Removal and Immobilization of Arsenic in Water, Ion Exchange Brine, and Soil

Abstract

Removal of arsenic, As(III) and As(V), in water and soils is one of the most challenging environmental issues. Six polymeric ligand exchangers (PLEs) were synthesized by functionalizing various polymeric matrices (known as XAD resins) with 2-picolylamine or di(2-picolyl) amine functional groups and by immobilizing Cu(II) ions onto the functional groups. The six PLEs were extensively tested for arsenate removal from a simulated groundwater water. The PLE’s displayed greater affinity toward arsenate than for sulfate. The binary arsenate-sulfate separation factor (αAs/S) ranged from 5.1 to 10. Bench-scale column breakthrough tests confirmed the greater selectivity for arsenate over other common anions (sulfate, bicarbonate, and chloride). A new class of starch-bridged magnetite nanoparticles was prepared for removal of arsenate from spent ion exchange brine. A low-cost, “green” starch was used as a stabilizer to prevent the nanoparticles from agglomerating and as a bridging agent allowing the nanoparticles to flocculate and precipitate while maintaining their high arsenic sorption capacity. The starch (0.049 wt.%)-bridged Fe3O4 nanoparticles had a mean diameter of 26.6 ± 4.8. The starch-bridged nanoparticles removed 5 times more arsenic than bare magnetite particles under otherwise identical conditions, yet the bridged nanoparticles can be easily separated from water by gravity. The optimum pH range was determined to be from 5 to 6. Based on FTIR results showing one single band for arsenate adsorption, inner-sphere complexation is the predominant mechanism. Stabilized Fe-Mn nanoparticles were prepared using carboxymethyl cellulose (CMC) as a stabilizer and were tested to remove both As(III) and As(V) from contaminated water and soil. The presence of MnO2(s) was able to enhance the sorption capacity of As(III). High sorption capacity was observed in the pH range from 6 to 7 for As(III) and less than 3 for As(V). Stabilized Fe-Mn nanoparticles can be delivered in a sandy soil. Batch tests showed that when an As-laden sandy soil was treated with CMC-stabilized Fe-Mn at an Fe-to-As molar ratio of 6.5 the leached arsenic concentration was reduced by 91%. FTIR results indicated a shift from 3444 to 3400 cm-1 can be attributed to the increased strength of intermolecular hydrogen bonds between the stabilizers and surface of the Fe-Mn particles. The toxicity characteristic leaching procedure (TCLP) leaching tests performed on the nanoparticle amended soil indicated that the leachability of arsenic was reduced by 94 and 90% for samples treated with CMC and starch-stabilized Fe-Mn, respectively.