SU757476A1 - Method of purifying fluorine-containing waste waters - Google Patents

Description

The invention relates to methods for the purification of fluorine-containing wastewater and can be used for the purification of wastewater generated in the production of mineral fertilizers.

At the chemical industry, producing phosphoric mineral fertilizers, fluorine-containing drains are usually neutralized with lime milk. To reduce the fluorine content, additional purification is assumed.

Lime | for example, the method of wastewater purification from fluorine by introducing lime milk in the first stage and adsorption by aluminum-containing reagents on the second [1].

To improve the deposition process flocculating agents are introduced into the effluent polyelectrolytes.

A known method of purification of fluorine-containing wastewater by treating them with water-soluble calcium salts, followed by separation of the precipitate from the liquid phase, the introduction of phosphoric acid to pH 4 and organic polymeric coagulant [2}.

Polyacrylamide (PAA) has the best flocculating effect. But with the use of flocculants speed

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clarifications of lime milk-neutralized suspensions are small.

The closest in technical essence and the achieved result to the proposed is a method of wastewater treatment in the production of mineral fertilizers from P ₂ 0 ₅₎ P and suspended solids, which consists in treating waste water with lime milk for 30-40 minutes to a pH of 6.78.5 and 0.11% PAA in the amount of 10 mg / l [3]. The rate of clarification of the suspension is 3.5-6.0 m / h.

The main disadvantage of this method is the small rate of clarification, which extends the process of wastewater treatment and does not allow installing settling tanks with mechanical discharge of sediment.

The purpose of the invention is to increase the speed of clarification neutralized with lime milk wastewater.

This goal is achieved by the fact that the wastewater, neutralized with lime milk to a pH of 6.7-8.5, is treated with sulfur dioxide in the presence of potassium permanganate, then the resulting suspension is clarified with polyacrylamide, after which the precipitate is separated.

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It is advisable as a source of sulfur dioxide to use the exhaust gases of sulfuric acid production emitted into the atmosphere, which is introduced in an amount of 2-3 liters (based on 100% 50 ₂ ) per 1 liter of suspension.

It is also advisable to take potassium permanganate in a 7.0-10.7% excess of stoichiometry with respect to the introduced sulfur dioxide.

The clarification of the suspension treated in this way occurs 4-5 times faster than in the known method.

The introduction of potassium permanganate in an amount less than 7%, and 50 ₂ , more than 3 liters, reduces the effect of increasing the speed by 1.5-2 times, and the introduction of KMpO ₄ in an amount greater than 10.7%, and 5 0 ₂ , less than 2 l, significantly affects the quality of clarified water (due to an increase in the amount of suspended solids).

PRI me R 1. 5600 ml of raw wastewater containing 1000 mg / l of P and 500 mg / l of P ₂ 0 ₅ is neutralized with a 12% solution of milk of lime to a pH of 6.8, add 1N KMpO solution in excess of 7% with respect to $ 0 ₂ and the stoichiometric amount of milk of lime (to neutralize the resulting H ^ AO ^.). Then, through a stirred suspension, flush 16.8 1 of 50 ₂ over 30 minutes. The deposition of the resulting suspension is carried out in the presence of 0.2% polyacrylamide (PAA) added in an amount of 0.08% of the suspended content. The deposition rate is 32.7 m / h. In this case, the clarified water contains 43 mg / l of suspended solids, 20.5 mg / l of P and 41.4 mg / l of p ₂ o ₅ .

For example, 2.5600 ml of waste water containing 3230 mg / l of P and 520 mg / l of P ₂ 0§ is neutralized with milk of lime to a pH of 8.4, 1N KMnO ₄ solution is added in excess of 10.7% relative to 50 _g and The stoichiometric amount of milk of lime to neutralize the resulting H ₂ 50 ₄ , and then 16.8'l 50 _{2 is} blown through the stirred suspension for 30 minutes. At the end of the purge, 0.2% PAA is added to the resulting suspension in an amount of 0.08% of the suspended content. The sedimentation rate of the suspension is 25.3 m / h. In clarified water contains 32.0 mg / l of suspended substances,

17.8 mg / l P and 12.0 mg / l P ₂ 0 ₅ .

Example 3. 5600 ml of initial water with a content of 5300 mg / l P and 520 mg / l P ₅ 0 ₅ neutralized with milk of lime to pH 7.5, add 1N solution of KIPoD in 10% excess relative to 50 _g and the stoichiometric amount of milk of lime to neutralize the resulting H ₂ 50 ₄ . Then rinse through a stirred suspension of 11.2 l 50-2 (based on 100% 50 ₂ ) for 30 minutes. At the end of the purge, 0.2% PAA is added to the suspension in an amount of 0.2% of the suspended matter content. The sedimentation rate of the suspension is 16.9 m / h with the content of suspended substances, fluorine and P ^ O ^ in clarified water, respectively 18.8, 15.6 and 3.8 mg / l.

Example 4. 5600 ml of wastewater from an extraction plant containing 5700 mg / l P and 470 mg / l P ₂ 0 ₅ is neutralized with 12% lime milk to a pH of 7.15 and then the stirred suspension is treated with sulfurous anhydride, blowing 11.2 l for 30 min. Before the start of the purge, add 1N KMn0 ₄ solution in a 10% excess relative to 5 0 ₂ and a stoichiometric amount of milk of lime to neutralize the resulting H ₂ 50 _{4 is} added to the suspension. The suspension is precipitated in the presence of 0.2% PAA in the amount 0.2% of the suspended content. The deposition rate is 16.9 m / h, the content of Р and Ρ ₂ 0δ ⁱⁿ clarified water is 24.8 mg / l and 9.4 mg / l, respectively.

The proposed method for purification of fluorine-containing wastewater makes it possible to increase the sedimentation rate of the suspension by 4–5 times, which makes it possible to increase the productivity of the settling tanks of the neutralization station by the same amount and, consequently, reduce the settling area. At the same time, the environmental problem is solved, since the use of 50 ₂ waste gases of sulfuric acid production reduces their release into the atmosphere.

Claims (3)

Claim 1. The method of purification of fluorine-containing wastewater, including neutralization with lime milk to a pH of 6.78.5, clarification with polyacrylamide with the subsequent separation of the sediment, in that, in order to increase the clarification rate, the neutralized drains are treated with sulfuric anhydride in the presence of potassium permanganate before clarification. 2. The method according to π. 1 _? characterized in that the sulfuric acid production off-gases are introduced as sulfurous anhydride in the amount of 2-3 liters (in terms of 100% 502) per 1 liter of suspension. 3. The method of pop. 1, characterized in that the permanganate co 757476 potassium is injected in a 7.0-10.7% excess relative to the injected $ 0 _g .