Abstract
Poisonous heavy metals in air, water, and soil produce global environmental problems that are considerable threats to humankind. To meet the local and international guidelines for heavy metal release, companies often use different approaches, such as chemical precipitation, chelating agents, or activated carbon produced by adsorption. One of these heavy and toxic metals is chromium(VI). Chromium(VI) is commonly used in many applications, such as dye fixation in the textile industry or as an anticorrosive agent in paints. The aim of this paper is to explore the factors affecting the removal of one of these deadly heavy metals, chromium(VI), from aqueous solutions. For this purpose, activated carbon from Turkish Tunçbilek lignite is prepared with both chemical and physical activation methods to investigate the adsorption behavior of chromium(VI). The effects of initial chromium(VI) concentration, adsorption temperature, and pH on adsorption are studied using a design of experiments method with a full 24 factorial design with center points. The Freundlich and Langmuir adsorption isotherms that are commonly used in chemical engineering are also applied both for predicting the amount of chromium(VI) adsorbed and confirming the validity and advantages of the obtained regression model. The results indicate that the design of experiments and regression can explain and support the design of new materials by using linear and physically meaningful equations instead of local nonlinear and empirical models that are usually insufficient. Additionally, three experiments were carried out in the liquid phase to test the activated carbon samples: chromium, chromium and sucrose, and chromium-sucrose-ion. A change in adsorption capacities of the activated carbon samples was observed. Sucrose was chosen for the experiments because it contains six carbon atoms in a slightly soluble structure. The results indicated that Tunçbilek lignite exhibits good adsorption capability.
Highlights
Heavy metal pollution is one of the environmental problems in the world today. e mixing of heavy metals with soil and water is dangerous
Heavy metals can be removed from wastewater by chemical precipitation, membrane filtration, ion exchange, solvent extraction, and adsorption methods [3, 4, 6]. e adsorption method has been used for water and wastewater for a long time to remove color, odor, and organic contaminants [3, 7]
E experimental conditions for the physical and chemical activation methods described are as follows: (i) Physical activation process: CO2 is used as activating gas in the production of physical activated carbon. e raw material was subjected to a thermal decomposition process at 1073 K with a heating rate of 30 K/min in a nitrogen gas environment. en, CO2 gas was supplied to the environment at a rate of
Summary
Heavy metal pollution is one of the environmental problems in the world today. e mixing of heavy metals with soil and water is dangerous. Despite having lower adsorption capacities than synthetic ion exchange materials for the removal of heavy metal ions from wastewater, the use of low-rank grade coals is widespread due to their lower cost [16, 17]. The adsorption of metal ions on active carbon produced by lignite has been studied extensively [2, 17,18,19,20,21,22]. E purpose of this paper is to investigate the extent to which chromium(VI) ions are removed from aqueous solutions of activated carbon samples produced by physical and chemical activation methods using Tunçbilek lignite. Experiments are conducted to indicate the capability of the active carbon samples obtained For this purpose, the organic matter effect is investigated by adding sucrose to the adsorption medium
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