Method for recycling Bayer sludge

Abstract

The invention discloses a method for recycling Bayer sludge, which comprises the following steps of: 1, leaching the Bayer sludge by using acid to obtain leachate; secondly, adsorption resin is adopted for adsorbing vanadium in the lixivium, and resin after adsorption and liquid after adsorption are obtained; carrying out desorption treatment on the adsorbed resin to obtain a vanadium-containing desorption solution; step 3, performing impurity removal treatment on the liquid after adsorption to remove impurity elements in the liquid after adsorption; impurity-removed and adsorbed liquid is obtained; and 4, preparing alkali by adopting the impurity-removed and adsorbed liquid. According to the method, the effective components in the Bayer sludge can be recycled; moreover, alkali in the Bayer sludge can be recycled, and the alkali consumption of the aluminum oxide industry can be reduced.

Description

A method for recycling Bayer sludge Technical Field

[0001] This invention belongs to the field of hydrometallurgical technology, specifically relating to a method for recycling Bayer sludge. Background Technology

[0002] Bayer sludge is a solid waste residue left over after alumina production from bauxite. Its main production process involves alumina manufacturers leaching bauxite with an alkali, followed by filtration to obtain an alkali-saturated solution of sodium aluminate. The solution primarily consists of sodium aluminate, alkali, and other impurities. Aluminum hydroxide seed crystals are then added, and the mixture is cooled to allow the sodium aluminate to precipitate as aluminum hydroxide. The filtrate is then precipitated to obtain vanadium-containing sludge. Its yield varies depending on ore grade, production method, and technological level; approximately 0.7 tons of Bayer sludge are produced for every ton of alumina produced.

[0003] Bayer, an alumina producer, primarily used land reclamation for sludge disposal. However, with increasing environmental awareness, land reclamation has been prohibited, and damming and stockpiling have become the main disposal methods. Due to geographical limitations, some alumina producers have traditionally relied on open-air damming and stockpiling of sludge. The construction and maintenance costs of these stockpiles are high, ranging from 50 to 100 yuan per ton, increasing alumina production costs. Currently, some alumina producers are directly discharging sludge into open fields to reduce costs. The large amount of sludge not being fully utilized and treated not only occupies significant land resources and incurs huge costs for stockpile construction and maintenance, increasing production costs, but also causes water and soil alkalization due to its highly alkaline and saline wastewater, polluting groundwater and significantly increasing environmental pressure. The sludge problem severely restricts the sustainable development of the alumina industry, and the technical research and comprehensive utilization of sludge are urgent issues that the alumina industry needs to address.

[0004] In order to achieve comprehensive utilization of sludge, solve sludge pollution, transform it into a secondary resource for reuse, save energy and reduce emissions, and optimize product structure, it is necessary to develop a recycling process route for Bayer sludge. Summary of the Invention

[0005] The main objective of this invention is to provide a method for recovering Bayer sludge; this method can effectively reduce the amount of Bayer sludge, recover the effective components in the sludge, recover the alkali in the sludge, and achieve comprehensive utilization of Bayer sludge.

[0006] The objective of this invention is achieved through the following technical solution: a method for recycling Bayer sludge, comprising the following steps: Step 1: Leaching Bayer sludge with acid to obtain leachate; Step 2: Adsorbing vanadium in the leachate with adsorption resin to obtain post-adsorption resin and post-adsorption liquid; Desorbing the post-adsorption resin to obtain vanadium-containing desorbed liquid; Step 3: Removing impurities from the post-adsorption liquid to obtain a purified post-adsorption liquid; Step 4: Preparing an alkali using the purified post-adsorption liquid.

[0007] Optionally, in step one, the leaching solid-liquid ratio is 1g:3~6ml, the leaching temperature is 30-95℃, and the leaching time is 1-2h; preferably, the mass fraction of the sulfuric acid solution is 1%-8%; preferably, the mass fraction of the sulfuric acid solution is 3%-5%; preferably, the Bayer sludge contains 2.9-20 wt% V2O5, 0.5-1.5 wt% As, and 0.1-0.4 wt% Fe2O3; preferably, the pH of the leachate is 7-11, more preferably 7-10.

[0008] Optionally, the adsorption resin is a styrene-based macroporous strong base anion exchange resin, the adsorption resin exchange group is -N(CH3)3Cl, the particle size range is 0.315-1.25mm, and the adsorption form is sulfate type.

[0009] Optionally, in step three, the rate at which the adsorption resin adsorbs vanadium in the leachate is 1-2 BV / h; adsorption is stopped when the vanadium concentration in the effluent reaches 0.5 g / L.

[0010] Optionally, an alkaline solution is used for desorption; preferably, the alkaline solution is a 5%-8% sodium hydroxide solution by mass; the desorption temperature is 55~65℃.

[0011] Optionally, step two further includes adding ammonium sulfate to the vanadium-containing desorption solution to form ammonium metavanadate; preferably, the ammonium metavanadate is calcined to obtain vanadium pentoxide product. Optionally, the impurity ions in step three are non-alkali metal elements; preferably, the impurity elements include: As, V, Al, and Si.

[0012] Optionally, in step three, a flocculant is used for impurity removal; preferably, the flocculant includes at least one of polyferric sulfate and PAM.

[0013] Optionally, in step four, a bipolar membrane device is used to treat the purified adsorption liquid to prepare an alkali.

[0014] Optionally, the method further includes step five: using the alkali prepared in step four to produce alumina from bauxite.

[0015] Compared with existing technologies, this invention has at least the following advantages: It can separate impurities from Bayer sludge and recover effective components; the vanadium recovery rate can reach over 80%, achieving comprehensive utilization of the sludge. This invention solves the problem of sludge pollution, transforming it into a secondary resource for reuse, thus achieving the goal of energy conservation and emission reduction.

[0016] The present invention uses the purified adsorption liquid to prepare alkali, which can realize the recovery of alkali from Bayer sludge, which is conducive to reducing the alkali consumption of the alumina industry, further improving the energy-saving and emission-reduction effect, and improving the overall benefits.

[0017] This invention can reduce the amount of sludge in Bayer, thereby reducing the amount of hazardous waste and lowering the company's hazardous waste treatment costs. Detailed Implementation

[0018] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention. It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the present invention.

[0019] Furthermore, regarding the numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, are also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0020] The terms “comprising,” “including,” “having,” “containing,” etc., used in this document are all open-ended, meaning they include but are not limited to. The terms “first” and “second” used in this document are for descriptive purposes only, and features specified as “first” or “second” may explicitly or implicitly include at least one of those features.

[0021] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. Unless otherwise specified, the technical means used in the following embodiments are conventional means well known to those skilled in the art; the experimental methods used are all conventional methods; and the equipment, apparatus, materials, reagents, etc., used are all commercially available.

[0022] This invention discloses a wet process for recovering Bayer sludge, comprising the following steps: Step 1: Leaching the Bayer sludge with acid to obtain a leachate; Step 2: Adsorbing vanadium in the leachate with an adsorption resin to obtain an adsorbed resin and an adsorbed liquid; Desorbing the adsorbed resin to obtain a vanadium-containing desorbed liquid; Step 3: Removing impurities from the adsorbed liquid to obtain a purified adsorbed liquid; Step 4: Preparing an alkali using the purified adsorbed liquid.

[0023] The Bayer sludge mentioned above is a byproduct of alumina production at the alumina plant.

[0024] Step 1) uses sulfuric acid with a concentration of 1wt%-8wt%, preferably 3wt%-5wt%. Using a high-concentration acid for leaching increases the concentration of impurities in the leachate, which is detrimental to resin adsorption and vanadium extraction. Using a lower acid concentration generates aluminum hydroxide precipitate, and the amorphous Al(OH)3 flocs adsorb the main component vanadate in the solution, leading to a white precipitate forming overnight and poor solution stability.

[0025] Step 1) The solid-liquid ratio used for leaching is 1g:3~6ml, preferably 1g:5ml. The leaching temperature is 30-95℃, and the leaching time is 1-2h.

[0026] Step 2) uses Seplite® LSC-2550 (strong base anion exchange resin) with a particle size range of 0.315-1.25 mm and sulfate adsorption form. This resin has a high adsorption capacity for vanadium and almost no adsorption for arsenic. The leaching solution is dynamically adsorbed using this resin at a rate of 1-2 BV / h.

[0027] Step 2) The desorbent used is a 5wt%-8wt% sodium hydroxide solution at 60℃. An 8wt% sodium hydroxide solution is preferred.

[0028] High-vanadium and low-vanadium-concentration eluents were collected separately. The low-vanadium-concentration eluent was treated with alkali to desorb the resin, thereby increasing the vanadium concentration in the eluent.

[0029] The impurity removal agents used in step 3) are polyferric sulfate and PAM (0.1-0.3wt%).

[0030] Polyferric sulfate is added at a molar ratio of 5-15:1 for iron to arsenic. PAM is added at 0.1-0.3 wt%.

[0031] The used resin can be regenerated and reused. Regeneration is performed using a 4wt%-8wt% sodium hydroxide solution at a temperature of 40~80℃, and a sulfuric acid solution is used for conversion.

[0032] Example 1 This example provides a method for the wet recovery of Bayer sludge, comprising the following steps: 1) Sulfuric acid leaching: Weigh 50g of Bayer sludge powder and add it to a beaker (the vanadium mass fraction of the waste is 2.6%, the iron mass fraction is 0.03%, and the arsenic mass fraction is 0.5%), add 250mL of 3wt% sulfuric acid solution, stir at 400rpm, react at 90℃ for 60 minutes, and separate the solid and liquid to obtain the leachate. The leaching results are shown in Table 1: Table 1 Ion concentrations in 3wt% sulfuric acid leachate

[0033] 2) Vanadium extraction from leachate: The leachate was collected and adsorbed using ion exchange resin. The ion exchange resin used was Seplite® LSC-2550, a styrene-based macroporous strong-base anion exchange resin with N(CH3)3Cl exchange groups. The resin particle size ranged from 0.315 to 1.25 mm, and the adsorption form was sulfate. Under alkaline pH conditions, this resin had a high adsorption capacity for vanadium and almost no adsorption for arsenic. Adsorption was carried out at a rate of 2 BV / h, and the adsorption tail liquid was collected. Adsorption was stopped when the V concentration in the effluent reached 0.5 g / L.

[0034] The adsorbed resin was desorbed using an 8wt% NaOH solution at 60℃. For each desorption cycle, the first 2 BV of the eluent was mixed and ammonium sulfate was added to prepare ammonium metavanadate. The remaining 2 BV was used in the next desorption cycle as the liquid phase of the first 2 BV for further desorption treatment of the resin. Then, another 2 BV was used for desorption with 8wt% NaOH solution, for a total elution and desorption of 6 BV. This method reduces the amount of alkali used while accumulating vanadium concentration in the eluent. Adsorption and desorption data are shown in Tables 2 and 3. The ammonium metavanadate product was calcined to obtain analytical grade vanadium pentoxide, with a calculated vanadium recovery rate of 80%.

[0035] Table 2 Data on adsorption of 3wt% sulfuric acid leachate by Lanxiao strong alkaline anion exchange resin

[0036] Table 3. Desorption data of Lanxiao resin

[0037] 3) Removal of impurities from the adsorption liquid: Remove impurities from the adsorption liquid by adding 4g of polyferric sulfate per liter of adsorption liquid, stirring for 40 minutes, and then adding 1mL of 0.1wt% PAM. The coagulation reaction time is 5 minutes.

[0038] Table 4. Data on impurity removal from adsorption effluent

[0039] The adsorbed liquid after impurity removal was enriched, and then alkali was prepared using a bipolar membrane.

[0040] Table 5. Data on alkali recovery via bipolar membrane

[0041] The alkali prepared by the bipolar membrane can be used for alkali leaching of bauxite slag to realize the recovery of alkali from Bayer sludge.

[0042] The used resin can be regenerated and reused. The regeneration process uses a 4wt%-8wt% sodium hydroxide solution at a temperature of 40~80℃, and a sulfuric acid solution is used for conversion.

[0043] Example 2 This example provides a method for the wet recovery of Bayer sludge, comprising the following steps: Weighing 50g of Bayer sludge powder into a beaker (the waste contains 2.6% vanadium, 0.03% iron, and 0.5% arsenic by mass), adding 250mL of 5wt% sulfuric acid solution, stirring at 400rpm, reacting at 30℃ for 120 minutes, and separating the solid and liquid to obtain a leachate. The leaching results are shown in Table 6: Table 6 Ion concentrations in 5wt% sulfuric acid leachate

[0044] The leachate was collected and adsorbed using BlueX strong-base anion exchange resin, specifically Seplite® LSC-2550, at a rate of 2 BV / h. The adsorption tail liquid was collected. Adsorption was stopped when the effluent concentration reached 0.5 g / L. Desorption was then performed on the resin using an 8 wt% sodium hydroxide solution at 60°C, as described in Example 1, and the eluent was collected. Adsorption and desorption data are shown in Tables 7 and 8. Ammonium sulfate was added to the eluent to obtain ammonium metavanadate. The ammonium metavanadate product was calcined to obtain analytical grade vanadium pentoxide, with a vanadium recovery rate of 83%.

[0045] Table 7 Data on adsorption of 5wt% sulfuric acid leachate by Lanxiao strong alkaline anion exchange resin

[0046] Table 8. Desorption data of Lanxiao resin

[0047] The adsorbed liquid was purified by adding 5g of polyferric sulfate per liter of wastewater, stirring for 50 minutes, and then adding 1mL of 0.1wt% PAM. The coagulation reaction time was 20 minutes.

[0048] Table 9. Data on impurity removal from adsorbed effluent

[0049] The adsorbed liquid after impurity removal was enriched, and alkali was prepared using a bipolar membrane.

[0050] Table 10 Data on Alkali Recovery via Bipolar Membrane

[0051] The alkali prepared by the bipolar membrane can be used for alkali leaching of bauxite slag to realize the recovery of alkali from Bayer sludge.

[0052] Compared to Example 1, Example 3 involved sulfuric acid leaching: 50g of Bayer sludge powder was weighed and added to a beaker, along with 250mL of 1wt% sulfuric acid solution. The mixture was stirred at 400rpm and reacted at 95°C for 60 minutes. Solid-liquid separation was then performed to obtain the leachate. The remaining steps were the same as in Example 1. The leaching results are shown below.

[0053] Table 11 Ion concentrations in 1 wt% sulfuric acid leachate

[0054] When using a 1wt% sulfuric acid leaching solution at pH 10.83, aluminum reacts with AlO2. - Unlike the 3% and 5% leaching solutions where aluminum is completely hydrolyzed into Al(OH)3 precipitate and remains in the residue, the aluminum concentration in the leaching solution is extremely low. At pH 10.8, the aluminum concentration in the leaching solution increases, but as time progresses, the aluminum in the system begins to slowly hydrolyze, forming aluminum hydroxide precipitate. Furthermore, the surface of the amorphous Al(OH)3 flocs adsorbs vanadate, the main component of the solution, leading to the formation of a white precipitate after overnight leaching, indicating poor solution stability.

[0055] Comparative Example 1: This comparative example provides a method for the wet recovery of Bayer sludge, comprising the following steps: Weighing 50g of Bayer sludge powder into a beaker (the vanadium mass fraction of the waste is 2.6%, the iron mass fraction is 0.03%, and the arsenic mass fraction is 0.5%), adding 250mL of 30wt% sulfuric acid solution, stirring at 400rpm, reacting at 90℃ for 60 minutes, and obtaining a leachate. The leaching results are shown in Table 12: Table 12 Ion Concentrations in 30wt% Sulfuric Acid Leachate

[0056] The leachate was collected and adsorbed using BlueX strong-base anion exchange resin, specifically Seplite® LSC-2550, at a rate of 2 BV / h. The adsorption tail liquid was collected. Adsorption was stopped when the effluent concentration reached 0.5 g / L. The resin was then desorbed using an 8 wt% sodium hydroxide solution at 60°C, following the method in Example 1, and the desorbed liquid was collected. The adsorption data are shown in Table 12.

[0057] Table 12 Concentrations of various ions in 30wt% sulfuric acid leachate adsorbed by Lanxiao strong base anion adsorption resin

[0058] The data shows that when using a high-concentration leaching solution, more aluminum ions are leached out, which leads to a decrease in the vanadium penetration and adsorption capacity. Therefore, a low-concentration acid should be used for leaching.

[0059] Comparative Example 2: The leaching steps were identical to those in Example 1, except that the resin was replaced with Seplite® D301 resin during adsorption. This resin is styrene-based, with an exchange group of -N(CH3)2, a particle size range of 0.315-1.25 mm, and an adsorption form of sulfate. The adsorption data are as follows.

[0060] Table 13 Concentrations of various ions in 3wt% sulfuric acid leachate adsorbed by Lanxiao weak base anion exchange resin

[0061] According to the comparison of the examples and comparative examples, the -N(CH3)3Cl quaternary ammonium salt group of the styrene-based macroporous strong base resin in the examples is strongly dissociable. In the strongly alkaline vanadium extraction system, it can completely dissociate to form a large number of permanent positively charged centers, which can efficiently and specifically exchange with vanadate. The vanadate can fully occupy the active sites of the resin, so the vanadate breakthrough adsorption capacity reaches 58.8 g / L, and the ion exchange effect is excellent. In contrast, the -N(CH3)2 tertiary amine group of the styrene-based weak base resin in this strongly alkaline system is inhibited by the high concentration of OH- and can only form a small number of positively charged centers. The effective ion exchange sites are insufficient, and the ion exchange with vanadate is weak. It can only bind a portion of the vanadate through a small amount of ion exchange. Therefore, the vanadate breakthrough adsorption capacity is 30.31 g / L, and the ion exchange effect is significantly weaker than that of the strong base resin.

[0062] Based on the experimental results of the above embodiments and comparative examples, it can be seen that the present invention can separate impurities from Bayer sludge and recover the effective components from Bayer sludge; the vanadium recovery rate can reach over 80%, realizing the comprehensive utilization of sludge. The present invention solves the problem of sludge pollution, transforming it into a secondary resource for reuse, thus achieving the goal of energy conservation and emission reduction.

[0063] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be covered within the scope of the claims and specification of the present invention.

Claims

1. A method for recycling Bayer sludge, characterized in that, The process includes the following steps: Step 1: Leaching Bayer sludge with acid to obtain a leachate; Step 2: Adsorbing vanadium in the leachate with an adsorption resin to obtain an adsorbed resin and an adsorbed liquid; Desorbing the adsorbed resin to obtain a vanadium-containing desorbed liquid; Step 3: Removing impurities from the adsorbed liquid to obtain a purified adsorbed liquid; Step 4: Preparing an alkali using the purified adsorbed liquid.

2. The method for recycling Bayer sludge according to claim 1, characterized in that, In step one, the Bayer sludge is leached with a sulfuric acid solution; the leaching solid-liquid ratio is 1g:3~6ml, the leaching temperature is 30-95℃, and the leaching time is 1-2h; preferably, the mass fraction of the sulfuric acid solution is 1%-8%; preferably, the mass fraction of the sulfuric acid solution is 3%-5%; preferably, the Bayer sludge contains 2.9-20 wt% V2O5, 0.5-1.5 wt% As, and 0.1-0.4 wt% Fe2O3; preferably, the pH of the leachate is 7-11.

3. The method for recycling Bayer sludge according to claim 1, characterized in that, The adsorption resin is a styrene-based macroporous strong base anion exchange resin, the exchange group of the adsorption resin is N(CH3)3Cl, the particle size range of the adsorption resin is 0.315-1.25mm, and the adsorption form of the adsorption resin is sulfate.

4. The method for recycling Bayer sludge according to claim 1, characterized in that, In step two, the adsorption rate of vanadium in the leachate using adsorption resin is 1-2 BV / h; adsorption is stopped when the vanadium concentration in the effluent reaches 0.5 g / L.

5. The method for recycling Bayer sludge according to claim 1, characterized in that, In step two, an alkaline solution is used for desorption; preferably, the alkaline solution is a 5wt%-8wt% sodium hydroxide solution; the desorption temperature is 55~65℃.

6. The method for recycling Bayer sludge according to claim 1, characterized in that, Step two further includes adding ammonium sulfate to the vanadium-containing desorption solution to form ammonium metavanadate; preferably, step two further includes calcining the ammonium metavanadate to obtain vanadium pentoxide.

7. The method for recycling Bayer sludge according to claim 1, characterized in that, The impurity ions in step three are non-alkali metal elements; preferably, the impurity elements include: As, V, Al, and Si.

8. The method for recycling Bayer sludge according to claim 1, characterized in that, In step three, a flocculant is used for impurity removal; preferably, the flocculant includes at least one of polyferric sulfate and PAM.

9. The method for recycling Bayer sludge according to claim 1, characterized in that, In step four, the purified and adsorbed liquid is treated using a bipolar membrane device to prepare an alkali.

10. The method for recycling Bayer sludge according to claim 1, characterized in that, The method further includes step five: using the alkali prepared in step four to produce alumina from bauxite.

Images