RU2840430C1 - Method of purifying industrial waste water from thiourea impurities - Google Patents

Abstract

FIELD: water treatment.

SUBSTANCE: invention relates to treatment of waste water, describes a method of purification, providing for removal of impurities and reducing their concentration in waste water of industrial nature. Industrial waste water containing an admixture of thiourea in an amount of up to 20 mg/dm³ is subjected to purification when adding polyvinyl alcohol to the solution in a calculated amount of 6 weight fractions per 1 weight fraction of thiourea. Coagulation step is carried out with stirring for 2 hours. Formed composition is passed through a column filled with activated carbon of the “ВСК-400” brand, taken at ratio of 20 cm³ per 10 ml of the solution.

EFFECT: provides for waste water treatment to the level of residual content of thiourea of not more than 1.5×10^-3 mg/dm³.

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Description

Field of technology to which the invention relates

The invention relates to wastewater treatment and describes a treatment method that involves removing thiourea impurities and reducing the concentration of this substance in industrial wastewater.

State of the art.

Organic compounds containing nitrogen and sulfur fragments in their structure are contained in wastewater from industrial production; in particular, from enterprises using these compounds as detergents and compositions based on surfactants - derivatives of thiourea (Patent 2058317 RF). The resulting industrial wastewater exceeds the permissible hygienic standards for the content of hazardous chemical factors in environmental objects and cannot be discharged into water bodies without treatment.

The method of purifying wastewater from thiourea eluates (Patent 1028607 SU), including their treatment with an oxidizer, which is hypochlorite, provides a high level of purification. At the same time, this method requires the introduction of hypochlorite into the aqueous composition containing thiourea compounds - a highly aggressive compound, the use of which requires the observance of safety precautions and the use of special corrosion-resistant equipment.

The method for cleaning waste water from thiourea (Patent B 18619 KZ) involves adding 0.3 equivalent of sulfate ions to waste water formed during gold desorption with thiourea solutions; then, copper ions in the amount of 0.6-0.8 equivalents are introduced into the resulting solution and the resulting sediment is separated. The technology for removing thiourea impurities proposed in this method is complex and multi-stage, requiring the use of two chemical components with subsequent additional purification of the solution from sediment.

A method for purifying wastewater from thiourea is known (AC 1473273 USSR), which includes a two-stage treatment with copper compounds in the presence of a reducing agent, and then neutralization of the solution with sodium hydroxide to pH 8.5-12.0 with intermediate separation of the sediment. This method is characterized by the complexity of organizing the technological process, requires separate stages and the use of a significant number of different reagents, which complicates the process flow. In addition, the use of copper compounds for the neutralization of wastewater is undesirable due to their toxicity and the need for additional purification of wastewater from impurities of copper compounds.

The method for rendering harmless spent thiourea solutions (Patent 2038327 of the Russian Federation) from the process of regenerating ion-exchange resin and cyanide-containing tailing pulps of gold extraction plants includes treatment with a chlorine-containing oxidizer followed by holding the composition for 18 hours. This method is proposed to be used as a prototype. The following can be attributed to the disadvantages of the prototype: chlorine-containing oxidizers exhibit the properties of highly aggressive compounds and their use requires the use of special corrosion-resistant equipment; the technological process of rendering harmless takes a significant period of time, therefore it is unsuitable for cleaning large volumes of industrial wastewater, and additional purification of wastewater from hypochlorite impurities is also required.

Disclosure of the essence of the invention

The aim of the proposed invention is: to implement a method for purifying industrial wastewater from thiourea impurities using a coagulation process with subsequent purification of the resulting composition on activated carbon.

To achieve this goal, industrial wastewater containing thiourea is treated in solution with a coagulant - polyvinyl alcohol, followed by sorption on activated carbon.

Analytical control of the content of thiourea impurity in aqueous solutions was carried out using high-performance liquid chromatography.

The technical effect of the proposed invention is determined by the fact that polyvinyl alcohol was added to an aqueous solution of thiourea containing a concentration of 20 mg/dm ³ of this substance to carry out the stage of coagulation of the dissolved impurity. The module of the introduced coagulant should be at least 6/1 mass fractions in relation to the dissolved impurity of thiourea. For successful coagulation, it is necessary to initiate the process over a certain period of time using intensive mixing. Mixing is carried out by a mechanical overhead mixing device with a glass two-blade stirrer; rotation speed is 125 rpm at a constant temperature of 22±0.2°C.

After the coagulation process of the thiourea impurity is complete, the solution is passed through a column filled with activated carbon.

Activated carbon VSK-400 produced by JSC ENPO Neorganika is used, which has a total pore volume for water of at least 0.46 cm ³ /g and an effective micropore volume of at least 0.46 cm ³ /g. The size of granules of the commercial form of activated carbon is 6.5-8.5 mm. The volume of the required amount of activated carbon is calculated from the ratio: for cleaning 10 ml of a solution with an initial concentration of thiourea of 20 mg / dm ³ , 20 cm ³ of activated carbon are consumed.

Carrying out the declared wastewater treatment operations in accordance with the justified conditions allows achieving a degree of purification to a level of residual thiourea content of no more than 1.5×10 ^-3 mg/dm ³ . The achieved impurity content after water purification by the proposed method is significantly lower than the MAC level for thiourea in water for cultural and drinking use - 0.03 mg/dm ³ (GOST 6344-73. Thiourea).

Example 1. Wastewater - a solution containing thiourea at a concentration of 20 mg/ ^dm3 , was placed in a glass flask. 0.12 g (modulus - 6/1 mass fractions) of polyvinyl alcohol were added. The mixing device was turned on and mixed for 2 hours. Then stirring was stopped, the composition was kept for 20 minutes at room temperature and passed through a column filled with 2.0 ^dm3 of activated carbon VSK-400. The resulting purified water was analyzed by high-performance liquid chromatography: the residual content of thiourea is - 1.4×10 ^-3 mg/ ^dm3 .

Example 2. Under the conditions of Example 1, except: 0.1 g (modulus - 5/1 mass fractions) of polyvinyl alcohol was added to a thiourea solution with a concentration of 20 mg/dm ³ . After passing through a column with activated carbon, the residual content of thiourea is -1.7×10 ^-3 mg/dm ³ .

Example 3. Under the conditions of Example 1, except: the column was filled with activated carbon in an amount of 0.7 dm ³ . After passing the column with activated carbon, the residual content of thiourea is -2.4×10 ^-3 mg/dm ³ .

Claims (1)

A method for purifying industrial wastewater from thiourea impurities, characterized in that polyvinyl alcohol is added to a solution containing thiourea impurities in a calculated amount of 6 mass fractions per 1 mass fraction of thiourea and a coagulation stage is carried out with stirring for 2 hours, followed by passing the resulting composition through activated carbon VSK-400, taken in the ratio: 20 cm ³ per 10 ml of solution with an initial thiourea concentration of 20 mg/dm ³ .