JP4118495B2 - How to reuse mud - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for recycling mud produced when refining crude salt water. Specifically, this is a novel recycling method for effectively utilizing sludge containing a sparingly soluble compound that has been precipitated by adding a refining agent to crude salt water.
[0002]
[Prior art]
Sodium chloride (NaCl), which is used as a raw material for producing caustic soda by the electrolytic method or a raw material for producing sodium carbonate by the ammonia soda method, is obtained in the form of a raw salt and is used after purification.
[0003]
In the above production process, impure ions such as calcium, magnesium and sulfate ions contained in the raw salt cause various problems. For example, in ion-exchange membrane electrolysis, polyvalent metal ions such as calcium and magnesium increase the electrical resistance of the ion-exchange membrane within a short time, and sulfate ions damage the ion-exchange membrane and increase the current efficiency. It has problems such as causing a decrease.
[0004]
As a purification method for reducing the above-mentioned impure ions, a purification agent such as caustic soda, soda ash, calcium chloride, barium chloride, barium carbonate is added to the crude salt water in which the raw salt is dissolved in water, and the impure ions are hardly soluble. A method of precipitating as a compound is generally carried out.
[0005]
The poorly soluble compound produced by the above method is then obtained as a slurry from the lower part of the static settling tank in which it is allowed to settle. Since the slurry obtained as described above uses salt solution close to saturation as a solvent, the solid content separated by filtration contains high-concentration salt and can be reused for other applications. It is difficult and is currently disposed of in landfills.
[0006]
However, in recent years when the movement to reduce industrial waste is promoted socially, it is desired to take advantage of such solid content effectively.
[0007]
[Problems to be solved by the invention]
Accordingly, an object of the present invention is to provide a novel recycling method that can effectively utilize a slurry containing a poorly soluble compound produced by adding a purification agent to the crude salt water.
[0008]
[Means for Solving the Problems]
As a result of intensive studies to solve the above-mentioned problems, the present inventors have unexpectedly found that the solid content mainly composed of a poorly soluble compound separated from the slurry contains a saturated saline solution. The filterability is further greatly improved by contacting with water having a specific salt concentration or less and then filtering, and the salt concentration in the solid content obtained can be easily reduced to a very low concentration. The knowledge that it can reduce was obtained.
[0009]
And when the said solid substance by which this chlorine concentration was reduced to very small quantity was utilized as a cement raw material, it discovered that it could be used effectively, hardly affecting the performance of the cement obtained, and completes this invention. It came to.
[0010]
That is, the present invention is a method for reusing a slurry containing a sparingly soluble compound produced by adding a purification agent to a crude salt water obtained by dissolving a raw salt in water so as to be a saturated aqueous solution , The slurry is filtered to separate a solid content containing a hardly soluble compound, and then the solid content is brought into contact with water having a salt concentration of 10% by weight or less, so that the salt concentration of the water in contact with the hardly soluble compound is adjusted. It is a method for recycling mud characterized in that it is adjusted to 10% by weight or less and then filtered, and the solid content obtained is used as a part of the raw material for cement.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, the crude salt water is an aqueous solution of sodium chloride (NaCl) containing at least one impurity ion composed of calcium ions, magnesium ions and sulfate ions, and representatively, the raw salt is a saturated aqueous solution. Examples thereof include crude salt water obtained by dissolving in water (hereinafter, this crude salt water is also referred to as prepared crude salt water).
[0012]
As the raw salt used for preparing the crude salt water, a known raw salt available from the salt producing country is used without particular limitation. In addition, as a method of dissolving the raw salt in water, a known method such as a method of allowing water to pass through the raw salt layer and taking it out as a saturated aqueous solution is employed without any particular limitation.
[0013]
In addition, in the production method using the salt water, the salt water that is circulated is also included in the crude salt water referred to in the present invention (hereinafter, this crude salt water is also referred to as the circulated crude salt water). Say.).
[0014]
The slurry which is the object of the present invention is mainly obtained by adding a refining agent to the above-mentioned crude salt water, thereby making the impurity ions composed mainly of calcium ions, magnesium ions and / or sulfate ions hardly soluble as poorly soluble compounds and sedimenting them. It can be obtained by removing the concentrated part.
[0015]
In the present invention, a known purification agent that reacts with the impurity ions to form a hardly soluble compound is used without particular limitation. For example, sodium carbonate is suitable for calcium ions and sodium hydroxide is suitable for magnesium ions. By the reaction with the purification agent, calcium ions become calcium carbonate and magnesium ions become magnesium hydroxide.
[0016]
For sulfate ions, calcium chloride, barium chloride, and barium carbonate are preferably used, and the sulfate ions become calcium sulfate and barium sulfate by the reaction.
[0017]
For the addition of the purifying agent, a known method is employed without any particular limitation depending on the impurity ions contained. For example, when sulfate ions and calcium ions are mixed, a method of adding sodium carbonate for removing residual calcium ions after adding calcium chloride for removing sulfate ions is preferable. Further, sodium hydroxide for removing magnesium ions is generally added simultaneously with sodium carbonate.
[0018]
The purification agent may be added in the form of a solid such as powder or granules, or in the form of a solution dissolved in water.
[0019]
In the present invention, the operation of obtaining sludge by precipitating and concentrating a poorly soluble compound in the above-mentioned brine is generally preferably performed by providing a static settling tank.
[0020]
In addition, it is preferable to add these purification agents by providing a separate reaction tank before the above-described static settling tank. Of course, when the sedimentation is severe in the reaction tank, the reaction tank also serves as a stationary tank, and part or all of the product can be taken out as a slurry from the lower part of the reaction tank. Further, such reaction vessels may be provided singly or in multiple stages. Further, a coagulant may be added to the outlet of the reaction tank in order to promote sedimentation of the hardly soluble compound in the static tank.
[0021]
Further, in the present invention, the slurry can be mixed with the slurry obtained from a plurality of statically settled tanks and subjected to the treatment described later. For example, the slurry obtained from the prepared crude salt water and the slurry obtained from the circulating crude salt water may be mixed and subjected to the treatment described later.
[0022]
In the present invention, the hardly soluble compound contained in the slurry is brought into contact with water having a salt concentration of 10% by weight or less, preferably 0.05 to 5% by weight, more preferably 0.1 to 0.5% by weight. After that, it is very important to filter and collect it as a solid content.
[0023]
That is, the present inventors have conducted a number of experiments, and the filterability of the hardly soluble compound contained in the slurry is surprisingly good due to the properties of the calcium carbonate and calcium sulfate to be produced. It has been found that the filterability is remarkably improved when the salt concentration of the water is adjusted to 10% by weight or less.
[0024]
The solid content obtained through the filtration is surprisingly reduced to a chlorine concentration of 0.1% by weight or less in the dry state, and even when used as a cement raw material, the cement production process or obtained It was confirmed that there was almost no adverse effect on the cement used.
[0025]
In the present invention, the method for bringing the sparingly soluble compound contained in the slurry into contact with water having a salt concentration of 10% by weight or less is not particularly limited.
[0026]
For example, the salt concentration in the slurry can be lowered and adjusted to the above range by directly adding water to the slurry and diluting it. However, in this method, the filtrate must be discarded, and the reuse rate of salt may be reduced.
[0027]
On the other hand, the method of filtering the dispersion with reduced salt concentration by once filtering the slurry, separating the solids, and then re-dispersing it in water is a high concentration obtained by filtering the slurry. Recommended because salt water can be collected and reused.
[0028]
As another method, after filtering the slurry, the obtained solid content is washed on the filter cloth with water until the salt concentration of the filtrate is not more than the above concentration.
[0029]
In addition, it is economical to use industrial water, pit drainage, etc. as water used for the dilution, dispersion, or washing.
[0030]
In the present invention, a known filtration device is used without particular limitation for filtration of the slurry, filtration of a dispersion obtained by redispersing the solid content obtained by filtering the slurry. For example, a filter press type filtration device is most efficient and economical.
[0031]
In the present invention, the proportion of moisture (water content) in the solid content obtained by filtration after bringing the sparingly soluble compound into contact with water having a salt concentration of 10% by weight or less utilizes the improvement in filterability by such contact. In order to keep the salt concentration in the solid content finally obtained low, it is preferable to keep it as low as possible.
[0032]
The moisture content is 50% by weight or less, preferably 40% by weight or less.
[0033]
In the present invention, the solid material obtained by the above method and containing as a main component a hardly soluble compound contained in the slurry is particularly a part of a cement raw material for producing various cements produced in a cement production apparatus. Used without limitation.
[0034]
In a cement manufacturing apparatus, a cement raw material is generally dried and pulverized, then supplied to a firing furnace (kiln) through a preheating device and fired to become a cement clinker. In the present invention, the above-mentioned solid cement The addition to the raw material is generally performed by mixing with the cement raw material supplied to the drying / pulverization step.
[0035]
In addition, since the above-mentioned solid content has a very low chlorine content, the proportion added to the cement raw material can be arbitrarily determined within a range that does not greatly change the composition of the cement. It is preferable to add the component in an amount of about 0.005 to 10% by weight, particularly about 0.01 to 5% by weight.
[0036]
The cement clinker obtained in the firing furnace is pulverized by adjusting necessary components and becoming a cement. For example, in the case of Portland cement, it is commercialized by adding gypsum to the cement clinker and grinding it.
[0037]
【The invention's effect】
As can be understood from the above description, according to the present invention, the solid content after filtration can be improved by selecting the treatment conditions for the slurry and by reducing the salt concentration in the water used as the mother liquor. The moisture content can be easily reduced.
[0038]
Therefore, as described above, the chlorine concentration in the obtained solid content can be dramatically reduced, and the solid content can be used as a raw material for producing cement without any problems.
[0039]
Therefore, according to the present invention, it is possible to effectively use solid matter mainly composed of poorly soluble compounds in the slurry generated in the purification process of salt water without discarding the industrial value or environmental value. Is extremely expensive.
[0040]
【Example】
EXAMPLES Hereinafter, examples will be shown to describe the present invention more specifically, but the present invention is not limited to these examples.
[0041]
Example 1
According to the process shown in FIG. 1, the present invention was implemented by the following method.
[0042]
Industrial water 11 was sprayed on the raw salt 1 containing 0.06 wt% Ca, 0.02 wt% Mg and 0.16 wt% SO ₄ , saturated brine was taken out from the line 12, and stored in the saturated tank 2. The salt water in the saturation tank 2 was sent from the line 13 to the reaction tank 3 with a stirrer, and calcium chloride 14 was added to make the sulfate ions hardly soluble as calcium sulfate.
[0043]
Since calcium sulfate, which has a higher specific gravity than salt water, settles in the lower part of the reaction tank, it was partially extracted as mud and stored in the storage tank 6 (not shown). On the other hand, the treated salt water is sent from the line 29 to the reaction vessel 4 equipped with a stirrer, and sodium hydroxide 15 and sodium carbonate 16 are added to make magnesium ions magnesium hydroxide and calcium ions calcium carbonate. .
[0044]
Next, the salt water in the reaction tank 4 is guided to the static settling tank 5 by the line 17, and the salt water containing 5 wt% of the hardly soluble compound produced in the reaction tank is taken out from the line 18 as a slurry from the lower part and stored in the storage tank 6. .
[0045]
The supernatant liquid of the static bath 5 is taken out from the line 22 as a salt water having a NaCl concentration of 25% by weight containing 2 ppm of calcium ions, 0.1 ppm of magnesium ions and 0.6% by weight of sulfate ions. Then, it was supplied to the ion exchange membrane electrolyzer 24.
[0046]
On the other hand, the slurry was supplied from the storage tank 6 through the line 19 to the filter press type filtration device 7 to obtain a solid content with a moisture content of 30% by weight.
[0047]
For reference, the solid content obtained by the filtration was dried and analyzed. As a result, it was 30% by weight calcium carbonate, 6% by weight magnesium hydroxide, 26% by weight calcium sulfate, and 6% by weight chlorine content.
[0048]
The solid content is re-dispersed in water by adding industrial water 21 in the dispersion tank 8, and the salt water concentration of the dispersion is adjusted to 0.3% by weight, and then supplied to the filter press type filtration device 9 via the line 25. As a result, a solid content having a moisture content of 30% by weight was obtained.
[0049]
Although the filter press type filtration device 9 has a total filtration area of about 30% less than that of the filter press type filtration device 7, the operation time of the device required for filtration is shortened by about 30%.
[0050]
As a result of drying and analyzing the obtained solid content, it was 35% by weight of calcium carbonate, 7% by weight of magnesium hydroxide, 25% by weight of calcium sulfate, and a chlorine content of 0.1% by weight or less.
The above solid content of 30% by weight was added to the raw material crushing process of the cement manufacturing apparatus 10 so that the ratio was 0.1% by weight of the total raw material. There was no.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing representative steps for carrying out the method of the present invention.
DESCRIPTION OF SYMBOLS 1 Raw salt 2 Saturation tank 3 Reaction tank 4 Reaction tank 5 Static determination tank 7 Filtration apparatus 8 Dispersion tank 9 Filtration apparatus 10 Cement production apparatus 11 Industrial water 14 Calcium chloride, barium chloride, barium carbonate 15 Sodium hydroxide 16 Sodium carbonate 22 Purification Brine 23 Brine refining equipment 24 Ion exchange membrane electrolytic cell 27 Solid content

Claims (3)

A method for reusing a slurry containing a sparingly soluble compound produced by adding a refining agent to a crude salt water obtained by dissolving a raw salt in water so as to become a saturated aqueous solution, and filtering the slurry the solids containing the poorly soluble compound is separated, then, the solid content in contacted with salt concentration of 10 wt% water, and 10 wt% or less of sodium chloride concentration of water in which the poorly soluble compound is in contact The method for recycling mud characterized by using the solid content obtained after filtration and filtering as a part of the raw material for cement. The method for recycling mud according to claim 1, wherein the purifying agent is at least one selected from the group consisting of sodium hydroxide, sodium carbonate, calcium chloride, barium chloride and barium carbonate. The method for recycling mud according to claim 1, wherein the moisture content of the solid is 50% by weight or less.

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