JPS6121691B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for treating H ₂ S in gas. More specifically, the present invention relates to a method for treating H ₂ S in gas. The ferrous sulfate solution that is regenerated by absorption is oxidized again by iron-oxidizing bacteria and used repeatedly to absorb H ₂ S as a ferric sulfate solution.
This provides an extremely inexpensive method for treating H ₂ S, which is fixed and recovered as H 2 S. Conventionally, absorption methods using caustic soda and absorption methods using ferric sulfate have been known to remove H ₂ S from gas, but methods using ferric sulfate are rarely used because they are extremely costly. Generally, a method using caustic soda is used, but this also requires considerable cost and is not an ideal treatment method. The present invention provides a method in which H ₂ S can be treated at a lower cost than the caustic soda method, and the S component can be recovered as So. That is, the present invention includes a first step of oxidizing a ferrous sulfate solution to ferric sulfate using iron-oxidizing bacteria;
The second step is to absorb H 2 S in the gas using the ferric sulfate solution obtained in the first step as an absorption liquid, and the liquid after _{the H 2 S} absorption in the second step is subjected to flotation to remove elemental sulfur. The third step consists of collecting the tail liquid and repeating the first step. Hereinafter, the method of the present invention will be explained in detail with reference to the flow sheet of the accompanying drawings. First, a sulfuric acid acidic solution containing ferrous sulfate is introduced into an oxidation tank, a small amount of inoculum of iron oxidizing bacteria (hereinafter simply referred to as bacteria) is added, and air is blown into the tank to grow the bacteria. Oxidation treatment to ferric iron (first step). In this case, when using nonferrous metal mine wastewater, smelting wastewater, or factory wastewater containing large amounts of ferrous sulfate,
Substances that normally inhibit the growth of said bacteria;
For example, since F ^- , Cl ^- , Hg, Ag, As, SS, etc. are present, these are removed or diluted in advance. The Fe ²⁺ concentration is 8-12 based on the oxidation efficiency of bacteria.
g/, PH is set to 2.0 or less by adding sulfuric acid if necessary to prevent iron content from precipitating in the oxidation tank and considering the oxidation efficiency of bacteria. In addition, when the liquid does not contain the nutrients for the bacteria, such as smelting wastewater, nutrients (N, P, K, etc.) are added to make the bacteria grow. Furthermore, in order to collect the grown bacteria without escaping, an acid-resistant porous material such as diatomaceous earth is added as a carrier agent to increase the bacterial concentration in the oxidation tank, and ferric sulfate is removed from the oxidation tank. It is preferable that the carrier agent overflowing with the solution is also collected by a thickener or the like and returned to the tank. Next, the second sulfuric acid is oxidized by bacteria in an oxidation tank.
H ₂ S is absorbed using an iron solution as an absorption liquid, and the absorbed gas is released (second step). The absorption method may be a method in which H ₂ S is diffused from the bottom of a tank filled with a ferric sulfate solution, or a method in which the solution is sprayed from above. The following reactions occur in the absorption process. Fe ₂ (SO ₄ ) ₃ +H ₂ S →2FeO ₄ +H ₂ SO ₄ +So This regenerates the ferrous sulfate solution, but
The reaction solution contains fine colloidal elemental sulfur, resulting in yellowish-white sulfur milk. If this is directly returned to the bacteria oxidation tank, sulfur will accumulate in the oxidation tank, creating a sulfur atmosphere. The properties of the bacteria change to sulfur-oxidizing bacteria, and since sulfur has poor sedimentation properties, the iron oxidizing ability decreases due to bacterial outflow due to overflow. Therefore, in the method of the present invention, in the third step, the post-reaction liquid is subjected to flotation to separate and remove elemental sulfur, and the tail liquid is repeated to the oxidation tank of the first step. A foaming agent is added to the sulfur milk in the second step for conditioning during flotation. As a result, the unstable sulfur colloid causes some aggregation, and when a scavenger such as a cation scavenger is added to this and stirred, the sulfur is completely agglomerated and the liquid becomes clear. By applying this to a flotation machine to perform flotation separation, sulfur can be almost completely removed. The clear flotation tail liquid from which sulfur has been removed in this way is a ferrous sulfate solution, which is returned to the bacterial oxidation tank in the first step, where it is oxidized by bacteria that have been sufficiently cultured and have become active. Sulfuric acid No. 2 again
Oxidized to iron and used for _H2S absorption. Furthermore, performing flotation as described above means that the liquid, which has absorbed H ₂ S and has become a reducing atmosphere, is returned to its normal state by aeration and stirring to facilitate bacterial oxidation in the first step. There are also secondary effects. On the other hand, since the sulfur separated by flotation is conditioned as described above, the colloidal sulfur, which is sticky and difficult to dehydrate using a filter, is covered with a scavenger and becomes sticky. This product adsorbed on the floss has been improved.
It can be easily fixed by adding a flocculant to So, allowing it to settle, then dehydrating and drying it. Note that the iron (ferrous sulfate) and diatomaceous earth lost during the process of the present invention are replenished into the bacterial oxidation tank in the first step. As described above, the method of the present invention repeatedly uses inexpensive ferrous sulfate, and can treat various exhaust gases containing H ₂ S at a lower cost than conventional methods (for example, less than 1/3 of the cost of the caustic soda method). can be done, and
The S content in H ₂ S has various advantages such as being able to be recovered as elemental sulfur in any form such as powder, flakes, pellets, etc. Example: Iron-oxidizing bacteria cultured at the M mine wastewater treatment plant
20 and diatomaceous earth with a pulp concentration of 15%, capacity 480
Sulfuric acid was added to the oxidation tank to adjust the pH to 1.8.
FeSO ₄ (Fe ²⁺ concentration 10 g/min) solution was continuously flowed in at a rate of 4/min, ammonium phosphate was continuously added as a nutrient at a concentration of 50 mg/min in the tank, and air was blown at a rate of 1.3 m ³ /min. I went to work. When the overflow liquid from the oxidation tank was led to a 262-capacity cone tank, the overflow water was investigated.
It was an almost completely oxidized Fe ₂ (SO ₄ ) ₃ solution. In addition, the diatomaceous earth mud containing bacteria precipitated in the cone tank was returned to the oxidation tank, and as a result of continuing the experiment, the oxidation of the liquid in the oxidation tank was completed in about 2 hours, and the loss of diatomaceous earth in the tank was reduced. The amount was around 50mg/. Next, an H ₂ S gas absorption experiment using the Fe ₂ (SO ₄ ) ₃ solution was conducted. The experiment was carried out by filling a flask with H ₂ S gas and expelling it with water using a metering pump.
Two absorption bottles, each containing a Fe ₂ (SO ₄ ) ₃ solution (10 gFe/), are connected through a connecting tube, and the gas is diffused from the bottom of each absorption bottle using a glass filter to process the gas in two stages. I did this.
The following table shows the results of measuring the H ₂ S concentration in the exhaust gas from the second-stage absorption liquid bottle using a Kitagawa detector. In addition,
The H ₂ S concentration of the original gas is too concentrated to be detected by a detector, so it is an estimated value obtained by simply diluting the volume. In addition, "0 minutes" in the table refers to the time when H ₂ S has started flowing and a stable state has been reached ( 5 minutes after the start) was defined as 0 minutes.

【table】

[Table] From the table, it can be seen that the absorption rate of H ₂ S is very good. The above H ₂ S absorption liquid with a So concentration of 2.32g/ is a sulfur colloidal emulsion, and this liquid 2 contains 0.01g of DOW#250 (trade name) or Yumin (trade name) as a foaming agent and a collecting agent. Duomin (product name)
0.01 g was added and stirred for 10 minutes to condition the solution. After the liquid was clarified, it was subjected to sulfur flotation for 3 minutes in a Kyoto University type flotation machine with a capacity of 1.8. When the flotation tail liquid was examined, the So concentration was 7ppm.
It was a clear solution of FeSO ₄ and could be used repeatedly in the bacterial oxidation tank. In addition, 0.005 g of Acofloc (trade name) was added as a flocculant to the flotation floc, and the floc was sedimented and passed through a filter. It is easy to dehydrate, and the water content after suction dehydration is 50%.
It was hot. The quality of the powder obtained by drying it with hot air was 97.6% S, 0.8% Fe, and 1.6% other, and could be formed into flakes or pellets.

[Brief explanation of the drawing]

The figure is a flow sheet of the method of the present invention.

Claims (1)

[Claims] 1. A first step of oxidizing a ferrous sulfate solution to ferric sulfate using iron-oxidizing bacteria, and using the ferric sulfate solution obtained in the first step as an absorbing liquid to remove H in the gas. _2S
and a third step in which the liquid after absorption in the second step is subjected to flotation to separate and recover elemental sulfur, and the flotation tail liquid is repeated in the first step. How to treat H ₂ S in gas. 2. In the gas according to claim 1, in which diatomaceous earth is used as a carrier agent for the bacteria.
How to process _H2S . 3 of the ferrous sulfate solution in the first step
3. The method for treating H ₂ S in a gas according to claim 1 or 2, wherein the Fe ²⁺ concentration is 8 to 12 g/ and the pH is adjusted to 2.0 or less.