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Accumulation and Release of Arsenic from Cast Iron: Impact of Initial Arsenic and Orthophosphate Concentrations
Citation:
Tang, M., D. Lytle, AND J. Botkins. Accumulation and Release of Arsenic from Cast Iron: Impact of Initial Arsenic and Orthophosphate Concentrations. WATER RESEARCH. Elsevier Science Ltd, New York, NY, 194:116942, (2021). https://doi.org/10.1016/j.watres.2021.116942
Impact/Purpose:
Various iron oxide and oxyhydroxide minerals commonly found in old cast iron pipe scale were shown to exhibit high and similar affinity for arsenate [As(V)] and orthophosphate (PO4) via adsorption, co-precipitation, and other factors. PO4 addition is a common corrosion control treatment for water utilities. This 2751-day study examined the accumulation and release of As(V) from an old cast iron pipe scale by changing initial As(V) (0, 75, or 180 µg As/L) and initial PO4 (0 or 3 mg PO4/L) levels. The results showed that iron scale surface sites could accumulate As(V) from simulated drinking water and concentrate As(V) in the scale with a large capacity and for a prolongated period. The pre-accumulated As(V) then was released into water at elevated levels (up to 38 µg/L) relative to the EPA regulation of 10 µg/L. Addition of 3 mg PO4/L increased As(V) release from iron scale in the short term while PO4 occupied certain iron scale sites that later became inaccessible for further As incorporation. The average As(V) accumulation rate was positively correlated with the initial As(V)/orthophosphate molar ratio. Proactive measures are recommended for water utilities to minimize the public health risk associated with elevated arsenic in tap water.
Description:
Various iron oxide and oxyhydroxide minerals commonly found in old cast iron pipe scale were shown to exhibit high and similar affinity for arsenate [As(V)] and orthophosphate (PO4) via adsorption, co-precipitation, and other factors. PO4 addition is a common corrosion control treatment for water utilities. This 2751-day study examined the accumulation and release of As(V) from an old cast iron pipe scale by changing initial As(V) (0, 75, or 180 µg As/L) and initial PO4 (0 or 3 mg PO4/L) levels. The results showed that iron scale surface sites could accumulate As(V) from simulated drinking water and concentrate As(V) in the scale with a large capacity and for a prolongated period. The pre-accumulated As(V) then was released into water at elevated levels (up to 38 µg/L) relative to the EPA regulation of 10 µg/L. Addition of 3 mg PO4/L increased As(V) release from iron scale in the short term while PO4 occupied certain iron scale sites that later became inaccessible for further As incorporation. The average As(V) accumulation rate was positively correlated with the initial As(V)/orthophosphate molar ratio. Proactive measures are recommended for water utilities to minimize the public health risk associated with elevated arsenic in tap water.
URLs/Downloads:
DOI: Accumulation and Release of Arsenic from Cast Iron: Impact of Initial Arsenic and Orthophosphate Concentrations
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