| Popis: |
The influence of dissolved natural organic matter (NOM) on the transport of Cu(II) in saturated media was investigated in controlled batch and column experiments. Six sources of natural organic matter (two in their ambient solution matrices and four isolated humic substances) were chosen to represent different environments and different humic fractions. 5i02 and a-Al203 comprised the mineral surfaces with which the NOM and Cu(II) interacted. The experiments were conducted at a constant ionic strength and buffer concentration and at pH 6.2 (all sources) and pH 7.5 (two sources). Equilibrium Cu(II) concentrations were monitored with an ion specific electrode and atomic absorption spectrophotometer and NOM was measured as UV absorbance at 254 rim. Adsorbate effect on particle surface charge was evaluated using microelectrophoresis and the effect of molecular weight on NOM breakthrough was determined with ultrafiltration of column influent and effluent. Column studies showed significant variation in NOM breakthrough as a function of source on a mixed bed of SiO₂ and a-Al203. Humic acid from the Suwannee River showed greater adsorption than the fulvic acid from the same source. The presence of Cu(II) resulted in greater retardation of all the NOM sources than in the Cu(II) free systems. Cu(II) transport was slightly facilitated at pH 6.2 by the Orange County NOM and Biscayne aquifer NOM, while the other NOM sources inhibited Cu(II) movement. At pH 7.5 the Orange County and Biscayne Aquifer sources greatly facilitated the transport of Cu(II) in a mixed bed column. The results of this research suggest that the following mechanisms can influence trace metal transport in saturated media: 1) competition of the NOM with the mineral surface for metal complexation; 2) formation of mixed ligand complexes (metal-NOM-mineral surface); 3) complexation of Cu(II) by adsorbed NOM; and 4) metal bridging of NOM to a mineral surface. The results also show that cations commonly found in natural waters, especially Ca(II) and Mg(II), can influence the interaction of trace metals and NOM with mineral surfaces. |
