Stabilization of arsenic-bearing solid residuals in polymeric matrices

This research investigates the use of polymeric matrices to encapsulate solid sorbents used to remove arsenic from drinking water. Arsenic-containing granular ferric oxy/hydroxide and ferric hydroxide amended alumina residuals were encapsulated in a polymeric matrix using a novel aqueous-based manufacturing process. The polymer was a blend of poly(styrene butadiene) and an epoxy resin. The polymeric waste forms produced were capable of containing more than 60 wt% of sorbent (dry basis), while keeping good mechanical properties. Arsenic leaching from encapsulated and unencapsulated residuals was evaluated using the standard toxicity characteristic leaching procedure (TCLP) and the California Waste Extraction Test (CA-WET). The results show that waste forms of the polymer-encapsulated residuals crushed for testing retain good leaching resistance when evaluated with the more aggressive CA-WET test, yielding leachate arsenic concentrations below the toxicity characteristic (TC) standard of 5mg/L. When residuals were preprocessed and encapsulated in a polymer form that avoided the size reduction required by leaching protocols, arsenic leached up to 700 times less than that from the unencapsulated residuals. Comparison of the waste form developed here with conventional cement matrices containing the same residuals show that the polymeric matrices were capable of encapsulating appreciably more material and leached arsenic at concentration levels that were more than an order of magnitude lower than cement.