High Efficient Removal of Trace Molybdenum from Water by FeCl_3:Effects of p H and Affecting Factors in the Presence of Co-existing Background Constituents

摘要

The effect of FeCl_3 coagulation-filtration on the removal of trace Mo(Ⅵ) from water is investigated in the p H range of 4. 00 to 9. 00 and the effects of sulfate,silicate,phosphate and humic acid( HA) on the process were determined. Overall,the removal of Mo(Ⅵ) is determined by two factors: the content of Fe intercepted from water( Intercepted Fe) and the affinity between Mo(Ⅵ)( or co-existing background constituents) and adsorption sites. At low p H,where the agglomeration of the iron flocs is limited,the former factor is dominant,so the methods that can promote the agglomeration of the iron flocs,such as increasing the p H,adding co-existing constituents( sulfate,phosphate or HA),can increase the removal of Mo(Ⅵ). While at high p H,the second factor dominated. Increasing the p H weakens the affinity between Mo(Ⅵ) and the iron flocs,and co-existing background constituents( sulfate,phosphate,silicate or HA) compete with Mo(Ⅵ) for adsorption sites,both effects result in a decrease in Mo(Ⅵ) removal. The Mo(Ⅵ) removal efficiency of FeCl_3 in natural water decreases as the p H increases from 4. 00 to 9. 00,and it is better to operate the coagulation process at p H 5.00 in the practical water treatment engineering.