THAI NGUYEN UNIVERSITY UNIVERSITY OF AGRICULTURE AND FORESTRY HA THI LAN ANH CHROMIUM (VI) REMOVAL FROM AQUEOUS SOLUTION BY USING SILVER NANO-ACTIVATED CARBON BACHELOR THESIS Study Mode: Full-time Major: Environmental Science and Management Faculty: Advanced Education Program Office Batch: 2014 - 2018 Thai Nguyen, 25/09/2018 h Thai Nguyen University of Agriculture and Forestry Degree Program Bachelor of Environmental Science and Management Student name Ha Thi Lan Anh Student ID DTN 1454290001 Thesis title Chromium (VI) removal from aqueous solution by using Silver nano-activated carbon Supervisor(s) Dr. Van Huu Tap (Faculty of Environment and Earth Science, Thai Nguyen University of Sciences) Abstract: Chromium (Cr(VI)) is a heavy metal that can cause a serious impact on the environment and human – being. The treatment of Cr(VI) was reported through several methods such as chemical precipitation, adsorption, membrane filtration, coagulation/flocculation, ion exchange and absorption. However, absorption is considered one of the most idea method for Cr(VI) removal.
Activated carbon is a low-cost material derived from wood or other organic waste from the shell and coir. As the main constituent of coal is carbon, so all the carbon-rich fuels can be used to make activated carbon. Besides, silver nano particles as a catalyst for modifying activated carbon to increase the adsorption capacity of activated carbon. In this study, the activated carbon loaded silver nanoparticle (AgNPs-AC) was used as a low-cost adsorbent to remove Cr (VI) from the aqueous solution.
Batch absorption i h experiments were conducted to evaluate the effects of pH, initial concentrations of Cr(VI), contact time and dose of AgNPs-AC on Cr(VI) removal efficiency. The results showed that at pH = 4, contact time of 180 min, 20mg AgNPs-AC/25mL of K2Cr2O7 solution with initial Cr(VI) concentration at 5 mg/L were the most suitable conditions for adsorption of Cr VI) from aqueous solutions. The optimum adsorption capacity achieved after processing was 27.70mg/g at 20 mg/25mL of AgNPs-AC dose and 40 mg/L initial Cr(VI). The adsorption kinetic data were found to fit well with the pseudo-first and second order models with very high correlation coefficients.
From this study, it can be concluded that AgNPs-AC is an interesting adsorbent, saving, easy to remove Cr (VI) from the aqueous solution. Keywords Silver nano-activated carbon, Chromium, Adsorption capacity, Activated carbon. Number of pages: 40 Date of submission: 25/09/2018 ii h ACKNOWLEDGEMENT First of all, I would like to thank you teachers at University of Agriculture and Forestry – University of Thai Nguyen has dedicated teaching me during the period of study at the school. I would like to express deep gratitude to the teachers Dr.
Van Huu Tap whose guidance, encouragement, suggestion and very constructive criticism have contributed immensely to the evolution of my ideas during the project. Without his guidance, I may not have this report. At the same time, I also want to express my deep gratitude to Dr. Vu Xuan Hoa, who gave me a chance to interact with a nanotechnology field.
I also thank faculty of Environment and Earth Science – Thai Nguyen University of Sciences - Thai Nguyen University has facilitated me throughout the course of the thesis. Finally yet important, I took this opportunity to express my deepest appreciation to my families, relatives, friends who encouraged and supported me unceasingly and all who directly or indirectly, have lent their helping hand in this venture. Thank you all very much! Thai Nguyen, 25/09/2018 Student Ha Thi Lan Anh iii h TABLE OF CONTENTS ACKNOWLEDGEMENT. iii TABLE OF CONTENTS.
iv LIST OF FIGURES. vi LIST OF TABLES .1 Electronic and molecular structure of hexavalent chromium compounds .2 Sources of Chromium .2 Routes of exposure (Chromium) .3 Coconut shell activated carbon .5 Silver nano-activated carbon (AgNPs-AC) .2 Location and research time .4 Adsorption experiments of Chromium (Cr6+) onto (AgNPs –AC). RESULTS AND DISSCUSSION .1 Characterization of the nano-activated carbon .2 Effect of impregnation ratio (AgNPs/AC) on Cr(VI) adsorption capacity .3 Effect of pH .4 Effect of contact time .5 Effect of adsorbent dose .6 Effect of initial Cr(VI) concentrations .8 Adsorption kinetics of AgNPs-AC .36 v h LIST OF FIGURES Figure 4.1 SEM image of (a) AC and (b) AgNPs-loaded activated carbon (AgNPs- AC), EDS spectra of (c) AC and (d) AgNPs-loaded activated carbon (AgNPs-AC) .2 XRD graph of (a) activated carbon from coconut shells (AC) and (b) AgNPs 2% - loaded activated carbon (AgNPs-AC) .3 The effect of the impregnation ratio on chromium adsorption at concentration of 10 mg/L, adsorbent dose: 10 mg AgNPs-AC/25mL Cr6+ solution, Contact time=60 min and Temp: 250C .4 Effect of pH on the removal of Chromium ion [Cr]=10mg/L, Contact time=60 min, adsorption dose=10mg/25mL, Temp (25C±20C) .5 Effect of Contact Time on the Removal of Chromium ion [Cr]=10 mg/L; adsorbent dose=10mg/25mL; pH=4;Temp (25C±20C).6 Effect of adsorbent dose on the removal of Chromium ion [Cr] =10mg/L: Contact time=180 min: pH=4: Temp (25±2oC).8 Adsorption isothermal equilibrium prediction of Cr(VI) onto AgNPs-AC at contact time = 180 min, Ag-AC dose = 20 mg/25mL, initial pH: 4, Temp: 250C) .9 Kinetics model of Cr(VI) adsorption onto AgNPs-AC (Co: 10mg/L; adsorbent dosage: 20 mg/25 mL, initial pH: 4, Temp: 250C). 33 vi h LIST OF TABLES Table 1: Levels of daily chromium intake by humans from different routes of exposure .7 Table 2: Adsorption isothermal parameters and correlation coefficients of Langmuir, Freundlich and Temkin models for sucrose adsorption on Chromium .31 Table 3: Calculated kinetic parameters of models for adsorption of Chromium onto AgNPs-AC.
Research rationale Chromium, named for its multicolored compounds, is a transition metal, number 24 in the periodic table of elements. This element is found in combination, mainly in chromite ores, and, even if in lower abundant amounts, as crocoites (PbCrO4) and chrome ochre (Cr2O3). Cr is a major element that exists primarily in two different oxidation states, hexavalent and trivalent. These oxidation states are denoted as Cr(VI) and Cr(III), respectively.
The rarely found naturally occurring element has zero oxidation, Cr(0), other oxidation states of Cr are not stable and therefore, are not found in the natural environment. Cr(VI) is more flexible than Cr(III) and dificult to remove in water (Elisabeth L. al, 2004) This chromium (VI) detoxification leads to increased levels of chromium (III) (ATSDR, 1998). Air emissions of chromium are predominantly of trivalent chromium, and in the form of small particles or aerosols (ATSDR, 1998) and (SAIC.
The most important industrial sources of chromium in the atmosphere are those related to ferrochrome production. Ore refining, chemical and refractory processing, cement- producing plants, automobile brake lining and catalytic converters for automobiles, leather tanneries, and chrome pigments also contribute to the atmospheric burden of chromium (U. Environmental Protection Agency, 1998). The general population is exposed to chromium (generally chromium [III]) by eating food, drinking water and inhaling air that contains the chemical.
The average daily intake from air, water, and food is estimated to be less than 0. Dermal exposure to chromium may occur during the use of consumer products that contain chromium, such as wood treated with copper dichromate or leather tanned with chromic sulfate (ATSDR, 1998). Occupational exposure to chromium occurs from chromate production, stainless-steel production, chromium plating, and working in tanning industries; occupational exposure can be two orders of magnitude higher than exposure to the general population (ATSDR, 1998). People who live in the vicinity of chromium waste disposal sites or chromium manufacturing and processing plants have a greater probability of elevated chromium exposure than the general population.
Several technologies have been applied to remove Cr(VI) from aqueous solutions including precipitation, reverse osmosis, ion exchange, filtration, sand filtration, chemical reduction/oxidation, electrochemical precipitation, membrane filtration, solvent extraction, and electrochemical deposition and adsorption (Chi- Chuan-Kan, 2017). Adsorption is an effective and low cost method. Particularly, the problem of chromium pollution in water resources is causing concern in major cities and industrial parks; therefore, it is necessary to have a method to remove Cr from the water environment. In this study, Cr was treated by adsorption with the adsorbed material is activated carbon coconut shell 1.
Research's objectives The purpose of this study was to load silver nanoparticles into activated carbon deriving from coconut shell and application for removing chromium from aqueous solution. Research on finding the appropriate impregnated rate, evaluation of appropriate conditions for adsorption, including: pH, sorption time, adsorbent dosages 2 h and initial concentrations. The adsorption kinetics, sorption isotherm and corresponding chromium removal mechanisms were also studied under optimal conditions. Research hypotheses With many advantages in the environment, the application of nano materials for wastewater treatment is an effective way to remove heavy metals.
And this scientific research will seek to answer the central research questions. What are the characteristics of the type (Ag - NPs) that can remove Cr from the aqueous solution? 2. What is the optimal condition for the removal of Cr from aqueous solutions? 1. Limitations Because the training time is too short, this research project can not perform other experiments and estimate deeply the factors affecting heavy metal adsorption in water using AgNPs-AC.5 Definitions - Research in the process of treating Cr in aqueous solution, conducted within the laboratory - Evaluate the positive side and show the limitations in the handling of heavy metals 3 h PART II.1 Electronic and molecular structure of hexavalent chromium compounds In aqueous solution hexavalent chromium exists as oxoforms in a variety of species depending on pH and the hexavalent chromium concentration (R.
For the oxo speciesof hexavalent chromium three main pH regions may be distinguished: (1) H2CrO4 (pH<0) (2) HCr and Cr2 (pH 2–6), (3) Cr (pH>6) The abundance of these forms is largely dependent upon concentration. In very acidic solutions two other forms have been detected, and (T. The equilibrium between protons, water molecules, and the hexavalent chromium species are as follows: ↔ HCr + (1) HCr ↔ Cr + (2) + ↔ 2HCr (3) H ↔ + (4) Cr ↔H + (5) The most important equilibria in hexavalent chromium aqueous solutions above pH 1.5 are deprotonation and dimerization reactions, which can be described by equations (ATSDR, 1998) and (SAIC. PM, 1998) 4 h The electronic structure of the tetrahedral chromate ion, a predominant oxo species at neutral pH, is second only to the permanganate ion (Mn ) in being thoroughly studied.
The chromate ion forms a regular tetrahedron with the chromium– oxygen distance being 1. Polyhedron, 1996) The schematic energy level diagram for the higher filled (HOMO) and lower unfilled (LUMO) orbitals in the ground state established the 1 orbital to the highest occupied level and 2e to be the lowest unoccupied (S. The highest occupied MO level 1 possesses pure oxygen character and the 2e orbital is mostly of chromium character (H.2 Sources of Chromium Most chromium is released into the environment from human activities at stationary point sources. Combustion and the processing of ore discharge primarily trivalent chromium into the environment as chromium oxide; however small amounts of hexavalent chromium does appear in fly-ash of coal-fired power plants (Donald G.
Barceloux, 1999) and from chromate manufacturing sites. The highest exposure to hexavalent chromium occurs during chromate production, ferrochrome and chrome pigment production, chrome plating, and stainless steel welding (Donald G.2 Routes of exposure (Chromium) 2.1 Air The bronchial tree is the primary target organ for carcinogenic effects of chromium (VI). Inhalation of chromium-containing aerosols is therefore a major concern with respect to exposure to chromium compounds. The retention of chromium compounds from inhalation, based on a 24-hour respiratory volume of 20 m3 in urban 5 h areas with an average chromium concentration of 50 ng/m3, is about 3–400 ng.
Individual uptake may vary depending on concomitant exposure to other relevant factors, e. tobacco smoking, and on the distribution of the particle sizes in the inhaled aerosol. Chromium has been determined as a component of cigarette tobacco produced in the United States, its concentration varying from 0.3 mg/kg (Lyon, 1990), but no clear information is available on the fraction that appears in mainstream tobacco smoke.