Biomimetic Synthesis Of Calcium Carbonate Minerals And Research On Phosphorus Adsorption Mechanisms

Calcium carbonate (CaCO3) minerals are friendly predominant in environments. It isvery important to remove phosphorus (P) from the water body using calcium carbonateminerals in order to protect the human health. The removal capacity of calcite and thesynthesized CaCO3materials to high P was addressed in this thesis. The combinationmethods of sorption isotherms and envelopes, FTIR and Zeta potentials were employedto investigate the sorption mechanisms of phosphorus onto CaCO3materials.The experimental data showed that the sorption of phosphate onto calcite and thesynthesized CaCO3materials obey Langmuir model; while sorption onto dolomite obeyFruendlich model. However, the dumbbell-like spherical aragonite has the strong sorptioncapacity with increasing the initial concentration of phosphate, which suggested thedifferent sorption behavior to phosphate.Generally, the solution pH was considered to be an important parameter whichcontrolled the adsorption at water-solids interfaces. In this study, series of aragonite,Mg/aragonite and amorphous calcium magnesium carbonate (ACMC) adsorbents weresynthesized through the simplified biomimetic mineralization process, characterized, andevaluated. For calcite, when pH<10.0, the adsorption efficiency to phosphate decreasedwith increasing the solution pH. And then it turned to be lowest during pH range of10.0-11.0. At pH>11.0, the adsorption efficiency of calcite was again improved with theincrease of solution pH. However, solution pH had little effect on the phosphateadsorption by the synthesized calcium carbonate adsorbents. At pH around10.0, thesorption capacity of dumbbell-shaped aragonite to phosphate which was3times strongerthan that of calcite. Especially, the removal efficiency is significantly improved about10times by the synthesized ACMC than calcite. The sorption capacity to high phosphatefollows the order of ACMC> Mg/aragonite> aragonite> calcite. Especially, the removalefficiency is significantly improved about10times by the synthesized ACMC thancalcite.FTIR and Zeta analysis revealed that the mechanism of phosphorus adsorption oncalcite and dumbbell-shaped aragonite was attributed to chemical adsorption at pHaround10.0of the phosphate solution. Thus the likely mechanisms involve that theaggregation of cluster leads to the nucleation and subsequent growth of Ca-P phases onthe surface of adsorbent to be ACP. And then, unstable ACP converts to HAP with increasing concentration in the second adsorption process. However, Mg component inMg-ACC-X structure tends to enhancing phosphate chemi-sorption on surface.