Process for obtaining a sorbent on base of diatomite for purification from fluorine ions

Description:

The invention relates to a process for obtaining diatomite sorbent for the purification of fluoride ion liquids and can be applied in different branches of the economy.

It is known that high quality diatoms containing 60 and more percent SiO₂ it has many useful properties - low volumetric weight, thermostability, porosity, low thermal and acoustic conductivity. They are used as additives in cement, in the textile, chemical, oil and food industries as adsorbents and fillers.

a considerable part of diatomite is used in the production of filter powders, as fillers in the production of paper, plastics and paints, polishing materials and insecticides. It can also be used in environmental protection and in particular, in wastewater, industrial and natural wastewater treatment technologies for organic toxic substances and heavy metal ions.

For solving specific tasks the untreated native diatom is rarely used and, as a rule, it is subjected to activation and modification by different physico-chemical methods, the most common being the thermal, acid, base or combined activation methods of the diatomite [1, 2].

A process for obtaining diatomite sorbent is known, which includes crushing the diatomite with subsequent thermal modification and treatment. At the same time, the modification and the heat treatment are carried out in a single stage by burning the mixture of natural sorbent and straws in a ratio of 1: 2 of their volumes [3].

The disadvantage of the given process is the use as a straw modifier in large quantities, and the heat treatment process requires a high consumption of electricity.

A process for obtaining diatomite sorbent is known, which includes mixing it with waste from the wine industry (tescovina), subsequent treatment with sulfuric acid with a concentration of 2 mol / 1 for 24 hours at 100 ° C, drying and calcining at 800 ° C for 2 hours. The disadvantage of the proposed process is the long duration of the process, the use of aggressive reagents and the high calcination temperature [4].

A process for obtaining diatomite-based filtration materials is known, which includes treating the diatomite with water, separating the fraction with dimensions of 0.1 ... 0.001 mm by obtaining suspensions having a solidicide ratio equal to 1: 9 and subsequent separation from they of the impurities during the sedimentation of the fine particles of sand and clay, the classification of the finite working fraction is also done by obtaining the suspensions and separating the fine fractions during the sedimentation of the particles, calcining the diatomite in mixture with the sodium carbonate at a temperature of 1000 ... 1150 ° C for 2 hours [5].

The shortcomings of this process are the long duration of the process, the large workload for separating the fine fractions of the diatomite, the use of large volumes of water and the high calcination temperatures.

The closest solution is the diatomite-based sorbent filling process, which consists in treating the diatomite mixture with 6M NaOH solution at 8O ... 9O ° C for 2 hours with subsequent maintenance in 2M solution. manganese (II) chloride for 10 hours, acidification with HO solution to pH 1 .. .2; repeated treatment with NaOH solution at room temperature for 10 hours, washing, precipitate separation, air drying, then at 120 ... 130 ° C [6].

As a drawback of this method it can be mentioned the use of the high temperatures of treating the diatomite, as well as of the concentrations of NaOH and the long duration of the process.

The problem solved by the invention is the increase of the selectivity and the capacity of the sorbent with respect to the fluorine ions and the concomitant reduction of the energy consumed, the reagents and the duration of the process.

The process, according to the invention, solves the problem by including the diatomite milling, its subsequent treatment with 1 ... 3 M sodium hydroxide solution in the diatomite ratio: base of 0.65 ... 1.35, at 5O ... 6O ° C for 30 ... 90 min, with aluminum salt solution of 1.25 ... 1.50 M in the atomic ratio Al: And of 1.95 ... 2.50 at pH less than 3.5 times

2 .. .5 hours with stirring and with 25% ammonia solution at a pH greater than 9 for 2 .. .5 hours with stirring, with subsequent washing until neutral pH, air drying for 24 hours , as well as at

120 .. .130 ° C for 2 hours.

The result consists in obtaining the sorbent with high selectivity, increasing its adsorption capacity against the fluoride ions 3 times, reducing the consumption of reagents and reducing the temperature and the treatment time.

The proposed process of obtaining the sorbent on the basis of the natural mineral substances is carried out in the following way.

After crushing and pruning the diatomite to concrete dimensions, separating the fraction with the particle size of 0.25 mm, the modification of this fraction is carried out by chemical treatment in alkaline base solution in the diatomite ratio: base from 0.65 to 1, 35 with heating at о temperature of 5O ... 6O ° C for 30 ... 60 min. After the solid is separated from the solution by filtration, it is dispersed and kept in the solution of aluminum salt in the ratio Al: Si of 1.95 ... 2.5 m medium acid under stirring for 2 ... 5 hours , again the diatomite is separated from the solution by filtration, it is introduced in 25% ammonia solution and kept at room temperature under stirring for 2 ... 5 hours.

MD 3973 C2 2009.11.30

The mixture is filtered, the modified diatom is washed with distilled water until the neutral reaction of the washing water, dried in air, then at 12O ... 13O ° C 2 hours, cooled desiccator with calcium chloride, after the fraction of 0.25 ± 0.04 mm, which is kept in the desiccator until used, is reduced and separated for adsorption studies.

Examples of concrete execution of the procedure:

Example 1

To 75 ml of 3M NaOH solution add 15 g of diatomite with 0.25 mm shaft in SiO ratio to continuous stirring.₂ : NaOH of 1.35, stirred at 50 ° C for 60 min. The diatomite is separated from the solution by filtration, the paste obtained! disperses! in 100 ml of 1.5M aluminum salt solution with Al: Si ratio of 1.95 and pH <3.5; stirring at room temperature for 5 hours; again we are separated! the solid, which introduces m 100 ml 25% ammonia solution at pH> 9, is stirred at room temperature for 5 hours. The mixture was filtered, the modified diatom was washed to the pH of neutral wash water (pH ~ 7), dried in air 24 hours, then 2 hours at 120 ° C, cooled in the desiccator with CaCl₂, after all! who is m runfeiss, washes! 0.25 + 0.04 mm fraphia, which is preserved! in the desiccator until! when in use.

The adsorption capacity of the diatomite determined after! adsorption of fluorine ions reaches 12.4 mmol F / g sorbent (Experiment 10 in the table).

Example 2

To 75 ml of 3M NaOH solution is added! the continuous stirring! 15 g of diatomite with 0.25 mm cleft in SiO ratio₂: NaOH of 1.35, stirred at 60 ° C for 30 minutes. The diatom is separated! of solution by filtration, paste obtained! disperses! m 100 ml of 1.25M aluminum salt solution with Al: Si ratio of 1.60 and pH <3.5; stirring at room temperature for 5 hours; again we are separated! the solid, which is introduced into 100 ml 25% ammonia solution at pH> 9, is stirred at room temperature for 5 hours. The mixture is filtered! The modified diatomite is washed! pan! at the pH of neutral washing water (pIF7), they dry out! by air for 24 hours, then at 120 ° C for 2 hours, in the desiccator with CaCl₂, after all! who gets lost, gets separated! 0.25 ± 0.04 mm fraphia, which is preserved! in the desiccator until! when in use.

The adsorption capacity of the diatomite determined after! adsorption of fluorine ions reaches 10.5 mmol F / g sorbent (experiment 7 in the table).

The main results for the fine tuning parameters of the sorbent, as well as the data regarding the adsorption capacity of the modified diatomite and the natural diatomite of the fluorine ions obtained in the performed experiments are presented in the table.

<td rowspan="3">Nr. experiment</td><td colspan="5">Conditions for modification of the diatomite</td><td rowspan="3">Adsorption capacity of sorbent, mmol F / g sorbent</td>

<td colspan="3">Treatment with NaOH solution</td><td rowspan="2">Treatment with aluminum salt solution Al: Si</td><td rowspan="2">Treatment with ammonia, pH</td>

<td>SiO₂NaOH</td><td>Temperature, ° C</td><td>Process duration, min</td>

<td> 1</td><td> -</td><td> -</td><td> -</td><td> -</td><td> -</td><td> 3,85</td>

<td> 2</td><td> 0,65</td><td> 60</td><td> 60</td><td> 1,60</td><td> &gt;9</td><td> 9,61</td>

<td> 3</td><td> 0,65</td><td> 60</td><td> 30</td><td> 1,60</td><td> &gt;9</td><td> 9,02</td>

<td> 4</td><td> 0,65</td><td> 50</td><td> 60</td><td> 1,60</td><td> &gt;9</td><td> 8,60</td>

<td> 5</td><td> 0,65</td><td> 50</td><td> 30</td><td> 1,60</td><td> &gt;9</td><td> 7,30</td>

<td> 6</td><td> 1,35</td><td> 60</td><td> 60</td><td> 1,95</td><td> &gt;9</td><td> 12,60</td>

<td> 7</td><td> 1,35</td><td> 60</td><td> 30</td><td> 1,60</td><td> &gt;9</td><td> 10,50</td>

<td> 8</td><td> 1,35</td><td> 50</td><td> 60</td><td> 1,60</td><td> &gt;9</td><td> 12,20</td>

<td> 9</td><td> 1,35</td><td> 50</td><td> 30</td><td> 1,60</td><td> &gt;9</td><td> 10,30</td>

<td> 10</td><td> 1,35</td><td> 50</td><td> 60</td><td> 1,95</td><td> 10</td><td> 12,40</td>

<td> 11</td><td> 1,35</td><td> 50</td><td> 60</td><td> 1,30</td><td> &gt;9</td><td> 8,61</td>

<td> 12</td><td> 1,35</td><td> 50</td><td> 60</td><td> 2,50</td><td> &gt;9</td><td> 12,45</td>

<td> 13</td><td> 1,35</td><td> 50</td><td> 60</td><td> 1,60</td><td> 8,3</td><td> 10,05</td>

From the data presented in the table it is obvious that! optimal adsorption capacity! о own! the sample of the modified diatonite at which the adsorption capacity of the fluorine ions makes up 12.4 mmol F / g experiment 10, therefore the synthesis conditions! of his are optimal, namely: the SiO ratio₂: NaOH of 1.35, treatment temperature of the mixture 50 ° C, duration 60 minutes, Al: and ratio of 1.95, the pH of the solution when treated with ammonia is equal to 10.

MD 3973 C2 2009.11.30

Raising the temperature when treated with NaOH up to 60 ° C slightly changes the value of the adsorption capacity of the modified diatomite (by 0.2 mmol / g), but leads to an additional increase of the specific consumption of electricity - experiment 6.

Increasing the Al ratio: And at the stage of treating the diatomite with Al salt up to 2.5, keeping the other parameters constant !, slightly increases the adsorption capacity (by 0.05 mmol F7g, experiment 12).

But the decrease of this ratio Al: And up to 1.30 leads to a considerable reduction in the adsorption capacity of the sorbent - 1.4 times (experiment 11) compared to the sorbent obtained under the optimum conditions - experiment 10.

Increasing the contact time of the diatomite mixture with the alkaline base up to 90 min, the other parameters being constants and characteristics for the optimum experiment, is not accompanied by the increase of the adsorption capacity of the sorbent, but it is related to the unofficial expenditure of electricity.

The contact time of the diatomite mixture with the modifier salt solution longer than 5 hours, as well as the subsequent meningure of the mixture with ammonia more than 5 hours is not cost effective, as this does not lead to the essential change of the adsorption characteristics of the modified sorbent, but it requires additional electricity consumption.

When treating the diatomite with an alkaline base, some oxides are removed - oxides of iron, aluminum and so on, ensuring the release of pores, channels, cracks. Due to this fact, the specific surface area and the adsorption characteristics of the sorbent are increased. Upon further treatment of the activated diatomite with aluminum ions (sulphate salt or aluminum nitrate) on its surface and in the pore volume, new adsorption centers are formed, such as positively charged aluminum ions and aluminum compounds, for example hydroxides. , which is formed at the final stage of diatomite modification when treating with ammonia solution at a pH greater than 9.

All these actions due to the increased adsorption capacity of the modified diatomite due to the formation and adsorption of both different aluminum complexes with the fluorine and on the basis of the coulombian interafaction of the positive and negative active centers of aluminum hydroxide (at pH 5.3. ..6,2) and the corresponding fluorine ions.

In this way the proposed diatomite modification procedure allows to increase its adsorption capacity three times compared to the unmodified native diatomite.

Thus, the treatment of the initial diatomite m the exposed conditions leads to the essential reduction of the temperature, the reagent consumption and the duration of the process. This process guarantees an optimal ratio between Al and Si at the treatment step of the diatomite with aluminum salt, in which the obtained modified adsorbent possesses selective properties with respect to the fluorine ions, ensuring their effective removal from the water.

As a result of the proposed treatment, a modified sorbent based on native natural diatomite with adsorption capacity of increased fluorine is obtained.

The adsorption capacity of the diatomite samples was determined after the adsorption of the fluoride ions from the model solutions based on the sodium acetate buffer at the pH of the mixture of 5.3 ... 6.2. In all experiments the adsorption capacity of the modified diatomite is compared with the capacity of the untreated natural one (experiment 1, table).

Considering the low cost of the diatomite, its industrial reserves in the republic, the possibility of excavating through an open procedure. the simple machine for carrying out the claimed process, the real possibility of producing an active, efficient and cheap sorbent with high adsorption capacity and high selectivity, which can be used in the treatment of natural and residual waters of fluorine toxic ions.