فایل ورد کامل بررسی حذف فلزات سنگین توسط نانو جاذب ها

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تعداد صفحات این فایل: ۲۰ صفحه

بخشی از مقاله انگلیسیعنوان انگلیسی:Removal of heavy metals by nanoadsorbents: A review~~en~~

Abstract

Discharge of heavy metals from industrial, municipal, agricultural and domestic wastewater has become a serious threat for the ecosystem. New class of adsorbents developed during past couple of decades has helped to overcome this growing threat. They have gained popularity due to their distinct characteristic and have shown excellent potential in treatment of wastewater and industrial effluents to be reused for various purposes for the sustainable development of growing society. This paper presents a scientific review of the nanoadsorbents used in recent times in the removal of heavy metals from wastewater, highlighting their efficiency, advantages and the mechanism involved in the removal.

۱ Introduction

Lead, mercury, nickel, chromium, thallium, zinc, copper, cobalt, selenium, arsenic and cadmium are the heavy metals known for their toxicity and persistency. Unlike organic pollutants, they do not easily degrade, but are mostly non-biodegradable. They find their way into water bodies through refineries, sludge disposal, mining operations, manufacturing industries such as paints, electronic and electrical devices, batteries, fertilizers, pesticides etc. Their presence in water may pose serious threats to all forms of life, because they may be mutagenic and carcinogenic. Their presence above prescribed limits in body can cause severe damages to vital organs of the body, such as kidney, liver and brain, reproductive and nervous system (Goel, 2006). The conventional methods of wastewater treatment employed since decades, such as ion exchange, lime coagulation, evaporation, reverse osmosis, electrochemical treatment methods, solvent extraction chemical precipitation and filtration, redox reactions resulted in low metal removal efficiencies for high operational costs and hence these are reported as expensive and inadequate.

Adsorption is a known phenomenon in water treatment since ancient times. It is a common phenomenon in gaseous phase, but is used effectively in treatment of wastewater. Granular activated carbon (GAC) has been used for treatment of wastewaters for decades because of its properties, such as adsorption capacity, ion selectivity, thermal stability, ease of activation and regeneration and resistance to transportation losses. Red mud, green sand, slags are the industrial waste found effective adsorbents for organic and inorganic materials including heavy metals from wastewater (Vigneswaran and Moon, 1999). Living or dead cells produced by sea bacteria used for biosorption of trace heavy metals helped in detoxification of wastewater (Lopez-Cortes and Ochoa, 1999). Low cost adsorbents prepared from agricultural waste were proved very effective in removal of heavy metals from wastewater even at very low concentrations. Also, these adsorbents have found to be promising in long terms as there are many materials available locally and abundantly which can be utilized as low cost adsorbents (Babel and Kurniawan, 2003). Polymeric membranes used in wastewater treatment are cross linked polyamide, poly sulfone and cellulose acetate materials and exhibit special characteristics such as chemical stability, high flux rate, better metal ion binding with chelating mechanism and resistance to ultraviolet radiations, ozone and chlorine (Lakshmanan, 2013). During last few decades, new classes of materials have been developed, such as derivatives of carbon, carbonaceous nanoporous materials, inorganic nano materials, magnetic and nano-magnetic materials, microporous glasses, molecular sieves, polymers, ceramics, silica nanoparticles etc. (Kumar, 2009). They have gained interest of new generation of researchers due to vast scope of research in treatment of wastewater using materials with distinct characteristics of reuse for the sustainable development of growing society. They also have been reported to exhibit high adsorption capacity for heavy metals from wastewater as compared to the materials used traditionally and commercially as adsorbents.

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