Reclamation of CO 2 sodium silicate used sands by steam leaching

The bond film on the surface of the CO 2 sodium silicate used sands is not easy to decompose, therefore, it is difficult to reclaim used sands. A new reclamation method of CO 2 sodium silicate used sands was developed by steam leaching, which can reduce the water consumption of reclamation and improve the removal effect of sodium silicate bond film. Firstly, the leaching effect of the sodium silicate sands after 20/200/400/600/800/1,000 °C heat preservation treatment was simulated. Furthermore, the influence of the leaching time on the removal effect of the sodium silicate bond film was studied. Finally, the casting properties of the reclaimed sands after the leaching reclamation treatment were tested. The results show for simulated used sands after 30 min of steam leaching, the removal ratio of the alkali exceeds 84.1%, the removal ratio of silicate is 86.2%, and the removal ratio of carbonate is 93.6%. The removal rate of alkali, silicate and carbonate is relatively low in the leaching time of 30–50 min. Considering the reclamation effect and cost, the leaching time is controlled in 30 min. Water consumption is only 60% of the mass of used sands for 30 min steam leaching, while it is 200% for wet reclamation. Morphological analysis shows that most of the hazardous substances in the used sands are removed in 30 min steam leaching, and the reclaimed sands surface after steam leaching in 50 min is as smooth as new sands. After 30 min of steam leaching, the alkali removal effect of the factory used sands can reach 81.5%, the water consumption by the steam leaching reclamation is 58% of the mass of the used sand, which is similar to the result of simulated used sands. The performance of reclaimed sands obtained after 30 min steam leaching is better than that of new sands when the amount of sodium silicate added is 6% of the mass of the reclaimed sands and the CO 2 blowing time is 15 s: the 24 h ultimate compressive strength of reclaimed sands is 5.6 MPa (equated with new sands), and the collapsibility compressive strength is 5.2 MPa, which is lower than the collapsibility compressive strength of new sands (7.7 MPa). This indicates that the reclamation of CO 2 sodium silicate used sands by steam leaching is a feasible method.