title: Geochemical modeling of reactions and partitioning of trace metals and radionuclides during titration of contaminated acidic sediments.
abstract: Many geochemical reactions that control aqueous metal concentrations are directly affected by solution pH. However, changes in solution pH are strongly buffered by various aqueous phase and solid phase precipitation/dissolution and adsorption/desorption reactions. The ability to predict acid-base behavior of the soil-solution system is thus critical to predict metal transport under variable pH conditions. This studywas undertaken to develop a practical generic geochemical modeling approach to predict aqueous and solid phase concentrations of metals and anions during conditions of acid or base additions. The method of Spalding and Spalding was utilized to model soil buffer capacity and pH-dependent cation exchange capacity by treating aquifer solids as a polyprotic acid. To simulate the dynamic and pH-dependent anion exchange capacity, the aquifer solids were simultaneously treated as a polyprotic base controlled by mineral precipitation/ dissolution reactions. An equilibrium reaction model that describes aqueous complexation, precipitation, sorption and soil buffering with pH-dependent ion exchange was developed using HydroGeoChem v5.0 (HGC5). Comparison of model results with experimental titration data of pH, Al, Ca, Mg, Sr, Mn, Ni, Co, and SO4(2-) for contaminated sediments indicated close agreement suggesting that the model could potentially be used to predictthe acid-base behavior of the sediment-solution system under variable pH conditions.
authors.affiliation: Environmental Sciences Division, Oak Ridge National Laboratory, P.O. Box 2008, MS 6038, Oak Ridge, Tennessee 37831, USA. zhangf@ornl.gov
authors.forename: Fan
authors.initials: F
authors.lastname: Zhang
authors.forename: Wensui
authors.initials: W
authors.lastname: Luo
authors.forename: Jack C
authors.initials: JC
authors.lastname: Parker
authors.forename: Brian P
authors.initials: BP
authors.lastname: Spalding
authors.forename: Scott C
authors.initials: SC
authors.lastname: Brooks
authors.forename: David B
authors.initials: DB
authors.lastname: Watson
authors.forename: Philip M
authors.initials: PM
authors.lastname: Jardine
authors.forename: Baohua
authors.initials: B
authors.lastname: Gu
mesh_terms: D000327:Adsorption; D011232:Chemical Precipitation; D003198:Computer Simulation; D019015:Geologic Sediments / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D007474:Ion Exchange; D008903:Minerals / Q000032:analysis; D008956:Models, Chemical; D011868:Radioisotopes / Q000032:analysis*; D012972:Sodium Hydroxide / Q000737:chemistry; D012987:Soil; D012989:Soil Pollutants / Q000737:chemistry*; D012996:Solutions; D017186:Titrimetry; D014131:Trace Elements / Q000032:analysis*
chemical_list: D008903:Minerals; D011868:Radioisotopes; D012987:Soil; D012989:Soil Pollutants; D012996:Solutions; D014131:Trace Elements; D012972:Sodium Hydroxide