DE3147549A1 - METHOD FOR REMOVING MERCURY FROM INDUSTRIAL WASTEWATER - Google Patents

Description

description

Process for removing mercury from industrial sewage

The invention relates to a method of removal of mercury from industrial wastewater containing chemically bound mercury. Dab3i will the well-known reaction for the precipitation of mercury present in the form of sulfide by treatment with Sodium sulphide in the presence of a flocculant exploited. The procedure is characterized by that alkaline conditions are maintained, with a pH value zvär.chsn 7 and 12 and the resulting alkaline After decanting, the sludge is treated with a proportion of the same wastewater from which the mercury is still must be removed. This portion is then filtered back into the precipitation stage with sodium sulfide returned.

It is well known how important the problem of mercury pollution of waste water is, especially after exceptionally severe cases of poisoning have become known some of which are even fatal and after the presence of large quantities Mercury in the flesh of fish has become known,

/ 2

1-55

that have been trapped in areas heavily contaminated by mercury wastewater was.

The increasing importance of the problem has led the governments of the major industrialized countries to extremely strict regulations for the reduction of mercury levels in both metallic as well as bound form in industrial waste, especially in waste water, to enact.

Ir. Italy the maximum allowable value is 5 yug / l.

Εε is believed to be one of the main sources of mercury pollution in water is electrolytic chlorine production using leaky silver cells, followed by

20 such catalytic processes in which mercury; ^; Oil salts used as catalysts for organic syntheses, for example the production of acetaldehyde and vinyl chloride from acetylene.

25 The industries concerned have made considerable efforts to solve this problem and various methods have been developed to reduce the mercury content in industrial wastewater to the values specified by the new laws .

. ■

Sd were used to remove metallic mercury special filtration processes, such as with activated carbon, or the formation of amalgams, while for bound, mercury precipitation, adsorption and ionon

35 exchange process as well as the reduction to elementary

3U7549

1A-55 ^ 58 - i -

Mercury and other chemical and electrochemical Procedures were considered.

Of the precipitation processes wix-d predominantly the one used, which leads to the formation of mercury sulfide. This procedure is generally used performed by connecting the mercury links contaminated wastewater with solutions of sodium sulfide or hydrosulfate at a pH of approximately 8 treated, with flocculation of the colloidal precipitate thus formed with, for example Iron-III-chloride or any other suitable flocculant and then filtered the resulting sludge after decanting.

However, such a method has several disadvantages. Of course it is to provide a quantitative precipitation possible to achieve the mercury necessary to use a strong excess of iJatriumsulfid: Hatri ⁿ imsulfid is readily hydrolyzed to form Schwef elv; ass he material which itself is highly toric.

It also occurs when using Sisen-III chloride as a flocculant has the problem that large amounts of iron hydroxide are formed extremely voluminous precipitate which is very difficult to collect on filters. This occurs in addition to another problem, namely the consumption of iron salts, the more serious problem of treatment large amounts of mud with little ouockr.ilbergo content and consequently an extraordinary one

/ 4

A-55 458 - y ~ ζ.

■ increase moisture content (up to 50 % or even 70 %) .

.Even by using non-ionic flocculants becomes the problem of the large amount of mud and the difficulty in collecting on filters, filtration and subsequent treatments is not resolved while of course the problem of iron depletion arises.

nowadays ν / ΐώ the filtration of colloidal precipitates carried out with the help of rotary filters lined with kieselguhr (decalite), the serves both as a carrier and as a filter aid and / on which the precipitate with the help of a scraper is scraped off. The diatomite lining prevents damage to the filter mesh during removal of precipitation. However, it will always be 2some kieselguhr removed so that a continuous Consumption of diatomaceous earth occurs during the filtration.

3s it has now been shown that the disadvantages indicated above can be largely overcome with the aid of the method according to the invention, which will be explained in more detail later and which essentially consists in that after decanting the alkaline sludge formed during the precipitation with catalytic sulfide with a small Proportion (10 to 20 %) of the total amount of water to be cleaned treated. It has been shown that this treatment makes it possible to redissolve the amorphous substances that have precipitated, whereby the mercury

1A-55 ^ 58 - 5 / -

sulfide precipitate "remains, which is easily on a Usual filter press. Collected can ocer in in any case without the use of filter aids, such as diatomaceous earth, and with a very low residual moisture content.

The mercury sulfide obtained in this way is also essentially free of coarse impurities, so that it can be used directly in the roasting stage for the extraction of elemental mercury.

For a more detailed explanation of the process, Ausfrillvernucho of mercury compounds are given below, contained in waste water from plants for the catalytic synthesis of vinyl chloride Acetylene .. The experiments indicated were initially carried out on a laboratory scale and then on a technical scale.

20 The only figure in the accompanying drawings

shows a block diagram of the method according to the invention.

In this block diagram, 1 denotes the flow of the alkali solution or suspension (e.g. a calcium hydroxide suspension), 2 the aqueous solution of flocculant, 3 the stream of water, of from which the mercury is to be removed, 4 the aqueous solution of sodium sulfide., 5 a reaction vessel equipped with a stirrer and in which a pH of 7 to 9 is maintained must be, 6 a sedimentation vessel, 7 the filter (coated with kieselguhr), 8 (activated carbon) -Filter through which the water is passed,

/ 6

3H7549

which still contains traces of mercury sulphide, 9 the derivation of the mercury-free ".. 'water, 10 the stream of alkaline sludge, 11 a (solution) · -Reaktionsgefäßjin which a portion of the stream 3 of the Water from which the mercury is to be removed is diverted, 14 a filter press or other the direct filtration device, 1? the returned Stream of the water to be freed from mercury and the acidic water obtained during the filtration Mud.

example

The waste water coming from a vinyl chloride synthesizer is acidic, has a pH of approximately

1.8 and contains mercury compounds in an amount _; which is almost 10 mg / l. In order to meet the legal requirements, the mercury level should not be reduced to more than 5 / ug / l. 20th

Be: '. such water was under the laboratory tests Stir treated with milk of lime (an aqueous slurry of lime) to make it alkaline until a pH of approximately 10 was reached. At the same time, 5 ml / l of an aqueous solution of a non-ionic Flocculant based on polyacrylamide (Prodefloc N2M, from PRODECO Company) at a concentration of 1 g / l.

Then, an aqueous solution of sodium sulfide having a concentration of 5 g / l was added in an amount added 3 times the stoichiometric amount Mercury, with stirring for approximately 1 hour. ■ / 7

A58

The stirring was then stopped to allow the precipitate to settle.

After standing for 3 hours, the excess became clear V / ater withdrawn and in a filtration stage with With the help of activated charcoal, the remaining mercury sulphide content was separated.

The mercury sulphide in the decanted water in an amount a little over 1.00. / ug / l present was decreased to a value of 2 to 5 / Ug / 1 after filtration.

In the meantime, the alkaline sludge from the sedimentation vessel was placed in a dissolving vessel, v / o a portion of the η wastewater to be freed from mercury, as it was, (with a pH value of approximately 1.8) was added until a pH- Value of 2.2 to 2.5 was reached ". At this stage approximately 80 % of the sludge had dissolved, while only the mercury sulphides and sulphides of all of the first and second groups of the periodic table, which were possibly still present in the water, remained unresolved in the form of a severe blow.

The remaining precipitate was filtered off in the usual way under vacuum with the aid of a filter cloth without the addition of a filter aid such as Dicalite had to become.

The aqueous filtrate, which still contained mercury compounds, was then again subjected to the sodium sulfide treatment

fed.

■ / 8

3U7549

1-55 458

The precipitate collected on the filter, which was approximately 0.1 g / l treated water, had a mercury content of approximately 10 % based on elemental metal.
5

Technical-scale attempts have been made in the like Order of ancestors i-urtuffn carried out, wrie on a laboratory scale.

However, metal equipment was used in place of the glass equipment.

The dimensions of the industrial apparatus were: reaction vessel 5 in which the solution was made alkaline: about 300 m; Flocculation vessel 6 approx. 120 m ^ activated carbon filter 8 3 m, dissolving vessel 11 3 m ^J.

The milk was also used in the technical process added with the help of a measuring device up to a pH value of 8 to 9. The alkaline solution was passed into the flocculation vessel, into which sodium sulfide was also passed (in an amount corresponding to 3 times the stoichiometric amount required to precipitate mercury sulfide is to also precipitate other metals that may be present) and the non-ionic flocculant was previously admitted.

30 It could be shown that the consumption of

Flocculant in the technical test was half that in the laboratory test.

Any remaining excess of sodium sulfide was on the activated carbon filter

adsorbed.

3U7549

1A-55 458 - / - {Ο-

The flaky mud became thorny settling into the solution:; vessel passed while the clear Water has been fed to your activated carbon filter.

The water exiting the sedimentation vessel contained mercury in an amount of 50 to <° 00 mg / 1. After adsorption on the activated carbon filter ' the mean mercury content in the exiting water was only 2 to 5 μg / l. 10

To prevent any with overriding A kieselguhr filter was installed upstream of flakes that would clog the activated carbon filter.

The sludge led into the dissolving vessel was mixed with the water to be freed from mercury treated.

The ratio of acidic water to alkaline » Sludge is a function of the pH of the water and the concentration of solids in the sludge and ranges from 10 to 20.

After each dissolution stage, the acidic sludge could settle, so that the water with the help of an overflow could be withdrawn.

The water was returned to the first reactor. The acidic sludge from the solution vessel was passed into a filter press, in which a compact filter cake was obtained, which was easily removed from the filter cloth removed.

For comparison, the mercury removal was carried out on the same wastewater without treatment of the alkaline sludge to be treated with that of mercury

/ 10

3H7549

1A-55 458

free water.

The most striking difference in these ways of working consisted in the fact that in the comparison procedure the settling tank was frozen daily and the alkaline sludge had to be filtered because it was an extraordinarily large volume ingested, while in the case of the procedure according to the invention that comprises the solution step, it was sufficient although it was not strictly necessary to have the filtration done weekly.

The activated carbon filter was regenerated in situ after more than 45 days of operation by leaching with a 3 % hydrochloric acid solution to which a corrosion inhibitor was added.

The following tables summarize data for a number of experiments according to the invention and comparative experiments: the values for the mercury contained in the water to be treated and the mercury emerging from the activated carbon filter are given for both cases, as well as the amounts of sludge _} in in both cases, their respective mercury content and other data.

/ 11

technical trials I— » O VO 00 INJ ON - UJ Vn i • P " Laboratory tests Ul co I— · P. cn <i
S3 C ro Q \ - i
INJ O cn 4 O 4
• Ily ^ 1 Φ M. O .p · co p ⁴ O O O ro sS ro P. U) Ul U) I - ¹ O μ- ' O Ι — ι ON O Vn P H H CO O cn a et -P- ON -ρ · (- ' ON Vn vo cn et O O O O O O ON O O Φ 4 P. O O O O O O O O O 4 Φ Ο O O ct Φ ro O P. p. co φ H· . co H σ * ro
4 · U) CO CO el " ü p VO U) O 4 Ö P H· ro op co et cn co Ui ON Previous year INJ ON Φ OQ Ρ · - VO U) ^ J O Co O ui O Vn Office ro
p.Ho3 CjJ vn φ ρ; oq Cn co ¹ ^ d H P O P O co is " U) CN • p- I I ON O ON 4 O p (1) U ¹ B ctP N) Ul U) N) Ul -P- Φ φ Ρ ·
ti Hi φ VO rv -J ON Ö piH-0
Φ Η Ο INJ cn et> ■ ro ^ r P H cn ρ <! cn p ι φ cn

P. φ Q ro cn et P " ¹ et H ₅ P. ro ro Ct Ct ro P. P. P. B. p. ro cn D. p. <! O ro ^ ¹ O P. 4th cn H- CO cn O H- ro J ^ H et σ * H ro Oq H· Φ P. Η · P. pi et φ 4th ro et H- Φ P. P. P-. pi φ H- P. ro ρ O Ρ · ro O P ^- cn CO H- H P. Cf H- Φ Φ 4th Cn I. Φ 4th

VJi

VJl

VJl

»-A φ

H H O

Table 2

Properties of the precipitation of mercury from wastewater
obtained sludge.

I.
! -j attempt ) lot Composition of the mud after filtration (% by weight) iron I.
j -%) j
1 Calcium I.
! ; §> No. ) (kg / m ' ) "Water Analysis of wet samples (wt. !
j ^, 56 5.23 (
I.
I. Labo ι 1 0.05 50 mercury 3.85 i 3.26 ^ 85 2 ) 0.06 55 8.90 2.8 5 5.3 3 0, 04-8 51 ⁹ (5th 3.3 5.0 0.051 53 8.85 2.80 6.24- i 13 (° 0.38 72 10.5 5.8! . ] Λ (° 0.311 74 · 3.33 S ² ! 15 (° 66 1.75 5.0: 16 (° 0.35 60 2.5 3.2 i
i

Table 2 (continued)

■ s attempt
TvT Lot-, Composition of the mud after filtration (wt .-? o) .iron 4.25 Calcium j -H
ω No. (kg / m- ') Analysis of wet samples (wt %) 4 _r 00 ' 5.35 1 5 0.056 52 mercury 3.25 4.95 6th 0.04 48 9 _r 2 3.80 5.00, ϋ 7th 0.048 50 10.1 3 ₇ 90 5.20 W.
• Η 8th 0.060 53 4 _? 15th 5.40 O 9 0.050 50 ⁹ I ⁹ 3.95 4.8; φ
• Ρ 10 0.042 52 8.95 4.30 5.3 11 0.055 51 8.4 2 _r 9 4.9 12th 0.051 49 9.2 5.5 y 17 (°) 0.311 71 10.3 2.85 4.9 18 (°) 0.330 70 2.2 h ¹ 5.8 ί 19 (°) 0.295 68 1.8 6.2 ■: 20 (°) 0.300 65 2.3 3t ³ 4.5 y 21 (°) 0.350 69 3 _P 2 2.95 5.9, I. 22 ( ^Ο ) 0.310 64 3.5 3 ^ n 5f °; 23 (°) 0.29θ 60 2.9 24 ( ^Ο ) 0 _f 3üb 6 5 3 _r 35 "> Ci r
L. , U J

(°) The experiments marked in this way relate to the precipitation of mercury as sulphide without subsequent treatment of the sludge with a proportion of the

Mercury to liberate water.
6268

Claims (1)

Claim 10 Process for removing mercury from wastewater containing chemically bound mercury by reaction with sodium sulfide in the presence of a flocculant, characterized in that the precipitation is carried out at a pH of 7 to 12 and the alkaline sludge obtained after settling treated with 10 to 20 ^ a ₁ based on the total amount of the wastewater that has not yet been purified of mercury and, after filtration, returns it to the aurfällstufe with sodium sulfide. 6268