RU2747974C2 - Method for waste water treatment from sulfate ions and heavy metals - Google Patents

Abstract

FIELD: treatment of water.SUBSTANCE: invention relates to methods of treatment of waste, mine and natural waters from sulfate ions and heavy metal ions and may be used for treatment of waste water in various lines of industry, including mining and chemical industries, as well as for treating galvanic waste at machine building plants. The waste water is neutralized by lime to pH of no more than 11.7. Calcium carbonate is introduced with mass ratio of calcium carbonate to lime of 1:3 to 8. It is processed using aqueous suspension of high alumina cement wherein processing with high alumina cement is conducted with pH of the aqueous suspension of 12 to 12.7. It is then deposited with a highly polymerized anionic flocculant and the residue is separated.EFFECT: technical result of the invention is the increase of waste water treatment level leading to a pollution rate not exceeding the maximum concentration limit of fish farms including pollution with nickel ions (no more than 0.01 mg/dm3).3 cl, 1 tbl

Description

The invention relates to methods of purification of waste, mine and natural waters (hereinafter referred to as SW) from sulfate ions and heavy metal ions and can be used for cleaning waste water in various industries, including mining, chemical, and for cleaning galvanic wastewater from machine-building plants.

One of the most effective methods of water purification from pollutants is reagent purification. Large particles of pollutants precipitate rather quickly under the action of gravity, and coagulation or flocculation is used to precipitate finely dispersed particles with a size of less than 10 microns. The use of milk of lime (Ca (OH) ₂ ) as a coagulant is due to the fact that Ca is an active metal that displaces heavy metals from soluble compounds, converting them into insoluble ones, and also precipitates various salts, including sulfates, phosphates, chlorides ... Moreover, such an amount of milk of lime is required so that all the necessary reactions take place with a minimum excess of it. (Milonov L.V. Wastewater treatment of non-ferrous metallurgy enterprises. - M .: metallurgy, 1971, p. 100).

There are a number of methods for purifying wastewater from sulfate ions as well as from accompanying heavy metal ions by neutralizing water to pH 9.5-12.5 with milk of lime and processing with aluminum-containing salts AlCl ₃ , Al ₂ (OH) ₅ Cl, NaAlO ₂ .

The use of chlorine-containing salts of aluminum or sodium aluminate as a reagent for the purification of wastewater from sulfate ions inevitably leads to secondary pollution of effluents with chlorine or sodium ions, exceeding the maximum permissible concentration of which entails a toxic effect on animals and plant organisms and, accordingly, has a negative effect on human health ...

A known method of purification of acidic wastewater containing ions of heavy metals and sulfates, including a two-stage precipitation using milk of lime in the first stage, alkalinization to pH 6.5-7, followed by treatment of the resulting suspension with sodium carbonate to pH 9.0-9.5 (RU No. 201013, C02F 1/62, pr. 02.08.1991).

The known method of wastewater treatment, which also includes a two-stage sedimentation. First, the wastewater is treated with milk of lime to pH 7.5-8.0, then after separating the precipitated sediment, barium carbonate is introduced into the clarified water and the resulting suspension is kept with stirring until it is converted into barium sulfate. After the completion of the exchange reaction, the barium sulfate precipitate is separated from the water and used, for example, as a weighting agent for drilling fluids (RU 2448054, C02F 1/62, etc. 07/08/2010). The use of barium carbonate makes it possible to reduce the residual salinity of the purified water due to the exchange reaction:

CaSO _{4 (solution)} + BaCO _{3 (solid precipitate)} = BaSO _{4 (solid precipitate)} + CaCO _{3 (solid precipitate)}

The water purified by the above methods does not comply with modern standards established in the Russian Federation for discharge into fishery water bodies in terms of the content of heavy metals and sulfates.

Closest to the proposed invention is a method for purifying wastewater from sulfates and ions of heavy metals, in which initially wastewater is neutralized with milk of lime to pH 10.5 ÷ 12.0, then treated with alumina cement (HC) in the form of 5 ÷ 12.5% aqueous suspension, taken in a mass ratio to the content of sulfates 1: 0.27-0.34, and then precipitated with a flocculant based on highly polymerized polyacrylamide, the resulting precipitate is separated by known methods.

This method allows to purify mine waters to a concentration of sulfate ions of no more than 100 mg / dm ³ , and to achieve the MPC values of _{fish farms} for the content of most heavy metals, such as iron, copper, zinc, etc. However, the known method does not ensure the extraction of nickel ions up to established MPC _{fish farm.} (0.019 mg / dm ³ at the established MPC of the _{fish farm} not more than 0.01 mg / dm ³ ).

The technical objective of the present invention is to increase the degree of wastewater treatment, including the content of nickel ions.

The specified technical result is achieved by the fact that in the method of purifying wastewater from ions of sulfates and heavy metals, which is characterized by the fact that it is first neutralized with lime, treatment is carried out with a 5-12.5% aqueous suspension of high-alumina cement, precipitated with a highly polymerized flocculant and the sediment is separated, according to the proposed the invention, before treatment with alumina cement, calcium carbonate is introduced into the water system in a mass ratio to the original lime of 1: 3-8, and the treatment with high-alumina cement is carried out at a pH value of the water system of 12-12.7, and high-alumina cement is used in a mass ratio to sulfate ions 1: 0.2-0.34.

Preferably, natural limestone is used as a source of calcium carbonate.

Preferably, the light portion of the aqueous system is acidified with carbon dioxide to a pH of 6.5-8.5.

The following are examples of mine water purification by the claimed method.

Working reagents used:

• Limestone (finely dispersed chalk);

• Building lime (slaked calcium), grade. 1 in accordance with GOST 9179-77.

• high-alumina cement (VHC) grade "CEMBOR-73 TU 14-194-215-97.

• Flocculant Flopam AN934 is a highly polymerized anionic flocculant.

• Carbon dioxide (liquefied CO ₂ )

Example 1

To 1 liter of mine water, with the established pH values and the concentrations of the polluting ions contained, 10% aqueous lime-limestone suspension was added with stirring, containing 36.2 g of dry matter, including 3.12 g of dry lime (calcium oxide) and 0 , 5 g of dry chalk finely dispersed (calcium carbonate) (mass. Ratio 6.25: 1), while the pH of the aqueous system reaches 12.5. After adjusting the pH to 12.5, 45 g of a 10% aqueous suspension of VHC is added with stirring (the mass ratio of VHC to the contained sulfate ions is 1: 0.25). The resulting reagent mass is stirred with an overhead stirrer for 1.5-2 hours at 1400 rpm. The formation of practically insoluble in water basic heavy metal carbonates and calcium hydrosulfoaluminate occurs. In order to separate the water treated with reagents into thickened and clarified parts, 0.3 ml is added with vigorous stirring. 0.1% flocculant solution. The resulting precipitate is separated from the clarified water by filtration.

Filtrate with pH = 12.5 is neutralized to pH = 6.5 ÷ 8.5 with carbon dioxide (liquefied CO2).

During the treatment with carbon dioxide, calcium carbonate is formed, which is separated by settling and filtration. Precipitated calcium carbonate can be used as a reagent instead of limestone.

Examples 2-5 the process was carried out analogously to example 1, with a different mass ratio of lime and limestone.

Example 6 (comparative). The process was carried out similarly to example 1, but without adding limestone.

The results of the tests performed are shown in the table.

As can be seen from the table, the purification of water containing sulfates and heavy metal ions by the proposed method can significantly reduce the content of these polluting components, incl. and the content of nickel ions to an indicator of not more than 0.01 mg / dm ³ .

An increase in the amount of added calcium carbonate above and a decrease below the stated range is impractical, since leads to an increase in the residual content of ions of some heavy metals (nickel, copper, zinc) above the maximum permissible concentration of _{fish farms} .

Lime and calcium carbonate can be introduced into the aqueous system, either in the form of an aqueous suspension or in a dry solid form. Limestone can be introduced either after lime treatment or together with it.

The best indicators for purification from sulfate ions are observed by treatment with high-alumina cement at a pH of the water system of 12-12.7 and a mass ratio of alumina cement to sulfate ions of 1: 0.2-0.34.

Claims (3)

1. A method of purifying wastewater from ions of sulfates and heavy metals, characterized by the fact that it is first neutralized with lime, treated with a 5-12.5% aqueous suspension of high-alumina cement, precipitated with a highly polymerized anionic flocculant and separating the sediment, characterized in that before treatment with alumina cement calcium carbonate is introduced into the water system in a mass ratio to lime of 1: 3-8, and the treatment with high-alumina cement is carried out at a pH value of the water system of 12-12.7, and high-alumina cement is used in a mass ratio to sulfate ions of 1: 0.2 -0.34. 2. The method according to claim 1, characterized in that natural limestone is used as a source of calcium carbonate. 3. The method according to claim 1, characterized in that after separation of the sediment, the clarified part of the aqueous system is acidified with carbon dioxide to a pH of 6.5-8.5.