KR20030016502A - Waste-water treatment method - Google Patents

Abstract

PURPOSE: A high level treatment of fluoride wastewater generated in the manufacture of semiconductor is provided to reduce sludge quantity by recycling Al(OH)3 contained in final sludge. CONSTITUTION: The treatment method of fluoride wastewater comprises the steps of reacting raw fluoride wastewater with aluminium hydroxide (Al(OH)3) to precipitate Al(OH)3·F; injecting a certain amount of polymer to the fluoride wastewater for flocculation so that the fluoride wastewater is divided into supernatant and slurry; after thickening the slurry, feeding Ca(OH)2, NaHCO3, and NaOH in due order to the slurry to stabilize Al(OH)3 and CaF2; injecting a polymer to Al(OH)3 and CaF2 so that Al(OH)3 and CaF2 are separated; recycling the separated Al(OH)3; dewatering the separated CaF2.

Description

Wastewater Treatment Methods {WASTE-WATER TREATMENT METHOD}

The present invention relates to a wastewater treatment method, and more particularly, to a wastewater treatment method for treating fluorine-containing wastewater widely used in semiconductor manufacturing processes.

Recently, with the development of the industry, wastewater containing a large amount of fluorine is generated in semiconductor manufacturing plants, steel mills, fluorine-based compound manufacturing plants such as CFC and hydrofluoric acid, CRT manufacturing plants, and phosphoric acid or fertilizer manufacturing plants.

Since the fluorine waste water pollutes the environment, the fluorine waste water is treated to suppress the generation of environmental pollutants.

Among the well-known treatment methods for treating fluorine wastewater, the calcium salt method uses Ca (OH) ₂ or CaCl ₂ , and treats the introduced fluorine wastewater by adding Ca (OH) ₂ in a first reactor, In the reactor, FeCl ₂ and H ₂ SO ₄ are added and treated, and in the third reactor, the polymer is added and treated, and the sewage sludge (CaF ₂ ) is precipitated and treated in the precipitation tank, and the remaining waste water is discharged.

Disadvantages of the calcium salt method are firstly the fluorine removal efficiency is very low, secondly the pH required in the first reactor is 10-11, Ca (OH) ₂ input amount is very high, the chemical handling facilities are very large, investment facilities are high, and third wastewater treatment Sludge generation is very large, so it is difficult to process and manage, and the final processing cost is also high.

In another method, the aluminum salt method treats the fluorine wastewater introduced by adding Al ₂ (SO ₄ ) ₃ in the first reactor, adding NaOH in the second reactor, and treating the fluorine wastewater by adding polymer in the third reactor. After the final treatment in the form of Al (OH) ₃ F in the sedimentation tank, it shows a relatively high treatment efficiency, but because of the use of expensive chemicals, a lot of burden on the treatment cost.

The present invention has been made to solve the problems of the prior art, the object is to significantly reduce the amount of wastewater treatment sludge finally generated, to suppress the generation of secondary environmental pollutants and to reduce the waste disposal cost The present invention provides a wastewater treatment method capable of significantly reducing the wastewater treatment cost by recovering and recycling the chemicals used in the treatment process from the wastewater treatment sludge.

1 is a block diagram illustrating a wastewater treatment method according to the present invention.

Waste water treatment method of the present invention for achieving the above object is by reacting the recycled and collected hydrofluoric acid wastewater Al (OH) ₃ was precipitated as Al (OH) ₃ · F, to form a floc incorporating a polymer after precipitation After the floc was formed, the mixture was separated into treated water and slurry, and the slurry was concentrated. Then, Ca (OH) ₂ , NaHCO ₃ , and NaOH were added to stabilize Al (OH) ₃ and CaF ₂ , and Al (OH) was added. ) utilized for the removal of fluoride CaF ₃ and the Al (OH added to separate and remove the polymer. _{2) 3,} hydrofluoric acid wastewater and, CaF _2, is characterized in that process as a waste after dewatering.

Hereinafter, a preferred embodiment according to the present invention will be described in detail with reference to the accompanying drawings. 1 is a block diagram illustrating a wastewater treatment method according to the present invention.

The wastewater treatment method according to the present invention is a process of recycling Al (OH) ₃ obtained by concentrating a wastewater treatment sludge from which fluorine is separated and then reprocessing.

First, in the separating step 10, the hydrofluoric acid wastewater collected in the wastewater collection tank 11 and recycled Al (OH) ₃ are reacted in the reaction tank 12 to precipitate into Al (OH) ₃ · F. Initially, small amounts of H ₂ SO ₄ and Al ₂ (SO ₄ ) ₃ are added. Al (OH) ₃ · F obtained at this time is about pH 7.

Then, in order to improve flocculation and precipitation efficiency in the flocculation tank 13 after precipitation, a floc is formed by adding a polymer.

After the formation of the flocs, the large flocs formed by the polymer in the first settling tank 14 are solid-liquid separated by natural sedimentation using gravity, and the separated supernatant (treated water) is finally discharged as about 5 ppm as the fluorine concentration.

The separated slurry is transferred to a concentration tank through a transfer pump and prepared for recycling with Al (OH) ₃ .

Next, in the stabilizing step 20, the slurry transferred to the concentration tank 21 is concentrated and then introduced into the first chemical reaction tank 22, and Ca (OH) ₂ is added thereto to obtain CaF ₂ . That is, it is defined by the following reaction.

_{Al (OH) 3 · F +} Ca (OH) 2 -> CaF 2 + Al + + OH - (PH8)

Subsequently, NaHCO ₃ and NaOH are added to each of the second chemical reactor 23 and the third chemical reactor 24 to stabilize Al (OH) ₃ and CaF ₂ .

In step 30 that last processed In the polymer in the flocculation tank (31) to separate the stabilized Al (OH) ₃ and CaF _2, and from the flock of CaF ₂ is the second settling tank 32 formed by a polymer Natural sedimentation completely separates Al (OH) _3, and the separated Al (OH) ₃ is used to remove fluorine contained in raw wastewater, and finally, the wastewater treatment sludge (CaF ₂ ) removed is waste after dehydration. Final processing.

As described above, according to the present invention, by recycling the Al component contained in the wastewater treatment sludge and removing the hydrofluoric acid component, the treatment efficiency of fluorine-containing hydrofluoric acid is increased, and waste is reduced by 1/10 or more. Stable processing efficiency is possible.

In addition, the amount of waste generated is reduced and the cost of waste disposal is reduced.

In addition, the drug cost is reduced by reusing Al (OH) ₃ .

In addition, the amount of waste generated and the amount of chemicals used are reduced to prevent environmental pollution.

Claims (3)

Reacting the collected waste hydrofluoric acid with recycled Al (OH) ₃ to precipitate with Al (OH) ₃ · F, and after precipitation, a floc is added to form a floc, and the floc is separated into treated water and slurry after formation of the floc. ; Concentrating the slurry and stabilizing Al (OH) ₃ and CaF ₂ by sequentially adding Ca (OH) ₂ , NaHCO ₃ , and NaOH; And The polymer is separated into Al (OH) ₃ and CaF ₂ , and the separated Al (OH) ₃ is recycled in the separating step to utilize fluorine in fluorine wastewater, and CaF ₂ is treated as waste after dehydration. Wastewater treatment method comprising the step. The method of claim 1, The operation of injecting Ca (OH) ₂ , NaHCO ₃ , and NaOH in turn is performed in a chemical reaction tank corresponding to each chemical. The method of claim 2, In the step of separating the treated water and slurry after the formation of the floc, the separation of the floc into the treated water and the slurry is a wastewater treatment method consisting of natural sedimentation using gravity.