title: Sorption of arsenic from soil-washing leachate by surfactant-modified zeolite.
abstract: Post-treatment of leachate from soil-washing remedial actions may be necessary depending on the amounts of dissolved contaminants present. Uptake of arsenic species by surfactant-modified zeolite (SMZ) from a synthetic soil leachate (pH of approximately 12 [NaOH]) was measured as a test of SMZ as a post-treatment sorbent. Batch sorption isotherms were prepared using leachate to SMZ ratios from 40:1 to 4:1, and temperatures of 25 and 15 degrees C. Equilibrium levels of dissolved and total solution arsenic were similar. At each temperature, sorption appeared to reach a plateau or maximum, then decreased at the highest solution concentration, corresponding to the lowest amount of zeolite added (2.5 g). A maximum sorption value of 72.0 mmol of arsenic per kg of SMZ (5400 mg/kg) was observed at 25 degrees C, and 42.1 mmol/kg (3150 mg/kg) at 15 degrees C. Total arsenic recoveries varied from 74 to 125%. Surfactant-modified zeolite removed up to 97% of dissolved organic carbon and decolorized the leachate solutions. Excluding the points for the highest arsenic to SMZ ratio, the sorption isotherms were well described by the linearized form of the Langmuir equation, with coefficients of determination greater than 0.90 at both temperatures. Sorption of arsenic by SMZ is attributed to anion exchange with counterions on the surfactant head groups, and/or partitioning of organic carbon-complexed arsenic into the surfactant bilayer.
authors.affiliation: Los Alamos National Laboratory, RRES Division, MS J599, Los Alamos, NM 87545, USA. ejs@lanl.gov
authors.forename: Enid J
authors.initials: EJ
authors.lastname: Sullivan
authors.forename: Robert S
authors.initials: RS
authors.lastname: Bowman
authors.forename: Irene A
authors.initials: IA
authors.lastname: Legiec
mesh_terms: D000327:Adsorption; D001151:Arsenic / Q000032:analysis* / Q000737:chemistry; D006801:Humans; D012989:Soil Pollutants / Q000032:analysis*; D013501:Surface-Active Agents / Q000737:chemistry*; D018505:Waste Management / Q000379:methods; D017641:Zeolites / Q000737:chemistry*
chemical_list: D012989:Soil Pollutants; D013501:Surface-Active Agents; D017641:Zeolites; D001151:Arsenic