Chemical regeneration method of water glass used sand

CROSS-REFERENCE TO RELATED APPLICATIONS

The application claims priority to Chinese patent application No. 201910849455.3, filed on Sep. 9, 2019, the entire contents of which are incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to the field of resource recycling in the casting industry, and particularly relates to a chemical regeneration method of water glass used sand.

BACKGROUND

As a large casting country, China needs to change to a strong casting country in the new era, which needs to pay more attention to environmental protection and energy conservation. Water glass used sand is divided into two types: ester hardened used sand and CO₂hardened used sand, in view of the widespread use of water glass sand in the casting industry, in order to avoid environmental damage and waste of resources caused by random abandonment, regenerating the used sand is necessary. In today's technology, there are multiple regeneration options including physical and chemical forms; for example, dry process regeneration, wet process regeneration, composite regeneration and chemical regeneration, etc., these technologies have their own advantages and disadvantages. Dry and wet process regenerations have been extensively studied at present. Dry process regeneration is simple and easy to realize, but it has low recycling and film removal rate; wet process regeneration works well, but it costs a lot of water, which remains tons of sewage to be treated difficultly. However, there are few researches on chemical regeneration technology world wide. Although the main achievement is that the strength of reclaimed sand is improved greatly by using sodium hydroxide for regeneration treatment, the continuous accumulation of reclaimed sand alkali will affect the use properties of reclaimed sand, and the waste sand will directly pollute the environment. There is still a lot of development space for chemical regeneration, and in the current research background, we hope to find a more suitable solution which can effectively reduce the content of sodium carbonate when the reclaimed sand meets the strength requirements.

This application is filed on the above grounds.

SUMMARY

For problems or defects existing in the prior art, the object of the present disclosure is to provide a chemical regeneration method of water glass used sand. In the present disclosure, under the condition of choosing a chemical reagent which has no pollution to the environment, the water glass used sand is recycled into a reclaimed sand which meets the use requirements. The present disclosure aims for the popularization and application of the water glass sand and reducing the enterprise cost.

In order to achieve the above object of the present disclosure, the technical solution adopted by the present disclosure is as follows:

a chemical regeneration method of water glass used sand, comprising the following steps:

crushing, screening and magnetically separating collected the water glass used sand to obtain water glass used sand at a desired particle size; and

S2: mixing a treatment reagent with the obtained water glass used sand in step S1 at room temperature and then stirring for 2 to 10 minutes; after stirring, sealing and placing a mixed sand sample for no more than 24 hours to obtain reclaimed sand; wherein: the treatment reagent is one of the following reagents:

a) an emulsion composed of sucrose and calcium oxide;

b) a two-component reagent composed of calcium oxide and tap water;

c) an aqueous calcium chloride solution;

d) an aqueous magnesium chloride solution or aqueous magnesium sulfate solution.

Specifically, in the above technical solution, the water glass used sand in step S1 is any of ester hardened used sand or CO₂hardened used sand.

Further, when the water glass used sand is the ester hardened used sand, the steps performed before step S2, also include: incinerating the ester hardened used sand, and an incineration atmosphere is air, an incineration temperature is from 350° C. to 800° C., preferably from 400° C. to 600° C., and 500° C. is better; and an incineration time is from 10 to 30 minutes.

Further, in the above technical solution, the normal temperature in step S2 refers to the natural room temperature conditions in the four seasons, without additional cooling or heating treatment, and the normal temperature is generally controlled from 10° C. to 30° C., preferably from 15° C. to 25° C.

Further, the two-component reagent composed of the calcium oxide and the tap water is preferably chosen as the treatment reagent of step S2.

Preferably, a mass ratio of the tap water to the water glass used sand is (from 1 to 10): 100, and more preferably the mass ratio of the tap water to the water glass used sand is (from 2 to 4): 100.

Preferably, the mass ratio of the calcium oxide to the water glass used sand is (from 0.5 to 5): 100, and more preferably the mass ratio of the calcium oxide to the tap water glass used sand is (from 0.5 to 1): 100.

Further, in the above technical solution, a concentration of calcium chloride aqueous solution, magnesium chloride aqueous solution or magnesium sulfate aqueous solution is 40 wt % to 60 wt %, and preferably 50 wt %.

Further, in the above technical solution, preferably sealing and placing the mixed sand sample for 12 hours.

Further, in the above technical solution, the packing of sealing the mixed sand sample described in step S2 is not limited, as long as the function of blocking air can be realized, and a plastic film bag is preferably chosen to seal the mixed sand sample.

Compared with the prior art, the present disclosure relates to the chemical regeneration method of water glass used sand, comprising the following beneficial effects:

The present disclosure chooses two-component reagent composed of calcium oxide and tap water, emulsion composed of sucrose and calcium oxide, calcium chloride aqueous solution, magnesium chloride aqueous solution and magnesium sulfate aqueous solution through an exploratory test to process the regeneration of the water glass used sand, and prepares the sample of the reclaimed sand obtained after the reagent mixed with the water glass used sand is sealed and placed in the 0 hour, 2 hours, 4 hours, 6 hours, 8 hours, 12 hours, 18 hours, 20 hours, and 24 hours respectively, and prepares the sample and tests the properties of the sample including: initial strength, final strength and collapsibility, as well as sodium carbonate content of reclaimed sand, and compares the properties of raw sand and water glass used sand after the tests. Among several regeneration methods of the present disclosure, each property index of the reclaimed sand obtained by using calcium oxide and tap water to regenerate for 12 hours is the best, and compared with the raw sand, the initial strength increases by 60%, the final strength increases by 154%, the collapsibility of the reclaimed sand is slightly worse than the collapsibility of the raw sand, and better than the collapsibility of the water glass used sand; the sodium carbonate content reduces by 1.38% compared with the used sand, which meets the use requirements.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 illustrates a process flow diagram of a chemical regeneration method of water glass used sand of the present disclosure.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The present disclosure is further explained by the embodiments. The embodiments of present disclosure is implemented under the premise of the technology of the present disclosure, detailed implementation method and specific operation process are presented to show the present disclosure has creativity, but the scope of protection is not limited to the following embodiments.

According to the information contained in the present application, it is easy for those skilled in the art to make various changes to the precise description of the present disclosure without departing from the spirit and scope of the appended claims. It should be understood that the scope of the present disclosure is not limited to a defined process, property or component, as these embodiments and other descriptions are intended solely to illustrate specific aspects of the present disclosure. In fact, it is apparent to those skilled in the art or related art that various changes that can be made to the embodiments of the present disclosure are covered by the appended claims.

In order to better understand the disclosure and not to limit the scope of the present disclosure, all numbers representing amounts, percentages, and other values used in the present application should in all cases be understood to be modified by the word “approximately”. Therefore, unless otherwise specified, the numerical parameters listed in the description and the appended claims are approximate values, which may vary depending on the desired nature sought to be obtained. At a minimum, each numerical parameter should be considered based on the significant figures reported and by the usual rounding method.

In the following embodiments from 1 to 14 of the present disclosure, the raw sand for producing steel castings made in Fujian, the grain size of which is 50/100, and the used sand is obtained by crushing and screening the waste used sand produced by a certain enterprise in Jiangsu after producing a steel casting piece (the same raw sand is used), and the grain size distribution of the raw sand and the used sand is shown in Table 1.

TABLE 1

Particle Size Distribution of Raw Sand and Used Sand (%)

Mesh

number

(No.)
30
40
50
70
100
140
200
>200
Total

Raw sand
6.04
5.74
28.49
36.76
22.86
5.04
0.40
0.10
99.30

Used sand
4.3
11.48
26.06
31.04
17.37
4.55
1.39
3.76
99.95

after

screening

The water glass is produced in Wuhan, with modulus of 3.1 and density of 1.32. When using the water glass, a certain amount of NaOH saturated solution is added and mixed evenly to adjust the modulus and density of water glass, and after the adjustment, the modulus of the water glass is 2.3 and the density is 1.37. The added amount of the water glass accounts for 6.0% of the raw sand; and the sand sample for properties test is prepared by hollow cylindrical sample bucket on hammer-type sample preparation machine, with a diameter of 30 mm and a height of 30 mm.

Carbon dioxide gas is used for water glass hardening: a bottle of industrial CO₂gas manufactured by a company in Wuhan is used, with blowing flow rate of 15 L/min and blowing time of 20 seconds.

Embodiment 1

a chemical regeneration method of water glass used sand of this embodiment, the regeneration process is as follows: putting 500 g of used sand into the stirring pot, adding 10 g of calcium oxide powder (2% by mass of sand), turning on the mixer, adding 20 g of tap water (4% by mass of sand) while stirring, and stirring for three minutes to obtain reclaimed sand.

Study on properties of the reclaimed sand: preparing samples of the reclaimed sand obtained separately, and testing the properties of the sample, including initial strength, final strength, usable time and collapsibility, and measuring sodium carbonate content of the reclaimed sand.

Sample preparation steps are as follows: taking 500 g of reclaimed sand, using a micro pipette to take 30 g of water glass, pouring it into a stirring pot and stirring the reclaimed sand sample for three minutes, and taking down the stirring pot after stirring; and carrying out the sample preparation with a hammer type sample preparation machine, using an electronic balance to weigh 33 g of mixed sand each time, and using 15 ml/min of CO₂to blow for 20 seconds to harden the sample; taking out the sample after blowing, when three consecutive samples are prepared, measuring their initial strength with hydraulic universal strength tester, which is 0.241 MPa, 0.402 MPa, 0.340 MPa respectively. Then, continuing to use the above steps for sample preparation and placing the sample in a tray for 24 hours; after 24 hours, measuring the final strength with hydraulic universal strength testing machine, and seeing Table 2 for each data.

Determination of collapsibility of reclaimed sand: selecting five samples for the determination of collapsibility, turning on the high-temperature box-type resistance furnace in advance and preheating for about two hours to make the furnace temperature reach 800° C.; when the temperature reaches the requirements, placing the sample with iron plate and putting the iron pliers into the high-temperature box-type resistance furnace, closing the furnace door and keeping the furnace heated at 800° C. for 20 minutes. When the time is up, taking out the sample for natural cooling, and using the hydraulic universal strength testing machine to measure the retained strength when the sample is prepared at normal temperature, and the greater the retained strength, the worse the collapsibility; and testing the retained strengths of the five samples respectively, and listing the initial strength, final strength and data of reclaimed sand in Table 2 below.

TABLE 2

Effect of Regeneration of Calcium Oxide and Tap Water for 20 Hours on

Strength of Used Sand

Initial strength
Final strength
retained strength

Embodiments
MPa
MPa
MPa

Reclaimed sand
0.241
3.670984
2.900

(20 h)
0.402
3.344838
2.921

0.340
3.088102
2.033

Determination of sodium carbonate content: using a volumetric carbonate content test device to test the determination of sodium carbonate content, putting 50 g of reclaimed sand or used sand into a beaker, and adding tap water to submerge, and putting into an ultrasonic cell mill, and then processing for 15 minutes. After the process, using circulating water type multi-purpose vacuum pump (SHB-111) to extract and filter, pouring the filtrate into the volumetric flask of carbonate content testing device, and adding tap water to constant volume to 250 ml; taking 10 ml (about 10 g) of the constant volume solution, and putting the constant volume solution into a round bottom flask, dropping in the methyl red indicator (yellow), and the putting the solution on the constant temperature magnetic heating stirrer (putting the magnet into the flask), and turning on the power supply after the installation is correct; taking note of the initial scale, titrating with hydrochloric acid at a concentration of 0.64 mol/L, and adjusting the switch of the U-tube next to it while dripping hydrochloric acid. When the solution in the round bottom flask turns red, stop dripping hydrochloric acid, and writing down the termination scale when the liquid levels on both sides of the U-shaped tube are level. The above process was carried out three times continuously, and the data are shown in Table 3 below.

TABLE 3

Sodium Carbonate Content Determination of CO₂Volume

Initial scale
End scale
CO₂volume(ml)

First group
5.5
16.1
10.5

Second group
17.1
26.3
9.8

Third group
26.3
37.1
10.8

The average CO₂volume is (10.5+9.8+10.8)/3=10.4 ml, and calculating the sodium carbonate content according to the following formula:

$sodium carbonate content (%) = \frac{V \times M r 1}{2 2.4 \times m \times 1 0 0 0} \times 1 00 %;$

wherein:

V—volume of carbon dioxide production (U-tube liquid level drop volume) ml;

Mr1—molecular weight of sodium carbonate is 106;

22.4 represents the volume (1) of 1 mol of gaseous substance in the standard case;

m—Mass of sample taken (g).

$Sodium carbonate content (%) = \frac{1 0.4 \times 1 0 6}{2 2.4 \times 1 0 \times 1 0 0 0} \times 100 % = 0.49 % .$

Embodiment 2

the chemical regeneration method of water glass used sand of this embodiment described is basically the same as the Embodiment 1, and the difference is only: adding 1.0 g of calcium oxide powder, after stirring, sealing and placing the mixed sand sample for 2 hours to obtain reclaimed sand.

Embodiment 3