Removal of Lead Ions in an Aqueous Medium with Activated Carbon Fibers
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Removal of Lead Ions in an Aqueous Medium with Activated Carbon Fibers Teresa Ramírez-Rodríguez and Fray de Landa Castillo-Alvarado Escuela Superior de Física y Matemáticas, Instituto Politécnico Nacional, 07738 Ave. IPN, D.F, México. ABSTRACT Poly(acrylonitrile) fibers are used in the manufacture of activated carbon fibers, which are activated with phosphate groups for the removal of lead ions in aqueous solutions. Removal of lead ions is performed in a water bath at 30°C. Trough isotherm models of Langmuir and Freundlich analyzed the aqueous solution. Kinetic analysis is performed using the model pseudofirst and pseudo-second order. The result show that adsorption equilibrium is adjusted to the Freundlich model and the kinetic model of pseudo-second order led to the best fit correlation. INTRODUCTION Different treatments for activated carbon adsorption are commonly used due to its relatively high performance and safety in the environment [1]. Activated carbon is manufactured in order to provide a high degree of porosity and high specific surface. In this paper have been used poly(acrylonitrile) fiber precursor material to produce activated carbon fibers (ACF). The aim of this study is to investigate the kinetic of adsorption and removal capacity in aqueous solutions of lead ions by ACF derived from acrylic fibers. THEORY Relationship Aqueous solution:mass of fiber is indicated as: 1:1, 1.5:1, 2:1, 3:1, 1:2, 1:3, and 1:1.5., [2mL:0.1g]. Removal of lead ions has been carried out in an aqueous bath at a temperature of 30°C. Samples are prepared by filtration and concentration of lead ions (II) is analyzed by an atomic absorption spectrophotometer. Each experiment is doubled under the same conditions. The following models are used for isothermal and kinetic analysis. Langmuir isotherm In 1916 Langmuir [2] developed a simple model to predict the adsorption of a gas on a surface as a function of fluid pressure. However, this model is applicable to solid-liquid interface as the solid-gas interface [3]. Liu [4] proposed a dynamic schema that represents the adsorption: (1)
A + B AB
Where A represents the adsorbate, B represents the solid adsorbent and AB represent the adsorbent-adsorbate complex. For equation (1) the equilibrium constant can be expressed as: ] K = [ A[ AB ][ B]
(2)
21
According to the definition of equilibrium constant [AB], [A] [B] are the molar concentrations of each component. The number of moles of adsorbate bound per mole of adsorbent (q) can be written as:
[ AB] [B] + [ AB]
q=
(3)
Substituting equation (2) in equation (3), we have:
q=
K [ A] 1+ K [ A]
(4)
Being 1/K a dissociation constant, on the other hand, if the adsorbent has n identical binding sites, the adsorption isotherm can be considered as the sum of each of the binding sites:
q=n
K [ A] 1+ K [ A]
(5)
Equation (6) shows that the theoretical maximum adsorption capacity is n mol mol-1. Multiplying both sides of equation (5) by the ratio of the molar weight of adsorbate (MA) and the molar weight of adsorbent (MB) gives:
M
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