Solidification Characteristics Of Heavy Metals Onto Clay Mineralat High Temperature

Sewage sludge incineration is a method of reducing and reusing.The volatility of heavy metals of fly ash cause environment secondary pollution.Solidification of gaseous heavy metals Zn,Cu,Pb,Cd and Cr onto kaolin and diatomite at different temperature and SiO₂/Al₂O₃ were studied.The volatilization characteristic and reaction kinetics model of heavy metal chloride were analyzed by Differential Scanning Calorimetry.The solidification mechanism of the crystal form,microstructure and chemical bonds of the samples was explored by XRD,SEM and FT-IR.The results indicated that the kaolin solidified semi-volatile heavy metal Pb was optimal at 1050°C,the solidification increased 49.3%from 33.023 mg·g^-1to 65.14 mg·g^-1.The solidification of Zn,Cu,Pb,and Cd onto diatomite were optimal at 850°C,which up to 76.76mg·g^-1,102.5 mg·g^-1,256.51 mg·g^-1 and 69.96 mg·g^-1,respectively.The addition of SiO₂ can promote the solidification of kaolin and diatomite onto heavy metals.When M_Si/Al>1,solidification of heavy metals onto kaolin and diatomite increased obviously.There is the competition between Si and Al for the solidification of heavy metals and the addition of silicon can promote the solidification of kaolin and diatomite on heavy metals.The silicon has a promoting effect on the solidification process.When M_Si/Al=3,solidification of Zn onto kaolin increased by 6 times.Volatilization of heavy metals Zn,Cu,Pb,Cd and Cr were studied by Arrhenius's law and M-K-N temperature integral approximate equation.The volatilization process of heavy metals is simulated,heavy metal Pb belongs to the one stage chemical reaction and the others belong to the zero stage chemical reaction.The volatilization process is mainly affected by temperature.The activity energy of Pb is 153.99 kJ/mol.The solidification of different heavy metals onto kaolin and diatomite depends on the porous structure and the spacing of the layers of the solidifying agent,the types of chemical bonds of solidifying agent.Clay minerals surface adheres to different sizes of heavy metal fine particles.Small particles of heavy metals have small kinetic energy,which are not easy to solidify after being solidified.Larger particles are formed by collision and condensation of small particles.