(11g) Competitive Adsorption Behavior on the Removal of Iron and Lead from Solution

Runoff from industrial sites may contain a variety of heavy metals that can adversely affect the ecosystem. One approach to this problem involves capturing the heavy metals onto an adsorbent, such as straw. The uptake of heavy metals [iron (Fe), lead (Pb), cadmium (Cd), and chromium (Cr)] was studied at various solution pH values. Initial heavy metal concentrations ranged from ~1 to ~12 mg/L for straw concentrations of 10 gm/L. Batch adsorption tests of various concentrations of heavy metals in contact with straw were performed, and the adsorption of heavy metals on straw was modeled using the Langmuir and Freundlich isotherm models:

Langmuir Model: q_e = (Q° b C)/ [1 + bC]

Freundlich Model: q_e = k C^1/n

The Langmuir isotherm provided a better description of the adsorption of iron, lead, cadmium, and chromium than did the Freundlich isotherm model. Competitive adsorption behavior was observed for solutions containing lead and iron; for concentrations < 2 mg/L, lead was preferentially adsorbed onto the straw, whereas for concentrations > 2 mg/L, iron was preferentially adsorbed onto the straw. The results from this study are compared to the adsorption of heavy metals onto other bio-based materials reported in the technical literature. Heavy metals were allowed to pass through beds packed with straw for adsorption and uptake by straw. The breakthrough characteristics of passing the solutions through the straw were determined for single heavy metals systems involving iron and lead. These breakthrough curves were compared to those obtained for multimetal systems (involving iron and lead simultaneously). The results showed that at high concentrations, both iron and lead were removed to nearly the same efficiency.