Effect of Filter Clogging on the Determination of Concentrations of Chemical Elements Migrating in River Water as Components of True Solutions or in Colloidal Forms

摘要

The effect of clogging of membrane filters on the chemistry of filtrates is characterized in the case of successive filtration of 100 to 500 mL of river water with a step of 100 mL. The examined samples were taken from typical rivers in the southern Far East at different water regimes and at suspension concentrations varying from 23 to 270 mg/L. The concentrations of sulfates, chlorides, dissolved organic carbon, nitrates, and elements Li, B, Si, Ni, Cu, As, Sr, Rb, Mo, Ba, U, V showed practically no dependence on the degree of filter clogging. At the same time, in the case of rare-earth elements and hydrolysate elements (Hf, Zr, Nb), as well as Mn and Co, a significant decrease in their concentration in the filtrate (by 30-60) was observed in the process of filtration of a 500-mL sample. The effect of clogging was especially strong in the case of Fe, Al, Ti, and Pb concentrations, which decrease by 70-90 already after the filtration of 200 mL compared with the results observed after the first 100 mL or after a capsule filter. Underestimation of the concentrations of colloidal forms of some metals in river waters is the most obvious result of neglecting the effect of clogging. Possible methods for minimizing the effect of clogging are discussed.