Study on adsorption of ciprofloxacin to insoluble humic acids

The present paper has investigated the removal of ciprofloxacin from the aqueous solutions via its adsorption to insoluble humic acid(IHA) at different pH values and ionic strength.As is known,insoluble humic acid enjoys an excellent adsorptive ability,which can be cultivated by heating the highly soluble humic acid at 330 ℃ and then treated with 2 mol/L CaCl2 solution or 2 mol/L AlCl3.Batch equilibrium experiments were used to reveal ciprofloxacin adsorption on two insoluble humic acids.The results show that the adsorption of isotherms can be well defined by using the Freundlich model and ciprofloxacin,for it tends to be adsorbed more strongly on the insoluble humic acid of calcium type than on the acid of aluminum type.At the same time,we have also investigated the effects of adding volume,time,pH value and ionic strength on the adsorptive behavior of ciprofloxacin.It can thus be said that the adsorptive capacity tends to decrease in a nonlinear relation with the increase of the ionic strength and pH value.The greatest removal efficiency of ciprofloxacin by insoluble humic acid of calcium type turns out to be as high as 95.3% in aqueous solutions at pH=5.5,2.13 times as high as that done by the insoluble humic acid of aluminum type,with the adsorption equilibrium gained within 24 hours.However,it was found that the adsorption of ciprofloxacin on insoluble humic acid of calcium type tends to decrease gradually with the increase of natural cation concentrations in solution in a nonlinear manner,which suggests that the absorptive process is mainly dominated by the cation exchange.In addition,it has been found that the adsorption coefficient of the ciprofloxacin tends to decrease with the increase of pH value in a range between 5.0 and 9.0.At the same time,we have gained quite a high and stable removing rate of ciprofloxacin on insoluble humic acid under nearly the same acid or faintly acid conditions.The above results reveal that insoluble humic acid of calcium type can be used as a potentially efficient absorbent for purifying water from the ciprofloxacin contaminants.