Effects of sodium, magnesium, and calcium salts on the coagulation performance of cucurbit [8]uril for humic acid removal from synthetic seawater

摘要

This study evaluates the coagulation performance of cucurbit [8]uril (CB[8]) for HA removal and the effects of salts on this process. Experimental results showed that HA removal efficiency improved as the increase of CB [8] dosage. When the CB [8] dosage was 0.2 mmol/L, less than 50% of the HA was removed from the synthetic freshwater at pH above 7.5. The presence of salts improved both the solubility and coagulation capacity of CB [8], which varied depending on the type of anion and cation, respectively. For the synthetic seawater with 1.0 mmol/L of Ca2+, 8.0 mmol/L of Mg2+, and 0.4 mol/L of Na+ co-existing, the HA removal efficiency increased considerably from less than 50% to 83-90% at pH 7.5-8.5. Relative to the amount of HA removed by adsorption, an additional 20-40% of the HA was removed by CB [8] coagulation under the same water quality condition. Further in-depth analysis showed that HA coagulation by CB [8] is primarily a physical process. In addition to charge neutralization and electrical double-layer compression, the formation of hydrogen bonds between CB [8] and HA also contributed to HA destabilization and led to a complete loss instability before all the negative charges on the HA were neutralized. (C) 2016 Elsevier B.V. All rights reserved.