Complexation of calcium ions by humic and fulvic acids

Complexe formation between humic matter and ions in soil can increase the solubility of several nutrients and consequently their biodisponibility. To give a better insight about such complexation, humic and fulvic acid were extracted from farmyard manure and their ability to complexe calcium ions was characterized experimentally through simultaneous potentiometric and conductimetric titration with NaOH and Ca(OH)2. Complexation power was assessed by pH Stat-conductimetric titration. Results shows that complexation of calcium by humic and fulvic acid was detected only at slightly acid, neutral and basic pH and complexation power was favored by increasing pH. The amount of protons released following calcium complexation humic and fulvic acid was determined for each pH studied and the nature of functional groups involved in complexation was discussed.