RU2207324C2 - Two-step method for neutralizing waste waters - Google Patents

Abstract

FIELD: waste water treatment. SUBSTANCE: neutralization of waste waters originated from mechanical engineering and metalworking industry, where acidic iron- containing waste waters are to be detoxified, is separated into two consecutive steps: first to pH 6-7 by filtration at depression 0.4-0.6 kg/sq. cm through thin (0.5-2.0 mm) bed of fine neutralization reagent (ferrochrome slag) for 1 min and then, to pH 8.5-9.5, using line-milk neutralization. EFFECT: reduced loading on waste disposal plants and accelerated sedimentation in settlers. 4 dwg, 1 tbl, 2 ex

Description

 The invention relates to the field of wastewater treatment and can be used in engineering and metalworking industries, where it is necessary to neutralize acidic iron-containing wastewater.

 A known method of purification of acidic iron-containing wastewater, including averaging, neutralization of wastewater with lime milk, sedimentation and mechanical dewatering of the formed sludge (Smirnov D.N., Genkin V.E. Wastewater treatment in metal processing. -M .: Metallurgy, 1980 , 195 p.). However, this method has significant disadvantages: high consumption of lime, plastering of pipelines, the difficulty of precipitating finely dispersed flakes of iron hydroxide, the large amount of sludge formed and the difficulty of dehydrating it.

 A known method of purification of acidic iron-containing wastewater by filtration through a layer of magnesite (Kozhevnikova EP, Volkov LS. Study of the operation of magnesite filters in neutralizing acidic iron-containing wastewater. In collection. Filtering processes in the treatment of natural and wastewater, South Ural book Publishing House, Chelyabinsk, 1965, 78 pp.). Filtration of wastewater through a loading layer from a burnt shop (grain size 1-3 mm high up to 2.5 m) at a speed of 2-4 m / h allows neutralization and retention of iron hydroxide in a conventional quick filter.

 At the same time, the use of this method is very limited due to the formation on the grains of the filter load of gypsum-iron deposits that impede the normal operation of the filters. As shown by numerous observations on the application of this method, after several filter cycles, the neutralizing ability of the load in the full neutralization mode decreases sharply, and then drops to almost zero. Frequent download replacement is inefficient in technical and economic respects.

 The disadvantages of this method should also include the difficulty of regeneration of the filter load and low filtering speed.

 A known method of two-stage neutralization of wastewater, including averaging, neutralization, sedimentation and mechanical dewatering of the formed sludge (Shabalin A.Yu. Wastewater treatment and use at the enterprises of ferrous metallurgy, Moscow, Metallurgy, 1968, p. 257-278), while neutralization sewage is divided sequentially into two stages: ferrochrome slag and lime milk.

 The disadvantages of this method are: high consumption FHSh; difficulties associated with sediment removal from sedimentation tanks.

 The technical task of the invention is the unloading of treatment facilities for pollution and an increase in the deposition rate in the sumps.

The technical result is achieved by the fact that the wastewater is subjected to averaging, neutralization, sedimentation and mechanical dewatering of the formed sludge and the process of neutralizing wastewater is divided in two stages sequentially to pH = 6-7 by filtration under a pressure of 0.4-0.6 kgf / cm ² through a thin layer (0.5-2.0 mm) of finely dispersed neutralizing reagent of ferrochrome slag for 1 min in the first stage, and until pH = 8.5-9.5 by neutralization with milk of lime in the second stage.

 In FIG. Figure 1 shows the dependence of the FCC layer height on the effect of neutralizing wastewater (initial runoff pH = 2, iron ion content (11): 0.025; 0.1; 1.0; 2.0 g / l).

 In FIG. Figure 2 shows the dependence of the FCC layer height on the effect of neutralizing wastewater (initial runoff pH = 3-6 (cf.), iron ion content 0.025-2.0 g / l).

 In FIG. Figure 3 shows the dependence of the% precipitation of iron (11) on the pH of the runoff.

 In FIG. Figure 4 shows the dependence of the rate of deposition of particles of iron hydroxide (11) in sedimentation tanks on the concentration of iron ion in the effluent.

 The proposed method is as follows. As a neutralizing filtering material, ferrochrome slag is used for large-tonnage waste of electric steel production. The degree of dispersion ranges from 1 to 15 microns. The neutralizing ability of PCh is determined by the content in its composition of up to 70% of dicalcium silicates capable of entering into neutralization reactions.

Filtration was carried out on a submersible vacuum filter funnel with a filter area of 0.004 m ² . Wastewater containing sulfuric acid (pH = 2-5-6) and an iron salt (11) (concentration of an iron ion (11) from 0.025 to 2.0 g / l) was filtered.

The thickness of the PCh layer varied from 0.5–2.0 mm from the condition that the pH of the filtrate was not less than 6–7. The filtering time did not exceed 1 min from the condition of ensuring maximum filtration rates. Filtering was carried out with a vacuum value of 0.3-0.6 kgf / cm ² . At lower rarefaction values, a slight increase in the pH of wastewater occurs during filtration. At large rarefaction values, it does not provide the effect of neutralizing wastewater in a thin layer of FCS.

 As can be seen from Fig.1-2, the process of neutralizing wastewater takes place in two stages: on the first, acid is neutralized, on the second, hydroxide formation occurs. Moreover, at the second stage, a substantial expenditure of reagent is required. With an increase in the concentration of metal ions, more and more reagent is required to change the pH by the same amount. It was found that to increase the pH from 2 to 6-6.5 in the range of iron ion content in wastewater 0.025-2.0 g / l, the required thickness of the FCC layer is 0.5-2.0 mm. To implement the full neutralization mode, the thickness of the layer of PCh lies in the range of 2.0-4.5 mm (Fig.1-2).

Filtration of acidic iron-containing wastewater through FChS layers 0.5-3.0 mm thick under a vacuum of 0.4-0.6 kgf / cm ² for 1 min provides fairly high filtration rates - from 2.5 to 6 m / h ( table 1).

 Neutralization of wastewater to pH 6-7 ensures the removal of the bulk of contaminants from wastewater, as when filtering through a thin layer of PCh, the free acid is neutralized and 80% of the iron ion is precipitated (11) (Fig. 3). This contributes to the unloading of treatment facilities and ensuring a stable pH value of wastewater.

 The second stage of neutralization is carried out by milk of lime in a known manner to a pH of 8.5-9.5 from the condition of the most complete precipitation of iron (11) in the form of hydroxide. At the same time, the consumption of a neutralizing reagent-lime is significantly reduced, because after the first stage of neutralization, only 20% of the iron ion remains in wastewater (11).

EXAMPLE 1. Acidic iron-containing wastewater (pH = 2, iron ion concentration (11) 50 mg / l is filtered through a 1.5 mm thick PCh layer under a vacuum of 0.5 kgf / cm ^2. Capron art. 56007 was used as a filter partition). A 1.5 mm thick FHS layer was obtained by filtering a 3% by weight FHS suspension under a pressure of 0.5 kgf / cm ² for 15 s. The average filtration rate for 2 minutes was 6.2 m / h. 6-7, the humidity of the resulting precipitate of iron hydroxide (11) after drying under vacuum was 45%.

EXAMPLE 2. Acidic iron-containing wastewater (pH 3-4, iron ion concentration (11) 200 mg / l is filtered through a 0.5 mm thick PCh layer under a vacuum of 0.5 kgf / cm ^2. Capron art was used as a filter septum. 56007. A 0.5-mm thick FHS layer was obtained by filtering a 3% by weight FHS suspension under a vacuum of 0.5 kgf / cm ² for 5 s. The average filtration rate for 3 min was 5.2 m / h, pH the filtrate is 6-7, the moisture content of the precipitate of iron hydroxide formed after drying under vacuum was 45%.

 An spent layer of PCh with delayed contaminants in the form of particles of iron hydroxide can be disposed of with the dehydrated sludge.

 It is known that flakes of iron hydroxide after neutralization with milk of lime are poorly precipitated in settlers, and the higher the concentration of iron ion in the effluent, the lower the rate of deposition of particles of iron hydroxide (Fig. 4). (Vasiliev V.I. Study of the conditions for the release of suspended solids from neutralized acidic iron-containing wastewater. Diss. For the degree of candidate of technical science, Chelyabinsk, 1972. 130 pp.). The two-stage neutralization mode contributes to a significant decrease in the concentration of iron ion in the effluent after the first stage of neutralization, and thus an increase in the rate of deposition of flakes of iron hydroxide (11) in sedimentation tanks, ensuring their stable operation and reducing their size.

 At the same time, the volume of sediment deposited in the settlers is much less (about 5 times) than when neutralizing wastewater with milk of lime only. Accordingly, for its dehydration requires a smaller number of devices.

 The implementation of the first stage of neutralization is possible on commercially available apparatuses of drum vacuum filters of the BOW type with an outer filtering surface, working with a thin layer of FCS. These devices can be placed in the mechanical dewatering workshop along with sludge dewatering devices (usually with the same vacuum filters of the BOW type). This leads to a significant reduction in operating costs for the implementation of the proposed cleaning method.

 The proposed method of two-stage neutralization of wastewater can be successfully used for the selective extraction of metals from wastewater. In this case, the pH range in which the metal is precipitated (Table 2), as well as the amount of neutralizing reagent for the precipitation of one weight part of the metal, should be taken into account.

 Implementation of the proposed method for the purification of acidic iron-containing wastewater will allow unloading treatment plants for pollution, increase the sedimentation rate of iron hydroxide flakes in sedimentation tanks by a factor of 2.5-3.

Claims (1)

A method of two-stage wastewater neutralization, including averaging, neutralization, sedimentation and mechanical dewatering of the formed sludge, characterized in that the wastewater neutralization is divided sequentially into two stages - to a pH of 6-7 by filtration under a pressure of 0.4-0.6 kgf / cm ² through a layer of ferrochrome slag with a thickness of 0.5-2.0 mm for 1 min in the first stage and up to pH 8.5-9.5 by neutralization with milk of lime in the second stage.

Images