JPS6143282B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for recovering tungsten, tellurium or molybdenum in high purity from wastewater containing heavy metals.

Tungsten and molybdenum are used as effective components in heat-resistant and acid-resistant alloys, as well as in electron tube electrodes, filaments, heating elements, hydrogenation catalysts, and
It is a useful metal that is used in a wide range of applications, including as an additive to lubricating oil and as a reagent for analysis. These metals are rarely contained alone in the wastewater generated and discharged as a result of various materials manufacturing processes.

In addition, it is impossible to efficiently recover tungsten, tellurium, and molybdenum, which coexist with other heavy metals, in high purity using conventional wastewater technology, so they are either discharged or collected along with other heavy metal sludge. The current situation is that it is being dumped. Although these metals are not currently included in the wastewater standards based on the Water Pollution Control Law, they are currently being considered as subject to future regulations, and are extremely valuable. It is also a metal that is highly desired to be recovered. In order to separate these metals from wastewater, it is necessary to make the wastewater strongly acidic using hydrochloric acid, etc. However, the precipitate that is produced during this process strongly adsorbs coexisting heavy metals, making it impossible to separate with high purity. It is known that cleaning after separation is extremely difficult.

The present invention provides a method for recovering tungsten, tellurium, or molybdenum, which has been impossible in the past.

The recovery method of the present invention is to add ferrous salt to wastewater containing molybdenum, tungsten or tellurium, and then add alkali to maintain the pH at 8 to 12, and if necessary, to 100℃ or less, preferably 60 to 90℃. By heating it to a temperature of 100°C and contacting it with an oxygen-containing gas, or by adding an oxidizing agent such as hydrogen peroxide, some of the ferrous ions are oxidized to form a spinel-type ferrite precipitate, which is then separated into solid-liquid. After that, this separated water
It is characterized by lowering the pH to 2 or less and separating the precipitates of hydrous oxides of molybdenum, tungsten or tellurium.

The ferrous salt used in the present invention is most conveniently the sulfate salt available at the lowest cost, but is not particularly limited to this salt. However, ferrous sulfate must be used if alkaline earth metal ions coexist in the waste liquid or if alkaline earth hydroxide or the like is used to adjust the pH in subsequent processing. It is usually necessary to add 2 to 5 times the equivalent of heavy metals other than tungsten, tellurium, and molybdenum in wastewater, but it is not necessary to add them all at once, and they can be added if they are found to be insufficient during the treatment process. There is no problem. Next, when adjusting the pH by adding alkali, the pH is limited to 8 or more and 12 or less.If the pH is lower than 8, it is not only difficult to obtain spinel-type ferrite precipitates by oxidation, but also the PH is not necessary for oxidation. This is because the time becomes too long, and even if the pH is set higher than 12, ferrite precipitate will still be formed, but a different phase will likely occur. Oxidation conditions should be optimally determined depending on the amount and concentration of wastewater. In general, heating and air oxidation are appropriate in the case of high-concentration, small-volume wastewater, and it is considered economical to oxidize at room temperature, in the case of low-concentration, large-volume wastewater.

While heavy metals such as manganese, cobalt, nickel, chromium, zinc, and copper cadmium are easily incorporated into the ferrite precipitate produced by oxidation, molybdenum, tellurium, and tungsten are incorporated, but to a small extent. Therefore, the concentration of heavy metals other than molybdenum, tellurium, and tungsten in the separated water from which the ferrite precipitate has been removed is only traces.
Only high purity tungsten remains. Therefore, PH is 2
By lowering the concentration below, it becomes possible to recover these hydrous oxide precipitates with high purity.

Next, the present invention will be specifically explained with reference to Examples.

Example 1 Chromium, cobalt, zinc, copper each at 200%
30 gv of ferrous sulfate to heavy metal-adjusted wastewater 1 containing approximately 100 mg/mg of tungsten.
Add and adjust the pH by adding approximately 30% caustic soda solution
Heat to 65℃ while maintaining the
Oxidation was carried out by blowing air at a rate of 2 hours, and the black ferrite production reaction was completed after 2 hours. Hydrochloric acid was added to the solution from which the ferrite precipitate was completely removed using a permanent magnet, the pH was lowered to around 0, and the formed precipitate was over-separated. After washing with water and drying at 105°C, 1.1 g of tungsten hydrous oxide was recovered. I was able to do that. This is tungsten
This corresponds to a recovery rate of 87%. The content of heavy metal impurities in these oxides was all below 0.1%.

Example 2 Nickel, iron, manganese, 50mg/each
10g of ferrous sulfate was added to 0.5% wastewater containing molybdenum at a concentration of 2000mg/2,000mg, and approximately 30% caustic soda was used to maintain the pH at 11 and gently stirred using a stirrer to separate air and liquid. The oxidation reaction was continued for 8 hours by contacting only the surfaces, the generated ferrite particles were magnetically separated, the separated water was adjusted to pH 1 with hydrochloric acid, and after excessive separation, it was rinsed and dried with a small amount of 1/10 NHCl. As a result, approximately 1.2 g of hydrous oxidation was obtained. We were able to recover molybdenum. This corresponds to a recovery rate of 80% for molybdenum. The impurity heavy metal concentration in this oxide is 0.1
% or less.

Example 3 The same treatment as in Example 1 was performed on the same wastewater as in Example 1, except that 1000 mg of tellurium was contained instead of tungsten.
I was able to collect g. This was a recovery rate of 83% as tellurium.

As specifically shown in the examples above, it is clear that the present invention provides a novel method that is extremely effective for recovering molybdenum, tellurium, and tungsten from wastewater.

Claims (1)

[Claims] 1. Ferrous salt is added to wastewater containing at least one of molybdenum, tungsten, and tellurium and heavy metals to maintain the pH between 8 and 12, and the ferrous water is brought into contact with oxygen-containing gas, or by adding an oxidizing agent. A step of oxidizing a part of the iron ions to produce a spinel-type ferrite precipitate containing the heavy metals, and after solid-liquid separation of the ferrite precipitate, the pH of the separated water is lowered to 2 or less and at least molybdenum, tungsten and tellurium are removed. 1. A method for recovering metals from wastewater, the method comprising: generating one hydrous oxide precipitate.