In-situ purification method of high-grade cement retarder phosphogypsum in cooperation with cement kiln

Abstract

The invention belongs to the technical field of environmental protection, and discloses a high-grade cement retarder ardealite in-situ purification method in cooperation with a cement kiln, and the method comprises the following steps: preparing slurry according to the solid content of 25-35 wt%, scrubbing ardealite for 5-10 min by using a wet rod mill, adjusting the pH value of the ball-milled ardealite slurry to be less than 3, removing organic soluble phosphorus and fluorine through reverse flotation and direct flotation, and obtaining the high-grade cement retarder ardealite. Wherein organic matters obtained through reverse flotation can directly enter a cement kiln to serve as fuel, and silicon impurities obtained through forward flotation can serve as fine aggregate filler; after flotation, phosphogypsum is filtered, slurry is prepared again according to the solid content of 30-50 wt% for alkali neutralization, the alkali neutralization reaction is that 1.5-5% of alkaline correction agent is added at the temperature of 50-80 DEG C for water bath reaction, the obtained slurry is centrifugally filtered and dried by a hammer type drying device, and the obtained product is purified phosphogypsum. The invention solves the technical problem that the existing ardealite purification method is difficult to realize synchronous removal of various impurities while ensuring energy conservation and environmental protection.

Description

Technical Field

[0001] This invention belongs to the field of environmental protection technology, specifically relating to an in-situ purification method for high-grade cement retarder phosphogypsum used in conjunction with cement kilns. Background Technology

[0002] Phosphogypsum is a large industrial solid waste generated during the wet process of phosphoric acid production. Its main component is calcium sulfate dihydrate (CaSO4·2H2O), but it contains various impurities such as undecomposed phosphate rock, free phosphoric acid, fluorides, fluorates, and organic matter. These impurities, especially soluble phosphorus, eutectic phosphorus, and fluorides, severely restrict the large-scale application of phosphogypsum as a retarder in the cement industry.

[0003] Existing phosphogypsum purification technologies have several drawbacks: While water washing is low-cost, its removal of insoluble eutectic phosphorus impurities is limited, and water consumption is high (at least 3 tons of water are needed to treat 1 ton of phosphogypsum), making wastewater treatment difficult; calcination can remove eutectic phosphorus, but it is energy-intensive, costly, and prone to secondary pollution; traditional chemical neutralization methods often use quicklime, which is ineffective at removing organic impurities and results in insufficient product stability; flotation is energy-efficient, cost-effective, and relatively environmentally friendly, and can remove organic matter from phosphogypsum to some extent, improving its grade, but its effect on insoluble impurities is not significant; traditional acid leaching uses strong acid solutions such as sulfuric acid and hydrochloric acid to soak phosphogypsum, dissolving insoluble phosphides and some metallic impurities bound to the gypsum. Its drawbacks include high acid reagent consumption, high raw material costs, and the corrosive effects of strong acids on equipment, increasing maintenance costs and safety risks. Acid residue requires large amounts of alkali for neutralization, affecting product purity. Furthermore, some existing processes suffer from incomplete modification and inconsistent product quality, making them unable to completely replace natural gypsum for high-quality cement production. Therefore, developing an efficient, energy-saving, environmentally friendly in-situ purification technology for phosphogypsum that can simultaneously remove multiple impurities, thereby promoting the resource utilization of phosphogypsum, reducing cement production costs, and alleviating environmental pressure, is a technical problem to be solved in this field. Summary of the Invention

[0004] The purpose of this invention is to provide an in-situ purification method for high-grade cement retarder phosphogypsum in conjunction with cement kilns, so as to solve the technical problem in the prior art that it is difficult to simultaneously remove multiple impurities while ensuring energy conservation and environmental protection.

[0005] The aforementioned method for in-situ purification of high-grade cement retarder phosphogypsum in a co-operating cement kiln includes the following steps: (1) Scrubbing: The phosphogypsum slurry is wet-grinded and scrubbed to adjust the pH of the slurry to acidic; (2) Reverse flotation: Add the first frother to the acidified phosphogypsum slurry to perform reverse flotation to obtain the first concentrate and the first tailings. Add the second frother to the first concentrate to perform reverse flotation to obtain the second concentrate and the second tailings. Mix the first tailings and the second tailings and then centrifuge them. Send the resulting filtrate to the flotation wastewater tank and send the filter residue to the cement kiln as fuel. (3) Direct flotation: Add the first capture agent to the second concentrate slurry obtained by reverse flotation and perform direct flotation to obtain the third concentrate and the third tailings. Add the second capture agent to the third concentrate and perform direct flotation to further obtain the fourth concentrate and the fourth tailings. Centrifuge the fourth concentrate and filter it. The filter residue is purified phosphogypsum. The filtrate is sent to the flotation wastewater tank. Mix the third tailings and the fourth tailings and centrifuge them. The filtrate is sent to the flotation wastewater tank. The filter residue is sent to the commercial concrete plant as fine aggregate filler. (4) Water bath neutralization: The purified phosphogypsum is remixed and heated to a constant temperature. An alkaline corrector is added to carry out the reaction. After the reaction is completed, the mixture is centrifuged, filtered, and dried by hammer drying. The resulting filter residue is a high-quality cement retarder.

[0006] Preferably, in step (1): phosphogypsum is prepared into a paste with a solid content of 25-35 wt%.

[0007] Preferably, in step (1), the duration of wet bar scrubbing is 5-10 minutes.

[0008] Preferably, in step (1): acid adjustment is to adjust the pH of the phosphogypsum slurry to <3.

[0009] Preferably, in step (2): the first frother is a mixture of flotation oil #2 and MIBC, and the second frother is flotation oil #2; the dosage of the first frother is 60-80 g / t, and the dosage of the second frother is 40-60 g / t.

[0010] Preferably, in step (3): both the first scavenger and the second scavenger are dodecylamine; the amount of the first scavenger is 60-80 g / t, and the amount of the second scavenger is 40-60 g / t.

[0011] Preferably, in step (4): the purified phosphogypsum is re-mixed into a paste with a solid content of 30-50 wt%.

[0012] Preferably, in step (4), the temperature of the isothermal reaction after adding the alkaline corrector is 50-80℃.

[0013] Preferably, in step (4): the pH of the purified phosphogypsum slurry is ≤6.5, and the amount of alkaline corrector is 1.5-5% of the mass of the purified phosphogypsum slurry.

[0014] Preferably, in step (2): the ratio of flotation oil #2 to MIBC in the first foaming agent is 5:1 or 4:1.

[0015] The technical advantages of this invention are as follows: Reverse flotation removes organic matter from phosphogypsum, while direct flotation removes siliceous impurities. The flotation process also removes water-soluble and insoluble phosphorus and fluorine impurities. The water bath neutralization method utilizes the residual acidity from the previous flotation step, heating the phosphogypsum to partially decompose it, followed by the addition of an alkali agent for neutralization, thus enhancing the removal rate of eutectic phosphorus (inerting). A pre-processing step involving water washing and rod milling is added before the process, which scrubs the phosphogypsum to improve the impurity removal rates of subsequent flotation and water bath neutralization. Through these steps, this invention can simultaneously remove multiple impurities in each step. Furthermore, in the flotation process, the reverse flotation tailings—organic matter—can be fed into a cement kiln as fuel, and the direct flotation tailings—silicon—can be fed into a commercial concrete plant as fine aggregate filler, solving the problem of secondary pollution from solid waste. Therefore, this invention solves the technical problem of existing technologies failing to simultaneously remove multiple impurities while ensuring energy conservation and environmental protection. Meanwhile, because rod milling improves the flotation and water bath neutralization and impurity removal rates, it can also solve the problems of incomplete phosphogypsum modification and uneven product quality in existing processes. Attached Figure Description

[0016] Figure 1 This diagram illustrates the basic steps of an in-situ purification method for high-grade cement retarder phosphogypsum in conjunction with a cement kiln, as described in this invention. Detailed Implementation

[0017] The following detailed description of the embodiments, in conjunction with the accompanying drawings, will further illustrate the specific implementation of the present invention, in order to help those skilled in the art to have a more complete, accurate, and in-depth understanding of the inventive concept and technical solution of the present invention.

[0018] like Figure 1 As shown, the present invention provides an in-situ purification method for high-grade cement retarder phosphogypsum in conjunction with cement kilns, comprising the following steps.

[0019] Scrubbing: The phosphogypsum slurry is wet-grinded and scrubbed.

[0020] The first step is to prepare the phosphogypsum slurry; after the slurry is prepared, the phosphogypsum slurry is wet-rolled and scrubbed; and an acidic substance is added to the scrubbed product to adjust the pH of the slurry to acidic.

[0021] The preparation of phosphogypsum slurry involves preparing phosphogypsum with a solid content of 25-35 wt%. The duration of wet rod milling is 5-10 minutes, followed by acid adjustment to bring the pH of the phosphogypsum slurry to <3.

[0022] Reverse flotation: Add the first frother to the acidified phosphogypsum slurry for reverse flotation to obtain the first concentrate (slurry) and the first tailings. Add the second frother to the first concentrate for reverse flotation to obtain the second concentrate (slurry) and the second tailings.

[0023] The first and second tailings are mixed and then centrifuged. The resulting filtrate is sent to a flotation wastewater tank, and the separated filter residue is sent to a cement kiln as fuel. The filter residue is composed of organic matter.

[0024] The first frother is a mixture of flotation oil #2 and MIBC (methyl isobutyl methanol), with a ratio of flotation oil #2 to MIBC of 5:1 or 4:1; the second frother is flotation oil #2.

[0025] The dosage of the first foaming agent is 60-80g / t, and the dosage of the second foaming agent is 40-60g / t.

[0026] Direct flotation: Add the first capture agent to the second concentrate slurry obtained from reverse flotation and perform direct flotation to obtain the third concentrate (slurry) and the third tailings. Add the second capture agent to the third concentrate and perform direct flotation to further obtain the fourth concentrate (slurry) and the fourth tailings. Centrifuge and filter the fourth concentrate. The resulting filter residue is purified phosphogypsum.

[0027] The filtrate obtained from centrifugal filtration is sent to the flotation wastewater tank. The third and fourth tailings are mixed and then centrifuged and filtered. The resulting filtrate is sent to the flotation wastewater tank. The filter residue is composed of silicon and is sent to the commercial concrete plant for recycling as fine aggregate filler.

[0028] Both the first and second scavenging agents are dodecylamine.

[0029] The dosage of the first capturing agent is 60-80 g / t, and the dosage of the second capturing agent is 40-60 g / t.

[0030] Water bath neutralization: The purified phosphogypsum is remixed and heated to a constant temperature. An alkaline corrector is then added to carry out the reaction. After the reaction is completed, the mixture is first centrifuged and filtered, and then dried by hammer drying. The resulting filter residue is the high-grade cement retarder.

[0031] Alkaline corrector is any one or a mixture of any two or three of cement, clinker, and lime.

[0032] The purified phosphogypsum was re-mixed into a slurry with a solid content of 30-50 wt%, and the pH of the resulting purified phosphogypsum slurry was ≤6.5. The amount of alkaline corrector added was 1.5-5% of the mass of the purified phosphogypsum slurry. The constant temperature reaction temperature after adding the alkaline corrector was 50-80℃.

[0033] The specific implementation of this solution is as follows.

[0034] Example 1 In this embodiment, a method for in-situ purification of high-grade cement retarder phosphogypsum in conjunction with cement kilns includes the following steps.

[0035] Phosphogypsum was prepared into a slurry with a solid content of 28 wt%. After preparation, the slurry was wet-rolled and scrubbed for 5 minutes. Then, the pH of the phosphogypsum slurry was adjusted to 2.8.

[0036] Add a mixture of flotation oil #2 and MIBC reagent to the acidified phosphogypsum slurry. The ratio of flotation oil #2 to MIBC is 5:1, and the dosage is 60 g / t. Perform reverse flotation to obtain the first concentrate and the first tailings. Continue to add flotation oil #2 to the first concentrate at a dosage of 40 g / t. Perform reverse flotation to further obtain the second concentrate and the second tailings. Mix the first tailings and the second tailings and centrifuge and filter. The filtrate is then sent to the flotation wastewater tank.

[0037] Dodecylamine is added to the second concentrate obtained from reverse flotation at a dosage of 60 g / t, and direct flotation is carried out to obtain the third concentrate and the third tailings. Dodecylamine is then added to the third concentrate at a dosage of 40 g / t, and direct flotation is carried out to further obtain the fourth concentrate and the fourth tailings. The fourth concentrate is centrifuged and filtered, and the resulting filter residue is purified phosphogypsum. The filtrate is sent to the flotation wastewater tank. The third tailings and the fourth tailings are mixed and centrifuged and filtered, and the resulting filtrate is sent to the flotation wastewater tank.

[0038] The purified phosphogypsum was remixed with a solid content of 50wt% and the slurry pH was 6.3. After heating to a constant temperature of 50℃, 2% alkaline corrector was added. After the reaction was completed, the mixture was centrifuged, filtered, and dried by hammer drying. The resulting filter residue was a high-quality cement retarder.

[0039] Example 2 In this embodiment, a method for in-situ purification of high-grade cement retarder phosphogypsum in conjunction with cement kilns includes the following steps.

[0040] Prepare the slurry with a solid content of 30wt%. After preparation, perform wet rod milling and washing for 5 minutes, and then adjust the pH of the phosphogypsum slurry to 2.0.

[0041] A mixture of No. 2 oil and MIBC reagent at a ratio of 4:1 and a dosage of 65 g / t is added to the acidified phosphogypsum slurry for reverse flotation to obtain the first concentrate and the first tailings. No. 2 flotation oil is then added to the first concentrate at a dosage of 40 g / t for reverse flotation to further obtain the second concentrate and the second tailings. The first tailings and the second tailings are then mixed and centrifuged and filtered, and the resulting filtrate is sent to the flotation wastewater tank.

[0042] Dodecylamine is added to the second concentrate pulp of reverse flotation at a dosage of 70 g / t, and direct flotation is carried out to obtain the third concentrate and the third tailings. Dodecylamine is then added to the third concentrate at a dosage of 40 g / t, and direct flotation is carried out to further obtain the fourth concentrate and the fourth tailings. The fourth concentrate is centrifuged and filtered, and the filter residue is purified phosphogypsum. The filtrate enters the flotation wastewater tank. The third tailings and the fourth tailings are mixed and centrifuged and filtered, and the filtrate is entered into the flotation wastewater tank.

[0043] The purified phosphogypsum was remixed to a solid content of 45wt%, and the slurry pH was 6.0. After heating to a constant temperature of 62℃, 3% alkaline corrector was added. After the reaction was completed, the mixture was centrifuged, filtered, and dried by hammer drying. The resulting filter residue was a high-quality cement retarder.

[0044] Example 3 In this embodiment, a method for in-situ purification of high-grade cement retarder phosphogypsum in conjunction with cement kilns includes the following steps.

[0045] Prepare the slurry with a solid content of 33wt%. After preparation, perform wet rod milling and washing for 7 minutes, and then adjust the pH of the phosphogypsum slurry to 2.5.

[0046] A mixture of No. 2 oil and MIBC reagent at a ratio of 5:1 and a dosage of 60 g / t is added to the acidified phosphogypsum slurry for reverse flotation to obtain the first concentrate and the first tailings. No. 2 flotation oil is then added to the first concentrate at a dosage of 45 g / t for reverse flotation to further obtain the second concentrate and the second tailings. The first tailings and the second tailings are mixed and centrifuged for filtration. The resulting filtrate is then sent to the flotation wastewater tank.

[0047] Dodecylamine is added to the second concentrate pulp of reverse flotation at a dosage of 80 g / t, and direct flotation is carried out to obtain the third concentrate and the third tailings. Dodecylamine is then added to the third concentrate at a dosage of 45 g / t, and direct flotation is carried out to further obtain the fourth concentrate and the fourth tailings. The fourth concentrate is centrifuged and filtered, and the resulting filter residue is purified phosphogypsum. The filtrate enters the flotation wastewater tank. The third tailings and the fourth tailings are mixed and centrifuged and filtered, and the resulting filtrate enters the flotation wastewater tank.

[0048] The purified phosphogypsum was remixed to a solid content of 42wt%, and the slurry pH was 6.1. After being heated to a constant temperature of 55℃, 2.5% alkaline corrector was added. After the reaction was completed, the mixture was centrifuged, filtered, and dried by hammer drying. The resulting filter residue was a high-quality cement retarder.

[0049] Example 4 In this embodiment, a method for in-situ purification of high-grade cement retarder phosphogypsum in conjunction with cement kilns includes the following steps.

[0050] Prepare the slurry with a solid content of 35wt%. After preparation, perform wet rod milling and washing for 10 minutes, and then adjust the pH of the phosphogypsum slurry to 1.8.

[0051] A mixture of No. 2 oil and MIBC reagent at a ratio of 5:1 and a dosage of 80 g / t is added to the acidified phosphogypsum slurry for reverse flotation to obtain the first concentrate and the first tailings. No. 2 flotation oil is then added to the first concentrate at a dosage of 50 g / t for reverse flotation to further obtain the second concentrate and the second tailings. The first tailings and the second tailings are mixed and centrifuged for filtration, and the resulting filtrate is sent to the flotation wastewater tank.

[0052] Dodecylamine is added to the second concentrate pulp of reverse flotation at a dosage of 65 g / t, and direct flotation is carried out to obtain the third concentrate and the third tailings. Dodecylamine is then added to the third concentrate at a dosage of 45 g / t, and direct flotation is carried out to further obtain the fourth concentrate and the fourth tailings. The fourth concentrate is centrifuged and filtered, and the resulting filter residue is purified phosphogypsum. The filtrate enters the flotation wastewater tank. The third tailings and the fourth tailings are mixed and centrifuged and filtered, and the resulting filtrate enters the flotation wastewater tank.

[0053] The purified phosphogypsum was remixed to a solid content of 45wt%, and the slurry pH was 6.5. After heating to a constant temperature of 60℃, 1.5% alkaline corrector was added. After the reaction was completed, the mixture was centrifuged, filtered, and dried by hammer drying. The resulting filter residue was a high-quality cement retarder.

[0054] Example 5 In this embodiment, a method for in-situ purification of high-grade cement retarder phosphogypsum in conjunction with cement kilns includes the following steps.

[0055] Prepare the slurry with a solid content of 30wt%. After preparation, perform wet rod milling and washing for 8 minutes, and then adjust the pH of the phosphogypsum slurry to 2.3.

[0056] A mixture of No. 2 oil and MIBC reagent at a ratio of 4:1 and a dosage of 65 g / t is added to the acidified phosphogypsum slurry for reverse flotation to obtain the first concentrate and the first tailings. No. 2 flotation oil is then added to the first concentrate at a dosage of 45 g / t for reverse flotation to further obtain the second concentrate and the second tailings. The first tailings and the second tailings are mixed and centrifuged for filtration. The resulting filtrate is then sent to the flotation wastewater tank.

[0057] Dodecylamine is added to the second concentrate pulp of reverse flotation at a dosage of 60 g / t, and direct flotation is carried out to obtain the third concentrate and the third tailings. Dodecylamine is then added to the third concentrate at a dosage of 40 g / t, and direct flotation is carried out to further obtain the fourth concentrate and the fourth tailings. The fourth concentrate is centrifuged and filtered, and the resulting filter residue is purified phosphogypsum. The filtrate enters the flotation wastewater tank. The third tailings and the fourth tailings are mixed and centrifuged and filtered, and the resulting filtrate enters the flotation wastewater tank.

[0058] The purified phosphogypsum was remixed with a solid content of 35wt% and the slurry pH was 5.8. After heating to a constant temperature of 58℃, 4.5% alkaline corrector was added. After the reaction was completed, the mixture was centrifuged, filtered, and dried by hammer drying. The resulting filter residue was a high-quality cement retarder.

[0059] Example 6 In this embodiment, a method for in-situ purification of high-grade cement retarder phosphogypsum in conjunction with cement kilns includes the following steps.

[0060] Prepare the slurry with a solid content of 30wt%. After preparation, perform wet rod milling and washing for 10 minutes, and then adjust the pH of the phosphogypsum slurry to 2.2.

[0061] Add a mixture of No. 2 oil and MIBC reagent at a ratio of 5:1 and a dosage of 80 g / t to the acidified phosphogypsum slurry for reverse flotation to obtain the first concentrate and the first tailings. Add No. 2 flotation oil to the first concentrate at a dosage of 40 g / t for reverse flotation to further obtain the second concentrate and the second tailings. Mix the first tailings and the second tailings and centrifuge and filter them. The filtrate is then sent to the flotation wastewater tank.

[0062] Dodecylamine is added to the second concentrate pulp of reverse flotation at a dosage of 80 g / t, and direct flotation is carried out to obtain the third concentrate and the third tailings. Dodecylamine is then added to the third concentrate at a dosage of 45 g / t, and direct flotation is carried out to further obtain the fourth concentrate and the fourth tailings. The fourth concentrate is centrifuged and filtered, and the resulting filter residue is purified phosphogypsum. The filtrate enters the flotation wastewater tank. The third tailings and the fourth tailings are mixed and centrifuged and filtered, and the resulting filtrate enters the flotation wastewater tank.

[0063] The purified phosphogypsum was remixed to a solid content of 32wt%, and the slurry pH was 6.3. After heating to a constant temperature of 75℃, 1.5% alkaline corrector was added. After the reaction was completed, the mixture was centrifuged, filtered, and dried by hammer drying. The resulting filter residue was a high-quality cement retarder.

[0064] Example 7 In this embodiment, a method for in-situ purification of high-grade cement retarder phosphogypsum in conjunction with cement kilns includes the following steps.

[0065] Prepare the slurry with a solid content of 33wt%. After preparation, perform wet rod milling and washing for 10 minutes, and then adjust the pH of the phosphogypsum slurry to 1.7.

[0066] A mixture of No. 2 oil and MIBC reagent at a ratio of 4:1 and a dosage of 70 g / t is added to the acidified phosphogypsum slurry for reverse flotation to obtain the first concentrate and the first tailings. No. 2 flotation oil is then added to the first concentrate at a dosage of 60 g / t for reverse flotation to further obtain the second concentrate and the second tailings. The first tailings and the second tailings are mixed and centrifuged for filtration. The resulting filtrate is then sent to the flotation wastewater tank.

[0067] Dodecylamine is added to the second concentrate pulp of reverse flotation at a dosage of 70 g / t, and direct flotation is carried out to obtain the third concentrate and the third tailings. Dodecylamine is then added to the third concentrate at a dosage of 60 g / t, and direct flotation is carried out to further obtain the fourth concentrate and the fourth tailings. The fourth concentrate is centrifuged and filtered, and the resulting filter residue is purified phosphogypsum. The filtrate enters the flotation wastewater tank. The third tailings and the fourth tailings are mixed and centrifuged and filtered, and the resulting filtrate enters the flotation wastewater tank.

[0068] The purified phosphogypsum was remixed with a solid content of 40wt% and the slurry pH was 5.8. After heating to a constant temperature of 70℃, 5% alkaline corrector was added. After the reaction was completed, the mixture was centrifuged, filtered, and dried by hammer drying. The resulting filter residue was a high-quality cement retarder.

[0069] Example 8 In this embodiment, a method for in-situ purification of high-grade cement retarder phosphogypsum in conjunction with cement kilns includes the following steps.

[0070] Prepare the slurry with a solid content of 27wt%. After preparation, perform wet rod milling and washing for 9 minutes, and then adjust the pH of the phosphogypsum slurry to 2.4.

[0071] A mixture of No. 2 oil and MIBC reagent at a ratio of 5:1 and a dosage of 65 g / t is added to the acidified phosphogypsum slurry for reverse flotation to obtain the first concentrate and the first tailings. No. 2 flotation oil is then added to the first concentrate at a dosage of 60 g / t for reverse flotation to further obtain the second concentrate and the second tailings. The first tailings and the second tailings are mixed and centrifuged for filtration. The resulting filtrate is then sent to the flotation wastewater tank.

[0072] Dodecylamine is added to the second concentrate pulp of reverse flotation at a dosage of 65 g / t, and direct flotation is carried out to obtain the third concentrate and the third tailings. Dodecylamine is then added to the third concentrate at a dosage of 60 g / t, and direct flotation is carried out to further obtain the fourth concentrate and the fourth tailings. The fourth concentrate is centrifuged and filtered, and the resulting filter residue is purified phosphogypsum. The filtrate enters the flotation wastewater tank. The third tailings and the fourth tailings are mixed and centrifuged and filtered, and the resulting filtrate enters the flotation wastewater tank.

[0073] The purified phosphogypsum was remixed with a solid content of 33wt% and the slurry pH was 6.0. After heating to a constant temperature of 65℃, 4% alkaline corrector was added. After the reaction was completed, the mixture was centrifuged, filtered, and dried by hammer drying. The resulting filter residue was a high-quality cement retarder.

[0074] Example 9 In this embodiment, a method for in-situ purification of high-grade cement retarder phosphogypsum in conjunction with cement kilns includes the following steps.

[0075] Prepare the slurry with a solid content of 25wt%. After preparation, perform wet rod milling and washing for 10 minutes, and then adjust the pH of the phosphogypsum slurry to 2.0.

[0076] A mixture of No. 2 oil and MIBC reagent at a ratio of 5:1 and a dosage of 60 g / t is added to the acidified phosphogypsum slurry for reverse flotation to obtain the first concentrate and the first tailings. No. 2 flotation oil is then added to the first concentrate at a dosage of 50 g / t for reverse flotation to further obtain the second concentrate and the second tailings. The first tailings and the second tailings are mixed and centrifuged for filtration. The resulting filtrate is then sent to the flotation wastewater tank.

[0077] Dodecylamine is added to the second concentrate pulp of reverse flotation at a dosage of 60 g / t, and direct flotation is carried out to obtain the third concentrate and the third tailings. Dodecylamine is then added to the third concentrate at a dosage of 55 g / t, and direct flotation is carried out to further obtain the fourth concentrate and the fourth tailings. The fourth concentrate is centrifuged and filtered, and the resulting filter residue is purified phosphogypsum. The filtrate enters the flotation wastewater tank. The third tailings and the fourth tailings are mixed and centrifuged and filtered, and the resulting filtrate enters the flotation wastewater tank.

[0078] The purified phosphogypsum was remixed with a solid content of 30wt% and the slurry pH was 6.2. After heating to 80℃ and maintaining a constant temperature, 2% alkaline corrector was added. After the reaction was completed, the mixture was centrifuged, filtered, and dried by hammer drying. The resulting filter residue was a high-quality cement retarder.

[0079] The high-quality cement retarder obtained in the above embodiments was tested, and the test results of the cement performance and the corresponding comparative reference material performance are shown in Table 1.

[0080] Table 1: Test Results of Cement Performance

[0081] As shown in the table above, the method provided by this invention can effectively achieve in-situ purification of phosphogypsum, resulting in a high-quality cement retarder, and the cement obtained after application has better performance than existing technologies.

[0082] The present invention has been described above by way of example with reference to the accompanying drawings. Obviously, the specific implementation of the present invention is not limited to the above-described manner. Any non-substantial improvements made using the inventive concept and technical solution of the present invention, or the direct application of the inventive concept and technical solution of the present invention to other occasions without modification, are all within the protection scope of the present invention.

Claims

1. A method for in-situ purification of phosphogypsum, a high-grade cement retarder used in cement kilns, characterized in that... It includes the following steps: (1) Scrubbing: The phosphogypsum slurry is wet-grinded and scrubbed to adjust the pH of the slurry to acidic; (2) Reverse flotation: Add the first frother to the acidified phosphogypsum slurry for reverse flotation to obtain the first concentrate and the first tailings. Add the second frother to the first concentrate for reverse flotation to obtain the second concentrate and the second tailings. Mix the first tailings and the second tailings and then centrifuge them. Send the resulting filtrate to the flotation wastewater tank and send the filter residue to the cement kiln as fuel. (3) Direct flotation: Add the first capture agent to the second concentrate slurry obtained by reverse flotation and perform direct flotation to obtain the third concentrate and the third tailings. Add the second capture agent to the third concentrate and perform direct flotation to further obtain the fourth concentrate and the fourth tailings. Centrifuge the fourth concentrate and filter it. The filter residue is purified phosphogypsum. The filtrate is sent to the flotation wastewater tank. Mix the third tailings and the fourth tailings and centrifuge them. The filtrate is sent to the flotation wastewater tank. The filter residue is sent to the commercial concrete plant as fine aggregate filler. (4) Water bath neutralization: The purified phosphogypsum is remixed and heated to a constant temperature. An alkaline corrector is added to carry out the reaction. After the reaction is completed, the mixture is centrifuged, filtered, and dried by hammer drying. The resulting filter residue is a high-quality cement retarder.

2. The method for in-situ purification of phosphogypsum, a high-quality cement retarder, according to claim 1, is characterized in that... In step (1): phosphogypsum is prepared into a slurry with a solid content of 25-35 wt%.

3. The method for in-situ purification of phosphogypsum, a high-quality cement retarder, according to claim 1, is characterized in that... In step (1): the duration of wet bar scrubbing is 5-10 minutes.

4. The method for in-situ purification of phosphogypsum, a high-quality cement retarder, according to claim 1, is characterized in that... In step (1): acid adjustment means adjusting the pH of the phosphogypsum slurry to <3.

5. The method for in-situ purification of phosphogypsum, a high-quality cement retarder, according to claim 1, is characterized in that... In step (2): the first frother is a mixture of flotation oil #2 and MIBC, and the second frother is flotation oil #2; the dosage of the first frother is 60-80 g / t, and the dosage of the second frother is 40-60 g / t.

6. The method for in-situ purification of phosphogypsum, a high-quality cement retarder, according to claim 1, is characterized in that... In step (3): both the first and second scavenging agents are dodecylamine; the amount of the first scavenging agent is 60-80 g / t, and the amount of the second scavenging agent is 40-60 g / t.

7. The method for in-situ purification of phosphogypsum, a high-quality cement retarder, according to claim 1, is characterized in that... In step (4): the purified phosphogypsum is re-mixed into a paste with a solid content of 30-50 wt%.

8. The method for in-situ purification of phosphogypsum, a high-quality cement retarder, according to claim 1, is characterized in that... In step (4): the temperature of the constant temperature reaction after adding the alkaline corrector is 50-80℃.

9. The method for in-situ purification of phosphogypsum, a high-quality cement retarder, according to claim 1, is characterized in that... In step (4): the pH of the purified phosphogypsum slurry is ≤6.5, and the amount of alkaline corrector is 1.5-5% of the mass of the purified phosphogypsum slurry.

10. A method for in-situ purification of phosphogypsum, a high-quality cement retarder, according to claim 5, characterized in that, In step (2): In the first frother, the ratio of flotation oil #2 to MIBC is 5:1 or 4:1.

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