RU2281918C1 - Method of removing hexacyanoferrates from waste waters - Google Patents

Abstract

FIELD: waste water treatment.

SUBSTANCE: invention relates to treatment of waste waters from gold mining enterprises, movie and photo industry as well as productions involving hexacyanoferrates. Waste waters containing hexacyanoferrates (II and III) preliminarily acidified with sulfuric acid are passed at ambient temperature through charge consisting of mixture of iron cuttings (metal machining waste) and coke taken in equal proportions while simultaneously supplying air oxygen. Precipitated insoluble mixed ferro- and ferricyanides are separated by filtration. Proposed method increases productivity and efficiency of treating water, expands possibilities of galvano-coagulation method for treating waste waters so allowing detoxification of stable complex heavy metal cyanides (hexacyanoferrates) and, at the same time, removal of heavy metal ions from effluents, reduced waste water treatment time, and also reduction of process expenses due to eliminated additional introduction of reagents and heating of solutions. Advantage of the method is further utilization of production waste (metal machining waste) and coke. In addition, the obtained precipitates can be used as paint pigments.

EFFECT: enhanced process efficiency.

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Description

The invention relates to wastewater treatment of gold mining enterprises, film industry and similar industries containing hexacyanoferrates.

A known method of wastewater treatment from hexacyanoferrates, including their oxidation with sodium hypochlorite when heated in the presence of a catalyst - a salt of divalent manganese [Method for wastewater treatment from hexacyanoferrates / Panova V.A., Lurie Yu.Yu., Chuchalina M.N. et al. // USSR Patent No. 941311, publ. 07/07/82, bull. No. 25]. Among the disadvantages of this method are the following: complexity, a long process time and high cost due to the additional introduction of reagents, the use of an expensive catalyst and additional heating of solutions.

Also known galvanic coagulation method of wastewater treatment from compounds of heavy metals using the effect of a short-circuited galvanic cell based on a pair of Fe-C [Ryazantsev A.A., Batoeva A.A. The method of wastewater treatment and device for its implementation. RF patent No. 2057080, publ. 03/27/96, bull. No. 9], including the passage of water through a stationary porous load, consisting of a mixture of iron chips (metal waste) and coke. At the same time, air is supplied through a porous plate located at the bottom of the module for water purification. As a result of the operation of the short-circuited Fe-C galvanic cell, iron dissolves and is intensively oxidized to Fe (III) by atmospheric oxygen. However, this method was not considered for the treatment of wastewater containing hexacyanoferrates.

Closest to the proposed invention in technical essence is a method of wastewater treatment from hexacyanoferrates, including pre-treatment of the source water acidified to pH 2.5-3 with a solution of bleach or hypochlorite, followed by treatment with hydrogen peroxide, alkalization to pH 9.5-10 and heating to a boil [Plotnikov N.I. The method of wastewater treatment from hexacyanoferrates (II, III). USSR patent No. 710980, publ. 01/25/80, bull. Number 3].

The prototype has the following disadvantages: the formation of large gelatinous hard-to-filter sediments; the high cost of the process due to the additional introduction of an oxidizing agent - hydrogen peroxide - and reagents for acidification and alkalization of solutions; heating of solutions, as well as its multi-stage.

The technical result of the invention is the elimination of these disadvantages, as well as increasing the productivity and efficiency of the water treatment process while reducing the cost of its implementation.

The technical result is achieved by the fact that wastewater containing hexacyanoferrates (II, III) at room temperature is pre-acidified to pH 2.0-2.5 and passed through a galvanic coagulation charge from a mixture of iron shavings (metal processing wastes) and coke taken in equal proportions, with simultaneous by supplying air oxygen in order to obtain insoluble precipitates of mixed ferrocyanide complexes such as Prussian blue and Turnbull blue, which are removed from the reaction zone by a stream of water and air.

The interaction of iron (II) and (III) ions obtained in the process of galvanic coagulation with Fe (CN) ₆ ^3- and Fe (CN) ₆ ^4- leads to the formation of insoluble compounds such as Prussian blue and turnblue blue, while, because . E ° (Fe ³⁺ / Fe ²⁺ ) = 0.76 V greater than E ° (Fe (CN) ₆ ^3- / Fe (CN) ₆ ^4- ) = 0.36 V, first the redox reaction occurs in the inner sphere of Fe ³⁺ + Fe (CN) ₆ ^4- = Fe ²⁺ + Fe (CN) ₆ ^3- , and then the reaction products react with each other with the formation of precipitation

Fe ²⁺ + Fe (CN) ₆ ^3- = [Fe ²⁺ Fe ^III (CN) ₆ ] ^- , which are removed from the reaction zone by a stream of water and air bubbles.

Cyanide-containing effluents, for example, of gold mining, along with simple ones, contain persistent complex cyanides of heavy metals, for example, copper [Cu (CN) ₃ ] ^2- . With this purification method, such complex cyanides are bound into insoluble mixed ferrocyanide iron complexes of the type MeFe ²⁺ Fe ^III (CN) ₆ , which helps to reduce the salt content in purified water. The iron ions formed upon dissolution of the iron shavings replace copper ions in the inner sphere of the Cu ₂ [Fe (CN) ₆ ] complex. Cu ₂ [Fe (CN) ₆ ] is characterized by the addition of an excessive amount of soluble ferric cyanide of the monovalent cation over time to form poorly soluble mixed salts. The formation of such salts can occur as a result of the addition reaction according to the equation:

Cu ₂ [Fe (CN) ₆ ] + M ₄ [Fe (CN) ₆ ] → 2M ₂ Cu [Fe (CN) ₆ ],

and due to the displacement of Cu ^{2+ ions} from the lattice of its ferrocyanide:

Cu ₂ [Fe (CN) ₆ ] + 2M ⁺ → M ₂ Cu [Fe (CN) ₆ ] + Cu ²⁺ .

The resulting iron compounds are effective coagulants that remove finely dispersed, emulsified and dissolved impurities from water. In our case, the conversion of oxidized forms of iron substantially depends on the conditions for galvanic coagulation treatment: pH values and properties of pollutants extracted from waste water. The method is confirmed by the following examples.

Example 1. Purify solutions containing hexacyanoferrates (II, III) to 85.0 mg / dm ³ at room temperature, having pH values of 6.7, 5.2, 4.1, 3.2 after preliminary acidification of the solutions, for which sulfuric acid is used. The solution is passed through a galvanic coagulator filled with iron chips and coke in equal proportions with the simultaneous supply of oxygen. The contact time of water and loading is 15 minutes As a result of the processes described above, a precipitate is formed, which is carried out by the flow of water and air from the reaction zone. Initial reagents were found in purified water at concentrations of 66.5, 65.3, 46.5, 22.8 mg / dm ³ , which corresponds to 21.8, 23.2, 45.3, and 73.2% of the cleaning efficiency.

Example 2. Similar to example 1, the difference is that solutions of hexacyanoferrates (II, III) at concentrations of 85.8 mg / dm ^{3 are} acidified to pH 3.1, 2.5 and 2.0, and the contact time of the solution with the load is reduced to 9 minutes. In purified water, the starting reagents were found at concentrations of 15.1, 0.5, and 0 mg / dm ³ . The cleaning efficiency is 82.4, 99.4 and 100%, respectively. Thus, the most effective is a pH range of 2.0-2.5.

The proposed method, in comparison with the known ones, expands the possibilities of the galvanic coagulation method for wastewater treatment, which makes it possible to neutralize stable complex heavy metal cyanides - hexacyanoferrates, simultaneously purify wastewater from heavy metal ions, reduce wastewater treatment time, and also reduce the cost of the process by eliminating additional reagent introduction and heating solutions used for loading industrial waste - iron shavings (metal waste) and coke. The proposed method from the point of view of ecology is safe and economically feasible. In addition, the resulting precipitates can be used as pigments for paints.

Claims (1)

A method of treating wastewater from hexacyanoferrates, including preliminary acidification of solutions, followed by separation of precipitates, characterized in that the solutions of hexacyanoferrates are pre-acidified to pH 2.0-2.5, using sulfuric acid, and passed through a porous charge from the mixture at room temperature iron chips and coke, taken in equal proportions, with the simultaneous supply of oxygen, while the resulting precipitation of insoluble complexes of mixed ferrocyanides are removed from the zone reactions with a stream of water and air.