Method for preparing road cement-stabilized layer aggregate from fresh phosphogypsum

Abstract

The invention discloses a method for preparing road cement-stabilized layer aggregates from fresh phosphogypsum. S1, adjusting the pH value of phosphogypsum; s2, adding an agglomeration performance regulator to obtain phosphogypsum with agglomeration performance; s3, preparing slurry of a waterproof ardealite water-stable layer material by adopting the ardealite with the agglomeration performance obtained in the S2; and S4, mold forming is conducted, and granules are manufactured. According to the phosphogypsum road water stable layer aggregate prepared by the invention, the use amount of cement is greatly reduced, the volume change caused by water absorption and drainage of crystal water after ettringite is generated in phosphogypsum serving as a paving material is overcome, the phosphogypsum road water stable layer aggregate has good strength, water stability, heat preservation property and volume stability, and the performance of the phosphogypsum serving as the paving material is greatly improved.

Description

Technical Field

[0001] The present invention relates to the field of separation science and technology, industrial solid waste treatment, and particularly to the treatment and resource utilization of phosphogypsum. Background Art

[0002] Phosphogypsum is an inevitable solid by-product in the wet-process phosphoric acid process and the phosphate fertilizer industry, with the main component being calcium sulfate dihydrate. Currently, more than 90% of the existing phosphoric acid is prepared by the wet-process. For every 1 ton of phosphoric acid produced, approximately 5 tons of phosphogypsum will be generated. In China, about 80 million tons of phosphogypsum are newly added each year, and globally, more than 200 million tons of phosphogypsum are newly added each year.

[0003] Phosphogypsum can be made into materials such as cement setting retarders, phosphate fertilizers, blocks, gypsum boards, and wall plastering mortars. It can also be stockpiled after harmless treatment. However, the comprehensive utilization rate of phosphogypsum is not very high, and more phosphogypsum has not been utilized. Coupled with the fact that most phosphogypsum repositories will be sealed, it is extremely urgent to improve the comprehensive utilization rate of phosphogypsum.

[0004] During the process of highway construction, a large amount of subgrade materials are required. Conventional subgrade materials include stones, sand, and soil, etc. The massive consumption of these natural resources has caused serious ecological and environmental hazards. Nowadays, the cost of one ton of stones has reached more than 400 yuan, and most quarries have limited production quotas. While the stockpile of phosphogypsum is huge, using phosphogypsum to replace stones is a win-win situation.

[0005] The highway cement stabilized base layer means that the stabilized crushed stones are used as aggregates, and a certain amount and sufficient volume are used to fill the voids of the aggregates, and it is compacted according to the interlocking principle. It is close to... The strength mainly depends on the interlocking and locking principle between the crushed stones, and at the same time, there is enough mortar volume to fill the voids of the aggregates. The hydrophobic granular material made of phosphogypsum can perfectly replace stones and be used in the laying of highway cement stabilized base layers. Summary of the Invention

[0006] The purpose of the present invention is to broaden the path of comprehensive utilization of phosphogypsum, reduce the usage amount of natural stones, and provide a method for making highway cement stabilized base layer granular materials from fresh phosphogypsum. Through technical means, it is ensured that phosphogypsum can be used as highway cement stabilized base layer granular materials, forming a green, environmentally friendly, low-cost, and safe cement stabilized base layer granular material. On the premise of meeting the strength, water stability, and volume stability required for a building material of a transportation facility, this cement stabilized base layer granular material also has the characteristics of being green, environmentally friendly, low-cost, and safe.

[0007] A method for making highway cement stabilized base layer granular materials from fresh phosphogypsum, the method comprising the following steps: S1: Adjust the pH of the phosphogypsum; S2: Add an agglomeration property regulator to obtain phosphogypsum with agglomeration properties; S3: Prepare a slurry of the waterproof phosphogypsum water-stabilized layer material using the phosphogypsum with the agglomeration property obtained in S2; S4: Mold forming to produce granular materials.

[0008] The pH adjuster for phosphogypsum is one or more of calcium oxide, sodium hydroxide, sodium carbonate, and ammonia water.

[0009] The dosage of the pH adjuster is 5%-7% of the mass of fresh phosphogypsum, and the pH value is adjusted to about 6-8.

[0010] The agglomeration property regulator for phosphogypsum is one or more of magnesium chloride, barium chloride, calcium chloride, zinc chloride, cobalt chloride, nickel chloride, and copper chloride.

[0011] The addition amount of the phosphogypsum agglomeration property regulator is 1%-2% of the mass of fresh phosphogypsum.

[0012] The composition of the phosphogypsum water-stabilized layer slurry is phosphogypsum: standard sand: cement: activator: hydrophobic material = 53% - 58%: 35% - 45%: 2% - 3%: 1.5% - 2.0%: 1% - 2%.

[0013] The hydrophobic material is one or more of perfluorodecyltrimethoxysilane, perfluorodecyltriethoxysilane, perfluorooctyltrimethoxysilane, perfluorooctyltriethoxysilane, polyamide, polyacrylonitrile, polyester, acrylate, and molten paraffin.

[0014] The described activator is fly ash, aluminum silicate, or water glass.

[0015] The granular materials poured out from the mold are dried in the dark and sprayed with water to prevent cracking until completely solidified.

[0016] The advantages of this method are that it improves the strength and water stability of the composite material system, greatly reduces the dosage of cement, and can effectively avoid the formation of ettringite, reducing the risk of late-stage expansion and damage of the system. At the same time, the incorporation of external substances such as cement, fly ash, and lime makes the water-stabilized layer granular materials made of phosphogypsum have more excellent strength performance. Specific embodiments

[0017] Example 1 The technical solutions in the embodiments of the present invention will be clearly and completely described below. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0018] A method for producing highway water-stabilized layer granular materials from fresh phosphogypsum proposed by the present invention includes the following steps: (1) Dry mix fresh phosphogypsum with calcium oxide accounting for 5.5% of the mass of phosphogypsum and stir for 1.5 h to adjust the pH of the fresh phosphogypsum to about 6.8.

[0019] (2) Add 1% magnesium chloride and 0.5% nickel chloride to the fresh phosphogypsum in step (1), stir for 1 hour and then settle for 10 h to obtain phosphogypsum with agglomeration performance on the surface.

[0020] (3) Mix the phosphogypsum with agglomeration performance on the surface obtained in step (2) with materials to obtain a slurry of waterproof phosphogypsum water-stable layer material. The mixing ratio is phosphogypsum:sand:cement:activator water glass:hydrophobic material = 56%:36%:4%:2%:2%. The hydrophobic material is perfluorodecyltrimethoxysilane and perfluorodecyltriethoxysilane, each accounting for 1%.

[0021] (4) Add water accounting for 60% of the mass of cement to the mixture in step (3), stir for 55 min, pour the stirred slurry into a pebble-shaped mold, and form the mold to make pellets.

[0022] (5) The pellets obtained in step (4) are air-dried in the dark and appropriately sprayed with water to prevent them from cracking until they are completely solidified.

[0023] The obtained pellets are placed outdoors. The specific experiment was carried out in Xiaoting District, Yichang from May 15 to July 15, 2022. The precipitation during this period was 400 - 800 mm, the highest temperature was 36 °C, and the lowest temperature was 22 °C. After various natural factors such as rain, sun, and wind, collect the rainwater leaching the phosphogypsum pellets, and at the same time test the elements of the leachate every half month, mainly focusing on phosphorus and fluorine.

[0024] Table 1 F in the leachate and extract of phosphogypsum pellets - / mg / kg 15 / days 30 / days 45 / days 60 / days Leaching solution 0.50 0.67 0.72 0.80 Leachate 1.02 1.32 1.30 1.95 Table 2 PO4 in the leachate and extract of phosphogypsum pellets 3- / mg / kg 15 / days 30 / days 45 / days 60 / days Leaching solution Not detected Not detected Not detected Not detected Leachate Not detected Not detected Not detected Not detected Due to the formation of the hydrophobic material layer, the surface of the phosphogypsum has strong hydrophobic properties, and water only slides off the surface of the phosphogypsum pellets without entering the interior of the pellets. Therefore, water-soluble phosphorus and fluorine will not be carried away (the concentration of fluorine is less than the national first-class solid waste discharge standard). Therefore, the step of harmless treatment can be omitted.

[0025] Example 2 A method for making highway water-stable layer pellets from fresh phosphogypsum proposed by the present invention includes the following steps: (1). Dry-mix fresh phosphogypsum and calcium oxide accounting for 5.5% of the mass of phosphogypsum for 1.5 h to adjust the pH of the fresh phosphogypsum to about 6.8.

[0026] (2) Add 1% magnesium chloride and 0.5% calcium chloride to the fresh phosphogypsum in step (1) and stir for 1 hour.

[0027] (3) Mix the phosphogypsum obtained in step (2) with materials. The mixing ratio is phosphogypsum:sand:cement:aluminum silicate activator:hydrophobic material = 57.5%:36%:3%:1.5%:2%, where hydrophobic material 1 is perfluorodecyltrimethoxysilane, hydrophobic material 2 is perfluorooctyltriethoxysilane, hydrophobic material 3 is methyl methacrylate, and hydrophobic material 4 is polyamide, each accounting for 2%.

[0028] (4) Add water accounting for 60% of the mass of cement to the mixture in step (3), stir for 55 min, pour the well-stirred slurry into a pebble-shaped mold, and form the mold to make granular materials.

[0029] (5) Air-dry the granular materials obtained in step (4) in the dark and spray water appropriately to prevent them from cracking until they are completely solidified to obtain phosphogypsum water-stable layer granular materials.

[0030] After curing the above phosphogypsum water-stable layer granular materials for 7 days, 14 days, and 28 days respectively, dry them at 50 °C for 24 hours and immerse them completely for 2 hours to measure the mass water absorption rate: water absorption ratio W = (G1 - G0) / (G0) * 100 (%); the water droplet effect is judged by dripping water droplets, and the waterproof effect levels are as follows: 1 = very good, the surface is not wetted, and no water droplets remain on the surface; 2 = good, the surface is not wetted, but some water droplets remain on the surface; 3 = slightly wetted, no water droplet effect, but there is a waterproof layer on the surface; 4 = mostly wetted, no water droplet effect, and no waterproof layer effect on the surface; 5 = completely wetted.

[0031] Table 3 Hydrophobic experiment results of phosphogypsum water-stable layer granular materials Regarding the curing test results of 7 days plus 28 days, hydrophobic materials 1, 2, 3, and 4 all show good hydrophobic properties. And hydrophobic materials 2 - 4 show slightly smaller advantages than hydrophobic material 1 in terms of water droplet effect and lower water absorption rate. Considering the actual external weather resistance, the hydrophobic property and reagent engineering performance of hydrophobic material 3 are better because its long-chain silane has longer weather resistance than hydrophobic material 1.

[0032] Example 3 A method for making highway water-stable layer granular materials from fresh phosphogypsum proposed by the present invention includes the following steps: (1) Dry-mix fresh phosphogypsum and calcium oxide accounting for 5.5% of the mass of phosphogypsum for 1.5 h to adjust the pH of the fresh phosphogypsum to about 6.8.

[0033] (2) Add 1% cobalt chloride and 0.5% copper chloride to the fresh phosphogypsum in step (1) and stir for 1 hour.

[0034] (3) Mix the phosphogypsum obtained in step (2) with materials. The mixing ratio is phosphogypsum: standard sand: cement: activator: hydrophobic material = 53%: 40%: 4%: 1.5%: 1.5%. The hydrophobic material is 1% each of perfluorodecyltrimethoxysilane and perfluorodecyltriethoxysilane.

[0035] (4) Add water accounting for 60% of the mass of cement to the mixture in step (3), stir for 55 min, pour the well-stirred slurry into a pebble-shaped mold, and form the mold to make pellets.

[0036] (5) Air-dry the pellets obtained in step (4) in the dark and spray water appropriately to prevent them from cracking until they are completely solidified.

[0037] The following performance indicators are detected with reference to JTGF801 - 2012, JTG / T F20 - 2015 and JTGB01 - 2014.

[0038] Performance indicators of the phosphogypsum water-stabilized layer pellets in Table 4 Due to the addition of the hydrophobic agent and the agglomeration property regulator, the mechanical properties of the phosphogypsum water-stabilized layer pellets have been greatly improved.

[0039] Example 4 (1). Dry-mix fresh phosphogypsum and calcium oxide accounting for 5.5% of the mass of phosphogypsum for 1.5 h to adjust the pH of the fresh phosphogypsum to about 6.8.

[0040] (2) Add 1% magnesium chloride and 0.5% zinc chloride to the fresh phosphogypsum in step (1) and stir for 1 hour.

[0041] (3) Mix the phosphogypsum obtained in step (2) with materials. The mixing ratio is phosphogypsum: standard sand: cement: activator: hydrophobic material = 56%: 38%: 3%: 2%: 1%. The hydrophobic material is 1% perfluorodecyltriethoxysilane.

[0042] (4) Add water accounting for 60% of the mass of cement to the mixture in step (3), stir for 55 min, pour the well-stirred slurry into a pebble-shaped mold, and form the mold to make pellets.

[0043] (5) The pellets obtained in Step 4 are dried in the dark and appropriately sprayed with water to prevent them from cracking until they are completely solidified.

[0044] Performance comparison is made with the phosphogypsum water-stable layer pellets that only have the pH adjusted and no phosphogypsum agglomeration property adjuster added under the same other conditions. The following performance indicators are detected with reference to JTGF801-2012, JTG / TF20-2015 and JTGB01-2014.

[0045] Table 5 Performance comparison of water-stable layer pellets with or without phosphogypsum agglomeration property adjuster It can be seen from Table 5 that after adding the agglomeration property adjuster, even when the amount of cement used is very small, the loudness of the water-stable layer pellets is much greater than that of the water-stable layer pellets without the agglomeration property adjuster.

Claims

1. A method for making highway water-stable layer aggregate from fresh phosphogypsum, characterized in that, The method comprises the following steps: S1: Adjust the pH of phosphogypsum; S2: Add an agglomeration property regulator to obtain phosphogypsum with agglomeration property; S3: Use the phosphogypsum with agglomeration property obtained in S2 to prepare a slurry of a waterproof phosphogypsum water-stabilized layer material; S4: Mold to form pellets.

2. The method for manufacturing the highway water-stable layer aggregate with fresh phosphogypsum according to claim 1, characterized in that, The phosphogypsum pH regulator is one or more of calcium oxide, sodium hydroxide, sodium carbonate, and ammonia water.

3. The method for manufacturing highway water-stable layer aggregate from fresh phosphogypsum according to claim 2, characterized in that, The dosage of the pH regulator is 5%-7% of the mass of fresh phosphogypsum, and the pH value is adjusted to 6-8.

4. The method for manufacturing highway water-stable layer aggregate from fresh phosphogypsum according to claim 1, characterized in that, The phosphogypsum agglomeration property regulator is one or more of magnesium chloride, barium chloride, calcium chloride, zinc chloride, cobalt chloride, nickel chloride, and copper chloride.

5. The method for manufacturing highway water-stable layer aggregate from fresh phosphogypsum according to claim 4, characterized in that, The addition amount of the phosphogypsum agglomeration property regulator is 1%-2% of the mass of fresh phosphogypsum.

6. The method for manufacturing highway water-stable layer aggregate from fresh phosphogypsum according to claim 1, characterized in that, The composition of the phosphogypsum water-stabilized layer slurry is phosphogypsum with agglomeration property obtained in S2: standard sand: cement: activator: hydrophobic material = 53% - 58%: 35% - 45%: 3% - 4%: 1.5% - 2.0%: 1% - 2%.

7. The method for manufacturing highway water-stable layer aggregate from fresh phosphogypsum according to claim 6, characterized in that, The hydrophobic material is one or more of perfluorodecyltrimethoxysilane, perfluorodecyltriethoxysilane, perfluorooctyltrimethoxysilane, perfluorooctyltriethoxysilane, polyamide, polyacrylonitrile, polyester, acrylate, and molten paraffin.

8. The method for manufacturing the road water-stable layer aggregate from fresh phosphogypsum according to claim 6, characterized in that, The activator is fly ash, aluminum silicate, or water glass.

9. The method for preparing highway water-stabilized layer pellets from fresh phosphogypsum according to claim 1, wherein The pellets poured out from the mold are dried in the dark and sprayed with water to prevent cracking until completely solidified.

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