title: Adsorption and co-precipitation behavior of arsenate, chromate, selenate and boric acid with synthetic allophane-like materials.
abstract: Pollution caused by boric acid and toxic anions such as As(V), Cr(VI) and Se(VI) is hazardous to human health and environment. The sorption characteristics of these environmentally significant ionic species on allophane-like nanoparticles were investigated in order to determine whether allophane can reduce their mobility in the subsurface environment at circum-neutral pH condition. Solutions containing 100 or 150 mmol of AlCl(3)x6H(2)O were mixed to 100 mmol of Na(4)SiO(4) and the pH were adjusted to 6.4+/-0.3. The mineral suspensions were shaken for 1h and incubated at 80 degrees C for 5 days. Appropriate amounts of As, B, Cr and Se solutions were added separately during and after allophane precipitation. The results showed that As(V) and boric acid can be irreversibly fixed during co-precipitation in addition to surface adsorption. However, Cr(VI) and Se(VI) retention during and after allophane precipitation is mainly controlled by surface adsorption. The structurally fixed As(V) and boric acid were more resistant to release than those bound on the surface. The sorption characteristics of oxyanions and boric acid were also influenced by the final Si/Al molar ratio of allophane in which Al-rich allophane tend to have higher uptake capacity. The overall results of this study have demonstrated the role of allophane-like nanoparticles and the effect of its Si/Al ratio on As, B, Cr and Se transport processes in the subsurface environment.
authors.affiliation: Laboratory of Environmental Geology, Division of Solid Waste, Resources and Geoenvironmental Engineering, Graduate School of Engineering, Hokkaido University, Sapporo 060-8628, Japan. einstine@eng.hokudai.ac.jp
authors.forename: Einstine
authors.initials: E
authors.lastname: Opiso
authors.forename: Tsutomu
authors.initials: T
authors.lastname: Sato
authors.forename: Tetsuro
authors.initials: T
authors.lastname: Yoneda
mesh_terms: D000327:Adsorption; D000538:Aluminum Silicates / Q000737:chemistry*; D001888:Boric Acids / Q000302:isolation & purification*; D011232:Chemical Precipitation; D002840:Chromates / Q000302:isolation & purification*; D004785:Environmental Pollutants / Q000302:isolation & purification; D053758:Nanoparticles / Q000737:chemistry; D064586:Selenic Acid; D018036:Selenium Compounds / Q000302:isolation & purification*
chemical_list: D000538:Aluminum Silicates; D001888:Boric Acids; D002840:Chromates; D004785:Environmental Pollutants; D018036:Selenium Compounds; D064586:Selenic Acid; C032688:boric acid