RU2104316C1 - Method for precipitation of ions of heavy metals from industrial sewage waters - Google Patents

Abstract

FIELD: treatment of industrial and household sewage waters fro removal of heavy metals ions. SUBSTANCE: initial solution is subjected to neutralization to pH value within 4.0 $$$ pH $$$ 12.0. Simultaneously introduced singly is bentonite clay in amount not more 5.0 g/cu.dm. Clarified aqueous phase is separated by decanting, and precipitate is multiply subjected to contact with next portions of initial solution up to ratio of L:S $$$ 2:1 with subsequent decanting of clarified aqueous phase. EFFECT: higher efficiency. 3 cl, 1 dwg, 7 tbl

Description

 Extraction of heavy metal ions from aqueous solutions relates to the field of extraction of substances from aqueous solutions using sorbents and / or flocculants in reagent deposition, the method can be used in non-ferrous and ferrous metallurgy, as well as for the treatment of industrial and domestic wastes.

 A known method of ion-exchange wastewater treatment [1], in which clay aluminosilicate minerals, mainly bentonite clays, are used for wastewater treatment.

 The disadvantage of this method is the lack of optimal conditions for the use of clays for the extraction of cations, which leads to increased consumption of reagents.

The closest technical solution is a method for the extraction of heavy metal ions using bentonite clays [2], which used model solutions of copper, zinc, cadmium and calcium sulfates with a concentration of initial metal solutions of 16 - 80 mg / dm ³ , mixing time 30 min, sedimentation - 2 hours, with the consumption of bentonite clays without additional use of a neutralizer of at least 15 - 20 g / dm ³ , while bentonite clays slowly settled.

In order to increase the degree of clarification of the solutions, activated clay was used, obtained by treating the latter under hydrothermal conditions with a 10% alkali solution at 105-110 ^° C for 5-6 hours.

The consumption of activated clay was 10 g / dm ³ , the mixing time was 30 minutes, and the settling time was 2 hours. The degree of purification from copper, zinc and cadmium ions was, respectively,%: 99.8; 99.7; 98.8. The solutions are completely clarified after settling for 30 minutes, while the degree of purification from suspended solids is 95 - 98%.

 The disadvantages of the method are the complexity of the preliminary preparation of activated clay, the high consumption of clay and other reagents, the invariable ratio of the compositions of clay and neutralizer - alkali, the latter is contained in the activated clay.

 The objective of the invention is to create optimal conditions for the extraction of heavy metal ions from water-intensive wastewater with a salt content that contributes to the formation of colloidal, finely dispersed systems with difficult to precipitate suspensions.

 The technical result that can be achieved by carrying out the invention lies in the efficiency of the process by reducing the consumption of reagents and the number of process steps, as well as by obtaining a dense precipitate with low moisture content.

This technical result is achieved by the fact that in the known method, comprising introducing into the initial solution of bentonite clay with a neutralizer, the bentonite clay is introduced once in an amount of not more than 5.0 g / dm ³ , while the clarified aqueous phase is separated by decantation, and the precipitate is repeatedly contacted with the following portions of the initial solution, followed by decantation of the clarified aqueous phase. The contact of the precipitate with the following portions of the initial solution is carried out to the ratio W: T≤2: 1. The introduction of the neutralizer is carried out to a pH value lying in the range of 4.0≤pH≤12.0.

 The essence of the method is illustrated by the technological scheme of the process shown in the drawing.

 Examples of specific implementation of the method.

 As the initial solution used wastewater of an industrial enterprise, the composition of which for the main components is presented in table. one.

 The initial solution was passed through carefully washed quartz sand to remove suspended solids.

 Bentonite clay contained aluminum, silicon, iron, magnesium, calcium as the main components, and sodium, barium, manganese, and titanium as impurities.

 The clay contained quartz, calcite, pyrite and other minerals.

 Clay swelled significantly in an alkaline environment and slightly in an acidic environment.

 The composition of clay fractions are given in table. A.

 Example 1 (table. 2, experiments 1.1. - 1.5).

In accordance with the technological scheme of the process shown in Fig., 0.5 g of bentonite clay (C _clay = 2.5 g / dm ³ ) was added to 200 cm ^{3 of the} initial solution, and at the same time, with a continuous stirring, the solution was neutralized with 10% a solution of alkali NaOH to the optimum pH of the deposition of heavy metal ions, equal to a value of 9.5 - 10.5 for this solution. During stirring for 10 minutes and settling for 15 minutes, a clear interface between the solution and the precipitate appeared. Sediment volume was estimated as a percentage of the total system volume. The clarified aqueous phase was separated from the precipitate by decantation, a new portion of the initial solution was added to the precipitate to a volume of 200 cm ³ , neutralization was carried out to pH = 9.5 - 10.5 with continuous stirring and subsequent sedimentation, as described above. A similar procedure was repeated five times, with each time the volumes of the precipitate and the clarified aqueous phase were measured, in the latter the concentration of heavy metal ions was determined. At all stages of the experiments, the pH was monitored using a pH meter and the consumption of the converter.

 In the table. 2 shows the results of industrial wastewater treatment using bentonite clay and a NaOH neutralizer, and the concentration and extraction of heavy metal ions are given for the main component of the initial solution - zinc.

From the data table. 2 (experiments 1.1 - 1.5), we can draw the following conclusions:
1. The extraction of zinc from the solution is 98.2%.

 2. Precipitation obtained in the previous stages of neutralization, contribute to the neutralization of the initial solution.

 Repeated contact of the precipitate with new portions of the purified solution increases the pH of the latter, which helps to remove impurities and reduces the consumption of reagents.

 Example 2 (table. 2, experiments 2.1 - 2.5).

The experiments were carried out similarly to experiments 1.1 - 1.5 table. 2 with the only difference that 1.0 g of bentonite clay (C _clay = 5 g / dm ³ ) was added to 200 cm ^{3 of the} solution, i.e. twice as much.

 From the data table. 2 (experiments 1.1 - 1.5 and 2.1 - 2.5) it follows that an increase in the amount of added clay leads to the formation of denser sediments and reduces the consumption of the neutralizer.

 Example 3 (table. 3, experiments 1.1 - 1.5).

The experiments were carried out similarly to experiments 1.1 - 1.5 table. 2, but as a neutralizer used cheaper than alkali - hydrated lime Ca (OH) ₂ in the form of a lime solution with a concentration of 1.496 g / DM ³ CaO.

 Comparison of experimental data 1.1 - 1.5 tab. 2 and 3 indicate that when using CaO as a neutralizer, more dense precipitation is formed.

 In the table. 4 presents data on the density of precipitation obtained in the conditions of the experiments table. 2 and 3.

 For comparison, the density of all precipitation was determined in relation to the most dense precipitate obtained in experiment 2.1 of the table. 2, its density is taken as 100%.

 From the data table. 4 it follows that the most dense precipitation formed in experiments 2.1, 1.1 (table. 2) and 1.1 (table. 3).

 In the table. 5 gives a characteristic of precipitation obtained in the conditions of the experiments of table. 2 and 3.

 From the data table. 5 that clay helps to reduce the moisture content of sediments and increase their density, the use of CaO as a neutralizer in comparison with alkali gives more dense precipitation with less moisture.

In the table. 6 shows the consumption of reagents per 1 m ^{3 of} purified solution, obtained according to the experiments of table. 2 and 3.

 From the data table. 6 it follows that an increase in the amount of clay reduces the consumption of the catalyst, especially if lime is used as the catalyst.

 It was established by experiments that in the presence of clay, the calcium content in the solution decreases, sulfur compounds of lower oxidation levels are removed from the solution, and metal recovery increases.

 The clarified aqueous phase is separated from the precipitate by decantation, bypassing the time-consuming filtering operation of usually moisture-intensive hydrophilic precipitates formed from large volumes of purified solutions.

 The clarified aqueous phase can be used for technological purposes, and precipitates are processed into useful products in various ways.

 Cleaning, especially large volumes of contaminated industrial solutions of the proposed method is environmentally friendly and cost-effective.

 The number of contacts of this precipitate with new portions of the initial solution is determined by the composition and volume of the solution to be purified, however, from a technological and economic point of view, it corresponds to the optimum W: T≤2: 1.

 The range of pH for the deposition of heavy metal ions is determined by the qualitative and quantitative compositions of the solution being cleaned and depends on the pH of the total precipitation of the removed ions, for many process wastewaters this range is in the range 4.0≤pH≤12.0.

 In the technological scheme shown in the figure, the neutralizer and bentonite clay are introduced simultaneously at the stage of mixing and neutralizing the solution to the optimum pH values. However, experiments have shown that the introduction of clay at the stage of settling after neutralization of the solution does not worsen the results of treatment of industrial wastewater.

 Compared with the prototype, the proposed method simplifies the process, there is no need for preliminary complex processing of bentonite clay, repeated contact of the precipitate with new portions of the initial solution reduces the consumption of the neutralizer and bentonite clay, allows you to get dense precipitation, which contain less moisture and quickly lose it in the open air .

More than 50% of the moisture is removed from the precipitate by drying in air during the day, more than 90% of the moisture is removed by drying in air for two days or by calcination at 200 ^o C for no more than two hours.

 The formation of denser sediments helps to reduce the time and increase the degree of clarification of the solution, which eliminates the time-consuming stage of filtration of difficult-to-filter hydrophilic precipitates, proceeding to the separation of the clarified aqueous phase from the precipitate by decantation.

 The proposed method allows to implement a waste-free, environmentally friendly, cost-effective technology with the processing of sludge into useful products and returning the purified clarified aqueous phase to the process.

Claims (3)

1. The method of deposition of heavy metal ions from industrial wastewater, comprising introducing into the initial solution of bentonite clay with a neutralizer, characterized in that the bentonite clay is introduced into the initial solution once in an amount of not more than 5 g / dm ³ , while the clarified aqueous phase is separated by decantation and the precipitate is repeatedly exposed to the following portions of the initial solution, followed by decantation of the clarified aqueous phase.  2. The method according to claim 1, characterized in that the contact of the precipitate with the following portions of the initial solution is carried out to the ratio W T ≤ 2 1.  3. The method according to claim 1, characterized in that the introduction of the neutralizer is carried out to a pH of 4 to 12.

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