JPS5822278B2 - Processing method for pickling waste acid - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention uses waste sludge generated when caustic soda is recycled by removing silicic acid valves from so-called waste caustic soda containing silicic acid valves used for removing sand from cast products, etc. to pickling waste acid. The present invention relates to a method for neutralizing.

Conventional methods for removing sand baked on the surface or inner surface of a cast product using a sand mold include knockout, hydro jet, shot blasting, sandblasting, etc.; This is extremely difficult and requires a large amount of man-hours.

Particularly in so-called precision casting products made by the lost wax method or the like, dents and other flaws are not allowed to form on the surface of the cast product.

Therefore, to remove sand from particularly complex cast products or cast products with strict dimensional accuracy, the tart bath method, in which the product is immersed in molten caustic soda at 500 to 550° C., is generally used.

In this case, due to long-term use, sand accumulates in the caustic soda or a part of it reacts to form water glass such as Na2O. be.

Since the accumulated sand scraped up in this way is fine particles, it coexists with a large amount of caustic soda and cannot be immediately disposed of, so it is generally neutralized with hydrochloric acid, sulfuric acid, etc.

However, disposing of waste caustic soda through the above-mentioned neutralization process not only increases the amount of waste, but is also extremely inconvenient from the viewpoint of resource conservation and productivity.

The present invention eliminates the drawbacks of the conventional separation method described above, and by effectively utilizing so-called waste caustic soda, it is not limited to simply recycling it as caustic soda, but it can also be used in a variety of ways. The purpose is to provide the following.

FIG. 1 is an explanatory diagram showing an embodiment of the method of the present invention.

In the figure, reference numeral 1 denotes a dissolution tank, which accommodates so-called waste caustic powder a containing silicic acid valves together with a water basin.

By stirring with the stirrer 2, waste caustic soda a
The foundry sand contained or mixed therein is precipitated and separated at the bottom of the melting tank 1.

Next, the aqueous solution is transferred to a reaction tank 4 by a pump 3, heated, for example, with high-temperature steam C, milk of lime d is added, and stirred by a stirrer 5.

In this case, water glasses such as Na2O.5i02 dissolved in the aqueous solution are decomposed by the following leather.

Na20-8 i 02 +Ca (OH) 2-+2
NaOH+CaO-8i02 Next, the dz'c pump 6 transfers the CaO-8iO2 to the tallifier 8 via the cooler 7 to precipitate and separate the CaO-8iO2.
The aqueous solution e can be extracted.

Incidentally, the sediment or sludge f is extracted from the lower part of the tallifier-8.

Next, the relationship between the heating temperature in the reaction tank 4 and the amount of Ca added in FIG. 1 will be explained.

FIG. 2 is a diagram showing the relationship between the molar ratio of Ca/S io 2 and the removal rate of 5i02.

In the figure, curves A and B show the cases when heated to room temperature and 80° C., respectively, and the 5i02 removal rate in curve B is clearly higher.

In other words, in the case of song MA at room temperature, Ca/5i0
The removal rate of 5i02 cannot be satisfied unless the molar ratio of 2 is 10 or more, whereas in curve B when heated to 80°C, the same removal rate is obtained when the molar ratio is 3 to 4. There is.

This is a result of the separation reaction being promoted by heating the aqueous solution in the reaction tank 4.

. Note that when the molar ratio of added Ca to 5i02 is less than 3, the 5i02 removal rate is unsatisfactory, so it is set to 3 or more, but as is clear from FIG. 2, the molar ratio is approximately saturated at around 6, so It may be selected appropriately within an economical range.

In addition, the heating temperature of the two aqueous solutions in the reaction tank 4 was 80°C in this experiment, but as a result of the experiment, if it is 60°C or higher, the SiO□ removal rate can be satisfied within the above molar ratio range. is obtained.

Furthermore, as the Ca to be added in the reaction tank 4, C
Of course, CaO other than a (OH) 2 exhibits the same S separation and precipitation effect.

In FIG. 1, the supernatant liquid e from the tallifier 8 is transferred to NaOH regeneration means, but the precipitated sludge f has strong alkalinity, but is generally treated as waste.

In the present invention, this sludge is transferred to a dewatering means 10 to be dehydrated and stored in a storage tank 11 as a cake.

The soaking liquid g from the liquid removing means 10 is returned to the reaction tank 4 and processed again.

Next, 12 is a pickling waste acid treatment means, and by mixing the cake stored in the storage tank 11 in the pickling waste acid treatment means 12, acid neutralization treatment is possible.

Caustic soda is generally used in waste acid treatment, but
The neutralization treatment using the sludge f has a better settling effect than the neutralization treatment using caustic soda.

Since the present invention has the structure and operation as described above,
It has the following effects.

(1) Since the separated and precipitated sludge generated in the means for recycling waste caustic soda can be utilized without being disposed of, it is possible to save resources and completely prevent environmental pollution caused by waste.

(2) It has a better neutralizing action, especially a precipitation action, than caustic soda, and is easy to handle because it is cake-like.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing an embodiment of the method of the present invention, and FIG. 2 is a C
FIG. 2 is a diagram showing the relationship between the a/SiO2 molar ratio and the SiO□ removal rate. DESCRIPTION OF SYMBOLS 1...Dissolution tank, 4...Reaction tank, 8-river dryer, 10...Deliquor removal means, 12...Waste acid treatment means.

Claims (1)

[Claims] 1. After dissolving waste caustic soda containing a silicic acid valve in water and precipitating and removing sand grains, add Ca(OH)2 or CaO so that the molar ratio of Ca to 5i02 is 3 or more, and add an aqueous solution. A method for treating pickling waste acid, which comprises heating to 60° C. or higher to precipitate and separate silicate valves as Ca()SiO□, deliquifying the sludge and mixing it with pickling waste acid.