HU194131B - Process for extraction of useful compositions from polluting environment quencher acid slag with poison content - Google Patents

Abstract

Pulverised hardened slag is extd. with a chloride soln. liberating HCN and CO2, which are partially absorbed in a NaCl soln. from which it is removed by boiling, air-blowing and centrifuge. Heavy metal ions pptd. from the filtrate with NaOH, are filtered and smelted. BaCO3 is pptd. from the filtrate and recovered by centrifuging. The remaining filtrate is evapd. The bulk of HCN is the absorbed in a suspension of ZnO in K2CO3 resulting in a K-Zn-CN complex. The remaining brine is mixed with NaOH and the resulting NaCN and NaOH are pptd.

Description

The present invention is capable of recovering valuable components of toxic contaminating training salt slags.

It is known that the iron industry uses a large amount of hardening salt, heat treatment salt bath during processing, and its slag is one of the substances which cause great problems for industrial plants during storage and disposal because they contain significant amounts of toxic substances, mainly cyano and barium compounds. in addition to sodium chloride and carbonate, iron waste and carbon. To our knowledge, the disposal of waste that is extremely hazardous to the environment is not a clear-cut issue, especially with regard to high-salinity and usually sewage discharged after detoxification.

Based on the literature review, apart from some widely applicable generic methods (such as HCN removal of coke oven gases, treatment of organic synthetic tail gas), a solution for handling the by-products of almost all cyanide technologies had to be developed.

Most detoxification processes accomplish the task by chemical conversion, usually oxidation, of the cyanide compound, which is usually present in low concentrations. During this process, the highly toxic cyanide ion is converted into the less toxic cyanate ion or, by complete oxidation, into nitrogen or ammonium compounds or carbon dioxide. A common disadvantage of oxidative detoxification processes is the extremely high chemical and / or electrical energy demand, which becomes particularly significant when the waste to be disposed contains other readily oxidizable materials. A further disadvantage is that the products generated in the process are either worthless or economically unavailable.

An example is West German Patent No. 2,531,721, in which the oxidation of HCN is carried out with 80-95% sulfuric acid. The products of oxidation and subsequent hydrolysis are NH ₄ HSO ₄ and CO. In the presence of nitrogen oxides, oxidation produces nitrogen, carbon dioxide and water. Further use should be made of 80% sulfuric acid, which is considered exhausted for detoxification purposes.

There are also widespread methods of detoxifying cyanide to sulfur and various sulfur containing compounds, which are economically viable only if the product is disposable or the resulting rhodanide is recovered and marketed in sufficient purity.

(e.g., in Japanese Patent No. 80,964,675, cyanide wastewater with a concentration of about 80 mg / dm ³ , which also contained ammonia and hydrogen sulphide, is oxidized by the addition of 1 g of sulfur per liter at 65 ° C. non-avoidable products: HCNS, H ₂ S ₂ O ₃ and various polysulphides.

Conventional methods include the use of transition metal compounds that bind cyanides in the form of stable, insoluble complexes. The most common of these is the use of iron salts in various ways to obtain insoluble complex ferricyanates. Their common disadvantage is that by binding relatively small amounts of cyanide, they generate a large volume of non-disposable, albeit less hazardous waste, which, although having many uses, virtually requires significant additional investment and operational costs.

Such a solution is disclosed in Japanese Patent 72.47.562 number can be almost classic that HCN and H ^ S-containing coker gases added or suspended in an alkaline medium vasszulfiddal and acidic medium iron Π salt (NH _4/2 Fe / Fe / CN ₆ ) to remove the HCN content of the effluent gas in the form of a precipitate.

In addition to the three types of solutions listed, there are many unique solutions that differ mainly in the quality of the absorbent or reaction medium used, e.g., U.S. Patent No. 121,952 to select HCN with dilute aqueous phenol, or 2,260,248 West German Patent No. 5,198,125, which discloses a solution in which the hydrogen sulfide and carbon dioxide gas to be removed are liberated from the methanol absorptive medium by multi-step rectification, and then the remaining HCN is converted to NaCN with NaOH. The resulting Na-formate is discharged with the effluent.

Recently, various catalytic processes have been gaining ground, which are novel solutions to conventional oxidation detoxification using the oxygen in the air. A homogeneous catalyst system is described in French Patent No. 2,340,126. In a solution of 2-methyl-1,4-naphthoquinone-3-sulfonate and iron II-tartrate in a solution of 2-oxoethanol dibutylamine + glycerol * in water, HCN is removed from the gas space at a pressure of 98.3%. a.

Also interesting are processes using solid catalysts, e.g. Japanese Patent Laid-Open No. 76,33,763; In this process, 95% of the HCN content of the gas passed through was converted to harmless compounds using oxide catalysts containing Fe, Cu, Ag containing Rh and Ru at a catalyst temperature of 350 ° C.

It is an object of the present invention to provide a process that can economically solve the recycling of cyanide-containing wastes, e.g. slags from heat treatment salt baths - containing a high percentage of other toxic or highly polluting compounds in addition to a few percent soluble cyanide.

The advantage of this process is that, as a result of the completely closed technology, the processed hazardous waste is completely reused as a raw material in other chemical operations, ie not to destroy the cyanide content but to recycle it.

The essence of our process is that the so-called cyanide-containing high-cyanide is formed in the salt-melt heat treatment operations. The training salt slurry is ground to a particle size of less than 5 mm at 30-50 ° C in a stirred reactor and initially acidified to pH = 1 by addition of concentrated hydrochloric acid. The CO, released from the carbonate components of the mixture and the resulting HCN were bubbled through a NaCl solution cooled to -25 ° C and then a 1: 1 aqueous suspension of ZnO-K, CO, to remove HCN from the solution in the stirring reactor. complete with boiling air during boiling. HCN was taken up in the cooled brine with NaOH to NaCN

194.131, crystallized with NaCl present and used as a heat treatment salt bath component. The potassium tetracyanocyanate formed in the ZnO suspension is recrystallized and sold as a galvanic raw material.

After the double extraction, HCN in the carbon dioxide leaving the gas was not detectable by the benzidine blue reaction and is thus freely released. The soluble cyanide-free solution was filtered through a centrifuge. The iron and heavy metal compounds are liberated by addition of NaOh to pH 7 and the barium content is removed in the form of BaCO ₃ . The solution treated in this way, in the processing of slags of the most common types of hard salt, is ca. 20% -25% aqueous solution of 98% pure NaCl, e.g. can be used directly in chlor-alkali electrolysis.

The insoluble residue formed during the dissolution of the training salt slag, which in its bulk is iron oxide, complex ferric cyanide, sand, mixed with calcined lime, is transferred to the blast furnace.

BaCo ₃ of 98% to 99% purity is utilized either in its original form or after processing into BaCl ₃ .

The following is an exemplary embodiment of the process without limiting the scope of the invention to the particular solution.

Example 1

100 kg of training salt slurry ground to a particle size of less than 5 mm (containing, according to laboratory analysis, NaCN 3.8%, NaCl 26.6%, Na CO ₃ 45.8%, BaCO 5%, iron reve 15%, other insoluble inorganic 3.8 under constant stirring dissolved in 45 ° C in% / 250 dm ³ of water, acid resistant lining, a closed stirred reactor so that under intensive stirring added released by 52 dm ³ concentrated HCl gas consisting mainly of CO ₂ of escape without the risk of kihabzás the acidifying from a solubilizing reactor, in which the hydrostatic resistance of the absorption system was measured to be 0.5-0.7 bar. The carbon dioxide HCN leaving the reactor is initially low, barely detectable, and when the pH of the solution reaches pH 7, later The cooled NaO absorption system only participates in the absorption process at the maximum of HCN release. Carbon dioxide was passed through three absorbers filled in series with a 1: 1 molar ratio of ZnO and K CO in an effective volume of 20 dm ³ each with an effective volume of 20 dm ³ .

It was necessary to refill the absorber with fresh mixture when, in the first of the three units connected in series, the amount of suspended ZnO in the first one fell below 10 g / l. In this case, according to the countercurrent principle, the contents of the second and third absorbers were pumped one at a time and the fresh absorbent suspension was added to the last. The cyanide-depleted solution was filtered through a bag centrifuge, and the filtrate was washed with 3 x 10 liters of water to obtain a portion of the insoluble component to be cured, to which was added a solution of iron hydroxides formed by iron removal with NaOH. Barium ions were removed by adding Na ₂ CO _{3 to} the iron-free solution. The resulting BaCo 1 was removed by centrifugation after settling. The remaining solution, which corresponds to a technical grade NaCl solution, was collected in a 5 m ³ reservoir until transport.

Characteristics of the products obtained in the regeneration process:

Dissolution residue: 18 kg total iron 47% complex iron cyanides 2.4%

SIIO, 12%

S 0.2%

P, 035% according to preliminary tests suitable for metallurgy. Barium carbonate: 5.2 kg BaCO ³

98.8, U 0.05%

NaCl

Fe Pollution is a technical grade raw material for the production of Ba compounds

NaCN-NaCl mixture: 6 kg

NaCN '37%

NaCl 61%

Na ₂ CO ₂ , by mixing _{> 6} % of potassium chloride and sodium chloride in suitable proportions, is suitable as a starting pad for heat treatment furnaces.

Recrystallized complex zinc cyanide filtered from a selective absorber: 3 l kg

K / Zn / CN / ₄ / 'Suitable for the preparation of 99.1% zinc baths with galvanic technology. NaCl solution solids: 80 kg

NaCl 98%

Na SO ₄ Q, 4%

MgCl 3, 3% κα i, i%

Ba less than 0.1 mg / l.

Claims (1)

A process for recovering valuable components of a poisonous, environmentally polluting training slag, characterized by: After grinding to 45 smaller particle sizes, hydrochloric acid, concentrated or diluted 1: 1 with water, is added until pH = 1, and the hydrogen cyanide is partially absorbed by passing the liberated hydrogen cyanide and carbon dioxide through a sodium chloride solution cooled to -25 to -30 ° C. absorbing the hydrogen carbonate content of the effluent gases with zinc oxide suspended in a solution of potassium carbonate, optionally recovering the resulting potassium zinc cyanide complex, centrifuging the cyanogenated slurry with boiling and air blowing, removing the heavy metal, 55 we pass combining centrifugátummal smelting, to harvest sodium hydroxide was added and the precipitated barium carbonate was centrifuged, the solution is optionally concentrated, whereby the chilled brine by the hydrogen cyanide-containing _cn sodium hydroxide was added thereto, the resulting mixture is crystallized NaCl NaCN.