Thermal regeneration of foundry sand
The invention relates to a method for regenerating used foundry sand, which is contaminated with soluble glass, wherein: used foundry sand is provided, which is tainted with a binding agent made of the soluble glass, to which a particle-shaped metal oxide is added; and the used foundry sand is subjected to a thermal treatment, wherein the foundry sand is heated to a temperature of at least 200° C., thereby obtaining regenerated foundry sand. The invention further relates to regenerated foundry sand, as that obtained from using the method.
1. A method for regenerating used foundry sand with binding agent based on dissolved sodium silicate or potassium silicate or both adhered thereto, said method comprising:
i) obtaining used foundry sand in the form of a used casting mould previously cured at least with dissolved sodium silicates or potassium silicates or both as a binding agent in the presence of heat and at least a particulate metal oxide, wherein the particulate metal oxide comprises at least amorphous silicon dioxide;
ii) subjecting the used foundry sand obtained in step (i) with adhered binding agent based on dissolved sodium silicate or potassium silicates or both to a thermal treatment, wherein the used foundry sand is heated to a temperature of higher than 300° C., to obtain regenerated foundry sand; and
iii) preparing a moulding material mixture comprising at least a portion of the regenerated foundry sand obtained in step (ii) and dissolved sodium silicates or potassium silicates or both as a binding agent and curing the moulding material mixture in a moulding tool wherein the curing exclusively consists of applying a heat treatment to the moulding material mixture by heating the moulding tool to 100 to 300° C. and/or by blowing heated air at a temperature of 100 to 180° C. into the moulding tool to obtain a cured casting mould comprising regenerated foundry sand, wherein the method further comprises adding as part of step (iii) at least one particulate amorphous silicon dioxide.
2. The method according to claim 1 , wherein the thermal treatment is carried out until the acid consumption of the foundry sand, measured by the consumption of 0.1 n HCl in a 50 g quantity of foundry sand, has decreased by at least 10%.
3. The method according to claim 1 , wherein the used foundry sand is present in the form of a casting mold.
4. The method according to claim 3 , wherein the used casting mold comprises a casting.
5. The method according to claim 4 , wherein the casting mold is separated from the casting before the thermal treatment.
6. The method according to claim 3 , wherein the casting mold is broken at least into coarse pieces before the thermal treatment.
7. The method according to claim 1 , wherein a mechanical treatment of the foundry sand for grain separation is carried out before or after the thermal treatment.
8. The method according to claim 3 , wherein the casting mold is transferred to a furnace for the thermal treatment.
9. The method according to claim 1 , wherein the used foundry sand is agitated during the thermal treatment.
10. The method according to claim 1 , wherein the thermal treatment is carried out under admission of air.
11. The method according to claim 1 , wherein the regeneration is carried out dry.
12. The method according to claim 1 , wherein the dissolved sodium silicates or potassium silicates or both has an SiO 2 /M 2 O modulus in the range of 1.6 to 4.0 wherein M denotes sodium ions and/or potassium ions.
13. The method according to claim 12 , wherein the dissolved sodium silicates or potassium silicates or both has a solid content of SiO 2 and M 2 O in the range of 30 to 60 wt. %.
14. The method according to claim 1 , wherein amorphous silicon dioxide is selected from the group of precipitated silicic acid and pyrogenic silicic acid.
15. The method according to claim 1 , wherein an organic additive is added to the molding material mixture.
16. The method according to claim 15 , wherein the organic additive is a carbohydrate.
17. The method according to claim 1 , wherein a phosphorus-containing additive is added to the molding material mixture.
18. The method according to claim 1 , wherein the dissolved sodium silicates or potassium silicates or both has an SiO 2 /M 2 O modulus range of 2.0 to 3.5 and M denotes sodium ions and/or potassium ions.
19. The method of claim 1 , wherein the particulate metal oxide is synthetically produced amorphous silicon dioxide.
20. The method of claim 1 , wherein the particulate amorphous silicon dioxide and at least the regenerated foundry sand are mixed and thereafter the water glass is added.