Study On Removal Mechanisms Of Antimony(Ⅴ) By Enhanced Coagulation Based On Mesoscopic Simulation

The mesoscopic scale simulation of negatively charged colloidal particles and ionic polymer chains withdifferent conditions(here,temperature, p H value, ionic degree and charged type of polymer chains) was conductedbased on the establishment of a coarse–grained model and force field of empirical potential function.Meanwhile, a series ofenhanced coagulation jar–tests were carried out to investgatethe effect of factors investigated during simulation on floc morphology and corresponding antimony(V) removal. The main objective of this study is to better understand themechanisms of antimony(V) removal by enhanced coagulation using polymeric flocculants with the help of both experimental and modeling methods.According to the mesoscopic scale simulation results, modeling conditionsgreatly affected the variation in virtual floc size, i.e., the size increased with thetemperature ranging from 0 to 40 degree centigrade, and similar variation trend was found for changing ionic degree at 25 degree centigrade; when the p H value was varied from 1.72 to 9.28(corresponding to calculated results), the flocsizeincreased first and then decreased, and reached themaximum size at p H=7.0; positively charged polymer chains were more conducive to the growth of colloidal particles with the negative electricity than the electronegativepolymer chains. Additionally, more colloidal particles were adhered to polymer chains as the floc size increased.The enhanced coagulation jar–tests using cationic polyacrylamide(CPAM) as flocculant, showed that theflocs formed under highertemperaturewere much larger butrelatively more loose structure, corresponding to the smaller fractal dimension values; under different p H value and ionic degree,the average particle sizefirstly increased and then decreased,and the maximum size was reached at p H=6.0 or ionic degree of 30%. For both experimental and simulation results, similar variation trend was observed under the conditions of temperature and p H, and however, the same was not true for the condition of ionic degree, possibly caused by ignoring the change of colloidal charge during simulation. In addition,larger floc size would lead to a higher turbidity removal rate, and unfortunately, the antimony(V)removal rate was only about 9.0%.This phenomenon may due to the reason that the neutralization behavior of positive charge orcationic groups was not the dominated mechanisms of antimony(V) removal.It was found that polymeric ferric sulfate(PFS) had the most significant effect, leading to a highest antimony(V)removal rate, among the coagulants of CPAM,anionic polyacrylamide(APAM), polyaluminum chloride(PAC) and PFS. In the enhanced coagulation process by PFS, the impacts of both raw– water p H value and PFS dosage on the removal of antimony(V) were much greater than water temperature and coagulation mixing intensity, reflected by an increase of antimony(V) removal efficiency with reducing p H value or incr easing PFS dosage.As aresult of competitive adsorption, coexisting anion(here, bicarbonate and phosphate) and HA have a negative influence on the removal of antimony(V) by coagulation, within the tests, reflected by an decrease of antimony(V) removal efficiency with increasing coexsiting anion and HA dosage.In addi tion,the effect of both floc average size and fractal dimension on coagulation was proved to have influence on the suspended antimony(V) concentration in settled water. However, the impact on the dissolved antimony(V) removal efficiency(determining the qu ality of treated water) was very limited.According to the above test results and referring to the existing literature,it shows that the major mechanism driving antimony(V) removal by PFS coagulation is attributed to adsorption(both surface and internal) onto the growing HFO which is the PFS hydrosis products. And the adsorption process has a certain selectivity, is the exclusive adsorption, also belongs to chemical adsorption. In practical operation, the number of small flocs in settled water should be m inimized in order to guarantee the working condition of following process and the quality of treated water.