Abstract
Water is an indispensable natural resource for sustaining life which is undoubtedly not free in all places. The chemical composition of surface or underground waters is one of the principal aspects upon which the relevancy of water for domestic, industrial or agricultural purposes hinges upon. Inorganic anions are commonly in existence in water; nonetheless, some of these including oxy-anions, are undesirable and continually accountable for the grave environmental and health problems. Such ions like arsenic (As(V)), hexavalent chromium(Cr(VI)), fluoride (F‒) phosphate (PO43‒) and nitrate (NO3‒) when in exceeding maximum limits, constitute some of the most hazardous water pollutants. Fluoride, at low a concentration of 0.8-1.5 mg/L as recommended by World Health Organisation (WHO) can prevent tooth decay and contribute to the development of strong bones, especially in young children. However, at higher concentrations it has catastrophic health effects ranging from dental related problems to debilitating skeletal fluorosis as well as affecting body parts like the muscles, brain, lungs, kidneys, thyroid, reproduction and enzymes. Its high concentration in ground water is primarily owing to the weathering of fluoride rich minerals, high ash volcanic eruptions and many anthropogenic activities. On the other hand, industrial activities such as electroplating, leather tanning, dye production, ferrochrome production, wood preservation, mining and paints manufacture have indirectly led to the discharge of Cr(VI) ions into environmental water. Cr(VI) is one of the most toxic, highly soluble and mobile anions in the environment which causes health problems in the form of dermatitis, damage to the liver, lung and skin cancer, skin irritation and internal haemorrhage. The WHO recommended level of Cr(VI) is 0.1 mg/L in surface waters and 0.05 mg/L in drinking water. Consequently, sustainable technologies have been developed to remove fluoride and Cr(VI) ions from water ranging from chemical precipitation, reverse osmosis, electrochemical methods, adsorption, membrane processes, ion exchange and phytoremediation. Among these techniques, adsorption has shown superiority, attributed to its simplicity in design, low operating costs, efficiency and reversibility. Several adsorbents have been utilised for adsorption successfully. However, some drawbacks such as high cost, low selectivity, narrow pH ranges, low adsorption capacity, slow adsorption and poor mechanical strength have been encountered with some of the adsorbent materials. Nano-metal oxides (NMOs) and conduction polymers have a better potential as adsorbents physical and chemical properties. However they have problems of agglomeration, hence low adsorption capacity and difficult to separate from aqueous media. More studies on modification and...
Ph.D. (Chemistry)