A preparation method of polyaluminium ferric chloride flocculant

Abstract

This invention provides a polyaluminum ferric chloride flocculant. The polyaluminum ferric chloride flocculant is prepared from secondary aluminum ash and coal-fired ash slag. The secondary aluminum ash is calcined and then hydrolyzed and polymerized with an acid extract of oxidized coal-fired ash slag to produce the polyaluminum ferric chloride flocculant. The resulting PAFC flocculant exhibits excellent flocculation properties and is effective in treating a variety of wastewaters, including domestic wastewater, printing and dyeing wastewater, and oily wastewater.

Description

Technical Field

[0001] The invention belongs to the technical field of sewage treatment, and particularly relates to a preparation method of a polyaluminium ferric chloride flocculant and a method for treating sewage by using the polyaluminium ferric chloride flocculant. Background Art

[0002] The production, processing, application, and recycling of aluminum products and related industries produces a type of scum, commonly referred to as aluminum ash, also known as secondary aluminum ash. For every ton of aluminum or aluminum alloy produced, approximately 30 to 50 kg of aluminum ash slag is generated. Consequently, the aluminum and aluminum alloy industries generate a significant amount of aluminum ash, the vast majority of which remains unused and is instead dumped in landfills. This not only results in a significant waste of resources but also has a significant impact on the environment. Therefore, developing low-cost, harmless treatment technologies or high-value-added resource recovery technologies is a key strategy to address the aluminum ash disposal challenge.

[0003] To ensure electricity safety and reduce costs, most aluminum smelters are built near power plants. Power plants' circulating fluidized bed boilers also produce tens of thousands of tons of circulating fluidized bed (CFB) ash annually. This ash, high in iron and aluminum, has high economic value and is an excellent raw material for producing highly efficient polyaluminum ferric chloride (PAFC) flocculants. Furthermore, compared to using FeCl₃ and AlCl₃ to produce PAFC, CFB ash is cheaper and more readily available.

[0004] PAFC flocculant is a highly efficient aluminum-iron inorganic composite flocculant widely used in the purification of various wastewaters. PAFC combines the excellent properties and strong charge neutralization capabilities of polyaluminum chloride flocculants with the strong adsorption capacity and rapid precipitation rates of polyferric chloride flocculants. This has made PAFC an increasingly popular choice for most wastewater treatment applications, leading to a surge in demand. However, the rising price of calcium aluminate powder, the raw material used in its preparation, has limited its research and application.

[0005] Therefore, this study aims to explore the harmless treatment process of secondary aluminum ash, prepare calcium aluminate material and use it as an alkalizing agent for CFB ash acid leaching solution, so as to prepare a high-efficiency composite flocculant PAFC. Summary of the Invention

[0006] To address these issues, the present invention harmlessly treats secondary aluminum ash to obtain a treated product containing calcium aluminate. This product is then added to an acid leaching solution from oxidized circulating fluidized bed (CFB) ash to produce a polyaluminum ferric chloride (PAFC) flocculant. The resulting PAFC flocculant exhibits excellent flocculation properties and is effective in treating a variety of wastewater types, including domestic wastewater, printing and dyeing wastewater, and oily wastewater.

[0007] One of the purposes of the present invention is to provide a method for preparing a polyaluminium ferric chloride flocculant. The method uses secondary aluminium ash and coal furnace ash slag as raw materials. After the secondary aluminium ash is calcified and roasted, it is hydrolysed and polymerized with an acid leaching solution of oxidized coal furnace ash slag to obtain the polyaluminium ferric chloride flocculant.

[0008] The calcification roasting is to mix the calcium source and the secondary aluminum ash, and then roast them in an oxygen-containing atmosphere, such as an air atmosphere.

[0009] The coal ash is added into the acid solution and kept warm for reaction to obtain the ash acid leaching solution.

[0010] The oxidized coal ash acid leaching solution is obtained by adding an oxidant to the coal ash acid leaching solution and reacting.

[0011] The present invention also aims to provide a sewage treatment method using the polyaluminium ferric chloride flocculant, preferably for treating domestic wastewater, printing and dyeing wastewater or oily wastewater. The sewage treatment method comprises adding the polyaluminium ferric chloride flocculant to the sewage.

[0012] The preparation method of the polyaluminium ferric chloride flocculant provided by the present invention has the following beneficial effects:

[0013] (1) The present invention uses secondary aluminum ash from aluminum smelting and coal furnace ash waste residue from power plants as raw materials to prepare polyaluminum ferric chloride flocculant, and performs harmless treatment on the secondary aluminum ash to achieve the reuse of solid waste.

[0014] (2) The preparation method of the polyaluminium ferric chloride flocculant provided by the present invention has a simple preparation process and can be processed on a large scale in an industrial process.

[0015] (3) The polyaluminium ferric chloride flocculant prepared by the present invention is non-toxic and has an excellent flocculation effect in an anhydrous treatment process.

[0016] For simulated domestic wastewater, the turbidity removal rate can reach 99%, the total phosphorus removal rate can reach 91.52%, and the COD removal rate can reach 61.56%. For simulated printing and dyeing wastewater, the color removal rate can reach 81.85%. For oily wastewater, the oil removal rate can reach 73.26%, and the suspension removal rate can reach 99.14%. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 The XRD pattern of the secondary aluminum ash in Example 1 of the present invention is shown;

[0018] Figure 2 The removal rate curves of turbidity, total phosphorus and COD in the wastewater at different flocculant addition amounts for treating simulated domestic wastewater in Example 5 of the present invention are shown;

[0019] Figure 3 The turbidity removal, phosphorus removal, and COD removal curves of PAFC at different pH values ​​in Example 5 of the present invention are shown;

[0020] Figure 4 The turbidity removal, phosphorus removal, and COD removal curves of PAFC at different temperatures in Example 5 of the present invention for treating simulated domestic wastewater are shown;

[0021] Figure 5 The chromaticity removal rate curves of acid red and vat blue simulated wastewater at different flocculant addition amounts in Example 6 of the present invention are shown;

[0022] Figure 6 The chromaticity removal rate curve of PAFCⅠ for vat blue and acid red dye wastewater at different pH values ​​in Example 6 of the present invention is shown;

[0023] Figure 7 The effect of temperature on the color removal performance of PAFC I in Example 6 of the present invention is shown.

[0024] Figure 8 The degreasing and suspended solids removal curves of PAFCⅠ for oil-containing anhydrous water at different flocculant addition amounts in Example 7 of the present invention are shown;

[0025] Figure 9 The oil removal and suspended solids removal capability curves of PAFCⅠ for oily wastewater at different pH values ​​in Example 7 of the present invention are shown;

[0026] Figure 10 FIG1 shows an XRD pattern of the calcified calcined product of secondary aluminum ash prepared in Example 1 of the present invention;

[0027] Figure 11 A graph showing the content of various components in the calcified roasted product of secondary aluminum ash prepared in Example 1 of the present invention;

[0028] Figure 12 Schematic diagram of the experimental setup for determining the content of aluminum nitride in secondary aluminum ash and its calcified roasted products by the Kjeldahl method. DETAILED DESCRIPTION

[0029] The present invention will be described in detail below through specific embodiments, and the features and advantages of the present invention will become clearer and more distinct with these descriptions.

[0030] The invention provides a preparation method of a polyaluminium ferric chloride flocculant. The method uses secondary aluminium ash and coal furnace ash slag as raw materials, calcines the secondary aluminium ash, and then hydrolyzes and polymerizes it with an acid leaching solution of oxidized coal furnace ash slag to obtain the polyaluminium ferric chloride flocculant.

[0031] The secondary aluminum ash is the slag produced by smelting aluminum or aluminum alloy from bauxite. The coal furnace ash is the ash produced by burning coal in a circulating fluidized bed boiler at 750-1000°C, preferably 800-950°C.

[0032] The secondary aluminum ash has an Al2O3 content of 35-45wt%, an AlN content of 15-25wt%, and an aluminum element content of 4-8wt%.

[0033] In the coal furnace ash, iron mainly exists in the form of oxides, and aluminum mainly exists in the form of anorthite and calcite.

[0034] The calcification roasting is to mix the calcium source and the secondary aluminum ash, and then roast them in an oxygen-containing atmosphere, such as an air atmosphere.

[0035] Preferably, the mixture of the calcium source and the secondary aluminum ash is first subjected to a grinding treatment, preferably a ball milling treatment, so that the average particle size of the mixture of the calcium source and the secondary aluminum ash after the treatment is 5-45 μm, preferably 10-35 μm, and more preferably 15-25 μm.

[0036] To ensure full contact between the secondary aluminum ash and the calcium source and increase the reaction area, ball milling and other methods are used to thoroughly mix the secondary aluminum ash and the calcium source. The grinding action also destroys the aluminum oxide layer on the AlN surface, exposing the AlN to air and facilitating the denitrification reaction. It also fully disperses the metallic aluminum, causing a significant degree of surface oxidation, thereby reducing its activity and avoiding the potential explosion caused by the combustion of the dust cloud.

[0037] The calcium source is selected from one or more of quicklime and calcium salts, preferably selected from one or more of quicklime, calcium carbonate and calcium nitrate, more preferably quicklime.

[0038] The mass ratio of the calcium source to the secondary aluminum ash is (0.3-0.9):1, preferably (0.4-0.8):1, and more preferably (0.5-0.7):1.

[0039] The calcination temperature is 500-1200°C, preferably 650-1100°C, and more preferably 800-1000°C. The calcination time is 1.5-5.5 hours, preferably 2-4.5 hours, and more preferably 2.5-3.5 hours. Calcification calcination under the above conditions can better achieve the harmless treatment of secondary aluminum ash and achieve optimal denitrification and fluorine fixation rates.

[0040] The AlN in secondary aluminum ash is unstable and can produce ammonia when exposed to water. It has poor thermal stability in air, and AlN and O2 are most likely to form N2 in the temperature range of 500-900°C. Furthermore, secondary aluminum ash contains soluble fluoride, making it classified as hazardous waste. Fluoride reacts with calcium aluminate at high temperatures to form calcium fluoroaluminate. Fluoride ions enter the calcium aluminate lattice, thereby securing fluoride and significantly reducing the leaching toxicity of the secondary aluminum ash. Therefore, the present invention uses the addition of a calcium source such as quicklime and high-temperature calcination to denitrify and secure fluoride from the secondary aluminum ash, producing a calcium aluminate material that can be used as an alkalizing agent.

[0041] In the present invention, after the secondary aluminum ash is calcined and roasted, the nitrogen in the secondary aluminum ash can be effectively removed, and the soluble fluoride can be fixed, thereby avoiding the dissolution of nitrogen and fluoride in the subsequent process, thereby realizing the denitrification and fluorine fixation harmless treatment of the secondary aluminum ash and resource utilization.

[0042] In the present invention, coal ash is added into an acid solution and kept warm for reaction to obtain an ash acid leaching solution.

[0043] The acid solution is hydrochloric acid or a mixed solution of hydrochloric acid and sulfuric acid. The hydrochloric acid concentration is 0.5-8 mol / L, preferably 1-10 mol / L, more preferably 1.5-6.5 mol / L. The sulfuric acid concentration is 1-3.5 mol / L, preferably 1.5-3 mol / L, more preferably 2-2.5 mol / L. Preferably, the acid solution is a mixed solution of 1.5-2.5 mol / L hydrochloric acid or 5.5-6.5 mol / L hydrochloric acid and 2-2.5 mol / L sulfuric acid (the volume ratio of the two is (2-4):1).

[0044] The solid-liquid ratio of the coal furnace ash slag to the acid solution is 1 g: (3-11) mL, preferably 1 g: (4-10) mL, and more preferably 1 g: (5-9) mL.

[0045] The heat preservation reaction temperature is 75-105°C, preferably 80-100°C, more preferably 85-95°C, and the reaction time is 2-8h, preferably 3-7h, more preferably 4-6h.

[0046] The oxidized coal ash acid leaching solution is obtained by adding an oxidant to the coal ash acid leaching solution and reacting. The oxidant is selected from one or more of chlorine water, hydrogen peroxide, and hypochlorite solution, preferably chlorine water and / or hydrogen peroxide, and more preferably hydrogen peroxide, such as 30 wt% hydrogen peroxide.

[0047] The calcined secondary aluminum ash is added to an acid leaching solution of oxidized coal furnace ash, heated to perform a hydrolysis polymerization reaction, filtered after the reaction, aged, and concentrated and dried to obtain a polyaluminum ferric chloride flocculant. The mass volume ratio of the calcined secondary aluminum ash to the acid leaching solution of oxidized coal furnace ash is 1.25:(4-18) mL, preferably 1.25:(6-15) mL, and more preferably 1.25:(8-12) mL.

[0048] The heating temperature is 50-110° C., preferably 60-100° C., more preferably 70-90° C. The heating time is 1-6 hours, preferably 1.5-5 hours, more preferably 2-4 hours.

[0049] The aging time is 10-36 hours, preferably 14-32 hours, and more preferably 20-28 hours.

[0050] The present invention also aims to provide a sewage treatment method using the polyaluminium ferric chloride flocculant, preferably for treating domestic wastewater, printing and dyeing wastewater or oily wastewater. The sewage treatment method comprises adding the polyaluminium ferric chloride flocculant to the sewage.

[0051] The pH value of the sewage is 3-14, preferably 4-12, more preferably 6-10. The treatment temperature is 15-70°C, preferably 20-60°C.

[0052] The mass volume ratio of the polyaluminum ferric chloride flocculant to sewage is (30-350) mg:1L, preferably (40-300) mg:1L, and more preferably (50-250) mg:1L.

[0053] Example

[0054] Example 1

[0055] Secondary aluminum ash was taken from an aluminum plant in Zouping City, Shandong Province. XRD analysis showed that its main components were aluminum oxide (Al2O3), aluminum nitride (AlN) and magnesium aluminum spinel. It also contained a small amount of elemental aluminum and some salts (calcium fluoride, sodium chloride). The XRD test results are as follows: Figure 1 shown.

[0056] Rietveld structure refinement was adopted and TOPAS software was used to fit the XRD data. The fitting degree was good and the Rwp value of the fitting was 15.8%. The contents of the components of the secondary aluminum ash were obtained as shown in Table 1.

[0057] Table 1

[0058] phase of matter <![CDATA[α-Al2O3]]> <![CDATA[γ-Al2O3]]> AlN Al MgO <![CDATA[MgAl2O4]]> NaCl <![CDATA[CaF2]]> <![CDATA[SiO2]]> Fitting data / wt% 16.55 23.09 21.72 5.16 4.52 10.12 11.82 4.52 2.52

[0059] Al2O3 accounts for approximately 39.64wt%, including α-alumina (approximately 16.55wt%) and γ-alumina (approximately 23.09wt%) with intact lattices but poor activity; the AlN content is approximately 21.72wt% and the aluminum content is approximately 5.16wt%. Among them, aluminum nitride is the main source of the pungent odor of secondary aluminum ash and is also one of the key issues to be solved.

[0060] The quicklime and secondary aluminum ash are mixed so that the mass ratio of calcium oxide to secondary aluminum ash in the mixture is 0.6:1. The quicklime and secondary aluminum ash mixture is ball-milled, and the average particle size of the mixture after ball milling is about 20 μm.

[0061] The mixture is placed in a muffle furnace and calcined at a temperature of 900° C. for 3 hours. After cooling, a calcified calcined product of secondary aluminum ash (whose main component is calcium aluminate) is obtained, and the pungent smell of the secondary aluminum ash disappears.

[0062] The calcified roasted product of secondary aluminum ash was analyzed by X-ray diffraction (XRD). The XRD analysis results are shown in Figure 10 and Figure 11 It can be clearly observed that XRD did not detect the presence of aluminum nitride, indicating that after roasting, the secondary aluminum ash basically achieved nitrogen removal.

[0063] Example 2

[0064] Coal ash was collected from the combustion of coal in a circulating fluidized bed boiler at a power plant in Zhejiang Province (combustion temperature: 850-900°C). X-ray fluorescence (XRF) analysis was performed on the ash. The results are shown in Table 2, where the XRF element contents are given as oxides.

[0065] Table 2

[0066] Element <![CDATA[Fe2O3]]> <![CDATA[Al2O3]]> <![CDATA[SiO2]]> CaO MgO Content (wt%) 13.3 16.7 31.6 16.27 7.523 Element <![CDATA[Na2O]]> <![CDATA[K2O]]> <![CDATA[SO3]]> <![CDATA[TiO2]]> <![CDATA[P2O5]]> Content (wt%) 1.49 1.29 3.82 0.97 1.38

[0067] 5 g of coal ash was added to 45 mL of 2 mol / L hydrochloric acid solution, heated to 90°C, and reacted for 5 hours to obtain Coal Ash Acid Leaching Solution I. ICP (Inductively Coupled Plasma) analysis revealed an iron leaching rate of 94.11 wt% and an aluminum leaching rate of 58.69 wt%.

[0068] 0.5 mL of 30 wt % hydrogen peroxide was added to the coal ash acid leaching solution I, and the oxidized coal ash acid leaching solution I was obtained after sufficient oxidation.

[0069] Example 3

[0070] 5g of coal ash was added to 25mL of a mixture of 6mol / L hydrochloric acid and 2mol / L sulfuric acid (3:1 by volume), heated to 90°C, and reacted for 5 hours to obtain Coal Ash Acid Leaching Solution II. ICP (Inductively Coupled Plasma) analysis revealed that the leaching rates of iron and aluminum reached 92.94wt% and 63.78wt%, respectively.

[0071] 0.5 mL of 30 wt % hydrogen peroxide was added to the coal ash acid leaching solution II, and the oxidized coal ash acid leaching solution II was obtained after sufficient oxidation.

[0072] Example 4

[0073] 1.25 g of the calcified roasted product of secondary aluminum ash obtained in Example 1 was added to 10 mL of the acid leaching solution I of the oxidized coal ash obtained in Example 2, and the mixture was stirred and heated to 80° C. for 3 h. 3+ With Al 3+ Hydrolysis and polymerization reactions occurred. After the reaction, the mixture was filtered and the filtrate was allowed to stand for 24 hours to allow for complete polymerization, resulting in a liquid polyaluminum ferric chloride flocculant. The liquid PAFC was then concentrated and dried to produce a solid polyaluminum ferric chloride flocculant (PAFC I). The alumina content at this point was 24.85 wt% and the basicity was 61.53 wt%.

[0074] Example 5

[0075] Take 1000mL of tap water, add 0.2g CaCO3, 1g tea leaves, 2g kaolin, and 0.5g ammonium phosphate, stir for 5h to mix them evenly, let it stand for 12h, and remove the larger tea leaves to prepare simulated domestic wastewater.

[0076] Table 3 Water quality of simulated domestic wastewater

[0077] Wastewater quality Turbidity (NTU) Total phosphorus (mg / L) COD (mg / L) content 317 11.8 225

[0078] 50, 100, 150, 200, and 250 mg of PAFC I prepared in Example 4 were added to 1000 mL of simulated domestic wastewater. The pH was adjusted to approximately 7 at room temperature. The mixture was rapidly stirred at 200 rpm for 2 minutes, then at 100 rpm for 15 minutes. The mixture was allowed to rest for 30 minutes. Turbidity, total phosphorus, and COD were measured at a depth 2-3 cm below the liquid surface. During the treatment process, it was observed that the simulated domestic wastewater became significantly clearer with increasing flocculant dosage.

[0079] Figure 2The following curves show the removal rates of turbidity, total phosphorus, and COD in wastewater at different flocculant addition levels. As shown in the figure, PAFC I has excellent turbidity removal performance. At a 50 mg / L addition level, the turbidity removal rate reaches 92.69 wt%, and at a 100 mg / L addition level, the turbidity removal rate exceeds 95 wt%. The total phosphorus removal rate in wastewater increases with increasing PFC addition level, reaching 91.52 wt% at a 250 mg / L addition level. The COD removal rate, however, is weaker, increasing with increasing flocculant addition level, reaching 61.56 wt% at a 250 mg / L addition level. After the PAFC I addition level reaches 200 mg / L, the total phosphorus and COD removal rates both increase slowly with increasing flocculant addition level.

[0080] The pH of the wastewater was adjusted to 4, 6, 8, 10, and 12, and the amount of PAFCⅠ added was 250 mg / L. The wastewater was stirred at 200 r / min for 2 minutes at room temperature, then stirred at 100 r / min for 15 minutes, and then allowed to stand for 30 minutes. The water 2-3 cm below the liquid surface was taken to measure its turbidity, total phosphorus and COD content. Figure 3 The following are the turbidity, phosphorus, and COD removal curves of PAFCⅠ at different pH values. The figure shows that within the pH range of 4-12, the turbidity, phosphorus, and COD removal capabilities of PAFCⅠ do not change much with pH, ​​indicating a wide pH treatment range.

[0081] The pH of the wastewater was adjusted to about 7, the amount of PAFCⅠ added was 250 mg / L, and the wastewater temperature was maintained at 20, 30, 40, 50, and 60°C, respectively. Sampling was carried out in the same manner as above to explore the turbidity, phosphorus, and COD removal capabilities of PAFCⅠ on simulated domestic wastewater at different temperatures. Figure 4 The following are the turbidity, phosphorus, and COD removal curves of PAFCⅠ at different temperatures. The figure shows that within the temperature range of 20-60℃, temperature has little effect on the flocculation performance of PAFCⅠ, and the turbidity, phosphorus, and COD removal capabilities remain relatively stable.

[0082] Example 6

[0083] Acid Red GR and Vat Blue 6 were used to prepare simulated printing and dyeing wastewater. 100 mg of each was added to 1000 mL of tap water and stirred at high speed for 1 hour to fully dissolve them. This produced 100 mg / L of Acid Red GR and Vat Blue 6 simulated printing and dyeing wastewater. The absorbance of the treated wastewater and the original wastewater under different conditions was measured using a spectrophotometer, and the corresponding chromaticity removal rate was calculated according to formula (1).

[0084] The chroma removal rate is expressed as η1 and is calculated according to formula (1):

[0085] η1=(A0-A1) / A0×100% Formula (1)

[0086] A0 - the chromaticity of the original wastewater before adding flocculant;

[0087] A1——The chromaticity of wastewater after adding flocculant.

[0088] Figure 5 The following curves show the color removal rates for Acid Scarlet and Vat Blue simulated wastewater at different PAFC I addition levels. The figure shows that with increasing PAFC I addition, the color removal rates for both simulated printing and dyeing processes increase. PAFC I also exhibits a superior removal effect on Vat Blue compared to Acid Scarlet. When the flocculant PAFC I addition level is 250 mg / L, the color removal rate for Vat Blue is 83.63%, while the color removal rate for Acid Scarlet is 62.63%. This is because Acid Scarlet is an acidic dye, while PAFC I is a strong acid and weak base salt, which weakens the charge neutralization effect of PAFC I. Figure 6 The following curves show the color removal efficiency of PAFC I for wastewater containing vat blue and acid red dyes at different pH values. The figure shows that the optimal pH for PAFC I to remove color from wastewater containing vat blue dye is 6-10, while the optimal pH for treating acid red dye wastewater is around 6-8. Excessive acidity or alkalinity will affect the color removal ability of PAFC I for both dye wastewaters. Figure 7 Figure 2 shows the effect of temperature on the color removal performance of PAFCⅠ. It can be seen from the figure that within the temperature range of 20-60℃, the color removal effect of PAFCⅠ on vat blue and acid red is not greatly affected by temperature.

[0089] Example 7

[0090] Weigh 150mg of NaCl, 280mg of NaHCO₃, 170mg of Na₂CO₃, 10mg of Na₂SO₄, 57mg of CaCl₂, and 35mg of MgCl₂·6H₂O into a 1000mL beaker. Add 1000mL of tap water, heat to 50°C, and stir thoroughly to produce mineralized water. Weigh 2g of clay mineral into 1000mL of mineralized water and stir at 2000 rpm for 10 minutes. Prepare a 1:1 oil-to-water ratio oil bead mother liquor using heavy oil and 5wt% OP-10 emulsifier at 50°C and 2000 rpm for 30 minutes. Weigh 1g of the prepared oil bead mother liquor, add it to the prepared 1000ml of sewage, and stir it thoroughly for 1h to produce oily sewage with a water temperature of 50℃, a mineralization of 542mg / L, an oil content of 500mg / L, and a suspended solids content of 2000mg / L.

[0091] Figure 8The following curves show the oil removal and suspended solids removal capabilities of PAFC I for oil-containing anhydrous water at different flocculant addition levels. As can be seen, as the flocculant addition level increases, both the oil removal rate and suspended solids removal capacity increase accordingly. When the PAFC I addition level is 250 mg / L, the oil removal rate is 73.26% and the suspended solids removal rate is 99.14%. Figure 9 The following curves show the oil and suspended solids removal capabilities of PAFC I for oily wastewater at different pH values. The figure shows that PAFC I has good flocculation performance within the pH range of 6-10, but the flocculation effect is reduced when the pH is too acidic or too alkaline.

[0092] Experimental example

[0093] Experimental Example 1

[0094] The Kjeldahl method was used to determine the content of aluminum nitride in the secondary aluminum ash and the calcified roasted product of the secondary aluminum ash, and to measure the denitrification rate. Figure 12 As shown. Add 300mL of 2.5% boric acid solution to the lower conical flask, add 200mL of 0.5mol / L sodium hydroxide solution to the upper conical flask, and add m=1.00g of the sample to be tested. Quickly close the stoppers and heat to boiling. After boiling for 2 minutes, the solution in the lower conical flask turns bright green. After about 2 hours, when the solution in the upper conical flask remains at about 50mL, stop heating. The volume of the boric acid solution at this point is V3. Take 50mL and titrate with 0.01mol / L hydrochloric acid standard solution. The titration endpoint is when the solution changes from bright green to purple-red. The volume of hydrochloric acid consumed is V2.

[0095] The aluminum nitride (AlN) content is expressed as mass fraction w1, and the value is expressed as wt%, and is calculated as follows:

[0096]

[0097] V1——the volume of hydrochloric acid consumed by the blank sample; the unit is mL;

[0098] V2——The volume of hydrochloric acid consumed by the sample to be tested; the unit is mL;

[0099] V3——the volume of the solution in the conical flask below; the unit is mL;

[0100] c——Concentration of hydrochloric acid standard solution; unit is mol / L;

[0101] M——relative molecular mass of aluminum nitride; unit is g / mol;

[0102] m——the mass of the sample to be tested; the unit is g.

[0103] Table 4

[0104]

[0105] Table 4 shows the aluminum nitride content of the secondary aluminum ash before and after calcination and roasting. The data in this table indicate that, at a calcium oxide to secondary aluminum ash mass ratio of 0.6:1 and a calcination temperature of 900°C for 3 hours, the denitrification rate of the secondary aluminum ash reached 97.2 wt%. This is very consistent with the XRD analysis results in Example 1, in which no aluminum nitride was detected. This is presumably due to the low aluminum nitride content in the calcined secondary aluminum ash product.

[0106] Experimental Example 2

[0107] Ion chromatography was used to determine the concentration of soluble fluoride ions in secondary aluminum ash and its calcified roasted product. A fluoride ion standard solution was prepared using sodium fluoride. Weigh 0.221 g of sodium fluoride, dissolve it in deionized water, transfer it to a 1L volumetric flask, and shake well. Transfer 0, 25, 50, 75, and 100 mL of the standard solution to a 100mL volumetric flask, dilute to the mark with deionized water, and shake well. The concentrations at these values ​​were 0, 25, 50, 75, and 100 mg / L, respectively. Ion chromatography was used to determine the values ​​and generate a standard curve.

[0108] 0.5g of secondary aluminum ash and its calcified calcined product were weighed and poured into a 500ml beaker. 200ml of deionized water was added and stirred on a magnetic stirrer for 3 hours. The mixture was allowed to stand for 12 hours. The supernatant was filtered through an injection syringe and a 0.22μm filter membrane to obtain a clear liquid. After dilution by a certain factor, the liquid was tested using ion chromatography. The data were applied to a standard curve to determine the fluoride ion concentration in the solution. As shown in Table 5, the conversion of soluble fluorine after calcination reached 87wt%, greatly reducing the harm caused by excessive fluoride ion concentration in the leachate.

[0109] Table 5

[0110]

[0111] The present invention has been described in detail above with reference to specific embodiments and / or exemplary examples and the accompanying drawings. However, these descriptions should not be construed as limiting the present invention. Those skilled in the art will appreciate that various equivalent substitutions, modifications, or improvements may be made to the technical solutions and implementations of the present invention without departing from the spirit and scope of the present invention, all of which fall within the scope of the present invention. The scope of protection of the present invention shall be determined by the appended claims.

Claims

1. A method for preparing a polyaluminium ferric chloride flocculant, characterized in that: The method uses secondary aluminum ash and coal furnace ash slag as raw materials. After the secondary aluminum ash is calcified and roasted, it is hydrolyzed and polymerized with the acid leaching liquid of oxidized coal furnace ash slag to obtain polyaluminum ferric chloride flocculant. The secondary aluminum ash is slag produced by smelting aluminum or aluminum alloy from bauxite, wherein the Al2O3 content is 35-45wt%, the AlN content is 15-25wt%, and the aluminum content is 4-8wt%. The coal furnace ash is ash produced by burning coal in a circulating fluidized bed boiler. Calcification roasting is to mix the calcium source and secondary aluminum ash, and then roast them in an oxygen-containing atmosphere at a temperature of 500-1200°C and a roasting time of 1.5-5.5h. First, the mixture of calcium source and secondary aluminum ash is ground. After the grinding, the average particle size of the mixture of calcium source and secondary aluminum ash is 5-45 μm. The mass ratio of the calcium source to the secondary aluminum ash is (0.3-0.9):1, Adding coal ash into an acid solution and keeping it warm for reaction to obtain a coal ash acid leaching solution; the acid solution is hydrochloric acid or a mixed solution of hydrochloric acid and sulfuric acid; The oxidized coal ash acid leaching solution is obtained by adding an oxidant to the coal ash acid leaching solution and reacting, wherein the oxidant is selected from one or more of chlorine water, hydrogen peroxide and hypochlorite solution. The secondary aluminum ash after calcification and roasting is added to the acid leaching solution of oxidized coal furnace ash slag, heated to carry out hydrolysis polymerization reaction, filtered after the reaction is completed, aged, concentrated and dried to obtain polyaluminum ferric chloride flocculant, The mass volume ratio of the acid leaching solution of the secondary aluminum ash after calcification roasting and the oxidized coal furnace ash slag is 1.25:(4-18)mL.

2. The preparation method according to claim 1, characterized in that The mixture of the calcium source and the secondary aluminum ash is first subjected to ball milling treatment. After the treatment, the average particle size of the mixture of the calcium source and the secondary aluminum ash is 10-35 μm.

3. The preparation method according to claim 2, characterized in that After treatment, the mixture of the calcium source and the secondary aluminum ash has an average particle size of 15-25 μm.

4. The preparation method according to claim 1, characterized in that The mass ratio of the calcium source to the secondary aluminum ash is (0.4-0.8):

1.

5. The preparation method according to claim 4, characterized in that The mass ratio of the calcium source to the secondary aluminum ash is (0.5-0.7):

1.

6. The preparation method according to claim 1, characterized in that The calcination temperature is 650-1100° C.; and the calcination time is 2-4.5 hours.

7. The preparation method according to claim 6, characterized in that The calcination temperature is 800-1000° C.; and the calcination time is 2.5-3.5 hours.

8. The preparation method according to claim 1, characterized in that The mass volume ratio of the secondary aluminum ash after calcification roasting to the oxidized coal furnace ash slag acid leaching solution is 1.25:(6-15)mL.

9. The preparation method according to claim 8, characterized in that The mass volume ratio of the acid leaching solution of the secondary aluminum ash after calcification roasting and the oxidized coal furnace ash slag is 1.25:(8-12)mL.

10. The preparation method according to claim 1, characterized in that The heating temperature is 50-110°C; The aging time is 10-36h.

11. The preparation method according to claim 10, characterized in that: The heating temperature is 60-100°C; The aging time is 14-32h.

12. The preparation method according to claim 11, characterized in that The heating temperature is 70-90℃; The aging time is 20-28h.

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