Heavy Metals Adsorption from Aqueous Solutions onto Unmodified and Modified Jordanian Kaolinite Clay: Batch and Column Techniques

Khansaa Al-Essa

doi:10.11648/j.ajac.20180601.14

Abstract

Awareness of, and concern about, water pollution all over the world has been increasing. In Jordan, water also has been polluted by different kinds of pollutants such as heavy metals, It is widely agreed that a properly developed green, low – cost and more efficient adsorbent is desired approach towards removing pollutants. Jordan has huge reserves of kaolinite. Unfortunately, it has a relative low cation–exchange capacity and a small surface area. However, it can be modified to enhance its adsorption capacity towards heavy metal ions. Humic acid was used to this purpose. Two types of humic acid were used; one was commercial from Fluka Company and the other was natural extracted from King Talal Dam sediments. Comparison of Pb (II), Cd (II) and Zn (II) adsorption from aqueous solutions onto unmodified and modified Jordanian kaolinite clay were studied using batch technique at different temperatures (25, 35 and 45°C) and different pH (4, 5 and 6). The effects of contact time, adsorbent dose, and the initial metal ion concentration were also studied. The uptake at low concentration reaches above 90% for Pb (II). The adsorbed amount trend was as follows: Pb (II) > Cd (II) > Zn (II) for both modified kaolinite clay. The column technique was used effectively for the determination of metal ion loading capacity. The uptake percentage fall in the same order (Pb (II) > Cd (II) > Zn (II)) for both modified kaolinite clay.

Highlights

Kaolinite, (SiIV)4 (AlIII)4 O10(OH)8, is the most common two–sheet type clay mineral layer
Kaolinite has a relative low cation–exchange capacity (CEC) of 3–15 meq/100 g of clay and a small surface area ranging from 10–20 m2/g [2, 3]
Effect of contact time The effect of contact time on the adsorption of Pb (II), Cd (II) and Zn (II) was shown in Figure 1, the equilibrium adsorption was established within 4 hours, indicating that the initial adsorption was very fast and the maximum uptakes recorded within the equilibrium period; at which the% uptake of metal ion is constant

Summary

Introduction

Kaolinite, (SiIV) (AlIII) O10(OH), is the most common two–sheet type clay mineral layer. Kaolinite has a small net negative charge arising on the clay crystals due to protonation/deprotonation influenced by the solution pH. This negative charge, small, is responsible for the surface not being completely inert; it allows electrostatic interaction with positively charged ions [1]. Kaolinite has a relative low cation–exchange capacity (CEC) of 3–15 meq/100 g of clay and a small surface area ranging from 10–20 m2/g [2, 3]. It can be modified from its natural state by physical or chemical treatment to improve its sorption capacity. Kaolinite coated with humic substances play an important role in the environmental behavior of various ions [5]

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