Metal Transport Mechanisms Research Articles

Rate and mechanism of divalent metal transport through supported liquid membrane containing di(2‐ethylhexyl) phosphoric acid as a mobile carrier

AbstractThe rate and mechanism of copper, cobalt, nickel and zinc transport through a supported liquid membrane containing di(2‐ethylhexyl) phosphoric acid as a mobile carrier were studied, respectively. The permeation rate equations have been derived taking into account aqueous film diffusion, interfacial chemical reaction and membrane diffusion as simultaneous controlling steps. The possible rate‐controlling steps were estimated by comparing the relative values of the three successive resistances. The measured permeation rates of zinc agreed well with the proposed mechanism in this study.

A preliminary evaluation of organic ligands and metal-organic complexing in mississippi valley-type ore solutions

The role of organic matter in mechanisms of base metal transport during Mississippi Valley-type mineralization is not well understood. Evidence from field, experimental, and theoretical studies suggests that ore metals may be transported as organic complexes in Mississippi Valley-type ore fluids. However, specific ligands capable of concentrating significant quantities of lead and zinc in these ore solutions have not been identified. As a preliminary evaluation of metal transport by metal-organic complexing, activities of lead and zinc complexes involving nine carboxylate ligands (acetate, propionate, n-butyrate, phthalate, oxalate, tartronate, malate, D-tartrate, and salicylate) have been calculated for PbS- and ZnS-saturated, average ore solutions (those proposed by Giordano and Barnes, 1981) at 100 degrees and 200 degrees C. Calculated concentrations of lead and zinc in all of the complexes considered are well below the 10 ppm (10 (super -4) ) molal) minimum required to form an ore deposit.To ascertain the nature of other organic ligands which may have contributed significantly to base metal transport during Mississippi Valley-type mineralization, speciations of acetate, phthalate, and salicylate were calculated for three different average ore fluids at, or near, 100 degrees C. Results suggest that for weakly alkaline, sulfide-rich ore solutions, organic ligands should have stability constants for 1:1 and 1:2 base metal complexes of at least 10 10 and 10 20 , respectively. Such high stabilities would not be required if actual ore fluids were more acid or more oxidized, contained lower amounts of inorganic sulfide, or contained specific organic ligands at concentrations greater than 10 (super -4) molal. In addition to carboxylate, or similar complexes, metal-organic sulfide complexes may have provided a mechanism to transport significant quantities of lead, zinc, and reduced sulfur in Mississippi Valley-type ore solutions.

Trace metals in a tropical river environment-distribution

Distribution of trace metals in the Periyar river has been investigated in detail. The fluvial concentrations of trace metals increase in river water and decrease in sediments during the summer months due to solubilization and concentration by evaporation. The levels, especially of Zn and Cd which are industrial pollutants increase by a factor of 10 both in water and sediments at the industrial zone. The concentration of Cd in the river water approaches the WHO standards for safe limits in drinking water. Solubilization at the backwater zone under high salinity is identified as one of the major mechanisms of trace metal transport to the marine environment. River meandering is responsible for large scale deposition of suspended solids at the industrial zone during the monsoon period. The trace metals exhibit build-up in specific concentration in the suspended solids in proportion to their residence time.

Distribution of some trace metals and their fluxes in the Genesee River, NY

Total and particulate metal concentrations, measured during intensive synoptic studies of the Genesee River, NY, correlated with suspended-sediment concentration and river discharge. Dissolved metal concentrations, on the other hand, showed little systematic variation over the length of the river. Metal and sediment fluxes for two elevated-discharged periods peaked at a midbasin sampling site. For most metals at most sampling sties particulate materials comprised over one-half of the total material. Comparison of particulate material metal concentrations, normalized to the measured suspended-sediment concentrations had with basinwide average values shows that sites having low suspended-sediment concentrations had high particulate material metal contents relative to the basin averages, while sites with high suspended-sediment concentration had low metal contents. These results are consistent with a metal transport mechanism in the Genesee River involving (1) a nearly constant dissolved component, (2) a fine acid-soluble component, and (3) a coarse component that is effectively a neutral diluent in the sediment. Chemical factors, such as sediment organic content, also appear to affect metal transport in the Genesee River.

Mechanisms of Trace Metal Transport in Rivers

Trace metals transported by the Amazon (and Yukon rivers were analytically partitioned among the transport phases: in solutions, ion exchange, organic materials, metallic coatings, and crystalline solids. The distribution for both rivers is similarly proportioned, with copper and chromium transported mainly in the crystalline solids, manganese in coatings, and iron, nickel, and cobalt distributed equally between precipitated metallic coatings and crystalline solids.