Lead adsorption on loess under high ammonium environment

Area of Science:

• Environmental Science
• Geochemistry
• Soil Science

Background:

• Lead (Pb) is a highly toxic pollutant found in landfill leachate.
• High ammonium (NH4+) concentrations (>1000 mg/l) are also present in landfill leachate, potentially affecting Pb transport.
• Loess-amended soils show promise for attenuating heavy metal migration.

Purpose of the Study:

• To investigate the adsorption mechanisms and capacity of loess for Pb under high NH4+ conditions.
• To evaluate the influence of temperature on Pb adsorption by loess.
• To understand the thermodynamic and kinetic aspects of Pb adsorption.

Main Methods:

• Adsorption isotherm tests were conducted at 25°C, 35°C, and 45°C with varying NH4+ concentrations.
• Thermodynamic and kinetic analyses were performed using pseudo-second-order and intraparticle diffusion models.
• Surface characterization techniques including SEM, XRD, and FTIR were employed.

Main Results:

• Maximum adsorption capacities for Pb were estimated at 2101.97 mg/g (25°C) and 4292.8 mg/g (45°C) under 1000 mg/l NH4+.
• Adsorption is an endothermic and non-spontaneous process, with increasing system randomness over time.
• Pb removal is governed by both membrane and intraparticle diffusion, involving flocculation, precipitation (PbCO3, Pb(OH)2, Pb2O(NO3)2), and ion exchange.

Conclusions:

• Loess exhibits a high capacity for adsorbing Pb, even in the presence of high NH4+ concentrations.
• Multiple mechanisms, including precipitation and ion exchange, contribute to Pb removal by loess.
• Loess-amended soils are effective for mitigating Pb pollution in landfill leachate.