This study investigated the adsorption of Pb(II) in aqueous solution onto humic acid (HA) surface. The adsorption of lead(II) ions was studied using montmorillonite clay as adsorbent in the presence of humic acid under fix pH condition. The effect of HA on the adsorption of Pb(II) onto montmorillonite depends on its concentration in the solution, i.e., metal adsorption decreases with increasing concentration of HA in the solution. The HA was found to enhance the metal adsorption capacity of mineral surfaces in ternary system. The adsorption for Pb(II) on HA was high and this may due to its strong affinity for carboxylic and phenolic groups of humic substances. Since Pb(II) is divalent cation so its adsorption may have consumed two carboxylic/phenolic groups of HA. The decrease in adsorption of Pb(II) in the presence of HA in a ternary system is may be due to the blocking of adsorptive surfaces and reduction of cation exchange capacity by the clay in the presence of HA through its polar adsorption on mineral surface.

Iffat Aziz, Muhammad Sirajuddin, Muhammad Haleem Khan, Shafqat Nadeem, Syed Ahmad Tirmizi and Rafaqat Ali Khan