RU2658032C1 - Method of purification of industrial sewage water from chromium compounds - Google Patents

Abstract

FIELD: water and air purification technology.

SUBSTANCE: invention can be used for the purification of waste water from the processes of deposition of galvanic coatings. To carry out the process, the wastewater containing the chromium(VI) compounds is treated with titanium compounds(II or III) in an amount of 100–200 % of the stoichiometric with vigorous stirring, followed by adjusting the pH of the medium to 8.5–9.0, precipitating the flakes of chromium(III) hydroxide and filtration.

EFFECT: invention provides purification of wastewater from chromium(VI) compounds with high speed and high efficiency in the absence of dependence of the reduction conditions of chromium(VI) from pH medium; in addition, the method is carried out according to a simple apparatus scheme, and also the method provides a reduction in the amount of sludge formed and a high rate of sludge filtration.

1 cl, 8 ex

Description

The invention relates to the field of treating industrial wastewater from heavy metals, in particular to a method for treating wastewater containing chromium (VI) compounds by reduction, which can be used to treat wastewater from electroplating processes.

Known methods for purifying chromium-containing wastewater by reducing chromium (VI) (Su 1813733 from 05/07/1993; Pat. RF No. 2025467, publ. 1994.12.30); US Pat. Romania No. 127099, publ. 2012.02.28; US Pat. Of Ukraine No. 70644, publ. 2004.10.15; RF patent No. 2550890) including their processing (transmission) through a layer of iron-containing material under external influence (electromagnetic or aeration treatment).

The disadvantages of these methods are the low efficiency of the cleaning process and the low reaction rate.

Known methods for wastewater treatment from chromium (VI) compounds by reduction (Pat. RF 2433961 from 11/20/2011; Pat. RF No. 2395463 from 08/13/2008), during which chromium recovery is carried out with organic compounds (hydrazine, formalin) followed by precipitation of hydroxides chromium (III).

The disadvantages of these methods include the use of toxic organic compounds and the low efficiency of the process.

A known method of purifying water from compounds of chromium (VI) (USSR AS No. 149354 from 01/01/1962) in the process of filtering chromium-containing effluent through a layer of anion exchange resin with its subsequent regeneration.

The main disadvantage of this method is the high cost of the cleaning process, as well as the low speed of the process and high material costs for equipment and reagents.

A known method of purification of galvanic runoff (Proskuryakov V.A., Schmidt L.I. Wastewater treatment in the chemical industry. L.: Chemistry, 1977. 464 p .; Vinogradov S.S. Environmentally safe galvanic production. M., 2002. - 352 s.) From chromium (VI) compounds by reduction of chromium (VI) compounds with bisulfite, sulfite or sodium pyrosulfite, followed by precipitation of chromium (III) hydroxides.

The disadvantages of this method include high reagent costs and low speed of the recovery process, as well as a high dependence of the efficiency of the process on the pH of the medium.

The closest analogue to the achieved result and technical essence (prototype) is a method for the reduction of chromium (VI) compounds to form (III) with iron (II) sulfate, followed by precipitation of hydroxides (US Pat. WO 2015076773 A1 of 05/28/2015).

The disadvantages of this method include high reagent costs (excess reducing agent), a complex hardware scheme.

The objective of the invention is to develop a method for removing chromium ions in (VI) with a high process speed, a simple hardware circuit, increased efficiency of water purification from chromium compounds and low reagent costs.

The problem is solved by the method of wastewater treatment from chromium (VI) compounds by reduction of titanium (II or III) compounds in an amount of 100-200% of stoichiometry, followed by stirring and adjusting the pH of the medium to 8.5-9.0, followed by precipitation of hydroxide flakes chromium (III) by sedimentation, filtration, coagulation or flocculation.

The essence of the proposed method and the achieved results can be clearly illustrated by the following examples

EXAMPLE No. 1

225 mg / l (100% of stoich.) Of titanium (III) chloride is introduced into the galvanic drain with the content of chromium (VI) ions 25 mg / L and pH 11.0 with vigorous stirring and stirred for 30 seconds. Then, within 10 minutes, with constant stirring with a solution of calcium hydroxide, the pH of the medium is raised to values of 9.0, followed by precipitation of the flakes of chromium (III) hydroxide with a flocculant (for example, Besfloc K051C). The total cleaning efficiency of chromium compounds (III) and (VI) is 99.5%.

EXAMPLE No. 2

225 mg / l (100% of stoich.) Of titanium (III) chloride is introduced into the galvanic drain with a content of chromium (VI) ions of 25 mg / L and a pH of 4.2 with intensive stirring and stirred for 1 minute. Then, within 10 minutes, with constant stirring with a solution of calcium hydroxide, the pH of the medium is raised to a value of 8.5, followed by precipitation of the flakes of chromium (III) hydroxide with a flocculant (for example, Polyacrylamide). The total cleaning efficiency of chromium compounds (III) and (VI) is 98.6%.

EXAMPLE No. 3

225 mg / l (100% of stoich.) Of titanium (III) chloride is introduced into the galvanic drain with the content of chromium (VI) ions 25 mg / L and pH 7.1 with vigorous stirring and stirred for 30 seconds. Then, within 10 minutes, with constant stirring with a solution of calcium hydroxide, the pH of the medium is raised to values of 8.6, followed by precipitation of the flakes of chromium (III) hydroxide with a flocculant (for example, active silicic acid). The total cleaning efficiency of chromium (III) and (VI) compounds is 99.4%.

EXAMPLE No. 4

450 mg / l (200% of stoich.) Of titanium (III) chloride is introduced into a galvanic drain with a content of chromium (VI) ions of 25 mg / l, heavy metals 200 mg / l and a pH of 4.3 with vigorous stirring and mixed in within 1 minute. Then, within 10 minutes, with constant stirring with a solution of sodium hydroxide, the pH of the medium is raised to values of 8.7, followed by spontaneous precipitation (sedimentation) of flakes of chromium hydroxide (III). The total cleaning efficiency of chromium (III) and (VI) compounds is 97.9%.

EXAMPLE No. 5

340 mg / l (150% of stoich.) Of titanium (III) sulfate is introduced into a galvanic drain with a content of chromium (VI) ions of 25 mg / l, heavy metals 95 mg / l and a pH of 5.2 with intensive stirring and mixed in within 1 minute. Then, within 10 minutes with constant stirring with a solution of sodium hydroxide, the pH of the medium is raised to values of 8.7, followed by spontaneous precipitation of flakes of chromium hydroxide (III). The total cleaning efficiency of chromium compounds (III) and (VI) is 98.6%.

EXAMPLE No. 6

112.5 mg / l (100% of stoich.) Of titanium (II) chloride is introduced into the galvanic drain with the content of chromium (VI) ions 25 mg / L and pH 3.1 with vigorous stirring and stirred for 1 minute. Then, over 10 minutes, with constant stirring with a solution of sodium hydroxide, the pH of the medium is raised to values of 9.0, followed by filtration of chromium (III) hydroxide. The total cleaning efficiency of chromium (III) and (VI) compounds is 98.3%.

EXAMPLE No. 7

112.5 mg / l (100% of stoich.) Of titanium (II) chloride is introduced into the galvanic drain with a chromium (VI) ion content of 25 mg / L and a pH of 3.0 with vigorous stirring and stirred for 1 minute. Then, within 10 minutes, with constant stirring with a solution of sodium hydroxide, the pH of the medium is raised to values of 8.7, followed by separation of the flakes of chromium hydroxide (III) by filtration. The total cleaning efficiency of chromium (III) and (VI) compounds is 99.1%. The filtration rate of 134 ml / min, the filtration rate of precipitates obtained with similar efficiency and the use of iron compounds, 102 ml / min.

EXAMPLE No. 8

112.5 mg / l (100% of stoich.) Of titanium (II) chloride is introduced into the galvanic drain with a chromium (VI) ion content of 25 mg / L and a pH of 3.0 with vigorous stirring and stirred for 1 minute. Then, over 10 minutes, with constant stirring with a solution of sodium hydroxide, the pH of the medium is raised to values of 8.7, followed by separation of the flakes of chromium hydroxide (III) by coagulation (for example, aluminum sulfate). The total cleaning efficiency of chromium (III) and (VI) compounds is 99.1%. The amount of precipitate formed is 4 vol.%, With a similar efficiency when using iron compounds - 13.4 vol.%.

The use of titanium compounds II and III as a reducing agent can significantly increase the overall removal efficiency of chromium ions and simplify the process hardware scheme by eliminating the aeration stage. The process takes place in one stage, and the consumption of the reducing agent does not depend on the pH of the water (reducing reagent costs). Also, a reduction in the amount of sludge (sludge) formed and a high rate of its filtration, which significantly increases the speed of the process.

Claims (1)

A method of purifying industrial and wastewater from chromium compounds, comprising treating wastewater containing chromium (VI) compounds with a reducing agent, followed by adjusting the pH of the medium and precipitating flakes, characterized in that 100 (100) titanium (II or III) compounds are used as reducing agent -200% of stoichiometry with stirring and adjusting the pH of the medium to 8.5-9.0, followed by precipitation of flakes of chromium hydroxide (III).