RU2747686C1 - Method for water purification from complex compounds of heavy metals - Google Patents

Abstract

FIELD: water treatment.

SUBSTANCE: invention discloses a method for water purification from complex compounds of heavy metals, including the conversion of complex compounds of metals into a cationic form, the formation and removal of insoluble hydroxides and subsequent deep purification. The method is characterized by the fact that the transfer of complex compounds of metals is carried out by lowering the pH level to values not higher than 3.5 by adding acid. Then iron salts are introduced, which play the role of a coagulant and an electron donor, in the amount required to destroy the complex and create coagulating flocs, then the pH is increased to values determined depending on the metals present in the source water, and the resulting suspensions are removed by precipitation or by filtration, after which the clarified water is passed through a layer of granular catalyst, which increases the alkalinity of the passed water, ensuring the simultaneous passage in the intergranular space of the processes of formation of insoluble hydroxides and their precipitation on catalyst grains having negative ζ-potential of the surface, and the formed precipitate is removed by washing the granular catalyst with water to create a boiling bed in which the precipitate is separated from the catalyst surface as a result of friction between the grains.

EFFECT: invention is aimed at increasing efficiency of cleaning, as well as increasing process safety, reducing the cost of equipment and operation, providing possibility of organizing a closed cycle of water use.

1 cl, 6 tb,l 4 ex

Description

The invention relates to the field of purification of drinking, industrial, waste water from the contained cations and complex metal compounds. The invention can be used in various fields of industry, municipal water supply and water treatment for industrial wastewater treatment, surface water treatment used for drinking water supply to the population and for technological water supply of industrial facilities.

From the patent RU 2601333 C1 a method is known for neutralizing acidic technogenic solutions and / or with the precipitation of valuable components from them - heavy non-ferrous metals. The method includes the treatment of solutions and / or effluents with a complex precipitant reagent including calcium carbonate, iron, silicon and magnesium oxides in a mass ratio CaCO3: Ftotal: SiO2: MgO = 100: 0.7-9.5: 1.3-4.8 : 2.5-6.5, with active stirring to obtain a pH of 5.0-5.5 in the pulp, and subsequent exposure of the pulp with active stirring for 0.5-2 hours, filtration and washing of the precipitate. The resulting precipitate is calcined at a temperature of 720-770 ° C for 1-2 hours. As a precipitating reagent, slimes of chemical water treatment of thermal power plants are used, including calcium carbonate, iron, silicon and magnesium oxides, when their composition is brought to the specified ratio. The method provides an increase in the productivity and efficiency of processing industrial solutions and / or effluents containing heavy non-ferrous metals and iron, as well as obtaining a complex sludge from them, suitable for the extraction of metals, and involving the obtained concentrates in recycling, which makes it possible to eliminate the discharge of toxic waste into the environment ...

The closest analogue is the water purification method disclosed in the application CN109607856A. The method includes the following stages: Stage 1, Adding sulfuric acid to the complex waste water, adjusting the pH to 2.5-3.5, adding ferrous sulfate and carrying out a complex degradation reaction; Step 2, Add NaOH, adjust pH to 9.5-10.5 to remove copper ions, then add coagulant, perform stirring, perform primary filtration or sedimentation to obtain intermediate wastewater 1 and perform collection of concentration on the sludge .; Step 3: Adding NaOH to intermediate wastewater 1, adjusting the pH to 9.5-10.5 and adding sodium sulfide for the secondary copper removal reaction; Step 4: Adding ferrous sulfate to remove excess sulfur ions; and Step 5: adding coagulant, performing agitation, performing secondary filtration or sedimentation to obtain intermediate wastewater 2, and performing collection of concentration on the sludge. According to the method disclosed in the invention, the copper removal reactions by the sodium hydroxide method and the sodium sulfide method are adopted for wastewater treatment, so that the concentration of copper ions in the preformed sedimentary water is reduced, poisoning by metal ions of bacteria and fungi in subsequent processes is eliminated, and material costs are reduced; and the method has the outstanding characteristics of good environmental performance and low production costs.

However, these known methods of water purification have a number of disadvantages:

- not great depth of cleaning up to tenths - hundredths of mg / l;

- hard-to-remove fine suspended solids such as metal sulfides are formed, which reduces the cleaning efficiency and increases equipment and operating costs;

- low safety of the water purification process, since hydrogen sulfide is formed in the process.

The object of the present invention is to eliminate the above disadvantages in wastewater treatment.

The technical result of the claimed method consists in purifying wastewater from cations and complex compounds of any heavy metals from solutions with a purification depth of up to thousandths - ten thousandths of mg / l, increasing the safety of the process, since no hydrogen sulfide is formed, increasing the purification efficiency and reducing the cost of equipment and operation , due to the fact that stubborn fine suspensions, such as metal sulfides, are not formed, the removal of associated contaminants from the effluent, the possibility of organizing a closed cycle of water use, the possibility of abandoning clarifying granular filters used only for removing suspended solids; excluding the breakthrough of hydroxides from the sump, in preventing the formation of colonies of microorganisms and various deposits on the granular catalyst. In addition, the water obtained after purification by this method has a high environmental efficiency, since the degree of water purification exceeds the MPC requirements for a fishery reservoir.

The specified technical result is realized through the following techniques. Conversion of complex metal compounds into cationic form is carried out. For this purpose, the destruction of complex metal compounds is carried out by lowering the pH level to values not higher than 3.5 by adding acid. In this case, any known acid that is available is suitable: sulfuric, hydrochloric, nitric, acetic. Then, iron salts are introduced, which can act as a coagulant and an electron donor, in the amount necessary to destroy the complex and create coagulating flocs. The specified required amount is determined either empirically during commissioning, or is calculated depending on the type of metals, their concentration, the concentration of other pollutants, and the pH level. Then the pH is increased to values determined depending on the metals present in the source water, and the resulting suspensions are removed by precipitation or filtration. Then the clarified water is passed through a bed of granular catalyst, which increases the alkalinity of the passed water, ensuring the simultaneous passage in the intergranular space of the processes of formation of insoluble hydroxides and their precipitation on catalyst grains having a negative ζ- potential of the surface. The resulting precipitate is removed by washing the granular catalyst with water to create a fluidized bed in which the precipitate is separated from the catalyst surface as a result of friction between the grains. At the same time, to purify water from metal cations, water is passed at a speed of no more than 8 m / h through a layer with a thickness of at least 0.8 m of a granular catalyst with grains of 0.5 ÷ 5 mm, which increases the alkalinity of the passed water, ensuring the simultaneous passage of processes in the intergranular space the formation of insoluble hydroxides and their deposition on catalyst grains having a negative ζ surface potential, and the formed precipitate is removed by washing the granular catalyst with water to create a fluidized bed in which the precipitate is separated from the catalyst surface as a result of friction between the grains.

The method is carried out as follows.

Reagent cleaning and catalytic deposition cleaning are based on the same processes. The principle of removing metals from a solution consists in converting metal cations into insoluble hydroxides, which allows them to be removed from the treated water by precipitation or mechanical filtration. The difference is that during reagent treatment, hydroxide is formed in a reactor or flocculation chamber and is deposited in a settling tank (the dimensions of these structures are measured in meters), and during catalytic deposition, the same hydroxide is formed in the intergranular space of the catalyst and is deposited on the catalyst grains, reliably retaining on them. The dimensions of such "reactors" and "settling tanks" are fractions of a millimeter, which significantly speeds up the cleaning process and increases its efficiency.

The removal of precipitated hydroxides occurs during the catalyst washing process with water supplied in such an amount to create a fluidized bed, i. E. the catalyst grains should be rubbed against the surfaces to separate the precipitated hydroxides.

The catalyst grains have a large surface area, the total area of their pores sometimes reaches 600 m ² per 1 g.

Since water is a weak electrolyte, it dissociates slightly into ions:

 H⁺ + OH^-.H ₂ O

H ⁺ + OH ^- .

In pure water, the concentrations of hydrogen ions and hydroxide ions are equal:

[H ⁺ ] = [OH ^- ].

The surface of the catalyst grains has a negative ζ potential. When the treated water passes through a layer of catalyst grains, some of the hydrogen ions are retained on their surface, which provokes an increase in the dissociation of water and increases its alkalinity (excess of hydroxide ions).

The liberated hydroxide ions react with heavy metal cations in water and form insoluble hydroxides, which are deposited on the catalyst grains, creating active deposition sites and increasing the purification efficiency.

Catalytic deposition differs from reagent purification in that the formation of insoluble compounds as a result of a chemical reaction occurs directly in the catalyst bed, while the zone of their deposition is minimal, which reduces the deposition time. There is a combination of the processes of chemical reaction and deposition of the formed suspensions in a limited (intergranular) space.

To create the optimal size of the intergranular space, the catalyst grains should be 0.5 ÷ 5 mm in size.

In order for the process of hydroxide formation to be completely completed, the layer of granular catalyst must be at least 0.8 m, otherwise there may be a "breakthrough" of metal cations, which will negatively affect the quality of cleaning.

To prevent the precipitated hydroxides from being "washed away" from the surface of the catalyst grains during processing, the rate of water passing through the catalyst should not exceed 8 m / h.

When using the proposed method, the following positive effects are achieved:

1. conditions are created for the reaction of the formation of metal hydroxides by means of a "soft" change in pH throughout the entire zone of the granular catalyst, which ensures the creation of intervals of pH values of the formation of hydroxides for all heavy metals and the timely removal of the formed hydroxides due to the reduction of the precipitation zone;

2. the zone of precipitation of the formed hydroxide, in comparison with the precipitation in the sump, is minimal, which shortens the precipitation time and increases the efficiency of the hydroxide retention. In addition, due to the presence of a negative ζ- potential on the surface of the catalyst grains, the deposition rate of positively charged particles of metal hydroxides increases and the cleaning efficiency increases;

3. The volume of the sediment accumulation zone is distributed over the entire volume of the granular catalyst, increasing the cleaning efficiency;

4. conditions are created for the creation of centers for the precipitation of insoluble substances (phosphates, fine suspensions), which contributes to their more complete removal from the water. The deposition of phosphates and fine suspensions is observed on the surface of metal hydrates (positively charged colloidal particles). As a result, it is not required to use various coagulants and flocculants;

5. due to the observance of the required water flow rate, conditions are created for the retention of suspensions on the catalyst grains;

6. Removal of sediment (catalyst regeneration) is carried out by washing with purified water;

7. as an additional effect: ammonium ion is converted into ammonia with the possibility of subsequent stripping, which allows to reduce its concentration in the treated water;

8. Purified water has a neutral or slightly alkaline reaction, which eliminates the need for chemically resistant equipment.

In this case, the catalyst should have the following properties

- have the properties of both a catalyst and a sorbent.

- have positive adsorption (i.e., the interaction energy of suspended particles with the surface of the adsorbent is higher than the energy of interaction with water molecules) in order to retain the formed metal hydroxides on the catalyst grains.

- have a negative ζ- potential of the surface, ensuring the retention of cations and other positively charged particles in an aqueous solution at a filtration rate of at least 5 m / h.

- have an optimal value of the ζ- potential of 14 ÷ 30 mV.

- to have a granular structure, while the grain size is 0.5 ÷ 5 mm, which provides the optimal size of the intergranular space required for chemical reactions, coagulation and sedimentation processes.

- have mechanical strength that allows grains not to collapse when rubbing against each other in a fluidized - fluidized bed.

- have chemical resistance to an environment with a pH of 6 and higher (almost all heavy metals contained in industrial wastewater precipitate at pH values of 6 and higher).

- have a working temperature of 10 ° C and above.

- in this case, the minimum contact time of the purified water with the catalyst is 10 minutes.

- the thickness of the granular catalyst layer must ensure that the purified water remains in the catalyst layer for at least 10 minutes (for example, at a filtration rate of 5 m / h, the catalyst layer thickness is at least 0.8 m, at 8 m / h - at least 1.3 m)

- the sediment on the catalyst granules must be separated during washing.

- the cost of the catalyst should not be much higher than the cost of sorbents used in water purification - activated carbon, HES sorbent, zeolites.

When using the proposed method at the existing treatment facilities does not require an increase in staff;

The granular catalyst provides the required cleaning quality for many years without replacing it;

Regeneration of the catalyst is carried out in the operating mode, without reloading;

When the technologies used in production change, the treatment facilities do not require reconstruction, since the salts of heavy metals are removed "in a complex", i.e. a change in the composition of wastewater does not affect the efficiency of the treatment plant;

The granular catalyst has a low hydraulic resistance, therefore, high pressures in the system are not required;

The amount of reagents used at the neutralization station is reduced;

Fluctuations in the concentration of one or more pollutants in water do not affect the cleaning process.

The cost of treatment facilities is much less than foreign analogues;

The costs of the customer will be only with the introduction of our technology, during operation the costs are minimal (there are practically no consumables);

Wastewater treatment projects are implemented without significant capital costs (much lower than similar, but less efficient);

Payments for the discharge of pollutants are significantly reduced;

It cleans water well from dissolved metals without the use of expensive ion-exchange resins.

Until recently, a significant drawback was the impossibility of purifying water containing dissolved metal complex compounds, but the developed method for water purification from heavy metal complex compounds solved this problem.

The present invention is aimed at increasing the efficiency of water purification from dissolved metals, reducing financial costs, increasing the stability of the purification process.

The method of water purification from dissolved metals was carried out according to the following examples.

Example 1. Tests of the water purification method were carried out with industrial waste water containing metal cations as follows.

The treated water was passed through a column 32 mm in diameter of a granular catalyst with a grain size of 0.5–5 mm, the height of the catalyst in the column —1500 mm. The rate of passage of water through the catalyst is 5 m / h.

Table 1.

Ingredient name Initial acidic effluent
mg / l Purified effluent
mg / l pH 6.78 8.83 Iron total 4.7 but Copper 0.88 0.0085 Zinc 40 but Nickel 3.89 0.0011 Manganese 0.16 but

The results obtained show the suitability of the proposed technology using a granular catalyst for the purification of acid-base waste containing metal cations.

Example 2. Tests of the method were carried out with industrial waters containing hexavalent chromium. A 4% hyposulfite solution was preliminarily added to the original chromium-containing wastewater.

After a 10-minute exposure, the treated water was passed through a column 32 mm in diameter of a granular catalyst with a grain size of 0.5-5 mm, the height of the catalyst in the column was 1500 mm. The rate of passage of water through the catalyst is 5 m / h.

Table 2 .

Ingredient name Original chrome runoff
mg / l Purified effluent
mg / l pH 7.53 8.89 Iron total 0.78 but Copper 0.096 0.0019 Zinc 0.084 but Nickel 2.34 0.0023 Chromium hexavalent 7.0 but Chromium trivalent 1.7 0.014 Manganese 0.1 but

The experimental results show the suitability of the proposed technology for purification of chromium-containing waste from heavy metal salts.

Example 3. Tests of the water purification method were carried out with industrial wastewater containing zinc complex compounds. The experiment was carried out as follows. The initial effluent was treated with sulfuric acid to lower the pH to 1.5. Then, a solution of ferrous sulfate was added to the treated water, after which a solution of sodium hydroxide was added to increase the pH. The formed flakes were retained on a filter cloth with a cleaning depth of 1 μm. The degree of purification of waste water from zinc ions was 94.14%.

The table shows the results of water purification carried out according to the given example:

Table 3.

Ingredient name Concentration before purification, mg / l Concentration after purification, mg / l pH 7.43 8.0 Zinc 15.7 0.92

At the next stage, the treated water was passed through a column with a diameter of 32 mm of a granular catalyst with a grain size of 0.5-5 mm, the height of the catalyst in the column was 1500 mm. The rate of passage of water through the catalyst is 5 m / h.

Table 4.

Ingredient name Concentration before purification, mg / l Concentration in after purification, mg / l pH 8.0 8.5 Zinc 0.92 0.0095

The experimental results show the suitability of the proposed wastewater treatment technology from zinc complex compounds.

Example 4. Tests of the water purification method were carried out with industrial wastewater containing complex compounds of iron, zinc, copper, chromium. The experiment was carried out as follows. The initial effluent was treated with sulfuric acid to lower the pH to 2.0. Then, a solution of ferrous sulfate was added to the treated water, after which a solution of sodium hydroxide was added to increase the pH. The formed flakes were retained on a filter cloth with a cleaning depth of 1 μm. Wastewater treatment degree:

• from iron ions - 97.64%;

• from zinc ions - 98.85%;

• from copper ions - 99.75%;

• chromium - 99.94%

The table shows the results of water purification carried out according to the given example:

Table 5.

Ingredient name Concentration before purification, mg / l Concentration after purification, mg / l pH 7.0 7.5 Iron 2.5 0.059 Zinc 0.96 0.011 Copper 4.0 0.01 Chromium common 3.27 0.002

Wastewater after the destruction of the complexes is directed through a column with a diameter of 32 mm of a granular catalyst with a grain size of 0.5-5 mm, the height of the catalyst in the column is 1500 mm. The rate of passage of water through the catalyst is 5 m / h.

Table 6.

Ingredient name Concentration before purification, mg / l Concentration after purification, mg / l pH 7.5 8.7 Iron 0.059 0.002 Zinc 0.011 0.003 Copper 0.01 0.0008 Chromium common 0.002 0.002

From the analysis of the data in the table, it follows that the use of a method for water purification from complex metal compounds, which consists in a preliminary decrease in pH, treatment with a coagulant followed by an increase in pH makes it possible to effectively remove complex metal compounds from the treated water and convert dissolved metals into a cationic form. The subsequent passage of the treated water through the bed of granular catalyst provides deep water purification.

Claims (2)

1. A method of water purification from complex compounds of heavy metals, including the conversion of complex compounds of metals into a cationic form, the formation and removal of insoluble hydroxides and subsequent deep purification, characterized in that the transfer of complex metal compounds is carried out by lowering the pH level to values not higher than 3.5 by adding acid, then iron salts are introduced, which play the role of a coagulant and an electron donor, in the amount necessary to destroy the complex and create coagulating flocs, then increase the pH to values determined depending on the metals present in the source water, and remove the resulting suspensions by precipitation or by filtration, after which the clarified water is passed through a layer of granular catalyst, which increases the alkalinity of the passed water, ensuring the simultaneous passage in the intergranular space of the processes of formation of insoluble hydroxides and their precipitation on catalyst grains having a negative ζ potential surface, and the resulting precipitate is removed by washing the granular catalyst with water to create a fluidized bed in which the precipitate is separated from the catalyst surface as a result of friction between the grains. 2. A method according to claim 1, characterized in that water is passed through the catalyst bed at a speed of no more than 8 m / h through a bed with a thickness of at least 0.8 m of a granular catalyst with grains of 0.5 ÷ 5 mm in size.