RU2576569C2 - Method for recovering heavy metal ions from aqueous solutions - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to a process for extracting heavy metal ions from aqueous solutions. Method comprises extracting of vegetable oils with extractant containing fatty acid, with the pH of aqueous solutions, equal to 9-11. Then occurs sedimentation of the formed system with its delamination and phase separation. In this settling system lead to the formation of three phases: a top - the oil, which is a regenerated extractant bottom - water, and the intermediate between them - a gel consisting of water, oil and comprising a net-like structure hydroxocomplexes heavy metals. A gel mass is dried at a temperature of 100-300 °C to form nanocrystals of heavy metal oxides.

EFFECT: technical result consists in the cleaning efficiency of aqueous solutions of metals with the use of renewable, non-toxic and inexpensive extracting effective.

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Description

The invention relates to the extraction of substances by organic extractants from aqueous solutions and can be used in non-ferrous and ferrous metallurgy, as well as for the treatment of industrial and domestic wastewater.

Known liquid extraction based on the distribution of substances between two immiscible liquids, which is widely used in analytical chemistry to separate the components of the solutions [L. Gindin Extraction processes and their application. M .: Nauka, 1984. 144 p.]. Usually, aqueous solutions and organic solvents are used as two liquid immiscible phases.

The disadvantage is that most organic solvents are highly volatile, flammable and toxic substances.

The closest technical solution is a method for the extraction of heavy metal ions from aqueous solutions [RF patent 2481409, IPC С22В 3/26, publ. 05/10/2013], including extraction using vegetable oils containing fatty acids as an extractant, at a pH value of aqueous solutions equal to 9-11, sedimentation of the resulting system with its separation into phases and their separation.

The disadvantage of this method is that no further processing of the phases after delamination is indicated.

The objective of the invention is to develop methods for processing phases after their separation and separation.

The technical result that can be achieved by carrying out the invention is a high degree of metal extraction efficiency, deep purification of the aqueous phase, regeneration of the extractant with simultaneous cost-effectiveness, process safety using a renewable non-toxic, inexpensive and effective extractant.

This technical result is achieved by the fact that in the known method for the extraction of heavy metal ions from aqueous solutions, including extraction using vegetable oils containing fatty acids as an extractant, when the pH of aqueous solutions is 9-11, sedimentation of the formed system with its delamination into phases and their separation, sedimentation of the system after extraction is carried out with the formation of three phases: the upper - oil, which is a regenerated extractant, the bottom - water, and the intermediate between them - gel figurative, consisting of water, oil and containing hydroxyl complexes of heavy metals in the form of a mesh structure, the gel-like mass is dried at a temperature of 100-300 ° C until the formation of nanocrystals of heavy metal oxides.

The essence of the method is illustrated by the data of the table and FIG. 1-6, which indicate the concentration of metal ions in the initial solutions, the extraction time at a given pH value, the metal concentration and pH in the clarified aqueous phase, the distribution coefficient D, calculated as the ratio of the equilibrium concentrations of metal ions in the organic and aqueous phases.

Stirring and maintaining the desired pH value was carried out until in the future, the acid-base characteristics of the system changed slightly. Upon reaching equilibrium between the organic and clarified aqueous phases, the organic phase was separated from the aqueous phase; in the latter, the pH value and the residual concentration of the metal ion were determined. To maintain a given pH value of the solution during the extraction, alkali or acid solutions were used as neutralizers.

Examples of specific performance of the method

Example 1 (Fig. 1)

In FIG. 1 shows the dependence of the residual concentration of metal ions on the pH of the solution. Extractant - olive oil; extraction time 1 hour; O: B = 1: 3, t = 24 ° C; initial concentration C ₀ , g / dm ³ : 1.1 Zn (II); 5.1 Pb (II); 1.2 Cu (II); 1.3 Fe (III). The best extraction results are shown in the table.

Example 2. The dependence of the residual concentration of metal ions on the ratio B: O was studied.

As extractant used olive oil; extraction time - day; t = 20-24 ° C.

Zn (II): C ₀ = 2.3 g / dm ³ , pH 10. Extraction is carried out at B: O≤7. When B: O≥8 precipitation is formed.

Pb (II): C ₀ = 5.24 g / dm ³ , pH 11. Extraction is carried out at B: O≤7. At B: O≥8, precipitates form, while the residual concentration included the sum of the concentrations of lead ions in solution and in the precipitate.

Cu (II):

- pH 6; C ₀ = 1.1 g / dm ³ . Extraction is carried out at B: O = 3-8.

At B: O> 8 precipitation forms;

- pH 10; C ₀ = 1.1 g / dm ³ . Extraction is carried out at B: O≤8.

When B: O≥8 precipitation is formed.

Fe (III). The extraction of Fe (III) ions is carried out at B: O≥3 almost immediately, the residual concentration is approximately the same and equal to C = 0.095 g / dm ³ . During the extraction of Fe (III) ions, a brown coating is formed at the bottom of the glass.

Fe (II) e7. The extraction of Fe (II) ions is carried out within B: O = 3-6. At B: O≥7, black precipitates form. In the process of extraction, the oxidation of Fe (II) ions to Fe (III) takes place.

Example 3 (Fig. 2, 3)

In FIG. Figure 2 shows the dependences of the residual concentration C, g / dm ³ , metal ions Zn (II), Pb (II), Cu (II) and Fe (II) on the time τ, min, and the initial concentration C ₀ , g / dm ³ . Extractant - olive oil; O: B = 1: 3. pH = 10, t = 20-24 ° C. Extraction is carried out in time, min, not more than: Zn (II) - 60; Pb (II) - 90; Cu (II) - 30; Fe (II) - 30 min at O: B = 1: 3 and 70 min at O: B = 1: 4.5.

The extraction of Fe (III) ions at pH 10 and O: B = 1: 3 occurs almost immediately, the residual concentration is approximately the same and equal to C = 0.095 g / dm ³ . At C ₀ > 3 g / dm ³ , brown precipitates form. The extraction of Fe (II) ions is carried out within 1 hour. At C ₀ > 1.6 g / dm ³ , black precipitates form.

In the range of the investigated initial concentrations for Zn (II), Pb (II) and Fe (II) ions, with an increase in the concentration of these ions, the process speed decreases slightly, and for Cu (II) ions it increases.

In FIG. Figure 3 shows the dependences of the residual concentration of metal ions on time and temperature. The extractant is olive oil, O: B = 1: 3.

In the temperature range studied, for Zn (II), Pb (II) and Fe (II) ions, the process speed increases with an increase in the temperature of these ions, and decreases for Cu (II) ions.

From FIG. 2, 3 it can be seen that the extraction of heavy metal ions depends on the initial concentration, time and temperature.

For Zn (II), and Fe (II) and Pb (II) ions, the extraction process lies in the kinetic region and is limited by the formation of a complex of these ions with extractant components, which is solvated into the organic phase.

For Cu (II) ions, an increase in the rate of the process with an increase in the initial concentration may indicate that extraction is limited by the rate of external diffusion. A decrease in the extraction rate with increasing temperature may be due to coalescence (coalescence of drops of vegetable oil) inside the mobile solution with stirring. With increasing temperature, the coalescence rate increases, and therefore, the interfacial surface between the organic and aqueous phases decreases, which, according to Fick's first law, reduces the diffusion rate. In addition, the position of the double bond in oleic acid can change when heated and under various chemical influences. For example, heat treatment in an alkaline medium promotes the migration of a double bond to a position adjacent to the carboxyl group. It should also be taken into account that with increasing temperature due to redox reactions between Cu (II) and vegetable oil, the concentration of Cu (I) increases, which is not extracted into the oil phase.

Example 4. The extraction of iron ions from a mixture of salts of Fe (II) and Fe (III). It was found that with increasing concentration, the separation coefficient increases. During the extraction, the volume of the extract increases by 5-10% of the volume of the extractant, and the extract has a gel structure. Precipitation of Fe (III) hydroxocomplexes is brown, and Fe (II) precipitation is black. The black precipitates after drying are magnetic and have the composition FeO · Fe ₂ O ₃ or Fe ₃ O ₄ .

Example 5 (Fig. 4)

In FIG. Figure 4 shows the dependence of the distribution coefficient D on the type of vegetable oil: 1 - apricot, 2 - pumpkin, 3 - cedar, 4 - soybean, 5 - grape, 6 - corn, 7 - walnut, 8 - sunflower, 9 - linseed, 10 - olive.

Vegetable oils have different ability to extract Zn (II), Pb (II), Cu (II) and Fe (II) ions. All studied oils extract well Fe (III) ions. The distribution coefficient D of Cu ions for a number of oils is an order of magnitude greater than that of other studied metal ions.

Example 6 (Fig. 5, 6)

When the system is defended after extraction for more than a day, it is stratified into three phases: the upper one is oil (regenerated extractant), the lower is aqueous, and the intermediate between them is a gel-like network structure of metal hydroxocomplexes with water and oil components. From the intermediate phase of the gel, metal or its compounds can be extracted.

In FIG. 5 shows the dynamics of sedimentation of the system after extraction of lead for various oils within a day, O: B = 1: 3, pH = 11, C ₀ = 5 g / dm ³ . The numbers indicate the phase heights in mm (vertical) and the settling time in min (horizontal).

Similar results were obtained for other metals studied. The data obtained give the prospect of technical use of vegetable oils, especially unsuitable for use in writing ("rancid" oils).

When drying hydroxocomplexes at temperatures above 100-300 ° C, nanocrystals of metal oxides are formed.

In FIG. 6 is a diagram of the extraction of metal ions by vegetable oils.

Claims (1)

The method of extraction of heavy metal ions from aqueous solutions, including extraction using vegetable oils containing fatty acids as an extractant, with a pH of aqueous solutions equal to 9-11, sedimentation of the resulting system with its separation into phases and their separation, characterized in that sedimentation of the system after extraction is carried out with the formation of three phases, the upper of which is oil, which is a regenerated extractant, the lower is water, and the intermediate is gel-like, consisting of water, oil and soda aschaya as crosslinking hydroxo heavy metals gel phase after separation is dried at a temperature of 100-300 ° C until the heavy metal oxide nanocrystals.

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