Adsorption Of Ca Research Articles

Variation of sticking probabilities with temperature and coverage, and desorption spectra for nitrogen on tungsten films

From 78 to 150°K, and at coverages < 8 x 10 14 molecules/cm 2 , the sticking probability s of nitrogen on tungsten films (= 0·9) is independent of both temperature and coverage, whereas at temperatures above 150°K it is a function of both these variables. These results are interpreted in terms of a physically adsorbed precursor state with a heat of adsorption of ca . 3 kcal/mole. It is concluded that only a fraction of molecules colliding with the surface enter this state and that it is this fraction which determines the initial value of s at low temperatures. The decrease of s with increasing temperature above 150°K is a consequence of the inactivity of some planes, such as the (110), at the higher temperatures. Desorption spectra were obtained by warming films from 78°K to room temperature and recording the subsequent pressure changes as a function of time. From these data the distribution of site energies for the weakly held adsorbate (the αγ state) was evaluated, indicating a continuous distribution with heats of adsorption varying between 6 and 20 kcal/mole.

THERMODYNAMICS OF K–Ca ION EXCHANGE IN SOILS1

SummaryCation exchange characteristics of the K:Ca saturated forms of five soils were measured at 25°C and 50°C. The rates of isotopic exchange of 42K and 45Ca were too fast to be measured except that of 42K in the K:Ca Harwell soil at 25°C. The slower isotopic exchange of K in this soil was attributed to the presence of a zeolite, clinoptilolite. The intra‐particle diffusion coefficient, Di, of K in this soil increased with K‐saturation to a maximum at about 40 per cent K, probably because of the ‘blocking’ action of the larger hydrated Ca ions at small K‐saturations in clinoptilolite.The CEC, measured by isotopic exchange along the K:Ca adsorption isotherm, decreased with increasing temperature probably because some interlayer spaces collapsed.The standard free energy, enthalpy, and entropy changes were negative for the reaction Ca‐soil+2K+⇌ 2K‐soil+Ca++. These results seem to show that K is more strongly bound than Ca by the soil and that the Ca‐preference shown by the isotherm at small external electrolyte concentration is caused by entropy changes in solution.Calculated activity coefficients of the exchangeable ions changed with K‐saturation similarly at both temperatures but values at 50°C were smaller than at 25°C.

EFFECT OF INDUCED CHANGES IN ROOT CEC ON CA ADSORPTION FROM BENTONITE SYSTEMS BY EXCISED BARLEY ROOTS

EFFECT OF INDUCED CHANGES IN ROOT CEC ON CA ADSORPTION FROM BENTONITE SYSTEMS BY EXCISED BARLEY ROOTS

Monovalent‐Divalent Cation‐Exchange Equilibria in Soils in Relation to Organic Matter and Type of Clay

AbstractCation‐exchange equilibria at pH 7 were measured using ion pairs of Na‐Ca, Li‐Ca and Li‐Mg on each of 10 soils. Data on Li‐Mg and Na‐Ca ion pairs were nearly the same and data on Li‐Ca were highly correlated with exchange equilibria data on both Na‐Ca and Li‐Mg. Two soils containing largely amorphous clay minerals showed a higher preference for Li than soils containing dominantly crystalline clay minerals. Destruction of the organic matter in two soils increased the ratio of Na to Ca adsorption to a much greater extent than would be predicted by the decrease in measured surface charge density. At a sodium‐adsorption ratio (SAR) of 100 (mmole per liter)1/2, organic‐matter free soils containing dominantly montmorillonite and illite clays had ratios of Na to Ca adsorption of 1.66 to 1.94 (excluding one soil, 1.66 to 1.78). Two soils with dominantly amorphous minerals had ratios of 0.92 and 1.10, and one soil with a mixture of kaolinite, illite, and amorphous clays had a ratio of 1.35.

土壌吸着基の特性について(第2報) : NH_4^・吸収型およびCa^ , NH_4^・の選択吸収について

土壌吸着基の特性について(第2報) : NH_4^・吸収型およびCa^ , NH_4^・の選択吸収について

Characterization of Exchange Reactions of Strontium or Calcium on Four Clays

AbstractTo a series of calcium or strontium saturated clays suspended in 50 symmetry concentrations of the saturating ion, variable amounts of Sr85Cl2 or Ca45Cl2 were added. From the radiochemical analysis of the clay at equilibrium, the amount of exchange was determined.Plotting the data as [Cation‐Clay]/[Cation‐Solution] vs. [Cation‐Clay] yielded a curved line composed of at least two adsorption isotherms. This is interpreted to mean two independent sites of adsorption or that two mass action equations are necessary to describe the system.Following the cation desorbed by tracer technique resulted in almost identical curves as when the adsorbing cation was followed. This evidence showed that no precipitation or reaction other than the one described took place. Also, the sites were shown to be independent by introducing a third cation such as barium. Barium ions at an appropriate concentration prevented the adsorption of the cation being studied on the “tight site” but had no effect on the adsorption of the cation on “loose site.”The two sites were separated graphically and labeled “tight” and “loose” sites according to the bonding energies for the cation being studied. An apparent equailibrium constant was calculated from the slope of the “loose site.” The slope of the “tight site” could not be determined accurately enough to calculate an equilibrium constant, being less than 1% of the exchange capacity. Strontium is adsorbed more tightly than calcium on either site, but the difference becomes less as the exchange capacity of the clay decreases.It was necessary to define the data in terms of two mass action equations if the exchange reaction is to be stoichiometric at either site. Using one equation to compare the adsorption of Sr and Ca resulted in considerable hysteresis, largely due to the influence that the sites have on each other.

Factors Affecting Adsorption of Cations by Plant Roots

AbstractThe adsorption of Ca, Mg, K and Na by metabolically inactive H‐roots of wheat and alfalfa in relation to the nature of the anion has been studied. Titration curves and fH values showed wheat roots to have a weaker acid character than alfalfa roots. A high retention of H+ over metal cations was indicated. As a consequence, only small amounts of cations were adsorbed when offered as nitrates, but large amounts were adsorbed when offered as the bicarbonates. The order of increasing adsorption in either case was: Na, K, Mg, Ca.When Ca, Mg and K were offered in exchangeable form on a soil colloid with Ca/Mg and Ca/K ratios of 4, the Ca/Mg ratios on the roots were 4 and 8, and the Ca/K ratios were 10 and 24 for the wheat and alfalfa roots, respectively. The corresponding distribution of cations on the wheat roots were: Ca, 73%; Mg, 19%; K, 8%; and for alfalfa roots they were: Ca, 85%; Mg, 11%; and K, 4%.It is concluded that the adsorption of cations by metabolically inactive roots is a neutralization reaction involving principally Ca. The group of compounds involved in this reaction have been designated as RCOOH. Selective adsorption of cations involving exchange reaction, notably Mg and K, through RH is restricted to metabolically active roots. It is suggested that the proportions of K to Ca entering the plant is related to the concentration and proportion of RH to RCOOH of roots.

Cation exchange properties of alginic acid.

SummaryAlginic acid possesses sodium and potassium ion exchange properties which compare favorably with those of a carboxylic type cationic exchange resin. Under in vitro conditions alginic acid at pH 7.6 adsorbs 4.2 meq Na+ per g. The total cation adsorption from solutions containing K+ and Na+ is also 4.2 meq/g and the ratio of Na:K combined approximates that present in solution. The adsorption of Ca++ by alginic acid is irreversible and independent of pH. The hydrophilic character of the sodium and potassium alginates may contribute to the elimination of fluid and cause laxation.