RU2458010C2 - Method of purifying water from chromium compounds - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention can be used during treatment of industrial sewage containing chromium (VI) in form of chromate and dichromate ions, in metallurgical, machine- and motor-car construction industry, leather industry, as well as in textile industry, at organic synthesis companies, in pigment production, pharmaceutical, match and paint industries. To realise the method, water is purified from chromium compounds by reducing chromium (VI) and sorption of chromium (III) cations with a sorbent matrix. Hair and sulphonated coal are successively used as the sorbent. Regeneration of chromium in form of chromium (III) oxide is carried out by burning and pyrolysis of spent sorbents.

EFFECT: use of the present invention enables to simplify and improve the process of purifying chromium-containing sewage, and also widen the range of sorption materials which ensure full quantitative removal of chromium (VI) and chromium (III) from water; wherein there is no formation of wastes and sludge, and chromium is regenerated in form of chromium (III) oxide.

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Description

The invention relates to a method for treating waters contaminated with compounds of chromium (VI) and chromium (III), and can be used in the treatment of industrial wastewater. Sources of chromium (VI) entering the hydrosphere are the metallurgical, machine and automotive industries, leather production, as well as the textile industry, organic synthesis enterprises, pigment production, pharmaceutical, match, paint and varnish industries. The chromium (VI) content in the effluents of such plants varies from 0.005-0.2 g / l (in wash water) to 5-200 g / l (spent electrolytes) [1,2].

и

(в кислой и щелочной средах соответственно), а хрома (III) - в виде катиона Cr³⁺, поэтому способы и методы очистки воды от упомянутых соединений отличаются друг от друга по способу и по принципу.Compounds of chromium (VI) in water are part of anions

and

(in acidic and alkaline media, respectively), and chromium (III) - in the form of a Cr ³⁺ cation, therefore, the methods and methods for purifying water from these compounds differ from each other in the method and principle.

A known method of adsorption of chromium (VI) by reduction on activated carbon [3]. To implement this process, it is necessary to constantly monitor and adjust the pH of the aqueous solution. During the day of contact, 2 grams of coal in 200 ml of solution (initial concentration of CrO ₃ 100 mg / l) at pH 4, the sorption volumetric capacity (СОЕ) of coal reaches 8.25 mg / g, which is 82.5% of the initial amount of chromium oxide ( Vi). The residual concentration of chromium (VI) in the solution is 9 mg / l, which is 900 MAC. The maximum permissible concentration of chromium in the water of water bodies of domestic water use is 0.5 mg / l for chromium (III) and 0.05 mg / l for chromium (VI). For reservoirs of fishery water use - 0.005 and 0.001 mg / dm ^3, respectively.

A known method [4] of removing chromium (VI) from an acidic aqueous solution, including processing the solution to the optimum pH value, contacting the solution and the adsorbent. Alfalfa and / or clover seeds are used as adsorbent and / or reducing agent. Reduced chromium (III) is removed from the solution by sorption on cation exchangers or precipitation of hydroxide by neutralization of the solution with alkaline reagents.

The disadvantages of the above analogue methods are: low efficiency and high cost due to the high price of the used sorbent reducing agents (activated carbon, alfalfa or clover seeds). In addition, the methods do not indicate the ways of utilization and / or neutralization of spent sorbents, which in the environment can be sources of highly toxic chromium compounds.

Closest to the present is a method [5] for removing chromium from acidic aqueous solutions using bean seeds as a reducing sorbent. It was shown [5] that the bean skin absorbs (restores) mainly chromium (VI), and its cotyledons - chrome (III). That is, in different parts of the seeds are different forms of chromium. This does not allow the regeneration of chromium (III) from beans even with complete destruction of the seeds. The result is a mixture of chromium (III) and chromium (VI) compounds.

The disadvantages of the prototype are:

- the use of expensive food material as a sorbent.

- incomplete recovery of chromium (VI), as a result of which the used bean seeds become highly toxic and unclaimed waste. This creates additional technical and environmental problems;

The objective of the invention is the creation of an improved method for purifying water from chromium compounds using affordable and inexpensive sorbents that ensure complete quantitative removal of chromium (VI) and chromium (III) from water.

EFFECT: high-quality water purification with sequential use of sorbent reducing agents (hair and sulfonated coal, respectively). Chromium regeneration is carried out by burning spent sorbents.

This is achieved by the fact that in the method the purification of water in an acidic environment from chromium compounds is carried out by sorbents that reduce chromium (VI) and sorb chromium (III) cations by a sorbent matrix. Hair and sulfonated coal are successively used as sorbents, and chromium regeneration in the form of chromium oxide (III) is carried out by burning or pyrolysis of spent sorbents.

Examples 1-7. Seven samples of the initial CrO ₃ solution with a volume of 0.1 liter and a concentration of 41 mg / l per chromium at pH 2 were kept in contact with 2.5 g sorbents for 24 hours. The experimental results are presented in Table 1.

As can be seen from table 1 (paragraph 2), hair should be recognized as the best sorbent.

Example 8. The initial purification of water from chromium was carried out using hair as a sorbent, pH _about 2.5, V (solution) = 0.5 l, m (hair) = 12.5 g, C (chromium) = 100 mg / l

As can be seen from example 8, purified water satisfies hygienic requirements for chromium (VI) and chromium (III).

Disposal of spent sorbents containing chromium (III) and chromium (VI) was carried out by burning or pyrolysis. The residue after calcination is chromium (III) oxide. No chromium (VI) was found in the residue.

Thus, the advantage of the proposed method in comparison with the prototype is that the method allows you to purify the water to achieve the required sanitary standards and MPC, using affordable and inexpensive sorbents. Disposal of spent sorbents is carried out by burning or pyrolysis, which allows the regeneration of chromium in the form of its oxide (III).

Literature

1. Smirnov D.N., Genkin V.E. Wastewater treatment in metal processing. - M .: Metallurgy, 1980.195 s.

2. Cao Zhong Hua. Wastewater treatment of tanneries from chromium compounds. // Ecology and industry of Russia, March 1999. 14-15 p.

3. The method of adsorption of chromium (VI) on activated carbon. RU 2091318. Published on 09/27/1997.

4. A method for removing chromium (VI) from an aqueous solution. RU No. 2110481. Published on May 10, 1998.

5. A method for removing chromium (VI) from an aqueous solution. RU No. 2129096. Published on April 20, 1999.

Claims (1)

The method of purification of water from chromium compounds in an acidic environment by sorbents, reduction of chromium (VI) and sorption of chromium (III) cations by a sorbent matrix, characterized in that hair and sulfonated carbon are used successively as sorbents, and chromium is regenerated in the form of chromium (III) oxide burning or pyrolysis of spent sorbents.