JP2006212580A - Method for treating acid waste liquid containing iron and chromium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for treating an acid waste liquid containing iron and chromium which can sufficiently be used as an iron source and a stainless raw material separately by separating a metal hydroxide including iron and chromium to be precipitated by neutralization treatment of the acid waste liquid containing iron and chromium by each type. <P>SOLUTION: The acid waste liquid containing at least a trivalent chromium ion and a divalent iron ion generated when a chromium stainless steel sheet is subjected to an acid wash is continuously supplied to a first reactor, a pH is adjusted in a range of 4.5 to 6.5 by an alkaline agent, and a particle mainly having chromium hydroxide is deposited, separated from a liquid part and recovered. The liquid part is introduced into a second reactor, the divalant iron ion is oxidized by biological or chemical oxidation means, and a particle having mainly iron hydroxide (III) is precipitated, separated and recovered. Further, a waste liquid containing a hexavalant chromium ion is subjected to reduction treatment by slurry educed in the first reactor and a chromium concentration in the particle is increased to be recovered. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for separating and recovering a chromium content and an iron content in an acidic waste liquid by treating an acidic waste liquid containing divalent iron ions and chromium ions.

  When rolling a chromium-based stainless steel plate, the scale generated on the surface of the steel plate is removed by pickling treatment. Further, chromate composed of hexavalent chromium ions is used in the surface treatment of various metal products or coating factories.

  In the pickling treatment of the chromium-based stainless steel sheet, an acidic liquid containing sulfuric acid is used, so that an acidic waste liquid in which metals such as iron and chromium in the chromium-based stainless steel sheet are dissolved is generated.

  In addition, chromate containing hexavalent chromium ions is used for surface treatment in electronic parts manufacturing, machine parts manufacturing, automotive steel sheet manufacturing, stainless steel manufacturing, film factories, etc. Waste liquid containing ions is generated. This waste liquid is obtained by reducing hexavalent chromium ions with a reducing agent such as sodium sulfite or ferrous sulfate, adding an alkaline solution and neutralizing at pH 6 to 9, and then adding a flocculant to thickener or the like. The metal hydroxide is precipitated into a slurry by using the settling basin, and the slurry is dehydrated and processed into a sludge cake. Therefore, the sludge becomes a cake containing a metal such as chromium in addition to iron, and it is difficult to recycle components as an iron source. In addition, these metal hydroxides have small particles and a low sedimentation rate, and the water content of the sludge cake produced when the slurry is dehydrated is high, so that the sludge cake needs to be dried before use. Moreover, since the sludge is transported in a state containing a large amount of water, there is a problem that transportation costs increase.

On the other hand, there is a method disclosed in Patent Document 1, which adds metal iron powder to a sulfuric acid pickling waste liquid having a high chromium concentration to neutralize free sulfuric acid in the solution to pH 2-4. One step, a second step of adding chromium to the solution obtained in the first step to adjust the pH to 4-6 to produce chromium hydroxide, and separating the produced chromium hydroxide from the solution by precipitation The third step is a process, the fourth step is to filter the solution that has flowed out in the third step, and the step is to subsequently obtain iron oxide from the solution that has flowed out from the fourth step. Patent Document 1 aims to obtain a high-purity iron oxide powder raw material free from impurities by almost completely removing chromium.
JP-A-3-146422

  However, in Patent Document 1, when neutralizing with iron powder as metal powder, the neutralization reaction rate is slow, and it is necessary to input more iron powder than the theoretical equivalent required for neutralization in the first step and the second step. In the chromium hydroxide separated in the third step, unreacted iron powder is mixed and the purity of the separated chromium hydroxide is lowered. Therefore, in patent document 1, the solid substance containing the chromium hydroxide collect | recovered from the 3rd process cannot maintain chromium concentration stably so that it can fully be used as a chromium raw material.

  Accordingly, the present invention has been made in view of such circumstances, and separates metal hydroxides mainly containing iron and chromium, which are precipitated by neutralization treatment of an acidic waste liquid containing iron and chromium, for each type, For chromium, the chromium concentration that can be used when adjusting the chromium component at the time of stainless steel production, or the chromium concentration that can be used economically enough at the time of chromic acid production, and for iron compounds, it contains almost no chromium and can be used sufficiently as an iron source It aims at providing the processing method of the acidic waste liquid containing iron and chromium which can aim at effective utilization as sludge.

  The present invention also provides a slurry containing particles mainly composed of chromium hydroxide in a waste liquid containing hexavalent chromium ions discharged from an electronic component manufacturing industry, a machine parts manufacturing industry, an automobile steel plate manufacturing industry, a stainless steel plate manufacturing industry, or a coating factory. And reducing the hexavalent chromium ions, and then precipitating chromium to further increase the chromium concentration in the particles mainly composed of chromium hydroxide.

  In order to solve the above problems, the inventor of the present invention has an acidic waste liquid (hereinafter referred to as “pH 3” or less) containing at least trivalent chromium ions and divalent iron ions generated when the chromium-based stainless steel plate is pickled with sulfuric acid. It is also called “acid waste liquid”) and electronic component manufacturing industry, machine component manufacturing industry, automobile steel sheet manufacturing industry, stainless steel sheet manufacturing industry, or waste liquid containing hexavalent chromium ions discharged from coating factories. As a result of the examination, the following was found.

  By using a neutralizing agent such as magnesium hydroxide, caustic soda, calcium carbonate, quicklime, and slaked lime in the acidic waste liquid, it is possible to mainly precipitate chromium hydroxide by adjusting the pH to 4.5 to 6.5. Preferably, by adjusting the pH to 5 to 6, almost all of the trivalent chromium ions in the acidic waste liquid are precipitated as chromium hydroxide. At that time, a part of the divalent iron ions precipitates, but most remains dissolved. Compared to metal powders such as iron powder, these neutralizers have a high reaction rate, can be neutralized with an input of almost the theoretical equivalent, and unreacted neutralizers are mixed with chromium hydroxide. It's hard to get into the situation. The precipitated chromium hydroxide is colloidal and difficult to dehydrate, and the cake after dehydration becomes a cake having a moisture content of 60 to 80%.

  When recycling the cake as a chromium raw material used for applications such as stainless steel, the pretreatment such as drying is omitted or simplified, and the Cr content in a wet state is further improved as described above. It is possible to improve dehydration and filterability by increasing the particle size by further bringing trivalent chromium ions into contact with the precipitated particles of chromium hydroxide and precipitating them on the surface of the particles of chromium hydroxide. I found it. Thereby, the water | moisture content after spin-drying | dehydration can be improved greatly to 20 to 50%, and can be made more suitable for recycling. Further, it has been found that, due to the improved filterability, the filtration method can be applied as a solid-liquid separation method by improving the filtration rate by filtration other than the commonly used precipitation method and centrifugal separation method.

  Furthermore, it was discovered that the chromium hydroxide-based particles deposited as described above contain a compound containing divalent iron ions, and the electronic parts manufacturing industry, machine parts manufacturing industry, automobile steel plate manufacturing , A stainless steel plate manufacturing industry, or by introducing waste liquid containing hexavalent chromium ions generated in the film factory, the compound consisting of divalent iron ions in the particles reduces hexavalent chromium ions to trivalent chromium ions, It has been found that the chromium concentration in the particles can be further increased by binding trivalent chromium ions to chromium hydroxide on the particle surface.

  Further, the chromium hydroxide-based particles precipitated as described above are separated from the liquid part, and the divalent iron ions dissolved in the liquid part are used by using biological oxidation means or chemical oxidation means. It was found that iron can be separated from the liquid by oxidizing divalent iron ions to trivalent iron ions, precipitating and separating iron (III) hydroxide.

The present invention has been made on the basis of the above knowledge, and the summary thereof is as follows. (1) After charging an acidic waste liquid containing divalent iron ions and trivalent chromium ions into the first reaction tank. Or, while adding, adjusting the acidic waste liquid in the range of pH 4.5 to pH 6.5 by adding an alkaline agent, precipitated chromium hydroxide-based particles, and then concentrated by solid-liquid separation operation, A method for treating an acidic waste liquid containing iron and chromium, characterized in that the slurry or cake contains particles mainly composed of chromium hydroxide.

  (2) Including the iron and chromium as described in (1) above, wherein trivalent chromium ions are further brought into contact with the particles mainly composed of chromium hydroxide to increase the particle size, and then solid-liquid separation operation is performed. Treatment method of acidic waste liquid.

  (3) The method for treating an acidic waste liquid containing iron and chromium according to (1) or (2), wherein the dissolved oxygen concentration in the first reaction tank is 0 to 2 mg / L.

  (4) The method for treating an acidic waste liquid containing iron and chromium according to any one of (1) to (3), wherein the solid-liquid separation operation is filtration using a separation membrane.

  (5) The method for treating an acidic waste liquid containing iron and chromium according to (4), wherein the separation membrane has a pore size of 1 to 100 μm.

  (6) The iron and chromium according to any one of (1) to (5), wherein the acidic waste liquid is an acidic waste liquid generated during pickling treatment of a chromium-based stainless steel plate in an iron making process. Method for treating acidic waste liquid containing

  (7) The liquid part containing the divalent iron ions generated by the solid-liquid separation operation is put into a second reaction tank, and the divalent iron ions are oxidized into trivalent iron ions by a chemical oxidation means. The iron hydroxide (III) -based particles are precipitated and then concentrated by solid-liquid separation operation to obtain a slurry or cake containing the iron (III) hydroxide-based particles ( The processing method of the acidic waste liquid containing iron and chromium as described in any one of 1)-(6).

  (8) The liquid part containing the divalent iron ions generated by the solid-liquid separation operation is put into a second reaction tank, and an alkaline agent is added to change the pH in the second reaction tank from 3 to 5. Controlled and oxidized by oxidation of the divalent iron ions to trivalent iron ions by biological oxidation means to precipitate particles mainly composed of iron (III) hydroxide, and then concentrated by solid-liquid separation operation. The method for treating an acidic waste liquid containing iron and chromium according to any one of (1) to (6), wherein the slurry is a slurry or cake containing iron (III) -based particles.

  (9) The slurry or cake containing the chromium hydroxide-based particles and the waste liquid containing hexavalent chromium ions are added to and mixed in the third reaction tank, and the 2 remaining in the slurry or cake. A hexavalent chromium ion is reduced to a trivalent chromium ion with a compound containing a valent iron ion, and the trivalent chromium ion is precipitated on the surface of the chromium hydroxide-based particle, thereby reducing the chromium concentration in the chromium hydroxide-based particle. The method for treating an acidic waste liquid containing iron and chromium according to any one of (1) to (8), wherein the treatment is performed.

  (10) The alkali agent added to the first reaction tank is at least one selected from the group consisting of magnesium oxide, magnesium carbonate, and magnesium hydroxide. The processing method of the acidic waste liquid containing iron and chromium as described in any one of 9).

  According to the treatment of the acidic waste liquid containing divalent iron ions and chromium ions of the present invention, it can be separated into a chromium hydroxide-based dehydrated cake and an iron (III) hydroxide-based dehydrated cake, It can be effectively used as an iron source in the steel industry. Furthermore, by making the particles mainly composed of chromium hydroxide into dense particles having a large diameter, the filterability and dewaterability of the slurry containing the particles can be improved.

  Hereinafter, the present invention will be described in more detail.

  The processing method of the acidic waste liquid containing iron and chromium according to the present invention is an acidic waste liquid containing divalent iron ions and trivalent chromium ions.

  The acidic waste liquid is preferably an acidic waste liquid generated during pickling treatment of a chromium-based stainless steel plate in an iron making process. A general acidic waste liquid has a pH of 4 or less, preferably 3 or less, contains 0.1 to 10% by mass of a metal such as Fe, Cr, Ni, etc., and most of these metals exist as metal ions. Yes.

  FIG. 1 shows the relationship between the pH of a solution containing 23,000 mg / L and 3,000 mg / L of divalent iron ions and trivalent chromium ions, respectively, and the residual ratio of elements in the waste water. As shown in FIG. 1, trivalent chromium ions are precipitated at pH 4 or higher, and divalent iron ions are partially deposited at the same time as trivalent chromium ions are precipitated at pH 4 to 5, and are almost entirely precipitated at pH 7 or higher.

  In the present invention, in order to separate divalent iron ions and trivalent chromium ions, first, an acidic waste liquid containing divalent iron ions and trivalent chromium ions having a pH of 4 or less is charged into the first reaction tank or In addition to adding the alkaline agent and adjusting the pH of the acidic waste liquid to 4.5 to 6.5, the chromium hydroxide-based particles are precipitated, and then concentrated by a solid-liquid separation operation. The solid part is recovered as a cake or slurry containing the chromium hydroxide-based particles.

  The chromium hydroxide-based particles precipitated in the first reaction layer preferably contain 20 to 40% by mass of chromium (III) hydroxide with respect to the total amount of the particles.

  The separated liquid portion in which the divalent iron ions remain is put into the second reaction tank, and the divalent iron ions are oxidized to trivalent iron ions by using a chemical oxidation means or the like to be hydroxylated. After precipitation as iron (III) -based particles, a slurry or cake containing the iron (III) -based particles is preferably obtained by solid-liquid separation. As the chemical oxidation means, specifically, divalent iron remaining in the liquid part by aeration of air or oxygen to the liquid part while adjusting the pH of the separated liquid part to 7 to 10 A means for spontaneously oxidizing the ions into trivalent iron ions and precipitating them as iron (III) hydroxide is preferably used. Thereby, it can isolate | separate into iron and chromium. Here, aeration is one of chemical oxidation means. The iron (III) hydroxide-based particles preferably contain 75 to 100% by mass of iron (III) hydroxide with respect to the total amount of the particles. In order to oxidize divalent iron ions and precipitate iron (III) hydroxide, biological oxidation means using iron-oxidizing bacteria or the like can be used instead of the chemical oxidation means. The pH in the reaction tank is preferably adjusted to 3 to 5 suitable for growing bacteria such as iron-oxidizing bacteria. As an iron-oxidizing bacterium, Thiobacillus ferrooxidans can be used. Specifically, the liquid part containing divalent iron ions generated by the solid-liquid separation operation in the same manner as described above is put into the second reaction tank, and an alkali agent is added to the second reaction tank. The pH is controlled from 3 to 5, and bivalent iron ions are oxidized to trivalent iron ions by biological oxidation means to precipitate iron hydroxide (III) -based particles, and then concentrated by solid-liquid separation. Thus, a means for forming a slurry or cake containing the iron (III) hydroxide-based particles is preferably used.

  Although not shown in FIG. 1, trivalent iron ions are precipitated at a pH of 3 or higher, and the range in which the trivalent chromium ions are precipitated is close to the trivalent iron ions, so that the trivalent iron ions and the trivalent chromium ions are difficult to separate. Therefore, in order to increase the quality of chromium in particles mainly composed of chromium hydroxide, it is desirable not to oxidize divalent iron ions or to reduce trivalent iron ions generated by oxidation.

  In order not to oxidize divalent iron ions, it is desirable that the dissolved oxygen concentration in the first reaction tank is 0 to 2 mg / L. As a means for reducing the dissolved oxygen concentration, a deoxidizer such as sulfite is added, a gas containing no oxygen such as nitrogen gas or argon gas is vented, a lid is installed at the top of the reaction tank, and air and There are means such as mechanical stirring while cutting off the contact with the liquid part in the reaction tank.

  In order to reduce the oxidized trivalent iron ions, a reducing agent can be introduced into the acidic waste liquid and reduced. As the reducing agent, iron powder, sodium thiosulfate, hydroxylamine hydrochloride, and zinc powder can be used. In order to utilize the slurry or cake containing particles mainly composed of chromium hydroxide as a stainless steel raw material, the mass ratio of iron element to chromium element in the stainless steel product (Fe / Cr) is preferably about 8 times or less. Therefore, it is better to control the trivalent iron ion concentration in the iron (III) hydroxide-based particles after the reduction treatment within 8 mass times the chromium concentration. Preferably, if it is controlled at a lower magnification, it can be used more easily as a stainless material.

  As a neutralizing agent (also called an alkali agent) to be charged into the first reaction tank, sodium hydroxide (caustic soda), calcium hydroxide (slaked lime), calcium oxide (quick lime), calcium carbonate (limestone), magnesium hydroxide, An aqueous solution or slurry of magnesium oxide, magnesium carbonate or the like can be used. These neutralizing agents may be used individually by 1 type, and 2 or more types may be mixed and used for them. However, as the neutralizing agent, magnesium hydroxide, magnesium oxide, and magnesium carbonate are preferable in order to increase the chromium quality in the chromium hydroxide-based particles precipitated in the first reaction tank. As for sodium hydroxide, calcium hydroxide, calcium oxide, the pH of the alkaline aqueous solution or slurry containing them is as extremely high as 11 to 13, and the very small area around the alkaline agent charged into the first reaction tank is The pH rises and divalent iron ions are precipitated as iron (II) hydroxide. Once precipitated, the iron (II) hydroxide has a low dissolution rate and is difficult to dissolve even when the pH in the first reaction tank is in the range of 4.5 to 6.5. On the other hand, since the alkaline aqueous solution or slurry containing magnesium hydroxide, magnesium oxide, magnesium carbonate, calcium carbonate has a pH of about 9 to 11 and lower than the alkaline aqueous solution or slurry containing sodium hydroxide, calcium hydroxide, calcium oxide, When thrown into the first reaction tank, the pH rises in a very narrow region around the alkaline agent, but the degree of influence is low compared to an alkaline aqueous solution or slurry containing sodium hydroxide, calcium hydroxide, calcium oxide. Therefore, the precipitation amount of iron (II) hydroxide is reduced. In addition, sulfuric acid and hydrofluoric acid are used as the acid used for the chrome-based stainless steel pickling. However, if the alkaline agent is calcium hydroxide, calcium oxide or calcium carbonate, calcium fluoride or gypsum precipitates, The chromium quality in the chromium oxide-based particles cannot be increased. Therefore, magnesium hydroxide, magnesium oxide, and magnesium carbonate are suitable for the alkaline agent used in the first reaction tank.

  In the present invention, it is desirable to further increase the particle size by bringing trivalent chromium ions into contact with the chromium hydroxide-based particles precipitated in the first reaction vessel. Specifically, the chromium hydroxide-based particles precipitated in the first reaction tank are solid-liquid separation operations, and only the liquid portion is extracted into the second reaction tank, and then the solid containing the chromium hydroxide-based particles. The acidic waste liquid containing divalent iron ions and trivalent chromium ions was continuously charged into the first reaction tank while leaving the part in the first reaction tank, and the pH in the first reaction tank was adjusted to 4 By adjusting the pH to 5.0 to 6.0, preferably to pH 5.0 to 6.0, the surface of the chromium hydroxide-based particles deposited in advance is further brought into contact with trivalent chromium ions, so that chromium hydroxide is added. By precipitating, the particle diameter of the chromium hydroxide-based particles can be increased. Thus, dehydrating property and filterability can be improved by increasing the particle size of the chromium hydroxide-based particles. Moreover, as means for bringing the trivalent chromium ions into contact, instead of or continuously adding an acidic waste liquid containing divalent iron ions and trivalent chromium ions, an aqueous solution containing trivalent chromium ions or liquid A chromium (III) compound that dissolves in the solution to produce trivalent chromium ions may be added.

  The chromium hydroxide-based particles precipitated in the first reaction vessel contain divalent iron ions as described above, and the divalent iron ions are compounds (mainly iron (II) hydroxide). And having the ability to reduce hexavalent chromium ions with the divalent iron ions. Therefore, the slurry or cake containing the particles mainly composed of chromium hydroxide precipitated in the first reaction tank is transferred into the third reaction tank, and the waste liquid containing hexavalent chromium ions is added and mixed to obtain hexavalent. Chromium ions are reduced to trivalent chromium ions, and the resulting chromium hydroxide containing the trivalent chromium ions is deposited on the surface of the chromium hydroxide-based particles transferred from the first reaction tank. The chromium concentration in the particles can be increased. The processing capacity of hexavalent chromium ions is not more than 3 times the amount of divalent iron contained in the particles mainly composed of chromium hydroxide deposited in the first reaction tank.

  The chromium hydroxide-based particles whose chromium concentration is increased in the third reaction tank preferably contain 30 to 55% by mass of chromium (III) hydroxide with respect to the total amount of the particles.

  The waste liquid containing hexavalent chromium ions is not particularly limited, but is discharged from the steel sheet surface treatment process in the electronic component manufacturing industry, the machine parts manufacturing industry, the automotive steel sheet manufacturing industry, the stainless steel manufacturing industry, the coating factory, and the like. Waste liquid. The waste liquid preferably contains 1 to 30 g / L of hexavalent chromium ions in a total amount.

  Next, an embodiment of the present invention will be described with reference to FIG. In FIG. 2, an example of the processing apparatus which concerns on the processing method of the acidic waste liquid containing iron and chromium of this invention is shown.

  As shown in FIG. 2, the waste water treatment apparatus 10 applied to the method for treating an acidic waste liquid containing iron and chromium according to an embodiment of the present invention is a waste liquid after pickling treatment of a chromium-based stainless steel plate with sulfuric acid. An acidic waste liquid tank 12 that temporarily stores the acidic waste liquid 11, a first reaction tank 14 that receives the acidic waste liquid 11 from the acidic waste liquid tank 12 via the pump 13 and separates the chromium component, caustic soda, calcium carbonate , An alkaline agent tank 27 containing an aqueous solution or slurry of a neutralizing agent such as quicklime, slaked lime, magnesium hydroxide, a pump 28 for adding the alkaline agent to the first reaction tank 14, and the first reaction tank 14. A stirrer 16 that causes a circulating flow therein, a pH meter 24 that measures the pH in the first reaction tank 14, a dissolved oxygen concentration meter 25 that measures the dissolved oxygen concentration, and the first reaction tank 14. The pump 40 for pulling out the rally and sending it to the third reaction tank 43, the filter body 17 having a separation membrane for filtering the liquid part from the slurry in the first reaction tank 14, and the liquid part are sucked. A suction pump 18 for feeding water to the second reaction tank 30, a scraper 19 for scraping off the cake layer formed on the surface of the filter body 17 with a certain thickness, a support base 20 for fixing the scraper 19, and a support base 20 up and down In order to prevent contact with air, a lid 26 is installed on the upper part of the first reaction tank 14.

  As the filter body 17 used as the solid-liquid separation operation, it is desirable to use a separation membrane (also referred to as a filter cloth) made of a material such as polypropylene, polyester, polyvinylidene chloride, polyacryl, polyvinyl alcohol, and stainless steel. The pore size of the separation membrane is desirably 1 to 100 μm. When the pore diameter is smaller than 1 μm, fine particles mainly composed of chromium hydroxide may be clogged and the filtration rate may be remarkably reduced. On the other hand, when the pore diameter is larger than 100 μm, the number of particles that pass through the pores of the filtration membrane increases, and the recovery efficiency of the chromium hydroxide-based particles may be reduced. By scraping off the cake layer surface deposited on the surface of the filter body 17 by the scraper 19, the cake thickness is made constant, and the scraped cake is discharged from the space between the filter bodies 17 by a circulating flow, thereby increasing the filtration speed. Obtainable. Further, as the time passes, the cake layer formed on the surface of the filter body 17 becomes dense and the filtration performance decreases. Therefore, the washing water or the pressure air is pumped back into the filter body 17 every predetermined time. 23, the cake deposited on the surface of the filter body 17 is peeled off.

  The second reaction tank 30 includes an aeration pipe 31 for stirring the second reaction tank 30 and sending oxygen, a pH meter 33 for measuring the pH in the second reaction tank 30, and caustic soda. , An alkaline agent tank 34 containing a neutralizing agent such as calcium carbonate, slaked lime, magnesium hydroxide, a pump 35 for adding the alkaline agent to the second reaction tank 30, and the second reaction tank 30. And a solid-liquid separator 32 that separates the liquid part from the slurry mainly composed of iron (III) hydroxide, and a pump 36 that returns the slurry from which the liquid part has been removed to the second reaction tank 30.

  In the third reaction tank 43, a pump 42 for feeding the hexavalent chromium ion waste liquid 41 to the third reaction tank 43, a chromium hydroxide slurry drawn from the first reaction tank 14, and a hexavalent chromium ion waste liquid 41 A mixer 44, an ORP meter 45 for measuring the oxidation-reduction potential in the third reaction tank 43, and a pump 46 for placing the slurry after treating the hexavalent chromium ion waste liquid in the dehydrator. ing.

  Next, based on FIG. 2, one Embodiment of the processing method of the acidic waste liquid containing iron and chromium which is this invention is described.

Acid waste liquid after pickling the chromium-based stainless steel sheet with sulfuric acid, and rinse waste liquid generated when the acid remaining on the steel sheet is washed away with water (the acid waste liquid after pickling with sulfuric acid is approximately 100 to The mixed liquid 11 with the waste liquid diluted 1000 times is stored in the acidic waste liquid tank 12, and the pump 13 connected thereto is operated to bring the acidic waste liquid 11 into the first reaction tank 14 at 6 to 3000 m ³ / h. It is preferable to perform the charging continuously. In the case of 6 m ³ / h or less, the target water amount is small, and there is a possibility that the merit is small and not economical for the investment amount for carrying out the present invention. On the other hand, in the case of 3000 m < ³ > / h or more, there is a possibility that the solid-liquid separator becomes too large to maintain stable operation of the solid-liquid separator. The general acidic waste liquid 11 has a pH of 3 or less and dissolves metals such as Fe, Cr, and Ni in a total amount of 0.1 to 10% by mass, and most of these metals exist as metal ions. .

  The acidic waste liquid 11 is continuously charged into the first reaction tank 14 and stirred in the first reaction tank 14. The pump 28 connected to the alkaline agent tank 27 is operated to add an aqueous solution or slurry of an alkaline agent composed of any one of caustic soda, calcium carbonate, quicklime, slaked lime, and magnesium hydroxide. The pH is adjusted to 4.5 or more and 6.5 or less. More preferably, the pH is adjusted to 5 or more and 6 or less. Here, when the pH is 4.5 or less, the precipitation of trivalent chromium ions in the acidic waste liquid may be deteriorated. On the other hand, when the pH is 6.5 or more, divalent iron ions are likely to precipitate, and the chromium quality in the chromium hydroxide-based particles may be deteriorated.

  Although the particle diameter of chromium hydroxide mainly after precipitation in the first reaction tank 14 is small, these particles are solid-liquid separated by the filter body 17 having a separation membrane, and only the solid part is in the first reaction tank 14. Stays in. The inside of the first reaction tank 14 is in a stirring state by a stirrer 16, and these particles are in a floating state. Among them, by continuous supply of acidic waste liquid, trivalent chromium ions contained in the waste liquid come into contact with the particle surface mainly composed of chromium hydroxide to further precipitate chromium hydroxide on the particle surface, Chromium hydroxide-based particles can be bonded to each other, and the particle diameter can be increased. Depending on the supply amount of the acidic waste liquid, the chromium concentration, and the first reaction tank capacity, it takes several days to one month to make the particles mainly composed of chromium hydroxide.

  The flow rate of the circulating flow generated by the stirrer is preferably 0.05 to 10 m / sec. If it is 0.05 m / sec or less, there is a risk that particles mainly composed of chromium hydroxide will be deposited in the lower part of the first reaction tank 14.

  The particles mainly composed of chromium hydroxide deposited on the furnace cover 17 are accumulated to form a cake, which is scraped off by the scraper 19 to a predetermined cake thickness at a predetermined frequency, and contains slurry or cake containing acidic waste liquid. Is recovered from the lower part of the first reaction tank 14 by a pump 40 or the like.

  Next, the acid waste liquid treated in the first reaction tank 14 is continuously supplied into the second reaction tank 30 and a pump communicated with the alkaline agent tank 34 as the second neutralization treatment. 35 is operated to add an aqueous solution or slurry of an alkaline agent composed of any one of caustic soda, quicklime, slaked lime, and magnesium hydroxide, and the pH is desirably adjusted to a range of 6 to 10. Air or oxygen is blown from the air diffuser installed at the lower part of the second reaction tank 30 to stir the second reaction tank 30 and oxidize divalent iron ions in the acidic waste liquid to trivalent iron ions. To precipitate iron (III) hydroxide. Alternatively, an iron-oxidizing bacterium having an ability to oxidize divalent iron ions in a low pH region is placed in the second reaction tank 30 in advance, and the acidic waste liquid treated in the first reaction tank 14 is continuously supplied. In addition, the pH in the second reaction tank 30 can be adjusted to 3 to 5, and the divalent iron ions in the acidic waste liquid can be oxidized to precipitate iron (III) hydroxide.

  The slurry containing iron (III) hydroxide discharged from the second reaction tank 30 is separated into a liquid part and a solid part by a solid-liquid separator 32 (centrifuge, thickener, etc.), and the liquid part is discarded. Desirably, the solid part is returned to the second reaction tank 30 again. The trivalent iron ions that are oxidized in the second reaction tank 14 are deposited on the surface of the solid part returned to the second reaction tank 30, and the iron (III) hydroxide-based particles become larger. Slurries containing the larger particles of iron (III) hydroxide are separated by the solid-liquid separator 32 and intermittently dehydrated by a dehydrator (filter press dehydrator, vacuum dehydrator, centrifuge, etc.). Is done.

  Next, the slurry containing particles mainly composed of chromium hydroxide extracted from the first reaction tank 14 is charged into the third reaction tank 43, and then 1-30 g discharged from the surface treatment process of the ordinary steel sheet. The waste liquid 41 containing / L hexavalent chromium ions is charged into the third reaction tank 43 by the pump 42 and stirred by the stirrer 44. In a slurry containing chromium hydroxide-based particles, a compound composed of divalent iron ions (mainly iron (II) hydroxide) is present, causing an oxidation / reduction reaction with hexavalent chromium ions, and trivalent iron ions. And trivalent chromium ions, both of which precipitate as hydroxides. As a result, the chromium concentration in the slurry containing particles mainly composed of chromium hydroxide increases.

  The liquid part in the slurry extracted by the pump 40 contains divalent iron ions. The added hexavalent chromium ion-containing waste liquid is first reduced by divalent iron ions contained in the liquid part of the slurry, and iron (III) hydroxide and chromium hydroxide are precipitated in a molar ratio of 3 (iron / chromium). To do. In order to further increase the chromium concentration in the chromium hydroxide-based particles recovered from the first reaction tank, the slurry is liquid in a slurry containing divalent iron ions by an operation such as washing with water or concentrating with a centrifuge. The particles may be separated from each other, whereby the chromium hydroxide-based particles can reduce hexavalent chromium ions. By installing an oxidation-reduction potentiometer in the third reaction tank 43, it is possible to determine the presence or absence of hexavalent chromium ion reduction ability by the particles mainly composed of chromium hydroxide based on the oxidation-reduction potential. Although the oxidation-reduction potential varies depending on the pH conditions in the third reaction tank 43, it may be about 600 mV or less (standard electrode) at pH 4, about 500 mV or less (standard electrode) at pH 5, or about 400 mV or less (standard electrode) at pH 6. In other words, it can be determined that it has a hexavalent chromium ion reducing ability. Further, by measuring the divalent iron ion concentration in the liquid part in the third reaction tank 43, it can be determined whether or not the hexavalent chromium ion reducing ability is possessed. This is a phenomenon that occurs when a small amount of divalent iron ions are eluted from chromium hydroxide-based particles. Thus, the chromium hydroxide-based slurry used for the treatment of hexavalent chromium ions can raise the chromium concentration in the slurry, and is drawn out by the pump 46, dehydrated, and used as a chromium raw material. it can.

  Hereinafter, the present invention will be described in detail by way of examples.

  This example is an example conducted in a laboratory experiment while correlating with actual wastewater, and this experimental result is a desirable result for sludge recycling and is considered to be no different from actual wastewater.

  As an acidic waste liquid (pH 1.4) after sulfuric acid pickling of chromium-based stainless steel, a solution containing divalent iron ions and trivalent chromium ions shown in Table 1 is used, and this acidic waste liquid is treated using the treatment apparatus of FIG. Was processed. The capacities of the first reaction tank, the second reaction tank, and the third reaction tank are 3L, 3L, and 0.5L, respectively.

  While supplying acidic waste liquid continuously to the 1st reaction tank 14 at 20 mL / min, magnesium hydroxide slurry is added in the 1st reaction tank 14, and pH of the acidic waste liquid in the 1st reaction tank 14 is added. 5.2 was controlled, and a circulating flow was caused in the first reaction tank 14 by the stirrer 16, and the flow rate in the lower part of the first reaction tank was 20 cm / second. Thereby, the trivalent chromium ions in the acidic waste liquid charged into the first reaction tank 14 are precipitated as chromium (III) hydroxide, and at the same time, a part of the divalent iron ions in the acidic waste liquid is precipitated. The precipitated particles are separated from the liquid part by the filter body 17 and remain in the first reaction tank 14.

  By continuously supplying the acidic waste liquid to the first reaction tank 14, chromium (III) hydroxide and a part of iron hydroxide (II) are newly deposited on the particle surface, the particle diameter is densified, Moreover, the particle diameter was enlarged by integrating the aggregated particle group in which particles are in an aggregated state by intermolecular force or the like with a precipitate. The excess liquid in the first reaction tank 14 was solid-liquid separated by the filter body 17, and the filtrate was sucked by the pump 18. Moreover, in order to control the thickness of the cake layer deposited on the filter body surface, the cake thickness was controlled to about 10 mm by moving the scraper 19 up and down once every 30 seconds.

  The filtrate was put into the second reaction tank 30, and the pH in the second reaction tank was maintained at 7.5 with caustic soda. Aeration (0.5 NL / min) is performed from the bottom of the second reaction tank 30, the inside of the second reaction tank 30 is agitated, and oxygen is supplied to oxidize divalent iron ions. The whole amount was oxidized. The slurry in the second reaction tank is subjected to solid-liquid separation by a solid-liquid separator 32 (thickener), and the recovered solid content is returned again to the second reaction tank 30 to precipitate iron hydroxide (III ) Particle diameter was increased. Intermittently, a part of the slurry recovered by the solid-liquid separator 32 was dehydrated with a filter press dehydrator having a pressure of 0.5 MPa to obtain a dehydrated cake.

  From the first reaction tank, 75 ml of the slurry containing particles mainly composed of chromium hydroxide was drawn out once a day and charged into the third reaction tank. Into this, 270 ml of hexavalent chromium ion waste liquid (hexavalent chromium ion concentration: 10,000 mg / L) was added once a day and stirred. At that time, the pH in the third reaction tank was 4.0, the oxidation-reduction potential (standard electrode) was 580 mV, the divalent iron ion was 10 mg / L, and hexavalent chromium ion could not be detected. It pulled out from the 3rd reaction tank intermittently, and it spin-dry | dehydrated with the filter press dehydrator which has a pressurization force of 0.5 Mpa, and was set as the dewatering cake.

  At this time, the filtered water quality (treated water quality) from the first reaction tank 14 and the treated water quality after solid-liquid separation of the slurry from the second reaction tank 30 are shown in Table 2, and the inside of the first reaction tank 14 Table 3 shows the ratio of the solid components in the second reaction tank 30 and the third reaction tank 43 (in terms of Fe element, mass% in terms of Cr element). Table 3 also shows the average particle size of the enlarged particles in the steady state of the first reaction vessel. In Table 3, the total of the indicated components does not become 100% because the enlarged particles are mainly composed of iron hydroxide (III), iron hydroxide (II), and chromium hydroxide (III). is there.

  In the filtrate from the first reaction tank, almost no trivalent chromium ions are detected, and about 70% of the divalent iron ions in the acidic waste liquid are contained. It can be said that almost all the valent chromium ions are precipitated, and only about 30% of the divalent iron ions are precipitated. Moreover, the average particle diameter in a 1st reaction tank is 10.5 micrometers, and is increasing. The weight ratio of the chromium concentration to the iron concentration in the acidic waste liquid is 0.14, but the weight ratio of the chromium concentration to the iron concentration from the solid components in the first and third reaction tanks is 0.45 and 0, respectively. .74, clearly showing that the chromium component is rising.

  In addition, as shown in the prior art (Patent Document 1), when the pH is adjusted with metallic iron powder, that is, the metallic iron powder (reagent) is added to the first reaction tank 14 instead of magnesium hydroxide, When the pH of the acidic waste liquid in the first reaction tank 14 is controlled to 5.2, chromium hydroxide is precipitated, and the excess liquid part is solid-liquid separated by the filter 17, the first reaction tank 14 Since the component of the solid substance in the inside had poor reactivity as an alkaline agent of metallic iron powder, it became a cake containing much iron with Fe: 68% and Cr: 7%.

It is a graph which shows the relationship between pH of the solution containing a bivalent iron ion and a trivalent chromium ion, and the residual ratio of the element in waste_water | drain. It is the schematic of one example of the apparatus used for the processing method of the acidic waste liquid containing iron and chromium.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Waste water treatment apparatus 11 applied to the processing method of acidic waste liquid containing iron and chromium ... Acid waste liquid 12 ... Acid waste liquid tank 13 ... Pump 14 ... First reaction tank 15 ..Rectifying wall 16 ... Stirrer 17 ... Filter 18 ... Suction pump 19 ... Scraper 20 ... Support 21 ... Drive device 22 ... Connector 23 ... Backwash Pump 24 ... pH meter 25 ... DO meter 26 ... Lid 27 ... Alkaline agent tank 28 ... Pump 30 ... Second reaction tank 31 ... Diffuser 32 ... Solid-liquid separator 33 ... pH meter 34 ... Alkaline agent tank 35 ... Pump 36 ... Pump 40 ... Pump 41 ... Hexavalent chromium ion-containing waste liquid 42 ... Pump 43 ...・ Third reaction tank 44... Stirrer 45... Redox potential meter 46. Pump

Claims (10)

  After the acidic waste liquid containing divalent iron ions and trivalent chromium ions is charged into the first reaction tank or while being charged, an alkaline agent is added to adjust the acidic waste liquid to a range of pH 4.5 to pH 6.5. And depositing chromium hydroxide-based particles, and then concentrating them by solid-liquid separation operation to form a slurry or cake containing the chromium hydroxide-based particles. Processing method.   The treatment of an acidic waste liquid containing iron and chromium according to claim 1, wherein trivalent chromium ions are further brought into contact with the particles mainly composed of chromium hydroxide to increase the particle size, and thereafter solid-liquid separation operation is performed. Method.   The method for treating an acidic waste liquid containing iron and chromium according to claim 1 or 2, wherein the dissolved oxygen concentration in the first reaction tank is 0 to 2 mg / L.   The said solid-liquid separation operation is filtration using a separation membrane, The processing method of the acidic waste liquid containing iron and chromium of any one of Claims 1-3 characterized by the above-mentioned.   The method for treating an acidic waste liquid containing iron and chromium according to claim 4, wherein the separation membrane has a pore size of 1 to 100 µm.   The treatment of an acidic waste liquid containing iron and chromium according to any one of claims 1 to 5, wherein the acidic waste liquid is an acidic waste liquid generated during pickling treatment of a chromium-based stainless steel plate in an iron making process. Method.   The liquid part containing the divalent iron ions generated by the solid-liquid separation operation is put into a second reaction tank, and the divalent iron ions are oxidized to trivalent iron ions by a chemical oxidation means to be hydroxylated. The iron (III) -based particles are precipitated, and then concentrated by solid-liquid separation to form a slurry or cake containing the iron (III) -based particles. The processing method of the acidic waste liquid containing iron and chromium as described in any one of Claims.   The liquid part containing the divalent iron ions generated by the solid-liquid separation operation is put into a second reaction tank, an alkaline agent is added to control the pH in the second reaction tank from 3 to 5, The bivalent iron ions are oxidized into trivalent iron ions by biological oxidation means to precipitate particles mainly composed of iron (III) hydroxide, and then concentrated by solid-liquid separation operation. The method for treating an acidic waste liquid containing iron and chromium according to any one of claims 1 to 6, wherein the slurry is a slurry or cake containing main particles.   A slurry or cake containing the chromium hydroxide-based particles and a waste liquid containing hexavalent chromium ions are added to and mixed in a third reaction tank, and divalent iron ions remaining in the slurry or cake are mixed. Reducing the hexavalent chromium ion to the trivalent chromium ion with a compound containing, depositing the trivalent chromium ion on the surface of the chromium hydroxide-based particle, and increasing the chromium concentration in the chromium hydroxide-based particle The processing method of the acidic waste liquid containing iron and chromium of any one of Claims 1-8 characterized by these.   The alkali agent added to the first reaction tank is at least one selected from the group consisting of magnesium oxide, magnesium carbonate, and magnesium hydroxide. The processing method of the acidic waste liquid containing iron and chromium as described in a term.

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