RU2108301C1 - Method of removing heavy metal ions from acidic waste waters - Google Patents

Abstract

FIELD: waste water treatment. SUBSTANCE: invention focuses on acidic waste waters formed in nonferrous metal ore mining process involving shaft or pit excavation techniques. Method allows removing toxic metal ions such as copper, zinc, and iron and consists in two-stage precipitation of metals using lime milk and sodium carbonate to pH 6.0-6.5 in the first stage terminating by separation of precipitate. In the second stage, precipitate is separated by flotation at pH 7.5-8.0 using, as flotation regent, sodium salts of synthetic fatty acids with hydrocarbon moieties containing more than 21 carbon atoms. EFFECT: decreased alkalinity of dumped waste waters, reduced heavy metal content to maximum permissible concentration, and achieved high-speed separation of suspension. 2 cl, 1 tbl

Description

 The invention relates to the purification of acidic wastewater, for example, waters generated during the extraction of non-ferrous metal ores by mining or quarrying.

 Known methods for the purification of acidic wastewater from heavy metal ions by stage deposition of metals by adjusting the pH of the medium, followed by separate or collective separation of precipitates from effluents [1].

 The closest in technical essence is a method of purification of acidic wastewater from heavy metal ions, including two-stage precipitation in an alkaline medium using lime milk in the first stage at pH 6.5-7.0 and sodium carbonate in the second stage at pH 9.0- 9.5 [2].

The disadvantages of acidic wastewater treatment methods based on precipitation separation by precipitation methods include:
- maintaining a high level of pH (up to 9.5) in order to completely precipitate metals, which increases the maximum permissible concentration (6.5-8.5) for discharging treated wastewater;
- low deposition rate of fine impurities.

 The technical result of the invention is to reduce the harmful effects on the environment by reducing the alkalinity discharged into wastewater and a high degree of purification from heavy metals.

The technical result is achieved by the fact that in the method of treating wastewater from heavy metal ions by two-stage precipitation using milk of lime and sodium carbonate at the first stage when pH 6.0-6.5 is reached, followed by precipitation, and at 2- of the first stage, a pH of 7.5-8.0 is achieved by the addition of sodium carbonate, then the suspension is conditioned with a flotation reagent and the precipitate is released by flotation. At the same time, sodium salts of synthetic fatty acids with a hydrocarbon radical length above C ₁₂ are used as flotation reagent.

The precipitate formed at the 1st stage, consisting mainly of iron and copper hydroxides, is separated from the suspension by settling. The use of sodium carbonate ensures the binding of previously introduced calcium ions with the formation of sparingly soluble calcium carbonate. A decrease in calcium ions in the effluent after precipitation contributes to a decrease in the consumption of flotation reagent in subsequent flotation due to a decrease in the formation of poorly soluble calcium soaps and fatty acids. Sodium carbonate is additionally introduced into the clarified effluents to neutralize them to a pH of 7.5–8.0, condition them with an aqueous emulsion of the sodium salt of synthetic fatty acids with a hydrocarbon chain longer than C _21, and float.

 The foam product is filtered, and the bottom product is wastewater treated to the MPC requirements, which are used as process water or discharged.

Flotation is carried out by air bubbles with a particle size of 90% less than 0.8 mm with an air flow rate of 0.5-1 m ³ min • m ³ D> chamber volume. The process is carried out in pneumatic flotation devices of a column or compression-column type.

 The method is illustrated by the following example. As the initial solution, we use a model solution of a composition similar to the quarry and basement effluents of the Safyanovskoye copper pyrite deposit, where ore is mined open-pit [3].

 The composition of real effluents and model solution is presented in the table.

The model solution is treated sequentially with an aqueous 10% suspension of milk of lime based on CaO 3.5 kg / m ³ effluent to a pH of 4.8-5.4 and sodium carbonate based on 0.3 kg / m ³ effluent to a pH of 6, 0-6.5.

After settling for 2 hours, the suspension was separated. The composition of the precipitate is as follows, wt. %: total iron 21.12; copper 3.34; zinc 1.90. The degree of extraction at the 1st stage of deposition was,%: total iron 92-66; copper 80.62; zinc 50.10. The clarified solution was further neutralized with sodium carbonate to a pH of 7.5-8 in order to more fully precipitate the remaining metal ions, mainly zinc, in the form of hydroxides. The neutralized suspension was treated for 1-2 minutes. in a mechanical stirrer with an aqueous 2% emulsion of sodium salt of synthetic fatty acids with a hydrocarbon radical length greater than C ₁₂ and then sent to flotation separation in a column pneumatic apparatus.

 Flotation time 5 minutes The initial suspension before flotation had the composition, mg / l: total iron 76.0; copper 2.76; zinc 209.38. After flotation, purified water is obtained with a pH of 7.8 of the following composition, mg / l: total iron 0.29; copper 0.042; zinc 0.18. The degree of extraction in the flotation operation was,%: total iron 99.62; copper 98.48; zinc 99-91.

 The dry residue formed during the flotation of the foam product had the following composition, wt.%: Total iron 8.06; copper 0.29; zinc 23.75. As the chemical composition shows, the foam product can serve as a secondary raw material for the production of zinc.

 The use of Na-soaps of synthetic fatty acids provides the formation of insoluble compounds with metals at lower pH, in contrast to the pH value characteristic of a more complete precipitation of metals in the form of their hydroxides. In addition, the flotation method allows more efficient, compared with settling, to remove finely dispersed impurities and heavy metals of ionic form.

Using the proposed method for the purification of acidic wastewater from heavy metals with the replacement of the 2nd stage of deposition by flotation allows:
- reduce the alkalinity of purified water and, accordingly, the consumption of alkaline agents;
- provide a high degree of purification from toxic metals to the requirements of MPC;
- provide a high speed separation of suspensions.

LIST OF USED SOURCES
1. Pat. U.S. N 5128047, CL C 02 F 1/62, 1992.

 2. RF patent N 2010013, cl. C 02 F 1/62, 1993.

 3. Draft T.1. General explanatory note P-160-002-01 "Opening and development of the Safyanovsky deposit." Section: ore water treatment, water supply and sewerage. UNIPROMED, Ekaterinburg, 1994

Claims (2)

 1. A method for purifying acidic wastewater from heavy metal ions, including two-stage precipitation of heavy metals using lime milk in the first stage and sodium carbonate in the second stage, characterized in that in the first stage of precipitation, the wastewater is treated with milk of lime to pH 4.8 - 5.4 and the resulting suspension is additionally treated with sodium carbonate to a pH of 6.0 - 6.5, followed by precipitation, and in the second stage, the pH of the clarified effluent with a residual impurity content is adjusted to a level of 7.5 - 8.0, after which the suspension is conditioned with a flotation reagent followed by precipitation by flotation. 2. The method according to claim 1, characterized in that as the flotation reagent use sodium salts of synthetic fatty acids with a hydrocarbon radical length above C _{2 1} .

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