10.1021/es202376c.s001 Zhenqing Shi Zhenqing Shi Edward Peltier Edward Peltier Donald L. Sparks Donald L. Sparks Kinetics of Ni Sorption in Soils: Roles of Soil Organic Matter and Ni Precipitation American Chemical Society 2012 Soil Organic Matter soil Ni speciation SOM Ni adsorption XAS kinetics model Ni PrecipitationThe kinetics 2012-02-21 00:00:00 Journal contribution https://acs.figshare.com/articles/journal_contribution/Kinetics_of_Ni_Sorption_in_Soils_Roles_of_Soil_Organic_Matter_and_Ni_Precipitation/2548042 The kinetics of Ni sorption to two Delaware agricultural soils were studied to quantitatively assess the relative importance of Ni adsorption on soil organic matter (SOM) and the formation of Ni layered double hydroxide (Ni-LDH) precipitates using both experimental studies and kinetic modeling. Batch sorption kinetic experiments were conducted with both soils at pH 6.0, 7.0, and 7.5 from 24 h up to 1 month. Time-resolved Ni speciation in soils was determined by X-ray absorption spectroscopy (XAS) during the kinetic experiments. A kinetics model was developed to describe Ni kinetic reactions under various reaction conditions and time scales, which integrated Ni adsorption on SOM with Ni-LDH precipitation in soils. The soil Ni speciation (adsorbed phases and Ni-LDH) calculated using the kinetics model was consistent with that obtained through XAS analysis during the sorption processes. Under our experimental conditions, both modeling and XAS results demonstrated that Ni adsorption on SOM was dominant in the short term and the formation of Ni-LDH precipitates accounted for the long-term Ni sequestration in soils, and, more interestingly, that the adsorbed Ni may slowly transfer to Ni-LDH phases with longer reaction times.