RU2526986C1 - Method of purifying water from silicates - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: in order to realise method waters to be purified are filtered through layer of activated aluminium oxide, preliminarily modified by 0.5% sodium aluminate solution. Regeneration of spent activated sodium aluminate solution is realised by 0.1-0.5% sodium aluminate solution.

EFFECT: increased sorption capacity of charge by absorbed silicon, increased duration of filter-cycle between charge regenerations and creation of wasteless technology of water desilicinisation with re-application of spent regeneration solution.

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Description

The invention relates to the field of water treatment and can be used in wastewater treatment plants for industrial and drinking water supply, as well as in wastewater treatment.

A known method of desiliconization of water by filtration through a magnesian sorbent with a sorbent layer height of 3.4-4.0 m, a water temperature of 40-50 ° C and a filtration rate of up to 10 m / h (GI Nikoladze, Natural Water Treatment Technology: Textbook. universities / G.I.Nikoladze, - M .: Higher School, 1987, p. 438.).

The disadvantage of this method is the need to often change the load of the filter due to the impossibility of its regeneration.

Closest to the proposed invention is a method of filtering water through activated alumina, used as a load of a desilicon filter, and which consists in passing water at a speed of 5-6 m / h through a loading layer with a thickness of 1.5 m and periodic regeneration of the load, after its saturation silicon, a 0.1% solution of sodium hydroxide alkali (Nikoladze GI Technology of natural water purification: textbook for universities / GI Nikoladze. - M.: Higher school, 1987, p. 438.).

The disadvantage of this method is the low silicon content of activated alumina regenerated by alkali, a short inter-regeneration period of the filter and the formation of waste water treatment in the form of alkaline silicon-containing effluent, which requires subsequent neutralization and disposal.

The objective of the present invention is to increase the sorption capacity of the load on absorbed silicon, to increase the duration of the filter cycle between regenerations of the load and to create a waste-free technology for desiliconization of water with reuse of the spent regeneration solution.

The problem is achieved in that in a method for purifying water from silicates, including filtering water through a layer of sorbent, which uses activated alumina (AOA), the periodic regeneration of activated alumina is carried out with a solution of sodium aluminate.

Due to the regeneration of activated alumina with a solution of sodium aluminate, the method allows to achieve a depth of desiliconization up to 99.5% by increasing the sorption capacity of AOA on absorbed silicon while reducing water hardness.

Upon contact of sodium aluminate with AOA, sodium ions are partially surface embedded in the alumina lattice, displacing aluminum ions (with their subsequent hydrolysis) into the solution. In this case, silicon in the composition of the monomer Si (OH) _{4 is} adsorbed on the surface of AOA, forming a bond typical of silicates in the form of aluminum silicate Al ₂ Si ₂ O ₅ (OH) ₄ . In parallel, an aluminum hydroxide film forms on the loading surface. Filtration as a result of ion exchange of Na ⁺ for Ca ²⁺ and Mg ²⁺ reduces the stiffness of the solution, and the dissolved silicates, interacting with aluminum oxide and hydroxide, form aluminosilicate complexes adsorbed by the charge. In parallel with the exchange of Ca ²⁺ and Mg ²⁺ cations for Na ⁺ , partial reagent softening also occurs with a delay in the formation of CaCO ₃ and Mg (OH) ₂ , as well as insoluble CaSiO ₃ .

The method is illustrated by the following example.

The cleaning process according to the proposed method was carried out by filtering natural water with an initial silicon concentration of 34.2 mg / l in a column with a diameter of 32 mm loaded with crushed activated alumina grade AOA-1 GOST 8136-85 fraction size 1-2 mm, layer height 1.2 m, with a water filtration rate of 5.5-6.0 m / h and a temperature of 20 ° C.

Preliminary processing (modification) of the activated alumina filter layer was carried out by passing a 0.5% sodium aluminate solution through the loading volume at the rate of 5 volumes of reagent per 1 volume of AOA with a flow velocity of 2.5 m / h. At the end of the filter cycle (when the concentration of silicon in the filtrate reaches a maximum concentration limit of 10 mg / l), AOA is regenerated sequentially according to the scheme: loosening — passing a 0.5% solution of sodium aluminate (N a AlO ₂ ) through a layer of AOA — washing the load. The spent regeneration solution after 4-6 hours of standing (polymerization) and separation of this solution from the formed gel is adjusted to a 0.5% solution by adding a fresh portion of sodium aluminate (N a AlO ₂ ) to the solution and is used repeatedly and repeatedly in the developed technology of desalination water.

Regeneration completely restores the sorption properties of AOA, while the siliceous loading of the sodium aluminate-treated charge is twice as high as that of the prototype.

The experimental data are presented in table 1.

An advantage of the invention is that in the proposed method, the effect of purification from silicates is increased and the issue of processing, reuse and disposal of waste water treatment is solved.

The loose gel-like aluminosilicate precipitate formed in the spent regeneration solution occupies less than 0.5% of the total volume of the spent solution, easily releases moisture and crystallizes in the course of ordinary tissue filtration with the formation of scaly crystalline structures like mica. The resulting product is convenient for packaging and can be implemented as a commercial product as a valuable raw material component of the Portland cement mixture, as well as an additive in refractory concrete and as a raw material in the manufacture of ceramic products. The calculation of the economic efficiency of the developed new technology for a water treatment plant with a productivity of 45 thousand m ³ per day, at the same cost of electricity, depreciation and wages, is taken to show that the cost of technological reagents and materials in the new technology is up to 3 times less than in the compared version , with its complete non-waste, environmental safety and commercial feasibility, see table 2.

Table 1 Reagent Residual silicon in the filtrate, mg / l, with a duration of filtration, h: four 8 12 16 twenty 24 28 32 36 40 44 48 52 56 60 NaOH 1.82 2.85 4.07 5.09 6.31 7.12 8.34 9.77 10.78 12.82 14.85 17.10 20.36 23.61 26.97 NaAlO ₂ 0.21 0.23 0.26 0.31 0.40 0.51 0.72 1.92 3.05 4.47 5.29 6.51 8.14 9.77 11.13

table 2 Indicators Units measuring AOA regeneration with sodium aluminate AOA regeneration with caustic soda Useful performance of a water treatment plant thousand m ³ / day 45.0 45.0 Filter Cycle Duration day 4.4 2.1 Filtering speed m / h 5,0 5,0 Filter height m 2,5 2,5 Siliceous loading kg SiO ₂ / M ³ fifteen 7 Reagent consumption for load recovery t / year 476.5 1638 Filter Consumption m ³ / year 90 * 90 * Reagent cost thousand rubles / t 30.45 26.35 The cost of filter material thousand rubles / m ³ 55.0 55.0 Reagent costs thousand rubles / year 14509.4 43161.3 The cost of filter material thousand rubles / year 4950 4950 Unit costs for water treatment rub / m ³ 1.18 2.93

Claims (1)

A method of purifying water from silicates, including filtering water through a layer of activated alumina and its periodic regeneration, characterized in that the activated alumina is pre-modified with a 0.5% solution of sodium aluminate, and the regeneration of spent activated alumina is carried out 0.1-0 5% solution of sodium aluminate.