The Use of Cement and Zeolite for Enhancement of Buffering Capacity of Permeable Reactive Barrier

نوع: Type: thesis

مقطع: Segment: masters

عنوان: Title: The Use of Cement and Zeolite for Enhancement of Buffering Capacity of Permeable Reactive Barrier

ارائه دهنده: Provider: Elham Daraei

اساتید راهنما: Supervisors: Vahid Reza Ouhadi (Ph.D)

اساتید مشاور: Advisory Professors:

اساتید ممتحن یا داور: Examining professors or referees: Dr. Mohammad Maleki Dr. Abbas Qadimi

زمان و تاریخ ارائه: Time and date of presentation: March, 16, 2021 ; 11.30 AM

مکان ارائه: Place of presentation:

چکیده: Abstract: Groundwater is the most important source of drinking water for human societies. Lack of proper control and management of leachate as well as the presence of industrial wastes, municipal and agricultural wastes cause the pollution of environment and groundwater to organic, inorganic, heavy metals and hazardous chemical contaminants. Groundwater treatment is the most economical process for removing contaminants from groundwater. Permeable reactive barrier (PRB) is one of the main methods of groundwater treatment that are filled with various reactants or sorbents and placed underground in the groundwater path. Natural zeolites are one of the low cost materials that are often used as permeable reactive barrier (PRB) materials to remove contaminants from groundwater. Zeolites have been considered due to their porous nature and their effectiveness in adsorbing a variety of contaminants such as heavy metals, which often release non-toxic exchangeable cations (Mg2+, Ca2+, Na+ and K+) into the environment. In addition, the use of stabilization and solidification process in PRBs provides physical and chemical stabilization of organic matter in the long run and turns them into a suitable engineering material and allows the reuse of groundwater. Among the stabilizing materials, ordinary Portland cement is the most widely and common stabilizing material used in this method due to its availability, reasonable price and compatibility with many contaminants. In general, the main purpose of this study is to evaluate the mechanism of using cement and zeolite in increasing the buffering capacity of permeable reacting barriers (PRB). For this purpose, buffering capacity tests, heavy metal contaminant retention measurement, series of batch equilibrium experiments for different concentrations of cement in heavy metal contaminated zeolites were performed. Finally, series of X-ray diffraction microstructural experiments were implemented. The results of this study for buffering capacity and retention of heavy metal by zeolite modified with different percentages of cement as well as changes in pH due to the presence of heavy metal contaminants show that cation exchange capacity, carbonate and pozzolanic reactions of cement and zeolite have a significant effect on buffering capacity and heavy metal retention amount. According to this, with increasing the percentage of cement, the pH of the environment, the adsorption and retention of heavy metal contaminant increase due to the formation of hydrated cement compounds (CSH and CAH) and hydrated lime (Ca(OH2)). The results of the setting time tests show that the setting time of the specimen in the short term, can be attributed to the pozzolanic reactions of the cement and the formation of adhesive CSHs due to the hydration of cement. While, in the long term, the richness of zeolite from aluminosilicate and its dominant effect on the cement performance, caused some delays or non-setting of specimens. Then, due to the effect of heavy metal precipitation on the delay of hydration of cement, the setting time of contaminated zeolite postpones. The results of PRB column tests show that the contaminant retention rate is higher than the batch equilibrium tests. This is attributed to the possibility of formation of pozzolanic reactions in column test. Therefore, for permeability reactive barrier tests, the results of batch equilibrium experiments are not a suitable criterion for determining the amount of contaminant retention. To prove the obtained results, series of X-ray diffraction test was performed. According to the results of X-ray experiments the patterns of contaminant retention for modified contaminated zeolite with 2, 4, and 6% cement are different. In the contaminated zeolite which was treated by 2% cement, the solubility of clinoptilolite peak is the major governing phenomena in soil-contaminant-cement interaction. By an increase in cement concentration to 4%, the precipitation of HM becomes the controlling factor. However, as the concentration of cement increases to 6%, the solidification acts as the governing phenomena in contaminant retention. Generally, according to the results of this research the use of 6% cement is the optimum quantity of cement for treatment of HM contaminate zeolite which includes all of the retention mechanisms and achieves the appropriate delay in setting time. Keywords: Zeolite, Cement, Permeable Reactive Barriers, PRB, Hydration, Adsorption, pH, Solidification