Research On Effect Of Heavy Metal Ions On The Hydration Characteristics And Microstructure Of Alkali-activated Slag Cement

With the rapid development of our country’s economy, the environmental pollution is becoming serious increasingly, which has brought lots of pressure to our society, and the disposal of heavy metal waste is becoming more and more significant. At present, the cement solidification method is one of the important method to treat heavy metal waste.However, the traditional cement-based process curing heavy metal waste exists some obvious defects, such as, high heavy metal concentration of leaching solution, poor durability, poor acid resistance and sulfate resistance, etc. Alkali-activated slag cement(AASC) is superior to ordinary Portland cement in performance, such as high compressive strength, excellent pore structure, strong resistance to chemical corrosion, good durability, etc. And AASC is a new kind of low-carbon type cementitious materials with remarkable environmental benefit and economic benefit, which can solidify toxic heavy metal ions effectively owe to C-S-H gel with a low Ca/Si ratio as the main AASC hydration products. The research on hydration and structure formation of alkali-activated slag cement with heavy metal ions can provide technical basis about recognizing consolidation mechanism with heavy metal ions by the AASC stone, and also has important social significance to promote its application.With water-binder ratio 0.3 and Na2 O equivalent 5%, the effect of Cr6+/Pb2+/ Zn2+/Cd2+on the hydration heat evolution, setting and hardening performance and strength of alkali-activated slag cement were studied, and combined with microscopic test means, such as the FT-IR, SEM, this paper analyzed the effect of heavy metal ions on the structure of hydration products.The results show that:1)When the content of Cr6+ is in the 2% range and the alkaline constituent is water glass, with the dosage of Cr6+ increases, the hydration heat reduces, the setting time increases slightly and the compressive strength shows the trend of increasing firstly and then decreasing. The addition of Cr6+ makes the structure of hydration products loose and Cr6+ has a certain effect on the hydration products structure of AASC.2)When the content of Pb2+ is in the 2% range and the alkaline constituent is water glass, with the dosage of Cr6+ increases, the hydration heat reduces, the setting time increases slightly and the compressive strength shows the trend of increasing firstly and then decreasing. The addition of Pb2+ makes the crack between hydration products become more and wider and Pb2+ has a certain effect on the hydration products structure of AASC.3)When the content of Zn2+ is in the 1% range, with the dosage of Zn2+ increases, the hydration heat reduces, the setting time increases obviously and the compressive strength shows the trend of decreasing. When the alkaline constituent is water glass with 2.48 modulus values, the setting time of AASC shows a trend of decrease after the first increase. The addition of Zn2+ makes the structure of hydration products loose and Zn2+ has a certain effect on the hydration products structure of AASC.4)When the content of Cd2+ is in the 2% range and the alkaline constituent is Na OH, with the dosage of Cd2+ increases, the hydration heat reduces and the setting time increases slightly. While the alkaline constituent is water glass with 1.5 modulus values, Cd2 + has opposite effect. When the alkaline constituent is water glass with 2.48 modulus values, with the increase of dosage of Cd2 +, its initial setting time becomes shortened gradually, and final setting time becomes extended gradually. The addition of Cd2+ makes the whole structure present a loose state and Cd2+ has a certain effect on the hydration products structure of AASC.