title: Calcium-enhanced ferric hydroxide co-precipitation of arsenic in the presence of silicate.
abstract: This study focuses on the effectiveness of calcium (Ca2+) improving ferric (hydro)oxides precipitation and its subsequent effects on arsenic co-precipitation with ferric (hydro)oxides. The effects of Ca2+ on surface charge characteristics and precipitating behavior, which are respectively represented as zeta (zeta) potential and R(PDA), are investigated for ferric (hydro)oxides precipitates. The presence of Ca2+ increases the potential of ferric (hydro)oxides, and a more significant effect is observed at higher pH conditions. Calcium apparently facilitates ferric (hydro)oxide floc aggregation, increasing the maximum R(PDA) from 3.19 to 5.27% (in the presence of 3.5 mg/L silicate as silicon). These positive effects contribute to reduce the adverse effects resulting from the presence of silicate and enhance arsenic removal via ferric (hydro)oxides co-precipitation under different conditions. Furthermore, the effect of Ca2+ facilitating ferric precipitation (and therefore providing more precipitated solids for arsenic) is predominant in favoring arsenic removal compared with that of increasing surface charge. Calcium plays an important role in arsenic co-precipitation with ferric (hydro)oxides in the presence of silicate.
authors.affiliation: School of Municipal & Environmental Engineering, Harbin Institute of Technology, Harbin, Heilongjiang, PR China.
authors.forename: Ruiping
authors.initials: R
authors.lastname: Liu
authors.forename: Xing
authors.initials: X
authors.lastname: Li
authors.forename: Shengji
authors.initials: S
authors.lastname: Xia
authors.forename: Yanling
authors.initials: Y
authors.lastname: Yang
authors.forename: Rongcheng
authors.initials: R
authors.lastname: Wu
authors.forename: Guibai
authors.initials: G
authors.lastname: Li
mesh_terms: D001151:Arsenic / Q000737:chemistry*; D002118:Calcium / Q000737:chemistry*; D011232:Chemical Precipitation; D005290:Ferric Compounds / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D017640:Silicates / Q000737:chemistry*; D013499:Surface Properties; D018508:Water Purification
chemical_list: D005290:Ferric Compounds; D017640:Silicates; C021024:ferric hydroxide; D001151:Arsenic; D002118:Calcium