RU2233802C1 - Method of cleaning waste water from sulfate ions - Google Patents

Abstract

FIELD: cleaning of waste and natural water from sulfate ions; mining and chemical industries; cleaning galvanic runoffs of industrial plants.

SUBSTANCE: proposed method is based on neutralization of sulfate-containing waste water and introduction of reagent; prior to introducing reagent, water is subjected to neutralization to pH=8.5-12.1; used as reagent is mixture of lime with aluminum hydroxide of amorphous structure extracted from acid solution of aluminum salt and metered into neutralized water at subsequent additional neutralization of runoffs to pH=12.2-12.8; then water being cleaned is stirred to completion of settling of SO $\genfrac{}{}{0ex}{}{\text{2-}}{\text{4}}$ to solid phase. It is good practice to use mixture of line with aluminum hydroxide at ratio of CaO:Al(OH)₃ no less than 1:1.1. Proposed method ensures cleaning of waste water from sulfate ions to concentration not below 100 mg/cu dm stipulated by maximum permissible concentration.

EFFECT: reduction of cleaning time; enhanced efficiency.

2 cl, 1 tbl, 5 ex

Description

The invention relates to methods for treating wastewater and natural waters from sulfate ions and can be used for purification in various industries, including mining, chemical, and for cleaning the galvanic drains of engineering plants.

There are a number of methods for treating wastewater from sulfate ions by neutralizing water to a pH of 9.5-12.35 with 5-10% lime milk and using aluminum-containing salts AlCl ₃ , Al ₂ (OH) ₅ Cl, NaAlO ₂ as a reagent [1, 2] .

The use of chlorine salts of aluminum or sodium aluminate as a reagent for wastewater treatment from sulfate ions inevitably leads to secondary pollution of effluents with chlorine or sodium ions, the excess of which results in toxic effects on animals and plant organisms and, accordingly, has a negative effect on human health .

The closest method of the same purpose to the claimed invention according to a combination of features is the use of aluminum metal [3]. The essence of this method is as follows: upon contact of waste water containing sulfate ions with metallic aluminum, the formation of basic sulfates, then aluminum sulfate. With complete reaction of sulfate ions with aluminum, the pH of the medium reaches 3.7-3.8. Next, milk of lime is added to a pH of 11.5, and with stirring, the formation of NAO (calcium sulfoaluminate) and deep purification from sulfate ions occur. When using this method, additional pollution of the effluent with chlorine or sodium ions is eliminated.

The reasons that impede the achievement of the technical result indicated below is the use of expensive metallic aluminum, which excludes the possibility of widespread adoption, especially for large volumes of highly contaminated wastewater.

The objective of the present invention is to reduce the cost of technology while providing deep cleaning. The technical result is a reduction in the time of wastewater treatment from sulfate ions to a concentration below 100 mg / dm ³ , regulated by MPC for discharge of water into fishery bodies.

The problem is achieved in that in the method of purifying wastewater from sulfate ions, which consists in neutralizing a sulfate-containing wastewater and introducing a reagent, according to the invention, before introducing a reagent, the wastewater is neutralized to pH 8.5-12.1, and a mixture of lime and aluminum hydroxide is taken as a reagent amorphous structure extracted from an acid solution of aluminum salt, and dosed in neutralized water, followed by neutralization of the effluent to a pH of 12.2-12.8, and then the purified water is mixed until the deposition of SO $\genfrac{}{}{0ex}{}{\text{-2}}{\text{4}}$ in the solid phase.

It is advisable to take a mixture of lime with aluminum hydroxide of an amorphous structure extracted from an acid solution of aluminum salt in a ratio of CaO: Al (OH) _{3 of} at least 1: 1.1.

The use as a reagent of a mixture of lime with aluminum hydroxide of an amorphous structure extracted from an acidic solution of aluminum salt, in combination with the proposed sequence of operations, allows not only to achieve high quality of purified water and to exclude re-contamination of it with chlorine and sodium ions, but to significantly reduce processing time (mixing ) Amorphous aluminum hydroxide, extracted from an acidic solution of aluminum salt, is a cheaper reagent for the treatment of wastewater from sulfate ions compared to metal aluminum, which makes it possible to reduce the cost of purification technology to achieve high quality water, which ensures discharge of water into fishery bodies.

The analysis of the prior art by the applicant, including a search by patent and scientific and technical sources of information and identification of sources containing information about analogues of the claimed invention, allowed to establish that the applicant did not find a source characterized by features identical to all the essential features of the claimed invention. The definition from the list of identified analogues of the prototype, as the closest in the totality of the features of the analogue, allowed us to establish a set of significant distinguishing features in relation to the technical result perceived by the applicant in the claimed method set forth in the claims.

Therefore, the claimed invention meets the condition of "novelty."

To verify the compliance of the claimed invention with the condition "inventive step", the applicant conducted an additional search for known solutions in order to identify features that match the distinctive features of the claimed method from the prototype. The search results showed that the claimed invention does not follow explicitly from the prior art for the specialist, since the influence of the transformations provided for by the essential features of the claimed invention is not revealed from the prior art as determined by the applicant.

Therefore, the claimed invention meets the condition of "inventive step".

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

Wastewater containing sulfate ions is neutralized to pH 8.5-12.1 and a pre-prepared mixture of lime with aluminum hydroxide of amorphous structure extracted from an acidic solution of aluminum salt is introduced. In this case, the mixture is taken in a ratio of CaO: Al (OH) _{3 of} at least 1: 1.1 and dosed into neutralized water in the form of a paste. Then neutralize the treated water with a lime solution or lime paste to a pH of 12.2-12.8 and then mix it until the precipitation of SO is completed. $\genfrac{}{}{0ex}{}{\text{-2}}{\text{4}}$ .

The processing time (mixing time) and the consumption of aluminum hydroxide are determined by the composition of water and the concentration of sulfate ions in it, the parameters of which are presented in the table.

Purified from sulfate ions water with a pH of 12.3-12.6 after separation of the precipitate is subjected to sparging with air or sparging in the presence of CO ₂ to normalize the pH to pH 8.5.

As experiments have shown, when neutralizing wastewater before introducing the reagent to a pH of less than 8.5, the task is not achieved, because no precipitation of polluting cations in wastewater occurs. When water is neutralized to a pH greater than 12.2, dissolution of the precipitated hydroxides of a number of cations begins, as a result of which the task of water purification will also not be achieved.

The use of a mixture of lime with aluminum hydroxide of an amorphous structure in a ratio of less than 1: 1.1 does not allow to reduce the time of water treatment. Studies have shown that with an increase in the ratio of CaO: Al (OH) ₃ , the treatment time is reduced, but the volume of sediment increases.

The proposed method provides a deep purification of effluents from sulfate ions to a concentration below 100 mg / dm ³ , regulated by MPC for discharging water into fishery ponds, and can significantly reduce the processing time in comparison with known solutions.

Verification of the proposed method for wastewater treatment from sulfate ions was carried out on natural (mine) and artificial water.

Example 1. Wastewater treatment from sulfate ions was carried out on natural (mine) water with a pH of 4-8 and an ion concentration, mg / dm ³ :

Wastewater was neutralized with milk of lime to pH 11 to precipitate contaminating cations. Then, 433.5 mg / dm ³ (in terms of dry) of aluminum hydroxide of amorphous structure extracted from an acidic solution of aluminum salt with a moisture content of 86.3% was dosed into neutralized water.

At the same time, the pH of the water being purified decreases to 10.5, and to transfer the sulfate ions into the precipitate, the water is additionally limed to pH 12.2-12.8 with continuous stirring for 5 hours. After that, the residual content of SO ions $\genfrac{}{}{0ex}{}{\text{-2}}{\text{4}}$ amounted to 90 mg / dm ³ and the concentration of Cl ^- ions (17 mg / dm) remained unchanged.

As you can see, the purified water meets the MPC norm for the discharge of water into fishery ponds, and additional pollution with chlorine ions does not occur.

Example 2. Mine water with a concentration of polluting components specified in example 1 was subjected to neutralization with milk of lime to precipitate polluting cations. Then, a mixture of CaO and Al (OH) _{3 was} dosed into this neutralized water (the consumption of Al (OH) ₃ in terms of dry matter was 433.5 mg / dm ³ ) in a ratio of 1: 2.4, which was a paste. The water thus treated with a pH of 11.3 was further subjected to additional calcification to a pH of 12.8 with continuous stirring for 3 hours. Residual concentration of sulfate ions was reduced to 96 mg / dm ^3, which is correct MAC for discharge water into reservoirs fishery, and the content of Cl ions ^- remained unchanged (17 mg / dm ^3).

Example 3. Artificial water with ion concentration, mg / DM ³ :

It was preliminarily neutralized with milk of lime to pH 12.1, then a paste of a mixture of CaO and Al (OH) _{3 was} dosed into it in a ratio of 1: 1.2 at a flow rate of Al (OH) of ₃ 866 mg / dm ³ . Further, the water was subjected to additional liming (de-neutralization) to a pH of 12.8. After 3 hours of stirring, the concentration of SO ₄ ions was 96 mg / dm ³ .

As in the previous examples, the purified water complies with the MPC norm for the discharge of water into fishery reservoirs.

Example 4. With the initial data specified in example 3, the artificial water was purified with a flow of hydroxide of an amorphous structure extracted from an acidic solution of aluminum salt (in the ratio of CaO and Al (OH) ₃ as 1: 4.77) in an amount of 1750 mg / dm ³ . As a result, after 15 minutes, the residual concentration of sulfate ions was 80 mg / dm ³ .

Example 5. Mine water with a pH of 4.0 and an ion concentration, mg / dm ³ :

It was neutralized with milk of lime to pH 11 to precipitate contaminating cations. After that, a paste was dosed into neutralized water, which was a mixture of lime with aluminum hydroxide of an amorphous structure with a moisture content of 94%. The hydroxide consumption of 2.5 g / dm ³ at a ratio of CaO and Al (OH) ₃ , as in Example 2. After de-neutralization to pH 12.8 and continuous stirring for 30 minutes, the residual sulfate ion content decreased to 77 mg / dm ³ .

As you can see, the purified water meets the MPC norm for the discharge of water into fishery ponds, and additional pollution with chlorine ions does not occur. The use of a mixture of lime with aluminum hydroxide of amorphous structure allows to reduce the time of deposition of sulfate ions into the solid phase by 1.7-12.5 times, which accordingly reduces the technological process of wastewater treatment in comparison with the use of an amorphous structure extracted from an acid solution of aluminum salt as an aluminum hydroxide reagent .

The proposed set of features made it possible to achieve deep purification of wastewater from sulfate ions to a concentration below 100 mg / dm ³ , regulated by MPC for discharge of water into fishery reservoirs, as well as to eliminate its additional pollution with chlorine or sodium ions. The use of a mixture of lime with aluminum hydroxide of an amorphous structure extracted from an acid solution of aluminum salt as a reagent makes it possible to significantly reduce the cost of wastewater treatment from sulfate ions and reduce processing time, which will allow the proposed method to be used especially for large volumes of highly contaminated wastewater.

The use of a CaO mixture with aluminum hydroxide of amorphous structure extracted from an acid solution of aluminum salt at existing and newly designed treatment facilities of plants, mines, and mines makes it possible to realize the treatment of wastewater from sulfate ions to MPC regulated for water discharge into fishery water bodies at no additional capital cost. destination.

Claims (2)

1. The method of purification of wastewater from sulfate ions, which consists in neutralizing sulfate-containing wastewater and introducing a reagent, characterized in that before introducing the reagent, the wastewater is neutralized to pH 8.5-12.1, and a mixture of lime and hydroxide is taken as a reagent aluminum of an amorphous structure, extracted from an acid solution of aluminum salt, and dosed in neutralized water, followed by neutralization of the effluent to a pH of 12.2-12.8, and then the purified water is mixed until the deposition of SO $\genfrac{}{}{0ex}{}{\text{2-}}{\text{4}}$ in the solid phase. 2. The method according to claim 1, characterized in that the mixture of lime with aluminum hydroxide of an amorphous structure extracted from an acid solution of aluminum salt is taken in a ratio of CaO: Al (OH) _{3 of} at least 1: 1.1.