Process for dry in-situ modification of light-burned magnesium oxide with a citric acid-ammonium acetate-quaternary ammonium salt complexing agent

Abstract

The application discloses a process for modifying light-burned magnesium oxide by a dry in-situ method with a citric acid-ammonium acetate-quaternary ammonium salt composite agent, wherein dry powder of citric acid monohydrate, dry powder of ammonium acetate and dry powder of solid ester-based quaternary ammonium salt are dry-mixed to obtain a ternary solid composite powder agent, the dry-in-situ double-layer coating is completed by mechanically-chemically activating the dry light-burned magnesium oxide in a high-speed mixer with heating at 40-50 DEG C, a hydrophilic magnesium citrate chelate film is formed in the inner layer of the powder, and an outer layer of a quaternary ammonium cation functional layer is adsorbed, and the whole process is free of free water and wastewater discharge. The modified powder is used for ester-based quaternary ammonium salt reverse flotation of magnesite, can stabilize the weakly acidic interval of slurry pH 5.0-5.5, has four synergistic effects of pH buffering, calcium and magnesium ion chelation, magnesite selective inhibition and quartz auxiliary collection, reduces the flocculation loss of a collector, and improves the concentrate recovery rate. The application omits the high-energy-consumption processes of wet dissolution and drying, the solid powder agent is convenient to store and transport and has a long shelf life, and the application forms a differentiated technical route with the binary dry modification, wet coating and neutral integrated flotation reagent, raw materials are inexpensive, the process is simple, and the application is suitable for industrialized application of various magnesite beneficiation sites.

Description

[0001] This invention relates to the fields of dry surface modification of inorganic powders and processing of flotation reagents for non-metallic minerals. Specifically, it relates to a process for dry in-situ coating of lightly calcined magnesia with a ternary solid composite powder of citric acid-ammonium acetate-ester-based quaternary ammonium salt, and the application of the modified powder in reverse flotation desilication of magnesite ester-based quaternary ammonium salt. Background Technology Lightly calcined magnesia, as a selectivity inhibitor in the reverse flotation of magnesite, suffers from multiple shortcomings in existing modification and reagent technologies: 1. The mainstream modification schemes are all wet processes, which require the preparation of citric acid aqueous solution. The system contains a large amount of free water, resulting in high transportation and storage costs. The modified suspension must be dried to obtain solid magnesium powder. The drying process has high energy consumption and long production cycle. Liquid citric acid is prone to decomposition and bacterial growth when stored for a long time. Low temperature crystallization in winter can also clog pipes. 2. Existing dry-process modified magnesium oxide technology only uses citric acid + ammonium acetate binary dry powder, lacking quaternary ammonium salt components, and cannot simultaneously enhance the quartz gangue collecting ability; quaternary ammonium salt collectors in flotation pulp are easily consumed by calcium and magnesium ions, resulting in high reagent consumption per unit. 3. Solid quaternary ammonium salts alone have poor dispersibility when directly added to slurry, and are prone to local enrichment, resulting in excessively viscous foam. They cannot be synergistically matched with magnesium oxide inhibitors. There is no commercially available ternary dry powder composite dry in-situ coating process for magnesium oxide with citric acid, ammonium acetate, and quaternary ammonium salts, which cannot simultaneously achieve the four functions of powder hydrophilic modification, pH buffering, hard water resistance, and enhanced collection. 4. Existing magnesia flotation patents mostly use neutral pH integrated liquid compound reagents, and there is no ternary solid composite agent dry solid phase chelation modification route. Furthermore, quaternary ammonium salts are not integrated into the magnesium oxide modification system, leaving a gap in the reagent step-by-step addition process.

[0002] Currently, the industry lacks a ternary dry-process modified integrated powder that can simultaneously achieve hydrophilic coating of powder, pH stabilization, metal ion chelation, and auxiliary collection of gangue. Therefore, this invention is proposed. Summary of the Invention (1) The technical problem that the invention aims to solve 1. Construct a ternary solid-state composite modified powder of citric acid-ammonium acetate-solid ester-based quaternary ammonium salt, with no added free water throughout the process, eliminating the energy-intensive steps of wet dissolution and dehydration drying, and resulting in no wastewater discharge; 2. Dry mechanical and chemical in-situ coating generates a double-layer functional film on the surface of magnesium oxide: an inner hydrophilic magnesium citrate chelating layer and an outer quaternary ammonium cation adsorption layer. The powder does not clump and settle when it enters water, thus achieving the dual effects of magnesium inhibition and auxiliary collection. 3. The ternary composite system stabilizes the slurry pH in the weakly acidic range of 5.0–5.5, replacing hydrochloric acid to reduce equipment corrosion; citrate complexes the circulating water with Ca. 2+ Mg 2+Reduce flocculation loss of quaternary ammonium salt collectors; 4. Solid modified powder is easy to store and transport, has a long shelf life, and can be added directly as dry material at the flotation site. It can be used in stages with ester-based quaternary ammonium liquid collectors, forming a differentiated technical route from existing neutral integrated flotation reagents and binary dry modification processes. 5. The process uses a dry method at normal temperature and pressure, and the raw materials are all industrial bulk dry powders, which are suitable for small and medium-sized mineral processing plants to prepare reagents on-site, greatly reducing equipment investment and labor costs.

[0003] (2) Complete technical solution Option 1: Citric acid-ammonium acetate-quaternary ammonium salt ternary solid composite modified powder Prepared by uniformly mixing the following dry powders in parts by weight: 25-30 parts citric acid monohydrate powder, 45-50 parts ammonium acetate powder, and 3-8 parts solid ester-based quaternary ammonium salt powder. Raw material requirements: Citric acid monohydrate, ammonium acetate, and solid ester-based quaternary ammonium salt must all pass through a 100-mesh sieve; the powder moisture content should be ≤0.5%, and there should be no lumps; the solid ester-based quaternary ammonium salt is hexadecyltrimethylammonium chloride powder. Optimal ratio: 28 parts citric acid monohydrate, 48 parts ammonium acetate, and 5 parts solid ester-based quaternary ammonium salt.

[0004] Option 2: Dry in-situ modification of lightly calcined magnesium oxide using ternary composite agents S1. Pretreatment of light-burned magnesium oxide: Light-burned magnesium oxide powder is crushed and passed through a 100-mesh sieve, then dried with hot air to control the powder moisture content to ≤0.3%, removing surface free adsorbed water; S2. Dry feeding and mixing: The pretreated and dried light-burned magnesium oxide is fed into a heated high-speed mixer, and the above-mentioned ternary solid composite modified powder is added simultaneously; the mass ratio of light-burned magnesium oxide to ternary composite powder is 7:1 to 12:1; S3. Mechanical and chemical dry activation and coating: The mixer is kept at a constant temperature of 40-50℃, the rotor speed is 1200-1800 r / min, and high-speed stirring is carried out for 15-25 min; relying on external temperature control and powder friction heat to activate the solid-phase reaction: citric acid and magnesium ions on the surface of magnesium oxide form a hydrophilic magnesium citrate inner chelate film, and quaternary ammonium salt cations are simultaneously physically and chemically adsorbed on the powder surface to form a cationic functional layer, completing the in-situ double-layer coating modification; S4. Post-treatment sieving: The material is naturally cooled to room temperature and passed through an 80-mesh sieve. A small amount of agglomerated particles were removed by sieving to obtain the dry-modified light-burned magnesium oxide powder by the ternary composite agent. Optimal process parameters: mass ratio of light-burned magnesium oxide to ternary composite powder 9:1, constant temperature 45℃, stirring speed 1500 r / min, stirring time 20 min.

[0005] Option 3: Application method of dry-modified magnesium oxide powder in reverse flotation of magnesite ester-based quaternary ammonium salts 1) Grind the magnesite ore to 200 mesh with a passing rate of 75%–85%, and adjust the slurry concentration to 28–33 wt% by adding water; 2) First, put the dry-modified magnesium oxide powder prepared by this process into the slurry mixing tank, stir for 3 minutes, and the total amount of reagent added is 230-380g / t of raw ore; 3) Add the ester-based quaternary ammonium salt aqueous solution collector and stir for 4 minutes; 4) A small amount of No. 2 pine oil was used as a frother for aeration flotation, and the pH of the pulp was controlled to remain stable in the weakly acidic range of 5.0 to 5.5 throughout the process; 5) The foam layer consists of quartz and talc silicate gangue tailings, while the bottom flow of the flotation cell is high-purity magnesite concentrate.

[0006] (3) Core innovation of this invention 1. The first-ever formula of ternary solid composite modified powder: citric acid monohydrate (chelation) + ammonium acetate (pH buffer) + solid ester-based quaternary ammonium salt (auxiliary collection) dry powder dry mixing, without free liquid phase medium, one agent simultaneously achieves four functions: hydrophilic modification of powder, acid and alkali stabilization of pulp, resistance to hard water, and enhanced gangue flotation, which is different from the existing binary dry modification system; 2. Dry mechanochemical in-situ double-layer coating process: Under mild solid-phase conditions, a hydrophilic inner layer of magnesium citrate and an adsorption outer layer of quaternary ammonium cations are generated simultaneously, solving multiple defects such as agglomeration of ordinary magnesium oxide in water, lack of auxiliary collecting components in single binary modification, and poor dispersion when quaternary ammonium salt is used alone; the whole process is wastewater-free, eliminating the two high-energy-consuming processes of wet dissolution and drying. 3. Differentiated flotation process design: Locking in the weakly acidic pH window of 5.0–5.5, the dry-modified solid powder and liquid ester-based quaternary ammonium collector are packaged separately and added in stages. This design avoids all technical features of the neutral integrated liquid compound reagent of Zibo Kunxin CN115430525B and the single acid / phosphate flotation process of Donghe New Materials, thus eliminating any risk of literal or equivalent infringement. 4. Advantages of solid powder storage and transportation: The finished modified magnesium oxide is a dry powder, which is lightweight and requires little storage space. Its performance does not degrade after 12 months of sealed storage. It does not have problems with liquid crystallization or microbial deterioration, making it suitable for use in mines located far away.

[0007] (4) Beneficial effects 1. The entire process is a dry, closed-loop production, with no wastewater or corrosive waste liquid discharge. The overall energy consumption is reduced by more than 40% compared to wet modification, and the production cycle is shortened by 50%. 2. The double-layer in-situ coated modified magnesium oxide exhibits excellent water dispersibility, with no agglomeration or sedimentation in the slurry; the inner magnesium citrate film selectively occupies the active sites of magnesium in magnesite, reducing magnesite entrainment loss by 7%–13%; the surface quaternary ammonium cations assist in improving the hydrophobicity of the quartz gangue surface, increasing the desilication rate by 6%–10%. 3. The acetic acid-ammonium acetate buffer system stabilizes the pulp pH to 5.0–5.5, preventing drastic acid-base fluctuations, eliminating the generation of free amines from the hydrolysis of ester-based quaternary ammonium salts, resulting in good foam brittleness, and reducing the amount of No. 2 pine oil foaming agent by 15%. 4. Citrate ions strongly complex with circulating water Ca. 2+ Mg 2+ Quaternary ammonium salt collectors reduce flocculation loss by 8% to 12%, and mineral processing water can be recycled and reused for a long time, saving water and reducing costs. 5. All raw materials are general-purpose industrial dry powders, with wide procurement channels and low costs; small-scale mineral processing plants do not need to be equipped with heating and dissolving kettles and drying equipment, and only a high-speed mixer is needed on-site to complete the modification, which greatly reduces the input of equipment and labor. 6. The modified powder has the triple functions of inhibitor, buffer, and auxiliary collection, reducing the types of reagents to be added on-site and simplifying flotation reagent preparation. Detailed Implementation Example 1 (Standard mass production ternary dry modification process) The ternary composite powder formulation consists of 28 parts citric acid monohydrate, 48 parts ammonium acetate, and 5 parts solid ester-based quaternary ammonium salt. The dry powder is thoroughly mixed. Modification process: 9 parts lightly calcined magnesia and 1 part ternary composite powder are added to a high-speed heated mixer, kept at 45℃, and stirred at 1500 r / min for 20 min. After cooling and sieving, the finished modified magnesia dry powder is obtained. Flotation test: The raw ore SiO2 content is 4.7%, the total reagent dosage is 300 g / t, the pulp pH is stable at 5.2, the concentrate MgO recovery rate is 93.1%, the tailings magnesite loss is only 4.9%, and the quartz removal rate is 8.2% higher than that of the binary dry modification method without quaternary ammonium salt.

[0008] Example 2 (Special formula for high-calcium dolomite associated minerals) The mixture of 30 parts citric acid monohydrate, 50 parts ammonium acetate, and 7 parts solid ester-based quaternary ammonium salt enhances both chelation and auxiliary harvesting capacity, making it suitable for high-calcium circulating water treatment.

[0009] Example 3 (Economical coarse selection ratio) The raw materials consist of 25 parts citric acid monohydrate, 45 parts ammonium acetate, and 3 parts solid ester-based quaternary ammonium salt, resulting in lower raw material costs and meeting the roughing requirements for refractory-grade magnesite.

[0010] Comparative Example 1: Dry modification of citric acid and ammonium acetate (without quaternary ammonium salt) Incomplete flotation of quartz veins reduces the desilication rate by about 8%, and increases collector consumption by 10% for the same amount of raw ore.

[0011] Comparative Example 2: Magnesium Oxide Modified by Traditional Wet Process Composite Solution The addition of dissolving and drying processes increases overall energy consumption by 38%, and the liquid storage and transportation weight is 2.8 times that of dry powder, significantly increasing long-distance transportation costs.

[0012] Comparative Example 3: Flotation pH adjusted to the neutral range of 6.8 The ester-based quaternary ammonium salt showed decreased selectivity for quartz and a 9% reduction in gangue removal efficiency, demonstrating that the 5.0–5.5 weak acidity range is a unique advantage window for this invention.

Claims

1. A process for dry in-situ modification of lightly calcined magnesium oxide using a citric acid-ammonium acetate-quaternary ammonium salt composite agent, characterized in that... Includes the following steps: S1. Preparation of a ternary solid-state composite modified powder, comprising the following dry powders in parts by weight: 25-30 parts of citric acid monohydrate, 45-50 parts of ammonium acetate, and 3-8 parts of solid ester-based quaternary ammonium salt dry powder; wherein the citric acid monohydrate, ammonium acetate, and solid ester-based quaternary ammonium salt are all passed through a 100-mesh sieve, and the powder moisture content is ≤0.5%; S2. Pretreatment of lightly calcined magnesium oxide: lightly calcined magnesium oxide is crushed and passed through a 100-mesh sieve, and then dried with hot air to control the powder moisture content to ≤0.3%; S3. Dry Mechanochemical In-situ Coating: Pretreated light-burned magnesium oxide and ternary solid-state composite modified powder are fed into a heated high-speed mixer at a mass ratio of 7:1 to 12:

1. The temperature is kept constant at 40–50°C, the rotor speed is 1200–1800 r / min, and the mixture is stirred at high speed for 15–25 min. The solid-phase reaction is activated by mechanical frictional heat and external temperature control, and an inner layer of hydrophilic magnesium citrate chelate film and an outer layer of quaternary ammonium cation adsorption functional layer are simultaneously generated on the surface of the magnesium oxide powder. S4. Cooling and Sieving: The material is cooled to room temperature and passed through an 80-mesh sieve to obtain the dry-process in-situ modified light-burned magnesium oxide finished powder. No external free water or liquid solvent is added throughout the process, and no wastewater is discharged.

2. The process for dry in-situ modification of lightly calcined magnesium oxide using a citric acid-ammonium acetate-quaternary ammonium salt composite agent according to claim 1, characterized in that... The optimal ratio of the ternary solid composite modified powder is: 28 parts citric acid monohydrate, 48 parts ammonium acetate, and 5 parts solid ester-based quaternary ammonium salt.

3. The process for dry in-situ modification of lightly calcined magnesium oxide using a citric acid-ammonium acetate-quaternary ammonium salt composite agent according to claim 1, characterized in that... The optimal mass ratio of lightly calcined magnesium oxide to ternary composite powder is 9:1, the temperature is constant at 45℃, the stirring speed is 1500 r / min, and the stirring time is 20 min.

4. The process for dry in-situ modification of lightly calcined magnesium oxide using a citric acid-ammonium acetate-quaternary ammonium salt composite agent according to claim 1, characterized in that... The solid ester-based quaternary ammonium salt is hexadecyl ester-trimethylammonium chloride dry powder.

5. The method for applying the dry-modified magnesium oxide powder prepared by the process of claim 1 in the reverse flotation desilication of magnesite ester-based quaternary ammonium salt, characterized in that, The steps are as follows: (1) Grind the magnesite ore to 200 mesh, accounting for 75% to 85%, and adjust the slurry concentration to 28 to 33 wt%; (2) In the slurry adjustment stage, first add dry modified magnesium oxide powder, stir for 3 minutes, and the total amount of reagent added is 230 to 380 g / t of raw ore; (3) Then add ester-based quaternary ammonium salt aqueous solution collector and stir for 4 minutes; (4) Add No. 2 pine oil to foam, aerate and float, and control the slurry pH to 5.0 to 5.5 weakly acidic throughout the process; (5) The foam product is silicate gangue tailings, and the bottom flow in the tank is magnesite concentrate.

6. The application method according to claim 5, characterized in that, The dry-modified magnesium oxide solid powder and the ester-based quaternary ammonium salt aqueous solution collector are packaged separately and added sequentially in stages at the flotation site, without pre-mixing into an integrated reagent.

7. The solid composite modified powder contains citric acid, ammonium acetate, and solid ester-based quaternary ammonium salt, and may be further compounded with one or more of polyphosphates and organic chelate salts to form a quaternary or pentagonal composite system.