CHEMICAL INTERACTIONS OF CITRATE, CALCIUM AND PHOSPHATE IN A CALCAREOUS SASKATCHEWAN SUBSOIL
Date
2019-02-05
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
ORCID
0000-0003-3500-3853
Type
Thesis
Degree Level
Masters
Abstract
The addition of citrate into biostimulatory amendment solutions for the in-situ bioremediation of petroleum hydrocarbons is a relatively new concept. Research has shown that addition of citrate in combination with phosphate can potentially decrease P sorption and thus increase P mobility and bioavailability. In this thesis, soil cores from a hydrocarbon-contaminated site were first characterized to determine soil characteristics. The soil cores had a high clay content with heterogeneous soil layers, leading to the hypothesis that preferential flow paths are likely dominant in transport onsite. As a manipulative experiment, soil Ca levels were modified via three treatments, Ca Saturated, Ca Depleted, and the control soil to ascertain the effect of Ca upon citrate and P retention. X-ray fluorescence (XRF) and x-ray diffraction (XRD) confirmed the change in total Ca levels as well as differences in mineralogy of the treated soils. In chapter three, phosphate adsorption isotherms and citrate desorption isotherm experiments were designed to quantify the relationships among soil Ca, P adsorption, and the concentration of citrate (0-50mM) at equilibrium conditions. The results demonstrated that high citrate levels (above 5mM) would allow less P to be adsorbed onto the soil surface. Phosphorus K-edge XANES were measured on soil samples treated with citrate and Ca to determine the relationship between chemical speciation and citrate interactions. The research led to the discovery that higher than expected (>5mM) levels of citrate were required to get a significant desorption in P; higher levels of soil Ca were correlated with more adsorbed P. In chapter four, kinetics experiments combined with a spectroscopic approach yielded a better understanding of the citrate-phosphate-calcium reaction dynamics. By using the Pseudo Second order model, all parameters from the kinetics experiments were highly correlated to model experimental values. The major finding of the kinetic study was that soil Ca level strongly influenced citrate desorption effectiveness. Overall this thesis showed that the connection between Ca, citrate, and P was important in determining rates and mechanisms of chemical interaction and to be able to build and apply a model to the system.
Description
Keywords
Phosphate, Citrate, Pseudo second order, Adsorption, Precipitation, Bioremediation, Transport
Citation
Degree
Master of Science (M.Sc.)
Department
Soil Science
Program
Soil Science