SU916419A1 - Process for purifying effluents from silicon compounds - Google Patents

Description

The invention relates to the technology of silicon compounds and can be used in the chemical industry for the purification of silicon compounds from wastewater.

A known method of cleaning waste water ⁵ from silicon compounds using iron salts, forming hydroxides, by means of which silicon compounds coagulate (3].

The disadvantage of the reagent method is a high consumption of reagents and a low degree of purification.

Closest to the proposed

is a wastewater treatment method

_ν 15

from silicon compound by electrocoagulation with soluble aluminum anodes [2].

The disadvantage of this method is low productivity and high consumption of aluminum.

The purpose of the invention is to improve the performance of the cleaning process and reduce the consumption of reagents.

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This goal is achieved by the fact that electrocoagulation cleaning is carried out using anodes of iron at a current density of 0.2-0.5 A / dm ^d and pH 9.7-11.0.

The method is as follows.

Sewage water containing silicon compounds is fed to a flow cell with anodes of iron. The process is carried out at an anodic current density of 0.2-0.5 A / dm ^ room temperature. And a pH of 9.7 ~ 11.0, followed by the separation of the coagulated precipitate by filtration.

The proposed range of operating current densities of 0.2-0.5 'A / dm ^ during electrolysis is due to the need to maintain specific electric power consumption within acceptable limits for the practice of cleaning with sufficient performance of the electrolyzer, as well as to ensure favorable conditions for electrochemistry3

dissolution of iron anodes

with high current output (without passivation) in the conditions of formation

precipitation in runoff with a low content of activating anions (acids). $

The dissolution of iron at these current densities proceeds without difficulty with a current efficiency of 96.5 * 100% ·

The use of current densities above 0.5 A / dm \ is also not feasible, ₀ due to a slight increase in the specific consumption of iron for purifying wastewater from silicon.

The indicated ordinary (room) temperature provides the best ₁₅ conditions for the precipitation of silicon and its sorption by the resulting iron hydroxides, as well as flocculation and sedimentation of suspensions, i.e. It provides the most complete cleaning of this pri- ₂₀ impurity. At this temperature, reverse peptization of silicon precipitation is also minimal.

The specified pH range in the electrolyzer due to the need _g5

ensuring the absence of iron impurities in purified water. The pH of the completion of the precipitation of Ge ^{+ 1} ^ in the form of its hydroxide is 9.2 "9" 6.

At high pH, almost all of the iron is in the form of hydroxide precipitates and its content in water does not exceed the maximum permissible rate (0.2 mg / l). In addition, under these conditions, silica silicate is in an activated state and is more fully precipitated with iron hydroxides. At pH above 11, the filterability of precipitates may deteriorate, as well as their partial reverse dissolution.

PRI me R 1. Source water (condensate) containing 376 mg / l 510 ^

; in the form of N3 ^ 5ΐθ ^, subjected to electrocoagulation cleaning in a continuous manner: an active electrolyzer with soluble iron (steel) anodes [with a working surface of 120 dm * ^ at a current density of 0.2 A / dm ^.

The current efficiency of the anode reaction Ge ~ 2e · Fe is 100%, the cell performance at ⁵⁰ concentrations condensate 53.5 l / h, treated condensate pH 10.0.

After separation of the precipitation of the hydroxides of iron and silicon filtration condensate colorless pro- ⁵⁵ transparently. The degree of purification of condensate from silicon 97.5%, the concentration of iron in. condensate 0.2 mg / l.

thirty

35

40

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The unit cost of electricity during cleaning is 1225 Ah-kg 5ΐ0 ^ or 450 Ah-m ^. For the 10 mm interelectrode spacing used in the electrolyzer, the electrolyzer has a voltage of 4.7 V and a specific power consumption of 5.75 kWh / kg 5ΐ or 2.1 kWh / m ⁵ .

Specific consumption of iron for cleaning is 1.28 kg / kg or 0.47 kg / m ^e .

PRI mme R 2. In contrast to example 1, electrocoagulation purification of the condensate from silicon is carried out at a current density on the electrodes of 0.4 A / dm ^.

The current output of the anodic reaction p _e -2- * Ge is also 100%, the condensate capacity of the electrolyzer is 75 l / h, the pH of the treated condensate is 10.7 · The filtered condensate is also colorless and transparent. The residual concentration of $ ίθ ^ in the condensate 'is

1.9 mg / l, degree of purification from silicon is 99.5%, iron concentration is 0.02 mg / l.

The specific cost of electricity during the cleaning process is 1685 A> h / kg 5г0g? 640 A.h / m ³ , electrolyzer voltage of 8 V and specific energy consumption of 13.5 kWh / kg 5U £ or

5.1 kWh / m ³ .

Specific consumption of iron for cleaning is 1.78 kg / kg or 0.66 kg / m ³ .

Primer3 · Unlike example 2, the original condensate contains 376 mg / l 5ϊ0ι ^ β in the form Νθ ^ 510 ^, 198 mg / l CrO ^ in the form NaX ^ Cr ^ Oh-Y.

The current output of the Ge-2e - * Ge anodic reaction is also 100%, the condensate capacity of the electrolyzer is 75 l / h, the pH of the treated condensate is 10.2. The filtered condensate is also colorless transparent and does not contain hexavalent chromium (degree of purification from Cr ⁺ L is 100%). The degree of purification of condensate from silicon is 96., 0%, the concentration of iron is 0.1 mg / l.

The specific cost of electricity during cleaning is 1145 A · h / kg (BFU + CrOe) or in terms of 5ί0 ^ 1170 Ah-kg / 6 or 640 Ah-m ³ , the voltage on the electrolyzer is 8.5 V, the specific energy consumption 9 , 75 kWh / kg (BJU + CrO ^) or in terms of 5U ^

15 kWh / kg "or 5.4 kWh / ν?.’

Specific consumption of iron for cleaning is -1.2 kg / kg 510 ^ + CgOz

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916419

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or in terms of 5) 0 ^ 1.85 kg / kg or or 0.66 kg / m \

Higher performance electrocoagulation purification process compared to the reagent dosti- Gaeta ₅ due to the fact that the hydroxide formed by dissolving anodes of iron, is more reactive than hydroxide formed when introduced into the salt solution w iron.

When used for purification of wastewater from silicon compounds with aluminum anodes, the productivity of the process is lower, so, in the case of the conditions, ₅ as in example 1, the time spent on the removal of silicon is two times longer than when using anodes of iron, and the consumption anodes in terms of ATg ^ O ^ is 2 mol A1 ^ 0u At ₂₀ 1 mol 5U ^, while in the case of iron anodes the consumption is 0.685 mol Ge ^ O per 1 mol 5ίθι ^.

Higher performance of the proposed method of purification obus- ₂₅ catching and also in that the use higher current density of 2 ~ 5 times higher than with aluminum anodes.

The advantage of the proposed method is _3θ ba also the possibility of electrocoagulation treatment of wastewater with a higher silicon content of up to 400 mg / l.

In addition, when using anodes from iron, occurs in parallel with the purification of 510 ^ purification from hexavalent chromium impurities, which is reduced by ferrous iron and precipitates in the form of hydroxide.

Claims (1)

Claim The method of purification of wastewater from silicon compounds by electrocoagulation using soluble anodes, characterized in that, in order to improve the performance of the process and reduce the consumption of reagents, the process uses anodes from iron and purification is carried out at an anode current density of 0.2-0.5 A / DM ¹ at pH 9.7-11.0.