The Immobilization And Stability Of Heavy Metal Ions By Ettringite

The untreated heavy metal contained in the industrial wastes will causes pollution to the environment and affects the industrial and agricultural production and people's health.There are many advantages of technology of cement solidification,such as low cost,strong practicability and widely used.Ettringite is one of the main hydration products of portland cement.And ettringite play an important role in solidification and stabilization of heavy metals.Therefore,research on the solidification and stabilization of ettringite to heavy metals has significant meaningsIn this paper,two methods were used to prepare ettringite,that are solution synthesis and hydration of C3 A.Heavy metals were introduced in the form of soluble salts during the formation of ettringite.The solidification rate and mechanism of ettringite to Zn²⁺,Pb²⁺,Ni²⁺,Mn²⁺ were analyzed.In order to prevent heavy metal pollute once again,the stability of heavy metal-ettringite system under the environment such as high temperature,accelerated carbonation,freeze-thaw cycle,sulfate and chlorine salt erosion were analyzed.Then use the dynamic model and thermodynamic model to discuss the characteristics of adsorption kinetics and thermodynamics of ettringite to heavy metal.Ettringite prepared by those two methods both have a good ability to capture heavy metals Zn²⁺,Pb²⁺,Ni²⁺,Mn²⁺.The rate of solidification of ettringite to heavy metal ions increased with the increase of curing age while decreased with the increase of content of heavy metal ions.In addition,the ability of ettringite to Mn²⁺ was foreign to the form of incorporation.The results show that Zn²⁺,Pb²⁺,Ni²⁺,Mn²⁺ could enter into the crystal lattice of ettringite,then give rise to the micro topography and the molecular structure of ettringite.Such influence become more obvious with the increase of the content of heavy metals.MnCl2 has disadvantage to the development of micro topography of ettringite when its content up to 2%.In addition,the coexistence of heavy metal ions is not conducive to the formation of ettringite.Although heavy metal ions were leached but the solidification rate of the system of ettringite and heavy metals remains high value under these conditions,that are high temperature,accelerated carbonation,freezing and thawing cycle,sulfate and chloride corrosion.Kinetic features of adsorption of ettringite to Zn²⁺,Pb²⁺,Ni²⁺,Mn²⁺ were modeled by pseudo first-order and pseudo second-order equations The adsorption energy |E| calculated according to the D-R model were between 8¹6kJ/mol,therefore,we could know that the adsorption of ettringite on Zn²⁺,Pb²⁺,Ni²⁺,Mn²⁺ was achieved mainly by ion exchange.