RU2501743C1 - Method of sewage purification from cyanide-ions - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: method of sewage purification from cyanide-ions includes its processing with sulfate of bivalent iron in quantity 293 wt.p to 100 wt.p. CN-ions in presence in water of sorbent in form of fibrillated cellulose fibres, which contain in wt %: not less than 54% of fibres with length not more 0.63 mm and not less than 94% of fibres with length not more than 1.23 mm, with formation of reaction product in form of insoluble particles of iron cyanide. Reaction product is obtained in form of composite material, which consists of cellulose fibres with sorbed on them iron cyanide particles. Product of processing is discharged from water with application of pressured flotation.

EFFECT: invention makes it possible to simplify process of purification, reduce iron sulfate consumption, increase purification degree and provide possibility of carrying out purification in continuous mode.

2 cl, 3 ex

Description

The invention relates to technologies for the treatment of wastewater from cyanides and can be used in enterprises of non-ferrous and ferrous metallurgy, in the preparation of gold by the cyanide method, in chemical and machine-building industries.

A known method of treating wastewater from cyanide ions by treating it with ferrous sulfate at a flow rate of 10.5 wt.h. per 1 part by weight CN ions in the presence of sodium carbonate, or potassium, or ammonium in water in an amount of 0.4-6.1 g / l (SU 1215307, C02F 1/58, publ. 29.02.88). After stirring, the resulting suspension of the reaction product in the form of particles of iron cyanide is settled, the precipitate is separated. The residual content of CN ions is 0.06-0.40 mg / L.

The disadvantages of the method are the high consumption of iron sulfate, excipients, the long duration of the deposition of the treatment product, a noticeable residual concentration of CN ions in water, the frequency of the process.

There is also known a method of purifying wastewater from cyanide ions by treating it with a mixture of a solution of ferrous sulfate at a flow rate of 9.2 wt.h. per 1 part by weight CN ions with intensification of mixing (SU 1380179, C02F 1/58, publ. 10.04.96). In the method, a solution of iron sulfate is introduced into the water stream in a parallel directional stream equal in speed to the waste water stream, followed by twisting of the streams. The content of CN ions in purified water after it has settled is 0.08-2.86 mg / L.

The disadvantages of the method are the high complexity of the process, the high consumption of iron sulfate, a significant residual content of CN ions in the water, the frequency of the process.

New results from the use of the proposed method are the simplification of the process, reducing the consumption of iron sulfate, increasing the degree of purification, providing the possibility of purification in a continuous mode.

These results are achieved in that in a method for purifying wastewater from cyanide ions, including its treatment with ferrous sulfate to form a reaction product in the form of insoluble particles of iron cyanide, removing the product from water, according to the invention, the water is treated in the presence of a sorbent in the form fibrillated cellulose fibers containing in wt.% not less than 54% of fibers with a length of not more than 0.63 mm and not less than 94% of fibers with a length of not more than 1.23 mm, iron sulfate is consumed in an amount of 293 parts by weight per 100 parts by weight CN-ions, the reaction product is obtained in the form of a composite material consisting of cellulose fibers with particles of iron cyanide adsorbed on them, while the treatment product is removed from water using pressure flotation. Cellulose fibers are fed into the water in an amount of 50-150 mg per 1 liter.

Cellulose fibers (CV) with the indicated characteristics have a very high sorption capacity with respect to chemically deposited particles at the time of their formation. In the composition of the composite material (CM), the content of particles of iron cyanide (CG) can be more than 800 parts by weight per 100 parts by weight fibers (CF: CV> 800: 100). In practice, it is advisable to carry out the sorption of particles to a ratio of CI: CV = 300 (± 50): 100. With an increase in the length of the fibers, their activity and sorption capacity decrease, with a decrease in the length, the activity and capacity increase, however, at the same ratio of CF: CV, the water retention of KM increases and, accordingly, difficulties arise in its dehydration, necessary for its utilization.

Fibrillated cellulose fibers have another important property. In an aqueous medium, even at a concentration of, for example, 0.005% in water without stirring, they quickly form flocculi and flakes that hold air bubbles well, easily float to the surface of the water and form a stable flotation sludge. When using such fibers in the pressure flotation process, it is not necessary to use auxiliary reagents, such as coagulants, flocculants and flotation agents.

KM also fully possesses these properties.

The flotation sludge resulting from flotation, consisting of a composite material, should be disposed of or disposed of. To do this, it is first dehydrated, for example, using a filter press or centrifuge, washed, again dehydrated and dried. The dried material can be calcined at 500 ° C and obtained as a result of decomposition according to the scheme 3Fe (CN) ₂ → 3Fe ₃ C + 5C + 3N ₂ harmless products. You can also treat the composite material with a KCN solution and obtain a solution of a valuable product - yellow blood salt K ₄ [Fe (CN) ₆ ], as well as regenerated CV.

The method is as follows. A suspension of sorbent is prepared with the above characteristics of the fibers with their concentration, for example, 3 wt.%. Prepare a solution of ferrous sulfate with its concentration, for example, 10%.

The water is purified in a continuous installation, including a mixer, reactor, saturator, flotator and filter press.

Wastewater and a given amount of CV are fed into the mixer to obtain a dispersion with a fiber content of 50-150 mg / l of water. The dispersion is sent to the reactor, which also serves a solution of ferrous sulfate at the rate of 293 wt.h. per 100 parts by weight CN ions contained in water. As a result of reactions, a water-insoluble product is formed in the form of particles of iron (II) cyanide Fe ₂ [Fe (CN) ₆ ], which are sorbed on the CV with the formation of CM. The resulting dispersion is sent to a saturator, it is saturated with air under a pressure of 2-3 atmospheres and fed to a flotator. In the flotator, the composite material is completely floated to form a slurry. It is removed from the flotator, sent for dehydration and further for processing.

The following examples illustrate the possibilities of the proposed method.

Example 1. Purify water with a content of CN ions in the composition of NaCN or KCN 10 mg / L. In the mixer, water is added to the water at the rate of 50 mg / l. The resulting dispersion is sent to the reactor and FeSO ₄ solution is fed into it at the rate of 29.3 mg per 1 liter of dispersion. As a result of reactions, 20.75 mg of CG are formed in 1 liter of water and, accordingly, 70.75 mg of CM with a ratio in it in parts by weight of CI: CV = 41.5: 100. The dispersion is sent to a saturator, then to a flotator, in which the CM is floated. In the starting period of operation of the installation from the moment the flotation sludge is removed from the flotator chamber, it is completely fed into the mixer and from that moment the supply of fresh sorbent is stopped. Upon reaching the ratio of CI: CV in the CM equal to 300: 100, part of the CM is removed from the process, and fresh sorbent begins to be fed into the mixer in an amount equal to the amount of CV removed from the process in the CM.

The deduced CM is dehydrated, washed, dried, treated with a KCN solution, and 236.6 mg of yellow blood salt is obtained from every 100 mg of CN ions supplied with waste water during its purification.

The purified water contains sodium or potassium sulfate in an amount equivalent to the equal content of CN ions in the wastewater, i.e. 9.105 mg Na ₂ SO ₄ or 11.17 mg K ₂ SO ₄ in 1 liter of treated water. CN-ions are not detected in water.

Example 2. In contrast to example 1, wastewater contains 278 mg / l of CN ions, 150 mg / l of water are fed into the water. The FeSO ₄ solution is dosed into the dispersion in the reactor at a rate of 814.54 mg per 1 l of water. As a result of reactions in 1 liter of water, 576.57 mg of CG and, correspondingly, 726, 57 mg of CM are formed with a ratio of CG: CV = 384: 100 in it. The entire CM is derived from the process. It is washed, dehydrated, dried and calcined at 520 ° C. to form iron carbide FeC, carbon C and gaseous N ₂ . Purified water contains 253.12 mg Na ₂ SO ₄ or 310.5 mg K ₂ SO _4; CN ions are not detected in water.

Example 3. Purify water with a content of CN ions in the form of Na ₂ [Zn (CN) ₄ ] in an amount of 120 mg / L. CV is supplied to the water in a mixer at the rate of 100 mg / l. A solution of FeSO _{4 is} metered into the dispersion in solution in an amount of 351.6 mg / L. As a result of the reactions, 163.88 mg / L Na ₂ SO ₄ , 186.26 mg / L ZnSO ₄ and 248.95 mg / L CG particles sorbed per 100 mg of CV are formed to form 348.46 mg / L KM. KM can be processed as described in examples 1 and / or 2. Purified water can be used to obtain a composite sorbent in the form of CV with zinc hydroxide particles sorbed on them. This sorbent can be used in the preparation of gold by the cyanide method. In this method, after the separation of gold in the wastewater, Na ₂ [Zn (CN) ₄ ] is contained in dissolved form.

Claims (2)

1. The method of purification of wastewater from cyanide ions, including its treatment with ferrous sulfate to form a reaction product in the form of insoluble particles of iron cyanide, removing the product from water, characterized in that the water is treated in the presence of sorbent in the form of fibrillated cellulose fibers in water containing in wt.% not less than 54% of fibers with a length of not more than 0.63 mm and not less than 94% of fibers with a length of not more than 1.23 mm, iron sulfate is consumed in an amount of 293 parts by weight per 100 parts by weight CN-ions, the reaction product is obtained in the form of a composite material consisting of cellulose fibers with particles of iron cyanide adsorbed on them, while the treatment product is removed from water using pressure flotation. 2. The method according to claim 1, characterized in that the cellulose fibers are fed into the water in an amount of 50-150 mg per 1 liter.