Subscriber access provided by UNIVERSITY OF CONNECTICUT
Article
Competitive adsorption of arsenic and fluoride onto economically prepared aluminum oxide/hydroxide nanoparticles: Multicomponent isotherms and spent adsorbent management Vineet Kumar Rathore, and Prasenjit Mondal Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.7b01139 • Publication Date (Web): 23 Jun 2017 Downloaded from http://pubs.acs.org on June 25, 2017
Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.
Industrial & Engineering Chemistry Research is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.
Page 1 of 47
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Industrial & Engineering Chemistry Research
Competitive adsorption of arsenic and fluoride onto economically prepared aluminum oxide/hydroxide nanoparticles: Multicomponent isotherms and spent adsorbent management Vineet Kumar Rathore†, Prasenjit Mondal†* †Department of Chemical Engineering, Indian Institute of Technology Roorkee, Roorkee (Uttarakhand) India, 247667 KEYWORDS: Adsorption; Arsenic; Fluoride; Aluminum oxide/hydride nanoparticles; Multicomponent isotherms; Spent adsorbent management.
ABSTRACT: The present study deals with adsorptive removal of arsenic and fluoride in single as well as bi-component system using aluminum oxide/hydroxide nanoparticles (AHNP). For single component system, the Langmuir maximum adsorption capacity of the adsorbent is found as 833.33 µg/g for arsenic and 2000 µg/g for fluoride at optimum conditions. The adsorption process is well explained by Langmuir isotherm and pseudo second order kinetic models for both arsenic and fluoride. Real groundwater sample having arsenic 512 µg/L and fluoride 6300 µg/L along with other ions, has also been treated successfully. Among different isotherms, the modified competitive Langmuir isotherm is found to be most suitable to represent the bi-
ACS Paragon Plus Environment
1
Industrial & Engineering Chemistry Research
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 2 of 47
component system. Solidification of the spent adsorbent through brick formation is investigated and this process is found to be an effective option for its management. Through economic evaluation, the adsorbent and treatment costs are found as ~86.89 INR/kg and 0.36 INR/L respectively.
1. Introduction Water is an essential component of life and also a basic building block for the ecosystem. In the last few decades, due to exponential growth in human population and industries, this component of the ecosystem is facing some serious challenges and has become scarce in its usable form as drinking water. Groundwater is a primary source of drinking water and irrigation for more than 50 % of the world population1. The rapid increase in global population and industrial activities has caused over-exploitation of groundwater, which in turn has resulted in a drastic degradation of its quality. More and more cases of groundwater contamination with inorganic pollutants, salinity, heavy metals, etc. are coming into light day by day. Arsenic and fluoride are two of such contaminants, which possess greatest threats to the human beings. It is estimated that around ten million and hundred million people suffer from high arsenic and fluoride hazard worldwide, respectively2,3. The consumption of drinking water having excess quantities of these contaminants results in several types of diseases and health related problems like bone and skeletal fluorosis due to fluoride and different types of cancers due to arsenic4,5. Due to these probable severe adversities, WHO has issued guideline value of 10 µg/L for arsenic and 1500 µg/L for fluoride respectively6. Also, the maximum permissible limits for arsenic and fluoride as per the Indian Standard (IS 10500) are recommended as 10 µg/L for arsenic and 1500 µg/L for fluoride respectively and the permissible limits for other contaminants like Al, Fe, Zn and Cl are set as 200 µg/L, 300 µg/L, 15000 µg/L and 1000000 µg/L7. There are many countries
ACS Paragon Plus Environment
2
Page 3 of 47
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Industrial & Engineering Chemistry Research
around the world like India, China, Mexico, Argentina, and Pakistan, where, these contaminants are reported to co-exist in groundwater. In India, the co-occurrence of both these contaminants in the groundwater of Rajnandgaon District in the state of Chhattisgarh has been reported to be well above the permissible limits8. Co-occurrence of these pollutants may create more serious effects on human health. Various techniques such as ion exchange, reverse osmosis, chemical reduction, electrodialysis, distillation, biological processes, adsorption, and other processes have been investigated by different research groups to remove arsenic and fluoride from water and reported in literature5,9. Amongst them, the adsorption process with the help of natural or synthetic solid adsorbent is highly promising. This technique is of great interest because of its favorable economics, high energy efficiency, and ease of operation. Moreover, in many cases, it is also possible to reuse the spent adsorbents through its regeneration. A large amount of literature is available on aluminum, iron, manganese, zirconium, cerium, lithium based adsorbents for defluoridation and arsenic removal from water4,5. In many of the recently published papers, metal oxides, and metal hydroxides have been reported to be a good candidate for the adsorptive removal of arsenic and fluoride from water. These adsorbents are abundantly available in nature in the form of various types of minerals and can also be synthesized in the laboratories easily. In particular, oxides and hydroxides of aluminum are extensively studied for the remediation of fluoride bearing water as they have positively charged surface, which facilitates the adsorption of negatively charged fluoride ions due to electrostatic attraction. On the other hand, arsenic is reported to be removed primarily by metal oxides and hydroxides by ligand exchange mechanism.
ACS Paragon Plus Environment
3
Industrial & Engineering Chemistry Research
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 4 of 47
Alumina is one of the most widely studied adsorbents for the defluoridation of water. The research for defluoridation with alumina shows different kinds of compounds, which include different treatments to give it specific characteristics5. Similarly, arsenic removal with aluminum compounds being used as adsorbents is also reported in several researches10,11. It is noteworthy that in most of the literature reported for the adsorptive removal of arsenic or fluoride, the studies were performed for the single component system. Hence, there is an urgent need for the development of a new adsorbent having the ability to treat both the contaminants together while being cost effective and easy to synthesize as in many places both of these pollutants co-exists where economic conditions of the people are poor. Main aim of the present study is to improve the specific uptake of both As and F as well as reduce the cost of the material. In the present paper, a new aluminum oxide/hydroxide material has been synthesized with the help of electrochemical process and its application is studied for the removal of both the contaminants at the same time. The interaction study between arsenic and fluoride, which are often found together, is also carried out in order to get an insight on the mechanisms associated with their adsorption. This interaction study is explained with the help of various multicomponent adsorption isotherms. Further, after the adsorption of the contaminants, the management of the spent adsorbents in the form of clay bricks is also discussed herein. Finally, the costing of the adsorbent is carried out on the basis of a stipulated amount of contaminated water in order to ensure that the adsorbent is economically feasible for the people of the underdeveloped and developing countries. 2. Theory 2.1 Single component isotherm models
ACS Paragon Plus Environment
4
Page 5 of 47
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Industrial & Engineering Chemistry Research
Langmuir isotherm: Langmuir isotherm assumes a monolayer adsorption on a uniform adsorbent surface with energetically identical sorption sites10. The linear form of the Langmuir isotherm equation is given by:
=
+
(1)
Where Ce is the equilibrium concentration of the adsorbate (µg/L) in solution, qe is the amount of adsorbate per unit mass of adsorbent (µg/g), qo and bL are Langmuir constants related to adsorption capacity and rate of adsorption respectively. The feasibility of Langmuir isotherm can be described by a separation factor RL, which can be determined by the following equation: R =
(2)
Where, Co is the initial concentration of arsenic or fluoride (µg/L) and bL is the Langmuir constant (L/g). The value of separation factor RL, indicates the isotherm’s shape and the nature of the adsorption process, unfavorable for (RL > 1), linear for (RL = 1), favorable for (0 < RL < 1) and irreversible (RL = 0). Freundlich isotherm: Freundlich adsorption isotherm describes equilibrium on heterogeneous surfaces and hence does not assume monolayer capacity. The logarithmic form of the Freundlich isotherm expression is given by the following equation:
lnq = lnK + lnC
(3)
Where, KF and n are Freundlich constants which show the adsorption capacity and favorability
of adsorption respectively. The value of 1/n obtained from the slope of Eq. (3) should lie between 0 and 1 for favorable adsorption process12. 2.2 Multicomponent isotherm models
ACS Paragon Plus Environment
5
Industrial & Engineering Chemistry Research
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 6 of 47
Equilibrium adsorption in the binary system was studied using non-modified competitive Langmuir model, modified competitive Langmuir model, extended Langmuir model and extended Freundlich model, which are briefly described below. Non-modified competitive Langmuir model: This isotherm model is used for the competitive adsorption models for ith component in a system having n components. It is written as: , =
, , ,
∑ !" , ,
(4)
Where, qo and bL can be estimated from the experimental data by corresponding individual Langmuir isotherm equations. Modified competitive Langmuir isotherm: In this isotherm, an additional term η is introduced to show the competitive effect of the adsorbate species present in the solution13. It is written as: , =
%, ' &
. , $
∑ !" , (
%, &
(5)
)
Where, qo and b can be estimated from the experimental data by corresponding individual Langmuir isotherm equations and the value of η can be estimated from the competitive adsorption data. Extended Langmuir isotherm: According to assumptions in this isotherm, when the all the sites of adsorbent are available for both the adsorbates (ions) and both the ions have a non-interacting effect13, the equilibrium adsorption of any species can be written as:
*+, , = ∑
,
!" ,
(6)
Where, the values of qmax and bi can be calculated from the optimized fitting of Eq. (6) with the experimental data of components in the binary system. Extended Freundlich: This isotherm was proposed by Fritz and Schluender14, which is an extension of Freundlich model for binary mixtures. It can be written as:
ACS Paragon Plus Environment
6
Page 7 of 47
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Industrial & Engineering Chemistry Research
, = ,4 =
/ 0,"
-.," ,"" ,
3" ,"" 1" ,2
(7)
, 32 ,22 12 ,"
(8)
/ 0,2
-.,2 ,22
Where, KF,1, KF,2, n1, and n2 can be estimated from corresponding individual Freundlich isotherm equations while x1, y1, z1, x2, y2, and z2 can be estimated by fitting the Eq. (7) and (8) for binary system. Further, the accuracy and adequacy of data fitted for binary adsorption isotherms models (nonmodified competitive Langmuir model, modified competitive Langmuir model, extended Langmuir model and extended Freundlich model) were tested by calculating Marquardt’s Percent Standard Deviation (MPSD) formula using MS Excel 2007. The MPSD error function was calculated from Eq. (9)15: MPSD = 100;
