SIMULATED MODELING: CONTRASTING Ca/Mg AND Mn+-NATURAL ORGANIC MATTER COMPETITIVE COMPLEXATION IN WATER

Abstract

Complexing capacities of calcium and magnesium with natural organic matter (NOM)/selected organic chelating agents, in the presence and absence of other major and trace cations in water, were studied by anodic and cathodic square wave stripping voltammetry techniques (ASWSV and CSWSV). Under predetermined and optimized physico-chemical parameters (pH, temperature and ionic strength), calcium-NOM complexation and competitive complexation by other elements of known concentration (Pb, Zn, and Cu) were determined. Voltammetric measurements showed competition between calcium and the other cations for the binding sites of humic substances at depositing, measuring and equilibrating potential of -2V and +1V and scan time of 150seconds. Two systems were complexed by known concentrations of NOM fractions (Humic acid (HA), 1, 2-dihydroxybenzene (CAT/catechol) and tannic acid (TA)): Mn+-NOM; Mn+ Calcium-NOM complexes at different pH conditions. Results show significant differences in peak currents in the order Mn+> Ca/Mn+-TA/HA/CAT > Mn2+ TA/HA/CAT but differed depending on the metal species, type of humic chelant and pH. Visual Minteq and PHREEQC simulations show differences in distribution of scale causing species such as Ca2+, CaOH+, Mg2+ and MgOH+ that are highly dependent on the pH and concentration. This paper presents results of part of the work aimed at providing simulated modeling alternatives in combating scaling as a consequence of cooling water used in industry. It equally provides an assurance on the re-use of the scarce water resources by simulated water experiments and models