Study on Reclamation of CO2-hardened Sodium Silicate Used Sands by CaO Powder

Aiming at the problems of wet reclamation consuming a lot of water, dry (mechanical) reclamation having wear and power consumption, this paper to find suitable reclamation reagents to reduce the influence of harmful substances in used sodium silicate sands. By comparing the reclamation effect of CaO, Ca(OH)2 and Ba(OH)2 reclamation powder reagents, it was concluded that CaO had the best reclamation effect. Through the single factor experiment, the influence of CaO on the reclamation effect was explored: 1. addition amount of CaO; 2. the additional amount of water; 3. reclamation time. The orthogonal results showed that the CaO reclamation effect was the best when the amount of CaO was 1.5%, the amount of sodium silicate was 4.0%, the amount of water added was 6.0%, and the reclamation time was 12.0h. In this experiment, 82.2% carbonate and 75.0 % silicate in used sands can be removed. The microscopic analysis of the reclamation sands was carried out by scanning electron microscope (SEM); The surface was relatively smooth, without large area cracks and powder accumulation. Compared with the used sands, the instant, 24h ultimate, and residual strengths of the reclaimed sands were increased by 536.5%, 458.1%, and 89.8%, respectively, which was beneficial to the reclamation of the CO2 sodium silicate used sands.