21-09-2012, 11:14 AM
EVALUATION OF THE EFFICIENCY OF SULFONATED POLYSTYRENE IN SYNTHETHIC GROUNDWATER IN HEAVY METAL REMOVAL
EVALUATION OF THE EFFICIENCY.doc (Size: 642.5 KB / Downloads: 50)
Introduction
Metal contamination is a persistent problem in many contaminated sites. The most commonly occurring metals are lead, zinc, arsenic, cadmium, chromium, copper and mercury. Waste products from metal-based industries, irrigation especially with sewage, solid wastes, fertilizers and pesticides have contributed greatly to the introduction of these metals to the ecological system. The usage of fertilizers for example, requires the soil as its matrix in application to crops. However, these too eventually move from the surface of application when they are dissolved in runoff water or when they percolate down through the soil, infiltrated the solid and finally reaching the groundwater. Leaching of these metals into the groundwater are largely affected by natural phenomena such as rainfall and other factors including the depth of groundwater source and the mobility of the metal.
Groundwater is used for domestic chores, irrigation of vegetable gardens especially during dry seasons and considered as a source of clean potable water both for humans and animals. Groundwater contamination by heavy metals poses a significant threat for human health and ecological systems directly or indirectly by entering the animal and human food chain. Hazardous effects to human such as nerve, liver, kidney damage, bone effects and fractures and malfunctioning of other body organs can be acquired through the contamination of drinking water systems by these metals. (Jarup, 2003)
General Overview of the Study
Nowadays, there is a need to address the problem in the tremendous increase of wastes coming from plastic materials. Polystyrene is a plastic that is extensively used for packaging. This “foam packaging” is a lightweight yet sturdy, moisture resistant and an excellent thermal insulator. It does not support the growth of bacteria and it doesn’t breakdown in landfills to generate explosive methane gas. (Aguirre et al., 2004)
Investigations have adopted chemical recycling of waste polystyrene into the corresponding monomers or hydrocarbons. The process is not cost-efficient however, since the cost of the hydrocarbons and monomers is lower compared to that retrieved by recycling.(Bekri-Abes et al., 2006)
Sulfonation is a new reclamation technology reported in converting waste plastic to functional polymer. It is popularly known that the sulfonation of polystyrene can be used to create products such as cationic exchanger resin, polyelectrolyte and fuel cell membranes. The research was based on the sulfonation of wasted polystyrene in producing flocculant. This was then utilized to eliminate the turbidity from wastewater.(Bekri-Abes et al., 2006)
Significance of the Study
A research has established the applicability of sulfonated polystyrene in reducing the lead content in electroplating industry wastewater. (Arcega et al., 2006)Hence, this research was conducted to test its efficiency inthe reduction of cadmium metal found in synthetic ground water. It is a significant venture to further determine the adsorption capacity of the waste material when some manipulative variables are changed. This study will attempt to contribute in the synthetic groundwater treatment, setting forth depth in initiating the relevance of this method in decontamination of Taguig deep well water. This will also encourage future researchers to test the feasibility of this technique in other water sources, as it is more economical and accessible compared with other adsorption materials. Most importantly, this will help the readers become more knowledgeable in coping with possible contaminants from different sources and give them the initiative to prevent potential hazards that these may cause to the environment.
Scope and Limitations
This study will focus on the adsorption of cadmium solid using sulfonation of waste polystyrene. It will concentrate on removal of the heavy metal. The study will relate the effects of varying pH values on the efficiency of the treatment. It is limited however, in three different pH values initially set as 4, 7, and 10. In determining the impact on the results of altering the concentration of the sulfonated polystyrene, this study will be constricted in three values: 100 M, 200 M and 300 M. The effect of changing the optimum contact time will be determined by just using three different length of time: 10, 20 and 30 seconds. To prevent the occurrence of interferences caused by presence of other metals, the water source will be a simulated aqueous solution that contains cadmium metal.
Conceptual Framework
Adsorption Mechanism
Adsorption is a process that occurs when a gas or liquid solute collects on the surface of a solid or a liquid (adsorbent), forming a molecular or atomic film (the adsorbate). It is different from absorption, in which a substance diffuses into a liquid or solid to form a solution. The term sorption includes both processes, while desorption is the reverse process. It is widely used in industrial applications such as activated charcoal, synthetic resins and water purification.
Similar to surface tension, adsorption is a consequence of surface energy. All the bonding requirements (be they ionic, covalent or metallic) of the constituent atoms of the material are filled in bulk. But atoms on the (clean) surface experience a bond deficiency, because they are not fully surrounded by other atoms. (Uhríkova,2007)
There are three general types of adsorption: physical, chemical, and exchange adsorption (Sawyer et.al., 1978). Physical adsorption is defined as relatively general and is cause to the operation of weak forces of attraction or van der Waals’ forces between molecules. The adsorbed molecule is not affixed to a particular site on the solid surface, but is free to move about over the surface. The adsorbed material may condense and form several superimposed layers on the surface of the adsorbent. Physical adsorption is generally quite reversible with a decrease in concentration the material is desorbed to the same extent that it was originally adsorbed. While Chemical adsorption is the result of much stronger forces, comparable with those leading to the formation of chemical compounds. It is seldom reversible. The adsorbent must generally be heated to higher temperature to remove the adsorbed materials. (Chen et.al)
Ion Exchange
Ion exchange is a reversible chemical reaction between an insoluble solid and a solution during which ions may be interchanged, used in water softening and in the separation of radioactive isotopes.(American Heritage Dictionary) It describes the process: as water flows through a bed of ion exchange material, undesirable ions are removed and replaced with less objectionable ones.(Nalco,1998) When molecules or ions do not have all their forces satisfied by union with other particles, saturation will lead. Solid and liquid surfaces tend to have forces attracting onto and retaining on their surface gases which they come in contact, adsorption is when the concentration of substance on the surface of a solid or liquid having the said phenomenon. (Lando,1974)The solid ion exchange particles are either naturally occurring zeolites or synthetically produced organic resins. The use of ion exchange processes affords effective means of conditioning feed water. The proper selection of the specific ion exchange process depends on water quality needs, operating convenience, and economic considerations. For effective results, the system must be carefully selected, designed, operated and maintained. (Nalco, 1998)