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Aquatic Geochemistry (v.7, #3)
Influence of Temporal Variations in River Discharge, pH, Alkalinity and Ca on the Speciation and Concentration of Heavy Metals in Some Mining Polluted Rivers by Pål Gundersen; Eiliv Steinnes (pp. 173-193).
Dissolved (dialysis in situ) and total concentrations ofCu, Zn, Cd and Al in eight mining polluted rivers in the Røros area, central Norway, were determinedby atomic absorption spectrometry (flame and graphite furnace) and compared to pH, Caconcentration and alkalinity through seasonal variations in river discharge. Totalconcentrations of the metals were highest during early spring flood and during summer andautumn rain episodes. Dissolved concentrations also increased as the spring floodproceeded, but small discharge peaks within this ∼2 month period as well as a considerableautumn flood episode appeared to lower rather than to raise the dissolved metal concentrations.Consequently the dissolved fractions of Zn, Cd and Al showed a significant negative correlationwith river discharge, and were low at the discharge peaks. Possibly high sediment concentrationsoccurring at high flood conditions more than counteracted desorption induced by pHdecrease, and led to decreased dissolved fractions through adsorption. Cu speciationon the other hand seemed to be more closely linked to pH. Alkalinity and Ca concentration,both assumed to protect aquatic life from metal pollution, were significantly lowerduring episodes with high Cu and Al total concentrations.
Keywords: dialysis in situ ; Cu; Zn; Cd; Al; speciation; pH; alkalinity; discharge; variations; river; aquatic
Sulphide-bearing Waters in Northern Apennines, Italy: General Features and Water-rock Interaction by Lorenzo Toscani; Giampiero Venturelli; Tiziano Boschetti (pp. 195-216).
Sulphide-bearing Ca-carbonate, Na-carbonate, Na-hydroxide, Na-chloride and Ca-sulphate waters from Northern Apennines were investigated in order to determine their main chemical and isotopic composition and draw inferences on water-rock interaction. δ2H and δ18O values suggest an origin mostly meteoric for the analysed waters but a well drilled in Miocenic sediments. The Na-carbonate and the Ca-sulphate waters are the most interesting geochemically. Na-carbonate type, which sometimes reaches extreme composition (Na/Ca up to 228, equivalent ratio), may have been derived through prolonged interaction of Ca-carbonate waters with rocks containing feldspar, montmorillonite and illite under calcite saturation/oversaturation; the high F and pH and the very low PCO 2 agree with prograde dissolution of silicates and lasting water-rock interaction. However, Ca–Na ion exchange, involving clays of marine origin, cannot be excluded in addition. The Ca-sulphate waters, occurring in Messinian gypsum-bearing sediments, are saturated in gypsum and calcite and exhibit very high total H2S (up to 219 mg dm-3) and PCO 2 (up to 0.32 bar). Mass balance of sulphate sulphur, sulphide sulphur and delta34S suggests sulphate – derived from gypsum – as source for H2S; CH4 and organic matter generate the reducing conditions and sulphate reduction is mediated by bacteria. One Na-chloride water from a well in Miocenic sediments has unusual composition, containing about 700 mgdm-3 of potential CaCl2 and having δ2H and δ18O (-47.5 and -4.9‰ respectively) which plot far from the meteoric water lines; probably it is derived by mixing of meteoric and formation waters. The Na-hydroxide water, with very high pH (11.2), is generated through protracted interaction of meteoric waters with ultramafites.
Keywords: H2S-bearing waters; water-rock interaction; Northern Apennines; Italy
Evaluation of Experimental Procedures and Discussion of Two Different Modelling Approaches with Respect to Long-term Kinetics of Metal Cation Sorption onto (Hydr)oxide Surfaces by Johannes Lützenkirchen (pp. 217-235).
Experimental procedures as well as literature data and modelling of long-term kinetics of metal ion adsorption processes onto thermodynamically stable (hydr)oxide surfaces from aqueous solution are evaluated. It is concluded that when experimental uptake data are obtained by the solution depletion method precise information on experimental procedures is crucial. This is true both for preliminary kinetics studies (which intend to fix an equilibration time used for subsequent thermodynamic studies) and for true kinetic studies. For the usually given adsorption versus time curves the corresponding (possibly changing) values of pH should be added. The use of sorption pH edges measured at different times to obtain kinetics curves at constant pH may not correspond to the actual behaviour of the system but be rather an artificial construct.Concerning the models two basically different mechanisms have been used to account for the slow sorption step, which occurs in long-term studies: intraparticle diffusion of the adsorbing metal cation and slow redistribution of surface species. It is shown that the two mechanisms cannot be distinguished using macroscopic uptake data alone: data, which have been interpreted using one approach, may equally well be interpreted using the other one.
Keywords: Surface complexation; sorption; adsorption; sorption kinetics; adsorption kinetics; oxides; experimental procedures