Method of purifying waste water from hexalent chromium compounds

IPC classes for russian patent Method of purifying waste water from hexalent chromium compounds (RU 2550890):

C02F1/62 - TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE (processes for making harmful chemical substances harmless, or less harmful, by effecting a chemical change in the substances A62D0003000000; separation, settling tanks or filter devices B01D; special arrangements on waterborne vessels of installations for treating water, waste water or sewage, e.g. for producing fresh water, B63J; adding materials to water to prevent corrosion C23F; treating radioactively-contaminated liquids G21F0009040000)

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Water treatment process / 2244687

FIELD: chemistry.

SUBSTANCE: method of purifying waste water from hexavalent chromium compounds includes reaction thereof with an iron-containing dispersant with simultaneous exposure to a magnetic field generated by an electromagnet to obtain an insoluble precipitate. The iron-containing dispersant used is ground iron or steel chips. Exposure is carried out using a controlled magnetic field, the direction of the intensity vector of which is varied by periodically changing the polarity of current in the electromagnet windings, and the intensity value is controlled by varying the value of current in the windings. A chromium hydroxide Cr(OH)₃ precipitate is obtained by neutralising the unreacted mixture with an alkali.

EFFECT: high degree of purity of waste water while cutting the duration of the process, easy implementation and high efficiency of the method.

1 dwg, 2 ex

The invention relates to the purification of industrial effluents, in particular chromium-containing wastewater from toxic compounds hexavalent chromium and may find application in electroplating and other industries, having a chromium-containing effluents.

The known method of purification of chromium-containing wastewater (Pat. Of the Russian Federation No. 2025467, publ. 1994.12.30), including their transmission through a layer of iron-containing waste and the processing of the gas component, in which the effluent with a pH of 2.0 to 4.0 flow during aeration of the metal layer of air time consumption 192 DM³and a linear speed transmission hexavalent chromium 1920-3460 mg/h^-11 DM³metal waste. The disadvantage of this method is the need for high-performance pump units for transmission through a layer of metal waste and wastewater gas components with high linear velocity, which leads to significant energy costs and the high cost of cleaning. In addition, for the reactor operating at high pressure, required high-strength housing, which also leads to increased clean-up costs.

The known method of recovery of chromium (VI) in the wastewater (and.with. The USSR №1514815, publ. 1989.10.15), comprising mixing a chromium-containing solution with an acid solution in the layer of shavings from waste graffiti�created of cast iron with acid feed from the bottom up, the mixing chromadorida wastewater produced upflow of acid in the layer of shavings. As an acid solution can be used part of the original chromadorida water, acidified in the anode chamber of a diaphragm electrolyzer with an insoluble anode, while using acidified in the anode compartment of the cell chromium-containing waste water before serving it in a layer of shavings pass the hydrogen produced in the cathode chamber of the electrolytic cell. The disadvantages of the known method are not sufficiently high degree of purification of wastewater from compounds of hexavalent chromium, as well as significant energy consumption, multi-stage and duration of the cleaning process.

Known as described in the patent of Romania No. 127099, publ. 2012.02.28, the method of purification of wastewater containing hexavalent chromium in the amount of 1-100 mg/l, according to which for the recovery of hexavalent chromium to trivalent wastewater lead into interaction with iron shavings or sawdust) for 1-2 hours at a pH of 2-2. 5, and then placed in the container, add 30% NaOH to pH of 8.3 and leave for 5 hours. The achieved degree of purification allows effluent to drain into the sewer system. The disadvantage of this method is the lack of efficiency of the cleaning process, do not allow�traveler to process waste water containing chromium (VI) more than 100 mg/l, and its significant length.

The closest to the claimed is a method of sewage treatment from ions of hexavalent chromium (Pat. Of Ukraine No. 70644, publ. 2004.10.15), including their processing in acidified medium (pH of 1.65 to 2.0) in a flow system by deposition on particulate iron-containing working fluid, namely, a specially made iron needles, in a constant magnetic field 40-560 kA/m for 50-60 C, the speed of transmission of wastewater is calculated by a formula based on the parameters of the working chamber.

The known method does not provide a sufficiently high efficiency of wastewater treatment due to their interaction with the stationary displacement body, in most cases, not provide quick and at the same time full of chemical reactions. The bandwidth of wastewater is determined by the formula, not taking into account the concentration of ions of Cr⁶⁺fickle as any waste, excessive speed leads to a reduction in the recovery of Cr⁶⁺a deliberate decrease in the rate of bandwidth is wasted due to the duration of the cleaning process. The intensity of the known method is determined by the necessity of continuous operation of pumping units, and its hardware design OSL�ineeda the presence of control devices, maintains a given rate of transmission of wastewater, as well as equipment for loading and unloading of waste iron needles.

The closest to the claimed is a method of sewage treatment from ions of heavy metals (as.with. SU # 1761686, publ. 1992.09.15), including interaction containing hexavalent chromium compounds waste water with a mixture of suspensions of highly dispersed single crystals (0.05 to 0.1 μm) of iron dendritogenesis patterns with dispersed carbon powder in the presence of a magnetized spherical particles, preferably of sintered hexaferrite barium, fluid environment while exposed to an alternating magnetic field with precipitation of trivalent chromium compounds.

The known method requires the prior production of highly dispersed iron by electrolytic recovery hydrochloric or sulfuric acid solutions after etching become carried out to improve the dispersity of iron in a two-phase medium comprising a layer of organic matter or by plasma-physical dispersion, which complicates the method and increases the power consumption, the same method is not feasible without the use of additional reagents (magnetized spherical particles of hexaferrite barium, coal powder), which also increases the costs of holding the eyes�TCI wastewater. In addition, the movement of magnetized particles hexaferrite barium in a magnetic field with a constant value of tension does not provide sufficient intensification reaction between compounds of hexavalent chromium with iron-containing reagent.

The object of the invention is to provide an effective and economical method for purification of chromium-containing waste water from hexavalent chromium compounds.

The technical result of the invention is to reduce the duration of the process by increasing the speed and completeness of the reaction and increase the efficiency of the method due to its simplification, reduce labor costs, energy consumption and chemical usage.

Said technical result is achieved by a method of purification of wastewater from compounds of hexavalent chromium, including their interaction with containing dispersed iron reagent under the simultaneous effect generated by the electromagnet of the magnetic field to give an insoluble precipitate, which, in contrast to the known, as containing dispersed iron reagent crushed iron or steel shavings, the exposure is performed controlled magnetic field, the direction of the intensity vector which is changed by periodically changing the polarity of the current in the windings of the electromagnet, and the value at�ragnotti control, changing the strength of the current in its windings, wherein the precipitate of chromium hydroxide Cr(OH)₃get, neutralizing the reacted mixture with an alkali.

The method is carried out using the reactor, schematically shown in the drawing and comprising a plastic housing 1 in the form of a cylinder placed horizontally, with the end faces is provided with feed and discharge branch pipes in the upper part of one end it is provided with a pipe 2 for feeding the waste water and the pipe 3 for the supply of chemicals and in the bottom of the other end of the pipe 4 for discharging purified water and withdrawing a liquid slurry of the obtained hydroxides. In addition, two opposite end sides of the housing 1 is made bootable 5 and outlet 6 of the window to disperse the iron-containing working fluid (iron shavings). To create a managed AC magnetic field are provided with the control electronic circuit (not shown) of the coils (inductors) 7 placed in a certain order at a calculated distance from each other on the outer surface of the reactor 1.

The method is as follows.

Acidic wastewater containing hexavalent chromium ions, for example, spent electrolyte of chromium plating, pour in a plastic reactor 1 pre-loaded iron crushed Strug�Oh and actuate the coils (inductors) 7, creates a magnetic field that can move the iron working the body in the direction of the axis of the electromagnet, made in the form of a solenoid (coil winding).

During the flow of electric current in the coil of the solenoid occurs electromagnetic field, which interacts with iron working body in the notorious "rule of thumb", pulling or pushing it in the direction of the axis of the solenoid depending on the direction of the current in the coil. By periodically reversing the polarity of the current in the coils placed outside of the reactor 1 of the electromagnets 7 to displace iron working body forward and backward in a direction parallel to the axes of the solenoids, the intensity of interaction of the working body with the magnetic field, depending on the tension of the latter, adjust by changing the current in the windings.

Thus, with the help of a controllable variable magnetic fields offer intensive mechanical mixing and distribution throughout the volume of the reactor, the fine crushed iron shavings and establish an effective working body in the form of "clouds" moving weighted dispersed particles, which in addition, is heated due to the induction current induced by the inductor 7. Forming the working fluid of the dispersed iron particles, due to their small size, nagrevayushchiye, however, the observed increasing the temperature of the reaction mixture is sufficient to accelerate a chemical reaction.

A significant increase of effective area of interaction of the wastewater is dispersed with the working fluid and the temperature rise of the reaction mixture provides increased speed and completeness of a chemical reaction between hexavalent chromium compounds and iron compounds to form salts of trivalent chromium. After neutralizing the reacted contents of the reactor with an alkali solution, a precipitate of chromium hydroxide Cr(OH)₃in the form of a slurry of the chromium hydroxide and purified water.

At the end of the cleaning process, the time of occurrence of which depends on the volume and concentration of the wastewater to be treated, using a magnetic field of the electromagnets of the output inductors used working fluid (crushed iron shavings) from the reactor via a discharge window 6.

In the proposed method, as the reactor can be used inexpensive cylindrical plastic containers (large diameter pipe), as a working body - waste mechanical treatment of iron and steel, besides, he does not require receipt and use of additional reagents, which is of considerable importance for the practical implementation of the method.

Examples of specific implementation method

p> Example 1

The waste water of electroplating in the amount of 5 liters of solution containing ions of Cr(VI) concentration of 100 mg/l at a pH of 1.5, treated for 5 min in the reactor with the finest steel shavings grade St3 managed in an alternating magnetic field using electromagnets 6. Add the NaOH solution to pH 7.

The content of ions in the treated water Cr(VI) is 0.015 mg/L. the resulting precipitate contains about 50% of the chromium hydroxide, the rest is mainly ferric hydroxide.

Example 2

A solution of acidic waste water (5 l) containing ions of Cr(VI) concentration 50 mg/l at pH 2, was treated according to example 1 for 3.5 min using crushed iron shavings, then neutralize with a solution of Ca(OH)₂(to pH 7).

The content of ions in the treated water Cr(VI) is 0,010 mg/l. the resulting precipitate contains about 35% chromium hydroxide.

Method of sewage purification from compounds of hexavalent chromium, including their interaction with containing dispersed iron reagent under the simultaneous effect generated by the electromagnet of the magnetic field to give an insoluble precipitate, characterized in that the containing dispersed iron reagent crushed iron or steel shavings, the exposure is performed controlled magnetic field, the direction�of their intensity vector which is changed by periodically changing the polarity of the current in the windings of the electromagnet, but the strength of the control, changing the strength of the current in its windings, wherein the precipitate of chromium hydroxide Cr(OH)₃get, neutralizing the reacted mixture with an alkali.