الفهرس 
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Abstract
Water pollution is still a critical universal issue, and all countries give the appropriated attention. Intense industrial and agricultural activities result in the contamination of wastewater with several pollutants such as toxic heavy metals, dyes, organic compounds, phenols, pesticides and other persistent organic pollutants. These types of pollutants come in the food chain and cause toxic effects, cancer, and diseases, thus affecting the aquatic biota and human health.
Dyes are usually present in the wastewater from many industries such as textile, leather, rubber, plastic and paper. Dyes reduce the sunlight penetration and consume the dissolved oxygen. In addition, some toxic, mutagenic and carcinogenic intermediates were produced by different reaction such as hydrolysis and oxidation of dye
Several techniques are applied to remove dyes from wastewater such as membrane filtration, ion exchange, precipitation, oxidation, advanced oxidation, coagulation/flocculation, biological treatment, electrochemical process and Adsorption. These techniques differ in their efficiency, cost and environmental impact.
Adsorption can be thought to be the most efficient process for the treatment of wastewater due to high removal efficiency for different types of effluents, ease of operation, availability of a variety of cheap adsorbents and the absence of sludge and harmful by-product formation.
The main objective of this work is to evaluate the adsorption performance of dolomite and limestone as low cost adsorbents in the removal of crystal violet dye from aqueous solutions
The thesis consists of three chapters:
Chapter 1: Deals with a general introduction of the subject and a literature review is given.
Chapter 2: Includes the materials, experimental procedures instrumentation, the different advanced methods of data analysis and data transfer using Origin version 8.0.
Chapter 3: Deals with the obtained results and discussion that are reported as follow:
(1) The chemical composition of both of CDP and limestone shows calcium as main constituent and shows the presence of some transition metals which improve the adsorption process.
(2) The influence of pH on the adsorption capacity of CDP and limestone to CV has been investigated. The results indicated that there was a lower adsorption at acidic pH, pH < 3, followed by weak increasing up to pH = 9.0. Then, with further increasing in pH of solution and a noticeable increasing in qt values up to pH =12.0. This behavior may due to the competition between H+ ions and the cation groups on the dye for adsorption sites in the lower pH values causing little interaction between CV and adsorbent whereas at pH above 9.0 the value of the amount of adsorbed CV, qt, increases continuously due to increasing of the negative surface charge of adsorbent and then the electrostatic repulsion with CV dye will be lowered.
(3) By studying the effect of contact time on the adsorption process, results indicated that the sorption of CV increased with contact time. The sorption process was fast during the first 20 minutes and then remained constant with increasing in contact time. The fast sorption at initial stage can be interpreted according that a large number of active sites are available which are responsible for sorption of CV on both of CDP and limestone.
(4) The removal percent, R%, of CV increases by increasing the mass of adsorbent from 0.005 g to 0.05 gram and then it remains almost constant over 0.05 g. The stability of R% values obtained at high masses of adsorbent can be explained in terms of possible agglomeration of the active solid phase. This agglomeration is expected to decrease with the decrease in the mass of the solid phase to give almost constant value for the removal %.
(5) The adsorption capacity of the two adsorbents is found to increase with the increase in temperature confirming that the adsorption process is an endothermic process. The increase in the adsorption capacity may be a result of the increase in the mobility of CV molecules across the external boundary layer and in the internal pores of the adsorbent particles with increasing temperature
(6) Thermodynamic parameters including Gibbs free energy, ΔG°, enthalpy, ΔH°, and entropy changes, ΔS° for the sorption of CV dye were calculated at 298 K. They found to be -6.69 KJ/mol, 31 KJ/mol and 126.5 J/mol.K, respectively in case of CDP. And they found to be -6.11 KJ/mol, 37.97 KJ/mol and 147.9 J/mol.K, respectively in case of limestone. The negative values of ΔGo are referring to a spontaneous and thermodynamically favorable adsorption of CV onto adsorbent. The positive values of ΔHo confirm the endothermic nature of the adsorption process and the positive values of ΔSo may due to increasing the randomness during adsorption process and reflect the affinity of adsorbent towards CV.
(7) Adsorption equilibrium isotherms including Langmuir, Freundlich, Temkin and Dubinin-Raduskevich were applied to find a suitable model that describes equilibrium data. Results confirmed that Langmuir isotherm was the highest fitted model for the adsorption process in case of CDP and Freundlich isotherm was the highest fitted model in case of limestone.
(8) Adsorption kinetic models including Lagergren’s pseudo first-order kinetic model, pseudo second-order kinetic model and the intra-particle diffusion model were applied to analyze the obtained kinetic data. Results proved that the Pseudo-second-order kinetic model was the best applicable model in case of both of CDP and limestone.