JPS6127326B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention involves adding alkali carbonate to hot metal to desulfurize and
The present invention relates to a method for recovering alkali content by treating waste slag generated when one or both of dephosphorization processes are performed simultaneously.

Generally, pig iron contains C3.7~4.8%Si0.3~1.0%, manganese 0.2~0.8%, S0.02~0.05%, P0.10~0.180
It contains about %. Among these, S deteriorates the hot workability and impact performance of steel, and P deteriorates toughness and the like.

Therefore, it is preferable to remove S and P as much as possible as the steel becomes higher grade. Traditionally, desulfurization of hot metal was carried out outside the furnace using sodium carbonate or carbide.

However, since the waste slag from this process contains a large amount of soda, strict management was required to dispose of it. On the other hand, P was removed by adding quicklime to the converter or by the double slug method, but the waste slag from converter blowing (hereinafter referred to as converter slag) contains P, so it cannot be loaded into the blast furnace. It was not possible to enter the plant, and sufficient management was required to dispose of it.

Patented technology for recovering sodium bicarbonate from the slag produced when hot metal is desulfurized using sodium carbonate.
It is disclosed in specification No. 161054. This technique consists of an oxidation step in which oxygen is blown into the waste slag, an extraction step in which extraction is performed with hot water while applying carbon dioxide gas and oxygen, and a separation step in which the filtrate is concentrated and fractionally crystallized.

However, with this method, as the waste slag disintegrates during the oxidation process, it becomes sticky, and a large amount of power is consumed for stirring, and furthermore, the power consumption required for blowing oxygen to bring the slag into a sufficient contact reaction with oxygen is also large. , and the reaction takes a long time.

On the other hand, a method for simultaneously desulfurizing and dephosphorizing hot metal using sodium carbonate is known, for example, as described in JP-A-52-127420. This method requires 4 to 5 times the amount of sodium carbonate compared to the case where only desulfurization is performed, and there are economic problems in implementing it on an industrial scale. Therefore, it is desired to develop a technology for recovering sodium carbonate in order to reduce the consumption unit consumption of sodium carbonate and enable economical implementation.

By the way, when waste slag is treated by the method disclosed in Patent No. 161054, there are problems in industrial implementation such as adhesion of waste slag and reaction time as described above, and furthermore, sodium carbonate is recovered as sodium bicarbonate. Therefore, the problem remains that it cannot be reused as it is and must be burned.

In order to eliminate the above-mentioned disadvantages, the inventor of the present invention conducted intensive research on the desulfurization of hot metal using alkali carbonate and the treatment of waste slag after dephosphorization.
It was discovered that by treating the tailings with hot water while blowing carbon dioxide gas so that the carbon dioxide concentration is 9.0 to 11.5, the sulfur content can be precipitated and removed as iron sulfide, and that during this treatment, the alkali carbonate remains as it is without being bicarbonated. did. Further, by adding iron ions to the obtained extract, iron sulfide iron phosphate is precipitated to eliminate almost all the sulfur and phosphoric acid contents in the liquid, and then the alkali carbonate is recovered by fractional crystallization or flushing drying. The present inventors have discovered that they can be reused without such inconveniences, and have completed the present invention.

That is, the present invention involves treating and extracting hot metal with hot water while blowing carbon dioxide gas into the slag obtained by desulfurizing or dephosphorizing hot metal with an alkali carbonate so that the pH becomes 9.0 to 11.5, This is a waste slag treatment method in which iron ions are added to the extract, precipitates are filtered, and the filtrate is dried by fractional crystallization or flushing to recover alkali carbonate.

The alkali carbonate used in the present invention is sodium carbonate or potassium carbonate, but sodium carbonate is preferred from an economical point of view, and will be explained below using sodium carbonate as an example.

The present invention will be explained in detail with reference to FIG. For convenience of explanation, we will describe waste slag obtained by simultaneously desulfurizing and dephosphorizing with sodium carbonate.

If desulfurization and dephosphorization are performed at the same time, the converter slag does not contain phosphorus, so it can be reused as charging material for blast furnaces, etc., and the process is simplified compared to when desulfurization and dephosphorization are performed separately, and the refining process is The advantage is that there is less temperature drop in the hot metal, which is important in

Figure 1 is a conceptual diagram of an extremely simple process for recovering sodium carbonate from waste slag that has been simultaneously desulfurized and dephosphorized, and various modifications may be made as necessary without departing from the gist of the present invention. Of course, it is possible.

The hot metal obtained in blast furnace 1 is subjected to desulfurization and dephosphorization process 2.
sent to. In step 2, sodium carbonate
When about 15 to 45 kg/T hot metal is added and reacted with stirring for about 5 to 10 minutes, sulfur becomes sodium sulfide and phosphorus becomes sodium phosphate. The desulfurized and dephosphorized hot metal is transferred to converter 6.
It is then sent to the casting process 7 where it is refined using a known method such as adding quicklime or the like.

In the present invention, since the converter slag contains almost no phosphorus, it can be recycled to the blast furnace as it is. It is also conceivable to use alkali bicarbonate instead of alkali carbonate in step 2, but this is not preferable since it requires a larger amount than alkali carbonate.

Furthermore, gas generation increases and the temperature drop becomes severe.
The waste residue obtained from step 2 is sent to extraction and washing step 3. In step 3, gas containing carbon dioxide gas is blown into the mixture, and the mixture is treated and extracted with hot water.

In this case, the amount of hot water required should be 0.8 t/T or more, but if too much is used, the equipment will become oversized and post-treatment will be troublesome, so it is usually 0.8 t/T or more.
Approximately 3.5t/T of tailings is used. The water may be supplied either unheated or hot water, but cold water requires heating. In any case, it is efficient to extract and wash at a temperature in the range of 80100°C. In addition, it is preferable to supply steam together with cold water or hot water as a water source because it also serves as a heat source.

The purpose of blowing carbon dioxide gas is to lower the pH while generating sodium carbonate.By blowing carbon dioxide gas and treating with hot water, the pH stabilizes at around 10, for example, generally PH9.0 to 11.5, and most of the sulfur ions are sulfurized. It precipitates as iron, and soluble silicic acid does not elute. As a result, the solution can be easily stirred, unreacted sodium carbonate, phosphate, and a small amount of sulfur can be efficiently extracted, and filtration in the next step can be facilitated. Carbon dioxide gas preferably has a concentration of 10% or more and is supplied continuously or intermittently. The use of combustion waste gas from a hot stove of a blast furnace as a gas source serves as a heat source and is also very economically advantageous. As for the amount used
If 10 to 15% carbon dioxide gas is supplied at a level of 1000 to 2000 Nm ³ /T slag, the solution will settle to a pH of about 10, which allows for good sedimentation of insoluble residues, and alkali carbonate may change to alkali bicarbonate. do not have.

The extraction and cleaning device is not particularly limited, but a spiral blade feeding type is preferred over a rotating cylindrical type as it has better workability. Although a single extraction cleaning device may be used, it is desirable to install a plurality of extraction cleaning devices in a row in order to perform extraction cleaning more safely. The waste residue after extraction and cleaning is small in quantity and rendered harmless, so it can be disposed of as is. The extracted solution mainly contains dissolved sodium carbonate, as well as small amounts of sodium sulfide and sodium phosphate. Iron ions are added to the extract in a precipitation tank 4 to precipitate iron sulfide and iron phosphate.

One feature of the present invention is step 4 in which sulfur and phosphorus are precipitated and removed by adding iron ions. By providing this step, there is no need to provide an oxidation step in advance, the operation is simple, and sulfur and phosphorus can be removed before the fractional crystallization step, which is advantageous in fractional crystallization of sodium carbonate. As for the iron content, when only desulfurization is carried out, it is sufficient to use about 1 to 5 kg/t of waste slag, and when desulfurization and dephosphorization are carried out simultaneously, about 60 to 200 kg/t of waste slag can be used. of extract
Since the pH is about 9.0 to 11.5, it is very advantageous because the precipitate can be precipitated by iron ions without having to adjust the pH again. Of course, depending on the situation, appropriate pH adjustment may be optionally adopted. The iron ion source is not particularly limited, and known sources such as iron sulfate such as ferrous sulfate or ferric sulfate, iron chloride, etc. can be used, but if iron chloride is used, the chlorine content in the recovered sodium carbonate will increase. However, since it is expensive, it is preferable to use iron sulfate. If iron sulfate is used, the amount of sulfate in the liquid will increase, but if this becomes a problem when reusing the recovered product, it can be removed as sodium sulfate through fractional crystallization. The filtrate is concentrated and sent to fractional crystallization step 5. Concentration should be carried out to the extent that the sodium carbonate concentration is 30%, but it is preferable to concentrate until some crystallization occurs for fractional crystallization, and there are no restrictions on the equipment used for concentration, but if a Ventury tube concentrator is used. This is preferable because even a suspension in which some crystals have precipitated can be efficiently concentrated without fear of clogging.

The filtrate is blown into the throat of the device, while hot air is introduced into the ventilator tube of the device. The hot air sent into the apparatus can be used without any limitation as long as it does not contain sulfur and is inert to the liquid. Exhaust gas from a blast furnace, hot blast furnace, converter or heating furnace contains almost no sulfur content, can be used suitably, and is extremely economical.

In some cases, a fluidized drying granulator may be used instead of the fractional crystallization step 5 to recover the alkali carbonate.

As explained above, by carrying out desulfurization and dephosphorization simultaneously in the present invention, not only can the number of steps be reduced, but also a large amount of alkali carbonate required to carry out desulfurization and dephosphorization simultaneously can be unreacted by carrying out the present invention. The alkali carbonate can be recovered and reused, and since the converter slag contains almost no phosphorus, it can be recycled to the blast furnace, making it excellent not only technically but also economically.

The waste residue obtained in the washing and extraction process does not contain soluble alkali, sulfur, or phosphorus, so it can be disposed of at will, and the amount is small, so it does not pose an environmental pollution problem. Furthermore, it has various advantages, such as the fact that iron sulfide and iron phosphate can be easily precipitated by adding iron ions to the extract without having to adjust the pH separately, so that alkali carbonate can be obtained with high purity.

Next, an example will be given for more specific explanation.

Example 20 kg of sodium carbonate was added to 1 ton of hot metal containing 400 g (0.04%) of sulfur and 1 kg (0.10%) of phosphorus, and the mixture was stirred for about 20 minutes to obtain 20 kg of slag. The tailings contained 300g of soluble sulfur and 612g of phosphorus. The waste slag is heated to a gas temperature of approximately 300℃ using a spiral blade-feed type extraction cleaning device.
Extraction treatment was performed for about 30 minutes with about 50 kg of hot water while blowing 30% carbon dioxide gas. By blowing carbon dioxide gas, most of the sulfur content (70-80%) is precipitated as iron sulfide. On the other hand, phosphorus is extracted into the aqueous layer as phosphate.
The pH of the extract was 10.3. When 4.0 kg of iron sulfate was added to this extracted aqueous solution, 160 g and 2660 g of partially dissolved sulfur and phosphorus were precipitated as iron sulfide and iron phosphate, respectively. After filtration, the aqueous layer was concentrated to 40 kg using a Venture tube concentrator. At this time, as hot air,
Exhaust gas at 300℃ was used. Separately crystallize the concentrated liquid,
14Kg of sodium carbonate was recovered.

[Brief explanation of the drawing]

FIG. 1 is a process schematic diagram illustrating one embodiment of the method of the present invention. 1: Blast furnace, 2: Desulfurization and dephosphorization process, 3: Extraction cleaning process, 4: Sedimentation tank, 5: Fractional crystallization process, 6: Converter, 7: Casting process.

Claims (1)

[Scope of Claims] 1. A method for treating slag generated when hot metal is desulfurized and/or dephosphorized with an alkali carbonate, the slag being treated with hot water while blowing carbon dioxide gas. A treatment for waste slag, characterized in that the alkaline content is extracted by treatment, iron ions are added to the extracted solution to precipitate iron sulfide or iron phosphate, which is removed by filtration, and alkali carbonate is recovered from the filtrate. Method. 2. The method according to claim 1, wherein the solid alkali carbonate is recovered by evaporating the filtrate. 3. The method according to claim 1, wherein the alkali carbonate is recovered by fractional crystallization of the filtrate. 4. The method according to claim 3, wherein the filtrate is concentrated to have an alkali carbonate content of 30% or more, and the concentrated solution is fractionally crystallized. 5. The method according to claim 4, wherein a ventilate tube concentrator is used to introduce waste gas hot air generated in a steelworks into the ventilee tube, and to perform concentration by blowing a filtrate into the throat of the ventilee tube. 6. The method according to claim 1, wherein waste gas from a hot blast furnace attached to a blast furnace is used as carbon dioxide gas. 7. The method according to claim 1, wherein ferrous sulfate is used as the iron ion. 8. The method according to claim 1, wherein the alkali carbonate is sodium carbonate or potassium carbonate. 9. The method according to claim 1, wherein the recovered alkali carbonate is used for desulfurization and/or dephosphorization of hot metal.