RU2438999C1 - Method of neutralising underspoil acid sulphate-containing effluents - Google Patents

Abstract

FIELD: process engineering. ^ SUBSTANCE: invention may be used in mining. In compliance with this method, underspoil acid sulphate-containing effluents are neutralised by 5%-lime milk to pH 9.4-9.5. Then, added are anionic flocculant in concentration of 5-8 mg/l and pyrite final tailings in concentration of 2.5-10 g/l. Produced mix is mixed and settled. After settling, water is divided into two flows. One flow is directed for tertiary treatment before discharge into water structures. Another flow is directed for irrigation of spoils for partial neutralisation of underspoil waters to form circulation flow. Degree of water circulation for spoil irrigation purposes makes 20-30%. ^ EFFECT: reduced consumption of lime milk and amount of formed sediments. ^ 2 cl, 1 dwg, 3 tbl, 2 ex

Description

The invention relates to the field of neutralization of acidic industrial wastewater, in particular to methods for neutralizing basement waters of mining enterprises.

It is known that to neutralize wastewater containing sulfate ions, any alkaline reagent is used, but most often lime, milk of lime, calcium and magnesium carbonates.

Calcium sulfate (gypsum) formed as a result of neutralization crystallizes from dilute solutions in the form of CaSO ₄ · 2H ₂ O. The solubility of this salt in water at a temperature of 0-40 ° C ranges from 1.76 to 2.11 g / L. A significant drawback of the method of neutralizing lime is the formation of a supersaturated gypsum solution, the release of which can last several days, as well as a large volume of sediment, which is a suspension of colloidal particles. The sludge is extremely difficult to compact and dehydrate.

A known method of wastewater treatment, involving the combined use of alkaline reagents and flocculants / Yakovlev S.V., Karelin Y.A., Laskov Yu.M., Voronov Yu.V. Industrial wastewater treatment. - M: Stroyizdat, 1985 .-- 335 s. (see p.104) /. The use of this method is explained not only by the relatively high rate of sedimentation, but, unlike coagulants, by the lack of salinization of the treated water, since the entire flocculant is recovered with sediment. In addition, a simple and reliable sedimentation method requires the selection of the flocculant most suitable for this type of wastewater / Aksenov V.I., Ladygichev M.G., Nichkova I.I. and others. Water management of industrial enterprises. Reference edition. Book 1. - M.: Heat engineer, 2005. - 640 p. (see p. 322-323) /.

The closest in technical essence and the achieved result to the claimed one is a wastewater treatment method in which acidic sulfate-containing wastewaters are neutralized with milk of lime and precipitated suspended particles are precipitated in the presence of a flocculant. Neutralization is carried out with 5% milk of lime to a pH of 9.4-9.5, then anionic flocculant is introduced at a concentration of 5-8 mg / l and pyrite dump tailings of mining and processing industry at a concentration of 2.5-10 g / l, after which is mixed and defended. As the flocculant, it is preferable to use the anionic flocculant Floerger AN 905 SH. Used pyrite tailings should preferably contain -38% Fe and -36% S. The invention provides neutralization of sulfate-containing water, the use of which reduces the amount of sludge, which simplifies the further dewatering and disposal of sludge / Patent for the invention No. 2355647, IPC C02F 1 / 66, publ. 05/20/2009. Bull. No. 14 /.

The disadvantage of this invention is the high consumption of milk of lime to neutralize wastewater, the formation of a large amount of sediment.

The objective of the invention is to reduce the consumption of milk of lime, reducing the amount of precipitation formed.

This problem is solved by the fact that subsoil acid sulphate-containing wastewater is neutralized with 5% milk of lime to a pH of 9.4-9.5, then anionic flocculant is introduced at a concentration of 5-8 mg / l and pyrite dump tailings of mining and concentration production in concentration 2.5-10 g / l, after which they are mixed and defended, according to the invention, the resulting water is divided into two streams, one of which is sent for purification before discharge into water bodies, and the other is directed to irrigate the dumps to partially neutralize the waste water, image I recycle stream. The degree of recirculation of water used for irrigation of dumps is 20-30%.

The drawing shows a flow chart of wastewater treatment with a water cycle irrigation dumps.

The technological scheme contains a grate 1 for removing debris, a sand trap 2 for extracting sand fractions, a settling tank with a flocculation chamber 3, a clean water tank 4. The treatment plants are equipped with a reagent farm 5 with a lime milk metering pump, a reagent farm 6 with a flocculant metering pump and a reagent farm 7 with a metering pump for pyrite tailings. Sand fractions from the sand trap 2 are removed to the sand pads 8, equipped with a drainage water removal system using the pump 9. Sludge from the sump 3 is removed to the sludge trays 3, equipped with a drainage water removal system using the pump 11.

The neutralized water is pumped from the clean water tank 4 to the irrigation of rock dumps 13 using a pump 12. Under the dump water, it is discharged through a tray 14 to a reservoir 15, from where it is pumped to a treatment plant.

The method of neutralizing basement acid sulphate-containing wastewater is implemented as follows. Subsurface water with a pH of 3.0-3.2 by means of a tray 14 flows by gravity to the accumulator 15, from where it is pumped to the grates 1 to remove large debris and to the sand trap 2 to remove sand fractions. Wastewater neutralization is carried out with 5% milk of lime supplied to the pipeline using reagent farm 5. Flocculant is fed into the pipeline using reagent farm 6 and pyrite dump tailings using reagent farm 7. Metal hydroxides are formed in the flocculation chamber of settler 3 which in an alkaline environment become insoluble and form coagulant flakes. Organic flocculant molecules enlarge the coagulant flakes, on the surface of which colloidal particles of gypsum are sorbed. Pyrite tails act as a weighting agent, which helps to accelerate the deposition of suspended solids. Sludge from the sump 3 is periodically removed to the sludge pads 10 for dehydration and further disposal.

The water purified in the sump 3 is supplied to the clean water tank 4. This water has an alkaline reaction pH 9.4-9.5, contains sulfates and heavy metals in a concentration exceeding the permissible standards for discharge into water bodies, therefore, it needs to be treated. At the outlet of the clean water tank, two streams are formed, one of which is sent for purification before discharge into water bodies, and the other is directed to irrigate the dump 13 using pump 12 (recirculation stream). This measure is caused by the fact that as a result of long-term monitoring of the basement waters, it was found that with a decrease in the pH of the basement waters, the concentration of sulfates and heavy metals increases, therefore, irrigation of the dump with water with an alkaline reaction should lead to partial neutralization of the basement waters and reduce their pollution. Obviously, as a result of this, the amount of subsurface water will increase, which will require an increase in the productivity of treatment facilities, but, on the other hand, a decrease in the concentration of pollutants in the subsurface waters will require less consumption of milk of lime, as well as a decrease in the amount of sludge, and, accordingly, lower costs recycling.

Example 1. Experiments were carried out on a model of a rock dump of the Uchalinsky mining and processing plant on the effect of the degree of recirculation of treated waste water with a pH of 9.4-9.5 in the range from 10 to 50% on the pH of the waste water. The results are shown in table 1. The table also shows the concentration of sulfates and heavy metals, determined according to monitoring of basement waters of the same field, depending on the experimentally obtained pH value.

Table 1 The degree of recirculation,% pH Concentration, mg / L The consumption of milk of lime, T / day The proportion of reagent from the initial value,% SO ₄ Zn Fe Mn Cu 0 3.10 9500 530 280 110 80 92.7 one hundred 10 3.42 6300 470 230 90 fifty 70,2 75.7 twenty 3.64 4000 430 200 75 thirty 51.8 55.9 thirty 3.80 2600 400 175 60 twenty 39.5 42.6 40 3.94 1500 380 150 fifty 10 28,4 30.7 fifty 4.0 1000 375 140 45 5 23.7 25.5

The reagent consumption was determined according to the well-known formula / Yakovlev S.V., Karelin Y.A., Laskov Yu.M., Voronov Yu.V. Industrial wastewater treatment. - M .: Stroyizdat, 1985 .-- 335 s. (see p.105) /:

where k is the safety factor of the reagent;

In - the amount of active part in a marketable product,%;

Q = 3000 - the productivity of treatment facilities, m ³ / day;

a - dose of milk of lime to neutralize wastewater, kg / kg;

And the concentration of sulfates, kg / m ³ ;

b ₁ , b ₂ , b ₃ , b ₄ - the dose of milk of lime to extract Zn, Fe, Mn, Cu, kg / kg;

c ₁ , c ₂ , c ₃ , c ₄ - metal concentration, kg / m ³ .

From the data given in table 1, it follows that an increase in the degree of recirculation leads to a decrease in the consumption of milk of lime.

Table 2 shows the results of calculating the amount of precipitation represented by gypsum, metal hydroxides, depending on the degree of recirculation.

table 2 The degree of recirculation,% Sludge mass, t / day The sum of the mass of sediment, T / day The proportion of sediment from the original value,% CaSO ₄ Zn (OH) ₂ Fe (OH) ₂ Mn (OH) ₂ Cu (OH) ₂ 0 40.5 2.42 1.35 0/53 0.37 45,2 one hundred 10 29.5 2,36 1.22 0.48 0.25 33.8 74.8 twenty 20,4 2,36 1.16 0.44 0.16 24.5 54,2 thirty 14,4 2,37 1.10 0.38 0.12 18,4 40.7 40 8.9 2.43 1.01 0.34 0.06 12.7 28.1 fifty 6.4 2,57 1.01 0.33 0,03 10.3 22.8

From the calculation results it follows that the amount of sediment decreases with increasing degree of recirculation.

Example 2. The rationale for the degree of recirculation was carried out at the Uchalinsky mining and processing plant. An increase in the degree of recirculation, on the one hand, leads to a decrease in the reagent consumption and the amount of sludge, on the other hand, the water supplied for irrigation of the dump increases the amount of subsurface water, and accordingly, an increase in capital costs for the reconstruction of treatment facilities is required.

Comparison of options was carried out at the given costs and the cost of water treatment by the formulas:

P _i = E _i + E _H K _i

where P _i - reduced costs for options, rub .;

E _n = 0.14 - normative coefficient of deductions for renovation;

E _i - operating costs for options, rubles .;

K _i - capital costs for options, rubles .;

Seb _i - the cost of water treatment, rubles / m ³ ;

Q _i - the performance of treatment facilities by options, m ³ / year.

The results are shown in table 3.

Table 3 The degree of recirculation,% 0 10 twenty thirty 40 fifty Cost, rubles / m ³ 65.8 52,5 45.3 42.0 40,0 39,4

From the above results it follows that the optimal value should be considered the degree of recycling of 20-30%, since a further increase in water consumption for irrigation of the dump does not significantly reduce the cost of water treatment.

Claims (2)

1. The method of neutralizing base acid sulphate-containing wastewater, including neutralization with milk of lime, sedimentation of suspended particles in the presence of anionic flocculant and pyrite dump tailings of mining and processing plants containing iron and sulfur, mixing and settling, characterized in that the resulting water is divided into two streams , one of which is sent for purification before discharge into water bodies, and the other is sent for irrigation of dumps for partial neutralization of subsurface waters, forming a stream recycling. 2. The method according to claim 1, characterized in that the degree of recirculation of water used for irrigation of dumps is 20-30%.

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