JPS62234B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for recovering zinc compounds from zincate bath galvanizing process wastewater. In recent years, the galvanizing industry has been transitioning from traditional cyanide baths to zincate baths, zinc chloride baths, and zinc sulfate baths. The biggest reason for this trend is
The environmental pollution caused by cyanide wastewater is significant, and it is difficult to take measures to prevent it. However, even in galvanizing baths other than cyanide, it is still necessary to take measures against heavy metal contamination, and various measures are currently being taken. Currently, the most commonly used method for preventing environmental pollution from wastewater is turning it into sludge through coagulation and sedimentation treatment. However, zinc-based sludge has poor workability in handling water-containing materials, and the common method for disposing of sludge is to bury it in a landfill using concrete, which has the drawback of being too expensive. The present inventors anticipate that there will be a shift from cyanide-based zinc plating to zincate-based zinc plating in the future,
We have researched a treatment method for plating wastewater that can efficiently recover zinc components from zincate-based galvanizing process wastewater and reuse the treated water, and have developed an efficient and economical way to recover zinc components from zincate bath galvanizing process wastewater, which could not be recovered in the past. They found a way to recover it. That is, the present invention involves a pretreatment step in which wastewater from the zincate bath galvanizing process is adjusted to pH 6 to 10, and the pH-adjusted wastewater is filtered and the suspended solids are dissolved in acid or alkali without separating them from the filter medium to produce zinc. Zincate bath galvanizing process wastewater, characterized in that it is treated in a step consisting of a first step in which the compound is recovered as a solution, and a second step in which the filtrate is treated with a chelating ion exchanger and zinc ions are recovered by acid elution. This method recovers zinc compounds from In the present invention, the zincate bath galvanizing process wastewater refers to wastewater from washing plating products from the plating bath, and when waste liquid and plating liquid generated during partial disposal when the plating bath becomes obsolete is filtered and purified in the cycle line. This refers to wastewater from cleaning filter media, etc. The main components of these wastewaters are zinc compounds and sodium ions, and impurities include iron, calcium magnesium, etc. Since zinc is an amphoteric metal, its inorganic salt exists as zinc cation, zincate anion, a mixture thereof, and zinc hydroxide depending on the pH of the solution. Usually, it is a cation when acidic, a mixed system of cation and zinc hydroxide when it is weakly acidic to weakly alkaline, and a mixed system of zinc hydroxide and zincate anion when it is alkaline. An important treatment point in the present invention is to adjust the pH value of the liquid to be treated to between 6 and 10. By pre-treating in this way, the composition of the system can be adjusted to reduce the suspended solid content of zinc cations and zinc hydroxide. (hereinafter referred to as SS component), and in combination with the following treatments, it is possible to recover zinc compounds.
At this time, if the pH is less than 6, the concentration of zinc cations in the filtrate will be high and the subsequent second step will be overloaded, making it uneconomical. If the ingredients become high, the load on the subsequent first step becomes high, or the ratio of zincate anions becomes too high.
Adsorption treatment becomes virtually impossible. SS components exist in a fluffy, fluffy state in wastewater that is controlled to a pH range of 6 to 10. this
Although it is easy to filter the SS component using a filter medium such as sand, anthracite, or cloth, the filtered SS component is difficult to handle, so it is not easy to separate it from the filter medium. Therefore, in the treatment of the first step of the present invention, the SS component is not separated from the filter medium as a solid content,
When the SS component accumulates above a certain level, the SS component is dissolved by direct action of an acid or alkaline aqueous solution, and when the zinc concentration of this solution reaches a predetermined concentration, it is recovered as a solution. It is true. This dissolution can be easily carried out by directly showering acid or alkaline liquid on the deposited SS component. When dissolving SS components, if the zinc concentration in the solution is too low, add acid or alkali and reuse it as a showering solution to raise the zinc concentration in the recovered solution to a high concentration of 0.5% to several %. Then, the recovered zinc compound can be easily reused. Zinc cations and a large amount of sodium ions are dissolved in the filtrate filtered in the first step of the present invention. The concentration of this dissolved component is several mg/zinc ion.
~20mg/about, and sodium ions are few
100 to tens of thousands of mg/. In the second step of the present invention, only zinc ions are selectively adsorbed and removed, so treatment with a chelating ion exchanger is necessary. Usually, a cylindrical column is filled with a chelating ion exchanger, and the liquid to be treated is passed through the column in a downward or upward flow. When actually treating wastewater, usually 2
It is desirable to use towers to three towers and pass the treatment liquid in a merry-go-round style. Among the towers filled with chelating ion exchangers, mineral acids such as sulfuric acid and hydrochloric acid are passed through the tower saturated with zinc ions to remove zinc ions and recover them as an aqueous solution of zinc sulfate or zinc chloride. The liquid passing rate during adsorption and desorption, the amount of acid required for desorption, etc. depend on the type and amount of the chelating ion exchanger used, the quality of the recovered liquid, etc. The amount of zinc ions to be loaded in the second step depends on the amount of zinc ions remaining in the wastewater due to pH adjustment, and when the pH is adjusted to a range of 6 to 10, it is several mg/~20mg/
It will be about. If the pH is adjusted to lower than 6, the amount of zinc ions will greatly exceed 20mg/, but if the amount of dissolved zinc ions exceeds 20mg/, the load on the second process will become too large, increasing the initial cost of the equipment, and increasing the initial cost of the equipment. It is also extremely disadvantageous economically since it also increases running costs. The chelating ion exchanger used in this second step may have a matrix of either an inorganic polymeric substance or an organic polymeric substance, as long as it has a chelating ligand in the matrix. In particular, chelating ligands consisting of nitrogen (N) and oxygen (O) are excellent. Usually, the parent material of chelating ion exchangers is organic polymers such as silicone-based inorganic polymers, polystyrene-based, polyphenol aldehyde-based, polyacrylonitrile-based, etc., and those whose ligand consists only of nitrogen are urea derivatives and amino acids. Derivatives etc. are effective. Commercially available chelating ion exchangers include Dowex A-1 from Dow Chemical Co., Diaion CR-10 from Mitsubishi Chemical Co., Ltd.
Examples include CR-20, CR-40, and Uniselect UR-10, UR-20, and UR-30 manufactured by Unitika Co., Ltd., and all of these can be applied to the present invention. Although these chelating ion exchangers each have slightly different characteristics, they all have a common characteristic of selectively adsorbing heavy metal ions such as zinc in the coexistence of alkali metal ions and alkaline earth metal ions. After adsorption, the eluent can be eluted with the mineral acid necessary for a regeneration level that is approximately equivalent to the exchange capacity of the chelating ion exchange resin, so the quality of the eluent is better than that of ordinary ion exchange resins. In the method of the present invention, a zinc ion concentration of about 7 to 40 g/g is obtained. According to the method of the present invention, the troublesome treatment of zinc sludge is completely eliminated, and the zinc component can be recovered as a relatively high-grade zinc sulfate aqueous solution or zinc chloride aqueous solution, which can be reused as a galvanizing solution or an inorganic chemical. On the other hand, since the treated water contains almost no zinc ions or other heavy metal ions, there is no fear of environmental pollution due to heavy metal ions. Next, the present invention will be described in more detail with reference to Examples. Example 1 Experimental equipment consisting of a 1 m ² PH adjustment tank, a cylindrical PVC filter with a diameter of 100 mmφ and a height of 700 mm (filled with anthracite with an effectiveness of 0.8 mm to a height of about 300 mm), and a glass column with a diameter of 13 mmφ. After assembling the system, a metering pump was used to send the pH-adjusted water from the pH adjustment tank to the filter. In addition, the glass column was filled with approximately 133 ml of chelating ion exchange resin Uniselect UR-30 (manufactured by Unichita Co., Ltd.) to a resin height of approximately 1000 mm. Furthermore, as model washing water for zincate bath galvanizing, approximately 450 solutions of water quality as shown in the following table were prepared. This model solution was adjusted to pH 7.7±0.1 in a regulating tank, and then introduced into a filter with the SS component mixed therein, and the SS component was filtered out. The filtrate was further sent to a chelating ion exchange resin tower to adsorb dissolved zinc components.

[Table] As a result of passing the model solution in the order of PH adjustment → filtration → chelating ion exchange resin, zinc ions were found to be about 1 mg/approx. It started leaking. At this point, the flow of liquid was stopped, and the SS component deposited on the filter was dissolved by gently pouring 320 ml of a 2N-HCl aqueous solution. The liquid was gently drawn out from the bottom of the filter, the same drawn liquid was poured again, and the liquid was drawn out from the bottom of the filter. Thereafter, it was washed with about 2 ml of water and combined with the extracted liquid to obtain about 2,300 ml of a zinc chloride aqueous solution. Concentration as zinc ion is approximately 8.5g/
It was hot. Next, 85 ml of a 2N-HCl aqueous solution was poured into the chelating ion exchange resin column and eluted at a rate of SV=1.0 [1/Hr]. Following 85 ml of hydrochloric acid, 265 ml of water was flowed at the same speed to drain the water. At this time, the fractions from 80 ml to 220 ml were used as the collected liquid.
The recovered zinc chloride aqueous solution contains 19
The concentration was g/g/. Comparative Example 1 After stopping the liquid flow at the same point as in Example 1, the water height of the filter was adjusted to 20 cm above the anthracite surface, air was backwashed for 5 minutes at a linear velocity of 60 m/m, and then The treatment was carried out in the same manner as in Example 1, except that water backwashing was performed for 10 minutes at a linear velocity of 25 m/m to remove SS components deposited on the filter from the system. As a result, most of the SS components could be taken out of the system, but the liquid volume was 31.7. Example 1
By adding 320 ml of 2N-HCl in the same manner as above, an aqueous zinc chloride solution of 32 was obtained. The zinc ion concentration of the obtained aqueous solution was 0.6 g/, which was higher than that in Example 1.
It was 1/14 and had little utility value.

Claims (1)

[Claims] 1 Zincate bath Galvanizing process wastewater with pH 6 to 10
The first step is to filter the pH-adjusted wastewater and dissolve the filtered suspended solids with acid or alkali without separating them from the filter medium to recover zinc compounds as a solution. A method for recovering zinc compounds from wastewater from a zincate bath galvanizing process, characterized in that the treatment is performed in a second step of adsorption treatment with an ion exchanger and recovery of the adsorbed zinc ions by acid elution.