JPS63291690A - Treatment of waste water separated from metal cyanide - Google Patents

Abstract

PURPOSE:To treat waste water safely and efficiently by blowing air into waste water separated from metal cyanide, and allowing coexistent separation assistant through acidification of a solution after oxidation and decomposition of cyanide with addition of powder manganese dioxide. CONSTITUTION:Air is blown into waste water separated from metal cyanide as an oxidant, and further powder manganese dioxide is added as a promotion catalyst to allow oxidation and decomposition of cyanogen. Next, the solution is acidified and a separation assistant of coexistent organic matter is allowed to deposit perfectly to be removed. When oxidation and decomposition of the cyanogen in waste water separated from metal cyanide are performed, the pH value of waste water should preferably be kept to more than 10. In addition, the ideal addition dosage of powder manganese dioxide added to the waste water is 10g/l or less which meets the oxidation/decomposition rate of cyanide and the economical dosage is about 3-5g/l, although the more suspension amount, the better contact with air.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for treating metallic cyanide stripping wastewater generated from a precious metal layer recovery factory or the like.

(Prior art and its problems) Metal cyanide stripping wastewater generated from precious metal layer recovery factories, etc. contains a large amount of cyanide, and a considerable amount of an organic stripping aid is added. remove these things,
It cannot be discharged outside the factory unless it clears the wastewater standards stipulated by the Water Pollution Control Law.

Cyanide decomposition treatment is generally carried out by an alkali chlorine method, but in this method, in addition to decomposing cyanide, an oxidizing agent is consumed in oxidizing coexisting organic matter. For this reason, the cyan content concentration is 10
g/1, the same volume of hypochlorous acid solution as the wastewater is consumed, the amount of treated liquid is doubled, and subsequent treatment requires extra effort. Furthermore, when the wastewater is made acidic to remove the coexisting organic material stripping aid, if excess hypochlorous acid remains, harmful chlorine gas is generated.

In addition to the above-mentioned alkali chlorine method, cyanide decomposition treatment includes electrolytic treatment and evaporation to dryness, but electrolytic treatment has the disadvantage of being inefficient, taking a long time, and wasting energy.
The evaporation to dryness method consumes a large amount of thermal energy and requires considerable abatement equipment in addition to combustion equipment in order for the exhaust gas to pass air pollution prevention standards.

(Object of the invention) The present invention was made to solve the above problems.
In order to prevent the increase in processing solution and remove organic stripping aids, no harmful gases are generated even if the wastewater is made acidic, and a method for treating metallic cyanide stripping wastewater that is efficient, safe, and economical has been developed. The purpose is to provide

(Means for Solving the Problems) In order to solve the above-mentioned problems, the method for treating metallic cyanide stripping wastewater according to the present invention involves blowing air into the metallic cyanide stripping wastewater as an oxidizing agent, and using carbon dioxide as an oxidation promoting catalyst. This method is characterized by adding manganese powder to oxidize and decompose cyanide, and then making the solution acidic to completely precipitate and remove the coexisting organic stripping aid.

When cyanide in metal cyanide stripping wastewater is oxidized and decomposed, the pH of the wastewater is preferably maintained at 10 or higher. The amount of manganese dioxide powder to be added to the wastewater should be 10 g/A or less (preferably 3 to 5 g/A), which is appropriate for the oxidative decomposition rate of cyanide, although the larger the amount of suspension, the better the contact with the air.
) is added in an economical amount.

(Function) According to the method for treating metal cyanide peeling wastewater of the present invention,
Manganese dioxide (preferably activated manganese dioxide) oxidatively decomposes cyanide to form a lower oxide, which is oxidized with air to return to manganese oxide, thereby repeatedly contributing to the oxidative decomposition of cyanide.

By repeating the above cycle in the solution, cyanide is oxidized and decomposed, and cyano iron complex salts, cyano nickel complex salts, etc. are also decomposed.

During the above oxidative decomposition of cyanide, if the amount of manganese dioxide added is 10 g/l or less (preferably 3 to 5 g/l) and air is blown in, the oxidative decomposition rate of cyanide will be commensurate with the oxidative decomposition rate, and the decomposition will be slow. Cyano iron complex salts and cyano nickel complex salts are also decomposed. In addition, an increase in the amount of processing liquid is prevented.

In the method for treating metallic cyanide stripping wastewater of the present invention, the organic stripping aid coexisting in the solution dissolves in the form of alkali salts such as Na and K, and colors the solution, so this is neutralized. By adjusting the pH to 4 or less (preferably PH2 or less), it can be precipitated and removed. Therefore,
Even if the solution is made acidic, there is no risk of harmful effects. Furthermore, since no organic stripping aid remains, it does not interfere with the subsequent precipitation of heavy metals.

(Example) Examples and conventional examples of the method for treating metal cyanide peeling wastewater according to the present invention will be described.

First, to explain the example, the cyan density is 9.3g/
A, activated manganese dioxide was added at a rate of 5 g/l to an Au cyanide stripping solution with a pH of 12.80, and air was blown for 20 hours to completely oxidize and decompose the cyanide. Pour this solution with mineral acid.
It was set as H1.8, and in addition to this, 3 g/e of zinc powder was added, and precipitated Au and organic matter were removed. Then the pH of the solution is 8
．． When the heavy metals were coagulated and precipitated as No. 5, it cleared the wastewater standards. The amount of liquid after treatment was reduced to 0.92 times that of the original solution.

Next, to explain the conventional example, a sodium hypochlorite solution (12%
) to decompose the cyanide by adding 250 β of the secondary decomposition needle, and decompose the excess sodium hypochlorite by adding 0.3 J of pencil (SBH 16% solution).This solution was mixed with mineral acid. The pH of the solution was adjusted to 2, and 3 g/It of zinc powder was added to this to remove precipitated Au and organic matter.Then, the pH of the solution was adjusted to
8.5, and the heavy metals were coagulated and precipitated to clear the wastewater standards. The amount of liquid after treatment increased to 2.6 times that of the original solution.

As is clear from the comparison between the above example and the conventional example, in the conventional example, the amount of liquid after treatment increases significantly, whereas in the example, the amount of liquid after treatment decreases, completely preventing the increase in liquid amount. has been done. Further, in the conventional example, when excessive hypochlorous acid remained, harmful chlorine gas was generated, whereas in the example, no such harmful gas was generated.

In addition, in the method for treating metallic cyanide peeling wastewater of the present invention,
The heavy metals in the treated wastewater from which the organic stripping aid has been removed are precipitated as heavy metal hydroxides by conventional pH adjustment, or as sulfides by H and S. Alternatively, heavy metals are agglomerated by reduction with S B H, hydrazine, sulfite, periosulfate, or the like. Furthermore, an adsorption method using activated carbon or ion exchange resin may be applied.

(Effects of the Invention) As detailed above, according to the method for treating metallic cyanide stripping wastewater of the present invention, cyanide metal complexes, which are slow to decompose, can be decomposed together with the oxidative decomposition of cyanide, and an increase in the amount of treatment liquid can be prevented.
Rather, it can reduce the amount of processing liquid, and since it removes organic stripping aids, there is no generation of harmful gases even if the wastewater is made acidic.It is also highly efficient, safe and economical, and can be used especially for solutions with high cyanide concentrations. It has effects such as being advantageous for processing.

Claims (2)

[Claims] (1) Metallic cyanide stripping Air is blown into the waste water as an oxidizing agent, manganese dioxide powder is added as an oxidation accelerating catalyst, cyanide is oxidized and decomposed, and the solution is then made acidic to strip the coexisting organic matter. A method for treating metallic cyanide stripping wastewater, which is characterized by completely precipitating and removing the auxiliary agent. (2) Maintaining the pH of the metal cyanide peeling wastewater at 10 or higher,
The method for treating metallic cyanide stripping wastewater according to claim 1, wherein the amount of manganese dioxide powder added is 10 g/l or less.