Arsenic stabilization in mine tailings using nano-sized magnetite and zero valent iron with the enhancement of mobility by surface coating

Synthesized nano-sized zero valent iron coated by sodium dodecyl sulfate (SDS-nZVI) and nano-sized magnetite coated by sodium dodecyl sulfate (SDS-nMGT) were applied to stabilize arsenic in mine tailings. The physical properties of the synthesized nano-sized iron particles were characterized using HR-TEM, FE-SEM, XRD, and BET surface area. The spherical SDS-nZVI and SDS-nMGT particles were determined to be approximately 82.96 nm and 6.89 nm in diameter, respectively. The specific surface area of SDS-nMGT (120.8 m2/g) was higher than that of SDS-nZVI (1.8 m2/g) due to its smaller particle size. Arsenic concentration extracted by TCLP decreased by 73.94% and 52.25% after SDS-nMGT and SDS-nZVI stabilization, respectively, at an iron/tailings ratio of 0.34%. Sequential extraction analysis revealed that the addition of SDS-nZVI and SDS-nMGT increased the arsenic fraction bound with the amorphous and poorly-crystalline hydrous oxides of iron and aluminum phase and the well-crystalline hydrous oxides of iron and aluminum phase, respectively, implying arsenic stabilization. Surface modification of the particles did not significantly affect the arsenic immobilization efficiency. Surface modification of MGT by SDS, an anionic surfactant, enhanced the mobility of magnetite in soils. Column test for particle mobility confirmed that 86% of the SDS-nMGT passed through the column, which is 1.46 and 3.44 times higher than for nMGT and MGT, respectively, due to the surface modification and size control. The maximum arsenic immobilization efficiency of SDS-nMGT was calculated to be 86.13% (R2 = 0.93) and the maximum capacity of arsenic adsorption by iron reached 16.79 mg As/g Fe (R2 = 0.77).

► Nano-sized magnetite and zero valent iron coated by sodium dodecyl sulfate (SDS-nMGT and SDS-nZVI) were synthesized. ► SDS-nMGT and SDS-nZVI particles change arsenic speciation in mine tailings from sorbed to associated with iron oxide phase. ► Leachability of arsenic from mine tailings by TCLP decreased after stabilization with SDS-nMGT and SDS-nZVI. ► Surface coating with SDS enhances the mobility of nano-sized magnetite in soils.