AU2021104432A4

AU2021104432A4 - Spherical phosphogypsum, and preparation method and use thereof

Info

Publication number: AU2021104432A4
Application number: AU2021104432A
Authority: AU
Inventors: Xiaopei SUN
Original assignee: Hubei Xinyangfeng New Building Material Technology Co Ltd
Current assignee: Hubei Xinyangfeng New Building Material Technology Co Ltd
Priority date: 2021-04-25
Filing date: 2021-07-22
Publication date: 2021-09-16
Anticipated expiration: 2029-07-22
Also published as: ZA202105418B; CN113072318B; CN113072318A

Abstract

OF THE DISCLOSURE The present disclosure relates to the technical field of comprehensive utilization of solid waste, and provides a spherical phosphogypsum, and a preparation method and use thereof. The spherical phosphogypsum is prepared from raw materials including a phosphogypsum powder, a cement, and a modifying agent, wherein the modifying agent includes alkaline lignin and/or ferrous sulfate. The spherical phosphogypsum has a high physical strength, is not easy to break, and shows a prominent retarding effect. Where the modifying agent includes lignin, the spherical phosphogypsum could also increase the strength of the cement and reduce water demand for the mixing. Where the modifying agent includes ferrous sulfate, the spherical phosphogypsum could also reduce the content of water-soluble hexavalent chromium in the cement. The spherical phosphogypsum of the present disclosure includes a large amount of phosphogypsum powder, which helps to promote the balance between production and consumption of phosphogypsum, and fundamentally solves the ecological and environmental protection problems resulting from phosphogypsum. Furthermore, alkaline lignin used in the present disclosure comes from a papermaking black liquor, and ferrous sulfate used comes from waste residue of titanium dioxide production, which could realize the utilization of papermaking black liquor and waste residue of titanium dioxide production.

Description

SPHERICAL PHOSPHOGYPSUM, AND PREPARATION METHOD AND USE THEREOF TECHNICAL FIELD

[0001] The present disclosure relates to the technical field of comprehensive utilization of solid waste, and in particular to a spherical phosphogypsum, and a preparation method and use thereof.

BACKGROUNDART

[0002] Phosphogypsum is a solid waste produced in a wet process for producing phosphoric acid, which comprises a main component of calcium sulfate dihydrate (CSD). There is a relatively large discharge amount of phosphogypsum, and the composition of phosphogypsum varies greatly among different regions, with many impurity components. Therefore, it is difficult to achieve the comprehensive utilization of phosphogypsum, resulting in a very low utilization rate of phosphogypsum.

[0003] At present, from the perspective of the utilization quantity, products from the comprehensive utilization of phosphogypsum mainly include traditional building materials, such as building gypsum boards and gypsum bricks. These building materials have low added value and involve few categories, so it is difficult to increase the utilization rate of phosphogypsum. Unusable phosphogypsum is generally piled up in a stockyard or discarded in a sand pit. The long-term stockpiling of phosphogypsum requires a large amount of capital investment for anti-seepage treatment, also brings extremely high economic pressure to enterprises and local governments, and will also pollute the soil and water sources, thus seriously threatening the ecological security.

[0004] A cement retarder is mainly composed of phosphogypsum. Traditionally, phosphogypsum is subjected to water-washing or calcination to remove phosphorus, fluorine, and other impurities therein, and then is added as a retarder into a cement. However, phosphogypsum obtained as such is still powdery, has a high moisture content, high viscosity, and poor fluidity, and easily results in blockage and agglomeration in silos, adhesion to cement mills, etc. during use, thereby being difficult in industrialisation. In addition, the existing phosphogypsum powder shows a single function when used as a cement retarder, which is difficult to meet the requirements of high-performance cement.

SUMMARY

[0005] In view of this, the present disclosure is intended to provide a spherical phosphogypsum, and a preparation method and use thereof. The spherical phosphogypsum according to the present disclosure is a high-strength, multifunctional spherical phosphogypsum, which exhibits high physical strength and is not easy to break during transportation. The spherical phosphogypsum of the present disclosure, when used in cement, can play a role of retarding, increasing the strength of the cement, reducing a water demand of the cement (where the modifying agent includes alkaline lignin), and/or reducing the content of water-soluble hexavalent chromium in the cement (where the modifying agent includes ferrous sulfate).

[0006] To achieve the object of the present disclosure, the present disclosure provides the following technical solutions.

[0007] The present disclosure provides a spherical phosphogypsum, which is prepared from raw materials comprising, in parts by mass, 90 to 99 parts of a phosphogypsum powder, 3 to parts of a cement, and 0.1 to 2 parts of a modifying agent, wherein the modifying agent includes alkaline lignin and/or ferrous sulfate.

[0008] Preferably, alkaline lignin may be obtained by subjecting a papermaking black liquor to an evaporation to dry; and ferrous sulfate may be waste residue produced from the production of titanium dioxide.

[0009] Preferably, the cement may be one or more selected from the group consisting of a sulfoaluminate cement (SAC), a portland cement, an ordinary portland cement (OPC), a portland slag cement (PSC), a portland-pozzolana cement (PPC), a portland fly-ash cement (PFC), a portland composite cement (PCC), and a portland phosphorous-slag cement (PPSC).

[0010] Preferably, the OPC may have a model of P.052.5 or P.042.5R; the PSC may have a model of P.S.A32.5 or P.S.B32.5; the PPC may have a model of P.P32.5; the PFC may have a model of P.F32.5; the PCC may have a model of P.C42.5R; the PPSC may have a model of PPS32.5R; and the SAC may be rapid-hardening SAC.

[0011] Preferably, the outer surface of the spherical phosphogypsum may be covered with a cement shell, and the cement shell may be formed by solidifying a cement slurry and have a thickness of 2 mm to 3 mm.

[0012] Preferably, the spherical phosphogypsum may have a diameter of 20 mm to 30 mm, a 7-day strength of more than 80 N, a 7-day moisture content of less than 12 wt%, a crystal water content of more than 10 wt%, a SO3 content of more than 30 wt%, a pH value of more than 7.5, a water-soluble P205 content of 0.1 wt% to 0.8 wt%, a water-soluble F content of < 0.50 wt%, and a pelletizing rate of>89%.

[0013] The present disclosure also provides a preparation method of the spherical phosphogypsum according to the above technical solution, including the following steps: (1) mixing the phosphogypsum powder, the cement, and the modifying agent, and subjecting the resulting mixture to a pelletization to obtain a globular material; and (2) solidifying the globular material to obtain the spherical phosphogypsum.

[0014] Preferably, the pelletization may be conducted by using a pan-type double-stirring pelletizer, and the pan-type double-stirring pelletizer may have a pan rotational speed of 14 rpm to 16 rpm.

[0015] Preferably, after the globular material is obtained, the method may further include placing the globular material in a cement slurry to be coated with cement slurry.

[0016] Preferably, the cement slurry may have a solid content of 90% to 95%.

[0017] Preferably, solidifying the globular material may be achieved by stacking under normal conditions or an autoclave treatment; and the autoclave treatment may be conducted at 100 °C to 110 °C for 20 min to 40 min.

[0018] The present disclosure also provides use of the spherical phosphogypsum according to the above technical solution or the spherical phosphogypsum prepared by the preparation method according to the above technical solution in cement, wherein the spherical phosphogypsum is added in an amount of 5% to 8% of the mass of the cement.

[0019] The present disclosure provides a spherical phosphogypsum, which is prepared from raw materials comprising in parts by mass, 90 to 99 parts of a phosphogypsum powder, 3 to parts of a cement, and 0.1 to 2 parts of a modifying agent, wherein the modifying agent includes alkaline lignin and/or ferrous sulfate. The phosphogypsum powder includes soluble impurities such as phosphorous and fluorine, which will adversely affect the hydration process of the cement. The phosphogypsum powder has a low pH value, and the low pH value will cause the corrosion of equipment or facilities which contact the phosphogypsum powder, especially equipment or facilities made of iron or alloy materials, which adversely affects the hydration process of cement and even weakens the strength of set cement. In the present disclosure, the soluble phosphorus and fluorine in phosphogypsum are neutralized by adding cement to generate poorly-soluble phosphorus and fluorine, thereby realizing the modification of phosphogypsum; soluble harmful impurities are converted into insoluble impurities; and the pH value of the phosphogypsum powder is increased, such that the phosphogypsum meets the requirements of a cement retarder. In addition, the cement exhibiting hydraulic and air-hardening properties, can be hardened by reacting with the moisture (about 20% in phosphogypsum), thereby removing a part of the moisture in phosphogypsum; and the physical strength of the spherical phosphogypsum is greatly increased after the cement is hardened, such that the globular materials are not easy to break, which is convenient for transportation and use.

[0020] In addition, in the present disclosure, alkaline lignin and/or ferrous sulfate are added as a modifying agent to the spherical phosphogypsum. The alkaline lignin is a hydrophobic surfactant with an effect of reducing water demand, which could reduce water demand for cement mixing and increase set cement strength. The ferrous sulfate has reducibility, which could reduce the water-soluble hexavalent chromium in cement into trivalent chromium that is harmless to the human body, thereby reducing the content of water-soluble hexavalent chromium in a cement product to obtain a high-performance cement product. In the spherical phosphogypsum of the present disclosure, the alkaline lignin and ferrous sulfate could be added separately or simultaneously, which can be specifically determined according to requirements. Where the modifying agent includes both alkaline lignin and ferrous sulfate, the spherical phosphogypsum of the present disclosure has the functions of retarding, increasing set cement strength, reducing water demand for mixing, and reducing water-soluble hexavalent chromium content.

[0021] In the spherical phosphogypsum of the present disclosure, a large amount of phosphogypsum powder is used, with a high phosphogypsum utilization rate, which helps to promote the balance between production and consumption of phosphogypsum, fundamentally solves the ecological and environmental protection problems resulting from phosphogypsum, and promotes utilization of phosphogypsum to transfer from inefficient, low-value, and decentralized utilization to efficient, high-value, and large-scale utilization.

[0022] In addition, the outer surface of the spherical phosphogypsum of the present disclosure is also covered with a cement shell, which could further increase the hardness of the spherical phosphogypsum, such that the spherical phosphogypsum is more resistant to breakage and the transportation is more convenient.

[0023] Furthermore, in the present disclosure, the alkaline lignin is obtained by subjecting a papermaking black liquor to an evaporation to dry, the ferrous sulfate is waste residue produced from the production of titanium dioxide, and the phosphogypsum powder is waste residue produced in a wet process for preparing phosphoric acid from phosphate rock. That is to say, most of the raw materials used in the preparation of the spherical phosphogypsum of the present disclosure are waste, and thus the method makes it possible to realize the utilization of phosphogypsum, papermaking black liquor, and waste residue from titanium dioxide production to turn waste into treasure, and solve the ecological and environmental protection problems caused by the above-mentioned waste. Moreover, cement is added in the preparation of the spherical phosphogypsum of the present disclosure, and the spherical phosphogypsum will finally be used in cement. Therefore, it can be considered that only the phosphogypsum, papermaking black liquor, and waste residue from titanium dioxide production are additionally added during the whole process. The whole process is environmentally friendly, and provides a new way to consume the waste such as phosphogypsum.

[0024] The present disclosure also provides a preparation method of the spherical phosphogypsum according to the above technical solution, which involves simple steps and easy operations. Furthermore, the cement used in the present disclosure may be rapid-hardening SAC, which has a high setting rate. When rapid-hardening SAC is used, autoclave treatment is not required in the preparation process, that is, the spherical phosphogypsum with specified physical strength can be quickly obtained. Results of the examples show that, when rapid-hardening SAC is used, the physical strength of spherical phosphogypsum could reach more than 60 N at 45 min after pelletization. Therefore, when rapid-hardening SAC is used, no autoclave treatment is required in the preparation method provided in the present disclosure, which can further reduce production cost (the autoclave process requires about 20 RMB per ton), steam usage, and carbon emission.

[0025] The present disclosure also provides use of the spherical phosphogypsum according to the above technical solution in cement. The spherical phosphogypsum provided by the present disclosure exhibits high physical strength, is not easy to break, and shows the functions of retarding, reducing water, improving cement strength, and reducing water-soluble hexavalent chromium content. When used in cement, the spherical phosphogypsum of the present disclosure can solve the problems of difficult in adding retarders, frequent blockages, and difficult in adaptation of additives to cement and concrete; and can also reduce the amount of cement clinker and reduce the content of water-soluble hexavalent chromium in cement, such that a cement product has more excellent performance, which brings prominent economic and social benefits to downstream enterprises. In addition, the spherical phosphogypsum of the present disclosure, when used in cement, could reduce or eliminate the use of natural gypsum, thus realizing the purpose of protecting natural resources and promoting the national solid waste utilization.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0026] The present disclosure provides a spherical phosphogypsum, which is prepared from raw materials comprising, in parts by mass, 85 to 99 parts of a phosphogypsum powder, 3 to parts of a cement, and 0.1 to 2 parts of a modifying agent, wherein the modifying agent includes alkaline lignin and/or ferrous sulfate.

[0027] In parts by mass, the raw materials for preparing the spherical phosphogypsum of the present disclosure may include 90 to 99 parts, preferably 92 to 97 parts of the phosphogypsum powder. In the present disclosure, the phosphogypsum powder may be waste residue produced in a wet process for preparing phosphoric acid from phosphate rock; the phosphogypsum powder may comprises a main component of CSD (CaSO42H20); and the phosphogypsum powder may preferably have a P205 content of < 0.80 wt%; the phosphogypsum powder may preferably have an F content of < 0.50 wt%; and the phosphogypsum powder may preferably have a moisture content of < 16%.

[0028] In parts by mass, the raw materials for preparing the spherical phosphogypsum of the present disclosure may include 3 to 10 parts, preferably 5 to 8 parts of the cement. In the present disclosure, the cement may preferably be one or more of a SAC, a Portland cement, an OPC, a PSC, a PPC, a PFC, a PCC, and a PPSC; the OPC may have a model preferably of P.052.5 or P.042.5R; the PSC may have a model preferably of P.S.A32.5 or P.S.B32.5; the PPC may have a model preferably of P.P32.5; the PFC may have a model preferably of P.F32.5; the PCC may have a model preferably of P.C42.5R; the PPSC may have a model preferably of PPS32.5R; and the SAC may be rapid-hardening SAC.

[0029] In parts by mass, the raw materials for preparing the spherical phosphogypsum of the present disclosure may include 0.1 to 2 parts, preferably 0.5 to 1 part of the modifying agent. In the present disclosure, the modifying agent may include alkaline lignin and/or ferrous sulfate, and may preferably include alkaline lignin and ferrous sulfate. In the present disclosure, the alkaline lignin may preferably be obtained by subjecting a papermaking black liquor to an evaporation to dry; and the papermaking black liquor may specifically be wastewater produced by an alkaline pulping process in the papermaking industry, which includes a large amount of lignin and is called black liquor because of its dark brown color. The product obtained by directly subjecting a papermaking black liquor to an evaporation to dry comprises a main component of alkaline lignin. In the present disclosure, the evaporation product of a papermaking black liquor is used as a raw material, which could further reduce the preparation cost of the spherical phosphogypsum and meanwhile realize the utilization of the papermaking black liquor.

[0030] In the present disclosure, the ferrous sulfate may specifically be ferrous sulfate heptahydrate. In a specific example of the present disclosure, the ferrous sulfate may preferably be waste residue produced from the production of titanium dioxide. In this field, the titanium dioxide is produced mainly by a sulfuric acid method, and during the production of titanium dioxide by the sulfuric acid method, a large amount of iron sulfate heptahydrate waste residue is produced with a production 3.5 times more than that of titanium dioxide, which is difficult to treat and is the main bottleneck that hampers the rapid development of titanium dioxide preparation by the sulfuric acid method. In the present disclosure, waste residue from the production of titanium dioxide is used as a raw material to prepare a spherical phosphogypsum, which realizes the utilization of waste residue from titanium dioxide production while reducing the preparation cost, and provides a new way to consume waste residue from the production of titanium dioxide. In this field, water-soluble hexavalent chromium in cement has a high solubility, so when cement is mixed with water, the water-soluble hexavalent chromium is quickly dissolved. Hexavalent chromium has a strong oxidizing effect, which could cause harm to the human body and pollute underground water sources. Therefore, European Union countries stipulate that a soluble hexavalent chromium content in cement products shall not exceed 2 ppm. In the present disclosure, ferrous sulfate is added as a modifying agent to reduce the water-soluble hexavalent chromium in cement into trivalent chromium that is harmless to the human body. However, since the ferrous sulfate is used in an extremely-low amount, it is difficult to uniformly disperse when it is directly added into the cement. In the present disclosure, the ferrous sulfate is added to the spherical phosphogypsum, thus realizing uniform dispersion of low-dosage ferrous sulfate in cement and further improving the adaptability of cement and ferrous sulfate.

[0031] In the present disclosure, the spherical phosphogypsum may further include a cement shell covering the surface; the cement shell may be formed by solidifying a cement slurry, and the cement slurry may be prepared from a cement and water; the cement shell may preferably have a thickness of 2 mm to 3 mm; and the type of the cement may preferably be the same as described in the above technical solutions, which will not be repeated here. In a specific example of the present disclosure, the cement used in the cement slurry may preferably have a model of P.S.A32.5, P.S.B32.5, P.P32.5, P.F32.5, or PPS32.5R, and the cement of the above model has a low price, which is beneficial to control a production cost of the spherical phosphogypsum. In the present disclosure, the surface of the spherical phosphogypsum is covered with a cement shell, which could further improve the strength of the spherical phosphogypsum.

[0032] In the present disclosure, the spherical phosphogypsum may preferably have a diameter of 20 mm to 30 mm, and more preferably 22 mm to 28 mm; the spherical phosphogypsum may preferably have a 7-day strength of more than 80 N, and more preferably 80 N to 100 N; the spherical phosphogypsum may preferably have a 7-day moisture content of less than 12 wt%, and more preferably less than 10 wt%; the spherical phosphogypsum may preferably have a crystal water content of more than 10 wt%, and more preferably 10 wt% to 15 wt%; the spherical phosphogypsum may preferably have a S03 content of more than 30 wt%, and more preferably 30 wt% to 40 wt%; the spherical phosphogypsum may preferably have a PH value of more than 7.5, and more preferably 7.5 to 11; the spherical phosphogypsum may preferably have a water-soluble P205 content of 0.1 wt% to 0.8 wt%, and more preferably 0.3 wt% to 0.5 wt%; the spherical phosphogypsum may preferably have a water-soluble F content of < 0.50 wt%, and more preferably < 0.3 wt%; and the spherical phosphogypsum may preferably have a pelletizing rate of > 89%, and more preferably > 91%.

[0033] The present disclosure also provides a preparation method of the spherical phosphogypsum according to the above technical solution, including the following steps: (1) mixing the phosphogypsum powder, the cement, and the modifying agent, and subjecting the resulting mixture to a pelletization to obtain a globular material; and (2) solidifying the globular material to obtain the spherical phosphogypsum.

[0034] In the present disclosure, the phosphogypsum powder, the cement, and the modifying agent are mixed, and the resulting mixture is subjected to a pelletization to obtain a globular material. In the present disclosure, there are no particular limitations on a means for the mixing, as long as a uniform mixture could be obtained by mixing. In the present disclosure, the pelletization may preferably be conducted by using a pan-type double-stirring pelletizer; the pan-type double-stirring pelletizer may preferably have a pan rotational speed of 14 rpm to 16 rpm, and more preferably 15 rpm; and the globular material may preferably have a particle size of 20 mm to 30 mm.

[0035] In the present disclosure, after a globular material is obtained, the globular material is solidified to obtain the spherical phosphogypsum. In the present disclosure, the solidification may preferably be conducted by stacking under normal conditions or an autoclave treatment. In the present disclosure, there are no particular limitations on the time for the natural stacking, and the globular material could be naturally stacking for a period of time until that the strength of the spherical phosphogypsum could meet the requirements according to the above technical solution. During the stacking, the physical strength of the spherical phosphogypsum continues to increase. In a specific example of the present disclosure, when the cement is rapid-hardening SAC, the spherical phosphogypsum could have a certain physical strength after being stacked for 45 min.

[0036] In the present disclosure, the autoclave treatment may be conducted preferably at a temperature of 100 °C to 110 °C, and the autoclave treatment may be conducted preferably for 20 min to 40 min, and more preferably 30 min. In a specific example of the present disclosure, the autoclave treatment may be conducted preferably in a high-temperature and high-pressure reactor. The method of the present disclosure promotes the progress of cement hydration through the autoclave treatment, thereby promoting the solidification of the spherical phosphogypsum.

[0037] In the present disclosure, when the spherical phosphogypsum may further include a cement shell covering the surface. In the present disclosure, after the globular material is obtained, the globular material may preferably be placed in a cement slurry to be coated with the cement slurry, and then the coated globular material is solidified to obtain the spherical phosphogypsum. In the present disclosure, the cement slurry may preferably have a solid content of 90% to 95%. In the present disclosure, a solid content of the cement slurry defined within the above range facilitates a smooth coating on the surface of the globular material. In a specific example of the present disclosure, preferably, the globular material discharged from the pan-type double-stirring pelletizer may directly drop into a cement slurry such that the globular materials are uniformly coated with a layer of the cement slurry, and then the globular material is taken out by a mesh scraper and solidified. In the present disclosure, a means for the solidification may preferably be the same as described in the above technical solution, which will not be repeated here.

[0038] In the present disclosure, after the spherical phosphogypsum is obtained, the diameter and the physical strength of the spherical phosphogypsum are measured. The diameter is measured according to a method including the following steps: taking 2 kg of a reduced sample and sieving by using a sieve with an opening of 10 mm in diameter, and randomly selecting 20 solid globular materials in the sieve; and measuring the diameters of the selected solid globular materials by using a vernier caliper meeting the requirements in GB/T21389-2008, to the nearest 1 mm, wherein among the selected globular materials, 16 or more globular materials have a maximum diameter of 20 mm to 30 mm.

[0039] In the present disclosure, the physical strength is measured according to a method including the following steps: weighing 2 kg of a reduced sample and sieving by using a sieve with an opening of 10 mm in diameter, and selecting 20 solid globular materials with well-retained appearance in the sieve (the selected globular materials have a maximum diameter of 20 mm to 30 mm); and measuring a compressive strength by using a press machine conforming to the verification regulations of JJG-1986 Electronic Universal Testing Machine, to the nearest 0.1 N.

[0040] The present disclosure also provides use of the spherical phosphogypsum according to the above technical solution or the spherical phosphogypsum prepared by the preparation method according to the above technical solution in cement, wherein the spherical phosphogypsum may be added in an amount of 5% to 8%, preferably 6% to 7% of the mass of the cement. The spherical phosphogypsum of the present disclosure, when added into the cement, could have a retarding effect. Where the modifying agent includes alkaline lignin, the spherical phosphogypsum could also increase the cement strength and reduce the water used for mixing. Where the modifying agent includes ferrous sulfate, the spherical phosphogypsum could also reduce the content of water-soluble hexavalent chromium in cement. Where the modifying agent includes both alkaline lignin and ferrous sulfate, the spherical phosphogypsum has all the above-mentioned functions. In the present disclosure, there are no particular limitations on a specific method for using the spherical phosphogypsum, and a method well known to those skilled in the art may be adopted. Specifically, the spherical phosphogypsum may preferably be crushed and then added into a cement.

[0041] The technical solutions of the present disclosure will be clearly and completely described below with reference to the examples of the present disclosure.

[0042] In the following examples, waste residue produced in a wet process for preparing phosphoric acid from phosphate rock was used as a phosphogypsum powder; the product obtained by subjecting a papermaking black liquor to an evaporation to dry was used as alkaline lignin; and waste residue produced from the production of titanium dioxide was used as ferrous sulfate .

Example 1

[0043] In parts by mass, 97 parts of a phosphogypsum powder, 3 parts of rapid-hardening SAC, and 0.1 part of alkaline lignin (as a modifying agent) were taken and subjected to a pelletization in a pan-type double-stirring pelletizer until that the obtained globular materials had a diameter of 20 mm to 30 mm. The globular materials were discharged from a pelletizing plate and dropped into a PPS32.5R cement slurry (with a solid content of 95%), such that the globular materials were uniformly coated with a layer of the cement slurry

Then the globular materials were taken out by a mesh scraper, delivered into a high-temperature and high-pressure reactor over a conveyor belt, and subjected to an autoclave treatment at 105 °C for 20 min to obtain the spherical phosphogypsum.

[0044] The obtained spherical phosphogypsum had a 1-day strength of 30 N, a 3-day strength of 50 N, a 7-day strength of 90 N, a1-day moisture content of 15 wt%, a 3-day moisture content of 11 wt%, a 7-day moisture content of 9 wt%, a soluble P205 content of 0.6 wt%, a PH value of 8, a SO3 content of 38.5 wt%, a crystal water content of 12 wt%, a water-soluble F content of 0.30 wt%, and a pelletizing rate of 93%.

Example 2

[0045] Spherical phosphogypsum was prepared as described in Example 1, except that 97 parts of the phosphogypsum powder, 3 parts of P.052.5 cement, and 0.1 part of alkaline lignin (as a modifying agent) were used as raw materials instead, and a cement slurry with a solid content the same as in Example 1 was prepared with P.052.5 cement.

[0046] The obtained spherical phosphogypsum had a 1-day strength of 20 N, a 3-day strength of 45 N, a 7-day strength of 85 N, a1-day moisture content of 13.8 wt%, a 3-day moisture content of 10.5 wt%, a 7-day moisture content of 8.8 wt%, a soluble P205 content of 0.6 wt%, a PH value of 8.5, a S03 content of 38.7 wt%, a crystal water content of 12 wt%, a water-soluble F content of 0.30 wt%, and a pelletizing rate of 9 1 %.

Example 3

[0047] Spherical phosphogypsum was prepared as described in Example 1, except that 97 parts of the phosphogypsum powder, 3 parts of P.042.5R cement, and 0.1 part of alkaline lignin (as a modifying agent) were used as raw materials instead, and a cement slurry with a solid content the same as in Example 1 was prepared with P.042.5R cement.

[0048] The obtained spherical phosphogypsum had a 1-day strength of 12 N, a 3-day strength of 35 N, a 7-day strength of 82 N, a1-day moisture content of 12.6 wt%, a 3-day moisture content of 11.5 wt%, a 7-day moisture content of 9.2 wt%, a soluble P205 content of 0.6 wt%, a PH value of 8.3, a S03 content of 38.4 wt%, a crystal water content of 12 wt%, a water-soluble F content of 0.30 wt%, and a pelletizing rate of 90.5%.

Example 4

[0049] Spherical phosphogypsum was prepared as described in Example 1, except that 97 parts of the phosphogypsum powder, 3 parts of PPS32.5R cement, and 0.1 part of alkaline lignin (as a modifying agent) were used as raw materials instead, and a cement slurry with a same solid content the same as in Example 1 was prepared with PPS32.5R cement.

[0050] The obtained spherical phosphogypsum had a 1-day strength of 9 N, a 3-day strength of 29 N, a 7-day strength of 80 N, a1-day moisture content of 12.9 wt%, a 3-day moisture content of 11.8 wt%, a 7-day moisture content of 9.3 wt%, a soluble P205 content of 0.6 wt%, a PH value of 8.0, a S03 content of 38.0 wt%, a crystal water content of 11.8 wt%, a water-soluble F content of 0.30 wt%, and a pelletizing rate of 90%.

Example 5

[0051] In parts by mass, 97 parts of a phosphogypsum powder, 3 parts of rapid-hardening SAC, and 0.1 part of alkaline lignin (as a modifying agent) were taken and subjected to a pelletization in a pan-type double-stirring pelletizer until that the obtained globular materials had a diameter of 20 mm to 30 mm. The globular materials were discharged from a pelletizing plate and dropped into a PPS32.5R cement slurry (with a solid content of 94%), such that the globular materials were uniformly coated with a layer of the cement slurry. Then the globular materials were taken out by a mesh scraper, delivered to a warehouse over a conveyor belt, and stacked under natural conditions.

[0052] The obtained spherical phosphogypsum had a 1-day strength of 25 N, a 3-day strength of 49 N, a 7-day strength of 88 N, a1-day moisture content of 15.2 wt%, a 3-day moisture content of 11.5 wt%, a 7-day moisture content of 9.2 wt%, a soluble P205 content of 0.6 wt%, a PH value of 8, a S03 content of 38.6 wt%, a crystal water content of 11.8 wt%, a water-soluble F content of 0.30 wt%, and a pelletizing rate of 92%.

Example 6

[0053] Spherical phosphogypsum was prepared as described in Example 5, except that 97 parts of the phosphogypsum powder, 3 parts of P.052.5 cement, and 0.1 part of alkaline lignin (as a modifying agent) were used as raw materials instead, and a cement slurry with a solid content the same as in Example 5 was prepared with P.052.5 cement.

[0054] The obtained spherical phosphogypsum had a 1-day strength of 15 N, a 3-day strength of 37 N, a 7-day strength of 82 N, a1-day moisture content of 13.9 wt%, a 3-day moisture content of 10.8 wt%, a 7-day moisture content of 8.9 wt%, a soluble P205 content of 0.6 wt%, a PH value of 8.5, a S03 content of 38.8 wt%, a crystal water content of 11.7 wt%, a water-soluble F content of 0.30 wt%, and a pelletizing rate of 90.8%.

Example 7

[0055] Spherical phosphogypsum was prepared as described in Example 5, except that 97 parts of the phosphogypsum powder, 3 parts of P.042.5R cement, and 0.1 part of alkaline lignin (as a modifying agent) were used as raw materials instead, and a cement slurry with a solid content the same as in Example 5 was prepared with P.042.5R cement.

[0056] The obtained spherical phosphogypsum had a 1-day strength of 8 N, a 3-day strength of 29 N, a 7-day strength of 81 N, a1-day moisture content of 12.7 wt%, a 3-day moisture content of 11.7 wt%, a 7-day moisture content of 9.4 wt%, a soluble P205 content of 0.6 wt%, a PH value of 8.3, a SO3 content of 37.9 wt%, a crystal water content of 11.2 wt%, a water-soluble F content of 0.30 wt%, and a pelletizing rate of 90.3%.

Example 8

[0057] Spherical phosphogypsum was prepared as described in Example 5, except that 97 parts of the phosphogypsum powder, 3 parts of PPS32.5R cement, and 0.1 part of alkaline lignin (as a modifying agent) were used as raw materials instead, and a cement slurry with a solid content the same as in Example 5 was prepared with P.042.5R cement.

[0058] The obtained spherical phosphogypsum had a 1-day strength of 4 N, a 3-day strength of 12 N, a 7-day strength of 71 N, a1-day moisture content of 13.4 wt%, a 3-day moisture content of 12.5 wt%, a 7-day moisture content of 9.8 wt%, a soluble P205 content of 0.6 wt%, a PH value of 8.1, a S03 content of 39.2 wt%, a crystal water content of 12.3 wt%, a water-soluble F content of 0.30 wt%, and a pelletizing rate of 89%.

Example 9

[0059] Spherical phosphogypsum was prepared as described in Example 1, except that 97 parts of the phosphogypsum powder, 3 parts of P.S.A32.5 cement, and 0.1 part of iron sulfate heptahydrate (as a modifying agent) were used as raw materials instead, and a cement slurry with a solid content the same as in Example 1 was prepared with P.S.A32.5 cement.

[0060] The obtained spherical phosphogypsum had a 1-day strength of 8 N, a 3-day strength of 26 N, a 7-day strength of 73 N, a1-day moisture content of 12.6 wt%, a 3-day moisture content of 11.9 wt%, a 7-day moisture content of 9.4 wt%, a soluble P205 content of 0.5 wt%, a PH value of 7.6, a S03 content of 38.6 wt%, a crystal water content of 11.5 wt%, a water-soluble F content of 0.25 wt%, and a pelletizing rate of 92%.

Example 10

[0061] Spherical phosphogypsum was prepared as described in Example 1, except that 97 parts of the phosphogypsum powder, 3 parts of P.S.B32.5 cement, and 0.1 part of iron sulfate heptahydrate (as a modifying agent) were used as raw materials instead, and a cement slurry with a solid content the same as in Example 1 was prepared with P.S.B32.5 cement.

[0062] The obtained spherical phosphogypsum had a 1-day strength of 9 N, a 3-day strength of 30 N, a 7-day strength of 76 N, a1-day moisture content of 13.0 wt%, a 3-day moisture content of 12.1 wt%, a 7-day moisture content of 9.6 wt%, a soluble P205 content of 0.6 wt%, a PH value of 7.8, a SO3 content of 39.2 wt%, a crystal water content of 10.9 wt%, a water-soluble F content of 0.31 wt%, and a pelletizing rate of 91.4%.

Example 11

[0063] Spherical phosphogypsum was prepared as described in Example 5, except that 97 parts of the phosphogypsum powder, 3 parts of P.P32.5 cement, and 0.1 part of iron sulfate heptahydrate (as a modifying agent) were used as raw materials instead, and a cement slurry with a solid content the same as in Example 5 was prepared with P.P32.5 cement.

[0064] The obtained spherical phosphogypsum had a 1-day strength of 3.5 N, a 3-day strength of 12.8 N, a 7-day strength of 73 N, a 1-day moisture content of 12.6 wt%, a 3-day moisture content of 11.5 wt%, a 7-day moisture content of 8.9 wt%, a soluble P205 content of 0.4 wt%, a PH value of 8.0, a S03 content of 38.7 wt%, a crystal water content of 11.2 wt%, a water-soluble F content of 0.29 wt%, and a pelletizing rate of 90%.

Example 12

[0065] Spherical phosphogypsum was prepared as described in Example 5, except that 97 parts of the phosphogypsum powder, 3 parts of PPS32.5R cement, and 0.1 part of iron sulfate heptahydrate (as a modifying agent) were used as raw materials instead, and a cement slurry with a solid content the same as in Example 5 was prepared with PPS32.5R cement.

[0066] The obtained spherical phosphogypsum had a 1-day strength of 3.6 N, a 3-day strength of 12.5 N, a 7-day strength of 74 N, a 1-day moisture content of 12.2 wt%, a 3-day moisture content of 11.8 wt%, a 7-day moisture content of 8.3 wt%, a soluble P205 content of 0.5 wt%, a PH value of 8.0, a S03 content of 38.5 wt%, a crystal water content of 11.0 wt%, a water-soluble F content of 0.26 wt%, and a pelletizing rate of 91%.

Example 13

[0067] Spherical phosphogypsum was prepared as described in Example 5, except that 97 parts of the phosphogypsum powder, 3 parts of P.F32.5 cement, and 0.1 part of iron sulfate heptahydrate (as a modifying agent) were used as raw materials instead, and a cement slurry with a solid content the same as in Example 5 was prepared with P.F32.5 cement.

[0068] The obtained spherical phosphogypsum had a 1-day strength of 4 N, a 3-day strength of 15 N, a 7-day strength of 74 N, a1-day moisture content of 13.0 wt%, a 3-day moisture content of 12.1 wt%, a 7-day moisture content of 8.5 wt%, a soluble P205 content of 0.3 wt%, a PH value of 8.2, a S03 content of 39.4 wt%, a crystal water content of 10.9 wt%, a water-soluble F content of 0.34 wt%, and a pelletizing rate of 90.2%.

Example 14

[0069] Spherical phosphogypsum was prepared as described in Example 5, except that 97 parts of the phosphogypsum powder, 3 parts of P.C42.5 cement, and 0.1 part of iron sulfate heptahydrate (as a modifying agent) were used as raw materials instead, and a cement slurry with a solid content the same as in Example 5 was prepared with P.C42.5 cement.

[0070] The obtained spherical phosphogypsum had a 1-day strength of 7 N, a 3-day strength of 30 N, a 7-day strength of 82 N, a1-day moisture content of 12.1 wt%, a 3-day moisture content of 11.6 wt%, a 7-day moisture content of 9.2 wt%, a soluble P205 content of 0.26 wt%, a PH value of 7.9, a S03 content of 39.8 wt%, a crystal water content of 10.4 wt%, a water-soluble F content of 0.28 wt%, and a pelletizing rate of 9 1 %.

Example 15

[0071] Spherical phosphogypsum was prepared as described in Example 5, except that 97 parts of the phosphogypsum powder, 3 parts of rapid-hardening SAC, and 0.1 part of iron sulfate heptahydrate (as a modifying agent) were used as raw materials instead, and a cement slurry with a solid content the same as in Example 5 was prepared with P.S.B32.5 cement.

[0072] The obtained spherical phosphogypsum had a 1-day strength of 26 N, a 3-day strength of 50 N, a 7-day strength of 87 N, a1-day moisture content of 14.1 wt%, a 3-day moisture content of 12.3 wt%, a 7-day moisture content of 8.9 wt%, a soluble P205 content of 0.31 wt%, a PH value of 8, a S03 content of 39.4 wt%, a crystal water content of 10.1 wt%, a water-soluble F content of 0.24 wt%, and a pelletizing rate of 90.5%.

Example 16

[0073] Spherical phosphogypsum was prepared as described in Example 5, except that 99 parts of the phosphogypsum powder, 3 parts of rapid-hardening SAC, and 0.1 part of iron sulfate heptahydrate and 0.1 part of alkaline lignin (as a modifying agent) were used as raw materials instead, and a cement slurry with a solid content the same as in Example 5 was prepared with P.S.B32.5 cement.

[0074] The obtained spherical phosphogypsum had a 1-day strength of 24 N, a 3-day strength of 48 N, a 7-day strength of 85 N, a1-day moisture content of 13.9 wt%, a 3-day moisture content of 12.4 wt%, a 7-day moisture content of 8.7 wt%, a soluble P205 content of 0.39 wt%, a PH value of 7.5, a S03 content of 39.8 wt%, a crystal water content of 10.4 wt%, a water-soluble F content of 0.36 wt%, and a pelletizing rate of 89.5%.

Example 17

[0075] Spherical phosphogypsum was prepared as described in Example 5, except that 98 parts of the phosphogypsum powder, 4 parts of rapid-hardening SAC, and 0.1 part of iron sulfate heptahydrate, and 0.1 part of alkaline lignin (as a modifying agent) were used as raw materials instead, and a cement slurry with a solid content the same as in Example 5 was prepared with P.S.B32.5 cement.

[0076] The obtained spherical phosphogypsum had a 1-day strength of 26 N, a 3-day strength of 47 N, a 7-day strength of 86 N, a1-day moisture content of 14.1 wt%, a 3-day moisture content of 12.6 wt%, a 7-day moisture content of 8.9 wt%, a soluble P205 content of 0.31 wt%, a PH value of 7.9, a S03 content of 38.7 wt%, a crystal water content of 10.7 wt%, a water-soluble F content of 0.32 wt%, and a pelletizing rate of 89.9%.

Use Example

[0077] The spherical phosphogypsum products prepared in Examples 1to 17 were used in a cement clinker, separately, and the physical properties of obtained set cement were determined specifically as follows: the spherical phosphogypsum was crushed and mixed with a cement clinker, and the resulting mixture was milled in a small laboratory mill; the milled material was adjusted to a standard consistency with water (see GB/T1346 "Test method for water requirement of normal consistency, setting time, and soundness of the portlamd cements"), then incubated under natural conditions, and subjected to physical property tests. The cement clinker was an OPC clinker. The milling was conducted by using a small laboratory mill.

[0078] Natural gypsum was used as a control, which was labeled as Comparative Example 1, and desulfurized gypsum was also used as a control, which was labeled as Comparative Example 2. The natural gypsum had a S03 content of 36%, and the desulfurized gypsum had a S03 content of 36%.

[0079] The amount of cement clinker and spherical phosphogypsum (or other types of gypsum) and the milling time (by using a small laboratory mill) were shown in Table 1. The setting time, strength, and chromium content of the cement were tested, and the results were shown in Table 2.

[0080] Table 1 The amount of cement clinker and spherical phosphogypsum (or other types of gypsum) and the milling time

The amount of cement Milling time The amount of spherical Item clinker (wt%) (min) phosphogypsum (or other types of gypsum) (wt%) Examples I to 17 94 28 6 (spherical phosphogypsum) Comparative 94 28 6 (natural gypsum) Example_ I ___________

Comparative 94 28 6 (desulfurized gypsum) Example_2 ___________

Table 2 Performance test results Water Initial Final 3-day 28-day Water-solubl requireme Initia 3-day flexura 28-day flexura a o Item nt for compressiv 1 compressiv 1 chromium standard Time Time e strength strengt e strength strengt content consistency (min) (min) (MPa) h (MPa) h (mg/kg) y (%) (Mpa) (MPa) Example 1 21.70 90 148 34.0 6.5 8.7 58.2 9.8 Example 2 21.20 95 151 35.6 6.3 9.1 59.6 9.7 Example 3 21.40 96 159 34.2 6.1 9.0 58.8 9.7 Example 4 21.10 98 161 34.0 6.1 9.0 58.4 9.7 Example 5 21.00 85 139 37.2 6.7 9.1 59.5 9.7 Example 6 21.50 80 136 37.3 6.7 9.1 59.7 9.8 Example 7 21.80 84 142 35.4 6.6 9.0 58.0 9.7 Example 8 21.80 85 152 35.0 6.5 9.0 57.8 9.7 Example 9 23.00 90 143 35.8 6.4 8.6 57.6 3.2 Example 23.00 92 144 34.4 6.3 8.5 57.5 3.3 10 Example 11 22.90 96 150 34.4 6.2 8.4 57.7 3.2 Example 23.00 95 145 34.5 6.3 8.3 57.7 3.4 12 Example 23.00 99 157 34.1 6.3 8.3 58.0 3.2 13 Example 23.10 88 148 34.8 6.5 8.4 58.3 3.2 14 Example 22.30 92 152 35.9 6.6 8.7 57.8 3.3 151

Example 21.80 90 145 34.8 6.6 8.8 58.5 3.1 16 Example 21.30 90 147 35.0 6.6 8.7 58.1 3.2 17 Comparativ e Example 22.80 89 144 34.1 6.2 8.2 56.1 9.7 1 Comparativ e Example 23.40 90 147 34.0 6.2 8.2 56.8 9.8 2

[0081] It can be seen from Table 2 that, when added into a cement, the spherical phosphogypsum of the present disclosure could prolong the setting time of cement; where the modifying agent is alkaline lignin, the spherical phosphogypsum could also increase the cement strength and reduce water demand for the mixing; where the modifying agent is ferrous sulfate, the spherical phosphogypsum could greatly reduce the content of water-soluble hexavalent chromium in the cement; the spherical phosphogypsum of the present disclosure shows retarding performance similar to that of natural phosphogypsum, and thus could replace natural gypsum, thereby realizing the purpose of protecting natural resources and promoting the utilization of national solid waste .

[0082] The above descriptions are merely preferred implementations of the present disclosure. It should be noted that a person of ordinary skill in the art may further make several improvements and modifications without departing from the principle of the present disclosure, but such improvements and modifications should be deemed as falling within the protection scope of the present disclosure.

Item 1. A spherical phosphogypsum, which is prepared from raw materials comprising in parts by mass, 90 to 99 parts of a phosphogypsum powder, 3 to 10 parts of a cement, and 0.1 to 2 parts of a modifying agent, wherein the modifying agent comprises alkaline lignin and/or ferrous sulfate.

Item 2. The spherical phosphogypsum as set forth in Item 1, wherein the alkaline lignin is obtained by subjecting a papermaking black liquor to an evaporation to dry; the ferrous sulfate is waste residue produced from the production of titanium dioxide.

Item 3. The spherical phosphogypsum as set forth in Item 1, wherein the cement is one or more selected from the group consisting of a sulfoaluminate cement, a portland cement, an ordinary portland cement, a portland slag cement, a portland-pozzolana cement, a portland fly-ash cement, a portland composite cement, and a portland phosphorous-slag cement.

Item 4. The spherical phosphogypsum as set forth in Item 3, wherein the ordinary Portland cement has a model of P.052.5 or P.042.5R; the portland slag cement has a model of P.S.A32.5 or P.S.B32.5; the portland-pozzolana cement has a model of P.P32.5; the portland fly-ash cement has a model of P.F32.5; the portland composite cement has a model of P.C42.5R; the portland phosphorous-slag cement has a model of PPS32.5R; and the sulfoaluminate cement is a rapid-hardening sulfoaluminate cement.

Item 5. The spherical phosphogypsum as set forth in Item 1, wherein an outer surface of the spherical phosphogypsum is covered with a cement shell, and the cement shell is formed by solidifying a cement slurry, and has a thickness of 2 mm to 3 mm.

Item 6. The spherical phosphogypsum as set forth in any one of Items 1 to 5, wherein the spherical phosphogypsum has a diameter of 20 mm to 30 mm, a 7-day strength of more than 80 N, a 7-day moisture content of less than 12 wt%, a crystal water content of more than 10 wt%, a S03 content of more than 30 wt%, a pH value of larger than 7.5, a water-soluble P205 content of 0.1 wt% to 0.8 wt%, a water-soluble F content of < 0.50 wt%, and a pelletizing rate of > 89%.

Item 7. A method for preparing the spherical phosphogypsum as set forth in any one of Items 1 to 4 and 6, comprising (1) mixing the phosphogypsum powder, the cement, and the modifying agent, and subjecting the resulting mixture to a pelletization to obtain a globular material; and (2) solidifying the globular material to obtain the spherical phosphogypsum.

Item 8. The method as set forth in Item 7, wherein the pelletization is conducted by using a pan-type double-stirring pelletizer; the pan-type double-stirring pelletizer has a pan rotational speed of 14 rpm to 16 rpm.

Item 9. The method as set forth in Item 7 or 8, further comprising, after the globular material is obtained, placing the globular material in a cement slurry to be coated with the cement slurry.

Item 10. The method as set forth in Item 9, wherein the cement slurry has a solid content of 90% to 95%.

Item 11. The method as set forth in Item 7, wherein solidifying the globular material is achieved by stacking under normal conditions or an autoclave treatment; the autoclave treatment is conducted at 100 °C to 110 °C for 20 min to 40 min.

Item 12. Use of the spherical phosphogypsum as set forth in any one of Items 1 to 6 or the spherical phosphogypsum prepared by the method as set forth in any one of Items 7 to 11 in cement, wherein the spherical phosphogypsum is added in an amount of 5% to 8% of the mass of the cement.

Claims

WHAT IS CLAIMED IS:

1. A spherical phosphogypsum, which is prepared from raw materials comprising in parts by mass, 90 to 99 parts of a phosphogypsum powder, 3 to 10 parts of a cement, and 0.1 to 2 parts of a modifying agent, wherein the modifying agent comprises alkaline lignin and/or ferrous sulfate.

2. The spherical phosphogypsum as claimed in claim 1, wherein the alkaline lignin is obtained by subjecting a papermaking black liquor to an evaporation to dry; the ferrous sulfate is waste residue produced from the production of titanium dioxide.

3. The spherical phosphogypsum as claimed in claim 1 or 2, wherein an outer surface of the spherical phosphogypsum is covered with a cement shell, and the cement shell is formed by solidifying a cement slurry, and has a thickness of 2 mm to 3 mm.

4. The spherical phosphogypsum as claimed in any one of claims 1 to 3, wherein the spherical phosphogypsum has a diameter of 20 mm to 30 mm, a 7-day strength of more than N, a 7-day moisture content of less than 12 wt%, a crystal water content of more than 10 wt%, a S03 content of more than 30 wt%, a pH value of larger than 7.5, a water-soluble P205 content of 0.1 wt% to 0.8 wt%, a water-soluble F content of < 0.50 wt%, and a pelletizing rate of> 89%.

5. A method for preparing the spherical phosphogypsum as claimed in any one of claims 1 to 4, comprising (1) mixing the phosphogypsum powder, the cement, and the modifying agent, and subjecting the resulting mixture to a pelletization to obtain a globular material; and (2) solidifying the globular material to obtain the spherical phosphogypsum.