Characterizing As(III,V) adsorption by soils surrounding ash disposal facilities

Area of Science:

• Environmental Science
• Geochemistry
• Soil Science

Background:

• Coal ash disposal facilities are a significant source of environmental arsenic contamination.
• Leachate from these facilities is enriched in calcium and sulfate, influencing arsenic mobility.
• Understanding arsenic adsorption in soils is crucial for predicting environmental fate.

Purpose of the Study:

• To develop a theoretical framework for predicting arsenic attenuation in soils affected by coal ash leachate.
• To characterize the adsorption of arsenic(V) and arsenic(III) in various soils under simulated leachate conditions.
• To evaluate the influence of soil properties and leachate components (calcium, sulfate) on arsenic adsorption.

Main Methods:

• Adsorption experiments of As(V) and As(III) were conducted on 18 diverse soils using 1mM CaSO4 solution.
• Soil properties, including clay content, DCB-Fe, DCB-Al, and Ox-Fe/Al, were analyzed.
• Statistical models were used to correlate adsorption with soil properties and pH.

Main Results:

• Arsenic(V) adsorption was consistently an order of magnitude higher than arsenic(III).
• As(V) adsorption was best predicted by pH and DCB-Fe; As(III) by pH and Ox-Fe/Al.
• Calcium (Ca2+) enhanced As(V) adsorption, while sulfate suppressed both As(V) and As(III) adsorption.

Conclusions:

• Laboratory adsorption tests using 1mM CaSO4 provide a reasonable estimate of arsenic behavior in soils near ash landfills.
• Leachate-induced pH changes may have limited impact on As(V) adsorption at pH<7 but can affect As(III) adsorption more broadly.
• Predictive models incorporating soil properties and leachate chemistry are valuable for assessing arsenic mobility.