Method for preparing high-purity iron oxide red by microwave roasting and ultrasonic-enhanced acid leaching of coal gangue

Abstract

The present invention relates to the technical field of iron oxide red preparation. Disclosed is a method for preparing high-purity iron oxide red by microwave roasting and ultrasonic-enhanced acid leaching of coal gangue. By controlling the microwave roasting temperature of the coal gangue to be 500°C and the time to be 30 min, the iron dissolution rate reaches 93.6% under the conditions of an optimal ultrasonic power of 300 W, an acid concentration of 20%, an acid leaching temperature of 80°C, an acid leaching time of 30 min, and a liquid-solid ratio of 4 mL / g. A leaching solution is extracted by using a solvent extraction method (TBP-SK-hydrochloric acid system). After extraction, the content of iron ions in the solution is as high as 99.78%; and the optimal pH for hydrothermal treatment is controlled to 11, the temperature is controlled to 170°C and the time is controlled to 3 h, so as to prepare a high-purity iron oxide red product. The iron oxide red has a purity of 99.89%, which meets the requirement (98.5%) of "YHT4 Iron Oxide Standard for Ferrite" (GB / T 24244-2009), and can be used as a raw material for producing high-performance soft-magnetic ferrite.

Description

Method for preparing high-purity iron oxide red by microwave roasting combined with ultrasonic enhanced acid leaching of coal gangue TECHNICAL FIELD

[0001] The application belongs to the technical field of iron oxide red preparation, and particularly relates to a method for preparing high-purity iron oxide red by microwave roasting combined with ultrasonic enhanced acid leaching of coal gangue. BACKGROUND

[0002] Iron oxide red pigment is a kind of inorganic pigment with red or dark red color, and the main component is Fe2O3. The iron oxide red pigment has the characteristics of strong coloring capacity, high temperature resistance, alkali resistance and fine particles, and is widely applied in the fields of building and coating, and is a commonly used colorant with an annual usage of more than 1 million tons. The traditional production process of the iron oxide red pigment is complex, a large amount of chemical agents are needed, the production cost is high, and waste water and waste gas are generated in the production process, thereby causing secondary pollution.

[0003] Coal gangue is a solid waste generated in the process of coal mining and washing and processing, and is mainly treated by stacking, which occupies land resources and causes serious damage to the ecological environment, such as plant death and water pollution, due to the acid waste water generated by rain and oxidation. It is worth mentioning that the coal gangue is rich in various metal elements, and the content of iron element is the highest in most cases.

[0004] It is urgent to find a new method for resource utilization of coal gangue to reduce the harm of coal gangue accumulation to the environment. The existing resource utilization methods of coal gangue include physical landfill, building materials, fertilizer, and energy utilization (power generation). However, the use of coal gangue as a landfill material will indirectly pollute the underground environment, and the acid leaching liquid of coal gangue will pollute the groundwater; the use of coal gangue to make building materials has the disadvantage of low product added value; and the use of coal gangue for power generation has the problems of low calorific value of coal gangue, small heat output, and difficult to handle.

[0005] The existing iron oxide red production process has: the traditional iron oxide red preparation method can be roughly divided into two kinds: dry method and wet method. The dry method mainly includes green vitriol (i.e. ferrous sulfate heptahydrate) calcination method, natural iron oxide mineral superfine grinding method taking hematite as raw material, etc. The wet process mainly includes sulfate (i.e. ferrous sulfate or solution containing ferrous sulfate) method, nitrate (i.e. ferric nitrate, ferrous nitrate or solution containing ferric nitrate) method, mixed acid method; the wet process can be divided into iron skin method and ammonia method according to the different neutralizing agents used in the two-step oxidation process. However, the existing dry process has relatively poor product quality, and harmful gases are generated in the calcination process, which has a significant impact on the environment. For example, in the iron vitriol calcination method, a large amount of sulfur-containing gas is generated in the calcination process, and the energy consumption is also relatively large. The traditional wet process also has different defects, for example, the sulfuric acid method produces iron oxide red products with low purity and a large amount of acidic wastewater; the nitric acid method produces products with high purity, but also produces a certain amount of NO gas, which is harmful to the atmospheric environment, and also produces a large amount of acidic wastewater.

[0006] Therefore, it is urgent to provide a green and environmentally friendly preparation method for preparing high-purity iron oxide red.

[0007] SUMMARY

[0008] In view of the above technical problems, the present application provides a method for preparing high-purity iron oxide red by microwave roasting combined with ultrasonic enhanced acid leaching of coal gangue.

[0009] To achieve the above purpose, the present application provides the following technical scheme:

[0010] A method for preparing high-purity iron oxide red by microwave roasting combined with ultrasonic enhanced acid leaching of coal gangue, comprising the following steps:

[0011] The coal gangue is leached by microwave roasting and ultrasonic enhanced acid leaching to obtain an iron leaching solution;

[0012] The iron leaching solution is sequentially subjected to first evaporation concentration, extraction, second evaporation concentration and back extraction to obtain an iron solution;

[0013] The pH of the iron solution is adjusted, and then the solution is sequentially subjected to hydrothermal synthesis, centrifugation, drying and grinding to obtain iron oxide red.

[0014] Preferably, the conditions in the microwave roasting process are:

[0015] The microwave roasting temperature is 200-700℃, and the roasting time is 20-60min.

[0016] Preferably, the conditions in the ultrasonic enhanced acid leaching process are:

[0017] The ultrasonic power is 100-500 W; the temperature is 60-90 DEG C; the stirring speed is 50-300 r / min; the leaching time is 10-60 min; and the acid concentration is 5-25 wt.%.

[0018] Preferably, the acid used in the ultrasonic wave reinforced acid leaching process is hydrochloric acid; and the solid-liquid ratio of the coal gangue and the hydrochloric acid is 1g:(2-6)mL.

[0019] Preferably, the operation of the extraction treatment is as follows:

[0020] The first evaporated and concentrated leaching solution is placed in a separatory funnel and subjected to solvent extraction in a tributyl phosphate-sulfonated kerosene-hydrochloric acid system.

[0021] Preferably, the volume ratio of the first evaporated and concentrated leaching solution, tributyl phosphate, sulfonated kerosene and hydrochloric acid solution is 50:68:102:35.

[0022] Preferably, the operation of the back extraction treatment is as follows:

[0023] The second evaporated and concentrated liquid is mixed with a 37 wt.% hydrochloric acid solution and the extracted upper decolorized organic phase to obtain a high-purity iron solution.

[0024] Preferably, the reagent used for adjusting the pH of the iron solution is a 2 mol / L NaOH solution.

[0025] Preferably, the hydrothermal synthesis process is as follows:

[0026] The back-extracted liquid has a pH of 3-11; the hydrothermal temperature is 100-250 DEG C; and the hydrothermal time is 1-9 h.

[0027] The chemical reactions involved in the above hydrothermal synthesis process are as follows: FeCl3+3NaOH→Fe(OH)3↓+3NaCl (1); 2Fe(OH)3→Fe2O3+3H2O (2).

[0028] Preferably, the purity of the obtained red iron oxide after grinding is 99.89%.

[0029] Compared with the prior art, the present application has the following advantages and technical effects:

[0030] The application provides a method for preparing high-purity iron oxide red from coal gangue by microwave roasting combined with ultrasonic enhanced acid leaching, wherein the content of iron ions in the iron solution after extraction is as high as 99.78%; the purity of the iron oxide red finally obtained through hydrothermal synthesis is 99.89%, which meets the requirements of the YHT4 standard for iron oxide for ferrite (GB / T 24244-2009) (98.5%), and can be used as a raw material for producing high-performance soft magnetic ferrite. BRIEF DESCRIPTION OF DRAWINGS

[0031] The accompanying drawings, which form a part of the present application, are used to provide further understanding of the present application, and serve as an explanation of the illustrative embodiments of the present application, and are not intended to limit the present application. In the drawings:

[0032] Fig. 1 is a process flow diagram of the method for preparing high-purity iron oxide red from coal gangue by microwave roasting combined with ultrasonic enhanced acid leaching according to the present application;

[0033] Fig. 2 is an SEM image of the high-purity iron oxide red prepared by the method of Example 1 according to the present application. DETAILED DESCRIPTION

[0034] The technical solutions of the present application are further described below through examples.

[0035] Example 1

[0036] As shown in Fig. 1, a method for preparing high-purity iron oxide red from coal gangue by microwave roasting combined with ultrasonic enhanced acid leaching, comprising the following steps:

[0037] Step 1: The coal gangue is dried, crushed and ground, and then placed in a microwave oven, and the microwave roasting temperature is controlled at 500℃, and the sample is naturally cooled after roasting for 30 min to obtain a roasting activated sample;

[0038] Step 2: The roasting activated sample of coal gangue and hydrochloric acid solution are weighed and mixed in a conical flask, and the conical flask is placed in an ultrasonic water bath environment for ultrasonic leaching; wherein the stirring leaching is carried out under the conditions of ultrasonic power 300W, reaction temperature 80℃, 20wt.% hydrochloric acid concentration, stirring speed 100r / min and liquid-solid ratio 4mL:1g for 30 min, and after the leaching is completed, the leaching liquid and the residue are obtained by filtration, and the iron leaching rate of the coal gangue can reach 93.6%;

[0039] Step 3: The iron leaching liquid is evaporated and concentrated, and an organic solvent and a 37wt.% hydrochloric acid solution are added for extraction, and the specific experimental steps are as follows:

[0040] (1) The amount of tributyl phosphate 68mL, sulfonated kerosene 102mL and evaporated and concentrated leaching liquid 50mL is measured with a measuring cylinder, and then 37wt.% hydrochloric acid solution 35mL is added;

[0041] (2) The mixed solution of step (1) is placed in a constant temperature heating magnetic stirrer at 20°C and stirred for 10 min, poured into a separatory funnel, and allowed to stand for 5 min. The lower inorganic phase is allowed to flow out from the bottom of the separatory funnel, and the upper organic phase containing iron is poured into a beaker from the mouth of the separatory funnel, 170 mL of pure water is added, stirred in a constant temperature heating magnetic stirrer for 10 min, and back-extracted again, and transferred into a separatory funnel again;

[0042] (3) The lower inorganic phase containing iron is allowed to flow out from the bottom of the separatory funnel, and evaporated and concentrated to 50 mL. The decolorized organic phase is retained in the separatory funnel;

[0043] (4) The extracted solution after evaporation and concentration in step (3) is mixed with 35 mL of a 37% mass fraction hydrochloric acid solution and the decolorized organic phase produced in step (3), stirred in a magnetic stirrer for 10 min, and back-extracted;

[0044] (5) The above steps are repeated two to three times to obtain a high-purity iron solution, and the iron ion content in the solution after extraction is as high as 99.78%.

[0045] Step 4: The iron solution is poured into a beaker and placed on a constant temperature heating magnetic stirrer at a temperature of 60°C, and a 2 mol / L NaOH solution is added dropwise with a burette to adjust the pH, so that the iron solution and the sodium hydroxide solution are fully contacted and reacted. The solution gradually changes from green to red with the generation of a reddish-brown precipitate. The pH of the solution is adjusted to 11, and the constant temperature magnetic stirring is carried out at 80°C for 60 min. The mixed solution is poured into a hydrothermal reaction kettle. The hydrothermal temperature is set to 170°C, and the hydrothermal time is set to 3 h. After the reaction is completed, the reaction kettle is cooled to room temperature, the mixed solution in the reaction kettle is subjected to solid-liquid separation, washed twice with pure water, and then washed three times with anhydrous ethanol. The precipitate is placed in a petri dish and dried in an oven. The precipitate is ground into powder to obtain a high-purity red iron oxide product. The purity of the red iron oxide is 99.89%, which meets the requirements of the YHT4 standard for ferrite oxides (GB / T 24244-2009) (98.5%).

[0046] The above is only a preferred specific embodiment of the present application, but the protection scope of the present application is not limited thereto. Any changes or replacements within the technical scope disclosed in the present application can be easily thought of by those skilled in the art, and should be covered within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

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