Preparation method and application of hardness removal agent

Abstract

The invention relates to a preparation method and application of a hardness removal agent, and the method comprises the following steps: 1) alkali fusion reaction: mixing and fusing bauxite and NaOH to generate soluble sodium aluminate NaAlO2; 2) compounding silicon and aluminum: dissolving aluminum silicate in hot water, adding silica sol, stirring and mixing, and regulating the pH value to 11-12 by using NaOH; an aluminosilicate precursor gel is formed; 3) hydrothermal crystallization: transferring the aluminosilicate precursor gel into a high-pressure reaction kettle, and carrying out hydrothermal reaction to promote polymerization of a silicon-aluminum network; and 4) post-treatment: cooling aluminosilicate, centrifugally washing the aluminosilicate until the aluminosilicate is neutral, drying the aluminosilicate at 110 DEG C, and grinding the aluminosilicate to obtain a white powder product. A silicon-aluminum network structure of the hardness removal agent prepared by the method has regular pore channels, the highest calcium and magnesium removal rate can reach 90% or above, the hardness removal agent is high in anti-interference performance, is kept stable in a pH range of 6-12, is not influenced by common Cl <-> and SO4 < 2-> in water, and is high in stability.

Description

Technical Field

[0001] The invention belongs to the technical field of hardness removers, and particularly relates to a preparation method and application of a hardness remover. Background Art

[0002] Bauxite (also known as bauxite) is the primary raw material for the production of alumina (Al2O3) and aluminum. Its mining, beneficiation, and smelting processes generate significant amounts of solid waste. Improper disposal of this waste can lead to land occupation, environmental pollution, and resource waste. In recent years, with tightening environmental protection policies and the advancement of resource recycling technologies, the comprehensive utilization of bauxite solid waste has become a research hotspot.

[0003] At present, the main ways to utilize bauxite solid waste include:

[0004] (1) Building materials: used in the production of cement, ceramics, bricks and tiles, but with problems of low added value and limited consumption;

[0005] (2) Valuable metal recovery: extraction of metals such as aluminum, iron, and titanium, but economic feasibility is limited by extraction technology and market price fluctuations;

[0006] (3) Soil conditioner: Its alkalinity is used to improve acidic soil, but there is a risk that long-term use may cause soil compaction.

[0007] (4) Environmentally friendly materials: After modification, they can be used as adsorbents for wastewater treatment (such as removing heavy metals, phosphates, etc.), but the selective adsorption capacity for specific pollutants needs to be improved;

[0008] Although the use of modified bauxite as an environmentally friendly material has received widespread attention, the existing technology still has the following limitations:

[0009] (1) The modification process is complicated and often requires high temperature roasting or strong acid / alkali treatment, which is costly;

[0010] (2) For specific pollutants (such as Ca 2+ / Mg 2+ The adsorption selectivity of hardness ions is insufficient;

[0011] (3) The material has poor stability and is prone to structural collapse in complex water environments;

[0012] (4) The regeneration performance is poor, and the efficiency decreases significantly after multiple cycles.

[0013] It is worth noting that there has been no report on the use of bauxite to synthesize a water hardness remover (i.e., a hardness remover). The main technical challenges faced in this direction include:

[0014] (1) How to enhance Ca through directional modification 2+ / Mg2+ Selective adsorption;

[0015] (2) Develop efficient activation modification methods under mild conditions;

[0016] (3) Solve the stability problem of materials in acidic or high-salt water;

[0017] Breakthroughs in these key technologies are expected to open up new avenues for the high-value utilization of bauxite solid waste. Summary of the Invention

[0018] In view of the problems existing in the prior art, the purpose of the present invention is to provide a preparation method and application of a hardness remover, which is specifically achieved through the following technical solutions:

[0019] A method for preparing a hardness remover, the method comprising the following steps:

[0020] 1) Alkali fusion reaction: Bauxite is mixed with NaOH and melted at 500-600℃ for 1 hour to produce soluble sodium aluminate NaAlO2;

[0021] 2) Silicon-aluminum composite: dissolve aluminum silicate in hot water, add silica sol at a Si / Al molar ratio of 1:1-1.5:1, stir and mix, and adjust the pH to 11-12 with NaOH to form an aluminosilicate precursor gel;

[0022] 3) Hydrothermal crystallization: The aluminosilicate precursor gel prepared in step 2) is transferred to a high-pressure reactor and subjected to a hydrothermal reaction at a temperature of 120-180° C. for 6-12 hours to promote the polymerization of the aluminosilicate network;

[0023] 4) Post-treatment: The aluminosilicate after the hydrothermal reaction is cooled and then centrifuged and washed until neutral, dried at 110° C., and ground to obtain a white powder product.

[0024] Furthermore, in step 1), bauxite and NaOH are mixed at a mass ratio of 1:1-1.5, and the bauxite is pretreated by the following method: the bauxite is ground to 200 mesh and then calcined to destroy the crystal structure and improve the Al activity.

[0025] Furthermore, the calcination temperature is 600-800° C., and the calcination time is 2 hours.

[0026] Furthermore, in step 2), the silica sol is prepared by the following steps:

[0027] a) Using water glass as raw material, diluting the water glass and filtering to remove insoluble impurities;

[0028] b) passing the diluted water glass in step a) through a cation exchange resin column, Na + H +Replacement, generating active silicic acid solution, and then adjusting the pH with alkali to stabilize the colloid;

[0029] c) aging the active silicic acid solution of step b) at room temperature to promote the formation of SiO2 nuclei, and then concentrating it by evaporation under reduced pressure to a SiO2 content of 15-30% to obtain a stable silica sol.

[0030] Furthermore, in step a), the SiO2 content in the raw water glass is 20-30%, and the raw water glass is diluted to a SiO2 content of 5-10%.

[0031] Furthermore, in step b), the alkali adjustment of pH value is specifically to use NaOH to adjust the pH value to 8-10.

[0032] Furthermore, in step c), the aging at room temperature is specifically aging at 25-30° C. for 12-24 hours, and the temperature of the reduced pressure evaporation is 50-60° C.

[0033] The hardness remover prepared by the above preparation method is used to remove the hardness of black water and gray water in coal gasification.

[0034] The silicon-aluminum network structure of the hardness remover prepared by the method of the present invention has regular pores, and the calcium and magnesium removal rate can reach more than 90%. It has strong anti-interference ability and remains stable in the pH range of 6-12. It is not affected by common Cl - 、SO4 2- Impact, high stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 This is the infrared characterization spectrum of the hardness remover prepared in the embodiment of the present invention;

[0036] Figure 2 The XRD pattern of the hardness remover prepared in the embodiment of the present invention;

[0037] Figure 3 SEM images of the hardness remover prepared in an embodiment of the present invention ((a) is 195 times magnification, (b) is 450 times magnification);

[0038] Figure 4 This is an experimental effect diagram of the hardness remover prepared in an embodiment of the present invention;

[0039] Figure 5 This is a test diagram of the de-hardening agent prepared in an embodiment of the present invention for de-hardening black water from coal gasification;

[0040] Figure 6 This is a test diagram of the hardness removal agent prepared in an embodiment of the present invention on coal gas ash water;

[0041] Figure 7 The optimal dosage of the hardness remover prepared in the embodiment of the present invention is investigated. DETAILED DESCRIPTION

[0042] The present invention is further described below in conjunction with specific embodiments to facilitate a better understanding of the present technical solution.

[0043] Example: Preparation of hardness remover

[0044] 1. Preparation of silica sol (SiO2·nH2O)

[0045] 1) Dilution and filtration

[0046] Dilute water glass (Na2SiO3, SiO2 content 20-30%) to a SiO2 content of 5-10%, and filter to remove insoluble impurities.

[0047] 2) Ion exchange

[0048] The diluted water glass is passed through the cation exchange resin column, Na + H + Replacement, generating active silicic acid (H2SiO3) solution, and then adjust the concentration to 8-10 with NaOH to stabilize the colloid;

[0049] 3) Aging and concentration

[0050] The exchanged dilute silicic acid solution is aged at 25-30°C for 12-24 hours to promote the formation of SiO2 nuclei.

[0051] The mixture was concentrated by evaporation under reduced pressure (50-60° C.) to a SiO 2 content of 15-30% to obtain a stable silica sol.

[0052] 2. Pretreatment of bauxite (main component Al2O3·xSiO2·yH2O)

[0053] 1) Grinding: Grind to 200 mesh (≤75μm) to increase the reaction area.

[0054] 2) Calcination activation: Calcinate at 600-800℃ for 2 hours to destroy the crystal structure and increase the activity of Al.

[0055] 3. Synthesis of hardness remover (alkali fusion-hydrothermal synthesis method)

[0056] 1) Alkali fusion reaction

[0057] Bauxite and NaOH are mixed in a mass ratio of 1:1.2 and melted at 500-600℃ for 1 hour to generate soluble sodium aluminate (NaAlO2).

[0058] 2) Silicon-aluminum composite

[0059] The alkali fusion product was dissolved in hot water, and silica sol (Si / Al molar ratio 1:1-1.5:1) was added and stirred to mix.

[0060] The pH was adjusted to 11-12 with NaOH to form an aluminosilicate precursor gel.

[0061] 3) Hydrothermal crystallization

[0062] The mixture was transferred to a high-pressure reactor and subjected to hydrothermal reaction at 120-180° C. for 6-12 hours to promote the polymerization of the silicon-aluminum network.

[0063] 4) Post-processing

[0064] After cooling, centrifugation and washing are performed until neutrality is achieved, drying is performed at 110°C, and grinding is performed to obtain a white powder product, which is the hardness remover.

[0065] Characterization of the hardness remover obtained in the above embodiment:

[0066] 1. Infrared characterization spectrum of hardness remover Figure 1 As shown by Figure 1 Identify possible chemical bonds, 3442cm -1 and 1641cm -1 The two absorption peaks at 2346 cm are probably due to the stretching vibration of -OH and the bending vibration of adsorbed, polymerized and crystallized water in the coagulant. -1 The peak at 1390cm is caused by carbon dioxide in the air. -1 The absorption peak at 815 cm is attributed to the stretching and bending vibrations of Fe-OH-Fe or Al-OH-Al. -1 The absorption peak at wave number 665 cm corresponds to the Si-O-Si symmetric stretching vibration. -1 The peak at can be attributed to the bending vibration of Si-O-Fe bond. It indicates that polymer is formed in the sample. Figure 1 It can be seen that the new hardness remover is a complex compound formed by Fe, Al and Si.

[0067] 2. XRD pattern of the hardness remover Figure 2 As shown, Figure 2 The peaks at 15° and 17° are attributed to AlCl3·6H2O, which is due to the free Al 3+ The peaks at 32° and 46° are attributed to NaCl, which is a by-product formed during the drying process of the sample. Ca3Al2(SiO4)2(OH)4 (Hibschite) is a product formed during the synthesis of coagulants. It does not have much coagulation effect under neutral conditions, but it will release Ca under strong alkaline conditions (such as pH ≥ 12). 2+ and Al(OH)4 -This also explains why the coagulation effect improved with increasing alkalinity during the experiment. The AlFeSiO4 at 27° also corresponds to the Si-O-Fe and Si-O-Al bonds observed in the FT-IR. This indicates that the new de-hardening agent is a mixture of multiple complex compounds.

[0068] 3. The hard remover prepared in the embodiment of the present invention is an amorphous polymer composite material. The morphology thereof was observed by SEM. The results are as follows: Figure 3 As shown, from Figure 3 It can be clearly seen that many irregular particles are observed on the surface, the surface appears to be agglomerated, and a three-dimensional chain network structure appears. This structure has a good net-capturing and agglomerating effect.

[0069] The hardness remover prepared by the method of the present invention has the following advantages:

[0070] 1. Performance advantages:

[0071] 1. Highly efficient hardness removal capability

[0072] Synergistic effect: The silicon-aluminum network structure (NaP type zeolite) has regular pores Can be exchanged by ion (Na + Replacement of Ca 2+ / Mg 2+ ) and surface adsorption dual mechanism to remove hardness ions, with the calcium and magnesium removal rate reaching over 90% (traditional precipitation method is only 80-85%).

[0073] 2. Strong anti-interference ability: It remains stable in the pH range of 6-12 and is not affected by common Cl - 、SO4 2- Influence.

[0074] 3. Improved material stability

[0075] Thermal stability: Hydrothermally synthesized aluminosilicate crystals can withstand high temperatures of 300°C (traditional polyaluminium chloride decomposes at 150°C).

[0076] 2. Process economic advantages

[0077] The raw material cost of the present invention is 2.5 yuan / kg for bauxite + water glass, while the traditional chemical precipitation method uses sodium carbonate / calcium hydroxide for 4.8 yuan / kg. In terms of energy consumption, the hydrothermal reaction of the present invention consumes 1.2 kWh / kg, while the traditional chemical precipitation method consumes 3.5 kWh / kg for high-temperature calcination. The waste residue generated by the present invention is less than 3%, while the traditional chemical precipitation method produces 15-20% calcium sulfate residue. The de-hardening agent produced by the present invention maintains an efficiency of 90% after five regenerations, while the de-hardening agent produced by the traditional chemical precipitation method cannot be regenerated.

[0078] 3. Environmentally friendly advantages

[0079] The method of the present invention adopts a green synthesis process, without the use of sulfuric acid or hydrochloric acid in the whole process (compared to the 5% HCl required for ion exchange resin regeneration). The hydrothermal reaction is carried out in a closed manner, without the emission of volatile substances such as NH3 (different from the magnesium ammonium phosphate precipitation method). + Wastewater can be used to adjust pH, realizing sodium resource recycling. CO2 produced by roasting bauxite can be collected and used to adjust the pH of silica sol (forming a Na2CO3 buffer system).

[0080] 4. Water quality adaptability

[0081] The hardness remover prepared by the method of the present invention is still effective for high hardness (> 500mg / L CaCO3) water. 2+ / Mg 2+ ) and scale inhibition (silanol group inhibits the growth of CaCO3 crystal nuclei).

[0082] Application Examples

[0083] Study on the effect of hardness remover on the treatment of black water and gray water from coal gasification

[0084] The main components of coal gasification black water and gray water include suspended matter, hardness components and acidic gases. Common suspended matter in black water and gray water includes fine ash, slag, etc. These substances mainly come from the quenching chamber, carbon washing tower and slag pool in the entrained flow high pressure pulverized coal gasification process. In addition, black water and gray water also contain high hardness components, mainly calcium (Ca 2+ ), magnesium (Mg 2+ ) and other divalent cations, bicarbonate (HCO3 - ), sulfate (SO4 2- ), silicate (H3SiO4 - ) and phosphate (HPO4 2- ) and other anionic forms. These components not only affect the reuse of gray water, but also easily lead to scaling of pipes and equipment, increasing maintenance costs.

[0085] The main components and conventional indicators of the black water and gray water in the second phase of the coal-to-gas project of Zhejiang Petrochemical Co., Ltd. were analyzed, and the results are shown in Tables 1 and 2. As can be seen from the table, the black water and gray water both have high levels of inorganic ions. Inorganic ions such as calcium (Ca 2+ ), magnesium (Mg 2+ ) and other divalent cations, carbonate (HCO3 - ), sulfate (SO4 2- ), silicate (H3SiO4 -) are all high in content, which are ions that contribute to scaling and will form scaling components such as calcium carbonate (CaCO3), calcium sulfate (CaSO4), and magnesium silicate (MgSiO3).

[0086] Table 1 Routine analysis indicators of black water and grey water quality (1)

[0087]

[0088] Table 2 Routine analysis indicators of black water and grey water quality (2)

[0089]

[0090] During the production process, in order to ensure the stable operation of the ash water discharge and reuse system, key indicators are required, mainly including: pH 6-9, hardness mg / L <1000. In order to reduce the possibility of scaling in ash water reuse, the most effective measure is to reduce the cation that mainly contributes to scaling - calcium (Ca 2+ ), magnesium (Mg 2+ ) to remove it and reduce the burden of external drainage treatment.

[0091] Figure 4 The results of the hardness removal agent on coal gasification black water at different pH values ​​are shown. It can be seen that the hardness removal rate increases with increasing pH between 4 and 11, reaching 80% at a pH of 7.8 (raw water). The water after hardness removal is clearer, and the sediment appears as white, clumping flocs.

[0092] The effect of de-hardening agent on the de-hardening of coal gasification black water is as follows: Figure 5 As shown in the figure, the effect of removing hardness from coal gas ash water is as follows: Figure 6 As shown, the optimal dosage of the hardness remover is as follows Figure 7 shown.

[0093] Depend on Figure 5-7 It can be seen that low-sodium hardness remover is better for black water treatment, with the optimal dosage being 0.15-0.45 g / L, the hardness removal rate reaching 67%-73%, and the pH of the treated water being between 7-9, which is far better than the existing index requirements and on-site values, and meets the recycling requirements (hardness <500 mg / L).

Claims

1. A method for preparing a hardness remover, characterized in that: The method comprises the following steps: 1) Alkali fusion reaction: Bauxite is mixed with NaOH and melted at 500-600℃ for 1 hour to produce soluble sodium aluminate NaAlO2; 2) Silica-alumina composite: Dissolve aluminum silicate in hot water, add silica sol at a Si / Al molar ratio of 1:1-1.5:1, stir and mix, and adjust the pH to 11-12 with NaOH to form an aluminosilicate precursor gel; 3) Hydrothermal crystallization: The aluminosilicate precursor gel prepared in step 2) is transferred to a high-pressure reactor and subjected to a hydrothermal reaction at a temperature of 120-180°C for 6-12 hours to promote the polymerization of the aluminosilicate network; 4) Post-treatment: The silicic acid after the hydrothermal reaction is cooled and centrifuged and washed until neutral, dried at 110°C, and ground to obtain a white powder product.

2. The method for preparing a hardness remover according to claim 1, wherein In step 1), bauxite and NaOH are mixed at a mass ratio of 1:1-1.5, and the bauxite is pretreated by the following method: the bauxite is ground to 200 mesh and then calcined to destroy the crystal structure and improve the Al activity.

3. The method for preparing a hardness remover according to claim 2, wherein The calcination temperature is 600-800°C and the calcination time is 2 hours.

4. The method for preparing a hardness remover according to claim 1, wherein In step 2), the silica sol is prepared by the following steps: a) Using water glass as raw material, dilute the water glass and filter to remove insoluble impurities; b) passing the diluted water glass in step a) through a cation exchange resin column, Na + H + Replacement, generating active silicic acid solution, and then adjusting the pH with alkali to stabilize the colloid; c) aging the active silicic acid solution from step b) at room temperature to promote the formation of SiO2 nuclei, and then concentrating the solution by evaporation under reduced pressure to a SiO2 content of 15-30% to obtain a stable silica sol.

5. The method for preparing a hardness remover according to claim 4, wherein In step a), the SiO2 content in the raw water glass is 20-30%, and the SiO2 content is diluted to 5-10%.

6. The method for preparing a hardness remover according to claim 4, wherein In step b), the pH value is adjusted by using NaOH to adjust the pH value to 8-10.

7. The method for preparing a hardness remover according to claim 4, wherein In step c), the aging at room temperature is specifically aging at 25-30° C. for 12-24 hours, and the temperature of the reduced pressure evaporation is 50-60° C.

8. Use of the hardness remover prepared by the preparation method according to any one of claims 1 to 7 in removing the hardness of black water and gray water in coal gasification.

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