Synthesis, Stability, and Ion Exchange Behaviors of Feldspathoids Formed Under Carbonate-Rich Alkaline Conditions

Over 4 billion tonnes of bauxite residue have been generated globally by the alumina industry through the Bayer process. Most of this waste is stored in bauxite residue storage areas (BRSAs) as dry cakes or pumpable paste. Once BRSA capacity is reached, closure plans involving remediation and rehabilitation are required, often taking decades to complete depending on climate conditions. Sodalite and cancrinite are two common feldspathoids formed in the Bayer process. These feldspathoids can potentially serve as nutrient carriers under bauxite residue remediation, yet limited research explores their ion exchange capacity, structural variability, and chemical stability. The effects of structure disordering on kinetics and competitiveness for nutrient adsorption/desorption are also largely unknown. The overall objective of this dissertation is to fill these gaps. A synthesis procedure was developed to produce monomineralic sodalite (BayerSOD) and cancrinite (Bayer-CAN) containing structural CO3^2-. Both feldspathoids were stable under neutral and alkaline pH condition. Variations in carbonate concentration during synthesis affected their crystal structure and morphology, which influenced potassium ion exchange capacity. Bayer-SOD and Bayer-CAN can hold up 500 cmolc kg^-1 K+. Treatment with chloride solutions released CO3^2- but did not incorporate Cl- into the structure. Water replaced Na2CO3 ion pairs instead, showing their high affinity toward water. The observed similarities or differences in the exchange capacity were linked to the continuity of diffusion pathways in crystal structures. Combined with the Na+ presented originally, the following selectivity sequence was found on both feldspathoids: Na+> K+> NH4 +> Mg2+ > Ca2+. However, complete replacement was not achieved even after three times of exchange with cations at 80 degrees C. A detailed exchange mechanism and corresponding structural changes were investigated. Potential experimental precautions such as H3O + exchange and formation of impurities were proposed. Thermodynamic studies showed equilibrium constants of 0.063 for Na+ -K+ and 0.031 for Na+ -NH4 + exchange in Bayer-SOD, while divalent cations and all treatments for Bayer-CAN showed a constant < 0.01. Divalent cations had little competitive effect on monovalent cation adsorption. While sodalite and cancrinite can exchange Na+ with K+ or NH4+ during long-term remediation/rehabilitation processes, irreversible H3O+ exchange may deteriorate their performance over time.

Name thesis:degree_name

Doctor of Philosophy

Discipline thesis:degree_discipline

Soil Science

Grantor

Texas A&M University

Year dc:date.issued

2025

Author dc:creator

• Lin, Chia-Wei

Advisor dc:contributor.advisor

• Deng, Youjun

Committee members dc:contributor.committeemember

• Xie, Kelvin
• Markus Graefe

• Agriculture, Soil Science
• Environmental Sciences
• Chemistry, Agricultural

Language dc:language.iso

English

Handle dc:identifier.uri

https://hdl.handle.net/1969.1/1599695

OAI record oai:identifier

https://oaktrust.library.tamu.edu/server/oai/request?verb=GetRecord&metadataPrefix=dim&identifier=oai%3Aoaktrust.library.tamu.edu%3A1969.1%2F1599695