SORPTION STUDIES OF HEAVY METAL IONS (Cu, Pb, Fe) ON NATURAL CLAY FROM ITU L.G.A OF AKWA IBOM STATE
CHAPTER ONE
1.1 INTRODUCTION
Prior to the 1850’s scientists generally regarded soil as inert material that did not interact chemically with water. Then in 1848, Thompson, H. S. added a solution of ammonium sulfate to a column of soil and to his great surprise found calcium sulfate in the solution leaching out of the column (Thompson, 1850). Way, J. T. refined these studies in 1850 (Way, 1850), launching a century of work on nutrient retention and release by soil and the identification of minerals and organic matter as key components affecting chemical mobility. This seminal research was directed primarily at improving agricultural crop production, but today it forms the foundation for global efforts to characterize the fate of environmental contaminants and the retention of organic matter in soils and sediments. In this work, a general overview of sorption processes occurring in soil is presented. Following Sposito (2008), any removal of a compound from solution to a solid phase we define as “sorption”, whereas the inverse process — the release of ions or molecules from soil solids into solution — we define as “desorption”. These definitions are universally applicable and useful when one has no knowledge of the actual sorption mechanism. When such knowledge is available, we can refer to the accumulation of chemicals at the solid-liquid interface as “adsorption”, the accumulation of molecules within existing solids as “absorption”, and the incorporation of substances within an expanding three-dimensional solid as “precipitation”. When discussing sorption processes, we call the adsorbing/absorbing solid phase the “sorbent”; solutes in the liquid phase that could potentially sorb are known as “sorptives”, and constituents that accumulate on or within a solid are termed “sorbates”.
Adsorption of ions at the interface of clay minerals and aqueous solutions is ubiquitous and plays a pivotal role in a wide spectrum of colloidal, chemical, physical, and geological processes, such as the transport and bioavailability of ions, nutrients and contaminants (Jungwirth et al., 2006). Owing to the large surface area, low permeability and high retention capability, clay minerals show outstanding adsorption performances for metal ions, organic matters and other substances that further control the transport and bioavailability of metal ions, nutrients, and contaminants.
Adsorption isotherms; generally, adsorption isotherms provide vital information in optimizing the use of absorbents. The most commonly used models are the Langmuir and Freundlich isotherms,which have shown to be more suitable for describing short term and mono-component adsorption of metals ions by different materials.
- Langmuir Isotherm:These theory is based on the dynamic character of adsorption.At equilibrium, the number of adsorbed and desorbed molecules in unit time on surface are equal. It does not take the lateral interactions and horizontal mobility of the adsorbed molecules into account (Langmuir, 1918). It is applied for adsorption of heavy metal ions onto soils and soil components in the form:
qi (1)
Where the quantity qi of an adsorbate i adsorbed is related to the equilibrium solution concentration of the adsorbate ci by the parameters K and b. The steepness of the isotherm is determined by K. K can be looked upon as a measure of the affinity of the adsorbate for the surface. The value of b is the upper limit for qi and represents the maximum adsorption of i determined by the number of reactive surface adsorption sites. The parameters b and K can be calculated from adsorption data by converting Eq. (1) into the linear form:
= bK – Kq (2)
Then the ratio qi/ci (the so-called distribution coefficient Kd ) can be plotted against qi. If the Langmuir equation can be applied, the measured data should fall on a straight line with slope of −K and x intercept of bK.
- Freundlich Equation:It is applicable to both monolayer and multilayer adsorption and it’s based on the assumption that the adsorbate adsorbs onto theheterogeneous surface of an adsorbent(Yang,1998)
The Freundlich equation:
qi = (3)
Wherea and n are adjustable positive valued parameters with n ranging only between 0 and 1. For n = 1 the linear C-type isotherm would be produced. The parameters are estimated by plotting log qi against log ci with the resulting straight line having a y intercept of log a and a slope of n. The Freundlich equation will fit data generated from the Langmuir equation. Converting the Freundlich equation (3) to the logarithmic form, the equation becomes:
(4)
Considering the adsorption of heavy metals by soils, qi is equated to the total adsorbed metal concentration (MT in mg kg−1) and ci is equated to the dissolved metal concentration (MS in mg l−1) in the batch solution at equilibrium with the solid. Defining log a as a constant, the equation becomes:
(5)
This form of the equation can be used to relate the amount of heavy metal adsorbed on specific soils to the dissolved concentration of free metal ions. A generalized Langmuir– Freundlich isotherm can also be used as a model base for the interpretation of competitive adsorption isotherms.
1.2. STATEMENT OF THE PROBLEM
The growing industrialization, and extensive use of chemicals for various concerns, has increased the burden of unwanted pollution of heavy metals into our environment and aquatic lives. Pollution of our waters has increased health problems and soil damage, such as Skin inflammation (Petcu C. et al., 2005), Kidney damage (Qu X, et al., 2013), cancer, Joint and muscle ache, etc. has been the most common illness experiences by humans in this modern times unlike some of our grandparents who lived before us. Seeking for the solution/cause of these health issues and healthier drinking water, some sorption techniques were developed to control or remove these pollutants via adsorption onto sorbent using natural and modified adsorbents. These methods of purification have stood the taste of time compared with other low cost adsorbents. Clay soil has been found to have a good/better adsorption capacity from water.
1.3 AIMS AND OBJECTIVES OF THE STUDY
The aim of this work is to investigate on the adsorption of Copper, Lead, and Iron on the clay mineral in Itu L.G. A in Akwa Ibom State. This was achieved with the following:
- Investigation the relationship between the physicochemical properties and adsorption parameter of my selected clay soil samples.
- Investigation of the effect of the initial solute concentration on Cu2,Pb2+, and Fe2+ adsorption and desorption using batch experiments under laboratory conditions.
- Evaluating the sorption characteristics of Cu2+, Pb2+, and Fe2+ on to different clay soil sample using Langmuir and Freundlich adsorption isotherms.
- Investigation of the effect of contact time on Cu2+, Pb2+, and Fe2+ adsorption
- Investigation of the effect of solution PH on Cu2+ Pb2+, and Fe2+ adsorption
- Determination of the background levels of Cu2+, Pb2+, and Fe2+, and the physicochemical properties of the clay samples collected.