JPS5848266B2 - Wet treatment method for water glass-based foundry sand - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention utilizes water glass waste foundry sand, which is used as a mold by adding water glass as a binder to foundry sand such as CO2 process foundry waste sand and Dical method foundry waste sand, to an alkaline solution. The present invention relates to a processing method for wet dissolving and cleaning and recycling.

In recent years, from the standpoint of resource conservation and environmental conservation, it is not economical to simply detoxify and dispose of foundry waste sand, and recycling is becoming more and more popular.

There are two types of foundry waste sand: those using inorganic binders such as water glass, and those using organic binders such as resins and oils. Needs consideration.

That is, the water glass mold is made of a mold material in which water glass is added to silica sand, and the added water glass is an alkali-soluble silicate.

Even if this water glass changes chemically during molding, as in the case of a CO2-curing type, even if the mold is thermally affected by the molten metal, most of the water glass will still be Na2CO, , Na2 Si03, Na2
It is clear that the waste sand is present as an alkali-soluble salt such as 0-msio2 because when it comes into contact with water, wastewater with a considerably high pH gradually leaks out.

Conventional methods for treating water glass-based foundry waste sand include firing at high temperatures, but this requires high equipment operating costs and equipment costs.Also, there is a method of neutralizing adhering alkali salts with acid, but neutralization is difficult. There are many problems such as the residual -(St02)n- which is difficult to gel and remains.

These conventional treatment methods are not necessarily sufficient in terms of recycling waste sand, effectively removing attached alkali, and regenerating alkali.

The present invention has been developed based on the above-mentioned circumstances and has solved the drawbacks, by bringing water glass-based foundry waste sand into contact with a mixed alkaline solution of caustic soda and sodium silicate, and effectively removing the alkali attached to the waste sand. It is characterized by cleaning.

That is, the present inventors selected various acids and alkalis as wet cleaning agents for glass mold waste sand, and as a result of conducting experimental studies to find effective treatment agents and treatment conditions, as shown in Figure 3, caustic soda Is it sufficiently effective to use only 10,000 caustic soda as a cleaning agent?If you try to shorten the processing time, the amount required will increase, resulting in disadvantages such as increased processing agent cost. That is, it has been found that it is advantageous for the cleaning effect to reduce the required amount as much as possible and to use a mixed alkaline solution in which sodium silicate coexists.

In other words, as is clear from the comparison of the experimental data in (Figures 1 and 3), for example, if the time to dissolve and remove all the attached alkali contained in the waste sand at 100°C is set to 4 hours (
! It is sufficient to wash with a mixed alkaline mixture of 5% caustic soda and 5% sodium silicate, but with caustic soda alone a concentration of 63% is required, and with 5% caustic soda and 5% sodium silicate, the dissolution time is 4 hours. , caustic soda 5%
It will take 6.5 hours.

As mentioned above, the coexistence of sodium silicate is more effective in accelerating the dissolution rate than the use of caustic soda alone.

That is, the processing time is shortened and the amount of caustic soda required is also reduced.

Further, as shown in FIG. 2, at a high treatment concentration near 100 DEG C., a caustic soda solution containing sodium silicate exhibited the same dissolution and removal effect as caustic soda alone.

The above-mentioned removal of alkaline substances on waste sand by mixed alkali dissolution of caustic soda and sodium silicate is achieved by the dissolving action of highly gelled silica fraction (S102) n1 by caustic soda, the adhering sodium silicate, and the dissolving agent. It is presumed that the effect of dissolution due to increased affinity of sodium silicate as a compound works synergistically.

It goes without saying that a small amount of a known activator may be added to these mixed alkaline solutions to improve the dissolution and removal effect by improving the permeability to the waste sand.

The caustic soda used as a dissolving agent may be a general industrial one, and the commonly used sodium silicate with a SiO2/Na20 molar ratio of 1.8 to 3.5 is sufficient.

The ratio of amounts of caustic soda to sodium silicate varies depending on the target treatment time, as shown in Figure 1.
(NaOH+ Na20-n S t 02
) weight ratio is 0. 1~0. 9 is preferably 0.5, and the concentration of the total amount of NaOH+Na2o-nSio2 in the aqueous limb is 5 to 15% by weight, preferably around io% by weight.

The higher the treatment temperature, the better, from 50 to 200°C, and particularly preferably from 100°C to 110°C.

It goes without saying that if pressurized melting is used, melting can be carried out at higher temperatures and the processing speed is faster, but there are still aspects such as pressurized operation that are not necessarily appropriate in terms of equipment and operation.

Next, examples of the present invention will be shown.

Example 1 S i0 2 for 100 parts of new sand (triplet mountain silica sand)
/Na20 mol number 2.3 5 parts of water glass was added and kneaded,
Taking into consideration the thermal effect on actual casting, the test piece hardened with CO2 gas was heated and baked in an electric furnace set at 1000°C for 2 hours, and then crushed to produce old sand.

On the other hand, put sodium hydroxide, sodium hydroxide + water glass, or a water glass container into a separable flask with an internal volume of 2 liters equipped with a thermometer, liquid donor, and stirrer, and set the temperature to the specified temperature using a mantle heater. Add the old sand mentioned above, 10
While rotating the propeller stirrer at 0 rpm, water glass adhering to the surface of the old sand was dissolved.

Then, a solution for quantifying the amount of dissolved water glass was sampled at regular intervals.

After steeping the collected solution, strain it and remove it from the armpit.
2 was determined gravimetrically, and S in the solution before adding old sand was determined.
The i0 2 quantitative value was obtained as a blank, the difference was converted into water glass as eluted SiO2, and the removal rate was calculated by setting the amount of water glass attached to the old sand as 100.

The recycled sand in the separable flask was separated into solid and liquid by P filtration, and then thoroughly washed with water to recover the recycled sand.

Example 2 Figure 4 shows the same foundry sand and NaOH5wt% as in Example 1.
Na2 0 2. 3 S t02 A 5 wt% aqueous solution was placed in a 3 liter autoclave with a stirrer,
This is the water glass removal rate obtained by pressurizing and heating.

The effect of temperature on the dissolution rate was large, and the higher the pressure and temperature, the faster the water glass was removed.

Figure 1 shows the experimental results carried out using the above-mentioned experimental method in the accompanying drawings. By varying the mixing ratio of NaOH and Na20.2.38iO2, water glass adhering to the old sand produced by the above-mentioned method was reduced to 100%. This is the time required for removal.

1 in 10% Na20.23Si02 water-glass solution
It was difficult to remove 100% even after 2 hours of treatment.

Figure 2 shows an experimental study of the relationship between the treatment temperature and the removal rate of attached water glass.The effect of temperature on removal is exponential, and the closer the treatment temperature of the present invention is to the boiling state, the more effective it is. It is clear that it is large.

FIG. 3 shows the relationship between the time required for 100% removal and the NaOH aqueous solution concentration.

A casting test was conducted on a 690k9 strap using 100% recycled sand from which 100% of the adhering water glass had been removed by the above treatment, and the results were as good as those made of new sand.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the relationship between the time required to remove 100% of adhering water glass and the total concentration of the caustic soda/water glass mixture. FIG. 2 is a diagram showing the relationship between treatment temperature and adhering water glass removal rate. FIG. 3 is a diagram showing the relationship between the time required to remove 100% of the attached water glass and the caustic soda concentration.

Claims (1)

[Claims] 1. Waste foundry sand using a water glass binder is mixed with HaOH/
(NaOH+Na20-ns i02) Weight ratio (
However, n is a molar ratio of 1.8 to 3.5) is 0.1 to 0.9
It is characterized in that it is brought into contact with a mixed alkaline aqueous solution of 5 to 15 weight percent of NaOH+Na20-nSiO2 at 50 to 200°C. Wet treatment method for water glass-based foundry sand.