Sorbent for separating heavy metal ions from drinking water and a method for preparation thereof

FIELD: water treatment.

SUBSTANCE: sorbent according to invention represents dispersion of ferric and ferrous hydroxides and a bivalent metal hydroxide, the latter, in particular, being magnesium hydroxide at magnesium-to-iron molar ratio between 1:2 and 1;2.2. Preparation of sorbent consists in coprecipitation of bivalent metal and ferric hydroxides at pH 10-11 followed by filtration (formation of precipitate), drying, granulation, and heat treatment of precipitate at 210-270°C.

EFFECT: increased heavy metal sorption capacity.

2 cl, 5 tbl, 6 ex

 

Sobratema relates to the field of environmental protection, namely sorbents for water purification from heavy metals and methods for their preparation.

Known sorbent for purification of industrial waste water from heavy metal ions on the basis of ferropericlase and the method of its production [1]. Ferropericlase is electrogenerating suspension of hydroxides of divalent or trivalent iron and provides deep cleaning of waste water from heavy metal ions, forming a slurry with a solid spinel structure.

The method of obtaining this sorbent is that an aqueous solution containing Fe3+and Fe2+, is subjected to electrolysis, and the resulting suspension of hydroxides are used as adsorbent for wastewater treatment.

The disadvantage of this sorbent is that the sorbent receive immediately before the process of cleaning solution. A method of producing a sorbent makes it impossible to use it for local drinking water treatment in the home, because provides for sorbent directly before cleaning solution. Granulation same sorbent significantly impairs its sorption characteristics.

Closest to the present invention is a sorbent for extraction of ions gidroizoliruschim metals (II-IV), which is a margana the C-zinc ferrite with a ratio of manganese:zinc - 1:2 [2].

Its disadvantage is the low sorption capacity towards heavy metal ions by sorption of neutral, weakly acidic and weakly alkaline solutions (water). So when sorption from aqueous solution of zinc salts of Zn(II) concentration of 10-4mol/l at pH=6 capacity was 0.6·10-5mol/g at pH=8-2,6·10-5mol/g, pH=9-6,4·10-5mol/year

Closest to the proposed method is a method of producing ferrite sorbents composition [3]. It lies in the fact that the aqueous solution containing Fe3+and other metal ions, add alkali (usually NaOH) and produce a joint precipitation of hydroxides. After filtration, the product is subjected to drying, granulation and heat treatment at a temperature of 600-1000°C. the result is a sorbent that does not have sorption properties with respect to heavy metal ions.

The disadvantage of this method is that it does not allow the sorbent, which would have sorption properties with respect to heavy metal ions.

Object of the present invention is to provide a granular sorbent for purification of drinking water from heavy metal ions with high sorption capacity and development of a method of obtaining such a sorbent.

The problem is solved in that the sorbent for purification of drinking in the s from ions of heavy metals, represents dispersed system of ferric hydroxides and bivalent metal, as the divalent metal contains magnesium ions in a molar ratio of magnesium:iron - 1:2-1:2,2. Distinctive features of the proposed sorbent from the sorbent prototype - the use of magnesium as the divalent metal and the molar ratio of magnesium:iron - 1:2-1:2,2.

The task is also solved due to the fact that in the known method, which consists in the joint coprecipitation of the hydroxides of magnesium and iron (III), filtering (forming sludge), drying, granulation and heat treatment of the precipitate, the coprecipitation of the hydroxides of magnesium and iron (III) is carried out at pH=10-11, and heat treatment is at a temperature of 210-270°C. the Distinguishing features of the proposed method from the method on the prototype are the coprecipitation of hydroxides at pH=10-11, conducting heat treatment at a temperature of 210-270°C.

The set of distinctive features of the proposed solutions with known features will help to achieve such qualities of the sorbent, as the toxicity and chemical stability, high service life and deep cleaning, which allows to reduce the concentration of toxic substances to the level of the MPC; to provide a pH in the leachate within the limits established by GOST (pH=6-8).

The rationale for the selection of the sorbent composition.

The way the s sorbent were obtained by mixing an aqueous solution of iron chloride(III) with aqueous solution of various salts of divalent metals such as magnesium chloride, zinc sulfate, Nickel sulfate, copper sulfate, iron sulfate. To the mixture was added aqueous sodium hydroxide solution and held a joint precipitation of hydroxides. The precipitate was left to ripen for 2 hours, the mother liquor decantation, the precipitate was twice washed with distilled water. Next, the precipitate was centrifuged, the resulting paste is dried in air for 48 hours. The dried samples were heated up to T=80°and subjected to hot dekatirovke by placing hot samples in a container of cold distilled water. Pelleted samples were filtered, and dried in air.

The sorption capacity was determined under dynamic conditions by passing a solution of sulphate of copper(II) concentration of Cu2+75 mg/l, pH 5,3 through the layer of sorbent 10 cm (2.5 g). In the filtrate after layer of sorbent analyzed the content of C2+and ions included in the composition of the sorbent.

Comparative results and the dependence of the sorption capacity of the composite sorbent from the constituent ion of the divalent metal is given in table 1.

Table 1
Me2+Capacity for Cu(II), mg/g
Cu(II)0
Fe(II)15,2
Zn(II) 46,0
Ni(II)of 112.8
Mg(II)126,5

The optimum sorbent, containing magnesium ions, it provides the highest sorption capacity. Samples containing ions of Cu(II), Fe(II), Zn(II), have low sorption capacity. Sample containing ions Ni(II), has a high sorption capacity, but ions Ni(II) toxic, and even a little washed out in drinking water is undesirable.

The possibility of carrying out the invention confirm the following examples.

Example 1.

A sample of the sorbent was obtained: 1000 ml of 0.5m aqueous solution of ferric chloride (III) was mixed with 500 ml of 0.5m aqueous solution of magnesium chloride, to the mixture was added to 4000 ml of 0.5m aqueous sodium hydroxide solution and held a joint precipitation of hydroxides. The precipitate was left to ripen for 2 hours, the mother liquor decantation, the precipitate was twice washed with distilled water to a total volume of 10,000 ml Next, the precipitate was centrifuged, the resulting paste is dried in air for 48 hours. The dried sample was heated up to T=80°and subjected to hot descriptionan by placing hot sample in a container of cold distilled water. The granular sample was filtered and dried in air. The output of the sorbent 40-45 grams of the century The resulting sorbent contained Mg=0,1-0,11, Fe or=0.51-0.52 g/g of sorbent. The sorption capacity was determined under dynamic conditions by passing a solution of sulphate of copper (II) concentration of C2+75 mg/l, pH 5.3 sulfate copper (II) concentration of C2+75 mg/l, pH 5,3 through the layer of sorbent 10 cm (2.5 g). In the filtrate after layer of sorbent analyzed the content of C+2and ions included in the composition of the sorbent. The sorption capacity of the sample was 126,5 mg si2+/g of sorbent.

Example 2.

A sample of the sorbent was obtained: 500 ml of 0.5m aqueous solution of ferric chloride (III) was mixed with 500 ml of 0.5m aqueous solution of magnesium chloride, to the mixture was added 2500 ml of 0.5m aqueous sodium hydroxide solution. Further according to the example 1.

The output of the sorbent was 23-25 grams. The resulting sorbent contained Mg=0,15-0,18, Fe=0,41-0,43 g/g of sorbent. The sorption capacity of the sample was 30,25 mg si2+/g of sorbent.

Example 3.

A sample of the sorbent was obtained: 1500 ml of 0.5m aqueous solution of ferric chloride(III) was mixed with 500 ml of 0.5m aqueous solution of magnesium chloride to the mixture 5500 ml of 0.5m aqueous sodium hydroxide solution. Further according to the example 1.

The output of the sorbent was 50-52 grams. The resulting sorbent contained Mg=0,07-0,08, Fe=0,59-0.6 g/g of sorbent. The sorption capacity of the sample was 36,01 mg si2+/g of sorbent.

Example 4.

A sample of the sorbent was obtained: 1000 ml of 0.5m aqueous solution of CHL is reed iron (III) was mixed with 250 ml of 0.5m aqueous solution of magnesium chloride, to the mixture was added 3500 ml of 0.5m aqueous sodium hydroxide solution. Further according to the example 1.

The output of the sorbent was 30-36 grams. The resulting sorbent contained Mg=0,06-0,07, Fe=0,66-0,67 g/g of sorbent. The sorption capacity of the sample was 25,25 mg si2+/g of sorbent.

Example 5.

A sample of the sorbent was obtained: 500 ml of 0.5m aqueous solution of ferric chloride(III) was mixed with 1000 ml of 0.5m aqueous solution of magnesium chloride, to the mixture was added 3500 ml of 0.5m aqueous sodium hydroxide solution. Further according to the example 1.

The output of the sorbent was 28-30 grams. The resulting sorbent contained Mg=0,32-0,33, Fe=0,39-0.4 g/g of sorbent. The sorption capacity of the sample was 48,12 mg si2+/g of sorbent.

The dependence of the sorption capacity of the composite sorbent from the ratio of Fe/Mg in the initial solution in the synthesis of (comparative results for examples 1-5 are given in table 2.

Table 2
Fe/MgThe average capacity for Cu(II), mg/g
4/1-4,2/125,25
3/1-3,2/136,01
2/1-2,2/1126,5
1/1-1,2/130,25
0,5/1-0,7/148,12

The table shows that the optimal ratio of Mg:Fe ratio is 1:2-1:2,2. The increase in the content of Fe(III), as well as pony is giving, leads to deterioration of the sorption properties of the sample, namely a decrease in the sorption capacity.

Examples of the implementation of the proposed method of sorbent.

Example 6

A sample of the sorbent was obtained in the following way. 1000 ml of a 0.5m aqueous solution of ferric chloride(III) was mixed with 500 ml of 0.5m aqueous solution of magnesium chloride, the mixture was gradually added to 4000 ml of 0.5m aqueous solution of sodium hydroxide to different pH values (pH=5, 7, 10, 11, 12) and conducted joint precipitation of hydroxides. The precipitate was left to ripen for 2 hours, the mother liquor decantation, the precipitate was twice washed with distilled water to a total volume of 10,000 ml Next, the precipitate was centrifuged, the resulting paste was dried in the air. The dried sample was heated up to T=80°and subjected to hot descriptionan by placing hot sample in a container of cold distilled water. The granular sample was filtered and dried in air. The output of the sorbent 40-45 grams. The resulting sorbent contained Mg=0,1, Fe=0.52 g/g of sorbent. The sorption capacity was determined under dynamic conditions as in example 1. The results of the study (the dependence of the sorption capacity of the composite sorbent from the pH of the synthesis are given in table 3.

Table 3
pHCapacity for Cu(II), mg/gLeaching of ions included in the sorbent composition in the feed solution
5--
714Fe up to 6 mg/l, Mg<12 mg/l
10126,5Fe<0.1 mg/l Mg<12 mg/l
11118,4Fe<0.1 mg/l Mg<12 mg/l
1283Fe<0.1 mg/l Mg<12 mg/l

The optimum value of pH=10-11. At pH below 7, the pattern is not formed. The sorbent is deposited in the range of pH 7 to 10, has a low sorption capacity, in addition, it pollutes the feed solution ions Fe(III). The sorbent obtained in the range of pH 11-12, has a low sorption capacity.

Table 4 presents the rationale for the temperature range thermal modification of the sorbent. The adsorbent obtained in example 6 (pH=10), was subjected to heat treatment at different temperatures. It is shown that high sorption capacity have samples of sorbent treated in the temperature range 20-270°C. furthermore, thermal treatment of the sample at a temperature of 210-270°increases its mechanical strength. Heat treatment in the temperature range 300-540°With significantly affects the sorption properties of the sorbent.

Table 4

The dependence of the sorption capacity of the composite sorbent temperature thermal modification.
TThe average capacity for Cu(II), mg/g
20-25126,5
100-150128,4
210-270132,1
300-32050
360-39020
500-54018

Table 4 shows that the optimum is a sample of the sorbent, thermally modified at T=210-270°C.

Table 5 shows the values of sorption capacity of the proposed sorbent and sorbent prototype in relation to ions of Zn(II). The sorption capacity of the proposed sorbent was determined under dynamic conditions by passing an aqueous solution of zinc sulfate with a concentration of Zn2+=5 mg/l, then according to example 1 and from a solution of copper sulphate with a concentration of C2+=5 mg/l

Table 5
SorbentCapacity for Zn(II), mol/gCapacity for Cu(II), mol/g
The proposed sorbent0·5·10-30,6·10-3
The placeholder0,6·10-5-

As IDE from the table, the sorption capacity of the proposed sorbent exceed the sorption capacity of the prototype more than 50 times.

The proposed sorbent will reduce the concentration of heavy metal ions in drinking water below the level of the MPC without contamination of the filtrate ions present in the sorbent, and changes the pH of the filtrate. And the proposed method will allow you to get the sorbent high quality with stable properties.

References

1. Budilovsky Y. Effective and affordable wastewater treatment technology // Ecology and industry, 1996, No. 8, p.20-22.

2. Tikhomolov C.P., Vasiliev EO, Lunkov O.N. Extraction of zinc from aqueous solutions by their contact with the powder of manganese - zinc ferrite // Journal of applied chemistry, 1995, T, VIP, s-1074.

3. Takei Takeshi. Ferrites. M: Metallurgy. 1964, 162 S.

1. Sorbent for the extraction of heavy metal ions from drinking water, representing a disperse system hydroxides of divalent metal and a trivalent iron, characterized in that the divalent metal contains magnesium in a molar ratio of magnesium: iron 1:2-1:2,2.

2. A method of producing a sorbent for the extraction of heavy metal ions from drinking water, including coprecipitation of the hydroxides of magnesium and ferric iron at pH 10-11, formation of precipitate, drying, granulation, thermal treatment is otcu, characterized in that thermal treatment is carried out at a temperature of 210-270°C.



 

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