Premium
Modeling the Effects of Variable Groundwater Chemistry on Adsorption of Molybdate
Author(s) -
Stollenwerk Kenneth G.
Publication year - 1995
Publication title -
water resources research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.863
H-Index - 217
eISSN - 1944-7973
pISSN - 0043-1397
DOI - 10.1029/94wr02675
Subject(s) - ionic strength , adsorption , chemistry , molybdate , hydrous ferric oxides , aqueous solution , aquifer , desorption , groundwater , inorganic chemistry , sulfate , sorption , geology , geotechnical engineering , organic chemistry
Laboratory experiments were used to identify and quantify processes having a significant effect on molybdate (MoO 4 2− ) adsorption in a shallow alluvial aquifer on Cape Cod, assachusetts. Aqueous chemistry in the aquifer changes as a result of treated sewage effluent mixing with groundwater. Molybdate adsorption decreased as p H, ionic strength, and the concentration of competing anions increased. A diffuse‐layer surface complexation model was used to simulate adsorption of MoO 4 2− , phosphate (PO 4 3− ), and sulfate (SO 4 2− ) on aquifer sediment. Equilibrium constants for the model were calculated by calibration to data from batch experiments. The model was then used in a one‐dimensional solute transport program to successfully simulate initial breakthrough of MoO 4 2− from column experiments. A shortcoming of the solute transport program was the inability to account for kinetics of physical and chemical processes. This resulted in a failure of the model to predict the slow rate of desorption of MoO 4 2− from the columns. The mobility of MoO 4 2− ncreased with ionic strength and with the formation of aqueous complexes with calcium, magnesium, and sodium. Failure to account for MoO 4 2− speciation and ionic strength in the model resulted in overpredicting MoO 4 2− adsorption. Qualitatively, the laboratory data predicted the observed behavior of MoO 4 2− in the aquifer, where retardation of MoO 4 2− was greatest in uncontaminated roundwater having low p H, low ionic strength, and low concentrations of PO 4 3− and SO 4 2− .