Controlled synthesis of Zeolite adsorbent from low-grade diatomite: A case study of self-assembled sodalite microspheres

Highly efficient and sustainable conversion technologies to generate uniform sodalite (Na8(AlSiO4)6(OH)2) zeolite microspheres with low-grade waste natural diatomite as raw materials via a solution-mediated crystallization route were developed in the present study. The synthesis process can be considered as an in-situ zeolitization of diatomite precursor without involving any mesoscale template and any post-synthetic modification. The mass ratios of diatomite and AlCl3·6H2O have remarkable effect on the morphology, crystal structure and porosity of sodalite zeolite product. The preferred sodalite microspheres with uniform mesoporous of size 3.5–5.5 nm and large surface area of 162.5 m2/g exhibit well removal performance for heavy metal ions (Pb(II), Cd(II), Zn(II), and Cu(II)), with the highest adsorption abilities for Pb(II) ions of 365 mg/g. In addition, the effect of contact time, initial ion concentration, competitive adsorption and solution pH were evaluated. The removal performance results from synergistic effects of dominating cation-exchange and additional surface chemisorption. The study may broadly help unveil chemical control reactions of the zeolitization processes of diatomite, and thus facilitates the development of promising zeolite materials for the use in natural and engineered aquatic environments by recycling waste diatomite resources.