Enhanced Coagulation Removal Of FA In Water Using Nano Sized SiO₂

This paper mainly studied the coagulation characteristics of fulvic acid (FA), removed under three different temperature (normal , high and low temperature) with two different coagulants (aluminum sulfate, ferric chloride) enhanced by nano sized SiO2. Meanwhile, the effect of nano-SiO2 on removing FA and turbidity in water by coagulation was also analyzed.The results show that, for aluminum sulfate, the coagulant dosage is the dominant effecting factor to remove the FA and turbidity in water. With the increasing of aluminum sulfate dosage, the removing effect distinctively tends to become better, but it has a limit (30mg/L). Once it exceeds the limit, the changing rate of removing FA becomes little. For ferric chloride, it can have preferably effect of removing FA (around 70%) and very good effect of removing turbidity (residual turbidity about 2.2NTU) at much less dosage (5mg/L). Henceforth, with the increasing of dosage, the removing rate of FA change very little, while the residual turbidity may change reversely. Although ferric chloride is more effective than aluminum sulfate to remove FA and turbidity in water, it can not reach the best effect of removing FA by aluminum sulfate ( η =90%).The flocculating constituents formed by coagulation with ferric chloride is thinner and denser than with aluminum sulfate.At pH=4, the double-layer compression is the main coagulation mechanism; at pH=6, adsorption neutralization and deposition netting are the main coagulation mechanism; at pH=9, deposition netting mechanism dominates the reaction.It can improve the agglomeration and sedimentation performance of flocculating constituent to cast proper quantity of nano- SiO2. It can make the little flocculating constituents formed after rapid agitation phase to become thick at slow agitation phase, and they settle more quickly then the liquid become clear at sedimentation phase. After sedimentation, flocculating constituent stacked at the beaker center.For aluminum sulfate, at pH=4, it can achieve a better removing effect with less coagulant dosage at high temperature. Comparably, it can reach a much better effect of removing FA and turbidity with the same low dosage of ferric chloride than aluminum sulfate under low temperature.