DE3805722C1 - Process for purifying glass industry waste waters - Google Patents

Abstract

A process for purifying glass industry waste waters (effluents) is described which comprises adding lime to the waste water in a first separation phase up to a pH of 3-5, removing the resulting precipitate and further purifying the clear water in a second separation phase at a pH above 8.0. In the first separation phase, virtually all the amount of hydrofluoric acid present separates off as calcium fluoride and the majority of the sulphuric acid separates off as calcium sulphate. Since these precipitates contain most of the impurities present, but not the poisons, which cannot be stored in landfills, arsenic, antimony and lead, a precipitate is obtained in this manner which may be stored without risk in normal landfills. The poisons arsenic, antimony and lead do not arise until the second purification phase and pollute the relevant special waste landfills only to a slight extent because of the preliminary separation of the fluoride ions and sulphate ions.

Description

The invention relates to a method for cleaning Waste water from the glass industry through failures at least part of the contamination with lime.

In the glass manufacturing and processing industry wastewater of different composition occurs. The wastewater can essentially be divided into three groups can be classified, namely:

• - Waste water from the glass melt;
• - Waste water from mechanical grinding companies;
• - Waste water from acid polishing.

The waste water from the glass melt essentially arises from the fact that the gases extracted from the glass furnace are filtered and finally subjected to a flue gas scrubbing. The filter dust from the melt of lead glasses contains e.g. B. 0.05% As ₂ O ₃ , 0.3% Sb ₂ O ₃ and 25.3% PbO. In the absorption liquid from exhaust air scrubbers z. B. up to 200 mg As / liter occur.

The wastewater from mechanical grinding companies contain in particular glass abrasion as well as the Abrasive abrasion. The abrasion comes in different grain size and ranges from almost colloidal suspended matter down to sand-like low beat.  

Particularly large quantities of harmful contaminants contain the wastewater from acid polishing, namely Lead, antimony and arsenic as well as other heavy metals and up to 25% sulfuric acid and up to 9% fluorine hydrochloric acid.

Of course, this type of waste water to be cleaned before entering natural waters or municipal sewage systems can also be supplied. Out it is the European patent specification 00 72 012 known industrial wastewater that u. a. Lead, others Heavy metals as well as sulfates and fluorides included, and which are essentially acidic, by Add lime to a pH of about 9 too clean. With this treatment, the heavy metals as hydroxides, the sulfate ions and fluoride ions as calcium sulfate and calcium fluoride beaten. Arsenic drops, provided it is pentavalent Form is present as calcium arsenate. Indeed it was observed that further amounts of arsenic, which are in are in complex form, not clear water remain.

Other wastewater treatment processes that are special for the treatment of waste water from the glass industry developed in principle work according to the same Method: The wastewater is limed up to a pH value of about 9 or 10 added, whereupon the resulting Precipitation is decanted and filtered if necessary.

Considerable problems arise with this cleaning process the resulting solid residues. These Residues contain lead, arsenic and antimony can therefore not in normal household landfills be deposited. Rather, you have to Disposal can be done, which is not only significant Costs, but also in terms of  available capacities of these plants is limited in quantity.

The invention is based, which previously known process for the purification of waste water To further develop the glass industry in such a way that on the one hand a practical adequate disposal of the emerging clear water occurs and on the other hand at least the majority of the resulting solids are landfillable. Under "landfill capable" in this If the property is understood, the product on the to be able to deposit normal household waste landfill.

To solve this problem, a method for Purification of wastewater from the glass industry Failure of at least part of the contaminants assumed with lime and it is suggested in a first separation phase up to the wastewater lime to add to a pH of 3-5, the thereby to remove the resulting precipitate and that Clear water in a second separation phase with a pH value above 8.0. In the The first separation phase remains what needs to be cleaned Waste water slightly acidic. Under these conditions practically the entire amount of hydrofluoric acid separates as Calcium fluoride as well as the vast majority of Sulfuric acid as calcium sulfate. The rainfall settle easily and are decanted, if necessary also by filtering off the clear water separate. The clear water is through this pretreatment freed from most of the impurities and the resulting rainfall is usually ready for landfill in this form. Another Cleaning the precipitates is easily possible and is described below.  

Located in the clear water of the first separation level then the ions of lead, arsenic and antimony as well as some heavy metals. However, these ions are available in a relatively small amount and can then on in a second separation phase known way by adding lime up to pH values above 8.0 and weighting agents be deposited. Then another is created Precipitation that is not fed to the household waste landfill may be, but only in relatively small Quantities occur and therefore the special waste recycling operations as well as the costs of the process overburdened.

To carry out the process, it is proposed to add lime milk with a content of 5-20% by weight Ca (OH) ₂ to the waste water in the first separation phase. The lime milk is introduced with constant intensive stirring and continuous pH control, a process that can be easily automated with known means. As soon as the desired final pH value of 3-5, for example 4.0 (on average) is reached, the agitator is switched off and the treated waste water is left to its own devices. Depending on the composition and grain size, the resulting precipitation settles in about 0.2 to 3.0 hours, so that the excess clear water can be drawn off. The remaining sludge can then be further dewatered, for example, using a chamber filter press. The use of a chamber filter press also offers the advantage that the sludge can be further cleaned of liquid adhering to the surface, namely by washing it once or several times with neutral or weakly alkaline water, or with the clear water from the second cleaning phase. In this way, the sludge can be washed completely free of lead and arsenic, so that the requirements that are placed on a product capable of landfill must be met.

The proposed cleaning procedure turns out to be as extremely economical. In terms of It is easy to carry out with this method also possible, the glass melt in the factories, Grinding and acid polishing waste water merge and together the multi-phase Subject to cleaning procedures. This aspect of the proposed method is economical particularly important as separate cleaning systems for the waste water of the named sub-companies especially small and medium-sized businesses for a fee strain.

Lime is used to carry out the first cleaning phase preferably added in the form of milk of lime. It is however, it is also possible to use lime as a solid to be entered, provided that this is sufficient fine-grained form. When entering as Solid, it is recommended not to remove the lime completely dosing continuously, but the supply especially near the set pH end Interrupt values from 3 to 5 periodically but continue stirring to the registered Lime amounts give opportunity to yourself completely dissolve or with the existing amounts of acid react.

In tests carried out, it has been proven that Clear water in the second cleaning phase the precipitation medium as a dry mixture of the following composition to feed:  

•  30-60 parts by weight of clay mineral
• 35-45 parts by weight of Ca (OH) ₂
• 0.5-2.0 parts by weight of Na ₂ CO ₃
• 0.5-5.0 parts by weight of Na ₂ HPO ₄
•  0.3-3.0 parts by weight of flocculant

For example, Betonit-A comes in as a clay mineral Consideration; are used as flocculants known organic substances such as polyacrylamides and / or Polyacrylates used.

Depending on the composition of the wastewater to be cleaned it can also be advantageous to add the dry mix an oxidizing agent, for example ammonium peroxidi add sulfate. This gives the mixture oxidizing properties and has approximately the following Composition:

•  30-60 parts by weight of clay mineral
• 35-45 parts by weight of Ca (OH) ₂
• 0.5-2.0 parts by weight of Na ₂ CO ₃ ,
• 0.5-5.0 parts by weight of Na ₂ HPO ₄ ,
• 3.0-6.0 parts by weight (NH ₄ ) ₂ S ₂ O ₈
•  0.3-3.0 parts by weight of flocculant

Should the quality of the clear water obtained be the second phase in special cases still not can still be satisfactory now is known to replicate ion exchangers to further increase the content of foreign ions to reduce. As a rule, this will not to be required; only when the water is out special reasons in sensitive waters, for example wise fish waters, must be discharged, it can may need to resort to this remedy.  

The invention is based on the following Drawing explained in more detail.

In the Drawing is an embodiment described is for illustration but not limitative works.

In the upper part of the drawing, three companies in the glass industry are shown schematically, namely a glass melt ( 1 ), a mechanical grinding shop ( 2 ) and an acid polishing shop ( 3 ).

The glass melt ( 1 ) contains at least one glass melting furnace ( 4 ), the exhaust gases of which are sucked off via a suction line ( 5 ) with the aid of a suction blower ( 6 ). The extracted gases then pass through the filter ( 7 ) and finally enter a gas washing system ( 8 ). If necessary, the filter can also be omitted, so that the entire contents are removed in the gas washing system.

The mechanical grinding shop ( 2 ) has workstations ( 9 ) for grinding by hand as well as other workplaces ( 10 ) for the so-called machine grinding shop. In both cases, large amounts of cooling water or wastewater are generated, which are collected in the vats ( 11, 12 ).

The acid polishing is shown schematically at ( 3 ). It consists of the treatment tubs ( 13 ), to which the acid is automatically fed. This caustic acid contains about 25% sulfuric acid and about 9% hydrofluoric acid. The glass parts ( 14 ) to be polished are fed into the baths by machine. The vapors generated during the etching or acid polishing are collected in a hood ( 15 ) and fed to the washing towers ( 18 ) via suction lines ( 16 ) and a suction fan ( 17 ). Both the waste acid from the treatment tubs ( 13 ) and the wash water from the wash towers are collected in collecting tanks ( 19, 20 ).

To carry out the process, all waste water from the factories ( 1, 2 and 3 ) can be brought together and introduced into a first reactor ( 21 ). The first phase of the cleaning process is carried out in this reactor. The reactor is equipped with a device for introducing milk of lime or fine-grained solid lime, which is symbolically shown at ( 22 ). The reactor is further equipped with an agitator ( 23 ) and a pH measuring system ( 24 ).

The wastewater or wastewater mixture introduced into the reactor ( 21 ) in batches is slowly mixed with lime or lime milk after the reactor has been filled with good stirring. The pH value is continuously measured. The system is set so that the lime addition is stopped at pH 3-5, for example at pH 4. The agitator then continues to work for a while to give the reaction mass the opportunity to adjust its reaction equilibrium with the amount of lime added. After a predetermined time, for example after 15 or 30 minutes, the agitator is also turned off, so that the resulting deposits of calcium sulfate and calcium fluoride can settle on the ground. As soon as this has been done, the excess clear water is drawn off through line ( 25 ) and fed to the second reactor ( 26 ). The precipitate collected at the bottom is drawn off via line ( 27 ) and fed to the filter press ( 28 ). The filtrate emerging from the filter press reaches the second reactor ( 26 ) via line ( 29 ) and, if desired, the precipitate can be washed in the filter press ( 28 ), for which purpose washing water is fed to the filter press via line ( 30 ). Neutral pure water or optionally also alkaline water, for example 5% sodium hydroxide solution or the clear water or filtrate from the second cleaning phase, is used as wash water. The solid cake thus cleaned can then be periodically removed from the filter press and collected in the tub ( 31 ).

The second reactor ( 26 ) is a solid mixture consisting of clay mineral, lime, soda, sodium phosphate, flocculant and optionally oxidizing agent fed via the metering device ( 32 ). The embodiment of the second reactor shown as an example in the figure has a premixing tank ( 33 ) in which the solid mixture emerging from the metering device is initially pasted with a small amount of water under the action of an agitator ( 34 ). The resulting pre-suspension then enters the second reactor ( 26 ), where it is evenly distributed in the water to be cleaned under the action of the agitator ( 35 ).

By adding the dry mixture mentioned, the pH value of the clear water of the first cleaning phase is shifted to the alkaline range, approximately to 9.0. The impurities still present in the clear water then fall as hydroxides, carbonates, arsenates and the like. Like. From, the precipitation of the clay mineral present in the solid mixture, such as bentonite-A, is supported and suppressed. The second reactor is also preferably connected to a pH measuring device, which, however, is not shown in the drawing. If the device indicates the end of the precipitation reaction or if this has been determined otherwise, the two agitators ( 34 and 35 ) are switched off and the resulting precipitate is given the opportunity to settle down in the reactor ( 26 ), which is about 0.5 lasts up to 3.0 hours. Thereafter, the excess clear water is drawn off via line ( 36 ) and either immediately fed to the sewage system or a natural body of water, or - if desired and necessary - is first passed through an ion exchanger ( 37 ).

The solid precipitate formed in the reactor ( 26 ) is fed via line ( 38 ) to the filter press ( 39 ) and is further dewatered there. The resulting filtrate passes through the collecting trough ( 40 ) and the drain ( 41 ) into the common clear water line, from where it can be fed directly or in turn via the ion exchanger ( 37 ) to the sewage system. The solid cake formed in the filter press ( 39 ) can be drained into the tub ( 42 ).

Strong and medium-basic anion exchangers are suitable as ion exchange mass. Exchangers of this type are known per se. They allow the arsenic content of water to be reduced below a level of 1 mg / liter. The ion exchangers must be regenerated after exhaustion, and the regeneration waste liquor can be drawn off via the return line ( 43 ) and fed to the second reactor ( 26 ).

Reference numerals

1 glass melt
2 mechanical grinding shop
3 acid polishing
4 glass melting furnace
5 suction line
6 suction fans
7 filters
8 gas washer
9 hand grinding
10 machine grinding
11 vat
12 vat
13 treatment tub
14 glass parts
15 hood
16 suction line
17 suction fan
18 washing towers
19 collection tub
20 collecting tub
21 first reactor
22 limescale containers
23 agitator
24 pH measuring system
25 line
26 second reactor
27 line
28 filter press
29 line
30 wash water supply
31 tub
32 dosing device
33 premix container
34 agitator
35 agitator
36 line
37 ion exchangers
38 line
39 filter press
40 collecting trough
41 derivative
42 tub
43 return line

Claims (7)

1. Process for the purification of waste water from the glass industry by precipitation of at least some of the contaminants with lime, characterized in that lime is added to the waste water in a first separation phase up to a pH of 3 to 5, the resulting precipitate is removed and the clear water is further purified in a second separation phase at a pH greater than 8.0. 2. The method according to claim 1, characterized in that the wastewater in the first separation phase lime milk with a content of 5 to 20 wt .-% Ca (OH) _{2 is} supplied. 3. The method according to claim 1, characterized, that the one formed in the first deposition phase Precipitation after separation from the clear water Formation of a landfill product neutral or alkaline water or with the Clear water from the second cleaning phase washed and pressed in a filter press. 4. The method according to any one of the preceding claims, characterized in that in the factories

• - Melting glass
• - grinding and
• - acid polishing

resulting wastewater merged and together the multi-phase cleaning process according to the preceding claims. 5. The method according to any one of the preceding claims, characterized in that a dry mixture of the following composition is supplied to the clear water in the second cleaning phase:

• 30 to 60 parts by weight of clay mineral
• 35 to 45 parts by weight of Ca (OH) ₂
• 0.5 to 2.0 parts by weight of Na ₂ CO ₃
• 0.5 to 5.0 parts by weight of Na ₂ H PO ₄
• 0.3 to 3.0 parts by weight of flocculant.

6. The method according to any one of the preceding claims, characterized in that a dry mixture of the following composition is supplied to the clear water in the second cleaning phase:

• 30 to 60 parts by weight of clay mineral
• 35 to 45 parts by weight of Ca (OH) ₂
• 0.5 to 2.0 parts by weight of Na ₂ CO ₃
• 0.5 to 5.0 parts by weight of Na ₂ H PO ₄
• 3.0 to 6.0 parts by weight of (NH ₄ ) ₂ S ₂ O ₈
• 0.3 to 3.0 parts by weight of flocculant