Coagulation and precipitation is a widely applied method to remove F-from wastewater.In this work,the effect of coagulation on the removal of F-and organic matter from coking wastewater was studied using Al Cl3and Fe Cl3as compound coagulants.The removal rates of F-and organic matter under different coagulant doses and p H conditions were investigated.The results show that the highest removal rates of F-by Al Cl3and Fe Cl3are 94.4%and 25.4%,respectively;when the dosage is 10 mmol/L,the TOC removal rates of Fe Cl3and Al Cl3reach 20.4%and 34.7%,respectively.Therefore,the removal rate of F-by Al Cl3is higher than that of Fe Cl3,but the removal rate of organic matter by Fe Cl3is relatively higher.The addition of Ca2+can promote the removal of F-,but the removal rate of organic matter decreases.In addition,by investigating the effects of different p H and Fe–Al ratio on the removal rate,the removal effect of adding Fe Cl3and Al Cl3at the same time was discussed.The results show that the most suitable working condition for the removal of organic matter and F-is that the p H is 6.5 and the molar ratio of Al/Fe is 8:2.Overall,the removal mechanism of F-and organic matter in coking wastewater by Fe Cl3and Al Cl3was explored in this study.The experimental results can provide reference for the advanced treatment of coking wastewater.
Structure properties of flocs(size,fractal dimension(D_(f)),etc.)have a high impact on coagulation efficiency.In this work,the influences of three different additives(ferric salt(Fe),phosphate(P),and citric acid(CA))on coagulation process/efficiency were investigated.Results showed that a small amount of extra Fe can facilitate the growth of Al flocs by providing more'active sites'.Although zeta potential and D_(f) showed a limited change,the average floc size increased apparently and the increment was more obvious when Fe was added after the formation of the flocs.In contrast,P addition during the rapid mixing period will decrease the final average floc size,while the influence is less significant when P was added after the growth of the flocs.In terms of CA,a more striking negative effect on the growth ability of the flocs was observed compared to P.The strong complexing/coordination interactions between CA and aluminum hydroxide is the main reason behind the influence.CA also significantly decreased the D_(f) value of the flocs compared to P,and D_(f) showed a comparatively higher decrease when P or CA was added during the rapid mixing stage compared to the addition after the flocs formation.These results indicated that the addition of CA or P during the rapid mixing stage'inactivated'or occupied more'active sites'on the preliminarily formed Al NPs during the hydrolysis process,and therefore presented stronger impact on the morphology/size of the formed flocs.
