IONIC STRENGTH EFFECT ON PH DEPENDENT ZINC ADSORPTION BY PERLITE: MODELLING VS. EMPIRICAL RESULTS
Small perlite volume per plant and strong root activity induce large fluctua-tions in ionic strength (I) and pH in the growth substrate. We investigated experimentally and by modelling the combined effect of pH and I on Zn partitioning between solution and solid phases of perlite suspensions. Empirically obtained adsorption isotherms had a typical Langmuir shape at each pH with maximum adsorption of 7 mmol kg-1 Zn (pH 8) over a solution concentration range of 0 to 0.3 mM Zn. Zinc adsorption declined as suspension pH decreased from ~8 to ~5 or as I increased from 0.001 to 0.01 and 0.1 M. The effect of I stemmed from its effect on perlite surface charge vs. pH relationship. Considering the experimental variability in pH and I, the agreement between empirical and model computed adsorption is satisfactory, both in new and used perlite. The estimated Zn adsorption to organic matter found in used perlite was two orders of magnitude higher than to intact perlite, both per kg adsorbent.
Bar-Yosef, B., Ben Asher , J. and Silber, A. (2014). IONIC STRENGTH EFFECT ON PH DEPENDENT ZINC ADSORPTION BY PERLITE: MODELLING VS. EMPIRICAL RESULTS. Acta Hortic. 1034, 451-458
surface charge, affinity constants, solution concentration, organic matter