Enhancing Cadmium Immobilization on Halloysite through Varied Dissolved Organic Matter: Exploring the Role of Halloysite Aggregation

This research is focused on studying the effects of different dissolved organic matter (DOM) and electrolyte concentration on the Cd(II) adsorption on halloysite (HNT) surfaces. The DOM significantly decreased the Cd(II) adsorption by more than 25%. Soil derived dissolved organic matter (SDT) showed the greatest negative impact, followed by humic acid (HA) and Fulvic acid (FA). The effects of background electrolytes NaCl and NH4Cl showed that both salts can undergo complexation with metals. Furthermore, the DOM (SDT/FA/HA) can cover the major HNT surface and the Cd(II) adsorption may occur due to outer-sphere complexation and ion exchange. Additionally, the influence of 100 mML-1 of NaCl on the aggregation tendencies of HNT has demonstrated that the presence of DOM amplifies the aggregation behavior of these nanotubes. The interaction energy barrier between HNT particles is dependent on physicochemical characteristics of DOM that inhibits Cd(II) sorption. These findings suggested that the HNT reduction, electrostatic repulsion and site-competition are the prominent mechanisms to decrease the Cd(II) immobilization on the HNT. The extent of Cd(II) adsorption/desorption on HNT surface followed the order of FA > HA > SDT/ HA > SDT > FA.