Application of Magnetically Activated Carbon for the Separation of Nicotinic Acid from Aqueous Solution Dipaloy Datta,* Sanjana Sah, Nikita Rawat, and Rajat Kumar Department of Chemical Engineering, Malaviya National Institute of Technology (MNIT), Jaipur, Rajasthan, India ABSTRACT: The adsorption of nicotinic acid molecules from their solution in the aqueous phase was studied in batch mode by using magnetically activated carbon (M-AC) as the adsorbent. Activated carbon was magnetized by a coprecipitation method. The effects of the amount of adsorbent (0.25 to 5 g·L -1 ), initial acid concentration (2.46 to 14.77 g·L -1 or 0.02 to 0.12 mol·L -1 ), contact time (0 to 120 min), and temperature (298 to 333 K) on the percentage removal were investigated. Theoretically (from the Langmuir isotherm), an adsorption capacity of 23.28 g·g -1 was obtained by M-AC for acid removal. Equilibrium isotherms such as the Langmuir, the Freundlich, and the Temkin were applied to determine equilibrium parameters and to fit the equilibrium data, out of which the Langmuir gave the best match to the results. Nicotinic acid adsorption kinetics was modeled with pseudo-first order, pseudo-second order, and intraparticle diffusion models. The kinetic data was best described by the pseudo-second-order model. Thermodynamic parameters such as ΔH o , ΔS o , and ΔG o were calculated, and their values pointed out that the adsorption of acid molecules onto M-AC was exothermic and the process was spontaneous. 1. INTRODUCTION The use of activated carbon (granular and powdered) as the adsorbent has become popular because of the accessibility of the large surface area per unit volume and the presence of networks of submicroscopic pores where adsorption takes place. This material can be obtained from different carbonaceous sources such as coal, peat, coconuts, wood, lignite, nutshells, and so forth and has several applications in the pollution control of air and water. 1 It is also used as the catalytic support in various petrochemical industries 2 because of its extremely good physical and chemical properties such as a high specific surface area (varies from 200 to 2000 m 2 ·g -1 and depends upon the method of preparation), high thermal stability, porosity, and chemical inertness. 3 To enhance the rate of adsorption, powdered activated carbon with a small particle size is usually used. Compared to filtration, separation by using magnetic particles is considered to be a rapid and effective method, and this technique is widely used in many areas of biochemistry, cell biology, microbiology, mining ores, and environmental technol- ogy 4 in recent days. Magnetic particles have been used extensively for cleaning up oil spills 5 and speeding up the coagulation process in sewage, 6 and powder MnO-Fe 2 O 3 nanocomposite has been used for the removal of organic dyes containing wastewater. 7 These materials have very narrow application ranges, and also the applicable range of pH was very narrow. 8 Therefore, to get rid of these limitations of powdered activated carbon and magnetic particles, preparation methods such as ball milling, 9 impregnation, and chemical coprecipitation 10 have been applied to produce these magnetic composites, which can easily and conveniently get separated by a magnetic field. The chemical coprecipitation method is the most widely used preparation method as it is easy and does not require special chemicals and procedures. Nicotinic acid, which is also known as niacin or vitamin B3, is soluble in water and used as a necessary micronutrient in animal food or diets. It is also used in a wide variety of applications in the chemical, biochemical, and therapeutic fields. The acid helps in the reduction of the total cholesterol level in the human body. Nicotinic acid is a biologically active molecule and hence finds growing application as a food additive, fodder, in cosmetics, and several areas of science and technology. 11 The acid is also widely used in the treatment of dyslipidemia and is considered to be a very important hypolipidemic drug that helps to control and lower high cholesterol levels. 12 The annual worldwide output of Received: September 5, 2016 Accepted: January 11, 2017 Article pubs.acs.org/jced © XXXX American Chemical Society A DOI: 10.1021/acs.jced.6b00784 J. Chem. Eng. Data XXXX, XXX, XXX-XXX