Different layered materials for anion or cation uptake by ion exchange
Open Access
- Author:
- Zhang, Huaibin
- Graduate Program:
- Soil Science
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- June 26, 2021
- Committee Members:
- John Watson, Major Field Member
Dinesh Agrawal, Outside Field Member
Sridhar Komarneni, Chair & Dissertation Advisor
Ramakrishnan Rajagopalan, Outside Unit & Field Member
Patrick Joseph Drohan, Professor in Charge/Director of Graduate Studies - Keywords:
- Layered double hydroxide
Nickel-Zinc layered phase
SnP
ZrP - Abstract:
- The main goal of this research was to study the anion or cation exchange properties of different layered materials. Layered double hydroxide (LDH) and Nickel-Zinc layered phase were synthesized to investigate their exchange/uptake of anions such as chromate, phosphate and selenite. Layered 15 Å tin phosphate (SnP) and α-Zr(HPO4)2·H2O (ZrP or α-ZrP ) were prepared, and they were tested for the removal of cesium, potassium, lead and cadmium cations. For materials characterization, powder X-ray diffraction (XRD) was used to investigate the crystalline structure and crystallinity of layered materials while scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to investigate the size morphology of layered materials. Infrared spectroscopy (IR) and X-ray photoelectron spectroscopy (XPS) were also used to characterize and determine chemical composition of layered materials. The exchange/adsorption uptake of different anions and cations was investigated. For the anion uptake analysis, chromate, phosphate and selenite solutions were used to equilibrate LDH and Ni-Zn phase material. The maximum adsorption capacities of chromate, phosphate and selenite by nitrate form of LDH (LDH-N) were calculated to be 0.49mmol/g, 0.49mmol/g and 0.44mmol/g, respectively, while Ni-Zn phase showed 0.49mmol/g, 0.49mmol/g and 0.49mmol/g of chromate, phosphate and selenite uptake, respectively. For better understanding of their adsorption mechanisms, the Langmuir and Freundlich adsorption isotherms were applied. The uptake of anions by both LDH and Ni-Zn phase fitted well with Freundlich isotherm and the kinetic studies of chromate, phosphate and selenite showed that equilibrium was achieved within 2 hours and their uptake kinetics fitted well to the pseudo-second order model. Furthermore, the uptakes of phosphate by Ni-Zn phase and LDH were found to be highly selective in the presence of CO32-¬, Cl and SO42 anions, which are the most abundant naturally occurring anions. For cation uptake analysis, SnP and ZrP were treated by cesium, potassium, lead and cadmium ions. The maximum adsorption capacities of cesium and potassium ions by SnP were calculated to be 0.048mmol/g and 0.065mmol/g, respectively with initial concentrations of cesium and potassium ions at 0.627mM and 0.525mM, respectively. For the ZrP, the uptake amounts of cesium and potassium ions were 0.022mmol/g and 0.033mmol/g, respectively with the initial concentration of cesium and potassium ions at 0.627mM and 0.525mM, respectively. The SnP phase showed very high uptake amounts of lead ions. The removal amount of cadmium and lead ions by SnP were 1.78mmol/g and 0.38mmol/g, respectively using 2.62 mM PbCl2 and CdCl2 initial solutions. For the isothermal studies of SnP and ZrP, Langmuir isotherm doesn't fit on the current SnP and ZrP with uptake of Cs+ and K+ ions while Freundlich isotherm model shows very low correlation coefficients for both Cs+ and K+ ions with both SnP and ZrP phases. Langmuir model is better able to represent the adsorption isotherm of lead and cadmium ions, which indicates monolayer adsorption of cadmium and lead ions on SnP. Kinetic studies of uptake of cesium, potassium, lead and cadmium ions revealed that equilibrium was achieved within 2 days (48hours) and their uptake kinetics fitted well to the pseudo-second order model. Therefore, the presently studied layered anion exchange materials could be used as highly efficient adsorbents for the separation of anions, especially chromate and phosphate from drinking water, wastewater or ground water under certain conditions. Between the studied cation exchange materials of SnP and ZrP, SnP is highly useful for the separation of cations such as cesium ions by ion exchange and lead ions by ion exchange and also precipitation reaction, the latter with high concentrations of Pb2+ ions.