EA005782B1 - Method for removal of heavy metal ions from wastewater - Google Patents

Abstract

Embodiment of the invention relates to using prepared iron-containing suspension in which mass ratio (g/l) of components is: m (FeSO4x7H2O):m (NaOH):m(NaNO3) = 9.8:2.8:1, and optimum ratio their concentrations (mol/l) is m (FeSO4x7H2O):m (NaOH):m(NaNO3) = 9.8:2.8:1, having the pH=8-10, dosing of which to water to be purified is carried out taking into account mass ratio of the sum of heavy metal ions in them (mg/l) and dosed total iron (mg/l) correspondingly: Sigmam(Me<+N>):m(Fetotal)= 1:3, but not more than 1 g/l of iron (total) with mechanical agitation or air bubbling and reducing pH to 9-12.0 with sodium hydroxide solution (with mass wt 10-40%). Iron source for the process is technical ferric sulfate (II) of metallurgical industry wastes. Sodium nitrate promotes forming iron-containing suspension with high chemical activity for ferrite formation and increases its effectiveness to heavy metal ions adsorption.

Description

The invention relates to the protection of environmental water bodies from pollution with highly toxic heavy metal ions and is intended for use in the ferrous and nonferrous metallurgy enterprises, as well as in the engineering, electrical, metalworking industries and other industries that carry out waste water purification processes from heavy metal ions.

Known reagent methods mainly involve the precipitation of heavy metal ions in the form of hydroxides. The precipitation of metal hydroxides Me (OH) _n occurs in the pH range, the value of which is different for each metal.

In addition, a number of metals (A1, η, Sb. Pb, Cr) form amphoteric hydroxides, which makes it impossible to quantify them from solutions.

In addition, dilution of the treated solutions leads to the hydrolysis of compounds of these metals, which also prevents their deposition.

The resulting precipitates of metal hydroxides are large and difficult to dehydrate.

The closest in essence is the method of removing heavy metal ions from concentrated solutions and wastewater, including their treatment with excess ferrous iron salt, alkalinization to pH 9-10 units and the introduction of a catalyst for the process of ferritization of persulfates, or permanganates, or alkali metal perchlorides [1].

The known method requires heating the resulting suspension to 60-90 ° C, keeping at this temperature until complete completion of the ferritization process, after which the suspension is cooled and separated by filtration into liquid and solid phases.

The disadvantages of this method are

- process energy intensity;

- the duration of the cleaning process;

- the complexity and complexity of the process, which does not allow to apply it in a production environment.

The task of the proposed invention is to use the formed iron-containing suspension (SGS) with high chemical activity to ferrite formation and the ability to adsorb heavy metal ions, which will allow: cleaning wastewater without heating, increase the speed of the cleaning process, simplify the process and reduce its cost.

The task is solved by the fact that for purification of waste water from heavy metal ions a formed iron-containing suspension is used, in which the mass (g / l) ratio of the components is: w (Pe8O ₄ -7H ₂ O): w (NaOH): w (MaMO ₃ ) = 9.8: 2.8: 1, and the optimal ratio of concentrations (mol / l) of the components is C (Fe8O ₄ -7H ₂ O): C (IaOH): C (MaMO ₃ ) = 0.75: 1, 5: 0.25 and having a pH of 8-10 units.

The source of iron is technical ferrous sulphate (II), representing the waste of the metallurgical industry (Belarusian Metallurgical Plant, Zhlobin).

Sodium nitrate activates the process of ferritization and increases the efficiency of ferrites to adsorb heavy metal ions.

The mass ratio of the components and the choice of the optimal ratio of their concentrations are determined theoretically and experimentally, taking into account the stoichiometry of the reactions occurring during ferrite formation, which can be represented in general form [2, p. 167]:

6Re8O 12IaON ₄ + + O ₂ = 2Re ₃ O ₄ + 6H ₂ O + ₂ 6Ya 8o _4;

Me (OH) _n + pRe (OH) ₃ ^ Me (PeO ₂ ) _n + pN ₂ O, and also taking into account the solubility of iron (II) sulfate.

Sodium nitrate contributes to the oxidation of a certain amount of Fe ^{2+ ions} in Fe ³⁺ (1: 2), activating the ferritization process:

2Pe8O4 + IAIAh + H28O4 = Pe2 (8O4) g + Ia ^ + H2O.

Different variants of the composition to obtain a formed iron-containing suspension were determined and their physical properties were considered. The study was subjected to a suspension having a different quantitative composition of the components, presented in table. one.

The most acceptable options for suspension for its dosing into wastewater are № 6, 7 and 8, since have good fluidity, do not thicken and stratify over time.

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Table 1. The quantitative composition of the components and the physical properties of SGS

No. p / p C (Pe8O ₄ · 7H ₂ O); mol / l Mass ratio component. Physical properties (uniformity, fluidity, stability) 93 : 2.8 : one t (E8O ₄ · 7H ₂ O); g / l t (NO); g / l t (No. IO); g / l one 1.00 278.0 80.0 28.4 Heterogeneous, quickly hardens 2 0.95 264.1 76.0 27.0 3 0.90 250.2 72.0 25.6 - "- four 0.85 236.3 68 24.1 - "- five 0.80 222.4 64.0 22.7 Homogeneous, poor fluidity 6 0.75 208.5 60.0 213 Homogeneous, has good fluidity, does not stratify during long-term standing 7 0.70 194.6 56.0 193 - "- eight 0.65 180.7 52.0 183 -h <- 9 0.60 166.8 48.0 17.0 When standing for 24 hours stratified ten 0.55 152.9 44.0 15.6 - "- eleven 0.50 139.0 40.0 14.2 - "-

The preparation of the suspension (option No. 6) was carried out according to the following procedure. In a volumetric flask with a capacity of 1 l, 700 cm ^{3 of} tap water (1 = 18-20 ° C) were poured and 409 g of technical ferrous sulfate (II) with a mass fraction (Pe8O ₄ -7H ₂ O) equal to 51% was dissolved with constant stirring . Then, 60 g of technical sodium hydroxide was poured into the resulting solution with constant stirring. The result was a homogeneous, viscous suspension of dirty-green color, having an acid reaction medium (pH = 6.0). 21.3 g of sodium nitrate was added to the resulting suspension with constant stirring. After thorough mixing, the pH of the suspension was adjusted to 9 units with sodium hydroxide solution with ω = 40% and tap water was added to a volume of 1 l.

For the formation of high chemical activity to ferrite formation and the ability to adsorb heavy metal ions, the iron-containing suspension must be kept for at least 20 minutes before its introduction into the purified water [2, p. 168].

The formed iron-containing suspension is dosed into the purified water, taking into account the mass ratio of the sum of heavy metal ions in them (It (Me ^{+ p} ); mg / l) and the total iron w / w (Pe _total ); mg / l) respectively 1: 3.

The total mass of iron when dispensed to the water to be purified should not exceed 1 g / l. In this case, the ferromagnetic character of the formed precipitations is ensured [2, p. 168].

The amount of the formed iron-containing suspension should be increased if there are chromium (VI) ions in the wastewater - Cg ⁺⁶ , due to the fact that they need to be restored to Cr ⁺³ (16 mg Te8O ₄ 7H should be taken for 1 mg Cr ⁺⁶ ₂ O):

Cr ^{+ 6} + 3Re ²⁺ Cr ⁺³ + 3Re ³⁺ .

Volumes (V) of SGS doses (No. 6) for the purification of waste water having a different quantitative composition of heavy metal ions (ITM) are presented in Table. 2 and 3.

Table 2. Volumes of SGS dosed (No. 6), depending on the total mass of ITM in the treated water

ET (ITM) mg / l 5.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0 πι (Ε general); mg / l 15.0 30.0 45.0 60.0 75.0 90.0 105.0 120.0 Y (SGS number 6); cm ³ / l waste water 036 0.71 1.07 1.43 1.79 2.14 2.50 2.86

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Table 3. Volumes of SGS dispensed (No. 6), depending on the chromium (VI) content in the treated water

t (Cr ^{+ <>} ); mg / l P1 (Rvveb | c.), Mg / l V (SGS number 6); cm ³ / l waste water 1.0 3.2 0.08 1.5 4.8 0.11 2.0 6.4 0.15 2.5 8.0 0.19 3.0 9.6 0.23 3.5 11.2 0.27 4.0 12.8 0.30 4.5 14.4 0.34 5.0 16,0 0.38 5.5 17.6 0.42 6.0 19.2 0.46 6.5 20.8 0.50 7.0 22.4 0.53 7.5 24.0 0.57

The formed iron-containing suspension is dosed into the purified water with constant mechanical stirring or air sparging and a certain volume is added (depending on the initial pH of the purified water) sodium hydroxide solution (with a mass fraction of 10-40%) to pH 9-12.0.

The yield of the magnetic phase increases with increasing amount of alkaline reagent introduced. The appearance in the sediment of the magnetic phase occurs at pH = 10.5-12.0. Alkalinization of the treated solution is accompanied by a change in its color from dark green to black and the formation of flocculent structures, which, with further mixing, acquire a finely dispersed form. The moment of formation of a dispersed black suspension in the solution should be considered as the moment of completion of mixing [3, p.8].

The process of wastewater purification from heavy metal ions using the formed iron-containing suspension is carried out without heating.

The quickly formed precipitate of ferrites of heavy metals within 10-15 minutes is well compacted in the process of settling. The reason for the rapid settling is the dense nature of the particles formed, containing in their structure a small amount of intercrystallization water [3, p.8].

Ferrites well sorb ions of chromium, cadmium, lead, copper, nickel, cobalt, mercury, manganese and beryllium, they have a capacity for heavy metals 1000-10000 times greater than magnetite [2, p. 169].

Precipitation of ferrites of heavy metals, obtained by treatment of wastewater by the proposed method, can be subjected to environmentally safe long-term storage in the bowels of the earth, without resorting to the construction of bulky and expensive special polygons, since ferrites are resistant to the effects of an excess of dilute solutions of strong mineral acids and acidic natural waters, due to the special structure of their crystal lattice [1].

The degree of wastewater treatment by the proposed method was controlled by unified methods of analysis (Unified methods of water analysis. / Edited by Prof. Yu.Y. Lurie / .M .: Chemistry, 1973, p. 263, 270, 282, 304, 308) by the laboratory of chemical analysis of the environmental protection department accredited for testing in the Laboratory Accreditation System of the Republic of Belarus.

The averaged results of serial experiments on wastewater treatment of electroplating production (SHGP) (sample 1) using the formed iron-containing suspension of various quantitative composition (No. 6, 7, 8) are presented in Table. four.

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Table 4. The averaged results of serial experiments on the cleaning of SHGP (sample 1) using SGS of various quantitative composition (No. 6, 7, 8)

Characteristic of the VGP Concentrations of pollutants, mg / l Cr Re Νΐ Si Ζη MPC of pollutants in the PGV for their discharge into the sewer 0.50 2.00 1.00 1.00 2.00 Untreated SVGP (sample 1) 7.50 6.30 2.40 3.70 2.80 Sample 1, cleaned SGS number 6 0.03 0.10 0.07 0.02 0.40 The cleaning effect,% 99.6 98.4 97.1 99.5 85.7 Sample 1, cleaned SGS number 7 0.05 0.18 0.08 0.02 0.50 The cleaning effect,% 99.3 97.1 96.3 99.5 82.1 Sample 1, cleaned SGS number 8 0.05 0.20 0.09 0.02 0.50 The cleaning effect,% 99.3 96,8 96.2 99.5 82.1

The test results showed a high degree of purification of waste water from heavy metal ions by the proposed method:

cleaning effect (on average) higher than 90%;

the content of heavy metal ions in wastewater after their treatment (on average) is 10 times less than the MPC for their discharge into the sewage system.

The presented method of wastewater purification from heavy metal ions using a formed iron-containing suspension, which has a high chemical activity for ferrite formation and the ability to adsorb heavy metal ions does not require heating, has a high cleaning process, is simple, easily implemented on conventional process equipment, cost-effective and ecologically safe.

Information sources

1. RF patent 2082681, cl. C 02P 1/62, publ. 06/27/97. Bul.№18.

2. Vinogradov S.S. Ecologically safe galvanic production. M .: Globus, 1998, p. 167,168, 169.

3. Filinovsky V.F., Nikolskaya T.Yu., Shevchenko V.K. Ferritization cleaning of galvanic waste of enterprises for the production of electronic equipment // Ecology and Industry of Russia. 1998. June, p.

Claims (4)

1. A method of treating wastewater from heavy metal ions using a ferrous salt, characterized in that an iron-containing suspension is used in which the mass (g / l) ratio of components is: t (Fe8O ₄ · 7H ₂ O): t (NaOH) m (YaMO ₃₎ = 9.8: 2.8: 1, and the ratio of their concentrations (mol / l) is C (^ Re8O ₄ 7H ₂ O) C (NaOH): ί '(Ν; · ιΝΟ. ₃ ) = 0.75: 1.5: 0.25, having a pH of 810, the dosage of which in the treated water is carried out in accordance with the ratio: Tm (Me ^{p +} ): t (Pe _total ) = 1: 3, but not more than 1 g / l Re _total with mechanical stirring or bubbling with air and adjusting the pH of the purified water to 9-12.0 units with a solution of sodium hydroxide. 2. The method according to claim 1, characterized in that the source of iron is technical iron sulfate (II), representing waste from the metallurgical industry. 3. The method according to claim 1, characterized in that the iron-containing suspension is aged for the formation of high chemical activity to ferrite formation and the ability to adsorb heavy metal ions for at least 20 minutes before it is introduced into the purified water. 4. The method according to claim 1, characterized in that in the case of the presence of chromium (VI) ions in the purified water, the amount of the formed iron-containing suspension should be sufficient to restore them to chromium (III) ions. 5. The method according to claim 4, in which 16 mg of Fe8O ₄ ^ 7H ₂ O is used per 1 mg of Cr ⁺⁶ . 4 ^) Eurasian Patent Organization, EAPO