Calcium humates

Using Dextran for mass transfer coefficient estimation probably results in an overestimate of concentration polarisation, due to the larger size of Dextran compared to humic substances and calcium. However the diffusion characteristics of humic acid, calcium-humate complexes, and even calcium in the highly viscous boundary layer are not known, and Dextran is probably a conservative assumption. Corrections for calcium and HA (molecular weight 1 and 10 kDa) were performed using... 

XPS analysis was carried out on the TFC-S membranes with a calcite deposit, calcium-humate floes, and on clean membranes, calcium-humate precipitates, and pure HA. No calcium was found on the clean membrane. The identification of peaks is difficult, due to the complexity of the structure of humic acid and the similarity to the membrane (carboxylic groups). Jucker and Clark (1994) suggested the presence of a Ca-humic bond in their measurements at 349.8 eV. This result was confirmed with the calcium-humate complex sample of this study (349.6 eV). On the membranes the chemical shift is different, possibly indicating the presence of a calcite precipitate (346.7 eV) and a calcium-humate complex, but the peaks cannot be resolved due to the small amount of calcium present. 

Campbell (1965) made an extensive study of the carbon-dating method as applied to the study of problems in soil organic matter investigations and found it to be very satisfactory. The mean residence times of humus ftom the Ap-horizon of 5 Saskatchewan soils ranged from 250 years for a gray-wooded podzolic soil to 1000 years for black chernozemic soils the humus from chernozems from Alberta was even older. The calcium humates and non-hydrolyzable humic acids of the chernozems had an age of 1,400 years, whereas the age of the humic acid hydrolysate was only 25 years. This hydrolysate, which was a small fraction of the total humus, accounted for 80% of the nitrogen released per annum the major portion of the soil humus was found to be inert. In general, the humus of podzolic soils was much more labile than that of chernozems. 

Konya, J., N. M. Nagy, and K. Szabo. 1988. The study of the ion exchange processes in system of zinc ions and calcium-bentonite, clay soil, humate and sand by radioisotopic labelling method. React. Polym. 7 203-209. 

The effects of calcium and magnesium on the adsorption of humic substances have not been entirely explained. Humate adsorption on goethite is increased in the presence of calcium and magnesium, and clear saturation is not observed. These effects have been attributed to coadsorption of the divalent cations (47, 48) and may be related to the ability of calcium and magnesium to coagulate some fraction of humic substances (57, 58). 

Surface layers may be calcium carbonate, hydroxide or, in freshly broken crystals, possibly calcium oxide. It is now well established that coccoliths in chalk are coated with very thin aluminosilicates (smectites and other clay minerals) and organic matter (humates, etc) [6]. During comminution, compaction or metamorphosis, these coatings may be disrupted or may still adhere to the calcite surface. Aluminium silicates have been identified in pure limestones and pure marbles, and have been shown to be unattached to calcite fragments. 

LISIAK M.J. 1978. The effect of sodium humate upon phosphorus nutrition of plants with variable doses of iron and calcium in tomato water cultures. Acta Societatis Botanicorum Poloniae, 47, 429-440. 

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