WO2024183221A1 - Method for preparing titanium dioxide by using waste denitration catalyst - Google Patents

Abstract

The present invention relates to the technical field of resource utilization of waste denitration catalysts, and in particular to a method for preparing titanium dioxide by using a waste denitration catalyst. The method comprises: placing a waste denitration catalyst in a hydrogen peroxide solution, and then placing the waste denitration catalyst in an alkaline solution and adding persulfate; reacting the waste denitration catalyst with an acidic solution, and crushing; placing the powdery material into ethanol; performing first normal-pressure alkali leaching, pressure alkali leaching and second normal-pressure alkali leaching on the obtained solid-phase part; mixing the product with an aqueous organic solution, standing, mixing the obtained solid-phase part with ethanol, and performing ball milling; reacting the product with an acidic solution, standing, centrifugating at least twice, and washing the obtained solid-phase part; and roasting the washed product and crushing to obtain titanium dioxide. The titanium dioxide prepared by the method according to the present invention not only meets the standard of titanium dioxide special for denitration, but also improves the pore volume and the specific surface area of the titanium dioxide, and meanwhile, the arsenic content and heavy metal residue on the surface of the titanium dioxide are reduced.

Description

A method for preparing titanium dioxide using waste denitration catalyst

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Chinese patent application 202310214592.6 filed on March 8, 2023, the contents of which are incorporated herein by reference.

Technical Field

The invention relates to the technical field of resource utilization of waste denitration catalysts, and in particular to a method for preparing titanium dioxide by utilizing waste denitration catalysts.

Background Art

NH ₃ -SCR is an important denitrification technology in the coal-fired field, and the catalyst is the key to NH ₃ -SCR. After long-term use, the denitrification catalyst will be deactivated. The deactivated denitrification catalyst is filled with a large number of harmful elements, which are extremely harmful to humans and the environment. In addition, the discarded denitrification catalyst is defined as hazardous waste. If it is not handled properly, it will inevitably have an adverse impact on the environment. At the same time, the discarded denitrification catalyst contains a large amount of titanium dioxide. If it can be reused, it will inevitably save costs greatly. At the same time, the raw material of the denitrification catalyst requires denitrification titanium dioxide. If the titanium dioxide in the discarded denitrification catalyst can be reconstructed by chemical methods to obtain denitrification-specific titanium dioxide for the preparation of new denitrification catalysts, it will undoubtedly bring great economic benefits.

Summary of the invention

The purpose of the present invention is to address the shortcomings of the prior art in that there is little research on the preparation of titanium dioxide for denitration using waste denitration catalysts, thereby providing a method for preparing titanium dioxide using waste denitration catalysts. The method uses a series of chemical reconstruction methods to separate catalyst-irrelevant components, and accurately regulates the reaction conditions to purify titanium dioxide to obtain titanium dioxide for denitration that meets the corresponding standards. At the same time, the water dispersibility, pore volume and specific surface area of the final titanium dioxide are improved, and the amount of arsenic and heavy metal residues on the surface of titanium dioxide is reduced.

In order to achieve the above object, the present invention provides a method for preparing titanium dioxide using waste denitration catalyst. The method comprises the following steps:

(1) placing the waste denitration catalyst in a hydrogen peroxide solution for treatment, wherein the treatment conditions include: a temperature of 30-90° C. and a time of 1-12 hours, and then placing the treated waste denitration catalyst in an alkaline solution and adding persulfate for reaction, wherein the reaction conditions include: a temperature of 60-110° C. and a time of 1-12 hours;

(2) reacting the waste denitration catalyst after the reaction in step (1) with an acidic solution, wherein the reaction conditions include: a temperature of 30-90° C., a time of >0.5 h, and then washing, drying, and crushing, wherein the acidic solution is a reducing acid solution;

(3) placing the powdery material obtained in step (2) in ethanol for treatment to separate the solid from the liquid;

(4) subjecting the solid phase obtained in step (3) to a first normal pressure alkali leaching, and subjecting the solid phase obtained in the first normal pressure alkali leaching to a pressurized alkali leaching, and then subjecting the solid phase obtained in the pressurized alkali leaching to a second normal pressure alkali leaching, wherein the conditions of the first normal pressure alkali leaching include: solid-liquid ratio <1 g:2 mL, temperature of 80-110° C., and time of 2-10 h, the conditions of the pressurized alkali leaching include: pressure of 2-15 MPa, solid-liquid ratio <1 g:2 mL, temperature of >100° C., and time of 1-5 h, and the conditions of the second normal pressure alkali leaching include: solid-liquid ratio <1 g:2 mL, temperature of 50-90° C., and time of 2-10 h;

(5) mixing the product obtained in step (4) with an organic aqueous solution and letting it stand for 2-48 hours, and then mixing the obtained solid phase with ethanol and ball milling, wherein the organic aqueous solution is a mixed solution of water and an organic solvent, and the organic solvent is selected from one or more of methanol, ethanol and glycerol;

(6) reacting the product obtained in step (5) with an acidic solution and standing for 20-30 hours, then centrifuging at least twice, and washing the solid phase obtained after centrifugation, wherein the reaction conditions include: temperature of 30-90° C., time of 0.5-10 hours, and the acidic solution is selected from one or more of hydrochloric acid, sulfuric acid and nitric acid;

(7) The product obtained in step (6) is roasted and crushed to obtain titanium dioxide.

Preferably, in step (1), the mass concentration of the hydrogen peroxide solution is 5-20%.

Preferably, in step (1), the weight ratio of the persulfate to the waste denitration catalyst is 2-5:100.

Preferably, in step (1), the pH value of the alkaline solution is 10-14.

Preferably, in step (2), the acidic solution is oxalic acid solution, citric acid solution or hydrochloric acid solution. More preferably, in step (2), the concentration of the acidic solution is 0.02-6 mol/L.

Preferably, in step (3), the solid-to-liquid ratio of the powdered material to the ethanol is 1 g: 5-20 mL.

Preferably, in step (3), the treatment time is 2-72 hours.

Preferably, in step (5), the volume ratio of the product to the organic aqueous solution is 1:0.5-2.

Preferably, in step (5), the volume ratio of water to organic solvent in the organic aqueous solution is 1:1-4.

Preferably, in step (5), the solid-liquid ratio of the solid phase to the ethanol is 1 g: 5-10 mL.

Preferably, in step (5), the mixing time is 2-24 hours.

Preferably, in step (5), the ball milling time is >2 h.

Preferably, in step (6), the concentration of the acidic solution is 0.2-6 mol/L.

Preferably, in step (6), when two centrifugations are performed, the conditions for the first centrifugation include: a rotation speed of 2000-4000 rpm/min, and a time of 2-10 min, and the conditions for the second centrifugation include: a rotation speed of 8000-26000 rpm/min, and a time of >30 min.

Preferably, in step (7), the calcination conditions include: temperature of 600-700°C, time of 2-4h, and heating rate of ≤10°C/min.

Through the above technical solution, the present invention has at least the following beneficial effects:

(1) In the present invention, a series of chemical reconstruction methods are used to separate the irrelevant components of the catalyst, and the reaction conditions are precisely controlled to purify titanium dioxide, and the recovered titanium dioxide is optimized, and finally a titanium dioxide specially used for denitrification that meets the "HG/T 4525-2013" standard is obtained;

(2) In a preferred embodiment, the present invention optimizes various conditions and precisely controls relevant technical parameters in the waste denitration catalyst recovery process, thereby not only obtaining a titanium dioxide powder for denitration that meets the standards, but also increasing the pore volume and specific surface area of titanium dioxide, while reducing the amount of arsenic and heavy metal residues on the surface of titanium dioxide. The titanium dioxide powder finally obtained can accurately meet the use requirements of the denitration catalyst;

(3) In the present invention, the waste denitration catalyst is subjected to a series of chemical reconstruction methods to reconstruct the titanium dioxide structure therein, and then centrifuged at least twice, so that the part with better water dispersibility in the purified titanium dioxide can be separated separately, and at the same time, the separated titanium dioxide product with better dispersibility can be more uniformly enriched to make it uniform granular, and finally the titanium dioxide in the obtained titanium dioxide has good water dispersibility. Dispersibility and high specific surface area can effectively remove impurities.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a scanning electron microscope image of the product prepared in Example 1 of the present invention;

FIG. 2 is a scanning electron microscope image of the product prepared in Comparative Example 7 of the present invention.

DETAILED DESCRIPTION

The specific implementation of the present invention is described in detail below in conjunction with the accompanying drawings. It should be understood that the specific implementation described herein is only used to illustrate and explain the present invention, and is not used to limit the present invention.

The endpoints and any values of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the endpoint values of each range, the endpoint values of each range and the individual point values, and the individual point values can be combined with each other to obtain one or more new numerical ranges, which should be regarded as specifically disclosed in this article.

The present invention provides a method for preparing titanium dioxide using waste denitration catalyst, the method comprising the following steps:

(1) placing the waste denitration catalyst in a hydrogen peroxide solution for treatment, wherein the treatment conditions include: a temperature of 30-90° C. and a time of 1-12 hours, and then placing the treated waste denitration catalyst in an alkaline solution and adding persulfate for reaction, wherein the reaction conditions include: a temperature of 60-110° C. and a time of 1-12 hours;

(2) reacting the waste denitration catalyst after the reaction in step (1) with an acidic solution, wherein the reaction conditions include: a temperature of 30-90° C., a time of >0.5 h, and then washing, drying, and crushing, wherein the acidic solution is a reducing acid solution;

(3) placing the powdery material obtained in step (2) in ethanol for treatment to separate the solid from the liquid;

(4) subjecting the solid phase obtained in step (3) to a first atmospheric pressure alkali leaching, subjecting the solid phase obtained in the first atmospheric pressure alkali leaching to a pressurized alkali leaching, and then subjecting the solid phase obtained in the pressurized alkali leaching to a second atmospheric pressure alkali leaching, wherein the conditions of the first atmospheric pressure alkali leaching include: a solid-liquid ratio of <1 g:2 mL, a temperature of 80-110° C., and a time of 2-10 h, and the conditions of the pressurized alkali leaching include: a pressure of 2-15 MPa, a solid-liquid ratio of <1g:2mL, temperature>100°C, time 1-5h, the conditions of the second normal pressure alkali leaching include: solid-liquid ratio <1g:2mL, temperature 50-90°C, time 2-10h;

(5) mixing the product obtained in step (4) with an organic aqueous solution and letting it stand for 2-48 hours, and then mixing the obtained solid phase with ethanol and ball milling, wherein the organic aqueous solution is a mixed solution of water and an organic solvent, and the organic solvent is selected from one or more of methanol, ethanol and glycerol;

(6) reacting the product obtained in step (5) with an acidic solution and standing for 20-30 hours, then centrifuging at least twice, and washing the solid phase obtained after centrifugation, wherein the reaction conditions include: temperature of 30-90° C., time of 0.5-10 hours, and the acidic solution is selected from one or more of hydrochloric acid, sulfuric acid and nitric acid;

(7) The product obtained in step (6) is roasted and crushed to obtain titanium dioxide.

In the method of the present invention, the waste denitration catalyst is a vanadium-titanium denitration catalyst used in coal-fired power plants or coal-fired boilers. In a specific embodiment, the content of TiO ₂ , WO ₃ , V ₂ O ₅ and SiO ₂ in the waste denitration catalyst is relatively high. Taking the total weight of the waste denitration catalyst as 100 weight %, the waste denitration catalyst contains 65-89 weight % of TiO ₂ , 1-6 weight % of WO ₃ , 0.2-1.2 weight % of V ₂ O ₅ , 3-8 weight % of SiO ₂ , and the content of As ₂ O ₃ and other metal substances is relatively small, wherein the waste denitration catalyst contains 0.05-1200 μg/g of As ₂ O ₃ and 20-3000 μg/g of a mixture of Ni, Pb, Cr, Zn and Cu.

In the method of the present invention, the waste denitration catalyst needs to be pretreated first, and the pretreatment process is a conventional technical means in the art. Specifically, the pretreatment is to purge the surface and pores of the waste denitration catalyst.

In the method of the present invention, in step (1), the purpose of placing the waste denitration catalyst in a hydrogen peroxide solution for treatment is to cause an oxidation reaction of arsenic, oxidize low-valent arsenic to high-valent arsenic, and finally directly leach arsenic into the solution in the form of arsenate, which has a pre-removal effect on arsenic. At the same time, hydrogen peroxide can penetrate into some catalyst surfaces and adhere to them, avoiding a small amount of heavy metals reacting with fly ash to cause the formation of some gelling materials. Then, the reaction with an alkaline solution can remove oxidized arsenic and other chemical substances and part of the ash. Persulfate is mainly used to prevent some metals from being entrained in a small amount of gelling materials. At this time, the solid matter is a waste denitration catalyst with some impurities removed, and the main components are still titanium dioxide, silicon oxide, tungsten trioxide, etc.

In the method of the present invention, in step (1), in a specific embodiment, the waste denitration catalyst is an integral block structure, and the hydrogen peroxide solution needs to completely immerse the integral block of waste denitration catalyst, exceeding the upper surface of the block of waste denitration catalyst.

In the method of the present invention, the concentration of the hydrogen peroxide solution will affect the removal effect of arsenic and fly ash, and will also affect the generation of cementitious materials.

In the method of the present invention, in a specific embodiment, in step (1), the concentration of the hydrogen peroxide solution is 5-20%, for example, 5%, 8%, 10%, 12%, 15%, 18% or 20%. In a preferred embodiment, the concentration of the hydrogen peroxide solution is 5-10%.

In the method of the present invention, in order to accelerate the full contact between the hydrogen peroxide solution and the surface of the waste denitration catalyst, in a specific embodiment, while heating the solution, the bottom of the container containing the hydrogen peroxide solution and the waste denitration catalyst needs to be evenly aerated.

In the method of the present invention, in a specific embodiment, in step (1), the treatment conditions include: a temperature of 30-90°C, for example, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C or 90°C; a time of 1-12h, for example, 1h, 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h, 11h or 12h.

In the method of the present invention, in a preferred embodiment, in step (1), the treatment conditions include: temperature of 40-60°C and time of 2-4h.

In the method of the present invention, in a specific embodiment, the waste denitration catalyst in the process of placing the waste denitration catalyst in an alkaline solution and adding persulfate to react can be an integral block structure, or the integral block structure can be disassembled into two parts. Specifically, the waste denitration catalyst is completely immersed in the alkaline solution.

In the method of the present invention, in a specific embodiment, in step (1), the pH value of the alkaline solution is 10-14, for example, it can be 10, 11, 12, 13 or 14.

In the method of the present invention, in a specific embodiment, the alkaline solution is a conventional choice in the alkaline leaching process in the art, and the alkaline solution can be a sodium hydroxide solution, a potassium hydroxide solution or an ammonia solution.

In the method of the present invention, in a specific embodiment, in step (1), the weight ratio of the persulfate to the waste denitration catalyst is 2-5:100, for example, it can be 2:100, 2.5:100, 3:100, 4:100 or 5:100.

In the method of the present invention, in a specific embodiment, in step (1), the reaction conditions include: temperature of 60-110°C, and time of 1-12h. In a preferred embodiment, in step (1), the reaction conditions include: temperature of 80-100°C, such as 80°C, 90°C or 100°C, and time of 2-4h, such as 2h, 3h or 4h.

In the method of the present invention, in step (2), the purpose of the acidic solution is to remove or leach out some heavy metals and dissociate some ash attached to the surface of the waste denitrification catalyst. The concentration of the acidic solution will affect the effect of removing heavy metals and dissociating ash. At this time, the solid has removed some heavy metals and ash, and the main components are still titanium dioxide, silicon oxide, tungsten trioxide, etc.

In the method of the present invention, in step (2), in a specific embodiment, the acidic solution is oxalic acid solution, citric acid solution or hydrochloric acid solution.

In the method of the present invention, in step (2), in a specific embodiment, the concentration of the acidic solution is 0.02-6 mol/L. In a preferred embodiment, the concentration of the acidic solution is 0.02-2 mol/L, for example, 0.02 mol/L, 0.1 mol/L, 0.2 mol/L, 1 mol/L or 2 mol/L.

In the method of the present invention, in step (2), in a specific embodiment, the reaction conditions include: temperature of 30-90°C, time>0.5h. In a preferred embodiment, the reaction conditions include: temperature of 50-70°C, such as 50°C, 60°C or 70°C; time of 40-120min, such as 40min, 60min, 80min, 100min or 120min.

In the method of the present invention, in step (2), in a specific embodiment, the washing process is washing with water.

In the method of the present invention, in step (2), in a specific embodiment, the drying temperature is 80-110°C, for example, 80°C, 90°C, 100°C or 110°C, until the waste denitration catalyst is dried to constant weight.

In the method of the present invention, in step (2), in a specific embodiment, the pulverization is to pulverize the waste denitration catalyst to a particle size of <100 mesh. In a preferred embodiment, the pulverization is to pulverize the waste denitration catalyst to a particle size of <200 mesh.

In order to mix the obtained powdered material more evenly in the solution, the acidic substances remaining on the surface of the powdered material can be removed at the same time, and the internal pores of the catalyst can be cleaned and penetrated by utilizing the miscibility of ethanol and water and the permeability of ethanol, which has a certain effect on the subsequent partial titanium reaction and pore reconstruction. Therefore, in the method described in the present invention, the obtained powdered material is placed in ethanol for treatment.

In the method of the present invention, in step (3), in a specific embodiment, the solid-liquid ratio of the powdered material to the ethanol is 1g:5-20mL, for example, it can be 1g:5mL, 1g:10mL, 1g:15mL or 1g:20mL.

In the method of the present invention, in step (3), in a specific embodiment, the treatment time In a preferred embodiment, the treatment time is 20-30 hours, for example, 20 hours, 24 hours, 28 hours or 30 hours.

In the method of the present invention, in step (3), in a specific embodiment, the treatment method is mixing and stirring.

In the method of the present invention, before alkali leaching, the product after ethanol treatment needs to be separated into solid and liquid.

In the method described in the present invention, in step (4), the first normal-pressure alkali leaching can remove part of the silicon and most of the tungsten and vanadium. After filtration, the titanium slag is mainly titanium dioxide, and a certain amount of tungsten and silicon remain. Pressurized alkali leaching can effectively remove silicon and effectively convert part of the titanium dioxide into various titanates (insoluble in water). After filtration, the main components of the titanium slag are titanium dioxide and titanates. The second normal-pressure alkali leaching can continue to effectively remove residual silicon, tungsten, vanadium and other impurities, and further remove the titanates generated by the reaction. After filtration, the main components of the titanium slag are titanium dioxide and titanates.

In the method of the present invention, in step (4), in a specific embodiment, the alkaline solution used in the first normal pressure alkali leaching, the pressurized alkali leaching and the second normal pressure alkali leaching can be conventionally selected in the art. In a preferred embodiment, the alkaline solution used in the alkali leaching is a sodium hydroxide solution.

In the method of the present invention, in step (4), in a specific embodiment, after the first normal pressure alkali leaching and the pressurized alkali leaching, the product is subjected to solid-liquid separation, and then the obtained solid phase is dried before the next alkali leaching.

In the method of the present invention, in step (4), in a specific embodiment, the concentration of the alkaline solution used in the first atmospheric pressure alkali leaching is 10-50 weight%, for example, it can be 10 weight%, 20 weight%, 25 weight%, 30 weight%, 40 weight% or 50 weight%.

In the method of the present invention, in step (4), in a preferred embodiment, the conditions of the first normal pressure alkali leaching include: a solid-liquid ratio of 1 g: 5-30 mL, for example, 1 g: 5 mL, 1 g: 10 mL, 1 g: 15 mL, 1 g: 20 mL or 1 g: 30 mL; a temperature of 80-110° C., for example, 80° C., 90° C., 100° C. or 110° C.; and a time of 2-10 h, for example, 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h or 10 h.

In the method of the present invention, in step (4), in a specific embodiment, the concentration of the alkaline solution used in the pressurized alkali leaching is 10-50 weight%, for example, it can be 10 weight%, 20 weight%, 25 weight%, 30 weight%, 40 weight% or 50 weight%.

In the method of the present invention, in step (4), in a specific embodiment, the pressurized alkali leaching It is carried out in a closed reaction container. In a preferred embodiment, the conditions of the pressurized alkali leaching include: a pressure of 4-12 MPa, for example, 4 MPa, 6 MPa, 8 MPa, 10 MPa or 12 Pa, a solid-liquid ratio of 1 g: 5-30 mL, for example, 1 g: 5 mL, 1 g: 10 mL, 1 g: 15 mL, 1 g: 20 mL or 1 g: 30 mL; a temperature of 110-250°C, for example, 110°C, 130°C, 150°C, 200°C or 250°C; and a time of 1-5 h, for example, 1 h, 2 h, 3 h, 4 h or 5 h.

In the method of the present invention, in step (4), in a specific embodiment, the concentration of the alkaline solution used in the second atmospheric pressure alkali leaching is 5-30% by weight, for example, 5% by weight, 10% by weight, 20% by weight or 30% by weight.

In the method of the present invention, in step (4), in a preferred embodiment, the conditions of the second normal pressure alkali leaching include: a solid-liquid ratio of 1g:5-30mL, for example, 1g:5mL, 1g:10mL, 1g:15mL, 1g:20mL or 1g:30mL; a temperature of 50-90°C, for example, 50°C, 60°C, 70°C, 80°C or 90°C; and a time of 2-10h, for example, 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h or 10h.

In the method of the present invention, the titanium slag obtained in step (4) whose main components are titanium dioxide and titanate is mixed with an organic aqueous solution, which can effectively clean the pores in the titanium slag and remove water-soluble impurities more efficiently. At the same time, the organic matter can play a dispersing role, penetrate the newly generated titanate, and further disperse the titanate generated by the reaction; ethanol ball milling improves the dispersibility of ball-milled solid matter, and ethanol permeability is also strong, which improves the specific surface area of the obtained titanium powder to a certain extent.

In the method of the present invention, in step (5), in a specific embodiment, the volume ratio of water to organic solvent in the organic aqueous solution is 1:1-4, for example, it can be 1:1, 1:2, 1:3 or 1:4.

In the method of the present invention, in step (5), in a specific embodiment, the volume ratio of the product to the organic aqueous solution is 1:0.5-2, for example, it can be 1:0.5, 1:1, 1:1.5 or 1:2.

In the method of the present invention, in step (5), in a specific embodiment, the standing time is 2-48 hours, for example, it can be 2 hours, 8 hours, 16 hours, 24 hours, 32 hours or 48 hours.

In the method of the present invention, in step (5), in a specific embodiment, the solid-liquid ratio of the solid phase part to the ethanol is 1g:5-10mL, for example, it can be 1g:5mL, 1g:8mL or 1g:10mL.

In the method of the present invention, in step (5), in a specific embodiment, the mixing time is 2-24 hours. In a preferred embodiment, the mixing time is 2-6 hours, for example, 2 hours, 4 hours or 6 hours.

In the method of the present invention, in step (5), in a specific embodiment, the ball milling time is >2 h. In a preferred embodiment, the ball milling time is 4-12 h, for example, 4 h, 6 h, 8 h, 10 h or 12 h.

In the method described in the present invention, in step (6), the titanate on the surface of the catalyst is mainly reacted with the acid, and the titanate with good dispersibility is reacted to generate titanic acid and metatitanic acid (insoluble in water and synthesized by a new chemical reaction with a smaller particle size). The titanate-like substance generated by the new reaction has a small particle size and good dispersibility, and therefore mainly exists in the form of suspended titanium, while the original titanium dioxide and other titanium slag precipitates at the bottom of the solution, and a small amount of titanic acid with a large particle size that has not been successfully reconstructed also exists in the form of precipitation. The suspension can be taken and centrifuged to obtain a substance with successfully reconstructed titanic acid. At this time, the solid phase is mainly a titanate-like substance with good dispersibility and small particle size, and the purity is very high.

In the method of the present invention, in step (6), in a specific embodiment, the acidic solution is a strong acidic solution, which can be selected conventionally in the art, for example, one or more of hydrochloric acid, sulfuric acid and nitric acid.

In the method of the present invention, in step (6), in a specific embodiment, the concentration of the acidic solution is 0.2-6 mol/L. In a preferred embodiment, the concentration of the acidic solution is 1-2.5 mol/L, for example, 1 mol/L, 1.5 mol/L, 2 mol/L or 2.5 mol/L.

In the method of the present invention, in step (6), in a preferred embodiment, the reaction conditions include: temperature of 50-90°C, for example, 50°C, 60°C, 70°C, 80°C or 90°C; time of 1-2h, for example, 1h, 1.5h or 2h.

In the method of the present invention, in step (6), in a specific embodiment, the standing time is 20-30 hours, for example, it can be 20 hours, 24 hours, 28 hours or 30 hours.

In the method of the present invention, in step (6), in a specific embodiment, the product after standing is centrifuged at least twice. Centrifuging at least twice can separate the part with better water dispersibility in the purified titanium dioxide separately, and at the same time, the separated titanium dioxide product with better dispersibility can be more evenly enriched to be in a uniform granular form, thereby preparing a denitration catalyst with good performance.

In the method of the present invention, in step (6), in a preferred embodiment, the product after standing is centrifuged twice. In a specific embodiment, the conditions of the first centrifugation include: a rotation speed of 2000-4000rpm/min, for example, 2000rpm/min, 2500rpm/min, 3000rpm/min, 3500rpm/min or 4000rpm/min, a time of 2-10min, for example, 2min, 3min, 4min, 5min, 6min, 7min, 8min, 9min or 10min, and the conditions of the second centrifugation include: a rotation speed of 8000-26000rpm/min, for example, 8000rpm/min, 9000rpm/min, 10000rpm/min, 1500rpm/min, 2000rpm/min, 2500rpm/min, 3000rpm/min, 3500rpm/min or 4000rpm/min, a time of 2-10min, for example, 2min, 3min, 4min, 5min, 6min, 7min, 8min, 9min or 10min. 15000rpm/min, 20000rpm/min, 25000rpm/min or 26000rpm/min, time>30min. In a specific embodiment, the second centrifugation time is 2-6h, for example 2h, 3h, 4h, 5h or 6h.

In the method of the present invention, in step (6), in a specific embodiment, the washing is to wash the obtained solid phase part with water and ethanol for multiple times.

In the method of the present invention, in step (7), in a specific embodiment, the calcination conditions include: a temperature of 600-700°C, for example, 600°C, 650°C or 700°C; a time of 2-4h, for example, 2h, 3h or 4h; a heating rate of ≤10°C/min, for example, 1°C/min, 2°C/min, 3°C/min, 4°C/min, 5°C/min, 6°C/min, 7°C/min, 8°C/min, 9°C/min or 10°C/min.

In the method of the present invention, in step (7), in a specific embodiment, the particle size of the crushed material is <200 mesh.

The present invention will be described in detail below through examples, but the protection scope of the present invention is not limited thereto.

In the embodiments and comparative examples described in the present invention, unless otherwise specified, all reagents used are commercially available.

The waste denitration catalyst is a vanadium-titanium denitration catalyst used in a certain coal-burning field.

Example 1

The waste nitrate catalyst in this embodiment is _a waste denitrification catalyst from a coal-fired power plant in Jiangsu, which contains 76.85% _TiO2 , _3.47 % _WO3 , 0.78% _V2O5 , 4.96% _{SiO2 ,} 312.44μg/g As2O3, and 667.23μg/g other heavy metals (Ni+Pb+Cr+Zn+Cu).

(1) The surface and pores of the waste denitration catalyst are simply purged to remove fly ash on the catalyst surface and pores, and then 500 g of the block honeycomb waste denitration catalyst is placed as a whole in a 10% hydrogen peroxide solution to completely immerse the upper surface of the block waste denitration catalyst, and treated at a temperature of 50° C. for 3 h. Finally, the treated waste denitration catalyst is placed in a sodium hydroxide solution with a pH value of 10 and 12.5 g of sodium persulfate is added, and reacted at 90° C. for 3 h;

(2) reacting the waste denitration catalyst after the reaction in step (1) with a 0.2 mol/L oxalic acid solution at 60° C. for 100 min, then taking out the whole waste denitration catalyst and washing it with clean water, drying it at 100° C. to a constant weight after washing, and then crushing it to less than 200 mesh;

(3) 100 g of the powdered material obtained in step (2) was placed in 1000 mL of pure ethanol solution and mixed and stirred for 24 h, and then filtered;

(4) placing 50 g of the solid phase obtained in step (3) in 750 mL of a 20% sodium hydroxide solution, leaching it at 80° C. for 3 h under normal pressure, and then filtering and drying it;

30 g of the solid phase obtained by the first normal pressure alkali leaching was placed in 300 mL of a 30% sodium hydroxide solution, and then pressure alkali leaching was performed in a closed reaction vessel at a pressure of 8 MPa and a temperature of 130° C. for 3 h, and then filtered and dried;

The 20 g solid phase obtained by pressurized alkali leaching was placed in 200 mL of 20% sodium hydroxide solution and leached for a second time at 60°C for 2 h.

(5) mixing the product obtained in step (4) with a methanol aqueous solution in a volume ratio of 1:1, and letting it stand for 6 hours, filtering, and drying, wherein the volume ratio of water to methanol in the methanol aqueous solution is 1:2, and then mixing the obtained solid phase with ethanol and soaking for 4 hours, and then ball milling for 6 hours, wherein the solid-liquid ratio of the solid phase to ethanol is 1 g:10 mL;

(6) reacting the product obtained by ball milling in step (5) with a 1.5 mol/L hydrochloric acid solution at 90° C. for 1 h, then standing for 3 h, centrifuging the product obtained by standing at 2000 rpm/min for 3 min, then centrifuging the turbid liquid obtained by centrifugation at 10000 rpm/min for 3 h, and washing the obtained solid phase with clean water and ethanol for multiple times, and finally filtering;

(7) The product obtained in step (6) was heated to 650° C. at a heating rate of 5° C./min and calcined for 3 h, and the calcined product was crushed to a particle size of less than 200 mesh to obtain titanium dioxide.

Example 2

The waste nitrate catalyst in this embodiment _{is a} waste denitrification catalyst from a coal-fired power plant in Shandong, which contains 76.33% _TiO2 , 4.12% _WO3 , 0.33% _V2O5 , 5.34% _{SiO2 ,} 98.33μg/g As2O3, and 656.67μg/g other heavy metals (Ni+Pb+Cr+Zn+Cu).

(1) The surface and pores of the waste denitration catalyst are simply purged to remove fly ash on the catalyst surface and pores, and then 500 g of the block honeycomb waste denitration catalyst is placed as a whole in an 8% hydrogen peroxide solution to completely immerse the upper surface of the block waste denitration catalyst, and treated at a temperature of 60° C. for 3 h. Finally, the treated waste denitration catalyst is placed in a sodium hydroxide solution with a pH value of 12 and 15 g of sodium persulfate is added, and reacted at 90° C. for 3 h;

(2) reacting the waste denitration catalyst after the reaction in step (1) with a 0.2 mol/L oxalic acid solution at 60° C. for 100 min, then taking out the whole waste denitration catalyst and washing it with clean water, drying it at 100° C. to a constant weight after washing, and then crushing it to less than 200 mesh;

(3) 200 g of the powdery material obtained in step (2) was placed in 3000 mL of pure ethanol solution and mixed and stirred for 24 h, and then filtered;

(4) placing 100 g of the solid phase obtained in step (3) in 1500 mL of a 25% sodium hydroxide solution, leaching for 3 h at 80° C. under normal pressure, and then filtering and drying;

80 g of the solid phase obtained by the first normal pressure alkali leaching was placed in 800 mL of a 35% sodium hydroxide solution, and then pressure alkali leaching was performed in a closed reaction vessel at a pressure of 8 MPa and a temperature of 150° C. for 3 h, and then filtered and dried;

40 g of the solid phase obtained by pressurized alkali leaching was placed in 400 mL of 25% sodium hydroxide solution and leached for a second time at 60°C for 2 h;

(5) mixing the product obtained in step (4) with a methanol aqueous solution in a volume ratio of 1:1, and letting it stand for 6 hours, filtering, and drying, wherein the volume ratio of water to methanol in the methanol aqueous solution is 1:2, and then mixing the obtained solid phase with ethanol and soaking for 4 hours, and then ball milling for 6 hours, wherein the solid-liquid ratio of the solid phase to ethanol is 1 g:10 mL;

(6) reacting the product obtained by ball milling in step (5) with a 1.5 mol/L hydrochloric acid solution at 90° C. for 1 h, then standing for 2 h, centrifuging the product obtained by standing at 2000 rpm/min for 3 min, then centrifuging the turbid liquid obtained by centrifugation at 12000 rpm/min for 3.5 h, and washing the obtained solid phase with clean water and ethanol for multiple times, and finally filtering;

(7) The product obtained in step (6) was heated to 650° C. at a heating rate of 5° C./min and calcined for 3 h, and the calcined product was crushed to a particle size of less than 200 mesh to obtain titanium dioxide.

Example 3

The method of Example 2 was followed, except that the waste nitrate catalyst was a waste denitration catalyst from _a coal-fired power plant in Ningxia, containing 75.14% _TiO2 , 2.88% _WO3 , 0.46% _{V2O5 ,} 7.33% SiO2, 113.11 μg/g _As2O3 , _and 452.95 μg/g other heavy metals (Ni+Pb+Cr+Zn+Cu).

Example 4

The method of Example 1 is followed, except that in step (7), the temperature is raised to 950° C. and calcined.

Comparative Example 1

The method of Example 1 is followed, except that in step (4), no pressurized alkali leaching is performed, and only two normal pressure alkali leachings are performed.

Comparative Example 2

The method of Example 1 is followed, except that in step (4), normal pressure alkali leaching is not performed, and the solid phase obtained in step (3) is directly subjected to pressurized alkali leaching.

Comparative Example 3

The method of Example 1 is followed, except that in step (2), the waste denitration catalyst after treatment in step (1) is not reacted with the acidic solution, but is directly washed, dried and crushed.

Comparative Example 4

The method of Example 1 is followed, except that step (5) is not performed.

Comparative Example 5

The method of Example 1 is followed, except that in step (6), the product obtained in step (5) is directly centrifuged and washed.

Comparative Example 6

The method of Example 1 is followed, except that step (1) is not performed.

Comparative Example 7

The method of Example 1 was followed, except that in step (6), only one centrifugation was performed, and the centrifugation conditions were: rotation speed 10000 rpm/min, time 6 h.

Test Case

The purity, pore volume, water dispersibility, As content and heavy metal residue on the surface of the titanium dioxide prepared by the methods described in Examples 1-4 and Comparative Examples 1-7, and various technical indicators of the titanium dioxide specially used for denitrification were determined and calculated. The results are shown in Table 1.

The purity of titanium dioxide was measured using an X-ray fluorescence spectrometer (XRF).

The pore volume and specific surface area were measured using the BET test method.

Determination of the content of each element: The titanium dioxide obtained in Examples 1-4 and Comparative Examples 1-7 was digested, and then the content of As and heavy metal elements such as Ni, Pb, Cr, Zn and Cu in the solid sample was determined by inductively coupled plasma emission spectroscopy (ICP).

Various technical indicators of titanium dioxide specially used for denitrification: The laser particle size, sulfate, iron, potassium, sodium, drying loss and ignition vector of the titanium dioxide obtained in Examples 1-4 and Comparative Examples 1-7 were measured in accordance with "HG/T 4525-2013".

Water dispersibility measurement: The degree of dispersion of titanium dioxide particles is characterized by the height of the titanium dioxide particles settling in the aqueous solution within a certain period of time. The faster the settling speed, the worse the dispersion effect;

The specific method is: weigh 200g of the recovered sample, add 1L of water, stir in a high-speed disperser for 15min, speed 2000R/MIN, stir for 15min, let stand for 50h, and observe the dispersion effect (sedimentation height) of the solution.

The titanium dioxide prepared in Example 1 and Comparative Example 7 was subjected to morphological analysis using a scanning electron microscope.

As can be seen from Figures 1 and 2, in Example 1, according to the method described in the present invention, the waste denitration catalyst is restructured using a series of chemical means, and the reconstructed product is then centrifuged at least twice, so that the obtained titanium dioxide product can be more evenly enriched and present a uniform granular state, while Comparative Example 7 is only centrifuged once, and the titanium dioxide product obtained has a diverse and non-uniform structure and is not in a uniform granular state.

Table 1

As can be seen from Table 1, according to the method described in the present invention, a series of chemical reconstruction methods are used to separate irrelevant components of the catalyst, and the reaction conditions are precisely controlled to purify titanium dioxide, so that the purity of titanium dioxide reaches more than 96%. At the same time, the recovered titanium dioxide is optimized so that the final titanium dioxide not only meets the standard of titanium dioxide for denitrification "HG/T 4525-2013", so that titanium dioxide can accurately meet the use requirements of denitrification catalysts, but also improves the pore volume and specific surface area of titanium dioxide, and has excellent water dispersibility, as well as less surface arsenic and heavy metal residues.

The above are only embodiments of the present invention, and are not intended to limit the patent scope of the present invention. Any equivalent transformations made using the contents of the present invention specification, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims (16)

A method for preparing titanium dioxide using waste denitration catalyst, characterized in that the method comprises the following steps: (1) placing the waste denitration catalyst in a hydrogen peroxide solution for treatment, wherein the treatment conditions include: a temperature of 30-90° C. and a time of 1-12 hours, and then placing the treated waste denitration catalyst in an alkaline solution and adding persulfate for reaction, wherein the reaction conditions include: a temperature of 60-110° C. and a time of 1-12 hours; (2) reacting the waste denitration catalyst after the reaction in step (1) with an acidic solution, wherein the reaction conditions include: a temperature of 30-90° C., a time of more than 0.5 h, and then washing, drying, and crushing, wherein the acidic solution is a reducing acid solution; (3) placing the powdery material obtained in step (2) in ethanol for treatment to separate the solid from the liquid; (4) subjecting the solid phase obtained in step (3) to a first normal pressure alkali leaching, and subjecting the solid phase obtained in the first normal pressure alkali leaching to a pressurized alkali leaching, and then subjecting the solid phase obtained in the pressurized alkali leaching to a second normal pressure alkali leaching, wherein the conditions of the first normal pressure alkali leaching include: solid-liquid ratio <1 g: 2 mL, temperature of 80-110° C., and time of 2-10 h, the conditions of the pressurized alkali leaching include: pressure of 2-15 MPa, solid-liquid ratio <1 g: 2 mL, temperature of >100° C., and time of 1-5 h, and the conditions of the second normal pressure alkali leaching include: solid-liquid ratio <1 g: 2 mL, temperature of 50-90° C., and time of 2-10 h; (5) mixing the product obtained in step (4) with an organic aqueous solution and letting it stand for 2-48 hours, and then mixing the obtained solid phase with ethanol and ball milling, wherein the organic aqueous solution is a mixed solution of water and an organic solvent, and the organic solvent is selected from one or more of methanol, ethanol and glycerol; (6) reacting the product obtained in step (5) with an acidic solution and standing for 20-30 hours, then centrifuging at least twice, and washing the solid phase obtained after centrifugation, wherein the reaction conditions include: temperature of 30-90° C., time of 0.5-10 hours, and the acidic solution is selected from one or more of hydrochloric acid, sulfuric acid and nitric acid; (7) The product obtained in step (6) is roasted and crushed to obtain titanium dioxide. The method according to claim 1, characterized in that, in step (1), the mass concentration of the hydrogen peroxide solution is 5-20%. The method according to claim 1 or 2 is characterized in that, in step (1), the weight ratio of the persulfate to the waste denitration catalyst is 2-5:100. The method according to claim 1 or 2, characterized in that, in step (1), the pH value of the alkaline solution is 10-14. The method according to claim 1, characterized in that in step (2), the acidic solution is oxalic acid solution, citric acid solution or hydrochloric acid solution. The method according to claim 1, characterized in that in step (2), the concentration of the acidic solution is 0.02-6 mol/L. The method according to claim 1 or 5, characterized in that in step (3), the solid-liquid ratio of the powdered material to the ethanol is 1g:5-20mL. The method according to claim 7, characterized in that in step (3), the processing time is 2-72 hours. The method according to claim 1 or 8, characterized in that, in step (5), the volume ratio of the product to the organic aqueous solution is 1:0.5-2. The method according to claim 1 or 8, characterized in that, in step (5), the volume ratio of water to organic solvent in the organic aqueous solution is 1:1-4. The method according to claim 1 or 8, characterized in that in step (5), the solid-liquid ratio of the solid phase portion to the ethanol is 1g:5-10mL. The method according to claim 1, characterized in that in step (5), the mixing time is 2-24 hours. The method according to claim 1, characterized in that, in step (5), the ball milling time is >2h. The method according to claim 1 or 13, characterized in that in step (6), the concentration of the acidic solution is 0.2-6 mol/L. The method according to claim 1 or 13 is characterized in that in step (6), when two centrifugations are performed, the conditions for the first centrifugation include: a rotation speed of 2000-4000 rpm/min, and a time of 2-10 min, and the conditions for the second centrifugation include: a rotation speed of 8000-26000 rpm/min, and a time of >30 min. The method according to claim 1 or 13, characterized in that in step (7), the calcination conditions include: temperature of 600-700°C, time of 2-4h, and heating rate of ≤10°C/min.