SU1724595A1 - Method of cleaning sewage from heavy metals - Google Patents

Abstract

The invention relates to methods for purifying industrial wastewater, in particular, from heavy non-ferrous metals (copper, mercury, lead) by precipitating them with sulphide-containing reagents and allows for simplifying the process and increasing the degree of purification. In order to carry out the process, a reagent, a solution of sodium hydrosulfide with a sulfide sulfur content of 0.5-1.1 g / l, prepared using raw water neutralized to a pH of 6-7, is introduced into waste water containing heavy metals. The method allows to simplify the process by performing in one stage and reducing the residual content of heavy metals in water to the level of the maximum permissible discharge. 1 tab. Yo

Description

The invention relates to methods for treating industrial wastewater, in particular, from heavy metals (copper, mercury, lead, etc.) by treating them with sulphide-containing reagents and separating the resulting sludge.

A known method of purification of dilute solutions from mercury by treating them with sulphide-containing reagents at pH 6.3- 6.5 with the addition of 30 g / l of NaCl 1.

The disadvantages of this method are the presence of a large salt background (30 g / l NaCI), which is unacceptable when water is discharged into drinking and fish-producing water bodies, as well as the absence of deep cleaning, since the residual mercury content in the solution is many times higher than the sanitary standard. For example, with an initial mercury concentration of 5 m / l, a pH of 6.30, and an added amount of

precipitator (No. 28), equal to 1.6 of stoichiometric, the residual content of mercury in the solution after 0.5 h is 0.80 mg / l, after 2 h, 0.05 mg / l. Therefore, for a deeper purification of the solution from mercury after the separation of the main sulphide of mercury sulphide, it is additionally passed through sorption or ion exchange materials, which significantly complicates the cleaning process.

A known method of purification of acid wastewater from arsenic and heavy non-ferrous metals by treating them with water-soluble sulfides, followed by the precipitating of these elements with alkali in the form of hydroxides at pH 8-9 and separating the resulting precipitate 2.

The disadvantages of this method are the complexity of the process, consisting in fractional precipitation and the need for V4 U -N SL IO SL

the following acidification of the discharge water when discharging it into water bodies. In addition, this method does not allow deep cleaning of solutions with a low concentration of heavy non-ferrous metals.

For example, when cleaning diluted industrial solutions (pH 2.25) containing, mg / l: Cu 30.0; Nd 0.25; Pb 1.60, according to the described method, the residual amount of heavy non-ferrous metals in solution is mg / l: Cu 0.20; ND 0.02; Pb 0.06 suspended particles of 3.3 mg / l, which exceeds the maximum permissible discharge (MPD) for fish farm water bodies. The MPT for these metals is mg / L: Cu 0.0002; Nd 0.001; Pb 0.02 and suspended particles of 3.85.

The closest to the proposed method is the treatment of waste water from heavy non-ferrous metals by two-stage treatment with chemical reagents containing sulphide ions at a pH of 1.0-2.5 and then adjusting the pH to 6.5-7 and separating the precipitates by each stage 3.

For example, when cleaning diluted industrial solutions (pH 2.7), containing, mg / l: Cu 30.0; Nd 0.25; Pb 1.6 according to a known method, the residual content of heavy non-ferrous metals is equal to, mg / l: Cu 0.01; Nd 0.01; Pb 0, Ob particles suspended 25 mg / l (after 2-4 hours of settling).

The disadvantages of this method are the complexity of the purification process, consisting in the multistepness of the method, the need to bring the pH to a certain value and the separation of the sediment of heavy non-ferrous metals at each stage, the need to repeatedly adjust the amount of alkali added to establish a certain pH value and the amount of sulfide-containing reagent, and the absence of deep (before PDS) cleaning.

The purpose of the invention is to simplify the process and increase the degree of purification.

The goal is achieved by the fact that wastewater treatment is carried out with a solution of sodium hydrosulfide (NaHS) with a sulfide sulfur content of 0.5-1.1 g / l prepared on the original wastewater neutralized to a pH of 6.5-7.5.

A solution for precipitating heavy metals is obtained by diluting technical sodium hydrosulfide (e.g. MRTU 6-08-113-69) with wastewater from pH 6.5-7.5 to a content of 0.5-1.1 g / l sulfide sulfur. The stoichiometric amount of this solution is gradually poured into sewage with a pH of 1.5-3.0 and vigorously stirred for 5-10 minutes (its amount is judged by the potential jump

silver sulfide electrode that reacts to HS ions). After this drain water is neutralized with an alkali to a pH of 6.5-7.5. The precipitate of heavy metal sulphides is separated in settling tanks. A portion of the wastewater after neutralization with alkali to a pH of 6.5-7.5 without separating the precipitate is used to prepare a new portion of the sodium hydrosulfide solution for

0 precipitation of heavy metals.

When the sodium hydrosulfide content in the solution is less than 0.5 g / l of sulfide sulfur, very dilute drainage water is obtained, which increases the load on the equipment and the precipitation time of heavy metal sulfides. As a result, the completeness of wastewater treatment is reduced, and unreacted sodium hydrosulfide decomposes with the release of hydrogen sulfide into the atmosphere.

0 When the content in the solution is more than 1.1 g / l of sulfide sulfur, local supersaturation of the discharge water with sodium hydrosulfide occurs, which decomposes to release hydrogen sulfide into the atmosphere, which is unacceptable according to safety requirements. The preparation of a solution of sodium hydrosulfide on overflow waters with an H of less than 6.5 is accompanied by a noticeable decomposition of sodium hydrosulfide and the release of hydrogen sulphide into the atmosphere. In the case of pH 7.5, the complete purification of drainage water from heavy metals by MPD is not achieved. In addition, there is an unjustified alkali overrun to achieve, 5.

5 Neutralization of wastewater to a pH of 6.5-7.5 after treatment with sodium hydrosulfide solution allows precipitation of hydroxides of aluminum, iron, nickel and other metals, if they are contained in a solution, to increase the degree of purification from heavy metals and bring the pH of the drain waters to the PDS.

The implementation of the proposed method of purification of waste water from heavy metals

5 is illustrated by the following examples.

Example 1.K4l of sulphate solution of wastewater of electroplating (pH 2.25), containing, mg / l: copper 38; mercury 0.88; lead 0.74 with stirring

0 152 ml of sodium hydrosulfide (NaHS) containing 0.5 g / l of sulphide sulfur are added. A sodium hydrosulfide solution is prepared by diluting 0.7 ml of technical sodium hydrosulfide with a content of 230 g / l.

5 sulfide sulfur 151.3 ml of waste water with a pH of 6.5. The amount and end of the influx of sodium hydrosulfide is judged by the jump in the potential of the silver sulfide electrode. Then the solution with the precipitating reagent is stirred for 7 minutes and neutralized to pH

6.5% NaOH solution with a concentration of 27%, adding it in the amount of 14.5 ml. After stirring for 7 minutes, the solution is allowed to stand for 120 minutes. The precipitate is separated and the solution is analyzed for heavy metal content and suspension. According to the obtained results, the purified solution contains, mg / l: copper is not detected; mercury 0.001; lead 0,002, suspended solids 3,4.

The remaining examples are carried out analogously to example 1. The results obtained are tabulated.

Thus, the proposed method of purification of waste water from heavy metals is essentially simple, since it is carried out in one stage and can be implemented

0

five

in continuous mode. It allows for deep treatment of wastewater with a low content of heavy metals, the amount of which in the purified solution is lower than the MPT,

Claims (1)

Claims A method for purifying waste water from heavy metals, including treating reagent solutions containing sulfide ions and separating the precipitate formed, characterized in that, in order to simplify the process and increase the degree of purification, the treatment is carried out with a sulfide sulfur content 0 , 5-1.1 g / l, prepared on the original wastewater, neutralized to a pH of 6.5- 7.5.