SU1549925A1 - Method of treating hydroxide sediment containing heavy metals - Google Patents

Abstract

The invention relates to the protection of environmental water bodies from contamination by highly toxic components of sediments emitted from wastewater, in particular, to methods for treating hydroxide sludge formed during the treatment of wastewater from heavy metal ions. The aim of the invention is to increase the resistance of the precipitate to washing out by acidic natural waters and to increase the degree of ferritization of heavy metal hydroxides. Iron sulfate is introduced into the hydroxide precipitate in a mass ratio to the total content of heavy metal hydroxides (14-15): 1, alkalization leads to PH 10-11 and alkali metal permanganate or its mixture with manganese dioxide is introduced in an amount of 0.001-0.002% from the mass of the introduced ferrous sulfate. The resulting suspension is heated to 85-95 ° C and held while air is bubbling until the ferritization process is complete, after which the suspension is cooled, the crystalline precipitate is separated from the water and sent for disposal. 1 hp f-ly, 4 tab.

Description

The invention relates to the protection of environmental water objects from contamination by highly toxic sediment components released from wastewater, in particular, to methods for treating hydroxide deposits formed during the treatment of waste water from heavy metal ions, and is intended for use in black and white plants. non-ferrous metallurgy, as well as chemical, engineering, electrical and other industries that carry out the process of wastewater treatment from heavy metal ions with hydroxide and / or oxycao bonatny ways.

The aim of the invention is to increase the resistance of sediments to washing out by acidic natural waters and to increase the degree of ferritization of sediments.

To carry out the process, the hydroxide precipitates formed during the purification of waste water from heavy metal ions are heated in an alkaline medium with simultaneous bubbling with air, the resulting suspension is cooled and the crystalline precipitate is separated from the water, and iron sulfate is introduced in the amount of 14- before heating. 15 ma.ch. on 1 ma.ch. hydroxides, then alkalinized to a pH of 10-11 and the catalyst is introduced process CD

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in the amount of 0.001-0.002% of the mass of the introduced ferrous sulfate, the resulting suspension is heated to 85-95 ° C and maintained at the specified temperature with simultaneous bubbling with air until the ferritization process is complete, after which the suspension is cooled, the crystalline precipitate is separated from water in a known manner and sent for disposal.

Alkali metal permanganate or its mixture with manganese dioxide in a molar ratio of 1: (4-5) is used as a catalyst for the ferritization process.

In the process of a complex chemical process, a mixture of ferrite heavy metals of general formula I, is formed from mixtures of hydroxides and / or basic carbonates of divalent heavy metals contained in the initial sewage sludge and an excess of ferrous salts.

If, in addition to hydroxides and / or basic carbonates of bivalent heavy metals (nickel, cadmium, copper, zinc, etc.), the initial sludge of sewage contained hydroxides of trivalent heavy metals (for example, chromium and / or aluminum), Chromites are present along with ferrites of bivalent heavy metals, (Me 0) and aluminates (Me) of the same metals.

Like ferrites of heavy metals, chromites and aluminates are practically insoluble at ordinary temperatures in dilute aqueous solutions of strong mineral acids, which is due to the same structure of their crystal lattice. This makes it possible to safely dispose of sediments to a mixture of heavy metal compounds formed during the treatment of hydroxide sludge from sewage using the proposed method. The most appropriate disposal sites for such sediments are spent quarries for iron and polymetallic ores, where such natural heavy metal compounds already exist.

When the necessary conditions are met, complete ferritization of the mixture of hydroxides and / or basic carbonates of heavy metals is achieved at 85 ° C / vl h, and at 95 ° C in 30 minutes. Od

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However, the duration of the process of ferritization of heavy metal compounds into sewage sludge by the proposed method cannot serve as a parameter determining the completeness of this process, since the composition and reactivity of heavy metal compounds contained in hydroxide sludge is not constant. Under laboratory conditions, the completeness of the ferritization process can be judged with a sufficient degree of accuracy by the absence in the solid phase of the reaction mass of components soluble at ordinary temperature in dilute aqueous solutions of strong mineral acids, for example, in a 0.0001 M solution of sulfuric acid.

The use of ferrous sulfate in an amount less than 14 mach. on 1 ma.ch. the amount of hydroxides does not ensure complete precipitation. The use of iron sulphate in the amount of more than 15 mach. This is permissible, but not advisable, since this does not noticeably reflect on the properties of the resulting precipitate, but leads only to an unnecessary waste of iron sulphate.

When creating in the treated sewage sludge, the pH of the medium is less than 10, the duration of the ferritization process increases significantly, and this leads to unnecessary waste of thermal energy for processing. The creation of a medium pH above 11 in the sediment does not lead to a noticeable reduction in the duration of the ferritization process, all other things being equal, and causes only an unnecessary overrun of the alkaline reagent.

In the absence of a catalyst, the process of ferritization of mixtures of hydroxides and / or basic carbonates of heavy metals is relatively small: in 1 hour at 95 ° C and other conditions being equal, no more than 30% of the weight of the starting compounds of heavy metals is subjected to ferritization.

Use as a catalyst for the ferritization process of alkali metal permanganate, in particular potassium permanganate, in an amount of less than 0.001% of the weight of iron sulphate leads to a significant decrease in the rate of the ferritization process. The use of potassium permanganate in an amount of more than 0.02% of the mass of ferrous sulfate does not lead to a further noticeable reduction in the duration of the ferritization process, but only causes the overrun of the catalyst itself.

In the absence of potassium permanganate, manganese dioxide does not have a noticeable catalytic effect on the process of ferritization of a mixture of hydroxides and / or basic carbonates of heavy metals in concentrated aqueous alkaline suspensions, but does not have a mixture of 1 mole of potassium permanganate and 4–5 mole of manganese dioxide. approaching the activity of pure potassium permanganate.

An important condition for the completeness of ferritization of mixtures of hydroxides and / or basic carbonates of heavy metals is the continuous blowing of air into the reaction mixture throughout the whole process of ferritization. During interruptions in the air supply (for example, in emergency situations), to resume the ferritization process, some induction period or the introduction of an additional amount of catalyst (5-10% of the initial amount) is needed. This can be explained by the fact that the process of oxidative-catalytic ferritization of mixtures of hydroxides and / or basic carbonates of heavy metals in the presence of atmospheric oxygen is chain-like: additional introduction of the catalyst is necessary for the nucleation of new reaction chains.

The total content of hydroxides is preliminarily determined in the sludge, then the calculated amount of ferrous sulfate is introduced, alkalized, the catalyst for the ferritization process is added and the suspension is heated to a predetermined temperature, and it is maintained with continuous air blowing until the process is complete. Then the reaction mass is cooled to the usual temperature, the precipitate of a mixture of heavy metal compounds is separated from water and sent for disposal.

Example 1. Determination of the optimal amount of ferrous sulfate to achieve the completeness of ferritization of heavy metal compounds in aqueous-alkaline suspensions.

In an enameled tank, equipped with an annular sparger and a contact thermometer, 5 l of a 0.1 11 solution of ferrous sulfate is placed and, if not

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Discontinuous air bubbling (5 l / min rate) introduces in small portions a predetermined amount of wet sediment of a mixture of hydroxides or basic carbonates of heavy metals with a known amount of total solids.

The suspension, without stopping the bubbling with air, is alkalinized with chemically pure caustic soda to pH 11, then 27.8 ml of 1% potassium permanganate solution (0.002% of the mass of iron sulphate) is poured, and then heated to 95 ° C and kept at this temperature until the end of the ferritization process, as judged by the minimum content of heavy metal ions in the sulfuric acid extract from samples of the solid phase of the reaction mass. The duration of the ferritization process is 1 hour.

To determine the end of ferritization, stop the process at these 5 time intervals, take samples of 100 ml volume, cool them with running water and filter. The filter cake is washed with distilled water until the alkaline reaction in the wash water is removed, then removed from the filter and, without drying, stirred with 100 ml of 0.0001 M sulfuric acid solution for 15 minutes at room temperature, and then undissolved in sulfuric acid is filtered again. acid part of the sediment. In the sulfuric acid extract (filtrate), the content of heavy metal ions is determined by atomic adsorption spectroscopy.

For the optimal mass ratio of the initial compounds of heavy metals and ferrous sulfate, as well as for the complete termination of the ferritization process.

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They accept the results in which the found content of heavy metal ions in sulfuric acid extracts from two adjacent samples of the solid phase of the reaction mass did not exceed 0.001 mg / l.

Mixtures of hydroxides and basic carbonates of heavy metals, not subjected to ferritization, are dissolved in an excess of 0.0001 M of sulfuric acid at ordinary room temperature in 15 minutes.

The averaged results of serial experiments (10 experiments in each series) are presented in Table. one.

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As can be seen from the data table. 1, with an increase in the amount of ferrous sulfate (G) by the same amount of a mixture of heavy compounds, metals (STM), ceteris paribus, the content of heavy metal ions in the sulfuric acid extract from the solid phase of the reaction mass decreases. The optimal mass ratio of STMgLC, at which the content of heavy metal ions in sulfuric acid extracts is minimal, is within 1:: (14-15), respectively (see Table 1, tests series 13-16).

When using LCD less than 14 May. hours 1 ma.ch. a mixture of geological and technical measures or OKTM, the content of heavy metal ions in sulfuric acid extracts from the solid phase of the reaction mass increases, which indicates an incomplete course of the ferritization process (see Experiments 1-12). LCD use over 15 MAH. on 1 ma.ch. a mixture of geological and technical measures or OKTM does not lead to a further decrease in the content of heavy metal ions in sulfuric acid extracts, but only causes an unjustified overrun of G itself (see experiments 17-18).

Under the same conditions, the ferritization of GTM and OKTM proceeds at approximately the same speed, which can be judged by the proximity of the amounts of heavy metal ions found in sulfuric acid extracts from the solid phase of the other reaction mass (cf. experiments of even and odd numbers).

When conducting ferritization processes, GTM and OKTM in the absence of a catalyst and other conditions being equal, the speed of these processes slows down dramatically.

Example 2 Determination of the optimum pH value of the medium of the ferritization process for heavy metal hydroxides.

For all experiments, a geological and technical measures sediment with a known content of the sum of dry substances is used. Ferritization of a mixture of geological and technical measures is carried out analogously to example 1, but with a variable pH value of the medium.

The averaged results of the experiments are presented in table. 2

As can be seen from the table. 2, the optimum pH of the medium, corresponding to the achievement of the minimum content of heavy metal ions in sulfuric acid 30

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The extract from the solid phase of the reaction mass for the same period of time, is in the range of 10-11 (see Table 2, experiments 3 and 4).

When the pH of the medium is less than 10 and all other things being equal, the content of heavy metal ions in the sulfuric acid extract increases significantly (see Table 2, experiments 1 and 2), and at pH values above 11 remains unchanged (experiment 5).

The method was carried out with a mass ratio of GTM: LC 1:15, catalyst amount (KMpOF) - 0.002% of the mass of LC, temperature 95 ° C, intensity of air introduction into the reaction mixture 5 l / min and ferritization process duration 0.5 h.

Example 3: Determination of the optimal amount of catalyst for ferritization of heavy metal hydroxides.

Serial experiments of ferritization of a mixture of geological and technical measures are carried out according to the method of example 1 „

The variable parameter is the amount of catalyst, which is potassium permanganate or its mixture with manganese dioxide.

The averaged results of the experiments are presented in table. 3

As can be seen from the data table. 3, the optimal amount of potassium permanganate, i.e. Its amount, at which the content of heavy metal ions in the sulfuric acid extract from the solid phase of the reaction mass is minimal, is in the range of 0.001-0.002% of the mass taken in the reaction of iron sulphate (see Table 3, experiments 3-5).

The method was carried out at a ratio of 15, the pH of medium 11, the intensity of the introduction of air into the reaction mixture 5 l / min and the duration of the process of ferritization of 0.5 h.

When potassium permanganate is used in an amount less than 0.001% by weight of the liquid crystal, the content of heavy metal ions in the sulfuric acid extracts of their solid phase of the reaction mass increases sharply, which indicates a slowdown in the rate of the ferritization process and, consequently, an increase in the energy intensity of this process (see table 3 , experience 2). The use of potassium permanganate in an amount of more than 0.002% of the mass of W does not lead to a further noticeable increase in the rate of the process of ferritization of geological and technical measures, and the mass of the geological and technical measures do not increase;

it is only the unjustified overruns of the catalyst that cause it (see Table 3, experiments 5 and 6).

From tab. 3 that in the absence of a catalyst (experiment 1) or in the presence of manganese dioxide alone (experiment 7), the ferritization of GSH proceeds at approximately the same speed, from which it follows that manganese dioxide itself does not have a catalytic effect on this process.

From tab. 3 it can be seen that potassium permanganate and its mixtures with manganese dioxide in molar ratios 1: (1-5), respectively, in equal mass amounts, exert approximately the same catalytic effect on the process of GTM ferritization (see experiments 5 and 8-10) . With a molar ratio of KMnO. : MnOjL 1: 6, the catalytic effect of the mixture is reduced (see run 11).

Thus, in order to catalyze the ferritization of GSH in concentrated aqueous alkaline suspensions and in the sludge formed during the purification of waste water from heavy metal ions using a well-known hydroxide method, it is advisable to use its mixtures with cheaper and more available instead of pure potassium permanganate. manganese dioxide in a molar ratio of 1: (4-5).

Example 4. Determination of the optimum temperature for ferritization of a mixture of heavy metal hydroxides in concentrated aqueous alkaline suspensions and in sewage sludge.

For experiments, a mixture of heavy metal hydroxides isolated from model wastewater or directly from sewage sludge obtained from wastewater treatment is used. In the first case, a predetermined amount of a mixture of GTMs is suspended in the solution of ferrous sulfate, and in the second case, the total content of suspended solids in the sample is determined, after which the specified amount of ferrous sulfate is injected into the sludge. The ferritization process is carried out according to the general procedure described in Example 1. The variable parameter in all experiments is temperature.

The average results of experiments

are presented in table. four.

The method is carried out with a mass ratio of geological and technical measures: 1: 15 LC, the number of kata

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lysator, 0.0015% of the mass of the FA, pH of the medium 11, intensity of the introduction of air 5 l / min.

As can be seen from the table. 4, at 80 ° C (the maximum temperature of purification of waste water from heavy metal ions by the known variants of the ferrite method) complete ferritization of the mixture of hydroxides of heavy metals in the center of the aqueous alkaline suspensions is not achieved even in 90 minutes (see Table 4; experiments 1-3).

Complete ferritization of a mixture of heavy metal hydroxides in concentrated aqueous alkaline suspensions by the proposed method is achieved at 85 ° C in 60 minutes (experiments 4-7), at 90 ° C in 45 minutes (experiments 8-11), at 95 ° C in 30 minutes (experiments 12-15).

A further increase in the ferritization temperature, for example, to 100 ° C, is impractical, since the total duration of the processes for heating the suspensions from 95 to 100 ° C and the subsequent cooling from 100 to 95 ° C even under laboratory conditions is at least 7 minutes.

From tab. 4, it can be seen that, at the same temperature and other conditions being equal, there is no noticeable difference in the duration of complete ferritization of heavy metal hydroxides in concentrated alkaline water suspensions (experiments 8-11) and in the sewage sludge (experiments 16-19). It follows that all the regularities of the ferritization of hydroxides and basic carbonates of heavy metals, revealed in the previous examples, fully extend to the conduct of these processes in the sediments formed during the purification of waste water from heavy metal ions.

Using the proposed method, complete ferritization of heavy metal hydroxides, which are formed during the purification of waste water from heavy metal ions by known methods, is achieved. This provides the possibility of environmentally safe disposal of heavy metal compounds obtained in the processing of sediment sediments in the Earth’s interior without the construction of special facilities, as well as the release of land areas necessary for the disposal of special facilities for the disposal of heavy metals precipitates emitted from wastewater. in ways.

Claims (2)

1. A method of treating hydroxide precipitates containing heavy metals} by ferritization, including heating in an alkaline medium while bubbling with air, cooling the suspension and separating the crystalline precipitate from water, characterized in that, in order to increase the degree of ferritization and sedimentation resistance to washing out, before heating, iron sulfate is introduced in mass ratio to hydroxides (14-15): 1, alkali is introduced to pH 10-11, then alkali metal permanganate or its mixture with manganese dioxide in an amount of 0.001-0.002% of the mass of introduced vitriol, and then heated to 85-95 C. 2. A method according to claim 1, characterized in that the mixture of alkali metal permanganate and manganese dioxide is used in a molar ratio of 1: (4-5). Table 1 Table3