JPH052400B2 - - Google Patents

Description

[Detailed description of the invention]

Industrial Application Field Mercury can be efficiently removed from gas containing mercury vapor by absorbing it into an absorption liquid containing thiourea and copper ions. It relates to a method of recovering and utilizing components. Problems with conventional technology Wastewater containing thiourea has a high COD and has problems in treatment. It has been known that mercury can be removed from mercury-absorbing wastewater containing thiourea and copper ions by high alkali treatment, but after mercury and copper have been separated as SS, a large amount of Because thiourea remains, the COD is high and its disposal has become a problem. Means for Solving the Problems The inventors therefore tried and succeeded in reusing the waste liquid from which copper and mercury were over-separated using SS as a mercury absorption liquid instead of disposing of it as waste liquid. That is, the waste liquid is treated with alkali to precipitate the copper and mercury in the waste liquid as sulfide, and the pH of the separated liquid from which copper and mercury have been removed is adjusted, and the specified thiourea and copper salt are replenished to absorb mercury vapor. It can be recycled and reused as a liquid. Incidentally, the alkaline treatment of the waste liquid can be carried out by using any alkaline agent to adjust the pH of the liquid to 8 or higher, preferably 9 or higher. The present inventors further discovered a method for separating and recovering copper and mercury after separating copper and mercury sulfides. First, an acid such as sulfuric acid, hydrochloric acid, nitric acid, or an alkali such as aqueous ammonia is added to the separated copper and mercury sulfide, and if necessary, an oxidizing agent such as hydrogen peroxide or persulfuric acid is added to remove copper. Mercury can be recovered as sulfide by dissolving only the sulfide and separating the resulting product liquid as a solid by filtration or the like. Acid treatment is preferably carried out at a pH of 3 or lower, more preferably 2 or lower, and an alkali treatment is preferably carried out at a pH of 11 or higher, more preferably PH12 or higher. There is no particular restriction on the treatment temperature, and the treatment can be carried out at room temperature. By neutralizing the thus obtained separated liquid with a suitable neutralizing agent, copper can be precipitated and recovered as hydroxide. As described above, according to the present invention, the absorption waste liquid can be recovered in a pure form without discarding the useful components therein, and can also be recycled and reused as an absorption liquid, thereby establishing a mercury-containing waste gas treatment system. We were able to. Next, even with the present invention, there may be cases where it is necessary to dispose of the mercury absorbing solution, and in that case, as described above,
COD treatment was a problem, and separation treatment using an oxidizing agent was not sufficient. For example, when oxidizing with hypochlorous acid, for example, 5
g/The waste liquid containing COD shows a value of 4250ml/, but the theoretical equivalent of sodium hypochlorite 20g/
When added, the COD was 30ml/
Furthermore, 1.5 times the theoretical equivalent amount of sodium hypochlorite 30
Even when thiourea was added, the COD was 20mg/, and complete treatment was not possible. By adding the above and adjusting the pH to 8 or higher, preferably 9 or higher, the COD of the liquid can be lowered to mg/min, and the copper concentration can be lowered.
It was possible to reduce the amount to 0.1mg/or less. In this treatment method, the sulfur component in thiourea combines with metal ions such as copper and is removed, resulting in COD.
It is thought that the component is urea, which cannot be detected analytically. Although sufficient treatment is possible for COD treatment, urea is treated as BOD at 1g/g of urea.
It shows a value of 1000mg/ and requires treatment, but this is decomposed into ammonia and carbon dioxide gas by heat treatment, so complete wastewater treatment can be achieved by heat treatment after the COD treatment of the present invention. Examples Examples of the present invention will be described below. Example 1 An absorption waste liquid having a composition shown in Table 1 below, which was obtained by cleaning exhaust gas containing vaporized mercury, was treated as follows. That is, the pH of absorption waste liquid 1 was adjusted with 20% NaOH aqueous solution.
When the temperature was adjusted to 12, a blackish brown sulfide precipitate was formed. The precipitate was overseparated and adjusted, and the composition of the solution was analyzed. The results were as shown in Experiment 1 in Table 2. It is clear from Table 2 that 92% of thiourea was recovered and heavy metals (copper and mercury) were precipitated and removed as dark brown sulfides. The sulfide sludge precipitated in Experiment 1 was placed in a 200 ml beaker, water was added to make 100 ml, 5 ml of 30% H ₂ O ₂ aqueous solution was added, and 30% sulfuric acid was added to adjust the pH of the liquid to 2. After stirring at room temperature for 30 minutes, the liquid was overseparated. The results of analyzing this liquid were as shown in Experiment 2 in Table 2. From the results of Experiment 2 in Table 2, it is clear that copper is dissolved in the liquid by the above treatment, mercury is not dissolved, and that it can be separated and recovered from copper. Next, in experiment 3, the solution in which copper was dissolved was diluted with NaOH solution to pH 7.
When the temperature was adjusted to 1, a precipitate (copper hydroxide) was formed. As a result of analyzing the copper in the solution after over-separation, as shown in Experiment 3 in Table 2, Cu could be precipitated and recovered as hydroxide.

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Claims (1)

[Claims] 1. In treating a waste liquid containing thiourea, copper salts and mercury, (i) the waste liquid is treated with an alkali to precipitate the copper and mercury in the waste liquid as sulfides; (ii) the copper and mercury are precipitated as sulfides; After separating the mercury sulfide as a solid, the copper sulfide is solubilized by acid or alkali treatment or acid or alkali treatment and oxidation treatment, and (iii) the mercury sulfide is recovered as a solid and the separated copper A method for treating waste liquid, characterized by recovering copper hydroxide by neutralizing the aqueous solution containing it. 2. The waste liquid is a liquid obtained by washing a gas containing mercury vapor with an aqueous solution containing thiourea and a copper salt, and adjusting the pH of the separated liquid after separating the copper and mercury sulfides precipitated in the step (i), 2. The method according to claim 1, wherein the thiourea concentration is adjusted and the copper salt is replenished and then reused as a cleaning solution for gas containing mercury vapor.