CN114477573B - Method for separating trivalent chromium and aluminum in aluminum sulfate solution - Google Patents
Method for separating trivalent chromium and aluminum in aluminum sulfate solution Download PDFInfo
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- C25B9/17—Cells comprising dimensionally-stable non-movable electrodes; Assemblies of constructional parts thereof
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Abstract
The invention relates to a separation method of trivalent chromium and aluminum in an aluminum sulfate solution, which comprises the following steps: (1) Sequentially carrying out first diaphragm electrolysis and first precipitation treatment on an aluminum sulfate solution containing trivalent chromium and aluminum ions, and then carrying out solid-liquid separation to obtain chromate precipitation and first filtrate; (2) And (3) carrying out second precipitation treatment on the first filtrate obtained in the step (1), carrying out solid-liquid separation to obtain silver chloride precipitate and second filtrate, and carrying out second diaphragm electrolysis on the second filtrate to obtain an aluminum sulfate product. According to the separation scheme provided by the invention, the high-efficiency separation of chromium and aluminum is realized by adopting a specific separation process aiming at the solution containing trivalent chromium and aluminum with the pH value of 1.5-3, other impurities are not introduced in the separation process, and the separation efficiency is high.
Description
Technical Field
The invention relates to the field of element separation and purification, in particular to a method for separating trivalent chromium and aluminum in an aluminum sulfate solution.
Background
At present, aluminum mud produced by an aluminum product factory is aluminum hydroxide, and the recycling direction is to prepare an aluminum sulfate water purifying agent. However, the sludge contains a small amount of chromium due to slight corrosion of equipment possibly brought in the process of disposing the aluminum product, and is further transferred into the water purifying agent, wherein the content is 20-200ppm; and brings great risk to the use of the water purifying agent.
The conventional operation is to blend the product with normal aluminum sulfate and sell the product.
The mature chromium removal technology is basically concentrated in the fields of wastewater treatment and discharge, namely, reducing agents are added to ensure that chromium in the solution is trivalent chromium, and then the chromium is converted into chromium hydroxide to be removed from the solution by a method of regulating pH; in the process, other operations are assisted to strengthen the precipitation of chromium, so that the wastewater can reach the discharge standard.
As CN104761084a discloses a method for rapidly removing hexavalent chromium in water based on reduction precipitation, which comprises the following steps: (1) Adjusting the pH value of hexavalent chromium aqueous solution to 3.5-6.0 and the temperature to 10-30 ℃; (2) Adding water into ferric trichloride and sodium borohydride to prepare ferric trichloride mother solution and sodium borohydride mother solution respectively; (3) Sequentially adding the ferric trichloride mother solution and the sodium borohydride mother solution into the hexavalent chromium aqueous solution adjusted in the step (1) under the stirring condition; (4) Stirring is maintained until hexavalent chromium is reduced to trivalent chromium and a precipitate is formed and deposited. According to the scheme, hexavalent chromium in water is removed in one step through the synergistic effect of ferric trichloride and sodium borohydride, including reduction, adsorption and coprecipitation, and the method has the advantages of being easy to obtain, wide in pH value and concentration range of hexavalent chromium wastewater, mild in reaction condition, high in reaction rate, large in removal capacity, good in sedimentation effect and the like.
As disclosed in CN110818123a, a treatment method of trivalent chromium plating wastewater is disclosed, wherein a carboxyl-containing organic acid complexing agent in the wastewater is precipitated by using ferrous ions and calcium ions by utilizing the synergistic effect of the ferrous ions and the calcium ions, and trivalent chromium released from the complex forms a chromium hydroxide precipitate, thereby effectively removing trivalent chromium. And sodium hypochlorite solution is used as an oxidant, so that the ORP value and the oxidation time are controlled, the progress of the oxidation reaction is ensured, the organic additives in the wastewater can be effectively destroyed, and the COD (chemical oxygen demand) of the wastewater is reduced. So that each index meets the wastewater discharge standard, the environment is protected, the wastewater treatment cost is reduced, and the economic benefit is improved.
However, when chromium is removed by using a normal process, aluminum and chromium are precipitated at the same time, and then the aluminum mud is returned to the state; the chromium-containing aluminum sludge cannot be effectively utilized by using a normal process.
Disclosure of Invention
In view of the problems existing in the prior art, the invention aims to provide a method for separating trivalent chromium and aluminum in an aluminum sulfate solution, which solves the problem that the trivalent chromium and aluminum in an acidic aluminum sulfate solution cannot be separated efficiently at present.
To achieve the purpose, the invention adopts the following technical scheme:
the invention provides a separation method of trivalent chromium and aluminum in an aluminum sulfate solution, which comprises the following steps:
(1) Sequentially carrying out first diaphragm electrolysis and first precipitation treatment on an aluminum sulfate solution containing trivalent chromium and aluminum ions, and then carrying out solid-liquid separation to obtain chromate precipitation and first filtrate; the aluminum sulfate solution containing trivalent chromium and aluminum ions is a sulfuric acid system with the pH value of 1.5-3;
(2) And (3) carrying out second precipitation treatment on the first filtrate obtained in the step (1), carrying out solid-liquid separation to obtain silver chloride precipitate and second filtrate, and carrying out second diaphragm electrolysis on the second filtrate to obtain an aluminum sulfate product.
According to the separation scheme provided by the invention, the high-efficiency separation of chromium and aluminum is realized by adopting a specific separation process aiming at the solution containing trivalent chromium and aluminum within a specific pH value range, other impurities are not introduced in the separation process, and the separation efficiency is high. Wherein the solution containing trivalent chromium and aluminum can be obtained by dissolving an aluminum sludge containing chromium in an acid.
In the invention, the special diaphragm is adopted for electrolysis, so that the defect that new impurities are introduced when oxidants such as permanganate and homoferric are adopted for use is avoided, and the problem that hexavalent chromium generated by electrolysis is reduced again when conventional electrolysis equipment is adopted under an acidic condition is also avoided.
In the present invention, the pH of the aluminum sulfate solution containing trivalent chromium and aluminum ions in step (1) is 1.5-3, and may be, for example, 1.5, 1.6, 1.7, 1.8, 1.9, 2, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9 or 3, etc., but not limited to the listed values, and other values not listed in this range are equally applicable.
As a preferable technical scheme of the invention, the concentration of aluminum ions in the aluminum sulfate solution containing trivalent chromium and aluminum ions in the step (1) is 10000-50000ppm, and the concentration of chromium ions is 20-200ppm.
In the present invention, the concentration of aluminum ions in the trivalent chromium and aluminum ion-containing aluminum sulfate solution is 10000 to 40000ppm, and for example, 10000ppm, 12000ppm, 16000ppm, 18000ppm, 20000ppm, 22000ppm, 24000ppm, 26000ppm, 28000ppm, 30000ppm, 32000ppm, 34000ppm, 36000ppm, 38000ppm, 40000ppm, 45000ppm, or 50000ppm may be used, but the present invention is not limited to the values recited above, and other values not recited in the range are equally applicable.
In the present invention, the concentration of chromium ions in the trivalent chromium and aluminum ion-containing aluminum sulfate solution is 20 to 200ppm, and for example, 20ppm, 30ppm, 40ppm, 50ppm, 60ppm, 70ppm, 80ppm, 90ppm, 100ppm, 110ppm, 120ppm, 130ppm, 140ppm, 150ppm, 160ppm, 170ppm, 180ppm, 190ppm, 200ppm, or the like may be used, but the present invention is not limited to the recited values, and other values not recited in the range are equally applicable.
As a preferred embodiment of the present invention, the cathode in the first diaphragm electrolysis in the step (1) includes a titanium plate.
Preferably, the anode in the first diaphragm electrolysis of step (1) comprises a titanium plate plated with iridium ruthenium.
Preferably, the electrode plate voltage in the first diaphragm electrolysis in the step (1) is 20-24V, for example, 20V, 20.5V, 21V, 21.5V, 22V, 22.5V, 23V, 23.5V or 24V, but not limited to the listed values, and other non-listed values in the range are equally applicable.
Preferably, the membrane in the first membrane electrolysis of step (1) is a cation exchange membrane.
Preferably, the electrolyte of the oxidized end in the first diaphragm electrolysis of step (1) comprises a chromium-containing aluminum sulfate solution. Namely the aluminum sulfate solution containing trivalent chromium and aluminum ions in the step (1) of the invention.
Preferably, the electrolyte at the reducing end of the first diaphragm electrolysis in the step (1) comprises a sulfuric acid solution with a mass concentration of 0.5-10%, for example, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9% or 10%, etc., but not limited to the recited values, and other non-recited values within the range are equally applicable.
In a preferred embodiment of the present invention, the first separator in step (1) is electrolyzed for a period of time ranging from 1 to 4 hours, for example, 1 hour, 1.2 hours, 1.4 hours, 1.6 hours, 1.8 hours, 2 hours, 2.2 hours, 2.4 hours, 2.6 hours, 2.8 hours, 3 hours, 3.2 hours, 3.4 hours, 3.6 hours, 3.8 hours or 4 hours, etc., but the present invention is not limited to the recited values, and other non-recited values within the range are equally applicable.
As a preferred embodiment of the present invention, the precipitating agent in the first precipitation treatment in the step (1) includes silver sulfate.
Preferably, the amount of the precipitant added in the first precipitation treatment in the step (1) is 2 to 5 times the molar content of hexavalent chromium in the liquid phase, and may be, for example, 2 times, 2.2 times, 2.4 times, 2.6 times, 2.8 times, 3 times, 3.2 times, 3.4 times, 3.6 times, 3.8 times, 4 times, 4.2 times, 4.4 times, 4.6 times, 4.8 times, or 5 times, etc., but is not limited to the recited values, and other non-recited values within the range are equally applicable.
Preferably, the time of the first precipitation treatment in step (1) is 1-3h, for example, but not limited to, 1h, 1.2h, 1.4h, 1.6h, 1.8h, 2h, 2.02h, 2.04h, 2.06h, 2.08h, 2.1h, 2.12h, 2.14h, 2.16h, 2.18h, 2.2h, 2.4h, 2.6h, 2.8h, or 3h, and the like, and other non-enumerated values within this range are equally applicable.
Preferably, the concentration of chromium ions in the first filtrate in step (1) is less than 1ppm, and may be, for example, 0.9ppm, 0.8ppm, 0.7ppm, 0.6ppm, 0.5ppm, 0.4ppm, 0.3ppm, 0.2ppm or 0.1ppm, etc., but is not limited to the recited values, and other non-recited values within this range are equally applicable.
As a preferred embodiment of the present invention, the precipitant used in the second precipitation treatment of step (2) comprises aluminum chloride.
Preferably, the amount of the precipitant used in the second precipitation treatment in the step (2) is 1 to 3 times the molar amount of silver ions in the liquid phase, and may be, for example, 1 times, 1.2 times, 1.4 times, 1.6 times, 1.8 times, 2 times, 2.2 times, 2.4 times, 2.6 times, 2.8 times, or 3 times, etc., but is not limited to the recited values, and other non-recited values within this range are equally applicable.
Preferably, the second precipitation treatment in step (2) is performed for a period of time ranging from 1 to 2 hours, for example, 1 hour, 1.1 hour, 1.2 hours, 1.3 hours, 1.4 hours, 1.5 hours, 1.6 hours, 1.7 hours, 1.8 hours, 1.9 hours, or 2 hours, etc., but not limited to the recited values, and other non-recited values within this range are equally applicable.
As a preferred embodiment of the present invention, the cathode in the second diaphragm electrolysis in the step (2) includes a titanium plate.
Preferably, the anode in the second diaphragm electrolysis of step (2) comprises a titanium plate plated with iridium ruthenium.
Preferably, the electrode plate voltage in the second diaphragm electrolysis in the step (2) is 12-17V, for example, 12V, 12.2V, 12.4V, 12.6V, 12.8V, 13V, 13.2V, 13.4V, 13.6V, 13.8V, 14V, 14.2V, 14.4V, 14.6V, 14.8V, 15V, 15.2V, 15.4V, 15.6V, 15.8V, 16V, 16.2V, 16.4V, 16.6V, 16.8V or 17V, but not limited to the listed values, and other non-listed values in the range are equally applicable.
Preferably, the membrane in the second membrane electrolysis of step (2) is a cation exchange membrane.
Preferably, the electrolyte in the second diaphragm electrolysis of step (2) is the second filtrate.
Preferably, the electrolyte at the reducing end in the second diaphragm electrolysis in the step (2) comprises a chlorine-containing aluminum sulfate solution or a sulfuric acid solution with the mass concentration of 0.5-10%;
preferably, the chlorine-containing aluminum sulfate solution is a solution after oxidation end electrolysis in the second diaphragm electrolysis.
In the scheme, when the second diaphragm electrolysis is performed for the first time, the electrolyte at the reduction end is sulfuric acid solution with the mass concentration of 0.5-10% or prepared chlorine-containing aluminum sulfate solution, and the electrolyte at the oxidation end is second filtrate. When the process is carried out again, the electrolyte at the reduction end adopts the solution after the electrolysis at the oxidation end in the electrolysis as the electrolyte, the concentration of chloride ions in the electrolyte is less than 30ppm, and the concentration of aluminum ions is 9900-50000ppm.
In a preferred embodiment of the present invention, the time for electrolysis of the second separator in the step (2) is 1 to 4 hours, for example, 1 hour, 1.2 hours, 1.4 hours, 1.6 hours, 1.8 hours, 2 hours, 2.2 hours, 2.4 hours, 2.6 hours, 2.8 hours, 3 hours, 3.2 hours, 3.4 hours, 3.6 hours, 3.8 hours or 4 hours, etc., but the present invention is not limited to the recited values, and other non-recited values in the range are equally applicable.
As a preferred technical scheme of the invention, the separation method comprises the following steps:
(1) Sequentially carrying out first diaphragm electrolysis and first precipitation treatment on an aluminum sulfate solution containing trivalent chromium and aluminum ions, and then carrying out solid-liquid separation to obtain chromate precipitation and first filtrate;
(2) Performing second precipitation treatment on the first filtrate obtained in the step (1), performing solid-liquid separation to obtain silver chloride precipitate and second filtrate, and performing second diaphragm electrolysis on the second filtrate to obtain an aluminum sulfate product;
the concentration of aluminum ions in the aluminum sulfate solution containing trivalent chromium and aluminum ions in the step (1) is 10000-50000ppm, and the concentration of chromium ions is 20-200ppm; the pH value of the aluminum sulfate solution containing trivalent chromium and aluminum ions is 1.5-3; the aluminum sulfate solution containing trivalent chromium and aluminum ions is a sulfuric acid system; the cathode in the first diaphragm electrolysis comprises a titanium plate; the anode in the first diaphragm electrolysis comprises a titanium plate plated with iridium and ruthenium; the voltage between polar plates in the first diaphragm electrolysis is 20-24V; the membrane in the first membrane electrolysis is a cation exchange membrane; the electrolyte of the oxidation end in the first diaphragm electrolysis comprises a chromium-containing aluminum sulfate solution; the electrolyte at the reduction end in the first diaphragm electrolysis comprises sulfuric acid solution with the mass concentration of 0.5-10%; the first diaphragm electrolysis time is 1-4h; the precipitant in the first precipitation treatment comprises silver sulfate; the adding amount of the precipitant in the first precipitation treatment is 2-5 times of the mol content of hexavalent chromium in the liquid phase; the time of the first precipitation treatment is 1-3h; the concentration of chromium ions in the first filtrate is less than 1ppm;
the precipitant used in the second precipitation treatment of step (2) comprises aluminum chloride; the addition amount of the precipitant used in the second precipitation treatment is 1-3 times of the molar amount of silver ions in the liquid phase; the second precipitation treatment time is 1-2h; the cathode in the second diaphragm electrolysis comprises a titanium plate; the anode in the second diaphragm electrolysis comprises a titanium plate plated with iridium and ruthenium; the voltage between polar plates in the second diaphragm electrolysis is 12-17V; the membrane in the second membrane electrolysis is a cation exchange membrane; the electrolyte of the oxidation end in the second diaphragm electrolysis comprises a chlorine-containing aluminum sulfate solution; the electrolyte at the reduction end in the second diaphragm electrolysis comprises a chlorine-containing aluminum sulfate solution; the second diaphragm electrolysis time is 1-4h.
Compared with the prior art, the invention has at least the following beneficial effects:
(1) According to the technical scheme, trivalent chromium is oxidized by adopting a specific electrolysis process and a specific precipitation process under the condition that the specific pH value is 1.5-3, then a specific precipitant is selected to precipitate chromium, and then the specific electrolysis process is adopted to further purify aluminum, so that the problem that trivalent chromium and aluminum in the existing acidic aluminum sulfate solution are difficult to separate is solved, and the high-efficiency separation of chromium and aluminum is realized. The silver sulfate is used as a chromium precipitating agent and is also heavy metal, so that a certain risk exists, but aluminum chloride is used as a silver removing agent in the follow-up process, residual silver ions are removed, chloride ions are removed through electrolytic oxidation, hexavalent chromium ions are removed through electrolytic reduction, the whole process reduces the use risk of aluminum sulfate products (chromium in the aluminum sulfate products is removed), other impurities are not introduced into the final products, and products with higher quality can be obtained.
(2) The removal rate of chromium in the aluminum sulfate solution is more than 95%, the content of residual chromium is less than 1ppm, the content of residual silver ions is less than or equal to 0.03ppm, and the loss rate of aluminum is less than 1%.
Detailed Description
For a better illustration of the present invention, which is convenient for understanding the technical solution of the present invention, exemplary but non-limiting examples of the present invention are as follows:
example 1
The embodiment provides a separation method of trivalent chromium and aluminum in an aluminum sulfate solution, which comprises the following steps:
(1) Sequentially carrying out first diaphragm electrolysis and first precipitation treatment on an aluminum sulfate solution containing trivalent chromium and aluminum ions, and then carrying out solid-liquid separation to obtain chromate precipitation and first filtrate;
(2) Performing second precipitation treatment on the first filtrate obtained in the step (1), performing solid-liquid separation to obtain silver chloride precipitate and second filtrate, and performing second diaphragm electrolysis on the second filtrate to obtain an aluminum sulfate product;
the concentration of aluminum ions in the aluminum sulfate solution containing trivalent chromium and aluminum ions in the step (1) is 25000ppm, and the concentration of chromium ions is 20ppm; the pH value of the aluminum sulfate solution containing trivalent chromium and aluminum ions is 2; the aluminum sulfate solution containing trivalent chromium and aluminum ions is a sulfuric acid system; the cathode in the first diaphragm electrolysis is a titanium plate; the anode in the first diaphragm electrolysis is a titanium plate plated with iridium and ruthenium; the voltage between polar plates in the first diaphragm electrolysis is 22V; the membrane in the first membrane electrolysis is a cation exchange membrane; the electrolyte at the oxidation end in the first diaphragm electrolysis is a chromium-containing aluminum sulfate solution (the aluminum content is 25000ppm, and the trivalent chromium ion content is 20ppm, namely, the aluminum sulfate solution containing trivalent chromium and aluminum ions); the electrolyte at the reduction end in the first diaphragm electrolysis is sulfuric acid solution with the mass concentration of 5%; the first diaphragm electrolysis time is 2.5h; the precipitant in the first precipitation treatment is silver sulfate; the adding amount of the precipitant in the first precipitation treatment is 3.5 times of the mol content of hexavalent chromium in the liquid phase; the time of the first precipitation treatment is 1.5h; the concentration of chromium ions in the first filtrate is 0.8ppm;
the precipitant used in the second precipitation treatment in the step (2) is aluminum chloride; the addition amount of the precipitant used in the second precipitation treatment is 2 times of the molar amount of silver ions in the liquid phase; the second precipitation treatment time is 1.5h; the cathode in the second diaphragm electrolysis is a titanium plate; the anode in the second diaphragm electrolysis is a titanium plate plated with iridium and ruthenium; the voltage between polar plates in the second diaphragm electrolysis is 15V; the membrane in the second membrane electrolysis is a cation exchange membrane; the electrolyte at the oxidation end in the second diaphragm electrolysis is a chlorine-containing aluminum sulfate solution (the aluminum content is 24850ppm, and the chloride ion content is 1300 ppm); the electrolyte at the reduction end in the second diaphragm electrolysis is a chlorine-containing aluminum sulfate solution (the aluminum ion content is 24850ppm, the chloride ion content is 21ppm, and the solution is an electrolyte at the oxidation end after the second diaphragm electrolysis is treated once by adopting the same scheme); the second diaphragm electrolysis time is 1h.
The index of the separated aluminum sulfate product is shown in Table 1.
Example 2
The embodiment provides a separation method of trivalent chromium and aluminum in an aluminum sulfate solution, which comprises the following steps:
(1) Sequentially carrying out first diaphragm electrolysis and first precipitation treatment on an aluminum sulfate solution containing trivalent chromium and aluminum ions, and then carrying out solid-liquid separation to obtain chromate precipitation and first filtrate;
(2) Performing second precipitation treatment on the first filtrate obtained in the step (1), performing solid-liquid separation to obtain silver chloride precipitate and second filtrate, and performing second diaphragm electrolysis on the second filtrate to obtain an aluminum sulfate product;
the concentration of aluminum ions in the aluminum sulfate solution containing trivalent chromium and aluminum ions in the step (1) is 10000ppm, and the concentration of chromium ions is 200ppm; the pH value of the aluminum sulfate solution containing trivalent chromium and aluminum ions is 2.8; the aluminum sulfate solution containing trivalent chromium and aluminum ions is a sulfuric acid system; the cathode in the first diaphragm electrolysis is a titanium plate; the anode in the first diaphragm electrolysis is a titanium plate plated with iridium and ruthenium; the voltage between polar plates in the first diaphragm electrolysis is 20V; the membrane in the first membrane electrolysis is a cation exchange membrane; the electrolyte at the oxidation end in the first diaphragm electrolysis is a chromium-containing aluminum sulfate solution (the aluminum content is 10000ppm, and the chromium ion content is 200ppm, namely, the aluminum sulfate solution containing trivalent chromium and aluminum ions); the electrolyte at the reduction end in the first diaphragm electrolysis is sulfuric acid solution with the mass concentration of 2%; the first diaphragm electrolysis time is 1h; the precipitant in the first precipitation treatment is silver sulfate; the adding amount of the precipitant in the first precipitation treatment is 2 times of the mol content of hexavalent chromium in the liquid phase; the time of the first precipitation treatment is 2h; the concentration of chromium ions in the first filtrate is 0.4ppm;
the precipitant used in the second precipitation treatment in the step (2) is aluminum chloride; the addition amount of the precipitant used in the second precipitation treatment is 3 times of the molar amount of silver ions in the liquid phase; the second precipitation treatment time is 1h; the cathode in the second diaphragm electrolysis is a titanium plate; the anode in the second diaphragm electrolysis is a titanium plate plated with iridium and ruthenium; the voltage between polar plates in the second diaphragm electrolysis is 12V; the membrane in the second membrane electrolysis is a cation exchange membrane; the electrolyte at the oxidation end in the second diaphragm electrolysis is a chlorine-containing aluminum sulfate solution (the aluminum content is 9920ppm and the chloride ion content is 800 ppm); the electrolyte at the reduction end in the second diaphragm electrolysis is a chlorine-containing aluminum sulfate solution (the aluminum ion content is 9920ppm and the chloride ion content is 17ppm, and the solution is an electrolyte at the oxidation end after the second diaphragm electrolysis is treated once by adopting the same scheme); the second diaphragm electrolysis time is 2.5h.
The index of the separated aluminum sulfate product is shown in Table 1.
Example 3
The embodiment provides a separation method of trivalent chromium and aluminum in an aluminum sulfate solution, which comprises the following steps:
(1) Sequentially carrying out first diaphragm electrolysis and first precipitation treatment on an aluminum sulfate solution containing trivalent chromium and aluminum ions, and then carrying out solid-liquid separation to obtain chromate precipitation and first filtrate;
(2) Performing second precipitation treatment on the first filtrate obtained in the step (1), performing solid-liquid separation to obtain silver chloride precipitate and second filtrate, and performing second diaphragm electrolysis on the second filtrate to obtain an aluminum sulfate product;
the concentration of aluminum ions in the aluminum sulfate solution containing trivalent chromium and aluminum ions in the step (1) is 40000ppm, and the concentration of chromium ions is 20ppm; the pH value of the aluminum sulfate solution containing trivalent chromium and aluminum ions is 1.5; the aluminum sulfate solution containing trivalent chromium and aluminum ions is a sulfuric acid system; the cathode in the first diaphragm electrolysis is a titanium plate; the anode in the first diaphragm electrolysis is a titanium plate plated with iridium and ruthenium; the voltage between polar plates in the first diaphragm electrolysis is 24V; the membrane in the first membrane electrolysis is a cation exchange membrane; the electrolyte of the oxidation end in the first diaphragm electrolysis is a chromium-containing aluminum sulfate solution (the aluminum content is 40000ppm, and the chromium ion content is 20ppm, namely, the aluminum sulfate solution containing trivalent chromium and aluminum ions); the electrolyte at the reduction end in the first diaphragm electrolysis is sulfuric acid solution with the mass concentration of 10%; the first diaphragm electrolysis time is 4h; the precipitant in the first precipitation treatment is silver sulfate; the adding amount of the precipitant in the first precipitation treatment is 5 times of the mol content of hexavalent chromium in the liquid phase; the time of the first precipitation treatment is 3 hours; the concentration of chromium ions in the first filtrate is 0.2ppm;
the precipitant used in the second precipitation treatment in the step (2) is aluminum chloride; the addition amount of the precipitant used in the second precipitation treatment is 1 time of the molar amount of silver ions in the liquid phase; the time of the second precipitation treatment is 2h; the cathode in the second diaphragm electrolysis is a titanium plate; the anode in the second diaphragm electrolysis is a titanium plate plated with iridium and ruthenium; the voltage between polar plates in the second diaphragm electrolysis is 17V; the membrane in the second membrane electrolysis is a cation exchange membrane; the electrolyte at the oxidation end in the second diaphragm electrolysis is a chlorine-containing aluminum sulfate solution (the aluminum content is 39800ppm and the chloride ion content is 1400 ppm); the electrolyte at the reduction end in the second diaphragm electrolysis is a chlorine-containing aluminum sulfate solution (the aluminum ion content is 39800ppm, the chloride ion content is 11ppm, and the solution is an electrolyte at the oxidation end after the second diaphragm electrolysis is treated once by adopting the same scheme); the second diaphragm electrolysis time is 4h.
The index of the separated aluminum sulfate product is shown in Table 1.
TABLE 1
In the invention, the detection of hexavalent chromium in the solution is carried out according to GB 7467-87 to verify that trivalent chromium is converted into hexavalent chromium after first diaphragm electrolysis. The total chromium, al, ag and other elements are detected by ICP.
According to the embodiment provided by the invention, the problem that trivalent chromium and aluminum are difficult to separate in the acid system at present is solved by adopting a specific electrolysis process and a specific precipitation process, and the high-efficiency separation of chromium and aluminum is realized. The chromium-aluminum separation process is environment-friendly, no new impurity ions are introduced, and the method accords with the environment-friendly trend of the current chemical process.
It is stated that the detailed structural features of the present invention are described by the above embodiments, but the present invention is not limited to the above detailed structural features, i.e., it does not mean that the present invention must be implemented depending on the above detailed structural features. It should be apparent to those skilled in the art that any modifications of the present invention, equivalent substitutions of selected components of the present invention, addition of auxiliary components, selection of specific modes, etc., are within the scope of the present invention and the scope of the disclosure.
The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited to the specific details of the above embodiments, and various simple modifications can be made to the technical solution of the present invention within the scope of the technical concept of the present invention, and all the simple modifications belong to the protection scope of the present invention.
In addition, the specific features described in the above embodiments may be combined in any suitable manner, and in order to avoid unnecessary repetition, various possible combinations are not described further.
Moreover, any combination of the various embodiments of the invention can be made without departing from the spirit of the invention, which should also be considered as disclosed herein.
Claims (23)
1. A method for separating trivalent chromium and aluminum from an aluminum sulfate solution, the method comprising the steps of:
(1) Sequentially carrying out first diaphragm electrolysis and first precipitation treatment on an aluminum sulfate solution containing trivalent chromium and aluminum ions, and then carrying out solid-liquid separation to obtain chromate precipitation and first filtrate; the aluminum sulfate solution is a sulfuric acid system with the pH value of 1.5-3; the precipitant in the first precipitation treatment is silver sulfate;
(2) Performing second precipitation treatment on the first filtrate obtained in the step (1), performing solid-liquid separation to obtain silver chloride precipitate and second filtrate, and performing second diaphragm electrolysis on the second filtrate to obtain an aluminum sulfate product; the precipitant used in the second precipitation treatment is aluminum chloride.
2. The separation method according to claim 1, wherein the concentration of aluminum ions in the aluminum sulfate solution containing trivalent chromium and aluminum ions in the step (1) is 10000 to 50000ppm and the concentration of chromium ions is 20 to 200ppm.
3. The separation method of claim 1, wherein the cathode in the first diaphragm electrolysis of step (1) comprises a titanium plate.
4. The separation method of claim 1, wherein the anode in the first diaphragm electrolysis of step (1) comprises a titanium plate plated with iridium ruthenium.
5. The separation method of claim 1, wherein the first diaphragm electrolysis of step (1) has an inter-plate voltage of 20-24V.
6. The separation method of claim 1, wherein the membrane in the first membrane electrolysis of step (1) is a cation exchange membrane.
7. The separation method of claim 1, wherein the electrolyte at the oxidized end of the first diaphragm electrolysis of step (1) comprises a chromium-containing aluminum sulfate solution.
8. The separation method according to claim 1, wherein the electrolyte at the reducing end in the first diaphragm electrolysis of step (1) comprises a sulfuric acid solution having a mass concentration of 0.5 to 10%.
9. The separation method of claim 1, wherein the first membrane electrolysis of step (1) is performed for a period of time ranging from 1 to 4 hours.
10. The separation method according to claim 1, wherein the amount of the precipitant added in the first precipitation treatment in the step (1) is 2 to 5 times the molar content of hexavalent chromium in the liquid phase.
11. The separation process of claim 1, wherein the first precipitation treatment of step (1) is for a period of time ranging from 1 to 3 hours.
12. The separation method of claim 1, wherein the concentration of chromium ions in the first filtrate of step (1) is < 1ppm.
13. The separation method according to claim 1, wherein the amount of the precipitant used in the second precipitation treatment in the step (2) is 1 to 3 times the molar amount of silver ions in the liquid phase.
14. The separation method according to claim 1, wherein the second precipitation treatment of step (2) is performed for a period of 1 to 2 hours.
15. The separation method of claim 1, wherein the cathode in the second diaphragm electrolysis of step (2) comprises a titanium plate.
16. The separation method of claim 1, wherein the anode in the second diaphragm electrolysis of step (2) comprises a titanium plate plated with iridium ruthenium.
17. The separation method of claim 1, wherein the inter-plate voltage in the second diaphragm electrolysis of step (2) is 12-17V.
18. The separation method of claim 1, wherein the membrane in the second membrane electrolysis of step (2) is a cation exchange membrane.
19. The separation method of claim 1, wherein the electrolyte at the oxidized end of the second membrane electrolysis of step (2) is the second filtrate.
20. The separation method according to claim 1, wherein the electrolyte at the reducing end in the second diaphragm electrolysis of step (2) comprises a chlorine-containing aluminum sulfate solution or a sulfuric acid solution of 0.5 to 10% by mass concentration.
21. The separation method of claim 20, wherein the chlorine-containing aluminum sulfate solution is a solution after oxidation end electrolysis in the second diaphragm electrolysis.
22. The separation method of claim 1, wherein the second membrane is electrolyzed in step (2) for a period of time ranging from 1 to 4 hours.
23. The separation method according to any one of claims 1 to 22, wherein the separation method comprises the steps of:
(1) Sequentially carrying out first diaphragm electrolysis and first precipitation treatment on an aluminum sulfate solution containing trivalent chromium and aluminum ions, and then carrying out solid-liquid separation to obtain chromate precipitation and first filtrate;
(2) Performing second precipitation treatment on the first filtrate obtained in the step (1), performing solid-liquid separation to obtain silver chloride precipitate and second filtrate, and performing second diaphragm electrolysis on the second filtrate to obtain an aluminum sulfate product;
the concentration of aluminum ions in the aluminum sulfate solution containing trivalent chromium and aluminum ions in the step (1) is 10000-50000ppm, and the concentration of chromium ions is 20-200ppm; the pH value of the aluminum sulfate solution is 1.5-3; the aluminum sulfate solution is a sulfuric acid system; the cathode in the first diaphragm electrolysis comprises a titanium plate; the anode in the first diaphragm electrolysis comprises a titanium plate plated with iridium and ruthenium; the voltage between polar plates in the first diaphragm electrolysis is 20-24V; the membrane in the first membrane electrolysis is a cation exchange membrane; the electrolyte of the oxidation end in the first diaphragm electrolysis comprises a chromium-containing aluminum sulfate solution; the electrolyte at the reduction end in the first diaphragm electrolysis comprises sulfuric acid solution with the mass concentration of 0.5-10%; the first diaphragm electrolysis time is 1-4h; the precipitant in the first precipitation treatment comprises silver sulfate; the adding amount of the precipitant in the first precipitation treatment is 2-5 times of the mol content of hexavalent chromium in the liquid phase; the time of the first precipitation treatment is 1-3h; the concentration of chromium ions in the first filtrate is less than 1ppm;
the precipitant used in the second precipitation treatment of step (2) comprises aluminum chloride; the addition amount of the precipitant used in the second precipitation treatment is 1-3 times of the molar amount of silver ions in the liquid phase; the second precipitation treatment time is 1-2h; the cathode in the second diaphragm electrolysis comprises a titanium plate; the anode in the second diaphragm electrolysis comprises a titanium plate plated with iridium and ruthenium; the voltage between polar plates in the second diaphragm electrolysis is 12-17V; the membrane in the second membrane electrolysis is a cation exchange membrane; electrolyte at an oxidation end in the second diaphragm electrolysis is the second filtrate; the electrolyte of the reduction end in the second diaphragm electrolysis comprises a chlorine-containing aluminum sulfate solution or a sulfuric acid solution with the mass concentration of 0.5-10%, wherein the chlorine-containing aluminum sulfate solution is a solution after the oxidation end in the second diaphragm electrolysis is electrolyzed; the second diaphragm electrolysis time is 1-4h.
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