep stirring and heat to 100 °C, keep the temperature for 70 min to obtain pre-oxidized starch paste;

[0061] (2) After the pre-oxidized starch paste is cooled to 55°C, add 120g of sodium hydroxide (industrial flake alkali with a purity ≥96%) and stir at 400r / min for 30min to obtain sodium starch alcohol paste;

[0062] (3) Prepare a 50wt% aqueous solution of 2-bromohexyltrimethylammonium bromide from 150g of 2-bromohexyltrimethylammonium bromide for later use;

[0063] (4) Maintain the system temperature at 55℃, add 250g of 1-bromododecane dropwise over a time of 20min, and after the addition is complete, keep the temperature for 4h, then add the brominated quaternary ammonium salt aqueous solution dropwise over a time of 40min, and after the addition is complete, react for 18h to obtain the grafted modified starch paste.

[0064] (5) After the grafted modified starch paste cools to room temperature, adjust the pH of the system to neutral with a 0.5 mol / L dilute hydrochloric acid solution, add 1.2 kg of ethanol, stir for 60 min, and then collect the filter cake through plate and frame filtration. Wash the filter cake with deionized water 1-2 times, dry the filter cake with hot air at 80℃ until the moisture content is ≤5%, and then crush it to 80-120 mesh to obtain a filter aid that reduces the moisture content of iron ore slurry.

[0065] Example 4: The difference between Example 4 and Example 2 is that 1-bromododecane is replaced with 1-bromooctane.

[0066] Example 5: The difference between Example 5 and Example 2 is that 1-bromododecane is replaced with 1-bromodecane.

[0067] Example 6: The difference between Example 6 and Example 2 is that 1-bromododecane is replaced with 1-bromotetradecane.

[0068] Example 7: The difference between Example 7 and Example 2 is that 2-bromohexyltrimethylammonium bromide is replaced with 6-bromoethyltrimethylammonium bromide.

[0069] Comparative Example 1: The difference between Comparative Example 1 and Example 2 is that 1-bromododecane is replaced with 1-bromohexane.

[0070] Comparative Example 2: The difference between Comparative Example 2 and Example 2 is that 1-bromododecane is replaced with 1-bromohexadecane.

[0071] Comparative Example 3: The difference between Comparative Example 3 and Example 2 is that step (3) is omitted and the aqueous solution of quaternary ammonium bromide is not added in step (4).

[0072] Comparative Example 4: The difference between Comparative Example 4 and Example 2 is that 1-bromododecane is not added in step (4).

[0073] Comparative Example 5: The difference between Comparative Example 5 and Example 2 is that Comparative Example 5 uses a filter aid disclosed in patent CN104437435A.

[0074] Performance testing:

[0075] Preparation of iron ore slurry for testing:

[0076] Iron concentrate slurry from the solid-liquid separation filtration stage after magnetic separation and flotation in an iron ore beneficiation plant was selected and prepared into a slurry with a weight concentration of 65% and a pH value of 11.5.

[0077] Testing process:

[0078] Solid-liquid separation performance was tested using a vacuum filter. First, 1000g of the prepared iron ore slurry was accurately weighed and placed on the filter cloth of the filter. The filter aids prepared in Examples 1-7 and Comparative Examples 1-5 were accurately weighed at an addition rate of 150g / t dry ore. The filter aids were evenly sprinkled into the slurry and stirred at 300r / min for 5min to ensure that the filter aids and slurry were fully mixed. Then, the vacuum filter was started, and a stopwatch was started to record the time when the slurry was completely filtered dry, which was the filtration time. After filtration, the filter cake on the filter cloth was carefully removed, and the wet weight of the filter cake was accurately weighed with an electronic balance. Then, the filter cake was placed in an 80℃ atmospheric pressure hot air drying oven to dry to constant weight, and the dry weight of the filter cake was weighed again. The moisture content of the filter cake was calculated as (wet weight - dry weight) / wet weight × 100%. At the same time, the filtrate was collected, and the turbidity and final pH of the filtrate were measured. The experimental results are shown in Table 1.

[0079] Table 1 Performance Test Results

[0080]

[0081] Data Analysis:

[0082] As can be seen from the performance test data in Table 1, the technical solution of “starch pre-oxidation-dibromo grafting” based on the present invention in Examples 1-7 is significantly better than various comparative examples in terms of filtration efficiency, dehydration depth and impurity removal effect. Among them, Example 2 has the shortest filtration time, the lowest filter cake moisture content and the best filtrate turbidity, and the best overall performance.

[0083] Example 2 exhibits the best overall performance, likely due to the following reasons: At the raw material level, 1-bromododecane, as the optimal choice for the C8-14 carbon chain range, ensures a strong hydrophobic association effect, forming continuous and stable hydrophobic microdomains, while avoiding incomplete membrane rupture caused by excessively short carbon chains or dispersion problems caused by excessively long chains. 2-bromoethyltrimethylammonium bromide possesses a higher cation charge density, providing ample active sites for flocculation and impurity removal. At the grafting synergy level, after pre-oxidation treatment, starch selectively breaks some α-1,4 glycosidic bonds, reducing system viscosity while preserving the polymer chain skeleton. This provides a structural basis for the simultaneous grafting of hydrophobic alkyl chains and cationic quaternary ammonium salts, ensuring that the hydration membrane disruption function of the hydrophobic chains and the flocculation and impurity removal function of the cationic chains do not interfere with each other and synergistically enhance each other. Combined with the optimization effect of the rigid skeleton of the starch matrix itself on the filter cake pore structure, the triple function of "membrane rupture and dehydration + flocculation and agglomeration + skeleton support" is maximized. At the process parameter level, the kinetic requirements of the double grafting reaction are precisely matched to ensure that the grafting reaction is uniform and sufficient, the degree of substitution is controlled within the optimal range, and the problem of excessive or insufficient local reaction is avoided, so that each starch molecule can play a synergistic role in dehydration and impurity removal simultaneously.

[0084] The performance of Comparative Example 1 is inferior to that of Example 2. This may be because the carbon chain length of the 1-bromohexane used in Comparative Example 1 is shorter than the defined 8-14 range. The hydrophobic association effect of the short-chain hydrophobic group is weak, and it cannot form a continuous and stable hydrophobic micro-region. This results in incomplete destruction of the hydration film on the mineral surface and insufficient adsorption and fixation capacity for residual organic flotation reagents. Furthermore, the short-chain hydrophobic group cannot effectively assist the cationic group in locking fine impurities, resulting in a densely packed filter cake, increased resistance to water removal, increased impurities in the filtrate, and a significant deterioration in all core indicators.

[0085] The performance of Comparative Example 2 is inferior to that of Example 2 because the carbon chain length of the 1-bromohexadecane used in Comparative Example 2 exceeds the optimal range of 8-14. The steric hindrance effect of the long-chain alkyl group is significant, resulting in poor dispersibility in the starch colloidal system, reduced uniformity of nucleophilic substitution reaction with sodium starch alkoxide, and decreased grafting efficiency. The excessively long hydrophobic chain is prone to self-aggregation, which not only blocks some cationic active sites, weakening the flocculation and impurity removal effect, but also leads to uneven pore distribution of the filter cake and decreased permeability. Ultimately, the filtration efficiency, dehydration depth, and impurity removal effect are all inferior to those of Example 2.

[0086] Comparative Example 3 omits the cationic quaternary ammonium salt grafting step, retaining only the hydrophobic grafting function. It lacks the strong positive charge neutralization and bridging effect of cationic groups. Due to electrostatic repulsion, fine iron ore particles and impurities cannot effectively agglomerate, resulting in a densely packed filter cake with extremely poor pore connectivity, obstructing the water discharge channels. At the same time, it cannot neutralize the negative charge of viscous impurities such as fine silica mud and sodium silicate through cationic adsorption, and the slurry viscosity is not effectively improved. Furthermore, the hydrophobic groups can only disrupt the hydration film and cannot solve the filtration resistance problem caused by particle dispersion. Therefore, its performance is far inferior to that of Example 2.

[0087] Comparative Example 4 retains only the cationic grafting function and lacks the membrane-breaking effect of hydrophobic alkyl chains. The firmly attached hydration film on the mineral surface cannot be effectively destroyed, and a large amount of attached water remains in the filter cake, resulting in a high moisture content in the filter cake. Although the particle size can be increased through cationic flocculation, the presence of the hydration film still significantly increases the difficulty of water removal. Furthermore, the lack of hydrophobic micro-regions for adsorption and fixation of residual organic flotation reagents leads to increased impurities and turbidity in the filtrate. Its overall performance is significantly inferior to that of Example 2.

[0088] Comparative Example 5 uses the existing PAC+PAM+PAFS compound system. Although it can achieve particle flocculation through the bridging effect of PAM and neutralize the viscosity of the slurry through the cations of PAC and PAFS, this system lacks hydrophobic functional groups and cannot destroy the hydration film on the mineral surface. Therefore, the removal effect on attached water is limited. Moreover, the components in the compound system are only physically mixed and lack chemical bonding. The synergistic stability is insufficient, and some components are easily dissociated in the slurry, resulting in poor long-term flocculation and impurity removal. The fluffiness of the filter cake structure is not as good as the covalent grafting system of Example 2. Therefore, the filtration time, filter cake moisture content and filtrate turbidity are all worse than those of Example 2.

[0089] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A filter aid for reducing the moisture content of iron ore slurry, characterized in that, It includes the following components by weight: starch: 100 parts, bromoalkanes: 12-25 parts, bromoquaternary ammonium salts: 8-15 parts, sodium hydroxide: 8-12 parts, deionized water: 950-1050 parts, and ethanol: 80-120 parts. The bromoalkane is a normal monoalkyl bromine with a carbon chain length of 8-14, selected from one of 1-bromooctane, 1-bromodecane, 1-bromododecane, and 1-bromotetradecane; The brominated quaternary ammonium salt is selected from either 2-bromoethyltrimethylammonium bromide or 6-bromohexyltrimethylammonium bromide; The method for preparing the filter aid for reducing the moisture content of iron ore slurry includes the following steps: (1) Add starch and deionized water to the reactor and stir at room temperature for 10-30 min. Then add ammonium persulfate, keep stirring and heat to 90-100℃, keep the temperature for 50-70 min to obtain pre-oxidized starch paste. (2) After the pre-oxidized starch paste has cooled to 45-55℃, add sodium hydroxide and stir at 300-400r / min for 10-30min to obtain sodium starch alcohol paste; (3) Prepare an aqueous solution of the quaternary ammonium bromide salt for later use; (4) Maintain the system temperature at 45-55℃, add bromoalkanes dropwise, and after the addition is complete, keep the reaction at the temperature for 2-4 hours. Then add bromoquaternary ammonium salt aqueous solution dropwise, and after the addition is complete, react for 14-18 hours to obtain grafted modified starch paste. (5) After the grafted modified starch paste cools to room temperature, adjust the pH of the system to neutral with dilute hydrochloric acid solution, add ethanol, stir for 30-60 min, and then collect the filter cake through plate and frame filtration. Wash the filter cake with deionized water 1-2 times, dry the filter cake and crush it to 80-120 mesh to obtain a filter aid that reduces the moisture content of iron ore slurry.

2. The filter aid for reducing the moisture content of iron ore slurry according to claim 1, characterized in that, The starch is selected from one of corn starch, wheat starch, cassava starch, or potato starch.

3. The method for preparing the filter aid for reducing the moisture content of iron ore slurry according to any one of claims 1-2, characterized in that, Includes the following steps: (1) Add starch and deionized water to the reactor and stir at room temperature for 10-30 min. Then add ammonium persulfate, keep stirring and heat to 90-100℃, keep the temperature for 50-70 min to obtain pre-oxidized starch paste. (2) After the pre-oxidized starch paste has cooled to 45-55℃, add sodium hydroxide and stir at 300-400r / min for 10-30min to obtain sodium starch alcohol paste; (3) Prepare an aqueous solution of the quaternary ammonium bromide salt for later use; (4) Maintain the system temperature at 45-55℃, add bromoalkanes dropwise, and after the addition is complete, keep the reaction at the temperature for 2-4 hours. Then add bromoquaternary ammonium salt aqueous solution dropwise, and after the addition is complete, react for 14-18 hours to obtain grafted modified starch paste. (5) After the grafted modified starch paste cools to room temperature, adjust the pH of the system to neutral with dilute hydrochloric acid solution, add ethanol, stir for 30-60 min, and then collect the filter cake through plate and frame filtration. Wash the filter cake with deionized water 1-2 times, dry the filter cake and crush it to 80-120 mesh to obtain a filter aid that reduces the moisture content of iron ore slurry.

4. The method for preparing the filter aid for reducing the moisture content of iron ore slurry according to claim 3, characterized in that, The weight ratio of starch to ammonium persulfate in (1) is 1:0.0003-0.0006.

5. The method for preparing the filter aid for reducing the moisture content of iron ore slurry according to claim 3, characterized in that, The stirring rate in (1) is 300-400 r / min.

6. The method for preparing the filter aid for reducing the moisture content of iron ore slurry according to claim 3, characterized in that, The sodium hydroxide in (2) is an industrial-grade flake alkali with a purity of ≥96%.

7. The method for preparing the filter aid for reducing the moisture content of iron ore slurry according to claim 3, characterized in that, The concentration of the brominated quaternary ammonium salt aqueous solution in (3) is 30-50 wt%.

8. The method for preparing the filter aid for reducing the moisture content of iron ore slurry according to claim 3, characterized in that, The dripping time for the bromoalkanes in (4) is 10-20 min; the dripping time for the aqueous solution of the bromoquaternary ammonium salt is 20-40 min.

9. The method for preparing the filter aid for reducing the moisture content of iron ore slurry according to claim 3, characterized in that, The concentration of the dilute hydrochloric acid solution in (5) is 0.1-0.5 mol / L.

10. The method for preparing the filter aid for reducing the moisture content of iron ore slurry according to claim 3, characterized in that, The drying method in (5) is one of atmospheric pressure hot air drying, vacuum drying or paddle drying, and the drying temperature is controlled at 60-80℃, and the material is dried until the moisture content is ≤5%.

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