Recycling process of aluminum ash pickling waste liquid

Abstract

The invention provides an aluminum ash pickling waste liquid recycling process. The aluminum ash pickling waste liquid recycling process comprises the following steps that S1, aluminum ash is subjected to deamination treatment; s2, an HCl solution is added, and element ions such as Fe, Ca, Na and F are dissolved in the solution from the aluminum ash; s3, filtering and separating to obtain a solid, namely an aluminum ash product subjected to impurity removal, and a residual solution, namely the pickling waste liquid; s4, steam is blown into the pickling waste liquid, excessive HCl is evaporated, HCl acid mist gas is conveyed to a condensation heat exchanger through a draught fan and condensed into liquid hydrochloric acid again, the liquid hydrochloric acid is added into the step S2 to be recycled, meanwhile, the PH value of the pickling waste liquid is increased, and part of iron, magnesium and calcium impurity ions are precipitated; s5, CaO and Na2CO3 are added into the pickling waste liquid obtained after steam stripping, and Fe, Ca and F ions in filtrate are subjected to a reaction and then are precipitated respectively; s6, precipitating, filtering and separating Fe (OH) 3, CaCO3 and CaF2 in the neutralized and impurity-removed solution as byproducts; and S7, carrying out evaporation treatment on the waste liquid subjected to secondary filtration, wherein the concentrated halide salt is used as a byproduct. According to the process, hydrochloric acid in the pickling wastewater can be recycled, the subsequent alkali consumption is reduced, and the aluminum ash pickling treatment cost is reduced.

Description

Technical Field

[0001] The invention relates to a processing technology for aluminum ash, and in particular to a recycling technology for aluminum ash pickling waste liquid. Background Art

[0002] The utilization and treatment process of aluminum ash mainly includes pyrometallurgical process and hydrometallurgical process, among which aluminum ash deammoniation is a common treatment step. After a series of process steps, harmful components such as ammonia and aluminum nitride in aluminum ash are removed to make it harmless and further use it as a resource. The main component of aluminum ash after deammoniation is aluminum oxide. In addition, it also contains a small amount of fluoride, silicate, and other impurities such as iron ions, calcium ions, and sodium ions. It is further processed according to needs, and by-products are obtained after separating harmful impurities.

[0003] The existing aluminum ash processing technology mostly produces aluminum ash products with high impurity content, and the filter mud can only be pressed into bricks for reuse. The residual salts in the aluminum ash affect its recycling. Some patents use the process of washing salts. For example, CN106399693A discloses a comprehensive processing and utilization method for aluminum ash, in which the aluminum ash is separated, cooled, and then ground. The secondary ash is leached with excess water or dilute acid and then washed and filtered. After the filtrate is evaporated, soluble salts are obtained, which can be used to prepare refining aids. CN105271327A discloses a method for harmless treatment and recycling of aluminum ash, in which the valuable substances in the aluminum ash are removed through the steps of water leaching of the aluminum ash raw material for denitrification and chlorination, roasting and defluorination, alkali melting sintering, sintering material dissolution, purification and filtration. The components form a sodium aluminate solution as a raw material for producing sand-like alumina, achieving the purpose of comprehensive resource recycling of aluminum ash. Finally, after the liquid-solid separation of the slurry, the solid phase is mainly red mud composed of oxides such as calcium, magnesium, and iron, which does not cause harm to the environment. CN108217688A discloses a method for deep hydrolysis of aluminum nitride in aluminum ash, in which the aluminum ash is heated and mixed with water to form a high-temperature slurry, and ammonia gas is produced after grinding and hydrolysis, and absorbed to obtain ammonia water or ammonium salt. After the hydrolyzed slurry is dehydrated and filtered, the filtrate is circulated and enriched, and then evaporated to achieve the recovery of industrial salt. However, impurities such as iron, calcium, and magnesium in aluminum ash are insoluble in water, so they need to be dissolved and separated with acid, and the wastewater after pickling and impurity removal contains iron, calcium, fluorine and other ions. When environmental protection treatment is required, most of them use a neutralization method to use alkali to remove excess H + It is consumed to neutralize the acidity of the solution, increasing production costs. Summary of the invention

[0004] The invention discloses a recycling process for aluminum ash pickling wastewater to solve the problem that the byproducts obtained from the current deammoniation aluminum ash contain more impurities and the evaporation equipment corrodes faster, while realizing the recycling of hydrochloric acid in the pickling wastewater.

[0005] To achieve the above object, the present invention adopts the following technical solutions: A process for recycling aluminum ash pickling waste liquid comprises the following steps: S1, deammoniation: deammoniation treatment of aluminum ash; S2, pickling; adding HCl solution to the aluminum ash after deammoniation to dissolve element ions such as Fe, Ca, Na, and F from the aluminum ash into the solution; S3, filtering; filtering the slurry after pickling and impurity removal, the filter cake obtained after filtration and separation is the impurity-removed aluminum ash product, and the filtrate is the pickling waste liquid; S4, heating the pickling waste liquid; performing a stripping treatment on the pickling waste liquid with steam, that is, blowing steam into the pickling waste liquid to evaporate HCl, using a fan to extract the evaporated HCl gas and re-condense it into liquid hydrochloric acid, adding it to S2 for recycling, and at the same time increasing the pH value of the pickling waste liquid; S5, neutralization and impurity removal; adding CaO and Na2CO3 to the pickling waste liquid after stripping and stripping, so that the Fe, Ca, and F ions in the filtrate react to form Fe(OH)3, CaCO3, and CaF2 precipitates respectively; S6, secondary filtration; filtering and separating the Fe(OH)3, CaCO3, and CaF2 in the neutralized and impurity-removed solution as by-products; S7, evaporation treatment; the waste liquid after the secondary filtration is evaporated and the concentrated halide salt is used as a by-product.

[0006] Preferably, in step S1, the deammoniation treatment is carried out by a wet process or a pyrometallurgical process.

[0007] Preferably, in step S2, a 5-10% concentration of HCl solution is added, the solid-liquid mass ratio of aluminum ash to HCl solution is 1:1-4, the reaction temperature is 60-90° C., and the reaction time is 40-80 minutes.

[0008] Preferably, in step S3, the HCl concentration in the pickling wastewater is only 2-3%.

[0009] Preferably, in step S4, hot air is blown into the pickling waste liquid to perform an air stripping treatment; or steam is blown into the pickling waste liquid to perform a steam stripping treatment.

[0010] Preferably, a stripping pipe is connected to the bottom of the container containing the pickling waste liquid to directly feed hot air or steam into the container.

[0011] Preferably, in step S5, CaO is first added to adjust the pH value to 5-6, and then Na2CO3 is added to adjust the pH value of the filtrate to 8-9.

[0012] Preferably, in step S5, sodium ions, chloride ions and fluoride ions form an electrolyte balance.

[0013] Preferably, in step S7, the F ion content in the evaporated waste liquid is less than 10 mg / L.

[0014] Preferably, in step S7, the halide salt obtained after evaporation of the waste liquid includes NaCl and KCl.

[0015] Compared with the prior art, the present invention has the following beneficial effects: The present invention performs a treatment process of first pickling, then washing with water, and finally evaporating the aluminum ash. After pickling, a high-quality aluminum ash product is obtained, which can be used to produce refractory materials; after washing and filtering, iron, calcium, and fluorine byproducts are obtained for reuse; finally, the water content of the waste liquid is evaporated to obtain salt byproducts such as NaCl and KCl for reuse; each byproduct has a high removal rate and high purity; The process cost of the present invention is low and the process is relatively simple. Almost all components in the aluminum ash can be separated and reused as by-products. No waste liquid is generated and discharged, which is more environmentally friendly.

[0016] The fluoride ion release rate of the present invention is higher than that of the prior art, so the fluoride ions remaining in the solution during the final evaporation are less than 10 mg / L, which effectively avoids corrosion to the evaporation equipment and prolongs the service life of the equipment.

[0017] In step S4 of the present invention, excess HCl is blown off from the solution, re-condensed into a hydrochloric acid solution, and added to step S1 as a pickling agent, which not only saves the amount of hydrochloric acid used, but also increases the pH value of the pickling waste liquid, thereby reducing the amount of alkaline regulator used in step S5, effectively saving processing costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0019] Figure 1 The present invention is a flow chart of a recycling process of aluminum ash pickling waste liquid. DETAILED DESCRIPTION

[0020] In order to further understand the purpose, structure, characteristics, and functions of the present invention, this section will describe in detail the specific embodiments of the present invention. The preferred embodiments of the present invention are shown in the accompanying drawings. The purpose of the accompanying drawings is to supplement the description of the text part of the specification with graphics, so that people can intuitively and vividly understand each technical feature and the overall technical solution of the present invention, but it cannot be understood as a limitation on the scope of protection of the present invention.

[0021] Reference below Figure 1 The present invention provides a recycling process for aluminum ash pickling waste liquid.

[0022] A process for recycling aluminum ash pickling waste liquid comprises the following steps: S1, deammoniation: deammoniation treatment of aluminum ash; In some embodiments, the deammoniation treatment can be carried out by a commonly used wet process or a pyrometallurgical process. After deammoniation, Al and AlN in the aluminum ash are converted into Al2O3; the impurities contained include elements such as Fe, Ca, Na, F, and K. If a higher purity aluminum ash product is to be obtained, it is necessary to separate Fe, Ca, Na, F, K and other elements from Al2O3 as completely as possible.

[0023] S2, pickling; adding HCl solution to the aluminum ash after deammoniation to dissolve element ions such as Fe, Ca, Na, and F from the aluminum ash into the solution; The purpose of this pickling step is to dissolve the Fe, Ca, Na, F and other elements in the aluminum ash into the solution and remove them from the aluminum ash. The higher the removal rate, the better. Acid pickling usually uses hydrochloric acid or sulfuric acid as a solution and a detergent. However, after experiments, it was found that the removal rate of Ca element is low when using sulfuric acid for pickling. Some CaSO4 will not dissolve and remain in the aluminum ash, reducing the purity of the aluminum ash product and introducing SO4 2- , which increases the complexity of the pickling solution. Therefore, the present invention selects hydrochloric acid as the pickling agent. Aluminum ash itself contains Cl - , and will not produce precipitation with elements such as Fe, Ca, Na, F, etc., which is more convenient for subsequent waste liquid treatment.

[0024] In addition, the use of HCl solution as a pickling agent increases the chloride ion concentration, which is conducive to the formation of chloride ion rejection, thus facilitating the subsequent fluorine fixation and defluorination. In some embodiments, a 5-10% HCl solution is added, the solid-liquid mass ratio of aluminum ash to HCl solution is 1:1-4, the reaction temperature is 60-90°C, and the reaction time is 40-80 minutes. Specifically, a 5% HCl solution can be added, the solid-liquid ratio of aluminum ash to HCl solution is 1:2, the reaction temperature is 80°C, and the reaction time is 60 minutes.

[0025] After many experiments, it was found that the highest removal rates of Fe, Ca, Na, F and Si could reach about 44.87%, 84.03%, 93.95%, 70.11% and 32.32% respectively, and the mass fraction of alumina in aluminum ash was as high as 84.73%.

[0026] S3, filtering; filtering the slurry after pickling and impurity removal, and the filter cake obtained after filtering and separation is the aluminum ash product after impurity removal, and the remaining filtrate is the pickling waste liquid; the aluminum ash obtained by filtration after pickling according to the present invention is of high quality, wherein the mass fraction of alumina and magnesium aluminum spinel reaches more than 90%, and is a high-quality aluminum ash product.

[0027] In some embodiments, the high-quality aluminum ash product of the present invention can be used to make refractory materials after high-temperature sintering, such as producing refractory bricks, preparing brown corundum, preparing magnesia-alumina spinel, preparing mullite, etc.

[0028] In this step, the HCl in the pickling wastewater is consumed and the concentration is only 2-3%; more precisely, the H + The concentration is only 2-3%, Cl - It does not go through a series of reactions and ultimately remains in the solution, so the concentration remains high.

[0029] S4, heating the pickling waste liquid; using steam to perform gas stripping treatment on the pickling waste liquid, that is, blowing hot steam into the pickling waste liquid to evaporate HCl, using a fan to extract the evaporated HCl gas and re-condense it into liquid hydrochloric acid, adding it to S2 for recycling, and at the same time the pH value of the pickling waste liquid increases; after the stripping is completed, the H + The corresponding Cl - Still remains in the pickling wastewater, so Cl - The concentration is still higher than before the pickling step.

[0030] Cl - The beneficial effects of increased concentration include: forming chloride ion repulsion, chloride ions will exchange with fluoride ions on the surface of the ion layer, and chloride ions will throw fluoride ions out of the ion layer, making it difficult for fluoride ions to combine with the ion layer, thereby achieving the purpose of removing fluoride ions.

[0031] In one embodiment, hot air is blown into the pickling waste liquid to perform an air stripping treatment; in another embodiment, hot water steam is blown into the pickling waste liquid to perform a steam stripping treatment.

[0032] Specifically, a stripping pipe can be connected to the bottom of the container containing the pickling waste liquid, and hot air or steam can be sent into the pipe. The hot bubbles rise from the bottom to the top, which can fully preheat the pickling waste liquid, and use the principle that the solubility of HCl decreases with temperature and the partial pressure of gas to blow out HCl better and faster. Furthermore, multiple stripping pipes can be evenly connected to the bottom of the container containing the pickling waste liquid, and hot air or steam can be blown into the pickling waste liquid simultaneously, so that the heating is fast and uniform, and the stripping efficiency is further improved.

[0033] S5, neutralization and impurity removal; add CaO and Na2CO3 to the pickling waste liquid after stripping and blowing, so that the Fe, Ca, and F ions in the filtrate react to generate Fe(OH)3, CaCO3, and CaF2 precipitates respectively.

[0034] In this step, the pH value of the solution needs to be adjusted to the required value. Since the HCl in the pickling waste liquid has been blown out in step S4, thereby increasing the pH value, there is no need to add a large amount of highly alkaline reagents to precipitate Fe, Ca, and F ions.

[0035] In some embodiments, CaO is first added to adjust the pH value to 5-6, and then Na2CO3 is added to adjust the pH value of the filtrate to 8-9. Preferably, the pH value of the added filtrate can be controlled at 8.4. Specifically, lime is added to neutralize excess hydrochloric acid, and the reaction is CaO+2HCl=CaCl2+H2O, and then calcium ions and fluoride ions are combined to form calcium fluoride precipitation, which plays a role in defluorination. Finally, excess calcium ions react with soda ash to form calcium carbonate precipitate CaCl2+Na2CO3=CaCO3+2NaCl. Since the excess HCl has been stripped and blown off in step S3, only a small amount of CaO needs to be added in this step to neutralize the hydrochloric acid that has not been completely blown off, saving the amount of lime, and after defluorination and decalcification, the chloride ions always remain in the solution after multiple reactions.

[0036] The beneficial effects of adding CaO and Na2CO3 are: 1. Low cost; 2. + , Cl - 、F - The electrolytes are then distributed in the water under the action of the electric field to form an equilibrium system, namely electrolyte balance; + and Cl - The ions of F have a smaller radius and stronger polarity, so they will move toward the positive electrode under the action of the electric field, while F - The ions have a larger ionic radius and weaker polarity, so they will move toward the negative electrode. As a result, the fluoride ions will move toward the negative electrode under the action of the electric field, which is beneficial to the removal of fluoride ions; 3. Increasing the pH value and the fluoride removal efficiency is beneficial to the removal of fluoride by CaCl to form CaF2 precipitation.

[0037] S6, secondary filtration; Fe (OH) 3, CaCO3, CaF2 in the neutralized and impurity-removed solution is precipitated and filtered to separate as a by-product; in this step, the waste liquid obtained after filtering the precipitate contains Na + , K + , Cl - wait.

[0038] S7, evaporation treatment; the waste liquid after the secondary filtration is evaporated and the concentrated halide salt is used as a by-product.

[0039] In the prior art, the deammoniation process of the secondary aluminum ash treatment has a relatively low fluoride ion removal rate, so the fluoride ion concentration contained in the waste liquid is relatively high. During the evaporation process, the fluoride ions corrode the evaporation equipment, increasing the treatment cost. In this step of the present invention, the residual fluoride ion concentration is very low. In some preferred embodiments, after the present invention is first acid-washed and then neutralized and washed with water, the fluoride ion content in the obtained waste liquid is less than 10 mg / L, so that the evaporation equipment can be effectively prevented from being corroded, the service life of the evaporation equipment can be extended, and the purity of by-products such as NaCl and KCl can also be improved.

[0040] In addition, when the aluminum ash treatment process of the present invention is applied, during the pickling in step S2, the dilute hydrochloric acid used can be configured using an acid preparation tank, specifically by adding concentrated hydrochloric acid, condensed regenerated hydrochloric acid and washing wastewater and diluting them according to the required proportion; in the present invention, since the excess HCl in the pickling waste liquid is blown off in step S4, it can be put into the acid preparation tank as concentrated hydrochloric acid after re-condensation and reused as raw material; in addition, after the pressure filtration in step S3 is completed, the aluminum ash filter cake can be washed once and filtered twice, thereby washing away the impurity elements in the aluminum ash filter cake, increasing the aluminum content in the aluminum ash filter cake to obtain a high-quality aluminum ash filter cake product, and the washing wastewater after the secondary pressure filtration can also be put into the acid preparation tank for diluting concentrated hydrochloric acid, thereby realizing the recycling of washing wastewater; therefore, the raw material cost of the dilute hydrochloric acid configured in the acid preparation tank is greatly reduced. During the evaporation treatment in step S7, the distilled water used for evaporation can also be used to wash the aluminum ash filter cake, thereby realizing the recycling of water resources.

[0041] In some embodiments, before step S2, the aluminum ash is first calcined at a high temperature with a heating rate of 12-15°C / s, a calcination temperature of 1200°C, and a calcination time of 1-2h to convert the aluminum-containing compounds in the aluminum ash into stable α-crystalline alumina that does not react with acid.

[0042] The chemical composition of aluminum ash can be analyzed by X-ray fluorescence spectrometry (XRF) and chemical analysis, and the physical phase in aluminum ash can be analyzed by X-ray diffraction (XRD). After the aluminum ash is roasted and transformed, the aluminum oxide is transformed from γ-Al2O3 to stable α-Al2O3, α-Al2O3 and MgAl2O4, which are difficult to dissolve in acid and alkali solutions. Therefore, they will not be redissolved in the subsequent pickling process, which can effectively increase the Al content in the aluminum ash product obtained after pickling, impurity removal and filtration, thereby obtaining high-quality aluminum ash products.

[0043] In some preferred embodiments, the mass fraction of aluminum oxide in the solid aluminum ash product obtained after filtration and separation in step S3 is at least 85%, and the sum of the mass fractions of aluminum oxide and magnesium-aluminum spinel is at least 90%, and can be as high as 93.54%.

[0044] In summary, the recycling process of aluminum ash pickling waste liquid of the present invention utilizes a relatively low cost and relatively simple operation procedure to first pickle the aluminum ash, then wash it with water, and finally evaporate it. In the treatment process of the present invention, high-quality aluminum ash products, iron, calcium, fluorine byproducts, and salt byproducts such as NaCl and KCl are obtained in sequence. The present invention ultimately achieves full recycling of aluminum ash, and ultimately no wastewater will be discharged, which is more environmentally friendly; the byproduct extraction rate obtained in each step is relatively high, especially the fluoride ion extraction rate is higher than that of the prior art, so very few fluoride ions remain in the solution during the final evaporation, effectively avoiding corrosion to the evaporation equipment. The hydrochloric acid in the present invention can be recycled, while reducing the amount of alkaline reagents used, effectively saving processing costs.

[0045] In the above embodiments, the description of each embodiment has its own emphasis. For parts that are not described in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0046] The present invention has been described by the above-mentioned relevant embodiments, but the above-mentioned embodiments are only examples for implementing the present invention, which are used to help understand the technical solutions and core ideas of the present application. It must be pointed out that the disclosed embodiments do not limit the scope of the present invention; on the contrary, the technical solutions recorded in the above-mentioned embodiments can still be modified, or some of the technical features therein can be replaced by equivalents; modifications and embellishments made without departing from the spirit and scope of the present invention are all within the scope of patent protection of the present invention.

Claims

1. A process for recycling aluminum ash pickling waste liquid, characterized in that: The following steps are involved: S1, deammoniation: deammoniation treatment of aluminum ash; S2, pickling; adding HCl solution to the aluminum ash after deammoniation to dissolve element ions such as Fe, Ca, Na, and F from the aluminum ash into the solution; S3, filtering; filtering the slurry after pickling and impurity removal, the filter cake obtained after filtration and separation is the impurity-removed aluminum ash product, and the filtrate is the pickling waste liquid; S4, heating and stripping of the pickling waste liquid; using steam to strip the pickling waste liquid, that is, blowing steam into the pickling waste liquid to evaporate HCl, using a fan to extract the evaporated HCl gas and re-condense it into liquid hydrochloric acid, adding it to S2 for recycling, and at the same time increasing the pH value of the pickling waste liquid; S5, neutralization and impurity removal; adding CaO and Na2CO3 to the pickling waste liquid after stripping and stripping, so that the Fe, Ca, and F ions in the filtrate react to generate Fe(OH)3, CaCO3, and CaF2 precipitates respectively; S6, secondary filtration; filtering and separating the Fe(OH)3, CaCO3, and CaF2 in the neutralized and impurity-removed solution as by-products; S7, evaporation treatment; the waste liquid after the secondary filtration is evaporated and the concentrated halide salt is used as a by-product.

2. The aluminum ash pickling waste liquid recycling process according to claim 1 is characterized in that: In step S1, the deammoniation treatment is carried out by a wet process or a pyrometallurgical process.

3. The recycling process of aluminum ash pickling waste liquid according to claim 1 is characterized in that: In step S2, a 5-10% concentration HCl solution is added, the solid-liquid mass ratio of aluminum ash to the HCl solution is 1:1-4, the reaction temperature is 60-90° C., and the reaction time is 40-80 minutes.

4. The recycling process of aluminum ash pickling waste liquid according to claim 3 is characterized in that: In step S3, the HCl concentration in the pickling wastewater is only 2-3%.

5. The recycling process of aluminum ash pickling waste liquid according to claim 1 is characterized in that: In step S4, hot air is blown into the pickling waste liquid to perform air stripping treatment; or steam is blown into the pickling waste liquid to perform steam stripping treatment.

6. The recycling process of aluminum ash pickling waste liquid according to claim 5 is characterized in that: A stripping pipe is connected to the bottom of the container containing the pickling waste liquid to directly supply hot air or steam into the container.

7. The recycling process of aluminum ash pickling waste liquid according to claim 1 is characterized in that: In step S5, CaO is first added to adjust the pH value of the filtrate to 5-6, and then Na2CO3 is added to adjust the pH value of the filtrate to 8-9.

8. The recycling process of aluminum ash pickling waste liquid according to claim 1 is characterized in that: In step S5, sodium ions, chloride ions, and fluoride ions form an electrolyte balance.

9. The recycling process of aluminum ash pickling waste liquid according to claim 1, characterized in that: In step S7, the F ion content in the evaporated waste liquid is less than 10 mg / L.

10. The aluminum ash pickling waste liquid recycling process according to claim 1, characterized in that: In step S7, the halide salts obtained after evaporation of the waste liquid include NaCl and KCl.

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