Synthesis Of Differently Modified Montmorillonites And Application In Stabilization Of Soil Heavy Metals

Stabilization technology is one of the major technologies for remediation heavy metal contaiminated soil, in which stabilizing material is very important for the treatment efficiency. To reduce the cost of technical application and enhance the stabilizing performance, it is desirable to design efficient, low-cost stabilization treatment material. The montmorillonites were modified by acid treatment, heat treatment, organic and inorganic materials. Their structures and properties were characterized and the stabilization treatment performances were evaluated.Na-montmorillonite was first obtained by purification from raw montmorillonites. Then, the Na-montmorillonite was modified by acid treatment, heat treatment, organic and inorganic materials. The change of the montmorillonite structure before and after modification has been characterized using XRD, FT-IR, SEM, BET nitrogen adsorption and Zeta potential techniques. The result showed that:(1) acid-treatment, heat-treatment, and the reaction with organic and inorganic materials were successfully modified to montmorillonite structure, indicated by the appearance of characteristic peaks; (2) for organically-modified montmorillonite, particularly cetyl trimethyl ammonium bromide (HDTMA)-modified montmorillonite, the layer spacing significantly increased, the surface became more smooth, the BET surface decreased, and the surface charge increased with increasing the organo loading; (3) for Al-pillared montmorillonite, BET surface increased and the surface charge significantly changed; (4) the layered structure of Fe-Al pillared montmorillonite with obvious pillared structure stripped down into thin wafers, and with Fe content increasing, the specific surface area first increased and then decreasd.The result of stabilization performance experiment with HDTMA-modified montmorillonite showed that:(1) the stabilized rate for soil Cr (Ⅵ) was more than 95% when the content of HDTMA are more than twice of the cation exchange capacity (CEC) of the montmorillonite; (2) exchangeable adsorption was the major mechanism for Cr (Ⅵ) stabilization process.The result of stabilization performance experiment with Al-pillared montmorillonite showed that:the stabilized rate for soil Cr (Ⅵ) can be as high as 70% when using hydroxy aluminum (ALOH) pillared montmorillonite, whereas the stabilized rates were only 18%, 16%, when using polymer aluminum (Al13) and heat polymer aluminum modified (H-Al13) respectively; (2) the stabilizing peroformance was weakened in the order of H-Al13> Al13>ALOH; the stabilized rate for Ni (Ⅱ), Cu (Ⅱ), Zn (Ⅱ) and Cd (Ⅱ) was 80%,72%, 32%; 75%,65%,24%; 69%,43%,18%; 3%,2%, 1%,respectively.The result of stabilization performance experiment with Fe-Al pillared montmorillonite showed that:(1) Fe-Al pillared montmorillonite enhanced stabilization efficiency, compared with raw montmorillonite, the stabilized rate for Ni (Ⅱ), Cr (Ⅵ), Zn (Ⅱ), Cd (Ⅱ), Cu (Ⅱ) increased 890%,600%,100%,90% and 80%, respectively. (2) further heat treatment to Fe-Al pillared montmorillonite further improved the performance of stabilization; 300℃ heat deformated the original structure of montmorillonite and generared plenty of pores into the clay structure.