RU2615023C2 - Method for integrated wastewater treatment from cyanide, thiocyanate, arsenic, antimony and heavy metals - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: method comprises water treatment by oxidant, ageing without reagent supply not less than 0.5 hours, preferably 1-4 hours, before the ageing, the oxidant concentration should be minimal. Then the wastewater is treated with ions of iron (II) or (III) at pH 4.0-8.0. At high residual concentrations of heavy and non-ferrous metals, additional alkaline treatment is made with NaOH or CaO. Oxidation treatment, treatment with salts of iron (II) or (III) and alkalinization to remove residual metal concentration are performed with constant stirring, and ageing after oxidation treatment is performed under stirring or without it.

EFFECT: achievement of a high depth of toxic impurities removal from solutions and pulps, the process has a simple hardware design.

6 cl, 1 dwg, 6 tbl, 5 ex

Description

The invention relates to the field of wastewater and pulp treatment, containing cyanides, thiocyanates, heavy metals, arsenic and antimony. The method can find application in enterprises of non-ferrous metallurgy, in the gold mining industry and in galvanic production.

A known method of removing cyanides and other impurities from solutions, including adding to the solution of copper and iron ions as reagents at a pH of about 4-8. The ratio of copper / cyanide should be in the range from 3: 1 to 10: 1 by weight, the ratio of iron / copper is at least 0.3: 1 by weight. The process allows you to remove cyanides up to 0.13-0.86 mg / l, thiocyanates up to 24-27 mg / l, antimony up to 0.7-1.0 mg / l [1].

The disadvantage of this method is the need for the addition of copper as a reagent. Low removal rate of cyanides, thiocyanates and antimony.

A known method of removing cyanide, arsenic and antimony, including dosing into drains at a pH of more than 9.0 SO ₂ and air. If necessary, copper is added based on its content of at least 10 mg / l of solution. Under these conditions, the destruction of cyanides is carried out until the pH drops to 5.0-9.0. Then, an iron ion in the form of sulfate and an alkali in the form of Ca (OH) _{2 are} added if the pH value is different from the set value. From the description of the examples cited in the source, the following cleaning quality is achieved: when the content of cyanides in the treated waste is 2.4 mg / l, the concentration of arsenic is below the detection limit; with a cyanide content of 0.1 mg / l, the concentration of arsenic is 2.2 mg / l; when the cyanide content of 0.1 mg / l, the concentration of antimony is 5 mg / l [2].

The disadvantage of this method is the need for the addition of copper as a reagent. The process does not allow to achieve high quality cleaning at the same time for all toxic impurities. The possibility of removing thiocyanates is not mentioned.

A known method of removing cyanide and other inorganic impurities, including pre-treatment with an oxidizing agent in order to transfer arsenic to the pentavalent state, for example, hydrogen peroxide with a molar ratio to arsenic from 0.2: 1 to 2: 1. If the wastewater to be treated contains cyanides, a catalyst for their oxidation, for example copper sulfate, is also added. A sorbent is added to the oxidized solution, consisting of one or more components selected from the group - particles of iron oxides (II) and (III), hydroxides of iron (II) and (III) in an amount of 10-90% vol., Preferably not less than 50 % vol., stirred for 2-12 minutes and the purified solution is separated. During stirring, the pH is maintained at a level not higher than 8.0. Sorbent treatment is repeated three to seven times [3].

The disadvantage of this method is the presence of copper additives as a catalyst for the oxidation of cyanides. The need to organize a multi-stage circulation of precipitation and solutions with the separation of solid and liquid at each stage, which greatly complicates the hardware design of the process. The possibility of removing thiocyanates is not mentioned.

A known method of purifying cyanide-containing waters, including treating them with an alkali or alkaline earth metal percarbonate, preferably sodium percarbonate, with stirring, characterized in that the cyanide-containing water is treated with a percarbonate-containing reagent at a low copper content in the water without supplying any catalysts, activators or pH regulators in the reaction zone, and then they are maintained without stirring for a time sufficient to complete the oxidation processes [4].

The disadvantage of this method is the use for the oxidation of cyanides and thiocyanates of a low-active reagent - percarbonate of an alkali or alkaline earth metal; the need to use special measures to remove copper before reagent treatment; about the possibility of removing arsenic, antimony and iron, which is in the form of ferrocyanide complexes, is not mentioned.

A known method of extracting antimony from spent antimony-sulfur electrolyte in order to return the antimony compounds of the electrolyte back to electrolysis. The technical result is achieved in that an alkaline solution of antimony sulfosalts is precipitated with ferric sulfate, and antimony is extracted from the precipitate obtained by this method by treating the latter with a 20% sodium hydroxide solution when heated [5].

The disadvantage of this method is the impossibility of processing pulps. The method is intended for the treatment of solutions containing no cyanides, thiocyanates, heavy metals, arsenic. Otherwise, the technical result cannot be achieved, because precipitates will be contaminated with impurities, which will negatively affect the quality of products.

There is a method of cleaning solutions from arsenic and related heavy metals: chromium, manganese, nickel, zinc, strontium, cadmium, lead, by precipitation of sparingly soluble compounds with iron ions in the presence of an oxidizing agent. The solutions are processed in two stages with the removal of the precipitate formed after each stage, while in the first stage the precipitation is carried out with iron ions, then with an oxidizing agent, followed by adjusting the pH to 6.5-7.0, and in the second stage with ferric ions, followed by bringing pH up to 10.0-10.5 [6].

The disadvantage of this method is the impossibility of deep purification from cyanides and thiocyanates, the need to remove precipitation after each stage of processing. The use of iron salts with varying degrees of oxidation in the process, which complicates and increases the cost of technology. The method is not suitable for processing pulps.

The closest in technical essence to the proposed method is a method of removing cyanides and heavy metals from industrial wastewater, including at the first stage the addition of alkali to pH ~ 11.5 and the treatment of water with sodium or calcium hypochlorite at a value of redox potential (ORP), measured platinum calomel electrode, 300 mV. In the second stage, the solutions are treated with iron sulfate at a pH of ~ 9.5 and an ORP value of 16 mV. The reaction is carried out at an ambient temperature and a contact time of approximately 20 minutes. The precipitate formed is separated in clarifiers and / or on the filter and sent for storage. From the description of the patent it follows that the process is suitable for the purification of waters containing not more than 29.6 mg / l of cyanides. The concentration of these compounds after treatment is 0.04 mg / l, arsenic less than 0.01 mg / l [7].

The disadvantage of this method is as follows. The claimed quality of treatment is not achieved when treating wastewater containing high concentrations of toxic impurities. The possibility of removing thiocyanates and antimony is not mentioned. The method is not suitable for processing pulps.

The objective of the invention is to remedy these disadvantages by introducing exposure to oxidized solutions or pulps before treatment with iron ions, which allows us to divide into sufficient time the processes of removal of CN ^- and SCN ^- oxidizing agent and precipitation of As and Sb. Moreover, the concentration of cyanides and thiocyanates after oxidative treatment should not exceed a predetermined depth of purification from these compounds, and before starting the exposure, the concentration of the oxidizing agent should be minimal. In this case, a deep removal of cyanides, thiocyanates, arsenic, antimony and heavy metals from wastes containing both low and high concentrations of these impurities is achieved. The process is straight-through and simple in hardware design. Water, sediment and interstage precipitation are not circulated according to the scheme, which reduces the need for tank equipment and simplifies the technology. Any oxidizing agent can be used to remove cyanides and thiocyanates, for example hypochlorite, hydrogen peroxide, ozone, SO ₂ / air, sodium percarbonate, etc.

The technical result is achieved by the fact that in the method for the comprehensive treatment of wastewater from cyanides, thiocyanates, arsenic, antimony and heavy metals, during oxidative treatment, cyanides and thiocyanates are removed to a given cleaning depth from these compounds, soaking without reagents for at least 0 is carried out, 5 hours, before starting the exposure, the concentration of the oxidizing agent should be minimal, and then they are treated with iron ions (II) or (III) to transfer arsenic and antimony to an insoluble state at a pH of 4.0-8.0.

The technical result is also achieved by the fact that the water or pulp after oxidative treatment can withstand without supplying reagents, preferably within 1-4 hours.

The technical result is also achieved by the fact that at a high residual concentration of heavy and non-ferrous metals after treatment with iron ions (II) or (III), an alkaline treatment is additionally carried out, for example, NaOH or CaO.

The technical result is also achieved by the fact that the oxidation treatment, treatment with salts of iron (II) or (III) and alkalization to remove residual concentrations of metals is carried out with constant stirring.

The technical result is also achieved by the fact that the shutter speed after oxidative treatment is carried out both with stirring and without it.

The technical result is also achieved by the fact that wastewater and pulp treatment is carried out both in batch and continuous modes.

The essence of the method is as follows. Wastewater and pulps containing cyanides, thiocyanates, arsenic, antimony and heavy metals are treated with an oxidizing agent (hypochlorite, hydrogen peroxide, ozone, SO ₂ / air, sodium percarbonate, etc.), while cyanides and thiocyanates are removed. In the case of hypochlorite, the following reactions occur:

oxidation and removal of cyanide metal complexes also takes place (for example, zinc and copper):

arsenic and antimony are oxidized to a pentavalent state:

Immediately after oxidative treatment, the concentration of cyanides and thiocyanates in the solution or in the liquid phase of the pulp should not exceed the specified cleaning depth for these compounds.

Then the waste is maintained without reagent treatment with stirring or without it for at least 0.5 hours, preferably 1-4 hours. At this stage, the system comes into equilibrium. Before starting the exposure, the concentration of the oxidizing agent should be minimal, i.e. oxidative processes must be completed.

When the duration of the aging operation is less than 0.5 hours, the quality of purification from cyanides and thiocyanates deteriorates. With an increase in the duration of the aging operation for more than 48 hours, the high quality of treatment remains, but at the same time, the cost of construction and maintenance of the respective containers increases in the absence of qualitative changes in the efficiency of wastewater detoxification.

After exposure, iron (II) or (III) ions are treated to transfer arsenic and antimony to an insoluble state at a pH of 4.0-8.0, preferably 6.0-7.0. Under these conditions, the formation of iron hydroxides occurs, which are an effective sorbent of arsenic and antimony. Part of Fe is in ionic dissolved form, which contributes to the removal of As and Sb in the form of arsenates and antimonates, as well as the formation of insoluble hexacyanoferrates.

Iron ions are supplied in the form of a water-soluble salt, for example FeSO ₄ ⋅ 7H ₂ O. If the required pH value is not achieved with the addition of iron ions, an acid, for example, H ₂ SO ₄ , is used as an acidity regulator.

If the deposition of arsenic and antimony is carried out in an acidic or neutral region, an increased content of heavy metals, for example Fe, Mn, Ni, remains in the effluents. In this case, the alkaline treatment, for example, NaOH, CaO, at a pH of 8.5-12.0, preferably 9.0-10.0, is included in the process chain. Under these conditions, the removal of residual metal contents in the form of hydroxides is achieved.

Wastewater and pulp can be treated both in batch and continuous modes.

Carrying out the oxidation of cyanides and thiocyanates to a predetermined depth of purification from these compounds and subsequent exposure of wastewater or pulps for at least 0.5 hours, preferably 1-4 hours, before treatment with iron ions, the requirement for a minimum concentration of an oxidizing agent before exposure begins, the possibility Antimony removal distinguishes the proposed solution from the prototype and determines the compliance of the proposed proposal with the criterion of "novelty."

Each distinguishing feature is essential because the absence of any of them does not allow to obtain the specified technical result.

No technical solutions have been identified from the prior art that have features that match the distinguishing features of the invention, therefore, this proposal meets the criterion of "inventive step".

The proposed method for treating wastewater and pulps has several advantages: a deep removal of cyanides, thiocyanates, arsenic, antimony and heavy metals from wastes containing both low and high concentrations of these impurities is achieved. The process is simple in hardware design and can be implemented in both periodic and continuous modes.

The method is confirmed by the following examples.

Example 1. In accordance with the prototype, wastewater containing a relatively small amount of toxic impurities was neutralized, the composition is shown in Table 1. The wastewater was treated in mechanical stirring reactors in accordance with FIG. 2 prototypes. Peristaltic pumps were used to pump the solutions. Calcium hypochlorite was fed into the first reactor at a rate of 0.3 kg / m ³ for “active” chlorine and NaOH at a rate of 0.1 kg / m ³ . The ORP value, measured by a pair of gold - silver chloride electrodes, was 320-340 mV, pH - 11.5. The concentration of cyanides and thiocyanates immediately after oxidative treatment did not exceed 0.02 mg / L. The second reactor was treated with a solution of FeSO ₄ with a flow rate of 0.5 kg / m ³ , the pH value was 9.5. The composition of the purified solution is shown in table 1.

Purification of the same wastewater according to the proposed method was carried out in reactors with mechanical stirring in accordance with the scheme shown in Figure 1. Peristaltic pumps were used to pump the solutions. Calcium hypochlorite was fed into the first reactor at a rate of 0.3 kg / m ³ for “active” chlorine and NaOH at a rate of 0.1 kg / m ³ . The ORP value, measured by a pair of gold - silver chloride electrodes, was 320-340 mV, pH - 11.5. The concentration of cyanides and thiocyanates immediately after oxidative treatment did not exceed 0.02 mg / L. In the second reactor, the solutions were aged without reactants for 3 hours. In the third reactor, a FeSO ₄ solution was treated with a flow rate of 0.6 kg / m ³ , the pH value was 6.8. Due to the fact that in the third operation the pH value was below 7.0, alkaline treatment with NaOH with a flow rate of 0.2 kg / m ^{3 was used} , the pH was 9.8. The composition of the purified solution is shown in table 1.

When carrying out the treatment of wastewater containing a relatively small amount of toxic impurities, in accordance with the proposed method, a deeper removal thereof is achieved.

Example 2. In accordance with the prototype, wastewater containing a sufficiently large amount of toxic impurities was neutralized, the composition is shown in Table 2. The wastewater was treated in reactors with mechanical stirring in accordance with FIG. 2 prototypes. Peristaltic pumps were used to pump the solutions. Calcium hypochlorite was fed into the first reactor at a flow rate of 3.1 kg / m ³ for “active” chlorine and NaOH at a flow rate of 0.8 kg / m ³ . The ORP value, measured by a pair of gold - silver chloride electrodes, was 350-380 mV, pH - 11.4. The concentration of cyanides and thiocyanates immediately after the oxidative treatment was 0.05 mg / L and 0.04 mg / L, respectively. The second reactor was treated with a solution of FeSO ₄ with a flow rate of 3.2 kg / m ³ , the pH value was 9.5. The composition of the purified solution is shown in table 2.

Purification of the same wastewater according to the proposed method was carried out in reactors with mechanical stirring in accordance with the scheme shown in Figure 1. Peristaltic pumps were used to pump the solutions. Calcium hypochlorite was fed into the first reactor at a flow rate of 3.1 kg / m ³ for “active” chlorine and NaOH at a flow rate of 0.8 kg / m ³ . The ORP value, measured by a pair of gold - silver chloride electrodes, was 350-380 mV, pH - 11.4. The concentration of cyanides and thiocyanates immediately after the oxidative treatment was 0.05 mg / L and 0.04 mg / L, respectively. In the second reactor, the solutions were aged without reactants for 3 hours. In the third reactor, the solution was treated with FeSO ₄ with a flow rate of 3.8 kg / m ³ , the pH value was 6.8. Due to the fact that in the third operation the pH value was below 7.0, alkaline treatment with NaOH with a flow rate of 0.5 kg / m ^{3 was used} , the pH was 9.6. The composition of the purified solution is shown in table 2.

When carrying out the treatment of wastewater containing a significant amount of toxic impurities, despite the low concentration of cyanides and thiocyanates in the solution immediately after the oxidative treatment, the concentration of these compounds increases to 2.9 and 5.3 mg / l, respectively, during purification of the prototype. When using extract solutions according to the proposed method, deterioration in the quality of purification according to CN ^- and SCN ^- does not occur, a deeper removal of heavy metals, arsenic and antimony is also observed.

Example 3. The implementation of the proposed method on the pulps in a batch mode is shown. Continuous cleaning is carried out in the same manner as in examples 1 and 2.

Purification of the pulp by the proposed method was carried out in a reactor with mechanical stirring. The sample was sequentially processed in one reactor in accordance with the scheme shown in Figure 1. The solid content in the pulp was 48%, the composition of the liquid phase is shown in Table 3. At the first stage, calcium hypochlorite was fed into the reactor with a flow rate of 18.5 kg / t dry for “active” chlorine and CaO with a consumption of 2.3 kg / t dry. The value of the ORP, measured by a pair of gold - silver chloride electrodes, was 220 mV, pH - 11.3. The concentration of cyanides and thiocyanates immediately after the oxidative treatment in the liquid phase was 0.08 mg / L and 0.06 mg / L, respectively. Then spent exposure without supplying reagents for 2 hours. At the end of this operation, the sample was treated with a solution of FeSO ₄ with a flow rate of 6.0 kg / t dry, the pH value was 6.9. Due to the fact that in the third operation the pH value was below 7.0, alkaline treatment of CaO was used with a flow rate of 1.8 kg / t dry, the pH was 9.8. The composition of the liquid phase of the purified pulp are shown in table 3.

When cleaning the pulp according to the proposed method, a deep removal of toxic substances is achieved.

Example 4. The efficiency of using waste extracts was shown, from which cyanides and thiocyanates were removed by oxidative methods to a predetermined depth of purification from these compounds and the use of other oxidizing agents besides “active” chlorine.

Used solutions having the composition shown in table 4. They were treated with an oxidizing agent according to US Pat. 2010124769 [4]. Cyanide-containing water and sodium percarbonate were fed into a reactor equipped with mechanical stirring; the contact duration was 30 minutes. Then the water entered the next reactor to complete the oxidation processes, where it was for 12 hours, stirring in this reactor was not carried out. The consumption of sodium percarbonate (13% in “active oxygen”) was 27.0 kg / m. The change in the total concentration of cyanides and thiocyanates, as well as the residual “active” oxygen during 12-hour oxidation, is presented in Table 5. Then, upon reaching the specified depth of purification from CN ^- and SCN ^- , the sample was processed with a FeSO ₄ solution with a flow rate of 19.2 kg / m ³ , the pH value was 6.4. Due to the fact that in the third operation the pH value was below 7.0, alkaline treatment of CaO was used with a flow rate of 2.3 kg / m ³ , the pH was 10.0. The composition of the purified solution is shown in table 4.

Water purification by the proposed method was carried out as follows. The same solutions were treated with sodium percarbonate (the procedure described above). After 12 hours of oxidation without stirring, the total concentration of cyanides and thiocyanates was 0.21 mg / L, which corresponded to a given depth of purification from these compounds. From this moment, exposure was carried out (no reagents were added) for 4 hours, and then treatment with FeSO ₄ and CaO with the costs and conditions described above. The composition of the purified solution is shown in table 4.

Despite the considerable duration of the oxidation of impurities in water (holding in the presence of an oxidizing agent for 12 hours), the required depth of purification from the entire complex of toxic substances is not achieved. The desired technical result is observed only when using extracts of solutions in which cyanides and thiocyanates are oxidized to a predetermined depth.

If the aging of the waste begins at an earlier stage, when the oxidation processes are not completed and the required depth of removal of cyanides and thiocyanates is not reached, the increase in the concentration of CN ^- and SCN ^- after treatment with iron (II) or (III) salts will be even more significant, t .to. the system does not have time to reach an equilibrium state. The same is true for arsenic, antimony and ferrocyanides.

Example 5. The effectiveness of the operation of exposure by the proposed method for water purification when used to remove arsenic and antimony processes other than those used in protopite is shown.

Used solutions having the composition shown in table 2. They were chlorinated in accordance with the procedure presented in examples 1, 2. The concentration of cyanides and thiocyanates immediately after oxidative treatment was 0.05 mg / L and 0.04 mg / L, respectively. Then they were treated with iron salts and an oxidizing agent in accordance with US Pat. 2390500 [6]. The solution of Fe ions was supplied in a weight ratio of 3: 1 to all elements contained in the initial solution. Then, concentrated H ₂ O ₂ was introduced in an amount of 1% of the solution volume and pH was adjusted to 7.0 with soda. The water was held for 3 days, the precipitate was filtered, and then the filtrate was treated. FeSO _{4 was} added to the filtrate with stirring in a weight ratio of 2: 1 to the entire mass of metals removed, the pH was adjusted with sodium hydroxide to 10.5. The resulting mixture was kept for 3 days. An analysis of the clarified purified solution is shown in table 6.

The purification of the same waters in accordance with the proposed method is described in example 2. The composition of the purified solution is shown in table 6.

When conducting removal from wastewater in accordance with US Pat. 2390500 [6] of arsenic, antimony and heavy metals, despite the low concentration of cyanides and thiocyanates in solution immediately after oxidative treatment, an increase in the concentration of these compounds to 2.0 and 4.6 mg / l, respectively, is observed. When using exposure solutions according to the proposed method, with substantially more simple processing technology deterioration water purification CN ^- and SCN ^- does not occur, there is also a better removal of heavy metals and arsenic.

Regardless of which method, based on the reagent treatment, is used to remove heavy metals, arsenic and antimony and solutions and pulps, initially simultaneously containing CN ^- , SCN ^- , As, Sb and heavy metals, the exposure operation after oxidative treatment allows to achieve the set technical result for all components to be removed from the waste.

The proposed method of wastewater treatment from cyanides, thiocyanates, heavy metals, arsenic and antimony allows to achieve a high depth of removal of toxic impurities from solutions and pulps. The process is simple in hardware.

Information sources

1. Goodwin E. Process for the removal of cyanide and other impurities from solution. Pat. 1321429 Canada, C02F 1/62. Hemlo Gold Mines Inc. No. 5,404,430; declared 06/23/87; publ. 08/17/93.

2. Devuyst, Eric A.P .; Conard, Bruce R. Effluent Treatment. Pat. 1241774 Canada, C02F 1/62. Inco Limited, No. 454880, decl. 05/23/84; publ. 09/06/88.

3. Domvile Serena J. Process for removal of inorganic and cyanide contaminants from wastewater. Pat. 1333106 Canada, C02F 001/68, 009/00. NERCO Con Mine Ltd. No. 600472; declared 05/24/89; publ. 11/15/94.

4. Petrov V.F., Petrov S.V. The method of purification of cyanide-containing waters. Pat. 2010124769 RF, C02F 1/72, Open Joint-Stock Company Irkutsk Research Institute of Noble and Rare Metals and Diamonds Irgiredmet OJSC. No. 2010124769/05; declared 06/16/10; publ. 12/27/11.

5. Kaplan G.E., Mukhantseva V.V. A method of extracting antimony from spent antimony-sulfur electrolyte. A.S. 63111 A, claimed 01/20/39; publ. 01/31/44.

6. Kurskov S.N., Chupis V.N., Rastegaev O.YU. The method of purification of aqueous solutions of arsenic and related heavy metals. Pat. 2390500 RF, C02F 1/61, C02F 101/20, C02F 103/16, Federal State Institution “State Research Institute of Industrial Ecology”. No. 2008149995/15; declared 12/17/08; publ. 05/27/10, Bull. No. 15.

7. Klaus Schwitzgebel. Integrated process for cyanide and heavy metal removal from plating process waste streams. Pat. 5106508 USA, C02F 1/56. Klaus Schwitzgebel, No. 5888535; declared 09/26/90; publ. 04/21/92.

Claims (6)

1. The method of complex treatment of wastewater from cyanides, thiocyanates, arsenic, antimony and heavy metals, which consists in treating the water with an oxidizing agent, iron ions (II) or (III), characterized in that cyanides and thiocyanates are removed from the water or pulp during oxidative treatment to a predetermined depth of purification from these compounds, an exposure is carried out without supplying reagents with a duration of at least 0.5 hours, before starting the exposure, the concentration of the oxidizing agent should be minimal, and then they are treated with iron (II) or (III) ions to transfer arsenic and antimony in an insoluble state at a pH of 4.0-8.0. 2. The method according to p. 1, characterized in that the water or pulp after oxidative treatment can withstand without supplying reagents, preferably 1-4 hours. 3. The method according to p. 1, characterized in that at a high residual concentration of heavy and non-ferrous metals after treatment with iron ions (II) or (III), an alkaline treatment is additionally carried out, for example, NaOH or CaO. 4. The method according to p. 1, characterized in that the oxidation treatment, treatment with salts of iron (II) or (III) and alkalization to remove residual concentrations of metals is carried out with constant stirring. 5. The method according to p. 1, characterized in that the shutter speed after oxidative treatment is carried out both with stirring and without it. 6. The method according to p. 1, characterized in that the wastewater and pulp treatment is carried out both in batch and continuous modes.

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