Natural and modified zeolite to improve the adsorption of heavy metals from aqueous solutions

The present work describes the characterization of natural zeolites and adsorption results for Pb+2, Cd+2, Fe+2 and Mn+2 from aqueous solutions. The zeolitic-rich tuff samples provided from Bulgarian Beli Bair (BB) and Beli Plast (BP) deposits and from North Chile (NCl), were characterized by their chemical and mineralogical composition, adsorption and ion exchange properties and X ray analysis. The average content of clinoptilolite for both samples was found to be more than 75%. The materials had ion exchange capacity (NH4 +) varying from 107 to 121 meq/100g respectively. Thermo-chemical modification of natural clinoptilolite from BB and BP was made in order to increase the ion exchange capacity up to 180 meq / 100g. Results showed almost complete removal (>90 %) of the all metal ions studied. Activations of NClzeolite (118 m2 g-1). by pre-treatment with various ions greatly enhanced the Mn adsorption, in that order and mechanisms involved were elucidated. The maximum adsorption capacity (pH 6) were decreasing for activation with NaCl (0.77 meq Mn2+ g-1), NaOH (0.76 meq Mn2+.g-1), Na2CO3 (0.72 meq Mn2+ g-1), NH4Cl (0.67 meq Mn2+g-1) and natural (0.26 meq Mn2+ g-1). The Langmuir isotherm model showed excellent correlation to the equilibrium data, and maximum capacity to adsorption depends of the activation type realized before the adsorption. The treatment of heavy metals bearing solutions using filter packets and stirred flasks was studied experimentally. The filters were made by a special technology following standard requirements in Bulgaria; i.e.: particle size distribution, mass ratio (g/m2) and permeability. These filters purified the waters substantially lowering the metal ion concentrations well below sanitary standard limits. The reduction of Pb++ was about 18 times, Mn+2, more than 20 times and Fe+2 and Cd+2, 50 times. The total reduction of the heavy metals was more than 25 times and varied within the limits of 5 to 14 mg/liter after the third stage treatment. Best results were obtained with blends of BB and BP natural clinoptilolite at 50:50 ratios and after the thermo-chemical treatment.

کلیدواژه ها:

clinoptilolite ، ion exchange ، heavy metals