JP2548674B2 - Reclaiming method of sodium silicate casting sand - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to sand in a high temperature furnace for removing sodium silicate adhering to the fine sand particles of CO ₂ foundry sand.
Sodium silicate adhered to sand grains by heating and firing particles at high temperature
After sublimation, and further, the residual sodium silicate of still adhering to the sand grains
In order to remove it , it is washed with water, hydrolyzed and filtered to remove hydrogen peroxide from the filtrate.
The present invention relates to a method for reclaiming and recovering foundry sand which is inexpensive, easy to work with, and excellent in environmental resistance by drying the sand grains after neutralizing the pH value of the ON concentration to about 7 .

[0002]

2. Description of the Related Art There are the following problems as a conventional method for regenerating and recovering sodium silicate-based carbon dioxide sand.

(A) A method of adding a chemical for dissolving the sodium carbonate adhering to the sand grains, or a method of dissolving the water glass of the sand particles with an aqueous solution containing a hydroxide of an alkali metal has been devised. However, the recovery and recovery method is expensive and the recovery rate is not good.

(A) There is a floating separation method after washing sand particles with water, or a magnetic separation method by cooling after recirculation of large and small sand particles.

As described above, the conventional recycling method has a low recycling efficiency despite the high processing cost.

[0006]

SUMMARY OF THE INVENTION The present invention has been made by paying attention to the above-mentioned conventional problems, and does not require an expensive device, and does not use sodium silicate (including sodium carbonate) on the surface of sand particles. regardless of the chemicals added, the sand particle surface heating <br/> heated at a high temperature furnace (to dissipate sodium silicate of adhering to the sand grains), further
We provide a method that not only allows residual sodium silicate that adheres to the sand surface that cannot be removed by sublimation due to high-temperature heating to be easily precipitated and separated by washing with water, but can also neutralize the washing liquid to form droplets that are compatible with industrial waste liquid. The purpose is to do.

[0007]

A so-called CO ₂ type method in which a molding sand is kneaded and molded with a binder as a main component from a sodium silicate (water glass) solution and solidified through carbon dioxide gas is as follows.

[0008]

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In the CO ₂ -type sand reclaiming method that has been tried so far, it is impossible to completely separate the silicate gel and sodium carbonate fixed to the sand, and in particular, the residual sodium silicate is not completely removed. , The solution obtained by washing sand with post-treatment is P
It was necessary to apply an expensive solution processing method to the technique of suppressing the H value to about 7.

The present invention is to provide a method for regenerating and recovering foundry sand from a used CO ₂ casting mold.

The used mold is crushed to obtain sand particles having a particle size close to that of the sand before forming the mold.

[0012] The sand particles to be able to re-use as a skin sand, aligned to the size of the following sand 590μ m.

After that, it was inserted into a high-temperature furnace, and 900 to 11
The temperature is raised to about 00 ° C. while slowly heating the sand particles while stirring and firing.

At the same time as the sodium carbonate content adhering to the sand is sublimated by combustion, at the same time as the SiO ₂ and N contents of the sodium silicate composition.
The residual composition as a ₂ O is sublimated at a temperature above the melting point.

Residual Na _{2 on} the surface of the sand particles as unreacted
O ・ SiO ₂ or Na ₂・ SiO ₂・ 5H ₂ O or Na ₂ O ・ 2SiO _{2 and the} like are hydrated and filtered at a sand water ratio (g / 10 ml), then sand
Neutralization is performed so that the alkali concentration of the particles is a hydrogen ion concentration and the PH value is about 7.

The filtered Na ₂ O.SiO ₂ is in a state of being easily separated from the surface of the sand grains to some extent when the temperature is raised, and most of it is sublimated by the heat treatment above the melting point. There is almost no filtration component due to the effect of near heating.

After washing with water, the solution and the precipitated sand are separated from the sand by a floating sorting method, and the sand is recovered.

By drying the sand particles in a dryer, it is suitable for molding sand that can be reused for the casting surface. It should be noted that the pH value of the aqueous solution after washing with water is surely neutralized, and the water content is increased or decreased at the time of filtration in some cases.

[0019]

Function: The sand particles are mechanically crushed from the used mold to remove the sodium carbonate component and the unreacted sodium silicate component on the sand surface, or the sand particles are aligned in such a state that they are easily separated.

Conventionally, sodium carbonate-converted molecules have been dissolved by changing to soluble ones such as sodium sulfate.
Next water glass component in Table 1, including sodium silicate content of unreacted, as shown the physical properties of the various sodium silicate in Table 2, the melting point of _{Na 2 O · SiO 2 · Na} 2 O · 2SiO 2 9
Since the temperature is from 0 to 1100 ° C. or lower, the above components adhering to the sand particles in the high temperature furnace are often sublimated spontaneously, and the residual components are easily separated from the sand particles.

[0021]

[Table 1]

[0022]

[Table 2]

The residual Na ₂ O · SiO ₂ filtration washing with water, the sand particles are separated as a solution by flotation.

The solution so a state of residual Na ₂ O · SiO ₂ by sublimation hardly, exhibit approximately 7 degrees is neutralized摘定value by adjusting the hydrolysis.

[0025]

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When the temperature is raised to 900 ° C. below the melting point of sodium silicate or 1100 ° C. or below, the acid (H
CL) consumption is proportional to the amount of undissolved (which may be regarded as comparable to the amount of sublimation) sodium silicate.

Floating sorting of sand particles and solution after washing with water facilitates separation of the sand and at the same time contributes to cleaning of the sand surface, and the casting surface to be reused by the sand drying operation thereafter. Has an effect suitable for sand.

[0028]

Embodiments of the present invention will be described with reference to the drawings. The experimental apparatus used for this experiment is shown in FIG. Sodium silicate-based carbon dioxide type mold waste sand a is charged into the high temperature furnace 1. Vent 3 of furnace, chromel alumel thermocouple 4 for temperature measurement in the furnace
Then, the change of the sample a is recorded and the temperature of the electric furnace (high temperature furnace) 1 is controlled. a is a crushed molding sand particles, and sample size adjusted to below 490μ m. While measuring the temperature of the sample a, the sample is agitated by the stainless stirrer 2 so that the sample has a uniform temperature. A sample c (a sample in which the components of the sample a are changed) treated at a predetermined temperature is transferred to a container 6, pure water d (ion-exchanged water) is charged into the container 6, and a stainless stirrer 7 is used to make the aqueous solution uniform. Agitate until At the same time, the temperature of the solution is measured with a thermometer of 8. Usually, room temperature treatment is the target. PH
Measure the solution in 6 with a measuring instrument (alkali concentration measurement). That is, the acid (H) necessary for neutralizing the solution in the container 6
cl: hydrochloric acid) consumption adjustment and water-soluble extraction of sample c
Adjust the amount of alkali. The aqueous solution of 6 is transferred to the container 11 by the pump 10, and the solution component and the sand sample are separated by the drainer 12. At the same time, alkali concentration measuring device (PH value) measuring device 1
At 3, the change in the concentration of the solution is measured. That is, the solution
Potassium concentration is neutralized to about PH9 in hydrogen ion concentration
Check whether or not Further, the dewatered sand sample is transferred to the container 14 and then dried to obtain the reclaimed sand e in the reclaimed recovery device.

In the apparatus shown in FIG. 1, the name 2 in Table 1 (molar ratio 2,
Water glass of 5) was added at a sand ratio of 3%, and CO ₂ gas was blown into it to form a CO ₂ type mold, and bronze type 3 (JIS standard B
(C3 equivalent product) material was melted at a casting temperature of 1170 ° C., and mold sand was added. At that time, the method for extracting the water-soluble component of the sample c and the method for adjusting the amount of alkali used in the experiment for adjusting the consumption amount of acid (HCL: hydrochloric acid) necessary for neutralizing the solution in the container 6 in FIG. Shown in. Table 3 shows the extraction treatment conditions for the water-soluble components. The results are shown in Fig. 3.

[0030]

FIG. 2

[0031]

[Table 3]

FIG. 4 shows the particle size distribution of one example of the reclaimed and recovered sand used in the apparatus of FIG. 1 in FIG. 3 together with the particle size distribution of new sand (No. 6 silica sand).

As is clear from the graph of FIG. 4, recycled sand having a particle size distribution almost the same as the original sand can be recovered.
Reclaimed and recovered sand is clean sand from which fixed components such as sodium carbonate and sodium silicate have been removed, and can be used in the same manner as new sand for the production of CO ₂ type mold (sodium silicate casting sand). .

As is apparent from the graph of FIG. 3, when the waste sand (sample) temperature treatment is set at 25 ° C., the consumption amount of HCL (acid) necessary for neutralization is about 10 cc (1/10 normal { N}), the acid consumption value was 0.5 cc at 600 ° C., 0.3 cc at 700 ° C., and almost 0 cc at 1000 ° C. This means sublimation of the Na ₂ O.SiO ₂ component and sublimation of the sodium carbonate content by raising the temperature of the sand sample in the electric furnace with the apparatus of FIG.

[0035]

Since the present invention is configured as described above, it has the following effects.

According to the present invention, there is no difficult operation, no expensive equipment is required, and the regenerating cost is small.

The addition operations chemicals eluting undissolved or adhesion molecules sodium carbonate or sodium silicate sand particle surface and not require the device or the like, reclaimed sand particle size distribution of the original sand obtained, CO ₂ It can be used in the same way as new sand for the production of molds (sodium silicate casting sand).

Since the main work is a temperature control system using an electric furnace, the work management of waste sand and the degree of desilicating sodium treatment are poured out for each temperature, and the amount of sodium carbonate adhering to the sand and silica are removed by adjusting the amount of acid consumption. Management of acid soda can be deciphered from the graph,
It has excellent economic effects.

[Brief description of drawings]

FIG. 1 is a state diagram of an experimental apparatus used in this experiment.

FIG. 2 shows a method for extracting a water-soluble component and a method for adjusting an alkali amount of a template sand sample used in this experiment.

FIG. 3 shows the result of an experiment for acid consumption of mold sand after casting 3 kinds of bronze into CO ₂ mold sand using water glass with a molar ratio of 2.5, which was tested by the apparatus of FIG. The graph to represent.

[Fig. 4] Fig. 4 is a view of the reclaimed sand used in Fig. 3 in the apparatus of Fig. 1.
About the example, the graph which compared the particle size distribution with the particle size distribution of the new sand (No. 6 silica sand).

[Explanation of symbols]

1 High-temperature electric furnace 2 Stainless steel stirrer (driven by a DC motor) 3 Vent hole 4 Temperature measuring alumel chromel thermocouple 5 Sample peep hole (hole where gas such as Ar can be introduced if necessary) 6 Container 7 Stainless steel stirrer (Motor drive system) 8 Thermometer 9 PH meter (alkali concentration measuring instrument) 10 Pump 11 Container 12 Dewatering machine 13 PH meter 14 Container 15 Reclaimed sand recovery device a Sample b Argon gas c Sample (a component changed) Sample) d Pure water (ion-exchanged water) e Reclaimed sand

Claims (1)

(57) [Claims] 1. A method for regenerating and recovering carbon dioxide gas type self-hardening molding sand containing sodium silicate and a hardening material (1) crushing a used mold to obtain sand particles having a particle size close to that of the sand before forming the mold. after aligning it (2) the sand particles to a size of less sand 590Myu m to, inserted in a high temperature furnace, the temperature was elevated while stirring slowly at a temperature of about 900 to 1100 ° C., sintering is possible. In other words, in order to remove the sodium silicate adhering to the sand particles, the sand particles are heated to a high temperature.
The work of heating and firing in a furnace, in other words, of sand particles
Sodium silicate that adheres to the sand particles by burning work by heating at high temperature
Sublimate the da (3) Furthermore, remove the residual sodium silicate still adhering to the sand grains.
In order to do so , water is added to the sand particles and the sand water ratio (g / 10m
l) After filtering about 1), the sand particles are hydrated and filtered
Neutralize so that the PH value of the hydrogen ion concentration becomes about 7,
Then , a method for regenerating and recovering sodium silicate-based foundry sand, characterized by comprising drying sand particles