Association of calcium with colloidal particles and speciation of calcium in the Kalix and Amazon rivers

Abstract

Abstract-A considerable amount of colloidally bound Ca has been detected in water samples from Amazonian rivers and the Kalix River, a sub-arctic boreal river. Fractionation experiments using several analytical techniques and processing tools were conducted in order to elucidate the matter. Results show that on average 84% of the total Ca concentration is present as free Ca. Particulate, colloidal and complexed Ca constitute the remaining 16%, of which the colloidal fraction is significant. Ultrafiltration experiments show that the colloidal fraction in the sampled Amazonian rivers and the Kalix River range between 1% and 25%.In both the Amazonian and the Kalix rivers the technique of cross-flow ultrafiltration was used to isolate particles and colloids. The difference in concentration measured with ICP-AES and a Ca ion-selective electrode in identical samples was used to define the free Ca concentration and thus indirectly the magnitude of the particulate, colloidal and complexed fractions. Results from the Kalix and Amazonian rivers are in excellent agreement. Furthermore, the results show that the colloidal concentrations of Ca can be greatly overestimated (up to 227%) when conventional analysis and calculation of ultrafiltration data is used due to retention of free Ca ions during the ultrafiltration process. Calculation methods for colloidal matter are presented in this work, using complementary data from ISE analysis.In the Kalix River temporal changes in the fractionation of Ca were studied before, during and after a spring-flood event. Changes in the size distribution of colloidally associated Ca was studied using FlFFF (Flow Field-Flow Fractionation) coupled on-line to a HR ICP-MS. The FlFFF-HR ICP-MS fractograms clearly show the colloidal component of Ca, supporting the ultrafiltration findings. During winter conditions the size distribution of colloidally associated Ca has a concentration maximum at ϳ5 to 10 nm in diameter, shifting to smaller sizes (Ͻ5 nm) during and after the spring flood. This shift in size distribution follows a change in the river during this period from ironoxyhydroxy colloids being the most important colloidal carrier phase to humic substances during and after the spring flood.WHAM and NICA-Donnan models were used to calculate the amount of colloidally bound Ca. The results similar for both models, show that on average 16% of the Ca may be associated to a colloidal phase, which is in broad agreement with the measurements.

Trace Elements in River Waters

“…Lead et al (1997) have presented a critical review of the different techniques for separation and analysis of colloids (filtration, dialysis, centrifugation, but also voltametry, gels (DET/DGT), field-flow fractionation, SPLITT; Dahlqvist et al, 2004). Ultrafiltration membranes have been developed with nominal cutoff sizes ranging from the thousands of daltons (Da) to hundreds of thousands of daltons, which have been used to separate the colloidal pool into several fractions.…”

Geochemistry of Major Elements in a Pristine Boreal River System; Hydrological Compartments and Flow Paths

“…This catchment can therefore be used as a pristine reference system for studies of hydrogeochemical processes in boreal river basins. A number of trace element and isotope studies have previously been performed in this drainage basin (Ponte´r et al, , 1992Ö hlander et al, 1991, 2000Ingri and Widerlund, 1994;Ingri et al, 1997Ingri et al, , 2000Porcelli et al, 1997;Ö hlander, 1997, 2000;Andersson et al, 1998Andersson et al, , 2001Land et al, 1999Dahlqvist et al, 2004). In this study the major element geochemistry is presented.…”

Colloidal rare earth elements in a boreal river: Changing sources and distributions during the spring flood

“…The Kalix River, an unregulated pristine boreal river system, has previously been well characterized in several studies on major and trace elements and isotopes (Pontér et al, 1990;Ö hlander et al, 1991Ingri and Widerlund, 1994;Ingri et al, 1997Ingri et al, , 2000Ingri et al, , 2005Porcelli et al, 1997;Ö hlander, 1997, 2000;Andersson et al, 1998Andersson et al, , 2001Land et al, 1999aLand et al, ,b, 2000aDahlqvist et al, 2004). The study by Ingri et al (2000) showed that transport of REE in the Kalix River was closely associated with colloidal particles rich in C, Fe and Al.…”

“…This study on REE fractionation is part of the 'Kalix 2002' project, in which we have studied temporal changes in the geochemistry of colloids in the Kalix River from winter conditions, through the spring flood event and into summer conditions. Other papers from this project include a study of calcium association with colloids (Dahlqvist et al, 2004), together with studies of multiway analysis of organic matter fluorescence, and of the temporal changes of trace metals associated with colloidal material, which will be presented elsewhere.…”