RU2322398C1 - Process for treating waste water to remove sulfate ions - Google Patents

Abstract

FIELD: waste water treatment.

SUBSTANCE: invention relates to reagent treatment of waste and natural waters to remove sulfates and can be used in mining and chemical industries as well as to treat electrolytic effluents from engineering plants. Process comprises neutralization of waste water and adding amorphous-structure aluminum hydroxide reagent recovered from acid solution of aluminum salt. Neutralization is conducted to achieve pH 12.2-12.4, after which water is clarified. Reagent is added stepwise, first portion constituting 10-25% and the rest added after mixing it with water. Water is then further neutralized to pH 12.7-13.0 while being continuously stirred until sulfate ions are precipitated into solid phase.

EFFECT: enabled purification of waste waters highly polluted with sodium sulfate to limited sulfate ion concentration not higher than 100 mg/dm³ and not higher than 600 mg/dm³ when discharging waste water to fish farming reservoir and to household water supply, respectively.

2 cl, 1 tbl, 6 ex

Description

The invention relates to reagent treatment of wastewater and natural waters and can be used in the mining and chemical industries, as well as for the treatment of galvanic drains of engineering plants.

Known methods for reagent wastewater treatment using lime in combination with aluminum metal or freshly precipitated aluminum hydroxide of an amorphous structure, using which the water to be purified is not contaminated by the ions of the reagent used.

However, the possibility of using metallic aluminum is very limited due to its high cost and high demand in strategic technologies [1]. In addition, with this method, a deep purification of wastewater from sulfate ions is provided, but the reduction of heavy metals to standard values is not achieved, probably due to the low pH value (pH = 11.5) when dosing lime after contact of wastewater with metal aluminum.

The closest method of the same purpose to the claimed invention in terms of features is the use of freshly precipitated aluminum hydroxide of amorphous structure in combination with lime [2]. The essence of this method is as follows: the wastewater is initially neutralized with lime to pH = 8.5-12.1, then the aluminum hydroxide of amorphous structure extracted from the acid solution of aluminum salt is dosed, followed by neutralization of the wastewater to pH = 12.2-12 ,8. Initial neutralization ensures the precipitation of all cations, excluding Na ⁺ and Ca ^{2+ ions} , into the solid phase in the form of metal hydroxides according to the equations:

The resulting “free” CaSO ₄ molecule, upon subsequent dosing of aluminum hydroxide, binds to insoluble calcium sulfoaluminate, which ensures the purification of the liquid phase from sulfate ions.

It is known that the treatment of wastewater contaminated with a well-soluble salt of Na ₂ SO ₄ using lime is accompanied by a reversible hydrolysis reaction according to the equation [3]:

As a result, a “bound” CaSO ₄ molecule is formed, which upon subsequent dosing of Al (OH) ₃ cannot react with the formation of insoluble calcium sulfoaluminate and, therefore, water purification from SO ₄ ^2- cannot be achieved.

Violation of the reversible reaction of equation (3) is possible while ensuring its shift to the right and thereby the formation of “free” CaSO ₄ molecules, which cannot be achieved under the conditions of the prototype of the treatment technology for wastewater contaminated with sodium sulfates, and therefore, it is impossible to achieve standard treatment rates for this categories of wastewater.

Thus, the described prototype of the claimed invention in physicochemical conditions cannot provide the necessary wastewater treatment from sulfate ions in the presence of high sodium sulfate content in the water (more than 300 mg / dm ³ ).

The objective of the present invention is the purification of wastewater highly contaminated with sodium sulfate to a limited value of SO ₄ ² ions of not more than 100 mg / dm ³ and not more than 500 mg / dm ³ for their discharge into water bodies, respectively, for fishery and household water consumption while reducing consumption reagents. The technical result is the treatment of wastewater with a high concentration of Na ₂ SO ₄ from SO ₄ ^2– ions to the regulatory requirements for their discharge into water bodies.

The problem is achieved in that in the method of wastewater treatment from sulfate ions, based on the neutralization of wastewater and the introduction of a reagent - aluminum hydroxide of an amorphous structure, extracted from an acidic solution of aluminum salt, according to the invention, before the introduction of a reagent - aluminum hydroxide of an amorphous structure extracted from acid solution of aluminum salt, the wastewater is neutralized to pH = 12.2-12.4 and clarified, and the reagent - aluminum hydroxide of amorphous structure is introduced fractionally, while the first dose is 10-25%, and after by mixing it with water, the remainder of the reagent, aluminum hydroxide of amorphous structure, is introduced and then neutralized to pH = 12.7–13.0 with continuous stirring until the precipitation of SO ₄ ^2– ions is completed in the solid phase.

Then, purified from SO ₄ ^2- water, after separation from the precipitate, is subjected to air sparging or CO ₂ sparging to normalize the hydrogen index.

In the present wastewater treatment process of the sulfate-ion conducting neutralization to pH 12,2-12,4 before introducing reagent - aluminum hydroxide amorphous structure, extracted from an acidic aluminum salt solution, Al (OH) ₃ with subsequent fractional dosing of the reagent and further liming the treated water to pH = 12.7-13.0 provides a limited concentration of SO ₄ ^2- ions and a reduction in the consumption of reagents when implementing this technology.

Thus, the application of the described technology allows waste water with a high concentration of Na ₂ SO _{4 to be} purified from SO ₄ ^2– ions to the regulatory requirements for their discharge into water bodies of appropriate water use while reducing the consumption of reagents, which cannot be achieved using the known technology due to her physico-chemical parameters of treatment.

In the patent and scientific and technical literature unknown technical solutions containing features similar to those claimed, therefore, the proposal meets the criterion of "novelty." Also for the first time, on the basis of the developed method, the ways of treating wastewater highly contaminated with sodium sulfate to a limited value of SO ₄ ² ions of not more than 100 mg / dm ³ and not more than 500 mg / dm ³ for their discharge into water bodies, respectively, of fishery and economic domestic water consumption while reducing reagent consumption, available when used in various operating conditions, i.e. The claimed technical solution meets the criterion of "inventive step".

The proposed method to obtain the above technical result is as follows.

Wastewater with a high concentration of sodium sulfate is neutralized to pH = 12.2-12.4 and clarified. After that, aluminum hydroxide of amorphous structure extracted from an acid solution of aluminum salt is introduced fractionally (initially 10–25%, then 90–75% of the total flow rate) and mixed. Then it is re-treated with a lime solution or lime paste to pH = 12.7-13.0 and then the purified water is mixed until the precipitation of SO ₄ ^{2- is completed} . The processing time (mixing time) and the consumption of aluminum hydroxide are determined by the composition of the water, the content of sulfate ions in it and the limited residual concentration of SO ₄ ^2- for discharge into the corresponding water body.

Purified water from sulfate ions after clarification with pH≤12.7-13.0 is subjected to air sparging or sparging in the presence of CO ₂ to normalize the pH to pH = 8.5.

The proposed method provides deep wastewater treatment from sulfate ions to a concentration regulated by MPC for discharging water into water bodies of the corresponding water consumption, and does not pollute the purified water with additional components.

Verification of the proposed method for wastewater treatment from sulfate ions with a high content of sodium sulfate was carried out on natural mine water.

Example 1. Cleaning was carried out on natural mine water with a pH of 4.0 and an ion concentration of mg / dm ³ :

Na ⁺ Ca ²⁺ Mg ²⁺ Fe _commonly Al ³⁺ Mn ²⁺ Cl ^- SO ₄ ^2- 1384.5 605 970 187 thirty 49.5 360 8100

Wastewater was neutralized with milk of lime to pH = 12.2-12.4, followed by clarification and separation of the precipitate formed. Then, in the clarified water after neutralization, a one-time supply of aluminum hydroxide of an amorphous structure extracted from an acid solution of aluminum salt was carried out in an amount of 3620 mg / dm ³ (calculated on dry basis) with a humidity of 85% and stirring was carried out for 5 minutes. At the same time, the hydrogen index decreases to pH = 8.8–9.4, in order to increase it, the milk of lime is dosed again and after stirring for 5 minutes, pH = 12.7–13.0. With the completion of this mixing, the residual concentration of SO ₄ ^2- ions in the purified water is 410 mg / dm ³ , which corresponds to the maximum concentration limit for water discharge into water bodies of domestic water consumption (table, series of experiments No. 1). The reagent consumption amounted to: aluminum hydroxide of amorphous structure Al (OH) ₃ - 3620 mg / dm ³ , lime milk CaO - 4800 mg / dm ³ .

Further, the water purified from sulfate ions was sparged with carbon dioxide to normalize the hydrogen index to pH = 7.0-8.5.

Example 2. Mine water of the composition indicated in Example 1 was neutralized with milk of lime to pH = 12.2-12.4, followed by clarification and separation of the precipitate formed. Then, fractional dosing of aluminum hydroxide of an amorphous structure extracted from an acidic solution of aluminum salt was carried out in clarified water after neutralization, namely:

- the first dosage is 250 mg / dm ³ ;

- the second - 2250 mg / DM ³ .

Mixing water with each dose was carried out for 2.5 minutes (table, series of experiments 2).

After mixing water with a second dose of aluminum hydroxide of an amorphous structure Al (OH) _{3, the} value of the hydrogen index decreased to pH = 9.0-9.4, to increase which milk was re-dosed. Mixing the latter with the treated water was carried out for 5 minutes, i.e. at the same time as for a single dosing of aluminum hydroxide with an amorphous structure Al (OH) ₃ . After this time, the residual concentration of SO ₄ ^2- ions in purified water was 420 mg / dm ³ . The reagent consumption amounted to: aluminum hydroxide of amorphous structure Al (OH) ₃ - 2500 mg / dm ³ , milk of lime - 4300 mg / dm ³ .

Thus, using a fractional supply of aluminum hydroxide of an amorphous structure extracted from an acid solution of aluminum salt of Al (OH) ₃ , the specified quality of water purification from sulfate ions is ensured while reducing the consumption of aluminum hydroxide by 1120 mg / dm ³ , i.e. by 31%. At the same time, a 10% reduction in the consumption of CaO lime milk is achieved.

Example 3. Mine water of the chemical composition specified in examples 1 and 2 was subjected to purification according to the technology described in example 1, i.e. with a single supply of aluminum hydroxide of an amorphous structure extracted from an acidic solution of aluminum salt of Al (OH) ₃ . To achieve deep purification, to give a residual concentration of SO ₄ ^2-,-limited for water discharge into water fishery water consumption, reagent flow was increased and made of amorphous structure aluminum hydroxide Al (OH) ₃ - 4500 mg / dm ^3, of CaO - 6000 mg / dm ³ (table, series of experiments 3).

After mixing the water with the specified flow rate of lime, the residual concentration of SO ₄ ^2- ions in the purified water was 40 mg / dm ³ , which corresponds to the maximum concentration limit for the discharge of water into fishery water bodies.

Example 4. Mine water composition shown in Example 1, was subjected to purification by the technique described in Example 2. The total flow rate of the amorphous aluminum hydroxide structure, extracted from an acidic aluminum salt solution was 3250 mg / ^dm3, including 320 mg / dm ³ in the first dosage, which was mixed with water for 2.5 minutes, and 2930 mg / dm ³ in the second dosage at the same mixing time. With the completion of the reaction of water with aluminum hydroxide, as a result of which the pH decreased to 8.8–9.2, a secondary liming of water was applied with a CaO flow of 4,500 mg / dm ³ with stirring for 5 minutes.

As a result of this purification, the residual concentration of sulfate ions was 20-80 mg / dm ³ (table, series of experiments 4).

The use of fractional dosing of aluminum hydroxide allowed to reduce the consumption of this reagent by 1250 mg / dm ³ , i.e. by 28% compared with a one-time supply (example 3) and at the same time reduce the consumption of lime by 1500 mg / dm ³ , i.e. by 25%.

Example 5. Mine water of the composition indicated in the above examples was purified according to the technology described in example 4 using fractional dosing of aluminum hydroxide of an amorphous structure extracted from an acid solution of aluminum salt to provide MPC for sulfate ions for fishery purposes. In contrast to the conditions of example 4, in this example, the first dosage of the reagent - aluminum hydroxide Al (OH) _{3 is} reduced to 280 mg / dm ³ (i.e. 8%). As a result, to ensure a given cleaning efficiency (SO ₄ ^{2 -} ≤100 mg / dm ³ ), the second dosage of aluminum hydroxide of an amorphous structure extracted from an acid solution of aluminum salt of Al (OH) ₃ is increased to 3220 mg / dm ³ . The total consumption of the reagent - aluminum hydroxide Al (OH) ₃ amounted to 3500 mg / DM ³ , i.e. 250 mg / dm ³ more compared with the conditions of example 4, with a simultaneous increase in the consumption of lime by 300 mg / dm ³ .

Thus, reducing the flow rate of the first dosage below 10% of the total flow rate is impractical.

Example 6. Mine water of the composition indicated in the above examples was subjected to purification technology with fractional dosing of aluminum hydroxide of an amorphous structure extracted from an acid solution of aluminum salt Al (OH) ₃ , with a total reagent consumption of 3250 mg / dm ³ . The consumption of this reagent in the first dosage was 812.5 mg / dm, i.e. It was equal to 25% of the total consumption, which ensured the set efficiency of water purification from sulfate ions to MPC for fishery purposes.

Additional studies have shown that a further increase in more than 25% of the reagent consumption in the first dosage does not significantly increase the cleaning rates, and when the first dose is increased to 50%, a decrease in the cleaning parameters is observed.

Thus, the use of fractional dosing of aluminum hydroxide of an amorphous structure extracted from an acid solution of aluminum salt allows to reduce the consumption of both reagents with an appropriate flow of two limes, namely: the consumption of aluminum hydroxide of an amorphous structure Al (OH) ₃ by 28-31%, the flow rate CaO - by 10-25%.

The total consumption of these reagents is due to both the composition of the water and the limited requirements for the residual concentration of sulfate ions in purified water (below 100 mg / dm ³ or below 500 mg / dm ³ ).

With a residual concentration of SO ₄ ^{2 -} ≤100 mg / dm ^{3, the} water hardness does not exceed 1 mEq / dm ³ , which allows us to recommend it for use in housing and communal services technology instead of water used for this purpose from sources of underground and surface water bodies That along with environmental efficiency will provide an additional definite increase in the economic indicators of treatment facilities.

The use of fractional dosing of the reagent - aluminum hydroxide of amorphous structure in the indicated water treatment modes with neutralization to pH = 12.2-12.4 before the introduction of the reagent and additional neutralization to pH = 12.7-13.0 after the reagent is added to existing and newly designed sewage treatment plants will allow the implementation of wastewater treatment with a high concentration of Na ₂ SO ₄ to a regulated MPC for discharging treated water into water bodies of appropriate water use, as well as for use in the technology of housing and communal services economy, which will favorably affect the economic indicators of treatment facilities.

Table - Indicators of wastewater treatment with a high concentration of Na ₂ SO ₄ from sulfate ions during single and fractional dosing of aluminum hydroxide of an amorphous structure extracted from an acid solution of aluminum salt into wastewater

Experience Series No. The concentration of ions in the source water, mg / DM ³ Reagent dosing regimen Al (OH) ₃ The reagent consumption, mg / DM ³ Specific consumption of Al ³⁺ mg per 1 mg SO ₄ ^2- The consumption of CaO for the purification of wastewater from SO ₄ ^2- , mg / DM ³ The mixing time of the wastewater with the reagent during purification from SO ₄ ^2- , min. The residual concentration of SO ₄ ^2- in purified water, mg / DM ³ Na ⁺ SO ₄ ^2- Al (OH) ₃ in terms of Al ³⁺ Al (OH) ₃ Cao Total including due to Na ⁺ ions one 2 3 four 5 6 7 8 9 10 eleven 12 one 1384.5 8100 2890 disposable 3620 1250 0.154 4800 5,0 5,0 410 2 1384.5 8100 2890 fractional: 250 - - - 2,5 - - -first dosage-10% -second dosage -90% 2250 2,5 Total: 2500 865 0.107 4300 5,0 5,0 420 3 1384.5 8100 2890 disposable 4500 1557 0.192 6000 5,0 5,0 40 four 1384.5 8100 2890 fractional: 320 - - - 2,5 - - - first dosage 10% - second dosage - 90% 2930 2,5 Total: 3250 1124 0.139 4500 5,0 5,0 20-80 5 1384.5 8100 2890 fractional: 280 - - - 2,5 - - - first dosage 8% - second dosage - 92% 3220 2,5 Total: 3500 4800 5,0 5,0 one hundred 6 1384.5 8100 2890 fractional: 812.5 - - - 2,5 - - - first dosage 25% - second dosage - 75% 2437.5 2,5 Total: 3250 4500 5,0 5,0 95

Information sources.

1. Sargsyan N.S. et al. Wastewater treatment from sulfate ions / J. "Non-ferrous metals", 1989, No. 11, p. 51, 52.

2. Patent for the invention of the Russian Federation No. 2236384 "Method for the treatment of wastewater from sulfate ions." Publ. 09/20/2004, Bull. 26.

3. A guide to the solubility of salt systems. L .: Goskhimzdat, 1954, volume II, p. 1268.

Claims (2)

1. The method of purification of wastewater from sulfate ions, based on the neutralization of wastewater and the introduction of a reagent - aluminum hydroxide of an amorphous structure extracted from an acidic solution of aluminum salt, characterized in that before the introduction of the reagent - aluminum hydroxide of an amorphous structure extracted from an acidic solution of aluminum salts, waste water is neutralized to a pH of 12.2-12.4 and clarified, and the reagent is aluminum hydroxide of amorphous structure, extracted from an acidic solution of aluminum salt, is introduced fractionally, with the first dose being 10-25%, and after mixing it with water, the remainder of the reagent, aluminum hydroxide of amorphous structure, is introduced and then water is neutralized to pH 12.7–13.0 with continuous stirring until the precipitation of SO ₄ ^2– ions is completed in the solid phase. 2. A method according to claim 1, characterized in that the cleaned of SO ₄ ^2- water after separation from the sludge is subjected to air bubbling or by sparging CO _2.