JP2010099552A - Wastewater treatment method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wastewater treatment method which can reduce the loadings of inorganic coagulant in drinking water treatment to achieve cost reduction and stable operation by reducing fluorine as much as possible in a manganese and cadmium removing process to reduce a fluorine concentration in drinking water. <P>SOLUTION: Wastewater containing cadmium, or manganese and fluorine is loaded with aluminum sulfate and calcium hydroxide to adjust the pH equal to or more than a pH value generating cadmium hydroxide, manganese hydroxide, and aluminum hydroxide, and then retained in a neutralization tank 1 for a fixed time. The obtained slurry is loaded with sulfuric acid to reduce the pH of the slurry, thereby a part of the fluorine is adsorbed and coprecipitated with aluminum hydroxide. Subsequently the slurry is subjected to solid liquid separation, thereby removing the fluorine together with the cadmium hydroxide, manganese hydroxide, and aluminum hydroxide. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for treating wastewater containing cadmium or manganese and fluorine using a coagulation sedimentation method with an inorganic coagulant.

  Wastewater containing various pollutants such as cadmium or manganese and fluorine is subject to the regulation of wastewater standards, and it is necessary to discharge after removing the metal and fluorine to satisfy this. In addition, from the standpoint of environmental protection and pollution prevention, the wastewater treatment technology that can further reduce the fluorine concentration has been strengthened to 8 mg / L from 2001 for the fluorine concentration standard of wastewater discharged into public waters. Development is desired.

  For example, as a method of removing cadmium, manganese, fluorine, etc. contained in the wastewater, aluminum sulfate and calcium hydroxide are added to the wastewater, and kept in a neutralization tank for a certain period of time under a high pH region, and settled. After producing manganese hydroxide, cadmium hydroxide, calcium fluoride, and aluminum fluoride to form a deposit, solid-liquid separation into sediment and clean water removes some of the cadmium, manganese, aluminum, and fluorine. In the first step, aluminum sulfate is added until the fluorine concentration in the clean water reaches the drainage standard value, and the amount of aluminum hydroxide generated is increased under the intermediate pH region. A method for treating wastewater having a second step of removing fluorine by solid-liquid separation after adsorbing water has been known.

  However, in the above-described wastewater treatment method, only a trace amount of fluorine can be removed because fluorine is removed only in the form of precipitated calcium fluoride and aluminum fluoride in the high pH region of the first step. For this reason, the fluorine concentration of clean water is high, and in the fluorination treatment of clean water in the second step, a large amount of aluminum sulfate is required to remove the clean water fluorine to the drainage standard, which is costly and inefficient. There is a problem that it is stable.

  The present invention has been made to solve the above-mentioned problems of the prior art, and in the process of removing manganese and cadmium, removing as much fluorine as possible to lower the fluorine concentration of the drinking water, It is an object of the present invention to provide a wastewater treatment method that can reduce the amount of inorganic flocculant added during treatment and lead to stable operation.

  In order to solve the above-mentioned problems, the present invention according to claim 1 is characterized in that an inorganic flocculant containing aluminum and lime are added to waste water containing cadmium or manganese and fluorine, and the cadmium or manganese and aluminum are added. At least a part of the fluorine is adjusted by adding an inorganic acid to the slurry obtained after adjusting the pH to produce a porridge and maintaining the slurry in a neutralization tank for a certain period of time, thereby lowering the pH of the slurry. The cadmium or manganese and aluminum deposits are removed by adsorbing on an aluminum deposit and then solid-liquid separation of the slurry.

  Here, the present invention according to claim 2 is characterized in that at least a part of the cadmium or manganese and aluminum deposits separated by the solid-liquid separation is repeated in the neutralization tank. .

  Moreover, the present invention according to claim 3 maintains the pH in the neutralization tank in the range of 9.5 to 11, and the pH of the slurry is adjusted to 9.0 to 9 by adding the inorganic acid. It is characterized by being lowered to .5.

  Furthermore, the present invention described in claim 4 is characterized in that the inorganic flocculant is aluminum sulfate and the lime is calcium hydroxide.

  According to the invention described in any one of claims 1 to 4, an inorganic flocculant containing aluminum is added to wastewater containing cadmium or manganese and fluorine, and lime is added to add aluminum, manganese and cadmium. The pH is adjusted to above the pH at which the product is produced, and is maintained for a certain time in the neutralization tank. In addition, when the metal with the highest pH which becomes a hydroxide or an oxide among the metals is cadmium, the pH is adjusted to 10.4.

  Then, in the neutralization tank, for example, when the wastewater is held for a certain time under a high pH range of pH 10.4 or higher, cadmium and manganese contained in the wastewater are combined with hydroxide ions or oxygen ions contained in the lime. As a result, a hydroxide or an oxide is produced to form a sediment.

  Further, the aluminum ions contained in the inorganic flocculant and the hydroxide ions or oxygen ions contained in the lime are combined to produce a small amount of aluminum hydroxide or aluminum oxide, thereby forming a sediment. At this time, aluminum hydroxide or aluminum oxide that is chemically stable at pH 7 in a high pH region of pH 10.4 is chemically unstable and the amount produced is very small. Then, the fluorine contained in the waste water is adsorbed on the slightly produced aluminum hydroxide or aluminum oxide.

  On the other hand, a part of the fluorine contained in the wastewater is combined with calcium ions contained in the lime and aluminum ions contained in the inorganic flocculant to form calcium fluoride and aluminum fluoride that form a sediment.

  Next, by adding an inorganic acid to the slurry containing these compounds discharged from the neutralization tank, the pH of the slurry is lowered to at least the pH of the wastewater in the neutralization tank, so that aluminum hydroxide or aluminum oxide is chemically Therefore, the amount of aluminum hydroxide or aluminum oxide that adsorbs fluorine increases, and accordingly, the amount of fluorine adsorbed on aluminum hydroxide or aluminum oxide increases.

  As a result, the amount of fluorine removed together with the aluminum hydroxide or aluminum oxide, which is a sediment, during solid-liquid separation increases, and the fluorine concentration of clean water generated by solid-liquid separation is reduced. When removing fluorine in clean water, the amount of the inorganic flocculant that removes fluorine to the drainage standard value is reduced, enabling cost reduction and stable operation.

  In particular, according to the present invention described in claim 2, at least a part of manganese, cadmium and aluminum hydroxides or oxides, which are sediments separated by the solid-liquid separation, are repeated in the neutralization tank. For this reason, the sediment particles of the sediment are grown into large particle aggregates. As a result, the solid-liquid separation can be improved, and the adsorption of fluorine onto aluminum hydroxide or aluminum oxide can be promoted.

  According to the third aspect of the present invention, since the pH in the neutralization tank is maintained in the range of 9.5 to 11, one of cadmium, manganese, and aluminum contained in the inorganic flocculant. As the part is transformed, the fluorine partly becomes calcium fluoride. In addition, the pH required for the metal contained in the wastewater to be converted into a hydroxide or oxide is pH 9.5 or higher for the lowest metal and pH 11.0 or lower for the highest metal, and the metal contained in the wastewater. In the case where there are a plurality of the pHs, the pH is adjusted based on the pH at which the metal becomes a hydroxide or an oxide.

  Further, by adding sulfuric acid to the slurry, the pH of the slurry is adjusted to 9.0 to 9.5, so that it approaches pH 7 at which aluminum hydroxide or aluminum oxide becomes chemically stable. The generation of can be promoted. When the pH is adjusted to 9.0 or lower, the metal-containing hydroxide or oxide produced under the high pH region dissolves, so that the concentration of the metal contained in the water is reduced during solid-liquid separation. When the pH rises to 9.5 or higher, aluminum hydroxide or aluminum oxide that adsorbs fluorine becomes chemically unstable and only a trace amount can be generated. Therefore, the pH is adjusted to 9.0 to 9.5. .

  In addition, according to the present invention as set forth in claim 4, since aluminum sulfate is used as the inorganic flocculant and calcium hydroxide is used as the lime, the aluminum hydroxide is produced to generate fluorine. It becomes possible to adsorb and remove, and it is possible to generate calcium fluoride which becomes a sediment and to remove fluorine.

  Hereinafter, this embodiment of the present invention is described based on a drawing. When the wastewater treatment method containing cadmium, manganese, and fluorine in the present embodiment is performed, first, as shown in FIG. 1, a predetermined amount of aluminum sulfate is added as an inorganic flocculant containing aluminum to the wastewater, Introduce into Japanese tank 1. And in the neutralization tank 1, calcium hydroxide is added to this wastewater as lime, it adjusts to pH 10.4 or more, and it hold | maintains, stirring with the stirrer with which the neutralization tank 1 was equipped.

  Under the present circumstances, the addition amount of the aluminum sulfate added to the waste water of the neutralization tank 1 is set according to content of what is adsorbed and removed. In this embodiment, in order to adsorb and remove fluorine, aluminum sulfate is added according to the fluorine content.

  Further, the amount of calcium hydroxide added is set based on the pH at which the metal contained in the wastewater introduced into the neutralization tank 1 becomes a hydroxide. In this embodiment, manganese becomes a hydroxide at pH 10 or more, and cadmium becomes a hydroxide at pH 10.4 or more. Therefore, calcium hydroxide is added until the pH becomes 10.4 or more. In addition, when there are a plurality of metals contained in the wastewater, it is preferable to set the pH based on the pH at which the metal becomes a hydroxide among the pH at which the metal becomes a hydroxide.

  Here, in the neutralization tank 1, since the waste water to which aluminum sulfate and calcium hydroxide are added is adjusted to have a pH of 10.4 or more by calcium hydroxide, manganese and cadmium contained in the waste water are hydroxylated. Combined with calcium hydroxide ions, manganese hydroxide and cadmium hydroxide are formed, and these hydroxides become sediment.

  In addition, aluminum ions contained in aluminum sulfate and hydroxide ions contained in calcium hydroxide are combined to produce a trace amount of aluminum hydroxide that is chemically stable at pH 7, and this aluminum hydroxide is also precipitated. Become a temple. Then, fluorine contained in the wastewater is adsorbed on the slightly produced aluminum hydroxide.

  On the other hand, calcium ions combine with a part of the fluorine contained in the wastewater to form calcium fluoride and sediment.

  Thereafter, the slurry containing these compounds is discharged from the neutralization tank 1, sulfuric acid having a pH of 9.1 to 9.5 is added, the pH of the slurry is adjusted to about 9.0 to 9.5, and the solid is added. It introduce | transduces into the liquid separation tank 2, and hold | maintains.

  Under the present circumstances, the addition amount of the sulfuric acid added to the said slurry is set based on pH from which the hydroxide which adsorb | sucks the fluorine contained in the said slurry becomes chemically stable. In this embodiment, the hydroxide that adsorbs fluorine is aluminum hydroxide, and the pH at which aluminum hydroxide is chemically stable is 7, so that the pH is about 9.0 to 9.5. It is added. When sulfuric acid is added until reaching pH 7, manganese hydroxide and cadmium hydroxide generated in the neutralization tank 1 are dissolved, and the concentration of manganese and cadmium in the tap water is increased. It is preferable to set it to 0.0-9.5.

  Here, by adding sulfuric acid to the slurry and adjusting the pH of the slurry to 9.0 to 9.5, the pH of the aluminum hydroxide approaches pH 7 at which the aluminum hydroxide becomes chemically stable. The amount generated increases.

  In the solid-liquid separation tank 2, the slurry is gradually solid-liquid separated into a sediment and clean water. Thereafter, aluminum sulfate is added to the clean water, and solid-liquid separation is performed again, so that the fluorine concentration is reduced to the drainage standard value or less and discharged as final treated water.

  Under the present circumstances, the addition amount of the aluminum sulfate added to the solid water separated into solid and liquid is set according to the content of what is removed by adsorption and the drainage standard value. In this embodiment, in order to adsorb and remove fluorine, aluminum sulfate is added according to the fluorine content.

  Here, in the tap water, by adding aluminum sulfate, aluminum hydroxide is generated, and fluorine is adsorbed on the aluminum hydroxide.

  On the other hand, the sediment is gradually extracted from the lower part of the solid-liquid separation tank 2 and returned to the neutralization tank 1, so that the sediment is gradually accumulated in the system and intermittently extracted outside the system and deposited in the disposal site. To do.

  In the wastewater treatment method of the above-described embodiment, aluminum sulfate is added to wastewater containing a metal containing fluorine and cadmium or manganese, and calcium hydroxide is added to adjust the pH to 10.4 or more. Thus, in the neutralization tank, when the waste water is held for a certain time under a high pH region of 10.4 or more, the aluminum contained in the cadmium, manganese and aluminum sulfate contained in the waste water is a hydroxide of calcium hydroxide. It combines with ions to form cadmium hydroxide, manganese hydroxide, and aluminum hydroxide, and calcium ions combine with part of fluorine to form calcium fluoride. And fluorine adsorb | sucks to the produced | generated aluminum hydroxide.

  Next, by adding sulfuric acid to the slurry containing these compounds discharged from the neutralization tank to adjust the pH of the slurry to 9.0 to 9.5, pH 7 at which aluminum hydroxide becomes chemically stable is obtained. In order to bring the pH of the slurry closer to the above, the amount of fluorine adsorbed on aluminum hydroxide increases as the amount of aluminum hydroxide generated increases. As a result, the amount of fluorine removed together with the aluminum hydroxide, which is a sediment, increases during the solid-liquid separation, and the fluorine concentration in the clean water generated by the solid-liquid separation is reduced. In addition, it is possible to reduce the cost by reducing the amount of aluminum sulfate added to reduce the fluorine concentration to the drainage standard value, and to enable stable operation.

  Further, in order to repeat the step of returning a part of the precipitated sediment separated by the solid-liquid separation tank 2 to the neutralization tank 1, manganese hydroxide, cadmium hydroxide and aluminum hydroxide, Physical particles grow to become large particle aggregates. Thereby, while being able to improve solid-liquid separability, adsorption | suction of the fluorine and calcium fluoride to aluminum hydroxide can be accelerated | stimulated.

  And since the pH in the neutralization tank is maintained at 10.4 or higher, it is possible to convert a part of aluminum contained in cadmium and manganese and aluminum sulfate that become hydroxide at high pH. At the same time, fluorine partly becomes calcium fluoride, and fluorine and calcium fluoride can be adsorbed to aluminum hydroxide.

  Further, by adding sulfuric acid to the slurry, the pH of the slurry is adjusted to 9.0 to 9.5, so that the pH approaches 7 where the aluminum hydroxide is chemically stable. Facilitate.

  In addition, since aluminum sulfate is used as the inorganic flocculant in the waste water and calcium hydroxide is used as the lime, it becomes possible to generate aluminum hydroxide and adsorb and remove fluorine. It becomes possible to remove the fluorine by generating calcium fluoride as a sediment.

  In this embodiment, aluminum sulfate is added to the neutralization tank and clean water. However, sodium aluminate or basic aluminum chloride can be used instead.

  In addition, calcium hydroxide is added as lime, but calcium oxide can be used instead. It is also possible to use mixed use of calcium carbonate and calcium hydroxide or calcium oxide, or mixed use of sodium hydroxide, sodium carbonate and calcium hydroxide, calcium oxide, calcium carbonate and other alkaline agents. is there.

  Furthermore, although sulfuric acid is added to the slurry, it is possible to use hydrochloric acid instead.

  A predetermined amount of aluminum sulfate is added to the waste water containing manganese and fluorine and introduced into the neutralization tank 1. And in the neutralization tank 1, calcium hydroxide is added to this wastewater, it adjusts to pH 10.0 or more, and it hold | maintains, stirring with the stirrer with which the neutralization tank 1 was equipped. Thereafter, the slurry is discharged from the neutralization tank 1 and sulfuric acid having a pH of 9.1 to 9.5 is added to adjust the pH to about 9.4 to 9.5, and then introduced into the solid-liquid separation tank 2 and held. Then, in the solid-liquid separation tank 2, the slurry (thickener inflow slurry) introduced into the solid-liquid separation layer 2 is solid-liquid separated into the sediment and clean water, and the fluorine concentration and manganese concentration in the clean water (thickener overflow water). Was measured. At this time, the wastewater treatment method according to the conventional invention was carried out for 1 to 5 months, and the wastewater treatment method according to the present embodiment was carried out for 6 to 11 months. In addition, in the mine where the wastewater used in this embodiment is collected, the drainage standard value is set to 1 mg / L manganese concentration and the fluorine concentration is 8 mg / L. The wastewater treatment method of this embodiment is implemented.

  FIG. 2 is a graph showing the concentrations of fluorine and manganese contained in wastewater according to the elapsed month, with the X axis indicating the elapsed month and the Y axis indicating the concentration of fluorine and manganese.

  FIG. 3 is a graph showing changes in manganese concentration of thickener overflow water and pH of the thickener inflow slurry according to the elapsed month. The X axis is the elapsed month, the Y axis (1) is the thickener inflow slurry pH, and the Y axis. (2) shows the manganese concentration of thickener overflow water.

  Further, FIG. 4 is a graph showing changes in the fluorine concentration of thickener overflow water and the pH of the thickener inflow slurry according to the elapsed month, where the X axis is the elapsed month, the Y axis (1) is the thickener inflow slurry pH, and the Y axis. (2) shows the fluorine concentration of thickener overflow water.

  First, as shown in FIG. 2, when the concentration of fluorine and manganese contained in the wastewater are extracted, the concentration of fluorine is 23 to 27 mg / L throughout the period of 1 to 11 months, and the concentration of manganese is 9 to 10 mg / L. It can be confirmed that the fluorine and manganese concentrations are higher than the drainage standard value.

  Therefore, when the waste water treatment method in the conventional invention is used to extract the thickener inflow slurry pH, the manganese concentration and the fluorine concentration of the thickener overflow water, the thickener inflow slurry pH is as shown in FIGS. 9.7 to 9.8 are shown, the manganese concentration is 0.1 to 0.6 mg / L, and the fluorine concentration is 14 to 15 mg / L. Thereby, by the wastewater treatment method in the conventional invention, the manganese concentration is removed up to the wastewater standard value and satisfies the conditions, while the fluorine concentration is 6-7 mg compared with the wastewater standard value of 8 mg / L. It can be confirmed that it is shown as high as / L.

  On the other hand, when the thickener inflow slurry pH, the manganese concentration and the fluorine concentration of the thickener overflow water are extracted using the wastewater treatment method in this embodiment, the thickener inflow slurry pH is 9. As shown in FIGS. 4 to 9.5, a manganese concentration of 0.1 to 0.5 mg / L, and a fluorine concentration of 8 to 10 mg / L. Thereby, it can confirm that manganese concentration is removed even to the waste water reference value like the conventional invention, and satisfy | fills conditions. Furthermore, it can be confirmed that the fluorine concentration is reduced to the vicinity of 8 mg / L which is the drainage standard value.

  As a result, the wastewater treatment method in this embodiment increases the fluorine removal efficiency in the manganese removal step by reducing the pH of the thickener inflow slurry to such an extent that the removal performance of manganese does not deteriorate. It was demonstrated that the fluorine concentration of running water can be reduced.

It is the schematic which shows the processing method of the wastewater of one Embodiment of this invention. It is a figure which shows the fluorine concentration and manganese concentration of waste water used for a present Example. It is a figure which shows the change of pH of the thickener flowing-water slurry according to the elapsed month in the measurement result of a present Example, and the manganese concentration of thickener overflow water. It is a figure which shows the change of the pH of the thickener inflow slurry according to the elapsed month in the measurement result of a present Example, and the fluorine concentration of the thickener overflow water.

Explanation of symbols

1 Neutralization tank 2 Solid-liquid separation tank

Claims (4)

  Add the inorganic flocculant containing aluminum and lime to the waste water containing cadmium or manganese and fluorine, adjust the pH to above the level to produce the above cadmium or manganese and aluminum, and hold in the neutralization tank for a certain period of time Then, by adding an inorganic acid to the obtained slurry to lower the pH of the slurry, at least a part of the fluorine is adsorbed on the aluminum deposit, and then the slurry is solid-liquid separated. A method for treating waste water, wherein the cadmium or manganese and aluminum deposits are removed.   The method for treating wastewater according to claim 1, wherein at least a part of the cadmium or manganese and aluminum deposits separated by the solid-liquid separation is repeated in the neutralization tank.   The pH in the neutralization tank is maintained in the range of 9.5 to 11, and the pH of the slurry is lowered to 9.0 to 9.5 by adding the inorganic acid. The processing method of the wastewater of Claim 1 or Claim 2.   The wastewater treatment method according to any one of claims 1 to 3, wherein the inorganic flocculant is aluminum sulfate, and the lime is calcium hydroxide.

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