Desiliconization method for low-grade bauxite

Abstract

The invention provides a desiliconization method for low-grade bauxite. The desiliconization method comprises the following steps: (1) pretreatment; (2) surface modification; (3) chemical desilicication; (4) flotation strengthening; (5) post-treatment; according to the method, a four-stage combined system of mechanical crushing, surface modification, chemical desilicication and flotation strengthening is adopted, and the surface of the ore is modified by using a chemical agent through surface modification, so that the interface adsorption effect of silicon minerals and aluminum minerals is broken, the dissolution activity of the silicon minerals and the flotation selectivity of the aluminum minerals are enhanced, and the flotation efficiency of the aluminum minerals is improved. And the desiliconization efficiency and the resource utilization rate are both improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of mineral processing, and particularly relates to a desilication method for low-grade bauxite. BACKGROUND

[0002] Bauxite, as the main raw material for alumina production, directly affects the smelting efficiency and cost. The bauxite resources in China are mainly of diaspore type with high silicon and low aluminum-silicon ratio (A / S). The silicon minerals (such as kaolinite and illite) and aluminum minerals in the ore are finely disseminated and have a complex intergrowth relationship, which leads to a high silicon content in the traditional Bayer process, and the generation of hydrated sodium aluminum silicate (sodium-silicon slag), resulting in alumina loss, pipeline fouling and other problems.

[0003] The current desilication technologies can be divided into physical methods, chemical methods and biological methods: 1. Physical beneficiation desilication: including flotation method (positive / negative flotation), selective crushing, washing and grading, etc., but there are problems such as low separation efficiency of micro-fine particles (such as-500 mesh slurry is difficult to recover), high reagent cost, and large loss rate of tailings aluminum; 2. Chemical beneficiation desilication: such as pre-roasting-alkali leaching method, sodium hydroxide direct leaching method, etc., which can handle complexly disseminated ores, but has high energy consumption (roasting temperature > 1000℃), long process flow, and easy introduction of impurities; 3. Biological desilication: using microorganisms to decompose silicates, but the reaction period is long (several tens of hours to several days), the strain adaptability is poor, and the industrial application is limited.

[0004] In the prior art, the two-stage method (low temperature + high temperature digestion) can improve the silicon removal rate through staged leaching, but it still needs to add stabilizers (such as polyethylene glycol, sodium fluoroborate, etc.) to maintain the liquid silicon concentration, resulting in complex subsequent purification steps. In addition, although the improved processes such as classification flotation and combined desilication can improve the aluminum recovery rate, they are sensitive to the particle size distribution of the ore, and it is difficult to balance the desilication rate and the demand for iron enrichment of red mud.

[0005] In addition, the existing combined process (such as "crushing-flotation-chemical leaching") does not optimize the surface inertness of low-grade ores, and the interface interaction between silicon minerals and aluminum minerals is not effectively broken, resulting in limited improvement of the desilication rate (usually < 60%), and a large amount of flotation reagent consumption (the dosage of the collector is usually > 1000 g / t), which further increases the production cost. SUMMARY

[0006] In view of the above problems, the purpose of the present application is to provide a desilication method for low-grade bauxite, which can enhance the activity of the ore and improve the desilication efficiency through surface modification.

[0007] The present application is realized by the following technical solutions: A method for desilication of low-grade bauxite, comprising the following steps: (1) pretreatment: crushing and grinding the bauxite raw material to a particle size of 50-90% less than 0.074 mm; (2) surface modification: mixing the slurry obtained in step (1) with a modifying agent, stirring and treating at 20-80℃ for 0.5-5h to enhance the surface activity of the ore; (3) chemical desilication: mixing the modified slurry with an alkali solution, heating to 60-130℃ for 1-15h, and filtering to obtain desilicated aluminum residue and a silicon-containing solution; (4) flotation intensification: adding a flotation reagent to the desilicated aluminum residue for direct flotation or reverse flotation, the flotation reagent comprising a collector, an inhibitor and a pH regulator; (5) post-treatment: obtaining a high-aluminum-silicon bauxite concentrate after concentrating, dewatering and roasting the flotation concentrate, the roasting temperature being 300-700℃ and the time being 0.5-20h.

[0008] The grinding in step (1) is carried out in two stages, the first stage being controlled to a fineness of 50-70% less than 0.074 mm and the second stage being controlled to a fineness of 70-90% less than 0.074 mm.

[0009] The modifying agent in step (2) is selected from cationic surfactants (cetyltrimethylammonium bromide, dodecylammonium chloride), anionic surfactants (sodium dodecyl sulfate, sodium oleate) or inorganic activators (magnesium chloride, aluminum sulfate), the mass concentration of the modifying agent being 0.5-5% and the mass-volume ratio of the slurry to the modifying agent being 1: (1-10).

[0010] The alkali solution in step (3) is sodium hydroxide, potassium hydroxide or sodium aluminate solution, the mass concentration being 10-50% and the mass-volume ratio of the modified slurry to the alkali solution being 1: (0.5-50).

[0011] In the flotation reagent, the collector is selected from sodium oleate, benzenecarboxylic hydroxamic acid or naphthenic acid, the amount being 200-1000g / t; the inhibitor is sodium pyrophosphate or humic acid salt, the amount being 50-300g / t; and the pH regulator is sodium carbonate or sodium hydroxide, the amount being 1000-5000g / t.

[0012] The flotation process in step (4) includes roughing, scavenging and cleaning operations, the tailings produced in the scavenging operation being returned to the grinding process in step (1) after classification, and the cleaning operation being carried out 1-3 times.

[0013] Before the surface modification in step (2), 5-20% of an aluminum-containing auxiliary material is added, the auxiliary material being fly ash, coal gangue or kaolin.

[0014] A fluorine-containing additive is introduced in the roasting process, the additive being ammonium fluoride or fluoroaluminate, the amount being 1-10% of the mass of the slag.

[0015] After chemical desilication in step (3), the silicon-containing solution is subjected to silicon resource recovery, and the recovery method includes acidification precipitation, evaporation crystallization or ion exchange.

[0016] Advantages of the present application: The present application uses a four-stage combined system of mechanical crushing-surface modification-chemical desilication-flotation enhancement, and through surface modification, the surface of the ore is modified by chemical agents, the interfacial adsorption of silicon minerals and aluminum minerals is broken, the dissolution activity of silicon minerals and the flotation selectivity of aluminum minerals are enhanced, and the desilication efficiency and resource utilization rate are doubled. DETAILED DESCRIPTION

[0017] The embodiments of the present application are described below by specific examples, and those skilled in the art can easily understand other advantages and effects of the present application from the content disclosed in the description.

[0018] In the description of the present application, it should be noted that unless otherwise explicitly specified and limited, the terms "connected", "connected" should be understood broadly, for example, it can be fixedly connected, or it can be detachably connected, or integrally connected; it can be mechanically connected, or it can be electrically connected; it can be directly connected, or it can be indirectly connected through an intermediate medium. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances. It should be noted that the terms "include", "contain" or any other variant are intended to cover non-exclusive inclusion, so that the process, method, article or equipment containing a series of elements not only includes those elements, but also includes other elements not explicitly listed, or includes elements inherent to such process, method, article or equipment.

[0019] Example 1 (basic process) Step 1: Pretreatment Take a high-silicon bauxite (Al / Si=3.5) from somewhere, and after coarse crushing by a jaw crusher to a particle size of less than 5mm, use a two-stage grinding process: First stage grinding: rod mill grinding to less than 0.074mm accounting for 65%; Second stage grinding: ball mill fine grinding to less than 0.074mm accounting for 85%, forming a slurry.

[0020] Step 2: Surface modification Add 1% sodium dodecyl sulfate (anionic surfactant) to the slurry, and the mass-volume ratio of the slurry to the modification reagent is 1:4, stirring at 40℃ for 1.5h to enhance the surface activity of the silicon minerals.

[0021] Step 3: Chemical desilication The modified ore slurry was mixed with a 30% sodium hydroxide solution at a mass-volume ratio of 1:5, and placed in a high-pressure reaction kettle and heated to 100°C for 8h. After the reaction, the desilicated aluminum residue (Al / Si=6.2) and the silicon-containing filtrate were separated by pressure filtration.

[0022] Step 4: Flotation enhancement To the aluminum residue, the following were sequentially added: pH adjuster: sodium carbonate (4000g / t), to adjust the pH of the ore slurry to 9.5; Inhibitor: sodium pyrophosphate (200g / t), to inhibit the flotation of silicates; Collector: sodium oleate (600g / t), to enhance the collection of aluminum minerals.

[0023] A direct flotation process was used, including one roughing, two scavenging, and two cleaning, and the tailings of the scavenging were returned to the second stage of grinding after classification by a cyclone.

[0024] Step 5: Post-treatment and resource recovery After the flotation concentrate was concentrated and dewatered by pressure filtration, it was calcined in a rotary kiln at 550°C for 4h to obtain the final bauxite concentrate (Al / Si=12.3); The silicon-containing filtrate was adjusted to pH=2 by adding sulfuric acid to form a silica precipitate, which was washed and dried to obtain a white carbon black byproduct, with a silicon recovery rate of 92%.

[0025] Example 2 (co-modification with aluminum-containing auxiliary materials) On the basis of Example 1, the surface modification and chemical desilication steps were optimized: Step 2: Before surface modification, 15% kaolin (aluminum-containing auxiliary material) was added to the ore slurry, which was then mixed uniformly and 2% aluminum sulfate (inorganic activator) was added, with a mass-volume ratio of ore slurry to modification reagent of 1:3, and stirred at 60°C for 2h. The auxiliary materials and modification reagents synergistically further destroyed the intergrowth structure of silicon-aluminum minerals.

[0026] Example 3 (roasting aid enhancement) On the basis of Example 1, the post-treatment step was optimized: Step 5: After the flotation concentrate was dewatered, 5% ammonium fluoride (fluorine-containing aid) was added to the slag, and calcined at 650°C for 2h. The aid promotes the conversion of residual silicates to gaseous SiF4, which escapes, and the aluminum-silicon ratio is further increased to 15.6, while the calcination energy consumption is reduced by 30% compared to Example 1; the silicon-containing solution is recovered by evaporation and crystallization, with a recovery rate of 95%.

[0027] Example 4 (cationic surfactant modification) Step 1: Pretreatment Take a low-grade bauxite (Al / Si = 3.2), coarse crushing to a particle size of ≤5 mm, and two-stage grinding to less than 0.074 mm accounting for 80%.

[0028] Step 2: Surface modification Add 2% hexadecyl trimethyl ammonium bromide (cationic surfactant) to the slurry, with a mass-volume ratio of slurry to modifying agent of 1:3, and stir at 50°C for 2h. After modification, the zeta potential of the silicon mineral surface changes from -15mV to +8mV (hydrophilicity is enhanced, making it easier to be dissolved by alkali), and the contact angle of the aluminum mineral surface increases from 65° to 82° (hydrophobicity is enhanced, making it easier to be captured by flotation).

[0029] Step 3: Chemical desiliconization Mix the modified slurry with 25% sodium hydroxide solution at a mass-volume ratio of 1:4, and react at 80°C for 5h (20°C lower than the traditional process temperature, and 37.5% shorter in time), then filter to obtain desiliconized aluminum residue (Al / Si = 7.5).

[0030] Step 4: Flotation intensification Use reverse flotation, add benzohydroxamic acid (collector, 500g / t), humic acid salt (inhibitor, 250g / t), and sodium hydroxide (pH adjuster, 3000g / t), and use a process of 1 roughing, 2 scavenging, and 2 cleaning, with the tailings of the scavenging returning to grinding.

[0031] Step 5: Post-treatment Roast the flotation concentrate at 500°C for 3h to obtain a concentrate (Al / Si = 14.2); and recover silicon from the silicon-containing solution by ion exchange, with a recovery rate of 94%.

[0032] Example 5 (intensification with composite modifier) Step 2: Surface modification is changed to "0.5% sodium dodecyl sulfate (anionic surfactant) + 1% aluminum sulfate (inorganic activator)" composite reagent, with a mass-volume ratio of slurry to reagent of 1:5, and stir at 60°C for 1.5h. After modification, the dissolution activity of the silicon mineral surface is increased by 40% (verified by dissolution rate experiment).

[0033] Step 3: Chemical desiliconization uses 30% sodium aluminate solution, reacts at 100°C for 4h, and the desiliconized aluminum residue has Al / Si = 8.1.

[0034] The remaining steps are the same as in Example 4, the final concentrate has Al / Si = 16.5, the energy consumption is reduced by 25% compared to Example 1, and the silicon recovery rate is 96%.

[0035] Technical effect comparison:

[0036] From the systematic comparison of the data in the above table, it can be clearly seen that the present application realizes multiple technical breakthroughs by innovatively constructing a "surface modification-chemical desilication" synergistic process system: on the one hand, by means of the electrostatic adsorption of cationic surfactants (such as cetyltrimethylammonium bromide) or the complex synergistic effect of anionic surfactants and inorganic activators (such as the compounding of sodium dodecyl sulfate and aluminum sulfate), the electrochemical properties and interfacial wettability of the surface of silicon-aluminum minerals are targetedly adjusted - the hydrophilic sites on the surface of silicon minerals are significantly increased (the zeta potential changes from -15 mV to +8 mV), the dissolution activity is increased by more than 40%, and at the same time the hydrophobicity of the surface of aluminum minerals is enhanced (the contact angle increases from 65° to 82°), laying a foundation for subsequent separation; on the other hand, the synergistic effect still greatly improves the desilication efficiency under the premise of reducing the reaction temperature (20-30℃ lower than the traditional process), shortening the reaction time (from 8-15h to 4-5h, the compression rate is 37.5%-50%), ultimately the aluminum-silicon ratio of the concentrate is increased from 4.8-6 of the traditional method to 14.2-16.5, the silicon recovery rate is increased to 94%-96%, the dosage of flotation reagents is reduced by 15%-25% (the dosage of collector is reduced from 600g / t to 450g / t), and the comprehensive energy consumption is reduced by 30%-40% (from 850kWh / t to 390kWh / t). Among them, the embodiment 5 using "0.5% sodium dodecyl sulfate + 1% aluminum sulfate" composite modifier performs best in the aluminum-silicon ratio of the final concentrate (16.5), the silicon recovery rate (96%) and the energy consumption index (390kWh / t) because it realizes the simultaneous maximization of the dissolution activity of silicon minerals and the flotation selectivity of aluminum minerals, fully verifying the technical advantages of the synergistic process of the present application.

[0037] The protection scope of the present application is not limited to the technical solutions disclosed in the specific embodiments, and any modification, equivalent replacement, improvement, etc. made according to the technical essence of the present application to the above embodiments falls within the protection scope of the present application.

Claims

1. A method for desilication of low-grade bauxite, characterized in that... Includes the following steps: (1) Pretreatment: crush and grind the bauxite raw material to a particle size of less than 0.074 mm, accounting for 50%-90%; (2) Surface modification: mix the slurry obtained in step (1) with the modifying agent, stir at 20-80℃ for 0.5-5h to enhance the surface activity of the ore; (3) Chemical desilication: mix the modified slurry with the alkaline solution, heat to 60-130℃ for 1-15h, filter and separate to obtain desilication aluminum slag and silicon-containing solution; (4) Flotation enhancement: add flotation reagent to the desilication aluminum slag for positive or reverse flotation, the flotation reagent includes collector, inhibitor and pH adjuster; (5) Posttreatment: after the flotation concentrate is concentrated, dehydrated and roasted to obtain high aluminum-silicon ratio bauxite concentrate, the roasting temperature is 300-700℃ and the time is 0.5-20h.

2. The bauxite desilication method according to claim 1, characterized in that: In step (1), the grinding is carried out in two stages. The first stage of grinding is controlled to have a fineness of less than 0.074 mm, accounting for 50%-70%, and the second stage of grinding is controlled to have a fineness of less than 0.074 mm, accounting for 70%-90%.

3. The bauxite desilication method according to claim 1, characterized in that: In step (2), the modifying agent is selected from cationic surfactants (hexadecyltrimethylammonium bromide, dodecyl ammonium chloride), anionic surfactants (sodium dodecyl sulfate, sodium oleate) or inorganic activators (magnesium chloride, aluminum sulfate). The mass concentration of the modifying agent is 0.5%-5%, and the mass-volume ratio of the slurry to the modifying agent is 1:(1-10).

4. The bauxite desilication method according to claim 1, characterized in that: In step (3), the alkaline solution is sodium hydroxide, potassium hydroxide or sodium aluminate solution with a mass concentration of 10%-50% and the mass-volume ratio of modified slurry to alkaline solution is 1:(0.5-50).

5. The bauxite desilication method according to claim 1, characterized in that: The flotation reagents include: a collector selected from sodium oleate, benzohydroxyxamic acid, or naphthenic acid, with a dosage of 200-1000 g / t; an inhibitor selected from sodium pyrophosphate or humate, with a dosage of 50-300 g / t; and a pH adjuster selected from sodium carbonate or sodium hydroxide, with a dosage of 1000-5000 g / t.

6. The bauxite desilication method according to claim 1, characterized in that: The flotation process in step (4) includes roughing, scavenging and cleaning operations. The tailings generated in the scavenging are returned to the grinding process in step (1) after classification. The number of cleaning operations is 1-3.

7. The bauxite desilication method according to claim 1, characterized in that: Before surface modification in step (2), aluminum-containing auxiliary materials with a mass ratio of 5%-20% are added. The auxiliary materials are fly ash, coal gangue or kaolin.

8. The bauxite desilication method according to claim 1, characterized in that: A fluorine-containing additive is introduced in the roasting process. The additive is ammonium fluoride or fluoroaluminate, and the amount added is 1%-10% of the slag mass.

9. The bauxite desilication method according to claim 1, characterized in that: After chemical desilication in step (3), silicon resources are recovered from the silicon-containing solution. The recovery methods include acid precipitation, evaporation crystallization, or ion exchange.

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