DE2534892A1 - METHOD FOR OXIDATIVE TREATMENT OF SULFIDE, SULFITE AND THIOSULPHATE-CONTAINING WASTE - Google Patents

Description

Bayer Aktiengesellschaft 2534892

Central Patents Department. Trademarks and licenses

Gr / Hg 509 Leverkusen. Bayerwerk

* tos. 1975

Process for the oxidative treatment of wastewater containing sulphides, sulphites and thiosulphates

In the chemical industry there are large amounts of sulphide-, sulphite- and thiosulphate-containing wastewater, in particular in the form of their sodium salts, e.g. B. in paper and paint production. It is known to make sodium sulfide by air oxidation essentially to convert to thiosulfate (Air oxidation of sulfides in process waters and caustic solutions, PrOCAP I 36 (II) 1956, 313-317). It is also known that the oxidation of sodium sulfide and sodium thiosulfate to sodium sulfate with oxygen-containing gases proceeds only slowly (Petroleum and Coal, 14 (1961), 8, 621-626). In order to accelerate the reaction, one therefore works at high temperatures (at about 25o ° C), high pressures and long dwell times (DT-OS 23 34 994).

In the oxidation of bisulfite-containing wastewater, larger amounts of SO _{2 are} expelled during the oxidation with air, so that the wastewater problem becomes an exhaust air problem.

The present invention is based on the object of a simple Process for the oxidation of sulphide, sulphite and thiosulphate wastewater, the various sulphurous ones Compounds also contained in any mixtures

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can develop, in which practically a quantitative oxidation up to the stage of the sulfate, being as a by-product optionally sulfur is formed is carried out.

The present invention therefore provides a process for the oxidation of sulphide, sulphite, thiosulphate-containing wastewater, which contains these sulfur-containing compounds individually or in any combination, by oxidation with oxygen-containing gases in aqueous solution, characterized in that the wastewater, if it contains sulphide first at pH values} 7 and temperatures of 2.0 - be contacted 2oo C with technically pure oxygen at atmospheric pressure up to pressures of 2o bar, until substantially all of the sulfide is converted to thiosulfate, then at pH values of about 0 to 5 or 0 to 8 for wastewater containing only sulfite and at temperatures of 20-2oo ° C. with technically pure oxygen at normal pressure or pressures up to about 20 bar, optionally in the presence of catalysts, until sulfate is practically completely formed, with In the case of wastewater containing sulphide and / or thiosulphate, sulfur is also deposited.

In the context of the present invention, the term sulfide should also be understood as meaning hydrogen sulfide or polysulfides, and the term sulfite should also be understood as meaning hydrogen sulfites. Technically pure oxygen for the purposes of the present invention contains at least 90% by volume, preferably 99% by volume, O ₂ * The sulfur-containing compounds in wastewater are generally in salt form, preferably in the form of alkali, alkaline earth or ammonium salts; however, the underlying acids and / or acid anhydrides can also be oxidized according to the invention.

The oxidation of sulphide-containing wastewater to thiosulphate takes place preferably at temperatures of 100 - 14o C at pressures (bar) from 1 to 1o, and pH-7erten from 1o to 14, while the oxidation in the acidic pH range, preferably at pH values

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from about 1 to 3 "at temperatures between 7o and 15o C and pressures from 1 to" Io "bar. The oxidation in the acidic pH range is preferably carried out by adding catalysts such as copper salts, e.g. CuSO, CuCl ₅ ,

4 cobalt salts, e.g. B. CoSO ^, CoCl ₂ , iron salts, such as. B.

Fe (II) and / or Fe (IIl) salts accelerated. In the case of iron salts, FeCl ₂ , Fe ₃ (SO ^) ₃ , FeSO ^, FeCL ₅ are particularly suitable. It is particularly favorable if the ratio of Fe (III): Fe (II) ions is set to values between 2: 1 and 8: 1. The catalysts are used in amounts of about 0.01 to 100 ppm, based on the aqueous solution.

According to the process according to the invention, if sulfide is present in the wastewater, this is first oxidized to thiosulfate, what is the result of further oxidation in the acidic pH range with simultaneous sulfur deposition in the subsequent process step Forms sulfate. If sulfite and sulfide are present at the same time, thiosulfate is also formed. Below this is shown for sodium sulfide using the simplified reaction scheme Ia and Ib in the alkaline and II in the acidic: In the alkaline:

I a) 2

+ 2

^Na 2 ^S 2 ° 3

^{2 NaOH}

I b) Na ₂ S + SO ₂ + 1/2

In acid: II) Na ₂ S ₂ O

> S + NaHSO

+1/2 Q

NaHSO

If the oxidation is carried out in the acidic pH range at temperatures above the melting point of sulfur, can the resulting sulfur can be drawn off in liquid form at the bottom of the oxidation tank. With a driving style below

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the melting point of sulfur can this optionally with the additional use of flocculants and Filtration aids also on conventional filtration apparatus, such as. B. filter presses or vacuum filters split off.

The concentration of the sulfur-containing compounds in the wastewater can be within relatively wide limits, for example vary between 1 to 2oo g / l sulfide, 1 to 150 g / l sulfite, 1 to 2oo g / l thiosulfate; preferably it lies between 1 to 50 g / l sulfide, 1 to 100 g / l sulfite, 1 to 100 g / l Thiosulfate. In a particularly advantageous embodiment wastewater is treated in which the molar ratio sulphide / sulphite is between about 1: 0.6 to 1: 1.1 or is set.

A continuous process for the oxidation of a sulfide-, sulfite- and thiosulfate-containing substance is shown below with reference to a figure Waste water described, which represents a preferred embodiment of the method according to the invention.

In the figure, the numbers have the following meaning:

1 supply line for wastewater containing sulphides,

2 bubble column,

3 discharge line of the treated wastewater in the bite column,

4 packed column,

5 discharge line of the treated wastewater from the. _ Packed column,

6 bubble column,

7 addition of catalyst,

8 addition of acid,

9 sulfur extraction,

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10 supply line of the oxidizing gas for the Bubble column 2,

11 feed line of the oxidizing gas for the bubble column 6,

12 partial flow of the oxidizing gas for the bubble column 6, which is introduced at the bottom of the bubble column 6,

13 Feed line for products containing sulphite or thiosulphate Sewage,

14 packed column,

15 sulfur extraction,

16 extraction of the oxidized wastewater,

17 supply of technically pure oxygen,

18 Gas supply line

19 feed pump

20 gas circulation pump

21 Waste water overflow

22 Alkali feed

In detail, the treatment of sulfide, sulfite and wastewater containing thiosulphate as follows:

Sulphide-containing wastewater is introduced into the bubble column 2 via feed line 1, the pH is optionally adjusted to pH values of 7 by alkali, preferably NaOH, introduced via line 22 and with oxygen, introduced via the feed line 1o, with average residence times of about 5 to 2o Minutes treated. The wastewater is then fed via line 3 to packed column 4 for virtually complete oxidation to thiosulfate, with oxygen being fed in via line 18.

The wastewater, the sulphide content of which has essentially been converted to thiosulphate, leaves the packed column 4 via the outlet line 5 and enters the bubble column 6 via the pump 19. Acid is preferably added via line 8

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Sulfuric acid, supplied to the necessary in the bubble column set acidic pH range. Catalyst can be fed to the wastewater to be oxidized via 7. Oxygen becomes the Bubble column via the gas circulation pump 2o via the lines 11 and 12 supplied. Elemental sulfur can be withdrawn via line 9. This occurs from the bubble column 6 After an average residence time of 2 to 20 minutes, wastewater is fed into the packed column 14 via line 21, where practically complete oxidation of sulfite to sulfate takes place. Both packed columns 4 and 14 are preferred operated in a non-flooded state. Sulfur can also be removed in elemental form via line 15 will. The technically pure oxygen is fed in via line 17, via line 16 the wastewater, which practically only contains sulphate, is discharged.

If the wastewater is sulfide-free, the wastewater is only fed via 13 to the bubble column 6, the oxidation columns 2 and 4 are omitted.

The inventive method, it is possible to Oxidation of wastewater containing sulphide, sulphite and thiosulphate to be carried out quickly with the formation of sulphate and sulfur at relatively low temperatures and pressures. By separating the sulfur, the amount of oxygen required is reduced compared to known methods. Since the fed Oxygen is used practically quantitatively for the oxidation, an emission-free mode of operation is achieved.

example 1

In a semi-industrial plant according to FIG. 1, 200 l / hour of technical wastewater of the composition were continuously fed 34.6 g per 1 sodium sulfide, 2.5 g per 1 sodium thiosulfate and fed 1, o g per 1 sodium sulfite.

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After passing the first stage (alkaline oxidation), d. H. the bubble column 2 and packed column 4 at temperatures of 120 ° C in the bubble column and in the packed column and pressures of 4.5 "bar oxygen, fed in via 17 via 10, the water withdrawn at 5 contained 0.6 g per 1 sodium sulfide, 35.4 g sodium thiosulfate and 1, og per 1 sodium sulfite. After the subsequent Oxidation in the bubble column 6 and in the packed column 14, which were operated at temperatures of 130 ° C, the wastewater contained only 2.5 g per liter of sodium thiosulphate, otherwise sodium hydrogen sulfate or sodium sulfate.

The total residence time of the waste water for bubble column 2 + packed column 4 was 4.5 minutes, for the bubble column 6 + packed column 14 25 minutes. In the bubble column 2 or packed column 4, the pH was 14, in bubble column 6 or packed column 14 it was 0.6.

Example 2 (sulfide-free wastewater)

In the bubble column 6 were continuously 2oo liters per hour of a bisulfite waste liquor of 30 g HSO, ~ / liter and a pH value of 5.1 at 70 ° C. Oxygen at 5 bar, introduced via 17, caused the virtually quantitative oxidation of the Hydrogen sulfite, because at the outlet of the second stage was no HSO, detected. In this variant of the method according to the invention, the oxygen was only via the Lines 11 and 12 are introduced into the bubble column 6 and recirculated via the line 12 by means of the gas circulation pump 2o. the Gas discharge line 1o shown in FIG. 1 is omitted in this variant.

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Claims (9)

Claims A ^ Process for the oxidation of sulphide, sulphide, thiosulphate-containing wastewater, which contains these sulfur-containing compounds individually or in any combination, by oxidation with oxygen-containing gases in aqueous solution, characterized in that the wastewater, if it contains sulphide, initially at pH values > 7 and at temperatures of 20 to 2oo ° C with technically pure oxygen at normal pressure to pressures of 20 bar until substantially all of the sulfide has been converted into thiosulfate, then at pH values of about 0 to 5 or 0 to 8 for wastewater containing only sulfite and at temperatures from 2o to 2oo ° C with technically pure oxygen at normal pressure or pressure up to about 2o bar, optionally in the presence of catalysts to the virtually complete formation of sulfate, with sulfide and / or wastewater containing thiosulphate also separates sulfur. 2. The method according to claim 1, characterized in that the oxidation of sulphide-containing wastewater to thiosulphate in alkaline at temperatures of 100 to 14o C be Pressure from 1 to 10 bar is carried out. 3. The method according to claim 1, characterized in that the oxidation in acidic at pH 1 to 3 and temperatures is carried out between 7o and 15o ° C at pressures of 1 to 10 bar. 4. The method according to any one of claims 1 to 3, characterized in that the oxidation in the acidic pH range is accelerated by copper, cobalt or iron containing catalysts. Le A 16 577 - 8 - 709807/0499 5. The method according to claim 4, characterized in that in iron-containing catalysts the iron (III) -: Fe (II) ion ratio to values between 2: 1 and 8: 1 is set. 6. The method according to any one of claims 4 and 5, characterized characterized in that the catalysts are used in amounts of about 0.01 to 100 ppm, based on aqueous solution will. 7. The method according to any one of claims 1 to 6, characterized in that a waste water with 1 to 2oo g / l sulfide, 1 to 150 g / l sulfite, 1 to 200 g / l thiosulfate are used will. 8. The method according to any one of claims 1 to 7, characterized in that a waste water with a molar Sulphide / sulphite ratio between about 1: 0.6 to 1: 1.1 is used. 9. The method according to any one of claims 1 to 8, characterized in that both the oxidation in the alkaline as well as in acidic is carried out in two stages, each in a bubble column with a downstream packed column. Le A 16 577 - 9 - 709807/0499 JK) Blank page