RU2310614C1 - Method of neutralization of the cyanide-containing and the thiocyanate-containing waste waters - Google Patents

Abstract

FIELD: chemical industry; methods of neutralization of the cyanide-containing and thiocyanate-containing waste waters.

SUBSTANCE: the invention is pertaining to the method of neutralization of the cyanide-containing and thiocyanate-containing waste waters and may be used for neutralization of the liquid phase tailings of the process of the cyanide leaching of the noble metals from the ores, concentrates and technogenic wastes. The method of neutralization of the cyanide-containing and the thiocyanate-containing waste waters consists in their acidation with the sulphuric acid up to the medium pH = 2-4 with the subsequent flushing by the air of the formed hydrogen cyanide. At that for realization of the processes of the flushing and the hydrogen cyanide absorption use the centrifugally-bubble apparatuses. The processes of the flushing and the hydrogen cyanide absorption are conducted in the continuous mode with duration of treatment of the solutions in the reaction zone of the centrifugally-bubble apparatus less than 1 minute. The sulfuric acid is batched into the feeding main coming to the centrifugally-bubble apparatus. The technical result of the invention is the increased effectiveness of the neutralization of the cyanide-containing waste waters and the thiocyanate-containing waste waters, reduction of the oxidant consumption at the final phase of the neutralization of the spent technological solutions of the cyanide leaching of the noble metals.

EFFECT: the invention ensures the increased effectiveness of the neutralization of the cyanide-containing waste waters and the thiocyanate-containing waste waters, reduction of the oxidant consumption at the final phase of the neutralization of the spent technological solutions of the cyanide leaching of the noble metals.

3 cl, 1 dwg, 2 ex

Description

The invention relates to methods for purifying cyanide and rhodanide-containing wastewater and can be used to neutralize the liquid phase of the tailings of the cyanide leaching of precious metals from ores, concentrates and industrial waste. Wastewater of such industries contain toxic simple and complex cyanides, thiocyanates (hereinafter referred to as thiocyanates), heavy metal ions.

Known methods for the neutralization and regeneration of cyanides in liquid wastes of gold mines by cyanide leaching of precious metals from ores, concentrates and industrial wastes using the AVR method ("acidification - blowing - neutralization") [US Pat. No. 5254153, 1993. Cyanide recycling process / Madder, Terry I .; US Pat. No. 4994243, 1991. Cyanide regeneration process / Goldstone, Adrian J., Madder et al.], Based on the fact that in an acidic environment, free cyanides form a weak volatile HCN HCN:

CN ^- + H ⁺ → HCN (acidification)

Bubbling the acidified solution with air leads to the fact that hydrocyanic acid passes into the gas phase:

HCN → HCN ↑ (stripping - volatilization).

The released gaseous hydrogen cyanide is absorbed by alkaline solutions:

HCN ↑ + NaOH → NaCN + Н ₂ О, and the acidic solution is neutralized with an alkaline reagent and sent for further purification in one way or another (reneutralization).

When acidifying solutions, not only the binding of free cyanides in HCN occurs, but also the destruction of complex cyanides with the release of additional HCN and the formation of insoluble non-ferrous cyanides and thiocyanates:

In addition, in the presence of [Fe (CN) ₆ ] ^4- ions in the solution, complex ferrocyanides of copper, nickel, zinc, and iron precipitate:

[Fe (CN ₆ )] ^4- + 2Me ²⁺ = Me [Fe (CN ₆ )] ↓, (Me = Cu ⁺ , Cu ²⁺ , Ni ²⁺ , Zn ²⁺ )

3 [Fe (CN ₆ )] ^4- + 4Fe ³⁺ = Fe ₄ [Fe (CN ₆ )] ₃ ↓

To implement the AVR process in these methods use bubbler or packed columns for desorption of hydrocyanic acid.

The disadvantages of these methods are multi-stage and long (within 2-6 hours) aeration with air using sparging or packed columns, as well as the frequency of the processes.

A known method of neutralization and regeneration of cyanides during cyanide leaching of precious metals from ores, concentrates and industrial waste, including loading a cyanide solution or pulp into a reactor, treatment with sulfuric acid, absorption of the resulting hydrogen cyanide with an alkali solution, which consists in the fact that the treatment with sulfuric acid is carried out in a sealed the reactor with vigorous stirring and self-heating, leading to an increase in pressure in the reactor, under the influence of which the accumulating hydrogen cyanide enters it flows through a gas pipeline into a bubbler, 2/3 filled with an alkali solution, equipped with a dispersant and an irrigator [RF Patent No. 2141538 C1. The method of neutralization and regeneration of cyanides during the leaching of metals from ores, concentrates and industrial waste / V.V. Mamilov, V.P. Novik-Kachan, A.I. Doroshenko. - Publ. 11/21/99, Bull. No. 32].

The disadvantages of this method are the heating of the medium and the reactor, increased pressure in the stripper, batch operation and a long processing time of 20-30 minutes, as well as incomplete absorption of gaseous hydrogen cyanide by alkali. In addition, the process of desorption of HCN in the stripper — stripper and absorption of HCN in a bubbler absorber does not provide the intensity of mass transfer and the amount of air oxygen dissolved in water necessary for effective stripping of HCN.

A known method of purification of cyanide and rhodanide-containing wastewater, including their treatment with iron-containing reagents with the formation of insoluble compounds and other non-toxic reaction products [US Pat. 4312760. 1982. Method for the removal of free and complex cyanides from water / Neville, Roy G.].

A known method of neutralizing cyanides and thiocyanates, including their oxidation by treating the effluent with sulfur dioxide or sulfites of alkali or alkaline earth metals in the presence of atmospheric oxygen and a catalyst, mainly copper [US Pat. 4537686. 1985. Cyanide removal from aqueous streams / Borbely, Gyula J., Devuyst et al.].

Known methods for the neutralization of cyanide and rhodanide-containing wastewater of cyanide leaching of precious metals by treatment with chlorine-containing reagents containing "active chlorine", for example sodium hypochlorite, at a pH of 10-10.5 with the formation of chlorocyan and its hydrolysis to cyanate, followed by oxidation of cyanate to nitrogen and carbon dioxide gas at a pH of 6-7 [Milovanov S.V. Sewage treatment of non-ferrous metallurgy enterprises. M .: Metallurgy 1987; Maslenitsky I.N., Chugaev L.V. et al. Metallurgy of noble metals. M .: Metallurgy. 1987 .; Buchilo E. Wastewater treatment of non-ferrous metallurgy enterprises. M.: Metallurgy, 1976, S. 56-60].

Closest to the proposed technical essence is a method of neutralizing cyanide and rhodanide-containing wastewater by treating it with a chlorine-containing reagent to form chlorocyanine at a pH of 2-7 with simultaneous blowing of chlorocyanine with air [A.S. No. 650980. The method of neutralizing cyanide and rhodanide-containing wastewater. / Vrtanesyan S.G., Minasyan K.V., Gevorkyan E.A. and others. - Publ. 03/05/79, Bull. No. 9]. The process is carried out in sealed equipment. The waste mixture of chlorocyan and air is washed with a concentrated alkaline solution (milk of lime), in which hydrolysis of chlorocyan is carried out. Chlorocyanine-free air is again fed into the process.

The disadvantages of these methods and the prototype are the irretrievable loss of a valuable reagent - cyanide, accompanying noble metals of non-ferrous metals (copper, zinc, nickel, cobalt), the formation of toxic chlorocyanine, an increase in the total salinity of water, large amounts of precipitation, as well as increased consumption of oxidizing agents.

The technical result of the invention is to eliminate the noted drawbacks and increase the technological, economic and environmental efficiency of the process of cyanide leaching of precious metals from ores, concentrates and industrial wastes and the neutralization of cyanide and rhodanide-containing wastewater.

This result is achieved by the fact that cyanide- and thiocyanate-containing solutions are treated with concentrated sulfuric acid to a pH of 2-4, dosing it into a supply line to a centrifugal bubbler apparatus (CBA), followed by blowing, and then absorption of the resulting hydrogen cyanide by alkali solution in the reactors , which use centrifugal bubblers. The implementation of the AVR process in CBA allows for deep neutralization and regeneration in a continuous mode and with a processing time of solutions in the reaction zone of CBA of less than 1 min. The use of CBA as an absorber reactor also allows complete absorption of hydrocyanic acid by an alkali solution.

In addition, the process of blowing in a centrifugal bubbler apparatus allows you to return to production an additional amount of sodium cyanide (up to 30%) due to the partial oxidation of thiocyanates and, thus, reduce the oxidizer consumption at the final stage of neutralization of spent technological solutions of noble metal cyanide leaching, which is one of the distinguishing features of the proposed method.

The principle of operation of centrifugal bubblers is based on passing gas through a rotating layer of liquid, held by the gas stream in a vortex chamber. The specific contact surface of the phases in such devices reaches several thousand m ² / m ³ . The volumetric rate of chemical reactions in CBA due to the intensification of mass transfer is 40-60 times higher than in conventional bubble columns (drawing).

The inventive method is confirmed by the following examples.

Example 1. Recycled water containing, mg / l: simple and complex cyanides -1008.0, thiocyanates - 1797.0, iron - 96.0, copper - 734.0, zinc - 15.5 and having a pH value of 10.4, acidified with concentrated sulfuric acid to pH 3.7 and sent for HCN stripping and absorption into a centrifugal bubbler (liquid flow rate 60-80 l / h, specific contact surface of phases 714-920 m ² / m ³ ). Intensive mass transfer leads to the almost complete removal of cyanides from the solution, as evidenced by the following residual concentrations in the treated solutions: cyanides -1.9 mg / l, thiocyanates - 1133.0 mg / l, iron - 5.0 mg / l, copper - 106.0 mg / l, zinc - 0.1 mg / l. The residence time of the solutions in the reaction zone of CBA is less than 1 min.

Example 2. Recycled water containing, mg / l: simple and complex cyanides -1008.0, thiocyanates - 1797.0, iron - 96.0, copper - 734.0, zinc - 15.5 and having a pH value of 10.3, acidified with concentrated sulfuric acid to pH 2.5 and processed in a centrifugal spargers, as in example 1. The following residual concentrations, mg / L, were found in the neutralized water: cyanides — 0.4, thiocyanates — 996.0, iron — 6.8, copper — 3.5, zinc — 0.2.

It was found that during the processing of solutions in a centrifugal bubbler apparatus under conditions of intensive mass transfer, catalytic oxidation of thiocyanates occurs with the formation of an additional amount of HCN according to the following reaction:

A comparison of the results of determination of cyanides in solutions before and after treatment in CBA with the results of determination of CN ^- in an NaOH absorbing solution showed that the content of cyanides in the absorbing solution is 30% higher on average than would be expected even with the complete destruction of complex non-ferrous metal cyanides.

Thus, the proposed method allows for the deep neutralization of cyanide and rhodanide-containing wastewater and circulating water by acidifying the solutions to a pH of 2-4, followed by intensive blowing of the cyanide acid liberated in this case and its complete absorption with the formation of alkali metal cyanide in centrifugal bubblers. In addition, the proposed method allows to partially reduce the concentration of thiocyanates due to their oxidation in the CBA reactor.

EFFECT: invention makes it possible to repeatedly use expensive alkali metal cyanide in the process (about 1.15 kg of NaCN is extracted from 1 m ^{3 of the} spent solution). As well as the small size of the centrifugal bubbling modules for carrying out the AVR process, they can be compactly integrated into existing technological schemes at each enterprise and significantly reduce the cost of neutralizing waste solutions and wastewater from the cyanidation process. At the final stage, if necessary, the remaining thiocyanates are processed using one of the destructive methods.

Claims (3)

1. A method of neutralizing cyanide and rhodanide-containing wastewater of cyanide leaching of precious metals from ores, concentrates and industrial waste, carried out by acidification followed by air blowing of hydrogen cyanide, characterized in that the effluent is acidified to a pH of 2-4 with the formation of hydrocyanic acid , for the processes of stripping and absorption of hydrogen cyanide, centrifugal bubblers are used, which make it possible to neutralize cyanide and rhodanide-containing races thieves with complete absorption of gaseous hydrogen cyanide due to the intensive mass transfer in less than 1 minute. 2. The method according to claim 1, characterized in that the processing in centrifugal bubblers is carried out in a continuous mode. 3. The method according to claim 1, characterized in that sulfuric acid is dosed into the supply line to the centrifugal bubbler apparatus.