Thermal regeneration of foundry sand

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.