Impact of Heavy Metals and Selective Adsorption on Short Term and Long Term Swelling of Cement Solidified Contaminated Bentonite

نوع: Type: thesis

مقطع: Segment: masters

عنوان: Title: Impact of Heavy Metals and Selective Adsorption on Short Term and Long Term Swelling of Cement Solidified Contaminated Bentonite

ارائه دهنده: Provider: Nora hashempour

اساتید راهنما: Supervisors: Dr. Vahid Reza Ouhadi

اساتید مشاور: Advisory Professors:

اساتید ممتحن یا داور: Examining professors or referees: Dr. Maleki- Dr. Ghadimi

زمان و تاریخ ارائه: Time and date of presentation: 18/11/2022

مکان ارائه: Place of presentation: seminar 2

چکیده: Abstract: Industrial activities often introduce heavy metals into the environment, which are harmful to the ecosystem and human health in most cases. Among the heavy metals, metals such as lead (Pb) and zinc (Zn) are of particular socused, the reason being the toxicity and prevalence of these metals in nature. The entry of these pollutants into the soil is a problem from the point of view of environmental geotechnics and requires the need to provide suitable and optimal methods for engineering burial and correct waste management. The stabilization and solidification technology based on cement is an attractive option for the management of heavy metal pollutants, also prevent the transfer and facilitat the final burial of pollution, and it reduces the release of pollutants into the environment. Among the stabilizing materials, ordinary Portland cement is the most widely used and common adhesive material used in this method due to its availability, reasonable price, and compatibility with many pollutants. The stabilization and solidification process using clay minerals, especially montmorillonite, can be effectively used to deal with the transfer of heavy metals. In general, the main goal of this research is to evaluate the mechanism of the effect of cement in the solidification of contaminated bentonite on the swelling potential in the short and long term. The studies of the present research have been carried out in three geotechnical, environmental and microstructural sections. In the first part, the swelling potential and Etterberg's limits have been done in the samples stabilized/solidified with cement. The results of the Etterberg limit test show that in samples contaminated with lead and zinc solidified with 20% cement, the slope of the graph tends to the horizon, which indicates that the flow limit is independent of the pollutant concentration and only cement has an effect in reducing the flow limit. Also, the paste limit values in all samples are independent of pollutant concentration and cement amount. In single-component lead-zinc and two-component lead-zinc samples, the swelling has been observed with an increase in the amount of cement (20% cement), probably forming new metal crystals. And the internal force of these crystals has increased the volume of the sample. In the second part, the behavior of one-component and two-component cations on the swelling behavior of samples stabilized/solidified with cement is studied. In the pH test, the amounts of cement provide alkaline conditions for the contaminated sample. But in this experiment, the separate contribution of stabilization mechanism and solidification mechanism cannot be distinguished. Therefore, in order to determine the contribution of these mechanisms, the pollution washing test has been used. The results of environmental tests show that 10% cement is not able to keep the pollution in the allowed range and only the stabilization phase was active. But in 20% of cement, both mechanisms were active, which was able to keep the washing of all samples within the permissible limit. In the third part, the relationship between the amount and manner of formation of C-S-H calcium silicate hydrate nanostructure and the pozzolanic reactions with cement over time in the presence and absence of heavy metal pollutants and the effect of the amount and manner of C-S-H nanostructure formation on the environmental geotechnical behavior in the solidification process. The cement base has been examined by X-ray tests and scanning electron microscopy. In the X-ray test, in most single-component zinc and two-component lead-zinc samples solidified with 20% cement and cured for 90 days, the peak intensity of calcium zincite crystals has increased compared to the samples under care for 7 days, and in contrast to the intensity of the C-S-H peak in the samples, 90 days has decreased compared to 7 days samples, which is consistent with the SEM test. Also, the decrease in the intensity of the C-S-H peak in the samples solidified with 20% cement was more than in the samples solidified with 10% cement, which is consistent with the swelling test and also the formation of new crystals in the SEM test.

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